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41695 Publications

Auger scattering in massless Dirac and Kane materials

Winnerl, S.

Abstract

We present an overview that sheds light into the carrier dynamics of in Landau-quantized Dirac and Kane systems, namely graphene and mercury cadmium telluride (MCT). The non-equidistant Landau-ladder makes these materials highly attractive for realizing the old dream of the semiconductor physics community to fabricate a Landau-level laser. For a recent review on this topic, see Ref. [1]. In such a laser, stimulated emission is achieved between a pair of Landau levels and the emission wavelength can be tuned by the strength of the magnetic field. In graphene, we found evidence for strong Auger scattering for the lowest allowed transitions LL-1 → LL0 and LL0 → LL1 [2]. These energetically degenerate transitions can be distinguished by applying circularly polarized radiation of opposite polarization. In this configuration, Auger scattering can cause depletion of the LL0 level even though it is optically pumped at the same time. Recently, we have investigated the LL-2 → LL1 and LL-1 → LL2 transition under strong optical pumping. This transition is a candidate for the lasing transition for a Landau-level laser. We observed non-equilibrium carrier distributions by selective pumping before thermalization occurred. MCT, on the other hand, is even more attractive because of much longer relaxation times [3]. They are on the ns scale while in graphene thermalization occurs on a timescale of a few ps. The reason for the longer timescale is the different Landau ladder due to spin splitting.
[1] E. Gornik, G. Strasser und K. Unterrainer, Nature Photonics 15, 875 (2021).
[2] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski,
C. Berger, W. A. de Heer, H. Schneider, M. Helm und S. Winnerl, Nature
Physics 11, (2015).
[3] D. B. But, M. Mittendorff, C. Consejo, F. Teppe, N. N. Mikhailov, S. A. Dvoretskii, C. Faugeras, S. Winnerl, M. Helm, W. Knap, M. Potemski und M. Orlita, Nature Photonics 13, 783 (2019).

Keywords: graphene; HgCdTe; Dirac electrons; Kane electrons; Landau quantization; Landau level lasing

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  • Invited lecture (Conferences)
    International Conference on Free Electron Laser Applications and THz Studies of New States of Matter (TERFEL), 05.-08.07.2022, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-36438


Time-resolved nanospectroscopy on Si-doped GaAs-InGaAs core-shell nanowires

Luferau, A.; Obst, M.; Winnerl, S.; Kehr, S. C.; Dimakis, E.; Pashkin, O.; Klopf, J. M.; Eng, L. M.; Helm, M.

Abstract

High-quality epitaxial nanowires (NWs) based on III–V semiconductors such as (In)GaAs offer the possibility to fabricate ultrafast optical devices due to their direct bandgap and the high electron mobility. Contactless investigation of the charge carrier concentration and mobility in NWs is enabled by terahertz time-domain spectroscopy [1]. The determination of these properties locally on individual NWs can be carried out by scattering-type scanning near-field optical microscopy (s-SNOM), which provides spatial resolution far beyond the diffraction limit. In optical-pump THz-probe experiments the response of photogenerated carriers has been investigated on the 10 nm and 10 fs scale [2].
Time-resolved studies are still missing in both far-field and near-field spectroscopy for doped nanowires excited by far-infrared (FIR) radiation via free-carrier absorption. Here we report on FIR-pump MIR-probe s-SNOM studies on highly-doped GaAs/InGaAs core-shell NWs utilizing intense narrowband FIR radiation from the free-electron laser (FEL) FELBE.
The samples under study are Si-doped GaAs-InGaAs core-shell NWs grown by molecular beam epitaxy. They consist of a 25-nm-thick GaAs core and a 80-nm-thick In0.44Ga0.56As shell that is homogeneously doped with Si at a concentration of 9 × 1018 cm-3. For s-SNOM studies these NWs are transferred to a (100) Si substrate and dispersed randomly over the substrate.
The experiment was carried out with the s-SNOM setup from Neaspec GmbH equipped with difference-frequency generation (DFG) source (5 – 15 µm; 83 – 248 meV). For the pump-probe measurements the laser oscillator of the DFG source was synchronized to FEL and the time delay between the pulses was varied by an optical delay line. A low-pass filter suppress the scattered FIR radiation from FELBE going into the nano-FTIR unit (Fig 1,a).
In the unpumped case, a sharp plasma edge around 130 meV is observed. Upon below-bandgap pumping with 23 µm FEL radiation (pulse duration 2 – 5 ps, average power 15 mW), the near-field response of plasma resonance changes dramatically. The spectrally integrated pump-probe signal exhibits a small negative component followed by a stronger positive signal that decays with the longest time constant (1/e) of ≈7 ps (Fig. 1,b, Insert). The nano-FTIR studies reveal strong red shift and flattening of plasma resonance of spectra (Fig.1,b). We assign this effect to a substantial heating of the electrons in the conduction band and subsequent increase of the effective mass in the nonparabolic Γ-valley due to high peak electric field strengths up to several 10 kV cm−1 of pulsed FEL radiation [3]. Power-dependent and nanoimaging pump-probe studies are performed to conclude the nature of observed effects. In particular, the experiments should reveal if there is a contribution of carrier transfer to side valleys at high excitation fields.
[1] P. Parkinson, et al., Nano Lett. 7, 2162 (2007).

Keywords: core-shell nanowires; terahertz; near-field microscopy; time-resolved nanoscopy

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Related publications

  • Lecture (Conference)
    9th International Conference on Optical Terahertz Science and Technology (OTST 2022), 19.-24.06.2022, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-36437


Pump-induced terahertz anisotropy in graphene

Seidl, A.; Anvari, R.; Dignam, M. M.; Richter, P.; Seyller, T.; Schneider, H.; Helm, M.; Winnerl, S.

Abstract

Nonlinear optical properties of graphene have been discussed for a more than a decade [1]. Experimentally, the most prominent nonlinear effect is high harmonic generation in the THz range [2]. This phenomenon is caused by a reduced conductivity of hot thermalized electrons. In our study, we investigate an effect beyond the response of thermalized hot carriers, which by nature is isotropic. We observe anisotropic THz-induced bleaching related to a change in effective mass of charge carriers under strong THz excitation.
We investigated monolayer and bilayer graphene on SiC with carrier concentrations of 1.0 x 10^13 cm-2 and 6.5 × 10^12 cm−2, respectively. In degenerate pump-probe experiments at 3.4 THz utilizing linearly polarized radiation, the differential transmission was recorded for co- and cross-polarized probe beams. For bilayer graphene, co-polarized probing yields signals that are about two times larger as compared to the cross-polarized case (cf. Fig. 1) [3]. Since the response of thermalized carriers is isotropic, it cannot explain the observed anisotropic bleaching. We describe the physical origin of the anisotropic nonlinear response using a simple semiclassical model: In essence, the change in effective mass in x-direction differs strongly for carriers excited along or perpendicular to the direction of the probe field. For a quantitative comparison, modelling based on the density matrix formalism with a phenomenological scattering time was performed. For a momentum scattering time of 50 fs good agreement with the experimental data is obtained. The monolayer sample shows qualitatively similar behavior, however, the scaling of the induced transmission with the pump electric field is different. In summary, time-resolved THz nonlinear spectroscopy turns out as a powerful method to explore nonlinearities directly related to the bandstructure of Dirac materials.
[1] S. A. Mikhailov and K. Ziegler, J. Phys.: Condens. Matter 20, 384204 (2008).
[2] H. A. Hafez et al., Nature 561, 507 (2018).
[3] A. Seidl et al., Phys. Rev. B. 105, 085404 (2022).

Keywords: graphene; terahertz; nonlinear response

Involved research facilities

Related publications

  • Lecture (Conference)
    9th International Conference on Optical Terahertz Science and Technology (OTST 2022), 19.-24.06.2022, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-36436


Photoconductive THz emitters: a brief history and recent advances

Winnerl, S.

Abstract

In the late 1980ies the photoconductive switch revolutionized science and technology in the previously underdeveloped terahertz spectral range [1]. With these devices it was for the first time possible to produce picosecond coherent pulses and to characterize them in amplitude and phase. We discuss how photoconductive THz emitters profit from the rapid development of femtosecond laser sources: Initially dye lasers were used, in the 1990ies Ti:sapphire lasers became the workhorse in many laboratories and GaAs-based photoconductive fitted perfectly to these sources. Later, fiber lasers operating at 1550 nm allowed for more compact systems while amplified lasers can provide high THz field amplitudes. We present large area antennas [2, 3] that circumvent the issue of saturation by screening which limits the performance of single dipole antennas. Furthermore, we discuss the role of the photoconductive material for THz generation. In particular, we show that the non-polar material Ge is suitable for generating ultrabroadband pulses ranging up to 70 THz without a gap region [4, 5].
[1] Ch. Fattinger and D. Grischkowsky, Appl. Phys. Lett. 53, 1460 (1988).
[2] A. Dreyhaupt, S. Winnerl, T. Dekorsy, and M. Helm, Appl. Phys. Lett. 86, 121114 (2005).
[3] S. Winnerl, J Infrared Milli Terahz Waves 33, 431 (2012).
[4] A. Singh, A. Pashkin, S. Winnerl, M. Helm and H. Schneider ACS Photonics 5, 2718 (2018).
[5] A. Singh, A. Pashkin, S. Winnerl, M. Welsch, C. Beckh, P. Sulzer, A. Leitenstorfer, M. Helm and H. Schneider, Light: Science & Applications 9, 30 (2020).

Keywords: terahertz; photoconductive antennas

  • Lecture (others)
    Seminar Lehrstuhl Photonics and Ultrafast Laser Science (Prof. Clara Saraceno), 01.07.2022, Bochum, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36435


Direct numerical simulation of heat transfer on a deformable vapor bubble rising in superheated liquid

Li, J.; Liao, Y.; Bolotnov, I. A.; Zhou, P.; Lucas, D.; Li, Q.; Gong, L.

Abstract

Heat transfer on a vapor bubble rising in superheated liquid is investigated by direct numerical simulation. The vapor-liquid system is described by the one-fluid formulation with the level set method capturing the interface. The proportional-integral-derivative controller is employed to keep the bubble’s location fixed and evaluate interfacial forces. The heat transfer performance featured by the Nusselt number is evaluated based on the energy balance. Simulations are carried out for the bubble Reynolds number ranging from 20 to 500 and Morton number from 1.10×10-10 to 3.80×10-4. The aim of this paper is to shed some light on the effect of bubble deformation and oscillation on interfacial heat transfer. The results show that the front part of the bubble contributes to the majority of the interfacial heat transfer, while the rear part mainly affects the oscillation amplitude of the total heat transfer. The interface stretch during bubble oscillation is considered as a key mechanism in enhancing the instantaneous Nusselt number. The potential flow solution of the averaged Nusselt number is corrected by considering the influence of the aspect ratio. This research provides additional insights into the mechanism of interfacial heat transfer and the results apply equally to interfacial mass transfer.

Keywords: Deformation; Direct numerical simulation; Interfacial heat transfer; Shape oscillation; Vapor bubble

Permalink: https://www.hzdr.de/publications/Publ-36431


Strain engineering of Ge by ion irradiation and alloying

Wen, S.; Shaikh, M. S.; Steuer, O.; He, L.; Berencen, Y.; Prucnal, S.; Zhou, S.

Abstract

Germanium (Ge) is a traditional but promising material in integrated circuit (IC) due to the high mobility of hole carrier and highly compatibility in Si base-IC technology. However, the indirect band structure of Ge leading to low radiative recombination efficiency, limiting the application in opto-electronics. Strain engineering is a promising method to obtain energy band modification in semiconductors. Noble ions (He, Ar) are expected to induce tensile strain via bubbles formation or vacancy-related defect formation in Ge. A bubble-rich structure formation is accompanied by strongly amorphization process during 30 keV Ar+ ions irradiation, while fully liquid-phase epitaxy is necessary to achieve a high-quality crystalline structure. 4 MeV He+ ions irradiation in Ge can obtain a defect related tensile strain in Ge, which can be evaluated via Raman peak shift. IV-group heavy ions (Sn, Pb) alloying can lead a strong energy bandgap modification in Ge while the GeSn-alloy laser grown by RPCVD can work at low temperature. Here we use CMOS-compatible ion implantation to achieve a tensile GeSn alloy which shows a larger peak shift toward low wavenumber in Raman measurement. The photoconductivity detector based on Ge0.97Sn0.03 alloy shows a photo response to 1550 nm laser source.

Keywords: implantation; Germanium; bandgap; He; Sn; Pb

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Related publications

  • Poster
    NanoNet+ Annual Workshop 2022, 04.-06.10.2022, Görlitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-36430


Microfluidic droplet reactors to reveal bacterial community interactions in an antibiotic environment

Zhao, X.; Cuniberti, G.; Bachmann, M.; Ruelens, P.; Farr, A.; de Visser, J. A. G. M.; Baraban, L.

Abstract

Antibiotics have been widely used in clinics to treat infections, caused by bacteria. However, misuse and abuse of antibiotics over the past decades have led to the emergence of massively drug-resistant microorganisms, which result in a dramatic decline in their efficacy and a large number of deaths. The spread of resistance in bacterial communities is not limited to gene transfer; cross-protection also plays a role. Cross-protection is one of the mechanisms by which different bacteria, sharing the same environment, protect each other to survive in the presence of antibiotics. To investigate the bacterial community interaction in an antibiotic environment, the microfluidic droplet reactors are used to track the survival status of co-cultured antibiotic-sensitive and strong antibiotic-resistant strains in an antibiotic (Cefotaxime, CTX) environment with various harsh degrees. Microfluidic reactor system monitors in real time the growth status of two bacterial strains by detecting their different emission fluorescent signals; E.coli YFP (antibiotic-sensitive) produces yellow fluorescent protein and E.coli BFP (strong antibiotic-resistant strain) produces the blue fluorescent protein. As the fluorescent intensity change during incubation of both strains, a phenomenon of cross-protection is observed in the low concentration of CTX (0.05-5 µg/mL). In addition, to confirm the effect of cross-protection, cell status is also investigated using microscopy, as well as from cell-free media and β-lactamase activity with a plate reader.

  • Open Access Logo Poster
    EMBL Conference: Microfluidics 2022, 11.-13.07.2022, Heidelberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-36429


Microfluidic droplet reactors: reveal bacterial community interactions in antibiotics

Zhao, X.; Cuniberti, G.; Bachmann, M.; Ruelens, P.; Farr, A.; de Visser, J. A. G. M.; Baraban, L.

Abstract

Antibiotics are effective in treating infections caused by bacteria and are therefore widely used in clinical practice.1
However, the misuse and abuse of antibiotics have resulted in the emergence of large numbers of drug-resistant microorganisms, leading to a global crisis in the healthcare sector.2, 3
The spread of resistance in bacterial communities is not limited to gene transfer; cross-protection also allows different bacteria in the same environment to coexist through mutual protection in the presence of antibiotics.4
Here, a microfluidic droplet reactor system is used to investigate the bacterial community interaction in an antibiotic environment, tracking the survival status of co-cultured antibiotic-sensitive and strong antibiotic-resistant strains in an antibiotic (Cefotaxime, CTX) environment in various harshness.
The microfluidic reactor system monitors the growth status of two bacterial strains in real-time and high throughput by detecting their different emission fluorescent signals; E.coli YFP (antibiotic-sensitive) produces yellow fluorescent protein and E.coli BFP (strong antibiotic-resistant strain) produces the blue fluorescent protein.5
As the fluorescent intensity change during the incubation of both strains, the growth status of both bacterial strains is recorded. A phenomenon of cross-protection is observed in the low concentration of CTX (0.05-5 µg/mL). In addition, to confirm the effect of cross-protection, cell status is examined using microscopy, as well as studies fluorescence from resuspended cells and β-lactamase activity with a plate reader.
1. Hutchings, M. I., Truman, A. W. and Wilkinson, B., Antibiotics: past, present and future. Curr Opin Microbiol 51, 72-80 (2019).
2. Bell, M., Antibiotic misuse: a global crisis. JAMA Intern Med 174, 1920-1 (2014).
3. Murray, C. J. L., Ikuta, K. S., Sharara, F., et al., Global burden of bacterial antimicrobial resistance in 2019: a systematic analysis. The Lancet 399, 629-655 (2022)
4. Yurtsev, E. A., Conwill, A. and Gore, J. Oscillatory dynamics in a bacterial cross-protection mutualism. PNAS 113, 6236-6241 (2016)
5. Zhao, X., Illing, R., Ruelens, P., et al., Coexistence of fluorescent Escherichia coli strains in millifluidic droplet reactors, Lab on a Chip 11, 1492-1502 (2021)

  • Lecture (Conference)
    Seventh International Conference on Multifunctional, Hybrid and Nanomaterials, 17.-22.10.2022, Genoa, Italy

Permalink: https://www.hzdr.de/publications/Publ-36428


Integration of flexible sensors with 3D-printed structures for the development of customized in vitro monitoring platforms

Sandoval Bojorquez, D. I.; Oliveros Mata, E. S.; Peng, X.; Makarov, D.; Bachmann, M.; Baraban, L.

Abstract

Cell culture has been one of the most relevant techniques in biology, providing a platform to investigate fundamental research questions about biological processes [1-2]. However, the complexity of 3D tissue structure and the interactions between different cell types and signaling molecules in vivo make it evident that conventional 2D cell culture is not capable of properly recapitulating the physiological dynamics of the tissues in vivo [3]. The latter, in addition to the ethical concerns of animal and human testing, have driven the development of in vitro tissue models that can reassemble in vivo 3D tissue microenvironments known as microphysiological systems (MPSs) [2-3]. The integration of sensors in culture platforms enables in situ monitoring of MPSs providing high sensitivity, temporal, and spatial resolution [4]. In this work, we present the development of a 3D-printed in vitro culturing platform for in situ monitoring of microencapsulated spheroids (MCSs) [5]. Flexible interdigitated gold microelectrodes are integrated into the 3D-printed structures to locally monitor the changes in the environment of the microencapsulated spheroids [6]. The pH of the environment was monitored for different MCSs densities. This allowed us to study the relationship between acidification and MCSs density in controlled environmental settings. The development of novel sensing and culturing platforms provides the possibility to enhance the physiological understanding of in vivo systems through the study of MPSs.
References
[1] Segeritz, C. P., & Vallier, L. (2017). Cell culture: Growing cells as model systems in vitro. In Basic science methods for clinical researchers (pp. 151-172). Academic Press.
[2] Wikswo, J. P. (2014). The relevance and potential roles of microphysiological systems in biology and medicine. Experimental biology and medicine, 239(9), 1061-1072.
[3] Sohn, L. L., Schwille, P., Hierlemann, A., Tay, S., Samitier, J., Fu, J., & Loskill, P. (2020). How can microfluidic and microfabrication approaches make experiments more physiologically relevant?. Cell systems, 11(3), 209-211.
[4] Modena, M. M., Chawla, K., Misun, P. M., & Hierlemann, A. (2018). Smart cell culture systems: Integration of sensors and actuators into microphysiological systems. ACS chemical biology, 13(7), 1767-1784.
[5] Peng, X., Janicjievic, Z., Lemm, S., Laube, M., Pietzsch, J., Bachmann, M., & Baraban, L. (2022). Shell engineering in soft alginate-based capsules for culturing liver tumoroids. Authorea Preprints.
[6] Schütt, J., Sandoval Bojorquez, D. I., Avitabile, E., Oliveros Mata, E. S., Milyukov, G., Colditz, J., ... & Baraban, L. (2020). Nanocytometer for smart analysis of peripheral blood and acute myeloid leukemia: a pilot study. Nano Letters, 20(9), 6572-6581.

  • Lecture (Conference)
    EMRS 2023 Spring Meeting, 29.05.-02.06.2023, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-36427


Impedimetric detection of SARS-CoV-2 antigens and antibodies using interdigitated gold nanowires

Sandoval Bojorquez, D. I.; Janićijević, Ž.; Palestina Romero, B.; Oliveros Mata, E. S.; Laube, M.; Feldmann, A.; Kegler, A.; Drewitz, L.; Fowley, C.; Pietzsch, J.; Faßbender, J.; Torsten, T.; Bachmann, M.; Baraban, L.

Abstract

The development of point-of-care (POC) testing platforms has increased during the COVID-19 pandemic due to their multiple benefits including low cost, rapid turnaround time, on-site testing, and minimal sample preparation [1-2]. Although POC tests are a good alternative to the gold standard technique (reverse-transcriptase-polymerase chain reaction, RT-PCR) for SARS-CoV-2 detection, there are challenges regarding their sensitivity and specificity that need to be addressed [3-4]. One strategy to improve the performance of POC is the integration of nanostructures as sensing elements [5]. In this work, we used interdigitated gold nanowires (Au NWs) in combination with electrical impedance spectroscopy (EIS) for the detection of the receptor-binding domain of the S1 protein of the SARS-CoV-2 virus and the respective antibodies that appear during and after infection. Our sensor system was composed of six sensing devices, each of these sensors containing six pairs of interdigitated gold nanowires of 120 nm in width. The surface of the Au NWs was functionalized with antigens or antibodies of SARS-CoV-2 so that the molecules of interest present in the sample can bind to them. The adhesion of molecules to the surface of the Au NWs modulates the physicochemical properties of the surface [6]. As a result, it was possible to correlate the changes in electrical impedance with the binding of specific analytes to the surface of the Au NWs using EIS. The developed sensing platform is an attractive system for screening during pandemics and can be adapted for the detection of relevant target-analyte pairs in different diseases.

References
[1] E. Valera et al., ?COVID-19 Point-of-Care Diagnostics: Present and Future,? ACS Nano, vol. 15, no. 5, pp. 7899?7906, 2021, doi: 10.1021/acsnano.1c02981.
[2] E. Morales-Narváez and C. Dincer, ?The impact of biosensing in a pandemic outbreak: COVID-19,? Biosens. Bioelectron., vol. 163, p. 112274, 2020, doi: https://doi.org/10.1016/j.bios.2020.112274.
[3] W. Leber, O. Lammel, A. Siebenhofer, M. Redlberger-Fritz, J. Panovska-Griffiths, and T. Czypionka, ?Comparing the diagnostic accuracy of point-of-care lateral flow antigen testing for SARS-CoV-2 with RT-PCR in primary care (REAP-2),? EClinicalMedicine, vol. 38, p. 101011, 2021, doi: 10.1016/j.eclinm.2021.101011.
[4] I. Wagenhäuser et al., ?Clinical performance evaluation of SARS-CoV-2 rapid antigen testing in point of care usage in comparison to RT-qPCR,? EBioMedicine, vol. 69, pp. 1?7, 2021, doi: 10.1016/j.ebiom.2021.103455.
[5] N. Wongkaew, M. Simsek, C. Griesche, and A. J. Baeumner, ?Functional Nanomaterials and Nanostructures Enhancing Electrochemical Biosensors and Lab-on-a-Chip Performances: Recent Progress, Applications, and Future Perspective,? Chem. Rev., vol. 119, no. 1, pp. 120?194, 2019, doi: 10.1021/acs.chemrev.8b00172.
[6] J. L. Hammond, N. Formisano, P. Estrela, S. Carrara, and J. Tkac, ?Electrochemical biosensors and nanobiosensors,? Essays Biochem., vol. 60, no. 1, pp. 69?80, 2016, doi: 10.1042/EBC20150008.

