Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41396 Publications

Influence of 73Rb on the ashes of accreting neutron stars

Hoff, D. E. M.; Rogers, A. M.; Meisel, Z.; Bender, P. C.; Brandenburg, K.; Childers, K.; Clark, J. A.; Dombos, A. C.; Doucet, E. R.; Jin, S.; Lewis, R.; Liddick, S. N.; Lister, C. J.; Morse, C.; Schatz, H.; Schmidt, K.; Soltesz, D.; Subedi, S. K.; Wang, S. M.; Waniganeththi, S.

We find that the proton separation energy, S(p), of 73Rb is −640(40) keV, deduced from the observation of β-delayed ground-state protons following the decay of 73Sr. This lower-limit determination of the proton separation energy of 73Rb coupled with previous upper limits from nonobservation, provides a full constraint on the mass excess with ΔM(73Rb)=−46.01±0.04 MeV. With this new mass excess and the excitation energy of the Jπ=5/2− isobaric-analog state (T=3/2) in 73Rb, an improved constraint can be put on the mass excess of 73Sr using the isobaric-multiplet mass equation (IMME), and we find ΔM(73Sr)=−31.98±0.37 MeV. These new data were then used to study the composition of ashes on accreting neutron stars following Type I x-ray bursts. Counterintuitively, we find that there should be an enhanced fraction of A>102 nuclei with more negative proton separation energies at the 72Kr rp-process waiting point. Larger impurities of heavier nuclei in the ashes of accreting neutron stars will impact the cooling models for such astrophysical scenarios.

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Permalink: https://www.hzdr.de/publications/Publ-36484
Publ.-Id: 36484


Access to 18F-Labeled FAP Inhibitor variants via [18F]SuFEx Reaction

Kogler, J.; Craig, A.; Kopka, K.; Stadlbauer, S.

´Objectives:

The emerging significance of the tumor microenvironment (TME) as a new frontier for cancer diagnosis and therapy can be primarily attributed to its unique features, such as the interconnection between stromal and cancer cells.1 Cancer-associated fibroblasts (CAFs) within the TME are identified by biomarkers such as fibroblast activation protein alpha (FAP), which are expressed on their surfaces. Targeting FAP using small molecule 18F-labeled inhibitors (FAPIs) have recently garnered significant attention for noninvasive tumor visualization using PET.2 Currently, the predominant 18F-fluorination method for radiolabeling FAPIs involves chelation-based radiofluorination strategies using aluminum [18F]fluoride ([18F]AlF). Herein, a powerful radiofluorination protocol for the preparation of an 18F-labeled FAPI via the sulfur [18F]fluoride exchange ([18F]SuFEx) reaction is disclosed.3
Methods:

The incorporation of the aryl fluorosulfate motif into the linker of the FAPI core structure (2) via amide bond formation allowed the radiolabeling precursor 3 to be accessed in moderate yield (Scheme 1 A, 46%). The radiosynthesis commenced with [18F]fluoride loading onto a QMA-cartridge which was eluted with a methanolic solution containing Et4NHCO3, followed by evaporation of the solvent under reduced pressure at 70 oC for 5 min (Scheme 1 B). Thereafter, the precursor 3 (100 µg, 145 nmol) in MeCN was added to the reaction vial, and allowed to react by [18F]SuFEx at room temperature for 5 min. The reaction was quenched by water dilution followed by SPE-based purification using a C18 cartridge. [18F]3 was isolated by elution from the cartridge with EtOH and the identity of the product was confirmed by UHPLC.

Results

The optimized radiosynthesis of 18F-labeled FAPI ([18F]3) was obtained with non-decay corrected isolated activity yields (AY) of 54 ± 3% (n = 3) and >99% RCP in 25 min. The automated radiosynthesis afforded [18F]3 in an unoptimized 11% AY, with >95% RCP and molar activity (Am) of 25 GBq/µmol (n = 1) in 30 min. The product was obtained in 2 mL EtOH, which can easily be further diluted with water or saline solution for subsequent biological evaluation.

  • Lecture (Conference)
    International Symposium on Radiopharmaceutical Sciences iSRS 2022, 29.05.-02.06.2022, Nantes, Frankreich
    DOI: 10.1016/S0969-8051(22)00078-6

Permalink: https://www.hzdr.de/publications/Publ-36483
Publ.-Id: 36483


Data publication: Analysis of Cadmium Retention Mechanisms by a Smectite Clay in the Presence of Carbonates

Missana, T.; Alonso, U.; Mayordomo, N.; García-Gutiérrez, M.

Cadmium (Cd) is a toxic heavy metal with very low permissible exposure limits and is, thus, a very dangerous pollutant for the environment and public health and is considered by the World Health Organisation as one of the ten chemicals of major public concern. Adsorption onto solid phases and (co)precipitation processes are the most powerful mechanisms to retain pollutants and limit their migration; thus, the understanding of these processes is fundamental for assessing the risks of their presence in the environment. In this study, the immobilisation of Cd by smectite clay has been investigated by batch sorption tests, and the experimental data were interpreted with a thermodynamic model, including cation exchange and surface complexation processes. The model can describe the adsorption of Cd in smectite under a wide range of experimental conditions (pH, ionic strength, and Cd concentration). Under the conditions analysed in this study, the precipitation of otavite (CdCO₃) is shown to have a limited contribution to Cd immobilisation.

Keywords: contaminants; cadmium; adsorption; surface complexation modelling; cation exchange; risk assessment; clays; geochemical barrier; otavite

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Permalink: https://www.hzdr.de/publications/Publ-36480
Publ.-Id: 36480


Analysis of Cadmium Retention Mechanisms by a Smectite Clay in the Presence of Carbonates

Missana, T.; Alonso, U.; Mayordomo, N.; García-Gutiérrez, M.

Cadmium (Cd) is a toxic heavy metal with very low permissible exposure limits and is, thus, a very dangerous pollutant for the environment and public health and is considered by the World Health Organisation as one of the ten chemicals of major public concern. Adsorption onto solid phases and (co)precipitation processes are the most powerful mechanisms to retain pollutants and limit their migration; thus, the understanding of these processes is fundamental for assessing the risks of their presence in the environment. In this study, the immobilisation of Cd by smectite clay has been investigated by batch sorption tests, and the experimental data were interpreted with a thermodynamic model, including cation exchange and surface complexation processes. The model can describe the adsorption of Cd in smectite under a wide range of experimental conditions (pH, ionic strength, and Cd concentration). Under the conditions analysed in this study, the precipitation of otavite (CdCO₃) is shown to have a limited contribution to Cd immobilisation.

Keywords: contaminants; cadmium; adsorption; surface complexation modelling; cation exchange; risk assessment; clays; geochemical barrier; otavite

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Permalink: https://www.hzdr.de/publications/Publ-36478
Publ.-Id: 36478


Chemistry of the interaction and retention of TcVII and TcIV species at the Fe3O4(001) surface

Bianchetti, E.; Faria Oliveira, A.; Scheinost, A.; Di Valentin, C.; Seifert, G.

The pertechnetate ion TcVIIO4− is a nuclear fission product whose major issue is the high mobility in the environment. Experimentally, it is well-known that Fe3O4 can reduce TcVIIO4− to TcIV species and retain such products quickly and completely, but the exact nature of the redox process and products is not completely understood. Therefore, we investigated the chemistry of TcVIIO4− and TcIV species at the Fe3O4(001) surface through a hybrid DFT functional (HSE06) method. We studied a possible initiation step of the TcVII reduction process. The interaction of the TcVIIO4− ion with magnetite surface leads to the formation of a reduced TcVI species without any change in the Tc coordination sphere, through an electron transfer that is favored by the magnetite surfaces with a higher FeII content. Furthermore, we explored various model structures for the immobilized TcIV final products. TcIV can be incorporated into a subsurface octahedral site or adsorbed on the surface in the form of TcIVO2·xH2O chains. We propose and discuss three model structures for the adsorbed TcIVO2·2H2O chains in terms of relative energies and simulated EXAFS spectra. Our results suggest that the periodicity of the Fe3O4(001) surface matches that of the TcO2·2H2O chains. The EXAFS analysis suggests that in experiments TcO2·xH2O chains were probably not formed as an inner-shell adsorption complex with the Fe3O4(001) surface.