  • Lecture (Conference)
    EMRS 2022 Fall Meeting, 19.-22.09.2022, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-36426


Electronic Density Response of Warm Dense Matter

Dornheim, T.; Moldabekov, Z.; Ramakrishna, K.; Tolias, P.; Baczewski, A. D.; Kraus, D.; Preston, T. R.; Chapman, D. A.; Böhme, M.; Döppner, T.; Graziani, F.; Bonitz, M.; Cangi, A.; Vorberger, J.

Abstract

Matter at extreme temperatures and pressures -- commonly known as warm dense matter (WDM) in the literature -- is ubiquitous throughout our Universe and occurs in a number of astrophysical objects such as giant planet interiors and brown dwarfs. Moreover, WDM is very important for technological applications such as inertial confinement fusion, and is realized in the laboratory using different techniques. A particularly important property for the understanding of WDM is given by its electronic density response to an external perturbation. Such response properties are routinely probed in x-ray Thomson scattering (XRTS) experiments, and, in addition, are central for the theoretical description of WDM. In this work, we give an overview of a number of recent developments in this field. To this end, we summarize the relevant theoretical background, covering the regime of linear-response theory as well as nonlinear effects, the fully dynamic response and its static, time-independent limit, and the connection between density response properties and imaginary-time correlation functions (ITCF). In addition, we introduce the most important numerical simulation techniques including ab initio path integral Monte Carlo (PIMC) simulations and different thermal density functional theory (DFT) approaches. From a practical perspective, we present a variety of simulation results for different density response properties, covering the archetypal model of the uniform electron gas and realistic WDM systems such as hydrogen. Moreover, we show how the concept of ITCFs can be used to infer the temperature from XRTS measurements of arbitrarily complex systems without the need for any models or approximations. Finally, we outline a strategy for future developments based on the close interplay between simulations and experiments.

Permalink: https://www.hzdr.de/publications/Publ-36425


Imaginary-time correlation function thermometry: A new, high-accuracy and model-free temperature analysis technique for x-ray Thomson scattering data

Dornheim, T.; Böhme, M.; Chapman, D.; Kraus, D.; Preston, T. R.; Moldabekov, Z.; Schlünzen, N.; Cangi, A.; Döppner, T.; Vorberger, J.

Abstract

The accurate interpretation of experiments with matter at extreme densities and pressures is a notoriously difficult challenge. In a recent work [T.~Dornheim et al., Nature Comm. (in print), arXiv:2206.12805], we have introduced a formally exact methodology that allows extracting the temperature of arbitrarily complex materials without any model assumptions or simulations. Here, we provide a more detailed introduction to this approach and analyze the impact of experimental noise on the extracted temperatures. In particular, we extensively apply our method both to synthetic scattering data and to previous experimental measurements over a broad range of temperatures and wave numbers. We expect that our approach will be of high interest to a gamut of applications, including inertial confinement fusion, laboratory astrophysics, and the compilation of highly accurate equation-of-state databases.

Permalink: https://www.hzdr.de/publications/Publ-36424


Data publication: Ab initio Computation of the Static Exchange--Correlation Kernel of Real Materials: From Ambient Conditions to Warm Dense Matter

Moldabekov, Z.; Böhme, M.; Vorberger, J.; Blaschke, D.; Dornheim, T.

Abstract

This repository contains the DFT simulation results presented in the article "Ab Initio Static Exchange-Correlation Kernel across Jacob's Ladder without Functional Derivatives"

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Permalink: https://www.hzdr.de/publications/Publ-36423


Extraction of the frequency moments of spectral densities from imaginary-time correlation function data

Dornheim, T.; Wicaksono, D. C.; Suarez Cardona, J. E.; Tolias, P.; Böhme, M.; Moldabekov, Z.; Hecht, M.; Vorberger, J.

Abstract

We introduce an exact framework to compute the positive frequency moments M (α)(q) = 〈ωα〉
of different dynamic properties from imaginary-time quantum Monte Carlo data. As a practical
example, we obtain the first five moments of the dynamic structure factor S(q, ω) of the uniform
electron gas at the electronic Fermi temperature based on ab initio path integral Monte Carlo
simulations. We find excellent agreement with known sum rules for α = 1, 3, and, to our knowledge,
present the first results for α = 2, 4, 5. Our idea can be straightforwardly generalized to other
dynamic properties such as the single-particle spectral function A(q, ω), and will be useful for a
number of applications, including the study of ultracold atoms, exotic warm dense matter, and
condensed matter systems.

Permalink: https://www.hzdr.de/publications/Publ-36422


Detection of SARS-CoV-2 Antigens and Antibodies Using OFET Biosensors based on Soft and Strechable Semiconducting Polymer

Ditte, K.; Nguyen Le, T. A.; Ditzer, O.; Sandoval Bojorquez, D. I.; Chae, S.; Bachmann, M.; Baraban, L.; Lissel, F.

Abstract

In the midst of the COVID-19 pandemic, adaptive solutions are needed to allow us to make fast decisions and take effective sanitation measures, e.g., the fast screening of large groups (employees, passengers, pupils, etc.). Although being reliable, most of the existing SARS-CoV-2 detection methods, like polymerase chain reaction or paper-based immunosensors, lack the ability integrated into garments to be used on demand.
Here, we report – at the proof-of-concept level – an organic field-effect transistor (OFET)-based biosensing device detecting of both SARS-CoV-2 antigens and anti-SARS-CoV-2 antibodies in less than 20 min. The biosensor was produced by functionalizing an intrinsically stretchable and semiconducting triblock copolymer (TBC) film either with the anti-S1 protein antibodies (S1 Abs) or receptor-binding domain (RBD) of the S1 protein, targeting CoV-2-specific RBDs and anti-S1 Abs, respectively. The obtained sensing platform is easy to realize due to the straightforward solution-based fabrication of the TBC film and the utilization of the reliable physical adsorption technique for the molecular immobilization. The device demonstrates a high sensitivity of about 19%/dec and a limit of detection (LOD) of 0.36 fg/mL for anti-SARS-Cov-2 antibodies and, at the same time, a sensitivity of 32%/dec and a LOD of 76.61 pg/mL for the virus antigen detection. The TBC used as active layer is soft, has a low modulus of 24 MPa, and can be stretched up to 90% with no crack formation of the film. With proper transfer to a stretchable-flexible substrate, the presented concept offers the possibility to realize stretchable biosensors, which might allow the fabrication of wearable platforms for on-the-fly detections of biomolecules to aid reducing – and eventually stopping – the spread of COVID-19 and future pandemics.

  • Lecture (Conference) (Online presentation)
    European Materials Research Society Spring 2022 Meeting, 30.05.-03.06.2022, Virtual, Virtual

Permalink: https://www.hzdr.de/publications/Publ-36421


Cell Counting in Silicon Nanosensor for CAR T-Cell Therapy Monitoring

Nguyen Le, T. A.; Bartsch, T.; Feldmann, A.; Bachmann, M.; Baraban, L.

Abstract

Silicon nanowire sensors have demonstrated outstanding utility in biosensing, especially for small biomolecules at extremely low concentrations. However, the sensor is less commonly applied in whole-cell monitoring, such as CAR T-cell counting during cancer treatment. The patient’s T-cells are modified to express chimeric antigen receptors (CAR), targeting specific tumor cells in CAR T-cell treatment. Therefore, the CAR T-cell level in blood is an essential parameter when it comes to determining the immune system’s reactivity to fight cancer cells. Although nanosensors are typically beneficial for early cancer diagnosis and detection, we want to expand their application and explore their usage in cancer treatment monitoring and development. Our previous works showed promising results of using nanosensors to find the most effective immunotherapy. In this work, we study the response of silicon nanowire field-effect transistors (SiNW FET) to the binding of CAR T-cells and discuss the benefits and limitations of the sensors in cell monitoring. The SiNW FETs fabricated in a top-down manner showed superior sensitivity to IgG antibodies sensing in our previous study. A peptide with a high affinity to the designed CAR T-cells immobilized on SiNW FETs to detect the cell binding. We observed distinguished signals following the number of cells binding to the sensing area. The results pave the way for using nanosensors in monitoring cancer treatment, yet they suggest some room for improvement.

Keywords: biosensor; silicon nanowire; immunotherapy; CAR T-cell

  • Open Access Logo Contribution to proceedings
    The 9th International Symposium on Sensor Science), 20.-22.06.2022, Warsaw, Poland
    Engineering Proceeding 21(2022) 54: MDPI
    DOI: 10.3390/engproc2022021054

Permalink: https://www.hzdr.de/publications/Publ-36420


Gold nanoparticle-enhanced flexible electrochemical glucose biosensors

Tonmoy, T. H.; Huang, T.; Janićijević, Ž.; Ahmed, A.; Baraban, L.

Abstract

Close monitoring of rapidly changing physiological parameters is an integral part of managing critically ill patients in an intensive care unit (ICU). However, frequent blood draws and laboratory testing introduce delays, discontinuity, and wastage of blood, contributing to poor patient outcomes. Continuous monitoring of critical analytes such as pH, blood gases, glucose, lactate, etc., can provide early detection of complications and enable improved quality of patient care.¹ Although enzymatic sensors based on glucose oxidase offer good specificity, they are susceptible to pH and temperature alterations, loss of enzyme activity over time, denaturation of enzymes, etc.² Therefore, the use of spherical gold nanoparticles (AuNPs) is considered for the enhancement of sensitivity of such glucose sensors. The AuNPs can provide catalytic activity towards glucose or modify standard enzymatic systems by improving the efficiency of electron transfer between the enzymes and the electrodes. We present flexible sensors comprising gold electrodes on polyimide-based substrates fabricated using lithographic patterning and magnetron sputtering techniques. These sensors can be applied in wearable devices or implantable sensing systems to enable continuous monitoring. In our approach, we modify gold electrode surfaces to detect glucose levels by introducing AuNPs at different stages of functionalization to support the charge transfer in enzyme-based measurements or to exploit the modulation of AuNP catalytic activity for sensing. AuNPs with dimensions between 15 and 50 nm were incorporated for signal enhancement. The developed sensors were characterized extensively for sensitivity, reliability, and reproducibility. Our preliminary findings suggest improved stability of electrochemical signals and excellent dynamic range of glucose sensing when AuNPs are introduced. AuNP-enhanced flexible electrochemical biosensors show great promise for use in clinical monitoring settings and integration of these sensors into complete medical devices is part of our ongoing research.

1. Ho, K.K.Y.; Peng, Y.-W.; Ye, M.; Tchouta, L.; Schneider, B.; Hayes, M.; Toomasian, J.; Cornell, M.; Rojas-Pena, A.; Charpie, J.; Chen, H. Evaluation of an Anti-Thrombotic Continuous Lactate and Blood Pressure Monitoring Catheter in an In Vivo Piglet Model undergoing Open-Heart Surgery with Cardiopulmonary Bypass. Chemosensors 2020, 8, 56. https://doi.org/10.3390/chemosensors8030056.
2. Mohammadpour-Haratbar, A.; Mohammadpour-Haratbar, S.; Zare, Y.; Rhee, K.Y.; Park, S.-J. A Review on Non-Enzymatic Electrochemical Biosensors of Glucose Using Carbon Nanofiber Nanocomposites. Biosensors 2022, 12, 1004. https://doi.org/10.3390/bios12111004.

  • Poster
    8th International Winterschool on Bioelectronics (BioEl 2023), 11.-18.03.2023, Kirchberg in Tirol, Austria

Permalink: https://www.hzdr.de/publications/Publ-36419


Research data: Search for nonlinear thz absorption by electromagnons in multiferroic hexaferrites

Vít, J.; Repček, D.; Kadlec, C.; Kadlec, F.; Adhlakha, N.; Di Pietro, P.; Piccirilli, F.; Kovalev, S.; Deinert, J.-C.; Ilyakov, I.; Awari, N.; Chen, M.; Buršík, J.; Bae Park, C.; Hoon Kim, K.; Gensch, M.; Perucchi, A.; Kamba, S.

Abstract

Datasets measured at the TELBE THz facility consisting of raw (time-sorted) data and binned data that was used for further analysis. The xlsx-file contains measured THz powers. Metadata can be found in labbook file zip archive. Final data analysis was performed by Jakub Vít.

Keywords: Terahertz; Multiferroics; Hexaferrites; Electromagnons; Nonlinear dynamics

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Permalink: https://www.hzdr.de/publications/Publ-36418


Phase evolution of Te-hyperdoped Si upon furnace annealing

Shaikh, M. S.; Wang, M.; Hübner, R.; Liedke, M. O.; Butterling, M.; Solonenko, D.; Madeira, T. I.; Zichao, L.; Yufang, X.; Hirschmann, E.; Wagner, A.; Zahn, D. R. T.; Helm, M.; Zhou, S.

Abstract

Silicon doped with Tellurium (Te), a deep level impurity, at concentrations higher than the solid solubility limit (hyperdoping) was prepared by ion-implantation and nanosecond pulsed laser melting. The resulting materials exhibit strong sub-bandgap optical absorption showing potential for room-temperature broadband infrared photodetectors. As a thermodynamically metastable system, an impairment of the optoelectronic properties in hyperdoped Si materials occurs upon subsequent high-temperature thermal treatment. The substitutional Te atoms that cause the sub-bandgap absorption are removed from the substitutional sites to form Te-related complexes. In this work, we explore the phase evolution and the electrical deactivation of Te-hyperdoped Si layers upon furnace annealing through the analysis of optical and microstructural properties as well as positron annihilation lifetime spectroscopy. Particularly, Te-rich clusters are observed in samples thermally annealed at temperature reaching 950 °C and above. Combining the analysis of polarized Raman spectra and transmission electron microscopy, the observed crystalline clusters are suggested to consist of Si2Te3. The defect characterization using positron lifetime spectroscopy suggests the generation of vacancy complexes as a function of temperature, leading to the decrease of sheet carrier concentration.

Keywords: Ion-implantation; hyperdoping; Raman spectroscopy; positron annihilation lifetime spectroscopy (PALS); pulsed laser annealing

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  • Poster
    SNI2022, 05.-07.09.2022, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-36417


Soft, flexible, and conductive composite polycaprolactone/molybdenum films: A new type of reliable electrode materials for fully biodegradable electrochemical biosensors

Janićijević, Ž.; Huang, T.; Tonmoy, T. H.; Davydiuk, N.; Besford, Q. A.; Makarov, D.; Baraban, L.

Abstract

Use of fully biodegradable materials for temporary electrical sensing devices has become an attractive approach in healthcare monitoring to enable the elimination of surgical risks associated with the removal of implantable sensors and mitigate the environmental hazards caused by the increasing accumulation of electronic waste. However, the construction of fully biodegradable electronic sensors poses significant challenges in terms of materials selection and design considerations, especially in biochemical sensing where direct contact between the sensing element and aqueous analyte solution is required for detection. In such a sensing configuration, conductive films made of pure biodegradable metals dissolve rapidly and interfere with the measured signals. We present a new formulation of highly conductive, soft, and flexible composite polymer films suitable for biodegradable electrodes in electrochemical biosensors. The films are fabricated using conventional printing techniques from inks and pastes comprising polycaprolactone, molybdenum microparticles, and a biodegradable surfactant employed to ensure good microparticle dispersion and favorable mechanical properties. Obtained films exhibit excellent electrical conductivity (~1000 S/m) and stable impedance profile in a broad frequency range (10⁻¹–10⁴ Hz), which makes them particularly suitable for electrodes in impedimetric sensing. Under physiological conditions in vitro, the composite polymer films degrade in a controlled manner via gradual molybdenum corrosion and polycaprolactone hydrolysis. During the first weeks of degradation, composite films almost completely retain their geometry, electrical conductivity, and mechanical properties, which indicates great potential for reliable monitoring applications. To demonstrate the practical application of polycaprolactone/molybdenum composite films, we employ them as electrodes in fully biodegradable impedimetric sensors for amylase detection based on measuring the degradation of thin glycogen (polysaccharide) coatings. The innovative formulation of electrically conductive polycaprolactone/molybdenum films shows promising properties that can unlock the possibility of constructing fully biodegradable electrochemical biosensors for the point-of-care testing and monitoring of diverse relevant analytes in healthcare.

Keywords: composite polymer films; impedimetric biosensors; glycogen nanomaterials; biodegradable electronics

  • Poster
    Seventh International Symposium Frontiers in Polymer Science, 29.05.-01.06.2023, Gothenburg, Sweden

Permalink: https://www.hzdr.de/publications/Publ-36416


Search for nonlinear THz absorption by electromagnons in multiferroic hexaferrites

Vít, J.; Repček, D.; Kadlec, C.; Kadlec, F.; Adhlakha, N.; Di Pietro, P.; Piccirilli, F.; Kovalev, S.; Deinert, J.-C.; Ilyakov, I.; Awari, N.; Chen, M.; Buršík, J.; Bae Park, C.; Hoon Kim, K.; Gensch, M.; Perucchi, A.; Kamba, S.

Abstract

Complex frustrated magnetic structures in multiferroic hexaferrites are well tunable by temperature, magnetic field and doping. We investigated the influence of strong THz pulses generated by superradiant THz sources on magnetic structure and related electromagnons’ absorption in Y- and Z-type multiferroic hexaferrites. While in Z-type hexaferrite (Ba0.2Sr0.8)3Co2Fe24O41 polycrystal, the observed changes in transmission spectra were fully described by sample heating, a blue-shift of the electromagnon frequency observed in Y-type hexaferrite Ba0.2Sr1.8Co2(Fe0.96Al0.04)12O22 single-crystal could be possibly ascribed to the transition from the alternating longitudinal conical to the transverse conical magnetic structure. We elaborated a nonlinear model which explained absence of nonlinearity in Z-type hexaferrite (Ba0.2Sr0.8)3Co2Fe24O41. For Y-type hexaferrite Ba0.2Sr1.8Co2(Fe0.96Al0.04)12O22, we discuss possible transient or even permanent effects of both THz electric and magnetic fields on its magnetic structure.

Keywords: Terahertz; Multiferroics; Hexaferrites; Electromagnons; Nonlinear dynamics

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-36415


Extended-gate field-effect transistor-based platform for multiplexed sensing of biomolecules using gold nanoparticle-enhanced potentiometric measurement format

Janićijević, Ž.; Nguyen Le, T. A.; Ahmed, A.; Žilėnaitė, R.; Tonmoy, T. H.; Kubeil, M.; Bachmann, M.; Baraban, L.

Abstract

Biosensors based on the extended gate field-effect transistor (EG FET) differ from the traditional FET- based biosensors in terms of creating a spatial separation between the EG sensing element and the FET transducer. Thus, EG can be employed as a cost-effective and disposable unit, while the FET transducer is retained as a reusable component. These features make EG particularly attractive for multiplexed biosensing since an EG electrode array can be easily integrated within a single chip, and individual electrodes can be separately modified for the recognition of diverse analyte types. Although the use of EG FET-based platforms has been successfully demonstrated in advanced biosensing applications,¹˒² they still suffer from practical disadvantages including limited multiplexing, complex nanofabrication of FET transducers, and reliance on bulky specialized high-performance measurement instruments for readout of low current levels (~nA range), all substantially reducing their suitability for many applications in point-of-care (POC) diagnostics and monitoring. We present a custom-designed multiplexed standalone EG FET-based potentiometric biosensing platform relying on a commercial FET transducer, portable modular electronics, and innovative assay format for potentiometric response enhancement based on the conjugation of analyte antibodies (Abs) to gold nanoparticles (AuNPs). To achieve simplified signal readout, we employ an in-house fabricated common reference electrode for all sensing points and operate the FET in constant charge mode. Potential shifts at the EG surface during sensing are indirectly detected as voltage changes between the reference electrode and the FET source terminal. We demonstrate the sensing of antibody-antibody interactions on the immunoglobulin G system and realize the 5-fold amplification of the potentiometric response compared to the traditional label-free assay by introducing AuNP-based labeling of the target analyte. Using the described configuration of the EG FET-based biosensing platform, we can simultaneously obtain astonishingly low limits of detection (down to the aM range) and reach sufficient sensitivity for reliable readout at voltage levels of ~1 V using conventional low-cost electronic modules driven by a microcontroller. Our biosensing approach shows great promise for ultrasensitive and reliable POC measurements in the clinical setting as it already vastly overcomes the limit of detection of gold-standard enzyme-linked immunosorbent assays by several orders of magnitude and allows for robust measurement statistics with the incorporated reproducible multiplexing.

1. Kim, K.; Kim, M.-J.; Kim, D. W.; Kim, S. Y.; Park, S.; Park, C. B. Clinically Accurate Diagnosis of Alzheimer’s Disease via Multiplexed Sensing of Core Biomarkers in Human Plasma. Nat. Commun. 11, 119 (2020).
2. Park, S.; Kim, H.; Woo, K.; Kim, J.-M.; Jo, H.-J.; Jeong, Y.; Lee, K. H. SARS-CoV-2 Variant Screening Using a Virus-Receptor-Based Electrical Biosensor. Nano Lett. 22, 50–57 (2022).

  • Lecture (Conference)
    8th International Winterschool on Bioelectronics (BioEl 2023), 11.-18.03.2023, Kirchberg in Tirol, Austria

Permalink: https://www.hzdr.de/publications/Publ-36414


Optimization of the Extended Gate Field-Effect Transistor-Based Biosensing Platform for the Detection of Biomolecular Interactions

Janićijević, Ž.; Nguyen Le, T. A.; Žilėnaitė, R.; Kubeil, M.; Bachmann, M.; Baraban, L.

Abstract

Electrochemical biosensors are broadly applied to diverse diagnostic procedures, including many assays for the detection of therapeutic agents. Especially in theranostic applications, a controlled and cost-effective setting before entering the stage of in vivo trials is of crucial importance. However, to reach this goal, the performance of electrochemical biosensing platforms still should be improved in terms of stability and reliability. Multiplexing is a practical approach for improving biosensing performance by enabling simultaneous sensing of different analytes, accurate differential measurements, and robust measurement statistics. Biosensing devices based on field-effect transistors (FETs) are already widely used for electrical label-free detection of different biological and chemical analytes. Relying on the concept of the extended gate (EG) as an ultrasensitive and cost-effective sensing element, the EG electrode array can be integrated within a single chip while individual electrodes can be modified to target specific analytes or act as control sensing points. EG array coupled with a reusable FET transducer opens the
possibility for multiplexed analyte sensing when supported with appropriate control and measurement electronics. Typical EG FET-based platforms do not focus on multiplexing and rely on external modules such as specialized instruments for electrical measurements.