Keywords: Technetium; EXAFS; Magnetite (001); DFT

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Permalink: https://www.hzdr.de/publications/Publ-36477
Publ.-Id: 36477


Data Publication: Growth and Martensitic Transformation of Ferromagnetic Co-Cr-Ga-Si Epitaxial Films

Ge, Y.; Lünser, K.; Ganss, F.; Gaal, P.; Fink, L.; Fähler, S.

Raw data of a paper done by Yuru Ge. The paper title is finally signed as: Growth and Martensitic Transformation of Ferromagnetic Co-Cr-Ga-Si Epitaxial Films. The authors are Yuru Ge, Klara Lünser, Fabian Ganss, Peter Gaal, Lukas Fink,and Sebastian Fähler. This is the final version which is accepted by the journal Science and Technology of Advanced Materials on 07.08.2023

Keywords: martensitic transformation; epitaxial film; ferromagnetism

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Permalink: https://www.hzdr.de/publications/Publ-36476
Publ.-Id: 36476


Development and validation of a 6-gene signature for the prognosis of loco-regional control in patients with HPV-negative locally advanced HNSCC treated by postoperative radio(chemo)therapy

Patil, S.; Linge, A.; Grosser, M.; Lohaus, F.; Gudziol, V.; Kemper, M.; Nowak, A.; Haim, D.; Tinhofer, I.; Budach, V.; Guberina, M.; Stuschke, M.; Balermpas, P.; Rödel, C.; Schäfer, H.; Grosu, A.-L.; Abdollahi, A.; Debus, J.; Ganswindt, U.; Belka, C.; Pigorsch, S.; Combs, S. E.; Boeke, S.; Zips, D.; Baretton, G. B.; Baumann, M.; Krause, M.; Löck, S.

Purpose: The aim of this study was to develop and validate a novel gene signature from full-transcriptome data using machine-learning approaches to predict loco-regional control (LRC) of patients with human papilloma virus (HPV)-negative locally advanced head and neck squamous cell carcinoma (HNSCC), who received postoperative radio(chemo)therapy (PORT-C).

Materials and methods: Gene expression analysis was performed using Affymetrix GeneChip Human Transcriptome Array 2.0 on a multicentre retrospective training cohort of 128 patients and an independent validation cohort of 114 patients from the German Cancer Consortium - Radiation Oncology Group (DKTK-ROG). Genes were filtered based on differential gene expression analyses and Cox regression. The identified gene signature was combined with clinical parameters and with previously identified genes related to stem cells and hypoxia. Technical validation was performed using nanoString technology.

Results: We identified a 6-gene signature consisting of four individual genes CAV1, GPX8, IGLV3-25, TGFBI, and one metagene combining the highly correlated genes INHBA and SERPINE1. This signature was prognostic for LRC on the training data (ci = 0.84) and in validation (ci = 0.63) with a significant patient stratification into two risk groups (p = 0.005). Combining the 6-gene signature with the clinical parameters T stage and tumour localisation as well as the cancer stem cell marker CD44 and the 15-gene hypoxia-associated signature improved the validation performance (ci = 0.69, p = 0.001).

Conclusion: We have developed and validated a novel prognostic 6-gene signature for LRC of HNSCC patients with HPV-negative tumours treated by PORT-C. After successful prospective validation the signature can be part of clinical trials on the individualization of radiotherapy.

Keywords: Cancer stem cells; Gene signature; Head and neck squamous cell carcinoma; Hypoxia; Machine learning

Permalink: https://www.hzdr.de/publications/Publ-36475
Publ.-Id: 36475


Growth and Dynamics of Hydrogen Bubbles at Microelectrodes

Bashkatov, A.; Hossain, S. S.; Yang, X.; Mutschke, G.; Eckert, K.