We are developing a standalone multiplexed EG FET-based sensing platform with customized electronics enabling FET operation in constant charge mode for simplified signal readout and employing a common reference electrode for all measurement points. Interactions at the EG electrode surface are detected as a shift in voltage response between the source terminal of the FET and the reference electrode. Our platform aims to detect different analytes which are relevant for cancer theranostics such as cytokines, chimeric antigen receptor (CAR) T cells, and bispidine-based chelators used in positron emission tomography (PET) of cancer. Prerequisites for the emulation and detection of delicate biochemical interactions are careful optimization of the electrode surface functionalization process and stability of the voltage response between the extended gate and reference electrodes. Therefore, we present an optimization approach focusing on the pre-conditioning and functionalization of the EG gold electrode surface for the detection of biomolecular interactions also including the customized affordable reference electrode preparation for voltage response stability.

  • Lecture (Conference)
    2022 IEEE 12th International Conference “Nanomaterials: Applications & Properties” (IEEE NAP-2022), 11.-16.09.2022, Kraków, Poland

Permalink: https://www.hzdr.de/publications/Publ-36413


Influence of alginate-based microcapsule permeability on 3D cancer cell cluster proliferation

Peng, X.; Janićijević, Ž.; Lemm, S.; Laube, M.; Pietzsch, J.; Bachmann, M.; Baraban, L.

Abstract

Background: Functional interaction between cancer cells and the surrounding microenvironment is still not sufficiently understood, which motivates the tremendous interest in the development of numerous in vitro and in vivo tumor models.

Study Aims: To study the influence of different permeabilities of microcapsules (MCs) on different cancer cell proliferations, and to design and engineer the formation of 3D tumor clusters in MCs.

Materials and Methods: A fluidics-based low-cost methodology was used to reproducibly generate alginate (AL) and alginate-chitosan (AL-CS) MCs in a cross-junctions water-in-oil system. The diffusion through the shell of AL and AL-CS MCs was monitored using fluorescein sodium (376 Da), FITC-Dextran 70 (70 kDa), and FITC-Dextran 2000 (2000 kDa) as fluorescent probes representing small molecules, proteins, and macromolecules, respectively. HepG2 Red FLuc (human hepatoma cell line) and A375 (human melanoma cell line) cultured in high-glucose DMEM medium were used to study the proliferation differences in terms of dimensions and geometries in AL and AL-CS MCs. The metabolic activity of tumor clusters in MCs was confirmed by tracking the turnover of testosterone to androstenedione with lower case Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS).

Results: HepG2 Red FLuc and A375 cells show different proliferation properties in AL and AL-CS MCs. A375 tumor clusters grow faster in more permeable AL MCs and slower in less permeable AL-CS MCs. In the case of HepG2 Red FLuc, a significant difference in proliferation rate was not observed between AL and AL-CS MCs at the early stage (1 week). Interestingly, it was observed that different loose and tight cell cluster morphologies can form, also including cell proliferation along radial directions in both MC types and both cell lines. Cytochrome P450 (CYP)-dependent metabolization of testosterone by both HepG2 Red FLuc and A375 tumor clusters in the AL and AL-CS MCs showed the same trends in good agreement with their proliferation stages and the CYP expression of both cell lines reported in the literature.

Conclusions: A low-cost cross-junction-based microfluidic droplet system was constructed and used to generate AL MCs and AL-CS MCs with different permeability for culturing HepG2 Red FLuc and A375 cells. As the permeability differences between MCs influence tumor cluster formation, cell proliferation, and metabolic ability of cells, our controlled engineering of MC is an effective method for the targeted design of 3D tumor clusters.

  • Poster
    46th ISOBM Congress, 17.10.2022, Bled, Slovenia

Permalink: https://www.hzdr.de/publications/Publ-36412


Generation and metabolism of liver cancer organoids in alginate-chitosan hybrid microcapsules

Peng, X.; Janićijević, Ž.; Lemm, S.; Laube, M.; Pietzsch, J.; Bachmann, M.; Baraban, L.

Abstract

Liver cancer had the fastest increasing mortality for decades. Compared to 2D models, that cannot simulate the microenvironment, and key functions of organs, 3D organoids models are now entering the field of in vitro analysis. Here, alginate-chitosan hybrid microcapsules are fabricated with a high reproducible cross junction based microfluidic droplet generation system. With high reproducibility and compartmentalization, 103 of microcapsules can be generated within a few minutes. The effects of fluid flow rates on its sizes and shell thicknesses were systematically studied, forming microcapsules with different capsule diameters (~ 300 to 700 µm) and thicknesses (~ 5 to 150 µm). The semi-permeability of these capsules has been well studied, combined a COMSOL model. These microcapsules, with a suitable diffusion rate for nutrients, are applied for human hepatoma cell line encapsulation. Metabolic of organoids in capsules are confirmed by tracking substrates (testosterone) and metabolites (androstenedione). Overall, highly repeatable alginate-chitosan hybrid microcapsules obtained by microfluidic droplet method are not only suitable for liver cancer cells culturing, but also promising for various cell organoids generation.

  • Poster
    Seventh International Conference on Multifunctional, Hybrid and Nanomaterials, 22.10.2022, Genoa, Italy

Permalink: https://www.hzdr.de/publications/Publ-36411


Engineering of the alginate capsules for human hepatoma cell (HepG2) encapsulation

Peng, X.; Janićijević, Ž.; Lemm, S.; Laube, M.; Pietzsch, J.; Bachmann, M.; Baraban, L.

Abstract

Liver cancer is the second most lethal malignancy worldwide. Recently, three-dimensional (3D) cancer organoids models have been constructed and applied to liver cancer research, to predict the therapy outcomes. However, there is still low success and reproducibility rate for generating patient-derived liver tumoroids due to limitations in current technologies. Herein, a high reproducible cross junction based microfluidic droplet generation system is applied for human hepatoma cell line encapsulation and organoids engineering. The fabrication of alginate and alginate-chitosan microcapsules is systematically studied, forming microcapsules with different shell thicknesses (~ 5 to 150 µm) and tunable permeability. In combination with a COMSOL model, the size selective permeability of different molecular complexes through the capsule membrane has been investigated, which is essential to ensure efficient mass transfer of small molecules, and prevent large substances from reaching the loaded cells. Finally, we demonstrate that the cells are prone to aggregate more tightly in capsules with a lower permeability, which causing more hypotonicity and lower viability. Because of the high reproducibility, compartmentalization, and easily permeability tuning, this system not only provides a great platform for liver patient-derived tumoroids forming, but also is promising for other cell organoids design and engineering.

  • Poster
    EMBL Conference: Microfluidics 2022, 13.07.2022, Heidelberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-36410


Research data: High-order nonlinear terahertz probing of the two-band superconductor MgB2: Third- and fifth-order harmonic generation

Reinhoffer, C.; Pilch, P.; Reinold, A.; Derendorf, P.; Kovalev, S.; Deinert, J.-C.; Ilyakov, I.; Ponomaryov, O.; Chen, M.; Xu, T.-Q.; Wang, Y.; Gan, Z.-Z.; Wu, D.-S.; Luo, J.-L.; Germanskiy, S.; Mashkovich, E. A.; van Loosdrecht, P. H. M.; Eremin, I. M.; Wang, Z.

Abstract

Research data generated at the TELBE facility and used in the linked publication. The filenumber corresponding to the figures in the publication are as follows: Fig.1 (a): 032 (b): 032 (c)-(e): 023-033, 035-039 Fig.2 (a): 152 (b): 152 (c): 150-164 Fig. 3 (a): 023-033, 035-039, 108-120, 072, 073, 079-100.

Data evaluation and figure preparation was completed externally by Chris Reinhoffer.

Keywords: Terahertz; Superconductivity; Harmonic Generation; Magnetic Fields; Nonlinear Processes

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Permalink: https://www.hzdr.de/publications/Publ-36409


Transient dynamics of density-driven particle segregation in a rotating drum

Papapetrou, T. N.; Bieberle, M.; Barthel, F.; Hampel, U.; Lecrivain, G.

Abstract

The shearing of a particle bed composed of two or more species results in spontaneous segregation. This poses problems in many industries, where the mixing of granules and powders is a common process and a homogeneous product is desired. In this work, the segregation dynamics occurring in a horizontal rotating drum filled with two granular species that only differ in density is investigated. In this system, radial segregation is relatively fast and occurs over the course of a few drum rotations. State-of-the art techniques allow the study of segregation dynamics at the end walls of a drum, as well as the observation of slow axial dynamics and the steady state of radial mixing inside the drum bulk. They do not allow, however, continuous observation of the transient radial mixing in the bulk. Using the ultrafast X-ray computer tomography it is possible to to take cross-sectional images through the opaque granular systems at 1000 frames per second. The high-speed image sequences from intermediate planes of the drum can reveal the segregation dynamics in the bulk. Here we present experimental results from the transient state of radial mixing for a binary granular system with density difference (density ratio 2.8) and equal size (4 mm) spherical beads in a half-filled drum. Using a dimensionless mixing index (M), we compare the dynamics of radial mixing and segregation in transverse planes in the bulk of the drum, captured with UFXCT, with the dynamics from the circular end caps to highlight wall effects. We also compare two dynamic models for radial mixing and consider the effect of flow on mixing dynamics. We find that second-order dynamics fit better the data than the commonly used first-order, since it accounts for the overshooting mixing dynamics occurring at higher drum speeds. We also find that, compared to the end cap, the dense particle segregation core is larger in the bulk plane and the overshooting in the mixing index is smaller, suggesting a correlation between mixing and flow characteristics, such as the dynamic angle of repose. Our results, because of better describing overmixing, are highly relevant to the pharmaceutical, food and cement industries.

Keywords: ultrafast X-ray computer tomography; particle mixing; high-speed camera; rotating drum

Involved research facilities

  • ROFEX
  • Lecture (Conference)
    PARTEC 2023, 26.-28.09.2023, Nürnberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36408


Genetic, vascular, and amyloid determinants of cerebral blood flow in a preclinical population

Padrela, B. E.; Lorenzini, L.; Collij, L. E.; Vállez García, D.; Coomans, E.; Ingala, S.; Tomassen, J.; Deckers, Q.; Shekari, M.; de Geus, E. J. C.; van de Giessen, E.; Ten Kate, M.; Jelle Visser, P.; Barkhof, F.; Petr, J.; Den Braber, A.; Mutsaerts, H. J. M. M.

Abstract

Aging-related cognitive decline can be accelerated by a combination of genetic factors, cardiovascular and cerebrovascular dysfunction, and amyloid-β burden. Whereas cerebral blood flow (CBF) has been studied as a potential early biomarker of cognitive decline, its normal variability in healthy elderly is less known. In this study, we investigated the contribution of genetic, vascular, and amyloid-β components of CBF in a cognitively unimpaired (CU) population of monozygotic older twins. We included 134 participants who underwent arterial spin labeling (ASL) MRI and [18F]flutemetamol amyloid-PET imaging at baseline and after a four-year follow-up. General estimating equations were used to investigate the associations of amyloid burden and white matter hyperintensities with CBF. We showed that, in CU individuals, CBF: 1) has a genetic component, as within-pair similarities in CBF values were moderate and significant (ICC>0.40); 2) is negatively associated with cerebrovascular damage; and 3) is positively associated with the interaction between cardiovascular risk scores and early amyloid-β burden, which may reflect a vascular compensatory response of CBF to early amyloid-β accumulation. These findings encourage future studies to account for multiple interactions with CBF in disease trajectory analyses.

Involved research facilities

  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-36407


Imaging blood-brain barrier dysfunction: A state-of-the-art review from a clinical perspective

Moyaert, P.; Padrela, B.; Morgan, C.; Petr, J.; Versijpt, J.; Barkhof, F.; Jurkiewicz, M. T.; Shao, X.; Oyeniran, O.; Manson, T.; Wang, D. J. J.; Günther, M.; Achten, E.; Mutsaerts, H. J. M. M.; Anazodo, U. C.

Abstract

Background: The blood-brain barrier (BBB) consists of specialized cells that tightly regulate the in- and outflow of molecules from the blood to the brain parenchyma, protecting the brain’s microenvironment. If one of the BBB components starts to fail, its dysfunction can lead to a cascade of neuroinflammatory events leading to neuronal dysfunction and degeneration.
Main body: Preliminary imaging findings suggest that BBB dysfunction could serve as an early diagnostic and prognostic biomarker for a number of neurological diseases. This review aims to provide clinicians with an overview of the emerging field of BBB imaging in humans by answering three key questions: (1. Disease) In which diseases could BBB imaging be useful? (2. Device) What are currently available imaging methods for evaluating BBB integrity? And (3. Distribution) what is the potential of BBB imaging across all settings, particularly in resource-limited settings?
Conclusion: BBB imaging holds the potential to enable earlier diagnosis and aid in the recruitment of individuals and rapid assessment of treatment response in clinical trials. Further advances are needed, such as the validation, standardization, and implementation of readily available, low-cost, and non-contrast BBB imaging techniques, for BBB imaging to be a useful clinical biomarker in both resource-limited and well-resourced settings.

Involved research facilities

  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-36406


Advancing laser accelerated proton beam performance for dose controlled irradiation studies and beyond the 100 MeV frontier

Schramm, U.

Abstract

Advancing laser accelerated proton beam performance for
dose controlled irradiation studies and
beyond the 100 MeV frontier

Involved research facilities

  • ATHENA
  • Draco
  • Penelope
  • Invited lecture (Conferences)
    John D Lawson Lecture, 08.12.2022, Oxford, UK
  • Invited lecture (Conferences)
    ELI NP Colloquium, 31.05.2023, Magurele, Rumänien
  • Invited lecture (Conferences)
    Advancing Radiobiology Technology, 24.10.2023, London, UK

Permalink: https://www.hzdr.de/publications/Publ-36404


How martensitic transitions make materials smart

Lünser, K.

Abstract

Talk about the basics of martensitic transformations

  • Invited lecture (Conferences)
    How martensitic transitions make materials smart, 31.08.-02.09.2022, Deutschland, Berlin

Permalink: https://www.hzdr.de/publications/Publ-36402


Establishing Laser Accelerated Proton Beam Performance for Dose Controlled and High Dose Rate Irradiation Studies

Schramm, U.

Abstract

Establishing Laser Accelerated Proton Beam Performance
for Dose Controlled and High Dose Rate Irradiation Studies

Involved research facilities

  • ATHENA
  • Draco
  • Penelope
  • Invited lecture (Conferences)
    Plasma Physics Seminar GSI, 14.06.2022, Darmstadt, Deutschland
  • Invited lecture (Conferences)
    Laserlab Europe V JRA Meeting, 13.06.2022, Darmstadt, Deutschland
  • Invited lecture (Conferences)
    Euronnac EAAC, 19.09.2022, La Biodola Elba, Italien
  • Invited lecture (Conferences)
    Laserlab Europ General Assembly, 03.10.2022, Lausanne, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-36400


Science and Applications of Plasma‐Based Accelerators - Health and industrial applications

Schramm, U.

Abstract

Talk on Science and Applications of Plasma‐Based Accelerators - Health and industrial applications

Involved research facilities

  • ATHENA
  • Draco
  • Penelope
  • Invited lecture (Conferences)
    767. WE-Heraeus-Seminar, 16.-18.05.2022, Bad Honnef, Deutschland
  • Invited lecture (Conferences)
    CASUSCON, 11.07.2022, Breslau, Polen

Permalink: https://www.hzdr.de/publications/Publ-36399


Highly Altered State of Proton Transport in Acid Pools in Charged Reverse Micelles

Hao, H.; Adams, E.; Funke, S.; Schwaab, G.; Havenith, M.; Head-Gordon, T.

Abstract

Transport mechanisms of solvated protons of 1 M HCl acid pools,
confined within reverse micelles (RMs) containing the negatively charged surfactant
sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) or the positively charged
cetyltrimethylammonium bromide (CTABr), are analyzed with reactive force field
simulations to interpret dynamical signatures from TeraHertz absorption and dielectric
relaxation spectroscopy. We find that the forward proton hopping events for NaAOT are
further suppressed compared to a nonionic RM, while the Grotthuss mechanism ceases
altogether for CTABr. We attribute the sluggish proton dynamics for both charged RMs
as due to headgroup and counterion charges that expel hydronium and chloride ions
from the interface and into the bulk interior, thereby increasing the pH of the acid pools
relative to the nonionic RM. For charged NaAOT and CTABr RMs, the localization of
hydronium near a counterion or conjugate base reduces the Eigen and Zundel
configurations that enable forward hopping. Thus, localized oscillatory hopping
dominates, an effect that is most extreme for CTABr in which the proton residence time increases dramatically such that even
oscillatory hopping is slow.

Keywords: Counterions; Interfaces; Ions; Micelles; Oscillation

Permalink: https://www.hzdr.de/publications/Publ-36397


High mobility and nonlinear transport of electrons in core/shell nanowires

Rana, R.; Balaghi, L.; Shan, S.; Fotev, I.; Moebus, F.; Venanzi, T.; Hübner, R.; Mikolajick, T.; Schneider, H.; Helm, M.; Pashkin, O.; Dimakis, E.

Abstract

Optical pump – Terahertz (THz) probe (OPTP) spectroscopy has proven efficacy for contactless probing of electronic transport in semiconductor NWs [1]. Particularly in III-V NWs, scattering rates of charge carriers, as well as their plasmonic resonances for typical doping levels, are located in the THz range. The analysis of the optical conductivity spectra using the localized surface plasmon model allows estimating the carrier lifetime and the carrier mobility.
Here, OPTP spectroscopy is employed to study two unique phenomena in GaAs/(In,Al,Ga)As core/shell nanowires. First, it is demonstrated that the mobility of electrons in the hydrostaticallystrained GaAs core (owing to the lattice mismatch between the core and the shell [2]) exceeds the mobility in bulk GaAs by 30-50% [3]. The role of the various scattering mechanisms is analyzed as a function of strain and temperature. Depending on the density of NWs in the probed sample, some of them can form bundles or touch each other, leading to an inhomogeneous broadening of the plasmon resonance. We discuss the role of this effect and its impact on the estimation of carrier mobility [3, 4]. Second, we demonstrate a strong THz nonlinearity using single-cycle intense THz pulses with peak electric fields reaching up to 0.6 MV/cm. With the increase of the driving THz field, we observe a systematic redshift of the plasmon frequency, accompanied by a gradual suppression of the spectral weight. Remarkably, the spectral weight does not remain proportional to the square of the plasmon
frequency when the driving electric field exceeds 0.4 MV/cm, indicating an onset of a spatially inhomogeneous carrier distribution across the NW. The observed behavior can be ascribed to nonlinear effects caused by the scattering of electrons from the Gamma- to L-valley occurring in the high electric field regime. However, in contrast to bulk semiconductors, this effect initially sets in at hot spots of the NW, where the local electric field is enhanced by the plasmonic resonance [5].
All in all, our findings provide important guidelines for the exploitation of nanowires in high-frequency electronics, but also underline the unique strengths of OPTP spectroscopy for the study of electronic transport in nanowires.

[1] H. J. Joyce et al., Semicond. Sci. Technol. 31, 103003 (2016).
[2] L. Balaghi et al., Nat. Commun. 10, 2793 (2019).
[3] L. Balaghi et al., Nat. Commun. 12, 6642 (2021).
[4] I. Fotev et al., Nanotechnology 30, 244004 (2019).
[5] R. Rana et al., Nano Lett. 20, 3225 (2020).

Keywords: Optical Pump Terahertz Probe spectroscopy; III-V semiconductor nanowires; Plasmon resonance

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Related publications

  • Open Access Logo Lecture (Conference)
    Nanowire Week 2022, 25.-29.04.2022, Chamonix, France

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Permalink: https://www.hzdr.de/publications/Publ-36396


Advanced MR Techniques for preoperative Glioma Characterization - Part 2

Hangel, G.; Schmitz-Abecassis, B.; Sollmann, N.; Pinto, J.; Arzanforoosh, F.; Barkhof, F.; Booth, T.; Calvo-Imirizaldu, M.; Cassia, G.; Chmelik, M.; Clement, P.; Ercan, E.; Fernández-Seara, M.; Furtner, J.; Fuster-Garcia, E.; Grech-Sollars, M.; Guven, N. T.; Hatay, G. H.; Karami, G.; Keil, V.; Kim, M.; Koekkoek, J. A.; Kukran, S.; Mancini, L.; Nechifor, R. E.; Özcan, A.; Ozturk-Isik, E.; Piskin, S.; Schmainda, K.; Svensson, S.; Tseng, C. H.; Unnikrishnan, S.; Vos, S.; Warnert, E.; Zhao, M.; Jancalek, R.; Nunes, T.; Hirschler, L.; Smits, M.; Petr, J.; Emblem, K.

Abstract

Preoperative clinical MRI protocols for gliomas, brain tumors with dismal outcomes due to their infiltrative properties, still rely on conventional structural MRI, which does not deliver information on tumor genotype and is limited in the delineation of diffuse gliomas. The GliMR COST action wants to raise awareness about the state of the art of advanced MRI techniques in gliomas and their possible clinical translation. This review describes current methods, limits, and applications of advanced MRI for the preoperative assessment of glioma, summarizing the level of clinical validation of different techniques.
In this second part, we review magnetic resonance spectroscopy (MRS), chemical exchange saturation transfer (CEST), susceptibility-weighted imaging (SWI), MRI-PET, MR elastography (MRE), and MR-based radiomics applications. The first part of this review addresses dynamic susceptibility contrast (DSC) and dynamic contrast-enhanced (DCE) MRI, arterial spin labeling (ASL), diffusion-weighted MRI, vessel imaging, and magnetic resonance fingerprinting (MRF).

Involved research facilities

  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-36395


Advanced MR Techniques for preoperative Glioma Characterization - Part 1

Hirschler, L.; Sollmann, N.; Schmitz-Abecassis, B.; Pinto, J.; Arzanforoosh, F.; Barkhof, F.; Booth, T.; Calvo-Imirizaldu, M.; Cassia, G.; Chmelik, M.; Clement, P.; Ercan, E.; Fernández-Seara, M.; Furtner, J.; Fuster-Garcia, E.; Grech-Sollars, M.; Guven, N. T.; Hatay, G. H.; Karami, G.; Keil, V.; Kim, M.; Koekkoek, J. A. F.; Kukran, S.; Mancini, L.; Nechifor, R. E.; Özcan, A.; Ozturk-Isik, E.; Piskin, S.; Schmainda, K.; Svensson, S.; Tseng, C. H.; Unnikrishnan, S.; Vos, S.; Warnert, E.; Zhao, M.; Jancalek, R.; Nunes, T.; Emblem, K.; Smits, M.; Petr, J.; Hangel, G.

Abstract

Preoperative clinical MRI protocols for gliomas, brain tumors with dismal outcomes due to their infiltrative properties, still rely on conventional structural MRI, which does not deliver information on tumor genotype and is limited in the delineation of diffuse gliomas. The GliMR COST action wants to raise awareness about the state of the art of advanced MRI techniques in gliomas and their possible clinical translation or lack thereof. This review describes current methods, limits, and applications of advanced MRI for the preoperative assessment of glioma, summarizing the level of clinical validation of different techniques.
In this first part, we discuss dynamic susceptibility contrast (DSC) and dynamic contrast-enhanced (DCE) MRI, arterial spin labeling (ASL), diffusion-weighted MRI, vessel imaging, and magnetic resonance fingerprinting (MRF). The second part of this review addresses magnetic resonance spectroscopy (MRS), chemical exchange saturation transfer (CEST), susceptibility-weighted imaging (SWI), MRI-PET, MR elastography (MRE), and MR-based radiomics applications.

Involved research facilities

  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-36394


Flexible and printed magnetic field sensors

Zabila, Y.; Makushko, P.; Oliveros Mata, E. S.; Kosub, T.; Illing, R.; Volkov, O.; Faßbender, J.; Mönch, J. I.; Xu, R.; Pylypovskyi, O.; Makarov, D.; Cañón Bermúdez, G. S.; Milkin, P.; Ionov, L.; Hassan, M.; Laureti, S.; Rinaldi, C.; Fagiani, F.; Barucca, G.; Schmidt, N.; Albrecht, M.; Vladymyrskyi, I.; Varvaro, G.; Ha, M.; Wang, Y.

Abstract

Work with spintronic functional elements for flexible magnetic field sensors, we was interested
in improving their performance, relying on new materials and metrological approaches. We
employ novel fabrication technics as an alternating magnetic field activation of self-healing of
percolation network [1]. It allows to fabricate printable magnetoresistive sensors revealing an
enhancement in sensitivity of more than one and two orders of magnitude, relative to previous
reports. Printed electronics are attractive due to their low-cost and large-area processing
features, which have been successfully extended to magnetoresistive sensors and devices [2].
This technology was enabled initially, by thin films magnetic field sensors, embedded in a soft
and flexible format to constitute magntosensitive electronic skin (e-skins). But now we
demonstrate what interactive electronics, based on flexible spin valve switches [3] or printed
and stretchable Giant Magnetoresistive Sensors, could act also as a logic elements, namely
momentary and permanent (latching) switches. All this printing technology aspects are yet to
be developed to comply with requirements to mechanical conformability of on-skin appliances.
Due to the fact that the metallic layer is subjected to unsteady mechanical stresses, deposition
of the magnetic sensor onto few microns thick non-rigid substrate creates a numerous
problems, and the strain sensitivity is the first effect which have to be discussed. The
thermoelectric effect is the second effect that also have to be considered in order to minimize
thermal errors. These aspects will be discussed more detailed in this contribution.

References

[1] R. Xu, Nature Communications 13, 6587 (2022)
[2] E. S. Oliveros Mata, Applied Physics A 127, 280 (2021)
[3] P. Makushko, Adv. Funct. Mater. 31, 2101089 (2021)
[4] M. Ha, Adv. Mater. 33, 2005521 (2021)

Keywords: Flexible; Magnetic; Sensor

  • Poster
    776. WE-Heraeus-Seminar, 04.-06.01.2023, Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-36393


Homogenization and Chemical Ordering in Co-Pt Thin Films

Pedan, R.; Makushko, P.; Dubikovskyi, O.; Bodnaruk, A.; Burmak, A.; Makarov, D.; Vladymyrskyi, I.

Abstract

Binary alloys based on CoPt are attractive as a materials for spintronics, permanent magnets applications and data storage devices due to the high and tunable coercivity combined as well as an excellent corrosion resistance [1].
The formation of chemically ordered CoPt magnetic phases is intensively studied both in thin films and in nanoparticles [2, 3]. In Co-Pt alloys, a large coercive field and magnetic anisotropy can be achieved even in chemically disordered alloys due to short-range order [4]. We have implemented a systematic structural and magnetometry study of the diffusion-controlled formation of a homogeneous CoPt alloy by vacuum heat treatment of Pt/Co stacks, where diffusion processes are driven by diffusion-induced grain boundary migration mechanism.
Layered stacks of Pt(14 nm)/Co(13 nm)/Ta(3 nm) were magnetron sputter deposited and annealed in vacuum of 10‑6 mbar in the temperature range of 200 °С – 550 °С. The structure, chemical composition and magnetic properties of the films were analyzed by X-ray diffraction, secondary ion mass spectrometry, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and VSM magnetometry.
We demonstrate that a Co‑Pt alloy with a homogeneous structure is formed after annealing at temperature above 500 °C. Despite the fact that long-range chemical order in CoPt film was not formed, thermal treatment leads to an increase of the coercive field. We attribute the short-range chemical ordering as a mechanism responsible for the formation of a local anisotropy in Co‑Pt alloy. In this respect, our study suggests that the diffusion mechanism relying on grain boundary migration can be used to promote short-range ordering in binary magnetic alloys. These results will motivate further studies of diffusion processes and the formation of hard magnetic chemical

  • Lecture (Conference)
    IEEE 12th International Conferenfe "Nanomaterials: Applications & Properties", 11.-16.09.2022, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-36392


Flexomagnetism and vertically graded Néel temperature of antiferromagnetic Cr2O3 thin films

Makushko, P.; Kosub, T.; Pylypovskyi, O.; Hedrich, N.; Li, J.; Pashkin, O.; Avdoshenko, S.; Hübner, R.; Ganss, F.; Wolf, D.; Lubk, A.; Liedke, M. O.; Butterling, M.; Wagner, A.; Wagner, K.; Shields, B. J.; Lehmann, P.; Veremchuk, I.; Faßbender, J.; Maletinsky, P.; Makarov, D.

Abstract

Thin films of antiferromagnetic insulators (Cr2O3, NiO etc.) are a prospective material platform for magnonics, spin superfluidity, THz spintronics, and non-volatile data storage. A standard micromagnetic approach for the description of such thin films relies on the effective parameters being homogeneously distributed along the film thickness. The family of magnetomechanical effects includes piezo- and flexomagnetic responses, which determine the modification of the magnetic order parameters due to homogeneous or inhomogeneous strain, respectively. Accounting for the magnetomechanical coupling promises technological advantages: the cross-coupling between elastic, magnetic and electric subsystems opens additional degrees of freedom in the control of the respective order parameters [1, 2, 3].
In this work, we discover the presence of flexomagnetic effects in epitaxial Cr2O3[4]. We demonstrate that a gradient of mechanical strain affect the order-disorder magnetic phase transition resulting in the distribution of the Neel temperature along the thickness of a Cr2O3 film. The inhomogeneous reduction of the antiferromagnetic order parameter induces a flexomagnetic coefficient of about 15 µB nm-2. The antiferromagnetic ordering in the strained films can persist up to 100°C, rendering Cr2O3 as a prospective material for industrial electronics applications. Strain gradient in Cr2O3 thin films enables fundamental research on magnetomechanics and thermodynamics of antiferromagnetic solitons, spin waves and artificial spin ice systems in magnetic materials with continuously graded parameters.

  • Lecture (Conference)
    776. WE-Heraeus-Seminar Re-thinking Spintronics: From Unconventional Materials to Novel Technologies, 04.-06.01.2023, Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-36391


Curvature-induced Tilt and pinning in CrOx/Co/Pt corrugated strips

Fernandez Roldan, J. A.; Shakeel, S.; Quintana Uriarte, M.; Volkov, O.; Pylypovskyi, O.; Oliveros Mata, E. S.; Abert, C.; Suess, D.; Kronast, F.; Mawass, M.-A.; Erb, D.; Makarov, D.

Abstract

In recent years, curvilinear nanomagnetism is attracting attention for the broad range of effects emerging in curved geometries that are appealing for the innovative developments in stretchable and magnetoelectric devices, microrobots, sensors, flexible magnetic memories and nanoelectronics [1-5].
These phenomena encompass a vast range of exchange- and Dzyaloshinskii-Moriya (DMI)- induced interactions that typically result in topological magnetization patterning in shells, chiral symmetry breaking, and pinning of domain walls [1-5]. Less attention has been paid though to the role of the curvilinear effects in the magnetization dynamics of domain walls in curved geometries [4]. From application perspectives, spin-orbit torques are appealing as an alternative way to achieve the manipulation of magnetic domain walls and magnetization [8] with the breakthrough of lower power consumption. Recent developments in ultra-thin planar asymmetric multilayered strips describe a method to extract DMI and damping estimations from the dynamical tilt of domain walls from static measurements [9]. Following a similar approach, here we provide first results in single 100 nm-wide thin periodically corrugated strips of CrOx/Co/Pt with thickness of 2 nm and average curvature of 0.06 nm-1, tailored for an enhanced exchange-induced DMI. The orientation of the corrugation is tuned from the parallel to the perpendicular direction of the strip axis in different strips.
Our results indicate that curvature plays a crucial role in the pinning and tilting of domain walls through DMI-induced and exchange-induced effects. In particular, DMI-induced anisotropy leads the pinning mechanism, while its combination with exchange-induced effects enhances the domain wall tilt. This opens a perspective for quantification and design of curvature-induced effects with application prospects in current challenges of spin-based nanoelectronics [10].

[1] Denys Makarov, et al., Advanced Materials 34, 3 (2022)
[2] Denis D Sheka, Oleksandr V Pylypovskyi et al., Small 18, 12 (2022)
[3] D. Sander et al., J. Phys. D: Appl. Phys. 50, 363001 (2017).
[4] E. Y. Vedmedenko, et al., J. Phys. D. Appl. Phys. 53, 453001 (2020).
[5] D. Makarov et al., Applied Physics Reviews 3, 011101 (2016).
[6] E. Berganza et al., Sci Rep 12, 3426 (2022)
[7] J.A. Fernandez-Roldan et al., Sci Rep 9, 5130 (2019).
[8] O. V. Pylypovskyi et al., Scientific Reports 6, 23316 (2016).
[9] O. M. Volkov et al., Phys. Rev. Applied 15, 034038 (2021)
[10] B. Dieny, et al., Nat Electron 3, 446 (2020).

Keywords: curvilinear magnetism; nanomagnetism; domain wall; corrugated substrate

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  • Open Access Logo Lecture (Conference)
    International Conference IEEE Advances in Magnetics AIM2023, 15.-18.01.2023, Moena. Val di Fassa, Italy

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Skin-conformal magnetoreceptors human-machine interaction

Makushko, P.; Oliveros Mata, E. S.; Canon Bermundez, G. S.; Hassan, M.; Laureti, S.; Rinaldi, C.; Fagiani, F.; Barucca, G.; Zabila, Y.; Faßbender, J.; Vladymyrskyi, I.; Albrecht, M.; Varvaro, G.; Xu, R.; Makarov, D.

Abstract

Artificial magnetoception, i.e., electronically expanding human perception to detect magnetic fields, is a new and yet unexplored route for interacting with our surroundings. This technology relies on thin, soft, and flexible magnetic field sensors, dubbed magnetosensitive electronic skins (e-skins) [1]. These devices enable reliable and obstacle insensitive proximity, orientation and motion tracking features [2, 3] as well as bimodal touchless-tactile interaction [4].
Although, basic interactive functionality has been demonstrated, the current on-skin magnetoreceptors are not yet employed as advanced spintronics-enabled switches and logic elements for skin compliant electronics. The major limitation remains primarily due to the use of in-plane magnetized layer stacks. The predominant in-plane sensitivity prevents these devices from becoming intuitive switches or logic elements for interactive flexible electronics, as the natural actuation axis of switches is out-of-plane.
Here, we will introduce current technologies towards realization of skin-conformal magnetoelectronics for touchless and tactile interactivity in virtual and augmented reality. The focus will be put on the fabrication of on-skin spin valve switches with out-of-plane sensitivity to magnetic fields [5]. The device is realized on a flexible foil relying on Co/Pd multilayers with perpendicular magnetic anisotropy and synthetic antiferromagnet as a reference layer. Owing to the intrinsic tunability, these interactive elements can provide fundamental logic functionality represented by momentary and permanent (latching) switches and reliably discriminate the useful signals from the magnetic noise. The flexible device retain its performance upon bending down to 3.5 mm bending radii withstand more than 600 bending cycles.
We showcase the performance of our device as on-skin touchless human-machine interfaces, which allows interactivity with a virtual environment, based on external magnetic fields. We envision that this technology platform will pave the way towards magnetoreceptive human-machine interfaces or virtual- and augmented reality applications, which are intuitive to use, energy efficient, and insensitive to external magnetic disturbances.

  • Lecture (Conference)
    4th IEEE International Conference on Advances in Magnetics, 15.-18.01.2023, Moena, Italy

Permalink: https://www.hzdr.de/publications/Publ-36389


Curvilinear phenomena in magnetization dynamics and in stray field

Fernandez Roldan, J. A.; Quintana Uriarte, M.; Shakeel, S.; Volkov, O.; Pylypovskyi, O.; Oliveros Mata, E. S.; Kronast, F.; Mawass, M.-A.; Abert, C.; Suess, D.; Erb, D.; Faßbender, J.; Makarov, D.

Abstract

In recent years, curvilinear magnetism is captivating due to the broad range of phenomena emerging in curved geometries that are appealing for developments in stretchable and magnetoelectric devices, microrobots, sensors, flexible memories and nanoelectronics [1-5].
These phenomena encompass exchange- and Dzyaloshinskii-Moriya (DMI)-induced interactions that typically result in topological magnetization patterning in thin shells, symmetry breaking, and pinning of domain walls [1-9]. Less attention is been paid though to the role of the curvilinear effects in the stray field, and in the magnetization dynamics [4]. For application development, spin-orbit torques provide an alternative way to manipulate magnetic domain walls and magnetization [10, 11] with reduced power consumption.
Here we present first results in stray field calculation in curvilinear geometries, and domain wall tilts in single 100 nm wide 2 nm thin periodically corrugated strips of CrOx/Co/Pt with average curvature of 0.06 nm-1.

References

[1] D. Makarov, et al., Advanced Materials 34, 2101758 (2022)
[2] D. Sheka, et al., Small 18, 2105219 (2022)
[3] D. Sander et al., J. Phys. D: Appl. Phys. 50, 363001 (2017).
[4] E. Y. Vedmedenko, et al., J. Phys. D. Appl. Phys. 53, 453001 (2020).
[5] D. Makarov et al., Applied Physics Reviews 3, 011101 (2016).
[6] E. Berganza et al., Sci. Rep. 12, 3426 (2022)
[7] E. Berganza et al., Nanoscale 12, 18646 (2022)
[8] J. A. Fernandez-Roldan et al., APL Materials 10, 111101 (2022)
[9] J. A. Fernandez-Roldan et al., Sci Rep 9, 5130 (2019).
[10] O. V. Pylypovskyi et al., Scientific Reports 6, 23316 (2016).
[11] O. M. Volkov et al., Phys. Rev. Applied 15, 034038 (2021)

Keywords: curvilinear magnetism; domain wall; magnetization dynamics; corrugated; Co/Pt; XMCD; micromagnetic modelling

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  • Open Access Logo Poster
    776. WE-Heraeus-Seminar. Re‐thinking Spintronics: From Unconventional Materials to Novel Technologies, 03.-06.01.2023, Physikzentrum Bad Honnef., Germany

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Domain Wall Propagation and Pinning Induced by Current Pulses in Cylindrical Modulated Nanowires

Bran, C.; Fernandez Roldan, J. A.; Moreno, J. A.; Fraile Rodríguez, A.; Del Real, R. P.; Asenjo, A.; Saugar, E.; Marqués-Marchán, J.; Mohammed, H.; Foerster, M.; Aballe, L.; Kosel, J.; Vazquez, M.; Chubykalo-Fesenko, O.

Abstract

The future developments of three-dimensional magnetic nanotechnology require the control of domain wall dynamics by means of current pulses. While this has been extensively studied in planar magnetic strips (planar nanowires), few reports exist in cylindrical geometry, where Bloch point domain walls are expected to have intriguing properties. Here we report this investigation in cylindrical magnetic Ni nanowires with geometrical notches. Experimental work based on synchrotron X-ray magnetic circular dichroism (XMCD) combined with photoemission electron microscopy (PEEM) indicates that large current densities induce domain wall nucleation while smaller currents move domain walls preferably against the current direction. In the region where no pinning centers are present we found domain wall velocity of about 1 km/s. The domain wall motion along current was also detected in the vicinity of the notch region. Pinning of domain walls has been observed not only at geometrical constrictions but also outside of them. Thermal modelling indicates that large current densities temporarily raise the temperature in the nanowire above the Curie temperature leading to nucleation of domain walls during the system cooling. Micromagnetic modelling with spin-torque effect shows that for intermediate current densities Bloch point domain walls with chirality parallel to the Oersted field propagate antiparallel to the current direction. In other cases, domain walls can be bounced from the notches and/or get pinned outside their positions. We thus find that current is not only responsible for the domain wall propagation but is also a source of pinning due to the Oersted field action.

Keywords: cylindrical magnetic nanowires; domain wall dynamics; 3D nanomagnetism; XMCD-PEEM; micromagnetic modeling

Permalink: https://www.hzdr.de/publications/Publ-36387


CFD modelling of flashing flows for nuclear safety analysis: possibilities and challenges

Liao, Y.

Abstract

Due to its relevance for the safety analysis of pressurized water reactors, many research activities on flashing flows in pipes and nozzles arose from the mid of last century. Most of them have focused on the mass flow rate and pressure or temperature fluctuation by means of experiments and system codes. With the increase in computer speed, computational fluid dynamics is used more and more in the investigation of flashing flows, which has the advantage of providing further insights regarding the internal flow structure as well as its evolution. Various mixture or two-fluid models have been proposed in the literature. However, knowledge on the non-equilibrium effects, interphase transfer as well as interfacial area under different flashing conditions is still insufficient, and a general and precise definition of the problem remains a challenge. In this work, the two-fluid model is adopted to simulate various nuclear flashing scenarios (pipe blowdown, nozzle flashing flow, steam-generator leakage, flashing-induced instability, pressure release). It is shown that the thermal phase-change model is superior to pressure phase-change, relaxation and equilibrium models. Nevertheless, efforts are required to improve the interphase heat-transfer model. Furthermore, since flashing is often accompanied with high void fraction and broad bubble size range, a poly-disperse two-fluid model is recommended, and further research is needed to account for the effect of phase change on bubble coalescence and breakup. In addition, during flashing the flow pattern may change from single phase to bubbly flow, churn flow, annular flow, and even mist flow. The rapid change of interfacial topology as well as its influence on the applicability of closure models needs to be considered.

Keywords: Challenges; Computational Fluid Dynamics; Flashing flow; Interfacial heat transfer; Nuclear safety analysis

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  • TOPFLOW Facility
  • Lecture (Conference)
    34th German CFD Network of Competence Meeting, 14.-15.03.2023, Garching bei München, Germany
  • Kerntechnik 89(2024)2, 169-184
    DOI: 10.1515/kern-2023-0090

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  • Secondary publication expected from 20.03.2025

Permalink: https://www.hzdr.de/publications/Publ-36386


The effect of particles on the film drainage and bubble coalescence in a slurry bubble column

Liao, Y.

Abstract

Understanding bubble coalescence in slurry columns and how it is affected by the presence of particles is of great significance to a variety of engineering applications. Despite decades of research, high-resolution data on the film drainage process in a bubble column are scarce, which prevents a precise description of the phenomenon and the derivation of reliable models for further analyses. The existing work on bubble coalescence in the presence of particles either focuses on experimental or analytical studies under nearly hydrostatic conditions with very low approach velocity (up to 0.1 mm/s), or is limited to a mesoscopic scale, for example, by acquiring void fraction and bubble size distribution changes in the column. The present work aims to fill the gap in-between and provide insights into the film drainage process at the microscopic scale under bubble column hydrodynamic conditions. By coupling the volume-of-fluid (VOF) and multiphase particle-in-cell (MP-PIC) methods with a chimera mesh approach in OpenFOAM, a high resolution of the interface and fluid flow field is realized and meaningful results on the effect of particles are achieved. In the investigated parameter range and condition, the presence of particles in the liquid is shown to affect majorly the film drainage process, while have negligible effects on the bubble rise and approach velocity. The influence of particle number concentration is found to be complex and multimodal in co-axial coalescence. At sufficiently low concentration, particles are pushed out from the film and do not alter the drainage and coalescence rate noticeably. As the concentration increases, first a physical blocking effect then a slight promotion because of the drainage changing from axisymmetry to asymmetry is observed. The drainage process is greatly retarded by a conjunct motion, where the bubbles rotate along the colliding interfaces. Furthermore, no dimple formation is observed at high concentrations, which is typical at low particle load or in pure liquids. As the film is thinned down to a critical thickness in the conjunct stage, the interface becomes wavy and instable leading to film rupture. The presence of particles captured in the thin film affects its stability greatly. Both particle size and density are shown to have a dual effect on the coalescence time. Increasing of them leads to first suppression then promotion of coalescence. The results on the effects of number concentration, particle size and density agree with the observations of the previous literature.

Keywords: Bubble coalescence; OpenFOAM; VOF; Particle effect; Slurry column

  • Lecture (Conference)
    93rd GAMM Annual Meeting 2023, 30.05.-02.06.2023, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36385


Transport properties of Fe60Al40 during the B2 to A2 structural phase transition

Sorokin, S.; Anwar, M. S.; Hlawacek, G.; Boucher, R.; Salgado Cabaco, J.; Potzger, K.; Lindner, J.; Faßbender, J.; Bali, R.

Abstract

The variation of transport behaviour in a mesoscopic Fe60Al40 wire, initially possessing the ordered B2-phase structure, has been observed while inducing a phase transition to the disordered A2 structure. Gradual disordering was achieved using a highly focused beam of Ne+-ions. Both electrical resistance and anomalous Hall effect were measured in parallel with the local ion irradiation. Both the normal and Hall resistivity show a peak as a function of fluence. Moreover, the relationship between Hall resistivity and normal resistivity reconfirms the presence of two distinct regimes in the transition. Furthermore, field-dependence and temperature-dependence measurements were used to identify that it is necessary to consider the effect of scattering from magnetic clusters to understand these different regimes in transport properties.

Keywords: ion beams; magnetic materials; phase transitions; transport properties; ion microscope; magnetic clusters; ion irradiation

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Permalink: https://www.hzdr.de/publications/Publ-36384


Tuning catalytic activity of Ni–Co nanoparticles synthesized by gamma-radiolytic reduction of acetate aqueous solutions

Yang, Y.; Korzhavyi, P.; Nikolaychuk, P.; Bazarkina, E.; Kvashnina, K.; Butorin, S.; Tarakina, N.; Soroka, I.