The evolution and dynamics of gas bubbles has a strong impact on the efficiency
of water electrolysis. Our poster will summarize recent work of our group on the
hydrogen evolution at a microelectrode in acidic electrolytes. Depending on
the applied potential and the electrolyte concentration, three different growth
regimes are identified, among them oscillatory growth above a carpet of
microbubbles. The discussion of the force balance of the bubbles includes
thermocapillary effects and an electric force caused by charge adsorption
at the interface.

Keywords: electrolysis; gas evolution; hydrogen; Marangoni effect; microelectrode

  • Poster
    Nanobubble Conference 2022, 18.-21.09.2022, Magdeburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36474
Publ.-Id: 36474


Magnetic field assisted electrodeposition of nano-structured metal layers – does it work?

Mutschke, G.; Huang, M.; Skibinska, K.; Eckert, K.; Zabinski, P.

Magnetic fields are a beneficial tool for controlling the mass transport during electrodeposition processes and could possibly be used for improving the manufacturing of nanostructured metal layers. Recently, we found that the local electrolyte flow near ferromagnetic surface elevations of mm size driven by the Lorentz force and the magnetic gradient force can indeed promote their growth, if the magnetic field is oriented perpendicular to the working electrode. To explore the prospects of magnetic fields towards smaller conical structures, we perform experimental and numerical studies on the template-free electrodeposition of conically structured nickel layers, thereby including the discussion of global cell flows.

Keywords: electrodeposition; magnetic field; Lorentz force; Kelvin force; numerical simulation; nanostructured surface

  • Lecture (Conference)
    12th Int. PAMIR Conference on Fundamental and Applied MHD, 04.-08.07.2022, Krakow, Polen

Permalink: https://www.hzdr.de/publications/Publ-36473
Publ.-Id: 36473


Parametric Stochastic Modeling of Particle Descriptor Vectors for Studying the Influence of Ultrafine Particle Wettability and Morphology on Flotation-Based Separation Behavior

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

Practically all particle separation processes depend on more than one particulate property. In the case of the industrially important froth flotation separation, these properties concern wettability, composition, size and shape. Therefore, it is useful to analyze different particle descriptors when studying the influence of particle wettability and morphology on the separation behavior of particle systems. 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 characterize the separation behavior with respect to multidimensional vectors of particle descriptors. In the present paper, an alternative parametric approach based on copulas is proposed in order to compute multivariate Tromp functions and, in this way, to characterize the separation behavior of particle systems. In particular, bivariate Tromp functions for the areaequivalent diameter and aspect ratio of glass particles with different morphologies and surface modification have been computed, based on image characterization by means of mineral liberation analysis (MLA). Comparing the obtained Tromp functions with one another reveals the combined influence of multiple factors, in this case particle wettability, morphology and size, on the separation behavior and introduces an innovative approach for evaluating multidimensional separation. In addition, we extend the parametric copula-based method for the computation of multivariate Tromp functions, in order to characterize separation processes, also in the case when image measurements are not available for all separated fractions.

Keywords: multivariate Tromp function; stochastic modeling; copula; flotation; separation process

Permalink: https://www.hzdr.de/publications/Publ-36472
Publ.-Id: 36472


Modeling and kMC simulation to optimize nano-Si fabrication by AlSi micro-droplet quenching – a new reaction pathway to fabricate lithium-ion battery anodes

Tucholski, D.; Heinig, K.-H.; Engelmann, H.-J.