Abstract

Transition metal-based catalysts show great potential to replace Pt-based material in energy conversion devices thanks to their low cost, reason-able intrinsic activity, thermodynamic stability, and corrosion resistance. The electrochemical performance of such catalysts is sensitive to their composition and structure. Here, it is demonstrated that homogeneous alloy nanoparticles with varying Ni-to-Co ratio and controlled structure can be synthesized from aqueous Ni(Co) acetate solutions using a facile γ-radiolytic reduction method. The obtained samples are found to possess defects that are ordered to form polytypes structures. The concentration of these defects depends on the Ni-to-Co ratio, as supported by the results of ab initio calculations. It is found that structural defects may influence the activity of catalysts toward the oxygen evolution reaction, while this effect is less pronounced with respect to the oxygen reduction reaction. At the same time, the activity of Ni–Co catalysts in the hydrogen evolution reaction is affected by formation of NiOH bonds on the surface rather than by the presence of structural defects. This study demonstrates that the composition of NiCo nanoparticles is an essential factor affecting their structure, and both composition and structure can be tuned to optimize electrochemical performance with respect to various catalytic reactions.

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Permalink: https://www.hzdr.de/publications/Publ-36383


Group IV Nanowires for Reconfigurable Field Effect Transistors

Khan, M. M.; Steuer, O.; Prucnal, S.; Georgiev, Y.

Abstract

CMOS scaling is reaching physical limits in near future. Therefore, new approaches are required to continue achieving high speed and high performance devices. Replacing silicon with silicon-germanium alloy as a channel material having higher mobility contributes to faster and energy-efficient devices. In this work, we are investigating the transistor properties built from silicon germanium based nanowire channel. Schottky Barrier Field Effect Transistors are fabricated, which also have an additional functionality of re-configurability. This means that a single device can be operated as an N or P channel just by controlling the electric potential applied at the gate terminals. The devices are fabricated by top-down approach with nickel metal pads on both sides of the silicon-germanium nanowire. To form schottky junctions, flash lamp annealing is performed to diffuse metal into the nanowires. The schottky junctions formed at the interface between nickel-germano-silicide and nanowire are electrically controlled to operate the device. Transfer characteristics of these devices are measured to investigate the transistor properties.

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Related publications

  • Lecture (Conference)
    NANONET+ Workshop, 04.-06.10.2022, Görlitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-36382


Fabrication & Electrical characterization of Silicon-Germanium Nanowire Schottky Barrier Transistors

Khan, M. M.; Steuer, O.; Prucnal, S.; Georgiev, Y.

Abstract

CMOS scaling is reaching physical limits in near future. Therefore, new approaches are required to continue achieving high speed and high performance devices. Replacing silicon with silicon-germanium alloy as a channel material having higher mobility contributes to faster and energy-efficient devices. In this work, we are investigating the transistor properties built from silicon germanium based nanowire channel. Schottky Barrier Field Effect Transistors are fabricated, which also have an additional functionality of re-configurability. This means that a single device can be operated as an N or P channel just by controlling the electric potential applied at the gate terminals. The devices are fabricated by top-down approach with nickel metal pads on both sides of the silicon-germanium nanowire. To form schottky junctions, flash lamp annealing is performed to diffuse metal into the nanowires. The schottky junctions formed at the interface between nickel-germano-silicide and nanowire are electrically controlled to operate the device. Transfer characteristics of these devices are measured to investigate the transistor properties.

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Related publications

  • Poster
    DPG Meeting of the Condensed Matter Section (SKM), 04.-09.09.2022, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-36381


Group IV nanowires: a versatile toolbox for nano-and optoelectronic device

Khan, M. B.; Echresh, A.; Ghosh, S.; Arora, H.; Chava, P.; Jazavandi Ghamsari, S.; Khan, M. M.; Steuer, O.; Prucnal, S.; Hübner, R.; Rebohle, L.; Zhou, S.; Helm, M.; Erbe, A.; Georgiev, Y.

Abstract

The attractive properties of semiconductor nanowires (NWs) are making them an appealing platform for building a variety of nanoelectronic, optoelectronic, sensing, etc. devices. In the wide range of semiconductor NWs, the ones based on group IV elements deserve a special attention. Beside the extensively studied silicon (Si) and germanium (Ge), their alloys with tin (Sn) – GeSn and SiGeSn – are very promising because of a number of unique properties. Suitable Sn concentrations allow effective bandgap engineering as well as achieving high charge carrier mobility and even a direct Group IV semiconductor for optoelectronic applications. In such a way, the SiGeSn alloy system combines the flexibility of III/V compound semiconductors and heterostructures with the mobility gain of Ge/GaAs hybrid systems and the maturity of the Si processing technology. This makes it ideal for post-Si based nanoelectronic and optoelectronic applications, if SiGeSn heterostructures can successfully be integrated into the well-established Si fabrication platforms.

In this talk, the top-down fabrication of Si, Ge and alloy NWs with varying content of the different elements (Si1-x-yGeySnx) will first be presented. Then, their challenging structural and electrical characterisation will be discussed. Here, special attention will be paid to the transmission electron microscopy (TEM) as well as to the Hall Effect measurements using a novel six-contact Hall bar configuration with symmetric contact bars located opposite to each other. This configuration allows reliable evaluation of the electrical properties of even very small nanowires with widths down to 20-30 nm as well as quantification of such parameters as carrier concentration (n), Hall mobility (µH), and resistivity (ρ).

Finally, some innovative nanoelectronic devices based on the fabricated NWs will be reviewed, in particular junctionless nanowire transistors (JNTs) and reconfigurable field effect transistors (RFETs). Different configurations of such devices will be discussed together with their structural and electrical characterisation. A special focus will be put on Si JNTs for sensing application as well as on Si, Ge, SiGe, GeSn and SiGeSn JNTs and RFETs for digital logic.

Acknowledgments: This work was partially supported by the German Bundesministerium für Bildung und Forschung (BMBF) under the project "ForMikro": Group IV heterostructures for high performance nanoelectronic devices (SiGeSn NanoFETs), Project-ID: 16ES1075, and by the European Union’s Horizon 2020 Research and Innovation programme under the project RADICAL, Grant Agreement No. 899282. We gratefully acknowledge the HZDR Ion Beam Centre and nanofabrication facility NanoFaRo.

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  • Invited lecture (Conferences)
    2022 E-MRS Fall Meeting, 19.-22.09.2022, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-36380


Nemacol is a Small Molecule Inhibitor of C. elegans Vesicular Acetylcholine Transporter with Anthelmintic Potential

Harrington, S.; Pyche, J.; Andrew, R. B.; Spalholz, T.; Ryan, K. T.; Baker, R. J.; Ching, J.; Rufener, L.; Lautens, M.; Kulke, D.; Vernudachi, A.; Zamanian, M.; Deuther-Conrad, W.; Brust, P.; Roy, P. J.

Abstract

Nematode parasites of humans and livestock pose a significant burden to human health, economic development, and food security. Anthelmintic drug resistance is widespread among parasites of livestock and many nematode parasites of humans lack effective treatments. Here, we present a nitrophenyl-piperazine scaffold that induces motor defects rapidly in the model nematode Caenorhabditis elegans. We call this scaffold Nemacol and show that it inhibits the vesicular acetylcholine transporter (VAChT), a target recognized by commercial animal and crop health groups as a viable anthelmintic target. We demonstrate that it is possible to create Nemacol analogs that maintain potent in vivo activity whilst lowering their affinity to the mammalian VAChT 10-fold. We also show that Nemacol enhances the ability of the anthelmintic Ivermectin to paralyze C. elegans and the ruminant nematode parasite Haemonchus contortus. Hence, Nemacol represents a promising new anthelmintic scaffold that acts through an identified viable anthelmintic target.

Keywords: Nemacol; VAChT; nematicide; acetylcholine transporter; UNC-17; C. elegans; acetylcholine esterase; AChE; Ivermectin; structure-activity relationship

Permalink: https://www.hzdr.de/publications/Publ-36379


Group IV nanowires: fabrication, characterisation and applications

Khan, M. B.; Echresh, A.; Ghosh, S.; Arora, H.; Chava, P.; Jazavandi Ghamsari, S.; Khan, M. M.; Steuer, O.; Prucnal, S.; Hübner, R.; Rebohle, L.; Zhou, S.; Helm, M.; Erbe, A.; Georgiev, Y.

Abstract

Semiconductor nanowires (NWs) attract significant attention due to their superb electrical and
mechanical properties and large surface area to volume ratio. They are promising building
blocks of devices for a number of possible applications such as nanoelectronics, nanophotonics,
photovoltaics, sensorics, etc. Among the large variety of semiconductor NWs, the ones based
on group IV elements – mainly silicon (Si), germanium (Ge) and their alloys with tin (Sn) (Si1-
x-yGeySnx) – stand out because of their appealing properties and superior compatibility with the
well-established silicon technology. This is an important prerequisite for their relatively easy
integration into the existing semiconductor fabrication platforms.

In the talk, the NWs that we work with will first be presented. These include top-down
fabricated Si and Ge NWs as well as nanowires of binary and ternary Si1-x-yGeySnx alloys with
varying content of the different elements.

Particular attention will be paid to structural and electrical characterisation of the nanowires
and especially to Hall Effect measurements using a novel six-contact Hall bar configuration
with symmetric contact bars located opposite to each other. Such a configuration with narrow
bars increases the precision of Hall contacts fabrication and enhances the accuracy of the Hall
Effect measurement by avoiding shorting out the Hall voltage. This allows to reliably evaluate
the electrical properties of even very small nanowires, down to 20-30 nm, and quantify their
carrier concentration (n), Hall mobility (μH), and resistivity (ρ).

The innovative nanoelectronic devices that we are targeting will also be discussed, namely
junctionless nanowire transistors (JNTs) and reconfigurable field effect transistors (RFETs).
We are in particular interested in Si JNTs for sensing application as well as in Ge, SiGe, GeSn
and SiGeSn JNTs for digital logic. In the case of RFETs, we are currently working on Si, SiGe
and GeSn RFETs and planning to work also on SiGeSn RFETs. Different configurations of
such devices will be discussed together with their structural and electrical characterisation.

Acknowledgments: This work was partially supported by the German Bundesministerium für
Bildung und Forschung (BMBF) under the project "ForMikro": Group IV heterostructures for
high performance nanoelectronic devices (SiGeSn NanoFETs), Project-ID: 16ES1075, and by
the European Union’s Horizon 2020 Research and Innovation programme under the project
RADICAL, Grant Agreement No. 899282. We gratefully acknowledge the HZDR Ion Beam
Centre and nanofabrication facility NanoFaRo.

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Related publications

  • Invited lecture (Conferences)
    14-th International Conference on Electron Beam Technologies EBT 2022, 26.06.-01.07.2022, Varna, Bulgaria

Permalink: https://www.hzdr.de/publications/Publ-36378


Fabrication and Electrical Characterisation of Junctionless Nanowire Transistors for Detection of Atmospheric Radicals and Other Gases

Ghosh, S.; Bilal Khan, M.; Vardhan, V.; Kentsch, U.; Prucnal, S.; Biswas, S.; Holmes, J.; Erbe, A.; Georgiev, Y.

Abstract

Silicon junctionless nanowire transistors (JNTs) have shown excellent sensitivity to record-low concentrations of the protein streptavidin in liquid phase. However, JNTs have not yet been tested for sensing in gas phase. Here we present the fabrication and initial electrical characterisation of JNT-based electronic sensors for detection of atmospheric free radicals such as hydroxyl (•OH) and nitrate (•NO3), which are the main drivers of chemical processes in the atmosphere. The aim of this work is to develop small, low-cost JNT-based nanosensors for radical detection. Silicon-on-insulator wafers were doped by ion implantation and flash-lamp annealing. Device patterning was based on electron beam lithography, inductively-coupled reactive ion etching, metal deposition and lift-off. Initial electrical characterisation and gas sensing experiments on fabricated devices proved their good performance and potential suitability for detection of atmospheric free radicals

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  • Lecture (Conference)
    DPG Meeting of the Condensed Matter Section (SKM), 04.-09.09.2022, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-36377


International Roadmap for Devices and Systems (IRDS™) 2021 Edition, Brief Overview

Georgiev, Y.

Abstract

The talk presents a brief overview of the latest edition of the International Roadmap for Devices and Systems (IRDS™).

  • Lecture (others) (Online presentation)
    Nanoelectronics Seminar, 19.01.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36376


Data to the paper "Transport properties of Fe60Al40 during the B2 to A2 structural phase transition"

Sorokin, S.; Anwar, M. S.; Hlawacek, G.; Boucher, R.; Salgado Cabaco, J.; Potzger, K.; Lindner, J.; Faßbender, J.; Bali, R.

Abstract

Archive contatins all the data acquired with the respect to the paper mentioned in the title.

It is split in three folders by data type:

"Fabrication" folder contains all of the details related to the deposition, fabrication and testing of FeAl hall bars.

"Measurements" folder contains all experimental results. They are grouped by type (as subfolders) and then again by sample codes. Typically structure of the measurement subfolders are the following:

  • "Raw_data" - contains data in a form as it was acquired from the machine or very close to that.
  • "Cleaned_data" - contains processed raw_data according to the need for the specific plot. For example removal of extra columns, normalizations, unit conversions, fittings etc. Specific operations performed depend on the measurement type and described in "README.md" files.
  • "Plotting" - contatins Veusz (Free and Open source plotting software, https://veusz.github.io/) project files linked to the "Cleaned_data". Beware that moving the data on disk relative to the Veusz project file would destroy the links and the data files will have to be relinked. In order to avoid this created a copy of Veusz project and unlink all the datasets. This will embed the data within a project file and will make it independent from "Cleaned_data" file

"Modeling"  contains results of auxilary calculations and numerical modeling.

Keywords: magnetism; transport; ion beam modification; FeAl; phase transitions; magnetic clusters

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Permalink: https://www.hzdr.de/publications/Publ-36375


Novel Mixed Dimensional Reconfigurable Field Effect Transistors: Fabrication and Electrical Characterization

Ghosh, S.; Bilal Khan, M.; Chava, P.; Watanabe, K.; Taniguchi, T.; Prucnal, S.; Hübner, R.; Mikolajick, T.; Erbe, A.; Georgiev, Y.

Abstract

The physical downscaling of CMOS technology has reached its limitations. Subsequently, the quest for alternative technological solutions based on new materials and device concepts augment the downscaling of integrated circuits. One such concept is the reconfigurable FET (RFET), which can be dynamically programmed to n- or p-polarity by applying an electrostatic potential [1]. In this work, we present the idea of a novel mixed dimensional RFET device, which explores the potential of both one-dimensional (1D) channel materials (like silicon (Si) or silicon-germanium (SiGe) based nanowires) and two-dimensional (2D) materials. In the most generic process, an RFET device is based on intrinsic Si or SiGe nanowire with Nickel (Ni) placed on both ends. Subsequent annealing results in the formation of silicide regions in the nanowire. The junction of the silicide to Si or SiGe is a typical Schottky junction. By controlling the Schottky junction with the help of gating architectures, the flow of charge carriers within the channel can be modulated. For ambipolarity, an electrostatic potential on the back-gate or a single top-gate enables the n- or p-transport depending on the polarity of the gate voltage. The main aim of this work is to optimize the RFET architecture based on 2D materials like hexagonal boron nitride (hBN) as a dielectric and encapsulating layer instead of thermally grown oxide around the nanowire. 2D hBN comprises a structure very similar to graphene with its sub lattice consisting of boron or nitrogen atoms. However, contrary to graphene, hBN acts as an insulator with dielectric constant between 3-4 (similar to SiO2). The properties of atomically thin hBN like the absence of dangling bonds, resistance to oxidation and chemical stability makes it an ideal gate dielectric material for flexible electronics.

Top-down fabrication of RFETs is an essential requirement for large-scale device integration. The Si or SiGe nanowires are fabricated using electron beam lithography and reactive ion etching [2]. As reported in our previous works, the formation of silicided Schottky junctions by flash lamp annealing (FLA) yields better control over the silicide progression in the nanowire compared to rapid thermal annealing (RTA) [3,4]. This work focuses on the application of 2D hBN as a dielectric layer for nanowire-based devices. The devices fabricated and characterized consist of a mechanically exfoliated 2D hBN flake deposited on the single Si or SiGe nanowire-based devices by the dry viscoelastic stamping transfer technique. The thickness of the hBN flakes, investigated by atomic force microscopy and transmission electron microscopy, was between 5-10 nm (shown in figure 1). The energy dispersive X-ray analysis (EDX) was also carried out on the cross-sectioned devices for investigating the elemental distribution (figure 2). The ambipolar transfer characteristics of the Si-hBN devices with different gating architectures (compared in figure 3) show a significant improvement in subthreshold swing value due to the 2D encapsulation and passivation. The fabricated SiGe-hBN based devices also show an improvement of p and n on-currents and ION/IOFF ratio through back-gating due to the encapsulation and passivation of the nanowire by the hBN flake (figure 4).

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  • Poster
    MNE EUROSENSORS 2022, 19.-23.09.2022, Leuven, Belgium

Permalink: https://www.hzdr.de/publications/Publ-36374


Effect of a Discontinuous Ag Layer on Optical and Electrical Properties of ZnO/Ag/ZnO Structures

Vitanov, P.; Ivanova, T.; Dikov, H.; Terziyska, P.; Ganchev, M.; Petkov, N.; Georgiev, Y.; Asenov, A.

Abstract

ZnO/Ag/ZnO nanolaminate structures were deposited by consecutive RF sputtering at room temperature.The optical transparency, sheet resistance, and figure of merit are determined in relation to the deposition time of Ag and to the film thickness of the ZnO top layer. An improved transmittance has been found in the visible spectral range of the ZnO/Ag/ZnO structure compared to ZnO multilayers without Ag. High transmittance of 98% at 550 nm, sheet resistance of 8 W/sq, and figure of merit (FOM) of 111.01x10-3 Ω-1 are achieved for an optimized ZnO/Ag/ZnO nanolaminate structure. It is suggested that the good optical and electrical properties are due to the deposition of the discontinuous Ag layer. The electrical metallic type conductivity is caused by planar located silver metal granules. The deposition of a discrete layer of Ag nano-granules is confirmed by atomic force microscopy (AFM) and cross-section high-resolution transmission electron microscopy (HRTEM) observations.

Keywords: transparent conductive oxide (TCO) transparent conducting nanolam; magnetron sputtering; ZnO/Ag/ZnO; transparent conducting nanolaminate structures; discontinuous Ag layer; oxide/metal/oxide

Permalink: https://www.hzdr.de/publications/Publ-36373


Surface magnetization of Cr2O3 (104) quantified via scanning NV magnetometry

Lehmann, P.; Wagner, K.; Pylypovskyi, O.; Weber, S.; Hedrich, N.; Makushko, P.; Shields, B.; Kosub, T.; Veremchuk, I.; Sheka, D.; Spaldin, N.; Makarov, D.; Maletinsky, P.

Abstract

Magneto-electric antiferromagnets are candidate materials for future spintronic
devices. While antiferromagnets offer high speed, low power consumption and
robustness to external fields, magneto-electrics allow manipulation of the magnetic
order parameter not only via magnetic signals, but also via electric signals [1, 2].
Readout and manipulation of the antiferromagnetic order on the nanoscale typically
relies on local probes sensitive to the surface magnetization. Therefore, its optimization
is key challenge in device engineering. Here we investigate the surface magnetization
of an oblique cut of single crystal Cr 2 O3 using scanning probe nitrogen-vacancy center
magnetometry. The (104) surface normal is at an angle of 38.5° to the uniaxial
anisotropy axis of Cr 2 O3. By magneto-electric annealing [3], a homogeneous
antiferromagnetic order is initialized. We then measure the stray magnetic fields
produced by topographic steps fabricated by ICP etching. The steps have various
angles with respect to the c-axis in-surface component, allowing us to probe different
`cuts` of the magnetization. We finally consider a simple model based on a
homogenous surface magnetization strength and orientation for the various crystal
facets. We find good agreement between this model and the recorded stray fields for
a magnetization aligned with the bulk c-axis orientation. The predicted magnitude
agrees with previous results of measurements on (001) surfaces [4]. We hope that
these findings may aid in understanding the relation between surface and bulk
magnetic order in antiferromagnets and aid in the development of antiferromagnetic
spintronic devices.

Keywords: antiferromagnetism; Cr2O3

  • Lecture (Conference)
    WE-Heraeus-Seminar “Re-thinking Spintronics: From Unconventional Materials to Novel Technologies”, 03.-06.01.2023, Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-36372


Magnetic field-induced textures and phase transitions in antiferromagnetic spin chains: geometry-induced effects

Borysenko, Y.; Sheka, D.; Yershov, K.; Faßbender, J.; van den Brink, J.; Makarov, D.; Pylypovskyi, O.

Abstract

Easy axis antiferromagnets (AFMs) are robust against external magnetic fields of a moderate strength. Spin reorientation transitions in strong fields can provide an insight into more subtle properties of antiferromagnetic materials, which are often hidden by their high ground state symmetry. In curved intrinsically achiral AFM spin chains geometrical bends and twists provide helimagnetic responses, characterized as effective anisotropic and Dzyaloshinskii–Moriya-like (DMI) interactions [1]. Here, we address theoretically effects of curvature in achiral anisotropic ring-shaped AFM spin chains with even number of spins exposed to strong magnetic fields using the methodology of curvilinear magnetism. We identify the geometry-governed helimagnetic phase transition enabled in the spin-flop phase, which separates locally homogeneous (vortex) and periodic (onion) AFM textures [2, 3]. The curvature-induced Dzyaloshinskii–Moriya interaction results in the spin-flop transition being of the first- or second-order depending on the ring curvature. Spatial inhomogeneity of the Néel vector in the spin-flop phase generates the weakly ferromagnetic response in the plane perpendicular to the applied magnetic field [3]. In AFM spin chains possesing torsion, e.g. helices, these effects are enhanced by the inhomogeneity of local texture in the ground state. Our work provides further insights in the physics of curvilinear AFMs in static magnetic fields and guides prospective experimental studies of geometrical effects in the spin-chain nanomagnets.

Keywords: antiferromagnetism; curvilinear spin chains

  • Lecture (Conference)
    WE-Heraeus-Seminar “Re-thinking Spintronics: From Unconventional Materials to Novel Technologies”, 03.-6.01.2023, Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-36371


Nanoscale studies of antiferromagnetic spin-textures

Wagner, K.; Lehmann, P.; Pylypovskyi, O.; Hedrich, N.; Makushko, P.; Shields, B.; Kosub, T.; Sheka, D.; Makarov, D.; Maletinsky, P.

Abstract

Magneto-electric antiferromagnets hold promise for future spintronic devices, as they offer magnetic field hardness, high switching speeds and both electric and magnetic control of their order parameters, owing to the magneto-electric coupling [1]. As information and functionality is encoded in the antiferromagnetic order parameter, its manipulation, read-out and nanoscale textures are paramount for device operation, as well as interesting from a fundamental point of view. For applications the surface plays a key-role as the interface often dictates the read/write functionalities and gains importance as thin film devices are targeted. Using scanning nitrogen vacancy magnetometry [2] we study a ‘textbook’, single crystal magneto-electric antiferromagnet Cr 2O3 and perform nanoscale imaging of its surface magnetization, which is directly linked to its magnetic order parameter. We first confirm magneto-electric poling [3] of a homogeneous antiferromagnetic order and study the stray field polarity at the surface depending on the used field configuration. Our results are consistent with a theoretically predicted topmost disordered layer [4]. In the next step local electrodes are utilized to nucleate individual single domain walls. Manipulation of the domain wall path is demonstrated both by local laser heating, as well as the creation of an energy landscape for the domain wall position via topographic structuring [2]. Analysing the domain wall path yields further information about the boundary conditions for the order parameter at topographic edges and an estimate of the full 3D-profile of the texture based on minimizing the domain walls surface energy. A Snell like refraction of the domain wall path is found, that can be represented in an analytical approximation as a ‘refractive index’ for a given island dimension as demonstrated for a range of incidence angles. The demonstrated pinning and control of the domain wall position constitutes the main ingredients for logic devices based on domain walls in magneto-electric antiferromagnets and their fundamental study. Understanding the intrinsic properties and stability of the magnetic order at the direct surfaces may aid in exploring their functionality in spintronic devices that often rely on spin-scattering mechanisms at the interface.

Keywords: antiferromagnetism; Cr2O3; domain walls

  • Lecture (Conference)
    MMM 2022, 31.10.-4.11.2022, Minneapolis, USA

Permalink: https://www.hzdr.de/publications/Publ-36370


Domain walls in Cr2O3

Pylypovskyi, O.

Abstract

Presentation about our recent achievements on the domain wall studies in Cr2O3.

Keywords: antiferromagnetism; Cr2O3

  • Invited lecture (Conferences)
    Ukrapro workshop, 01.06.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36369


Skin-conformal magnetoreceptors for human-machine interaction

Makushko, P.; Oliveros Mata, E. S.; Canon Bermundez, G. S.; Hassan, M.; Laureti, S.; Rinaldi, C.; Fagiani, F.; Barucca, G.; Zabila, Y.; Faßbender, J.; Vladymyrskyi, I.; Albrecht, M.; Varvaro, G.; Xu, R.; Makarov, D.

Abstract

Artificial magnetoception, i.e., electronically expanding human perception to detect magnetic fields, is a new and yet unexplored route for interacting with our surroundings. This technology relies on thin, soft, and flexible magnetic field sensors, dubbed magnetosensitive electronic skins (e-skins) [1]. These devices enable reliable and obstacle insensitive proximity, orientation and motion tracking features [2, 3] as well as bimodal touchless-tactile interaction [4].
Although, basic interactive functionality has been demonstrated, the current on-skin magnetoreceptors are not yet employed as advanced spintronics-enabled switches and logic elements for skin compliant electronics. The major limitation remains primarily due to the use of in-plane magnetized layer stacks. The predominant in-plane sensitivity prevents these devices from becoming intuitive switches or logic elements for interactive flexible electronics, as the natural actuation axis of switches is out-of-plane.
Here, we will introduce current technologies towards realization of skin-conformal magnetoelectronics for touchless and tactile interactivity in virtual and augmented reality. The focus will be put on the fabrication of on-skin spin valve switches with out-of-plane sensitivity to magnetic fields [5]. The device is realized on a flexible foil relying on Co/Pd multilayers with perpendicular magnetic anisotropy and synthetic antiferromagnet as a reference layer. Owing to the intrinsic tunability, these interactive elements can provide fundamental logic functionality represented by momentary and permanent (latching) switches and reliably discriminate the useful signals from the magnetic noise. The flexible device retain its performance upon bending down to 3.5 mm bending radii withstand more than 600 bending cycles.
We showcase the performance of our device as on-skin touchless human-machine interfaces, which allows interactivity with a virtual environment, based on external magnetic fields. We envision that this technology platform will pave the way towards magnetoreceptive human-machine interfaces or virtual- and augmented reality applications, which are intuitive to use, energy efficient, and insensitive to external magnetic disturbances.

  • Lecture (Conference)
    MMM 2022 Conference, 31.10.-04.11.2022, Minneapolis, USA

Permalink: https://www.hzdr.de/publications/Publ-36368


Flexible magnetoreceptive switch for on-skin touchless human-machine interaction.

Makushko, P.; Oliveros Mata, E. S.; Canon Bermundez, G. S.; Hassan, M.; Laureti, S.; Rinaldi, C.; Fagiani, F.; Barucca, G.; Schmidt, N.; Zabila, Y.; Kosub, T.; Illing, R.; Volkov, O.; Vladymyrskyi, I.; Faßbender, J.; Albrecht, M.; Varvaro, G.; Makarov, D.

Abstract

Skin compliant magnetoreceptive electronics is a game changer for prospective
human-machine interactions and augmented reality applications [1].
Mechanically flexible magnetoresistive sensors enabled proximity sensing
as well as motion and orientation tracking features[2,3] via interaction with
magnetic objects. However, current on-skin magnetoreceptors are not yet
employed as advanced spintronics-enabled switches and logic elements for
skin compliant electronics. The major limitation is the use of in-plane magnetized
layer stacks, sensitive mainly to magnetic fields oriented within the
sensor plane. Flexible Hall effect sensors[4,5] provide out-of-plane sensitivity
but no intrinsic logic, thus requiring more complex electronics. Considering
the lower performance of flexible electronics compared to their rigid counterparts[
6], full-fledged flexible interactive systems should be based on smart
receptors with intrinsic logic functionality. Here we present the first mechanically
flexible switch based on spin valves sensitive to out-of-plane magnetic
fields[7]. The device is realized on a flexible polyethylene naphthalate (PEN)
foil and rely on Co/Pd multilayers with perpendicular magnetic anisotropy
and synthetic antiferromagnet as a reference layer. By tuning the magnetic
coupling strength between the free and the reference layers, the functionality
of the device can be tailored between momentary or permanent (latching)
switch. The flexible device retains its performance upon bending down to
a bending radius of 3.5 mm and withstand more than 600 bendings. We
demonstrate the performance of our device as touchless interactive interface
for augmented reality systems, as well as its tolerance to the magnetic field
disturbances. We showcase the potential of this new kind of flexible magnetoreceptive
functional elements as on-skin human-machine interfaces for
virtual and augmented reality applications

  • Lecture (Conference) (Online presentation)
    2022 Joint MMM-Intermag Conference (INTERMAG), 10.-14.01.2022, New Orleans, USA

Permalink: https://www.hzdr.de/publications/Publ-36366


Electrical characterization of highly doped germanium nanowires using Hall bar configuration

Echresh, A.; Prucnal, S.; Wang, M.; Zhou, S.; Erbe, A.; Rebohle, L.; Georgiev, Y.

Abstract

Germanium (Ge) is the most compatible material with silicon-based complementary metal-oxide-semiconductor processes. Ge has a higher electron and hole mobility compared to Si, leading to improved device performance. Moreover, Ge nanowires (GeNWs) are promising nanostructures for future nano- and optoelectronics due to their unique properties. In this work, ion implantation of phosphorous followed by flash lamp annealing (FLA) operated in millisecond time scale were used to fabricate highly-doped n-type Ge layer on insulator. Raman spectroscopy and Rutherford backscattering spectrometry were performed to characterize the crystallinity of the Ge layers after FLA. Subsequently, doped GeNWs were fabricated using electron beam lithography and inductively coupled plasma reactive ion etching. Electrical characterization of the GeNWs was conducted using a symmetric six-contact Hall bar configuration. The effect of nanowire width on transport parameters was investigated. Moreover, FLA were applied to fabricate NiGe alloy on highly doped Ge layer for low-resistance ohmic contacts.

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  • Poster (Online presentation)
    Helmholtz MML workshop, 22.-24.11.2021, Jena, Germany

Permalink: https://www.hzdr.de/publications/Publ-36365


Size-dependent electrical characteristics of highly doped Germanium nanowires

Echresh, A.; Prucnal, S.; Georgiev, Y.; Rebohle, L.

Abstract

Germanium (Ge) is the most compatible material with silicon (Si)-based complementary metal-oxide-semiconductor processes. Ge has a higher electron and hole mobility compared to Si, leading to improved device performance. Moreover, Ge nanowires (GeNWs) are promising nanostructures for future nano- and optoelectronics due to their unique properties. In this work, ion beam implantation and flash lamp annealing (FLA) were used to dope phosphorous into the top Ge layer of Ge-on-insulator (GeOI) substrates, achieving a highly n-type doped semiconductor. Raman spectroscopy and Rutherford backscattering spectrometry were performed to characterize the crystallinity of the Ge layers after ion beam implantation and FLA. Subsequently, doped GeNWs were fabricated using electron beam lithography and inductively coupled plasma reactive ion etching. Electrical characterization of the GeNWs was conducted using an innovative Hall bar configuration. The effect of nanowire width on transport parameters such as resistivity and carrier mobility was investigated. Moreover, a nickel germanide layer was made using Ni deposition, followed by FLA to create ohmic contacts on n-type GeNWs.

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  • Lecture (Conference) (Online presentation)
    DPG Spring Meeting SKM, 27.09.-01.10.2021, Virtual, Germany

Permalink: https://www.hzdr.de/publications/Publ-36364


Developing a Hall Bar Configuration for semiconducting Nanowires

Echresh, A.; Arora, H.; Prucnal, S.; Rebohle, L.; Georgiev, Y.

Abstract

Despite constant improvement in the performance of semiconducting nanowires (NWs) based devices, evaluating electrical properties of single NWs still remains a challenging task. So far, several techniques have been developed to this end. The field effect (FE) mobility measurement is the most commonly used technique, although it has some shortcomings [1,2]. The accuracy of this method depends largely on the precision of the estimated gate capacitance. Also, it characterizes only the depleted layer of charge carriers close to the gate, and estimates the carrier concentration of NWs by assuming a radially constant mobility. Unlike the FE measurement, the Hall Effect measurement provides a more direct characterization of carrier concentration by considering the entire cross-section of the semiconducting NWs [2,3]. However, the fabrication of NW based Hall devices is a challenging process and requires a very high accuracy regarding the alignment of the Hall contacts. The Hall bar configuration with narrow bars can increase the precision of Hall contacts fabrication and enhance the accuracy of the Hall Effect measurement by avoiding shorting out the Hall voltage. Recently, the Hall bar configuration has been used for SiNWs with a five-contact geometry [4]. To the best of our knowledge, such a Hall bar configuration has not been developed for GeNWs so far.

In this work, GeNWs were fabricated on Ge-on-insulator (GeOI) substrates with a top-down approach using electron beam lithography (EBL) and inductively coupled plasma reactive ion etching (ICP-RIE). To investigate the electrical properties of the fabricated NWs, we propose a six-contact Hall bar configuration with symmetric contact bars located opposite to each other, as shown in Figure 1. Using this configuration, the Hall Effect and four-probe measurements were performed on single GeNWs to quantify their carrier concentration (n), Hall mobility (µH), and resistivity (ρ). A nanowire with a width down to about 40 nm was characterized to show the capability of the proposed Hall bar configuration to reliably evaluate the electrical properties of even very small nanowires. Moreover, the effect of NW width on transport parameters such as resistivity, carrier concentration and mobility was investigated. With decreasing nanowires width, the resistivity increases and carrier concentration decreases, which is mainly attributed to the diffusion of carriers into the surface. Figure 2 shows the size-dependent resistivity and temperature-dependent Hall mobility of the Ge NWs.

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  • Lecture (Conference) (Online presentation)
    47th International Conference on Micro and Nano Engineering (MNE), 20.-23.09.2021, Turin, Italy

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Flexible Magnetoreceptive Switch for On-Skin Touchless Human-Machine Interaction

Makushko, P.; Oliveros Mata, E. S.; Cañón Bermúdez, G. S.; Hassan, M.; Laureti, S.; Rinaldi, C.; Fagiani, F.; Barucca, G.; Schmidt, N.; Zabila, Y.; Kosub, T.; Illing, R.; Volkov, O.; Vladymyrskyi, I.; Faßbender, J.; Albrecht, M.; Varvaro, G.; Makarov, D.

Abstract

Artificial magnetoception, i.e., electronically expanding human perception to detect magnetic fields, is a new and yet unexplored route for interacting with our surroundings. This technology relies on thin, soft, and flexible
magnetic field sensors, dubbed magnetosensitive electronic skins (e-skins) [1]. These devices enable reliable and obstacle insensitive proximity, orientation and motion tracking features [2, 3] as well as bimodal touchless-tactile
interaction [4].
Although, basic interactive functionality has been demonstrated, the current on-skin magnetoreceptors are not yet employed as advanced spintronics-enabled switches and logic elements for skin compliant electronics. The
major limitation remains primarily due to the use of in-plane magnetized layer stacks, sensitive mainly to the magnetic fields oriented within the sensor plane. This prevailing in-plane sensitivity has prevented them from becoming intuitive switches or logic elements for interactive flexible electronics, as the natural actuation axis of switches is out-of-plane. Flexible Hall effect sensors [5, 6] could provide out-of-plane sensitivity, but not intrinsic logic functionality.
In this work, we present the very first tunable magnetoreceptive platform for on-skin touchless interactive electronics based on flexible spin valve switch elements with dedicated out-of-plane sensitivity to magnetic fields [5]. The device is realized on a flexible polyethylene naphthalate (PEN) foil relying on Co/Pd multilayers with perpendicular magnetic anisotropy and synthetic antiferromagnet as a reference layer. Owing to the intrinsic tunability, these interactive elements can provide fundamental logic functionality represented by momentary and permanent (latching) switches and reliably discriminate the useful signals from the magnetic noise. The flexible
device retain its performance upon bending down to 3.5 mm bending radii and withstand more than 600 bending cycles.
We showcase the performance of our device as on-skin touchless human-machine interfaces, which allows interactivity with a virtual environment, based on external magnetic fields. Depending on the material properties of the on-skin switch used, the virtual functions can be impervious to (latching) or controlled by (momentary) ambient
magnetic stimuli. We envision that this technology platform will pave the way towards magnetoreceptive humanmachine interfaces or virtual- and augmented reality applications, which are intuitive to use, energy efficient, and insensitive to external magnetic disturbances.

  • Lecture (Conference) (Online presentation)
    2022 IEEE 12th International Conference "Nanomaterials: Applications & Propertie", 11.-16.09.2022, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-36362


Axial p–n junction photodetectors based on single germanium nanowires

Echresh, A.; Shaikh, M. S.; Arora, H.; Erbe, A.; Rebohle, L.; Georgiev, Y.

Abstract

Germanium (Ge) is considered as a promising candidate for designing near-infrared photodetectors. Ge has a bandgap of 0.67 eV, which induces a large absorption coefficient at near-infrared frequencies. Also, Ge has excellent compatibility of parallel processing with silicon technology [1,2]. Photodetectors based on Ge material have been fabricated with different structures such as metal-semiconductor-metal (MSM) and p−n junctions. On the other hand, the observation of high photoresponsivity in semiconductor nanowires with a high surface-to-volume ratio has attracted growing interest in using nanowires in photodetectors. So far, significant efforts have been made to fabricate single nanowire based photodetectors with different materials such as Si, Ge, and GaN to achieve miniaturized devices with high responsivity and short response time [3-5]. Hence, Ge nanowires are an excellent candidate to fabricated single nanowire based near-infrared photodetectors.

In this work, we report on the fabrication and characterization of an axial p−n junction along Ge nanowires with different widths. First, through a resist mask created by electron beam lithography (EBL), the Ge layers were locally doped with phosphorus ions using ion beam implantation followed by rear-side flash lamp annealing. Then, the single Ge nanowire based photodetectors containing an axial p−n junction were fabricated using EBL and inductively coupled plasma reactive ion etching (ICP-RIE). The fabricated single Ge nanowire devices demonstrate the rectifying current-voltage characteristic of a p−n diode in dark conditions. Moreover, the photoresponse of the axial p−n junction based photodetectors was investigated under three different illumination lights of 637 nm, 785 nm, and 1550 nm wavelengths. It appears that fabricated photodetectors can be operated at zero bias and at room temperature under ambient conditions. A high responsivity of 3.7×102 AW-1, and detectivity of 1.9×1013 cmHz1/2W-1 were observed at zero bias under illumination of 785-nm-wavelength. The responsivity of the single Ge NW photo-detectors was increased by applying a reverse bias of 1V.

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  • Lecture (Conference)
    Nanonet+Workshop, 04.-06.10.2022, Jugendherberge Görlitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-36361


Optical design, microstructural characterization and high-temperature in-air stability study of solar selective coatings based on aluminium- (titanium, chromium) oxynitride multilayers

Escobar-Galindo, R.; Heras, I.; Guillén, E.; Munnik, F.; Azkona, I.; Caro, A.; Rojas, T. C.; Sánchez-López, J. C.; Krause, M.

Abstract

The development of new solar selective coatings (SSCs) operating in air at high temperatures is an actual challenge for the development of Generation 3 concentrated solar power (CSP) plants. In particular, current central tower systems operate at maximum temperatures of 550 ºC mainly due to the severe degradation that the state of the art absorber paints (i.e. Pyromark®) suffer at higher temperatures. Aluminium metal oxynitrides AlyMe1-yOxN1-x (Me = Ti, Cr) prepared by physical vapour deposition (i.e. cathodic vaccuum arc and HiPIMS) were selected as candidate materials for SSCs on the basis of stability considerations of the tentatively formed nitrides and oxides. The optical properties of these films can be controlled in a wide range from a metallic to a dielectric character by varying the oxygen and nitrogen content.
In the last years we have performed an extensive research on the design, fabrication and high-T exposure of SSCs based on aluminium-titanium [1,2] and aluminium-chromium oxynitrides [3]. Once single thin films were fully characterized by ion beam analysis, scanning and transmission electron microscopy and X-ray diffraction, complete SSCs were designed with optical simulations, based on measured optical constants of each of the individual layers, providing excellent optical selective properties in terms of solar absorptance (α) and thermal emittance (εRT). The selected multilayers stacks were deposited, obtaining excellent agreement between simulated and experimental reflectance spectra. Finally, the thermal stability in air of the complete deposited SSCs was analyzed by isothermal and cyclic heating tests simulating operating conditions. AlyTi1-yOxN1-x SSCs showed no degradation after 750h of cycles in air at 600ºC and these results were compared with in-situ high temperature annealing performed in vacuum at the multi-chamber cluster tool situated at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) [4], confirming that these stacks withstand breakdown at 600ºC in air and 800ºC in vacuum. AlyCr1-yOxN1-x SSCs stacks presented a good solar selectivity with solar absorptance > 95% and thermal emittance < 15%, and fulfilled the performance criterion after 600 and 700 ºC short term heating treatments. At 800 ºC, they underwent a further structural transformation, provoked by the oxidation of the inner layers, and they consequently lost their solar selectivity.

In this invited talk, we will summarize these results and present current research strategies to further improve the performace of the developed materials.

1. I. Heras, E. Guillén, F. Lungwitz, G. Rincón-Llorente, F. Munnik, E. Schumann, I. Azkona, M. Krause, R. Escobar-Galindo. Sol. Energy Mater. Sol. Cells 176 (2018) 81-92.
2. R. Escobar-Galindo, E. Guillén, I. Heras, G. Rincón-Llorente, M. Alcón-Camas, F. Lungwitz, F. Munnik, E. Schumann, I. Azkona, M. Krause. Sol. Energy Mater. Sol. Cells 185 (2018) 183-191.
3. T.C. Rojas, A. Caro, R. Escobar-Galindo, J.C. Sánchez López. High-temperature solar-selective coatings based on Cr(Al)N. Part 2: Design, spectral properties and thermal stability of multilayer stacks. Sol. Energy Mater. Sol. Cells. 218 (2020) 110812
4. R. Wenisch, F. Lungwitz, D. Hanf, R. Heller, J. Zscharschuch, R. Hübner, J. von Borany, G. Abrasonis, S. Gemming, R. Escobar-Galindo, M. Krause. Anal. Chem. 90 (13) (2018) 7837-7842.

Keywords: solar selective coatings; thermosolar energy; PVD; thin films; in-situ characterization

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  • Invited lecture (Conferences)
    SICT 2022 / PlasmaTech 2022 / Tribology 2022 Joint Hybrid Conferences, 27.-29.04.2022, Barcelona, Espana

Permalink: https://www.hzdr.de/publications/Publ-36358


Environment-dependent friction, Raman and µ-RBS study of ta-C coatings deposited by filtered Laser arc

Krause, M.; Härtwig, F.; Munnik, F.; Garcia Valenzuela, A.; Makowski, S.; Lorenz, L.

Abstract

Tetrahedral, hydrogen-free amorphous carbon (ta-C) is characterized by the highest sp3-carbon content and the highest hardness of HIT > 40 GPa of the group of diamond-like carbon (DLC) coatings [1]. The formation of sp3-C bonds in this material requires impinging atoms or ions with energies of around 100 eV, provided by cathodic vacuum arc or laser arc deposition [2]. Plasma filter techniques implemented in the recent years enable the production of ta-C coatings with significantly improved surface quality.
In this study, friction and wear properties of ta-C coatings deposited by filtered Laser arc are studied as a function of the environment: in humid and dry air, in nitrogen as well as in vacuum from 1 mbar to 10-7 mbar. Low friction with coefficients of friction (COF) < 0.1 is found for the friction pair ta-C/ ta-C at normal pressure, nearly independently on the relative humidity. Likewise, the wear rates are not dependent on whether dry or humid conditions are established. In vacuum, the COF and wear rates increased by a factor of approx. ten and three, respectively. Raman studies reveal a complex structure evolution of ta-C in the wear track and on the contact area of the counter body with decreasing pressure. In the wear tracks at least two types of carbon are found. One of them shows an almost unchanged G line position and an unmeasurable ID/IG ratio as the initial coating, while the second one has a by 20 cm-1 lowered G line position and an ID/IG ratio of approx. 0.4. This structure has similar Raman signatures as the counter body contact area, indicating the formation of an identical tribolayer on both friction partners. Laterally and depth resolved atomic insight in the transfer layer formation is obtained by micro-beam Rutherford backscattering spectrometry for ta-C coatings in contact with steel, brass, alumina, and silicon carbide.
Financial support by the DFG, grant No. 415726702, project TRIGUS, is gratefully acknowledged.
[1] J. Robertson, Diamond-like amorphous carbon. Materials Science & Engineering R-Reports 37, 129-281, doi:10.1016/s0927-796x(02)00005-0 (2002).
[2] F. Kaulfuss, et al. Effect of Energy and Temperature on Tetrahedral Amorphous Carbon Coatings Deposited by Filtered Laser-Arc. Materials 14, 13, doi:10.3390/ma14092176 (2021).

Keywords: ta-C; diamond-like coatings; wear; friction; µ-RBS; Raman spectroscopy

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  • Poster
    PSE 2022 - 18th International Conference on Plasma Surface Engineering, 12.-15.09.2022, Erfurt, Deutschland

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3D Quantum-inspired Self-supervised Tensor Network for Volumetric Segmentation of Medical Images

Konar, D.; Bhattacharyya, S.; Gandhi, T. K.; Panigrahi, B. K.; Jiang, R.

Abstract

This paper introduces a novel shallow 3D self-supervised tensor neural network for volumetric segmentation of medical images with merits of obviating training and supervision. The proposed network is referred to as 3D Quantum-inspired Self-supervised Tensor Neural Network (3D-QNet). The underlying architecture of 3D-QNet is composed of a trinity of volumetric layers viz. input, intermediate and output layers inter-connected using an S-connected third-order neighborhood-based topology for voxel-wise processing of 3D medical image data suitable for semantic segmentation. Each of the volumetric layers contains quantum neurons designated by qubits or quantum bits. The incorporation of tensor decomposition in quantum formalism leads to faster convergence of the network operations to preclude the inherent slow convergence problems faced by the classical supervised and self-supervised networks. The segmented volumes are obtained once the network converges. The suggested 3D-QNet is tailored and tested on the BRATS 2019 Brain MR image data set and Liver Tumor Segmentation Challenge (LiTS17) data set extensively in our experiments. 3D-QNet has achieved promising dice similarity as compared to the intensively supervised convolutional network-based models like 3D-UNet, Vox-ResNet, DRINet, and 3D-ESPNet, showing a potential advantage of our self-supervised shallow network on facilitating semantic segmentation.

Keywords: Quantum computing; Volumetric Medical Image Segmentation; QIS-Net; 3D-UNet; Vox-ResNet

  • Open Access Logo IEEE Transaction on Neural Networks and Learning Systems (2024), 10038494
    Online First (2023) DOI: 10.1109/TNNLS.2023.3240238
    arXiv: https://doi.org/10.36227/techrxiv.12909860.v4

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Characterization of Tri- and Tetravalent Actinide Complexes with Amidinate Ligands

Hong, B.; Fichter, S.; Näder, A.; März, J.; Kaden, P.; Patzschke, M.; Schmidt, M.; Stumpf, T.

Abstract

Understanding the physical and chemical properties of radionuclides interacting with organic ligands is fundamental for a reliable evaluation of the migration behaviour of radionuclides in the environment. In this context, our group has been conducting research with a particular emphasis on the complexation of early actinides with relatively soft N-donor ligands, and recently, the tetravalent actinide complexes with the chiral benzamidinate ((S)-PEBA) have been successfully synthesized. The present study is inspired by these precedent studies to synthesize a new series of amidinate compounds with An(III) and An(IV) to provide and expand a comprehensive understanding of the electronic properties of actinide complexes.

In this study, we succeeded to obtain a series of tetravalent actinide amidinate chloro complexes [AnClx(amid)y] (An= Th, U, and Np; amid= iPr2BA, (S)-PEBA, and Cy2TA). The crystal structures of the benzamidinate complexes were determined by single-crystal XRD, all showing three amidinates and one halide ligand coordinated to the actinide metal center in a mono-capped distorted octahedral coordination geometry. In the case of the Cy2TA ligand with a sterically bulky tert-butyl substituent, only the complex with a metal-to-ligand ratio of 1:2 [UCl2(Cy2TA)2] was obtained. The paramagnetic effects of these actinide complexes were investigated extensively in solution with NMR spectroscopy. Furthermore, the reduction of An(IV) to An(III) afforded the corresponding homoleptic amidinate complexes [An(amid)3] (An= U and Np; amid= iPr2BA and (S)-PEBA), allowing the comparison of structural and chemical bonding situations with isostructural Ln(III) complexes via paramagnetic NMR studies.

Keywords: actinides; lanthanides; coordination chemistry; SC-XRD; NMR; amidinate; N-donor ligands

  • Poster
    ATAS-AnXAS 2022, 17.-21.10.2022, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-36355


Coordination Chemistry of Tri- and Tetravalent Actinides with Benzamidinate Ligands

Hong, B.; Fichter, S.; Näder, A.; März, J.; Kaden, P.; Patzschke, M.; Schmidt, M.; Stumpf, T.

Abstract

Because of their excellent properties of stabilizing transition metal complexes in various oxidation states, amidinate ligands have received considerable attention in the field of coordination chemistry over the last decades as versatile soft N-donor ligands. There have been a number of studies on transition metal amidinate complexes including lanthanides and some early actinides. Still, these studies are mainly limited to thorium (Th) and high valent (V, VI) uranyl complexes. Recently, the tetravalent actinide complexes with the chiral benzamidinate ((S)-PEBA) have been successfully synthesized in our group. The present study is inspired by these precedent studies to synthesize a new series of benzamidinate compounds with An(III) and An(IV) to provide and expand a comprehensive understanding of the electronic properties of actinide compounds.

In this study, we succeeded to obtain a series of tetravalent actinide tris-benzamidinate chloro complexes [AnCl(amid)3] (An= Th, U, and Np; amid= iPr2BA and (S)-PEBA). The crystal structures of the model actinide complexes were determined by single-crystal XRD, showing three benzamidinates and one halide ligand coordinated to the actinide metal center in a mono-capped distorted octahedral coordination geometry. We also synthesized additional halide complex series (F, Br) by halogen exchange reactions on these chloro complexes to investigate the conformational stability of the complex. The paramagnetic effects of these actinide complexes were investigated extensively in solution with NMR spectroscopy. Furthermore, the reduction of An(IV) to An(III) afforded the corresponding homoleptic benzamidinate complexes [An(amid)3] (An= U and Np; amid= iPr2BA and (S)-PEBA), allowing the comparison of structural and chemical bonding situations with isostructural Ln(III) complexes via paramagnetic NMR studies.

Keywords: actinides; lanthanides; coordination chemistry; SC-XRD; NMR; amidinate; N-donor ligands

  • Poster
    Actinide revisited 2022, 21.-23.09.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36354


Thermal Performance Study of a Heat-Pipe in Comparison with Experiments Using CFD

Höhne, T.

Abstract

Heat pipes are playing a more important role in many industrial applications, particularly in improving the thermal performance of heat exchangers and increasing energy savings in applications with commercial use. In this paper, a Computational Fluid Dynamics (CFD) model was built to simulate the details of the steam/water two-phase flow and heat transfer phenomena during the operation of a heat pipe. The homogeneous model in ANSYS CFX was used for the simulation. The evaporation, condensation and phase change processes were modelled. The 3D simulations could reproduce the heat and mass transfer processes in comparison with experiments from the literature. Reasonable good agreement was not only observed between CFD temperature profiles in relation with experimental data but also in comparing the thermal performance of the heat-pipe. It was found that the heating power should not increase above 1000 W for the analyzed type of TPCT using copper material.

Keywords: Two-phase flow; Boiling; CFD; Condensation; Heat-pipe

Permalink: https://www.hzdr.de/publications/Publ-36353


Synthesis and Characterization of Tetravalent Actinide Amidinate Halide Complexes

Hong, B.; Fichter, S.; März, J.; Kaden, P.; Patzschke, M.; Schmidt, M.; Stumpf, T.

Abstract

Amidinate ligands have attracted considerable attention in the field of coordination chemistry over the last decades as versatile soft N-donor ligands to stabilize the transition metal complexes in various oxidation states. The additional advantages of employing amidinates over other ligand systems are their high modularity and easy access to a variety of analogs by altering the substitution patterns through straightforward synthetic procedures. There have been a number of studies on the transition metal amidinate complexes including lanthanides, and even some early actinides. Still, these studies are mainly limited to thorium(Th) and high valent(V,VI) uranium(U) complexes. Here we focused on the interaction of An(IV) complexes (An= Th, U, and Np) with benzamidinate ligands to provide a comprehensive understanding of the electronic properties of actinide compounds.

In this study, we successfully synthesized a series of tetravalent actinide tris-benzamidinate chloro complexes [AnCl(amid)3] (An= Th, U, and Np; amid= iPr2BA and (S)-PEBA). Furthermore, we also obtained additional halide complex series (F, Br) by halogen exchange reactions on chloro complexes as precursors to investigate the conformational stability of the complex. The crystal structures of the model actinide complexes were determined by SC-XRD, showing three benzamidinates and one halide ligand coordinated to the actinide metal center in a mono-capped distorted octahedral coordination geometry, resulting in a propeller-like shape with the halide lying on the rotation axis. The actinide complexes were also
characterized in solution by using paramagnetic NMR spectroscopy to elucidate structural and chemical bonding situations with an increasing number of unpaired electrons along the 5f series.

Keywords: actinides; coordination chemistry; NMR; SC-XRD; N-donor ligands; amidinate; halogen

  • Open Access Logo Lecture (Conference)
    19th Radiochemical Conference, 15.-20.05.2022, Marianske Lazne, Czech Republic

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Particle based characterization of lithium ion battery recycling using automated mineralogy

Vanderbruggen, A.; Hayagan, N.; Bachmann, K.; Rudolph, M.; Serna, R.

Abstract

Presentation about Li-ion battery characterization ia automated mineralogy with a particular focus on the flotation of graphite in black mass.

  • Lecture (Conference) (Online presentation)
    AABC2021 - International Advanced Automotive Battery Conference, 07.-09.12.2021, San Diego, USA

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The effects of iron-rich ultramafic pegmatite on the composition and mineralogy of the UG2 chromitite: a case study in the western Bushveld Complex, South Africa

Zhoua, H.; Trumbull, R. B.; Veksler, I. V.; Bachmann, K.

Abstract

Discordant iron-rich ultramafic pegmatites (IRUPs) intersect the UG2 chromitite at many places in the Bushveld Complex. The effects of IRUP interactions on the UG2 ore mineralogy and PGE grade are assessed at the Thaba mine, north-west Bushveld, based on a borehole profile through the UG2 layer and detailed analysis of mineral textures and compositional variations across the UG2-IRUP contacts using micro-XRF element mapping. The UG2-IRUP interaction operated at different scales and probably by different mechanisms. At the local scale (< 10 cm), a thin layer of Fe–Ti–Cr spinel and ilmenite formed on the IRUP side of the contact with UG2, whereas the UG2 chromitite developed grain coarsening, loss of interstitial silicates, and chemical gradients in Cr, Al, Fe, and Ti that extend a few centimeters from the contact into the seam. These local effects are attributed to the intrusion of IRUP melt into the solidified UG2 layer, followed by re-equilibration of the oxide minerals across the contact during cooling. On a larger scale, changes in the ore and gangue mineral assemblages in UG2 took place throughout the entire meter-thick main seam. Compared with regional UG2 compositions, chromite has higher TiO2 and lower Mg#, and there is an anomalously low abundance of interstitial plagioclase. The IRUP-affected UG2 shows relatively abundant secondary hydrous silicates, replacement of PGE sulfides by PGE alloys and PGE-As–Sb–Bi–Te–Pb phases, and formation of secondary Ni–Cu–Fe sulfides after pentlandite and chalcopyrite. These large-scale effects are attributed to hydrothermal fluids derived from IRUP melts. The IRUP bodies at the Thaba mine caused redistribution of PGE within the UG2 layer but did not significantly reduce the overall grade. However, significant changes in the ore mineral assemblage and an increased abundance of secondary silicates can reduce the efficiency of PGE recovery.

Permalink: https://www.hzdr.de/publications/Publ-36350


Online-adaptive particle therapy: Current status and vision for the future

Richter, C.

Abstract

In this overview talk the following questions will be addressed: - What
is the status concerning fast adaptations in particle therapy also in
relation to photon therapy?

  • Why we need online-adaptive particle therapy (OAPT)?
  • What are different approaches also in relation to different adaption
speed?
  • What are the different imaging approaches for OAPT?
  • How can we verify the treatment delivery when no pre-treatment
phantom QA is performed?
  • What is the role of AI-based decision support?
  • What initiatives exist on national and international level? Where
do we stand?

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  • OncoRay
  • Invited lecture (Conferences)
    SMuK 2023 - DPG-Frühjahrstagung der Sektion Materie und Kosmos, 23.03.2023, Dresden, Deutschland

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Synthesis and complexation of nitrogen donor ligands with tetravalent uranium

Duckworth, T.; Schwarz, N.; März, J.; Patzschke, M.; Schmidt, M.; Stumpf, T.

Abstract

The knowledge of complexation reactions of early actinides with nitrogen donor ligands serves not only as fundamental research in this underrepresented field of chemistry but also contributes to a deeper understanding of their reactivity and coordination chemistry. In contrast to the lanthanides, with the dominating oxidation state of + III, actinides, especially the early actinides up to Plutonium, can exist in a variety of different oxidation states ranging from +II to +VI.
The coordination chemistry of tri- and tetravalent actinides with selective soft nitrogen donor ligands is of special interest, with a potential use as extraction and/or decontamination agents.
In order to understand the bonding trends and electronic structure, the nitrogen donor ligand 2,6-bis(1-(4-bromo-2,6-dimethylphenyl)-1H-1,2,3-triazol-4-yl)pyridine, a BPTP-type ligand, was used as the compound of choice in this contribution. BPTP-type ligands are based on the commonly known BTP-ligand, a tridentate chelating ligand which was designed for the purpose of separating lanthanides from actinides.[1] The BPTP ligand was synthesized by a copper mediated click reaction of 2,6-diethynylpyridine with the corresponding azide.
Within this ongoing study, we focus on the synthesis and characterization of tetravalent actinides, which are readily available for all of the early actinides from Thorium up to Plutonium.
The obtained U(IV) complex was characterized by single crystal X-ray diffraction (SC-XRD). Further characterization of the novel coordination complex using NMR, IR, and EPR, as well as an expansion to the transuranic elements will complete this study.

  • Lecture (Conference)
    19th Radiochemical Conference - RadChem 2022, 15.-20.05.2022, Mariánské Lázně, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-36348


Synthesis and Coordination Chemistry of N-Donor Ligands with early Actinides

Duckworth, T.; März, J.; Kaden, P.; Patzschke, M.; Schwarz, N.; Greif, G.; Stumpf, T.

Abstract

Understanding the subtle differences between lanthanide and actinide complexation chemistry with different ligand systems is an ongoing field of resarch. Soft donor ligands, especially ligands containing nitrogen, have shown to be promising for the investigation of the small differences in bonding behavior of actinides compared to lanthanides particularly with regards to the covalent contribution within the bond.

BTP type ligands have been used as an extacting ligand for the separation of lanthanides from actinides.1 Therefore, new soft nitrogen donor ligands based on the BTP type ligand (2,6-Bis(1,2,4-Triazin-3-yl)Pyridine) or Schiff base lig-ands have been synthesized to explore the fundamental chemistry of the early 5f-elements. In order to investigate the coordination environment, ligand selectivity, bonding trends and electronic properties a series of actinide complexes ranging from thorium to plutonium has been characterized in solid state as well as in solution.

In the present study the synthesis of the new soft donor ligand L1 was carried out via a copper mediated click reaction of the corresponding alkyne and azide. The bipyridine based ligand L2 was obtainend in a three step synthesis starting from bipyridine via the corresponding N-oxide and cyanide to give the tetrazine.
Both ligands L1 and L2 were succesfully applied in the complexation reaction with trivalent lanthanides e.g. Er and Sm. In this contribution the investigation of the coordination chemistry of these soft N-donor ligands is exended to the early actinides in their tri- and tetravalent oxidation state.

First experimental results show the formation of a 3:1 complex in the case of trivalent Er. In contrast, the same ligand system L1 forms a 2:1 complex with U(IV) including methanolato and iodo ligands for charge compensation. Further results including first structural characterization as well as results from quantum chemical calculations to elucidate the binding situation, will be presented in this contribution.

  • Poster
    Actinides revisited 2022, 21.-23.09.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36347


CT-based stopping-power ratio prediction using a Hounsfield look-up table: A consensus guide

Taasti, V.; Peters, N.; Bolsi, A.; Vallhagen Dahlgren, C.; Ellerbrock, M.; Gomà, C.; Góra, J.; Cambraia Lopes, P.; Rinaldi, I.; Salvo, K.; Sojat Tarp, I.; Vai, A.; Bortfeld, T.; Lomax, A.; Richter, C.; Wohlfahrt, P.

Abstract

Motivation
Large variations in stopping-power ratio (SPR) prediction from computed tomography (CT) across European proton centres were observed in recent studies. To standardise CT-based SPR prediction using a Hounsfield look-up table (HLUT), a step-by-step consensus guide, created within the ESTRO Physics Workshop 2021 in a joint effort with EPTN-WP5, is presented.
Methods
The HLUT specification process includes six steps: Phantom setup, CT acquisition, CT number extraction, SPR determination, HLUT specification, and HLUT validation. Appropriate phantom inserts are tissue-equivalent for both X-ray and proton interactions and are scanned in head- and body-sized phantoms to mimic different beam hardening conditions. Soft tissue inserts can be scanned together, while scanning bone inserts individually reduces imaging artefacts. For optimal HLUT specification, the SPR of phantom inserts is measured and the SPR of tabulated human tissues is computed stoichiometrically. The HLUT stability is increased by including both phantom inserts and tabulated human tissues. Piecewise linear regressions of CT numbers and SPRs are performed for four tissue groups (lung, adipose, soft tissue, and bone) and then connected. Finally, a thorough validation is performed.
Results
The best practices and individual challenges are explained comprehensively for each step. A well-defined strategy for specifying the connection points between the individual line segments of the HLUT is presented. The guide was tested exemplarily on three CT scanners from different vendors, proving its feasibility on both single-energy CT and virtual monoenergetic images from dual-energy CT.
Conclusion
The presented step-by-step guide for CT-based HLUT specification with recommendations and examples can increase the clinical range prediction accuracy and reduce its inter-centre variation.

Involved research facilities

  • OncoRay
  • Lecture (Conference)
    PTCOG 2023, 10.-16.06.2023, Madrid, Spain

Permalink: https://www.hzdr.de/publications/Publ-36346


Quantitative assessment of separation quality, using neural networks and multivariate stochastic modeling

Kirstein, T.; Furat, O.; Leißner, T.; Bachmann, K.; Gutzmer, J.; Peuker, U. A.; Schmidt, V.

Abstract

The quality and behavior of application specific industrial materials, such as those used for the production of coatings, membranes and electrodes, are influenced by the properties of particles within the materials, for example, particle size, flatness and sphericity. To fabricate materials with desired properties, particle systems may undergo processes such as fractionation or magnetic separation for quality adjustment. X-ray computed tomography (CT) can image large volumes of given particle systems with a sufficiently good resolution to allow for the analysis of individual particles. However, methods to efficiently analyze such image data and model the observed particle properties are still an active field of research. When image data of particles exhibiting a wide range of shapes and sizes is considered, traditional image segmentation methods, such as the classic watershed algorithm, struggle to recognize particles with satisfying accuracy. Therefore, more advanced methods of machine learning can be utilized for such image segmentation tasks to improve the validity of further subsequent analyzes.

In this talk, experimentally measured three-dimensional CT images of a zinnwaldite-quartz composite material are considered before and after a magnetic separation process is applied to enrich valuable mineral ores. Therefore, an image segmentation method using a deep convolutional neural network (CNN), specifically an adaptation of the U-net architecture, is used. This has the advantage of requiring less hand-labeling than other machine learning methods, while also being more flexible with the possibility of transfer learning. In addition, a fully parametric vine copula based model is designed to determine multivariate probability distributions of particle size/shape/textural/composititional characteristics—allowing for the estimation and interpretable characterization of highly-dimensional interdependencies of particle characteristics. The described methodology is then applied to describe image data of particle systems before and after magnetic separation, to quantitatively evaluate the separation success.

  • Lecture (Conference)
    5th International Conference Hybrid 2022 - Materials and Structures, 20.-22.07.2022, Leoben, Austria

Permalink: https://www.hzdr.de/publications/Publ-36345


Coordination chemistry of N-Donor Ligands with early Actinides

Duckworth, T.; März, J.; Kaden, P.; Schmidt, M.; Stumpf, T.

Abstract

The development and investigation of N-donor ligands e.g. for actinide / lanthanide separation is an ongoing field of study, in particular with respect to understanding the structure-property-relationship.
In this context we have been exploring the coordination chemistry of the early actinides (Th – Am) with tridentate chelating ligands containing pyridine and bipyridine moieties.
Ligands 1 and 2 were successfully used for complexation with trivalent lanthanides.
Encouraged by these results, we have been focusing on their coordination chemistry with tri- and tetravalent early actinides. We aim to understand the reactivity of these ligands that exploit the unique electronic structure of the early 5f-elements.
The synthesis of such complexes was carried out in acetonitrile with recrystallization from methanol.
For instance, the synthesized U(IV) complex of 1a which was characterized by single crystal XRD revealed a nine-fold coordinated uranium center. In contrast to the nine-fold Ln(III) complex which exhibits a ligand to metal ratio of 3:1 the U(IV) complex shows a 2:1 ratio with additional methanolato and iodo ligands for charge compensation.
Expanding the series to the tri- and tetravalent transuranic metals and characterizing the obtained complexes both structurally and spectroscopically will help to elucidate the differences between the coordination behavior of the lanthanides compared to the actinides.

  • Poster
    Plutonium Futures – The Science 2022, 26.-29.09.2022, Avignon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-36344


Quantitative assessment of separation quality, using neural networks and multivariate stochastic modeling

Kirstein, T.; Furat, O.; Leißner, T.; Bachmann, K.; Peuker, U. A.; Schmidt, V.

Abstract

Particle properties such as size, shape and composition are key for many products and in many processes. For example, in order to enrich minerals in a targeted manner, an ore must be crushed, classified and sorted so that high grades are achieved with a high recovery at the same time. To describe and optimize the processes, the influence of particle properties on the process result must be determined. X-ray computed tomography (CT) can image large volumes of given particle systems with a sufficiently good resolution to allow for the analysis of individual particles. However, methods to efficiently analyze such image data and model the observed particle properties are still an active field of research. When image data of particles exhibiting a wide range of shapes and sizes is considered, traditional image segmentation methods, such as the classic watershed algorithm, struggle to recognize particles with satisfying accuracy. Therefore, more advanced methods of machine learning can be utilized for such image segmentation tasks to improve the validity of further analyzes. In this talk, experimentally measured three-dimensional CT images of a zinnwaldite-quartz composite material are considered before and after a magnetic separation process is applied to enrich valuable minerals. Therefore, an image segmentation method using a deep convolutional neural network (CNN), specifically an adaptation of the 3D U-net architecture, is used. This has the advantage of requiring less hand-labeling than other machine learning methods, while also being more flexible with the possibility of transfer learning. In addition, a fully parametric vine copula based model is designed to determine multivariate probability distributions of particle size/shape/textural/composititional characteristics—allowing for the estimation and interpretable characterization of highly-dimensional interdependencies of particle characteristics. The described methodology is then applied to characterize the particle systems before and after
magnetic separation, to quantitatively evaluate the separation success.

  • Lecture (Conference) (Online presentation)
    IMPC Asia-Pacific 2022, 21.-23.08.2022, Melbourne, Australien

Permalink: https://www.hzdr.de/publications/Publ-36343


Application of mineral liberation analysis to determine the spatial association of accessory minerals with biotite in granitic rocks

Bachmann, K.; Gilbricht, S.; Renno, A.; Hamilton, D. C.; Clarke, D. B.

Abstract

We apply mineral liberation analysis (MLA) to resolve and automate highly specific petrological questions. In this study, we quantify the spatial association of more than 15,000 grains of accessory apatite, monazite, xenotime, and zircon with essential biotite, and clustered with themselves, in a peraluminous biotite granodiorite from the South Mountain Batholith in Nova Scotia (Canada). A random distribution of accessory minerals demands that the proportion of accessory minerals in contact with biotite is identical to the proportion of biotite in the rock, and the binary touching factor (percentage of accessory mineral touching biotite divided by modal proportion of biotite) would be ~1.00. Instead, the mean binary touching factors for the four accessory minerals in relation to biotite are: apatite (5.06 for 11168 grains), monazite (4.68 for 857 grains), xenotime (4.36 for 217 grains), and zircon (5.05 for 2876 grains). Shared perimeter factors give similar values. Monazite and zircon have approximately log-normal grain-size distributions, but apatite is strongly skewed toward larger grain sizes, and xenotime is skewed toward smaller grain sizes. Accessory mineral grains that straddle biotite grain boundaries are larger than completely locked, or completely liberated, accessory grains. Only apatite-monazite clusters are significantly more abundant than expected for random distribution. The high, and statistically significant, binary touching factors and shared perimeter factors suggest a strong physical or chemical control on their spatial association. We discuss several petrogenetic processes that may lead to this spatial association. This study is an example of how modern methods of automated mineralogy, combined with powerful statistical methods, allow petrographic observations defined as "well known" and "given" to be transformed into viable scientific statements that are verifiable and falsifiable.

  • Poster
    Geoanalysis 2022, 06.-12.08.2022, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36341


Drill Core Scanning using MLA - Micro Methods for Macro Samples

Guy, B. M.; Renno, A.; Sittner, J.; Gutzmer, J.

Abstract

SEM-based automated mineralogy represents an established mineral identification and quantification technique in the mineral processing industry. The technique is routinely used to characterise the mineralogy of various mining and plant-related products (e.g., feed samples, concentrates, leach residues etc.). Automated mineralogical analyses are typically conducted on small 20-30 mm diameter epoxy mounts of fine-grained milled material. In contrast, mineralogical analyses of larger samples, such as drill core, can be obtained by non-destructive analytical techniques, such as hyperspectral scanning, micro-XRF and computed tomography (CT). Hyperspectral and micro-XRF methods are relatively rapid and inexpensive, whereas CT scans produce a three-dimensional model (Sittner et al., 2021). However, these methods are not currently suited for detailed mineralogical mapping and/or micron-scale mapping.

In this contribution, we present automated mineralogical scans of 40 cm of drill core from the Au-U Witwatersrand Supergroup, South Africa. The cores intersect approximately 10 cm of the quartzitic footwall and 30 cm of the overlying pyritic conglomeratic reef. The spatial distribution and mode of occurrence of the gold and uranium minerals was accurately recorded at both the macro and micrometer scale. Core scanning by automated mineralogy can be employed when core material is limited, which precludes the preparation of thin sections or milled pulps.

Keywords: MLA; Drill core; Modal Mineralogy; Gold and Uranium Search

  • Poster
    GeoAnalysis, 06.-12.08.2022, Freiberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-36340


Towards Atmospheric Radical Sensing: Fabrication of Junctionless Transistors

Khan, M. B.; Ghosh, S.; Vardhan, V.; Biswas, S.; Maciel, T.; Holmes, J. D.; Erbe, A.; Georgiev, Y.

Abstract

Down-scaling of complementary metal-oxide-semiconductor (CMOS) technology faces strong challenges. Therefore, new device and logic concepts, advanced nanomaterials, and advanced fabrication techniques have gained importance in the last few decades. Nanomaterials and nanostructures hold the key for next-generation information processing due to their reduced sizes and new properties [1]. Silicon nanowires, in particular, have been used successfully in new electronic devices, including thermoelectric energy harvesting, sensors, and solar cells.
Silicon nanowires, due to their high surface-to-volume ratio, have demonstrated energy efficient devices. In the case of nanowire based field-effect transistors (FETs), excellent control of conductance across the nanowire is achieved through the electrostatic potential applied at the gate [2]. Moreover, nanowires have been used for fabrication of high sensitivity biochemical sensors, since small volumes allow effective control of the electrostatic potential across a nanowire. Such sensors have been used for various applications, including diagnosing cancer biomarkers and viruses [3], sensing gases such as ammonia (NH3), nitrogen dioxide (NO2) [4], and hydrogen (H2) [5].
One of the new, nanowire based, device concepts mentioned above is the junctionless nanowire transistor (JNT) [6]. A JNT consists of a highly doped nanowire channel without p-n junctions, where the flow of carriers is controlled by the gate potential. JNTs have already shown excellent performance as biosensors [7]. In this work, we report on the fabrication of such transistors for the detection of atmospheric free radicals. Intrinsic silicon-on-insulator (SOI) wafers are n-doped by ion implantation. Flash lamp annealing is performed for dopant activation and mitigation of implantation defects. Nanowires are fabricated following a top-down approach using electron beam lithography and reactive ion etching. Then, Nickel/Gold contacts are fabricated. Electrical characterisation of the fabricated devices is performed by back-gating the nanowires. The devices show an on/off current ratio of ca. 106. This will be followed by the functionalization of the fabricated devices for the selective and highly sensitive electrical detection of ꞏOH and ꞏNO3 atmospheric radicals, which affect the air quality and climate and have a direct impact on our lives.

1. Amato, M., et al., Silicon–Germanium Nanowires: Chemistry and Physics in Play, from Basic Principles to Advanced Applications. Chemical Reviews, 2014. 114(2): p. 1371-1412.
2. Grigorescu, A.E., et al., 10 nm lines and spaces written in HSQ, using electron beam lithography. Microelectronic Engineering, 2007. 84(5–8): p. 822-824.
3. Zhang, G.-J., et al., Silicon nanowire biosensor for highly sensitive and rapid detection of Dengue virus. Sensors and Actuators B: Chemical, 2010. 146(1): p. 138-144.
4. Wan, J., et al., Silicon nanowire sensor for gas detection fabricated by nanoimprint on SU8/SiO2/PMMA trilayer. Microelectronic Engineering, 2009. 86(4–6): p. 1238-1242.
5. Skucha, K., et al., Palladium/silicon nanowire Schottky barrier-based hydrogen sensors. Sensors and Actuators B: Chemical, 2010. 145(1): p. 232-238.
6. Colinge J P, et al., Nanowire transistors without junctions. Nature Nanotech. 2010 5 225-229.
7. Georgiev, Y. M., et al., Detection of ultra-low protein concentrations with the simplest possible field effect transistor. Nanotechnology, 2019 30 324001 (8pp).

Keywords: Juntionless transistors; nanowires; Radical sensing

Involved research facilities

Related publications

  • Poster
    Micro and Nano Engineering (MNE) Eurosensors 2022, 19.-23.09.2022, Leuven, Belgium

Permalink: https://www.hzdr.de/publications/Publ-36339


Prediction of mineralogical particle composition using CT data and R-vine copulas

Furat, O.; Kirstein, T.; Leißner, T.; Bachmann, K.; Gutzmer, J.; Peuker, U. A.; Schmidt, V.

Abstract

Computed tomography (CT) can capture volumes large enough to measure a statistical meaningful number of micron-sized particles with a sufficiently good resolution to allow for the analysis of individual particles. However, the development of methods to efficiently investigate such image data and interpretably model the observed particle features is still an active field of research. When image data of particles exhibiting a wide range of shapes and sizes is considered, traditional image segmentation methods, such as the watershed algorithm, struggle to recognize particles with satisfying accuracy. Thus, more advanced methods of machine learning must be utilized for image segmentation to improve the validity of subsequent analyzes. Moreover, CT data does not include information about the mineralogical composition of particles and, therefore, additional SEM-EDS image data must be acquired. Here, micro-CT data of a particle system mostly composed of zinnwaldite-quartz composites is considered. First, an image segmentation method is applied which uses deep convolutional neural networks (CNN), namely a U-net. This has the advantage of requiring less hand-labeling than other machine learning methods, while also being more flexible with the possibility of transfer learning. Then, parameterized models based on vine copulas are designed to determine multivariate probability distributions of descriptor vectors for the size, shape, texture and composition of particles. For model fitting, the segmented three-dimensional CT data and co-registered two-dimensional SEM-EDS data are used. The models are applied to predict the mineralogical composition of particles, solely on the basis of particle descriptors observed in CT data. The power of the introduced prediction models for estimating the mineralogical composition of particles by means of CT-based descriptor vectors, are evaluated with respect to the prediction of the zinnwaldite volume fraction of particles. Results obtained for the goodness of fit and the predictive power are quantitatively assessed.

  • Lecture (Conference)
    WCPT9 - World Congress on Particle Technology, 18.-22.09.2022, Madrid, Spanien

Permalink: https://www.hzdr.de/publications/Publ-36338


Multidimensional characterization of particle morphology and mineralogical composition using CT data and R-vine copulas

Furat, O.; Kirstein, T.; Leißner, T.; Bachmann, K.; Gutzmer, J.; Peuker, U. A.; Schmidt, V.

Abstract

Computed tomography (CT) can capture volumes large enough to measure a statistically meaningful number of micron-sized particles with a sufficiently good resolution to allow for the analysis of individual particles. However, the development of methods to efficiently investigate such image data and interpretably model the observed particle features is still an active field of research. When image data of particles exhibiting a wide range of shapes and sizes is considered, traditional image segmentation methods, such as the classic watershed algorithm, struggle to recognize particles with satisfying accuracy. Thus, more advanced methods of machine learning must be utilized for image segmentation to improve the validity of subsequent analyzes. Moreover, CT data does not include information about the mineralogical composition of particles and, therefore, additional SEM-EDS image data has to be acquired. In this paper, micro-CT image data of a particle system mostly consisting of zinnwaldite-quartz composites is considered. First, an image segmentation method is applied which uses deep convolutional neural networks, in particular an adaptation of the U-net architecture. This has the advantage of requiring less hand-labeling than other machine learning methods, while also being more flexible with the possibility of transfer learning. Then, fully parameterized models based on vine copulas are designed to determine multivariate probability distributions of descriptor vectors for the size, shape, texture and composition of particles -- allowing for the estimation and interpretable characterization of interdependencies between particle descriptors.

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Permalink: https://www.hzdr.de/publications/Publ-36337


Multivariate stochastic modeling of the influence of particle descriptors on flotation-based separation behavior

Wilhelm, T.; Sandbrink, J.; Furat, O.; Bachmann, K.; Rudolph, M.; Schmidt, V.

Abstract

Many separation processes are based on particle properties like wettability, composition, size and shape. Therefore, it is necessary to analyze the influence of different particle properties on the particle separation behavior. A common tool for classifying particle separation processes are Tromp functions. Recently, multivariate Tromp functions, computed by means of non-parametric kernel density estimation, have emerged which describe the separation behavior with respect to multidimensional particle properties. In this paper, an alternative flexible parametric modeling approach is proposed to model the separation behavior of particle systems with multivariate Tromp functions observed by mineral liberation analyzer (MLA) image measurements. However, different particle properties such as particle wettability cannot be observed in MLA data, although many separation processes such as flotation-based particle separation processes rely on differences in wettabilities. In order to analyze the influence of wettability on particle separation behavior, bivariate Tromp functions for area-equivalent diameter and aspect ratio of differently shaped glass particle systems with differently modified wettabilities are computed in a case study. Comparing the computed Tromp functions reveals
the influence of particle wettability on the separation behavior. In addition, we extend the parametric approach to model multivariate Tromp functions to handle separation processes when image measurements are not available for all separation streams.

  • Lecture (Conference)
    German probability and statistics days, 07.-10.03.2023, Essen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36336


Multivariate stochastic modeling of particle descriptors for studying the influence of wettability on flotation-based separation behavior

Wilhelm, T.; Sygusch, J.; Furat, O.; Bachmann, K.; Rudolph, M.; Schmidt, V.

Abstract

In the context of mineral processing, the separation of particles of some feed material into a valuable and a waste fraction is commonly achieved by processes like magnetic (1) or flotation separation (2). The outcome of such processes often depends on particle properties like wettability, but it can also depend on the composition, size and shape of particles. Therefore, with regard to the goal of optimizing separation processes, it is useful to analyze different particle descriptors when studying the influence of wettability on the particle separation behavior. A common tool for classifying particle separation processes are Tromp functions (3). Recently, multivariate Tromp functions, computed by means of non-parametric kernel density estimation, have emerged which characterize the separation behavior with respect to multidimensional vectors of particle descriptors (4). However, estimating multivariate probability densities of particle descriptors using methods of kernel density estimation requires a relatively large sample size (5). Therefore, we propose an alternative parametric approach based on copulas (6) in order to compute multivariate Tromp functions and, in this way, to characterize the separation behavior of particle systems, see Figure 1. Moreover, the parametric modeling approach is extended by an optimization routine to handle separation processes when measurements are not available for all separated fractions. A potential application of the optimization routine is to reduce the measurement effort in a series of separation experiments for a given feed material and various separated fractions. A simulation study has been performed in order to quantitatively compare the parametric with the non-parametric modeling approach. This comparison focuses especially on scenarios for which only a relatively small number of particles is observed in measurements. Such scenarios occur, for example, when image data of particle systems are considered, from which descriptors of individual particles can be determined, but
the number of observed particles tends to be smaller than the number of particles obtained with other measurement techniques. However, some particle properties like wettability cannot be directly deduced from image data, although many separation processes, such as flotation-based particle separation processes, rely on differences in wettabilities. Building on recent studies regarding flotation separation (2), bivariate Tromp functions for the area-equivalent diameter and aspect ratio of glass particles with differently modified wettabilities have been computed. Comparing the Tromp functions obtained in this way reveals the influence of particle wettability on the separation behavior.

  • Poster
    PARTEC 2023, 26.-28.09.2023, Nürnberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36334


Quality Assessment of Cyclotron-produced 67Cu

Brühlmann, S. A.; Walther, M.; Kreller, M.; Pietzsch, H.-J.; Knieß, T.; Kopka, K.

Abstract

This project aims to explore the cyclotron-based production of 67Cu through the 70Zn(p,α)67Cu reaction, in contrast to other possible routes (e.g. photonuclear reaction). The reaction features a low yield and the need of expensive target material, thus demanding a recycling strategy. Although by this reaction no carrier added 67Cu is produced, contamination with or co-production of stable copper (via 68Zn(p,α)65Cu) cannot be entirely excluded.

  • Contribution to proceedings
    Fourth international edition of the symposium on Technetium and Other Radiometals in Chemistry and Medicine (TERACHEM 2022), 14.-17.09.2022, Brixen, Italien

Permalink: https://www.hzdr.de/publications/Publ-36332


Antiferromagnetic spin chains: ground states and phase transitions in static magnetic field of arbitrary direction

Borysenko, Y.; Sheka, D.; Yershov, K.; Faßbender, J.; van den Brink, J.; Makarov, D.; Pylypovskyi, O.

Abstract

While easy axis antiferromagnets (AFMs) are robust against external magnetic fields of a moderate strength, spin reorientations in strong fields provide an insight into subtle properties of materials, which are usually hidden by the high symmetry of the ground state [1]. In absence of external magnetic fields, they reveal geometry-driven chiral and anisotropic responses supplemented by weak ferromagnetism [2]. Here, we address theoretically the effects of curvature in achiral anisotropic ring-shaped AFM spin chains exposed to strong magnetic fields using the methodology of curvilinear magnetism [3]. We identify the geometry-governed helimagnetic phase transition enabled in the spin-flop phase, separating locally homogeneous (vortex) and periodic (onion) AFM textures (Fig. 1). The curvature-induced Dzyaloshinskii–Moriya interaction results in the spin-flop transition being of the first- or second-order depending on the ring curvature. Spatial inhomogeneity of the Néel vector in the spin-flop phase generates the weakly ferromagnetic esponse in the plane perpendicular to the applied magnetic field, which is inherent to curved systems. In AFM spin chains possesing torsion, e.g. helices, these effects are enhanced by the inhomogeneity of local texture in the ground state. Our work provides further insights in the physics of curvilinear AFMs in static magnetic fields and guides prospective experimental studies of geometrical effects in the spin-chain nanomagnets.

Keywords: antiferromagnetism; curvilinear spin chains

  • Lecture (Conference)
    AIM 2023 Advances in Magnetics, 15.-18.01.2023, Moena, Italy, 15.-18.01.2023, Moena, Italy

Permalink: https://www.hzdr.de/publications/Publ-36331


A Contribution to a Better Understanding of Lithium-Ion Battery Recycling by Using Automated Mineralogy

Vanderbruggen, A.; Bachmann, K.; Rudolph, M.; Gutzmer, J.

Abstract

Recycling is a potential solution to narrow the gap between the supply and demand of battery materials such as Co, Ni, Mn and graphite. However, increasing the efficiency of the recycling of lithium ion batteries (LIB) remains a challenge. This paper evaluates the influence of the recycling routes on the liberation of LIB components and on the joint recovery of lithium metal oxides and spheroidized graphite particles using froth flotation. The products of the two different recycling routes – mechanical, and thermomechanical – were analyzed using a particle-based method, namely scanning electron microscopy (SEM)-based automated image analysis. The mechanical process enabled the delamination of active materials from the foils. However, binder preservation hinders active materials liberation as indicated by their aggregation. In contrast, the thermo-mechanical process showed a preferential liberation of individual anode active particle thus identified as an upstream route for flotation. However, this thermal treatment led to a lack of liberation of cathode material and to the oxidation of aluminium foil resulting in its distribution in all size fractions. Among the two, the thermo-mechanical black mass showed the highest flotation selectivity due to the removal of the binder thereby producing liberated active particles.

  • World of Metallurgy - Erzmetall 75(2022)3, 144-152

Permalink: https://www.hzdr.de/publications/Publ-36330


Production of 67Cu at the TR-FLEX Cyclotron

Brühlmann, S. A.; Walther, M.; Kreller, M.; Pietzsch, H.-J.; Knieß, T.; Kopka, K.

Abstract

For the cyclotron-based production of the theranostic radionuclide 67Cu through the 70Zn(p,α)67Cu reaction electroplated metallic Zn and ZnO powder targets are being studied. Highly enriched 70Zn targets were designed and optimized considering nuclear and thermal aspects.

  • Open Access Logo Contribution to proceedings
    18th Workshop on Targetry and Target Chemistry, 21.-26.08.2022, Whistler, Canada

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Permalink: https://www.hzdr.de/publications/Publ-36329


Synthesis of [18F]FMISO, a hypoxia-specific imaging probe for PET, an overview from a radiochemist’s perspective

Knieß, T.; Zessin, J.; Mäding, P.; Kuchar, M.; Kiß, O.; Kopka, K.

Abstract

[18F]Fluoromisonidazole ([18F]FMISO, 1H-1-(3-[18F]fluoro-2-hydroxypropyl)-2-nitroimidazole) is a commonly used radiotracer for imaging hypoxic conditions in cells. Since hypoxia is prevalent in solid tumors, [18F]FMISO is in clinical application for decades to explore oxygen demand in cancer cells and the resulting impact on radiotherapy and chemotherapy.
Since the introduction of [18F]FMISO as positron emission tomography (PET) imaging agent in 1986, a variety of radiosynthesis procedures for the production of this hypoxia tracer has been developed. This paper gives a brief overview on [18F]FMISO radiosyntheses published so far from its introduction until now. From a radiopharmaceutical chemist’s perspective, different precursors, radiolabeling approaches and purification methods are discussed as well as used automated radiosynthesizers, including cassette-based and microfluidic systems.
In a GMP compliant radiosynthesis using original cassettes for FASTlab we produced [18F]FMISO in 49% radiochemical yield within 48 min with radiochemical purities >99% and molar activities >500 GBq/µmol . In addition, we report an easy and efficient radiosynthesis of [18F]FMISO, based on in-house prepared FASTlab cassettes, providing the radiotracer for research and preclinical purposes in good radiochemical yields (39%), high radiochemical purities (>99%) and high molar activity (>500 GBq/µmol) in a well-priced option.

Keywords: [18F]FMISO; [18F]Fluoromisonidazole; automated radiosynthesis; FASTlab

Involved research facilities

  • PET-Center
  • ZRT

Permalink: https://www.hzdr.de/publications/Publ-36328


Joint recovery of lithium metal oxides and graphite particles from spent lithium-ion batteries using froth flotation

Vanderbruggen, A.; Bachmann, K.; Olutogun, M.; Bresser, D.; Rudolph, M.; Serna, R.

Abstract

Recycling symposium This talk presents how we can separate the fine active particles (lithium metal oxides and graphite) from the black mass by using froth flotation. This research demonstrates that graphite can be recovered from spent lithium ion batteries and recycled into new anodes

  • Lecture (Conference)
    Advanced Automotive Battery Conference AABC 2022, 19.-22.06.2022, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36327


Cyclotron-based Production of 67Cu for Radionuclide Theranostics Via the 70Zn(p,α)67Cu Reaction

Brühlmann, S. A.; Walther, M.; Kreller, M.; Reissig, F.; Pietzsch, H.-J.; Knieß, T.; Kopka, K.

Abstract

Theranostic matched pairs of radionuclides have aroused interest during the last couple of years and in that sense copper is one element that has a lot to offer. While 61Cu and 64Cu are slowly being established as nuclides for diagnostic with PET, the availability of the therapeutic counterpart 67Cu plays a key role for further radiopharmaceutical development in the future. Up to date, the 67Cu shortage has not been solved, however, different production routes are being explored. This project aims at the production of no carrier added 67Cu with high radionuclidic purity with a medical 30 MeV compact cyclotron via the 70Zn(p,α)67Cu reaction.

Permalink: https://www.hzdr.de/publications/Publ-36326


Years: 2023 2022 2021 2020 2019 2018 2017 2016 2015


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