Si as anode material for lithium-ion batteries promises 10x the capacity of state-of-the-art graphite. However, Si anodes suffer from pulverization and electrode collapse due to large volume increase during lithiation. It has been shown that Si structures with sizes below about 200 nm remain stable [1]. Therefore, we try to understand the formation of Si nanosponge in µ-sized particles during quenching of AlSi droplets. Subsequently Al is removed from the as-produced particles by etching. Phase separation of Si and Al upon solidification of the molten AlSi alloy occurs in two stages: First nucleation and growth of primary Si grains and second formation of eutectic sponge in the Si depleted melt, with faster cooling leading to finer structures. Through modelling and simulation, the reaction pathway can be understood, allowing to optimize process parameters. For this, a model was developed, which has as initial state a fully liquid, spherical droplet with random distribution of atom species Al, Si, vacancies and oxygen impurities. A many body angular-dependent potential (ADP) has been employed which reproduces the Al-Si phase diagram quite reasonable. As the melt cools below the liquidus temperature, precipitation of primary Si takes place, followed by spinodal demixing of the melt upon reaching the eutectic. Nucleation is influenced by trace oxygen which modifies surface energies and leads to formation of sites for heteronucleation. The diffusion-reaction behavior of the species, including nucleation and/or spinodal decomposition are simulated with a 3D kinetic lattice Monte Carlo program [2] using the ADP-potential for the Al-Si system [3] with modifications added to model surface oxidation. This program enables large scale calculations by a bit-encoded lattice and lattice jumps via bit-manipulation. Our simulations qualitatively reproduce the Al-Si phase diagram, as well as composition dependent interface energies of solid Si to Al-Si melt and the nucleation behavior. The simulation results agree with the experimentally found Si nanostructures and highlight the relevance of oxygen impurities for their formation.
This work is supported by the German federal ministry for economic affairs and climate protection under grant number 01221755/1.
[1] Su et al., Adv. En. Mat. 4 (2014) 1300882
[2] Strobel et al., Phys. Rev. B 64 (2001) 245422
[3] Starikov et al., Comp. Mat. Sc. 184 (2020) 109891

Related publications

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

Permalink: https://www.hzdr.de/publications/Publ-36471
Publ.-Id: 36471


Comprehensive Evaluation of Multiple Approaches Targeting ABCB1 to Resensitize Docetaxel-Resistant Prostate Cancer Cell Lines

Linke, D.; Donix, L.; Peitzsch, C.; Erb, H.; Dubrovska, A.; Pfeifer, M.; Thomas, C.; Fuessel, S.; Erdmann, K.

Docetaxel (DTX) is a mainstay in the treatment of metastatic prostate cancer. Failure of DTX therapy is often associated with multidrug resistance caused by overexpression of efflux membrane transporters of the ABC family such as the glycoprotein ABCB1. This study investigated multiple approaches targeting ABCB1 to resensitize DTX-resistant (DTXR) prostate cancer cell lines. In DU145 DTXR and PC-3 DTXR cells as well as age-matched parental controls, the expression of selected ABC transporters was analyzed by quantitative PCR, Western blot, flow cytometry and immunofluorescence. ABCB1 effluxing activity was studied using the fluorescent ABCB1 substrate rhodamine 123. The influence of ABCB1 inhibitors (elacridar, tariquidar), ABCB1-specific siRNA and inhibition of post-translational glycosylation on DTX tolerance was assessed by cell viability and colony formation assays. In DTXR cells, only ABCB1 was highly upregulated, which was accompanied by a strong effluxing activity and additional post-translational glycosylation of ABCB1. Pharmacological inhibition and siRNA-mediated knockdown of ABCB1 completely resensitized DTXR cells to DTX. Inhibition of glycosylation with tunicamycin affected DTX resistance partially in DU145 DTXR cells, which was accompanied by a slight intracellular accumulation and decreased effluxing activity of ABCB1. In conclusion, DTX resistance can be reversed by various strategies with small molecule inhibitors representing the most promising and feasible approach.

Keywords: ABCB1; P-glycoprotein; chemoresistance; docetaxel; elacridar; glycosylation; prostate cancer; siRNA; tariquidar; tunicamycin

Permalink: https://www.hzdr.de/publications/Publ-36470
Publ.-Id: 36470


Fabrication of microspheres of nanoporous Si for lithium-ion batteries anodes

Heinig, K.-H.; Engelmann, H.-J.; Andersen, O.; Hauser, R.; Tucholski, D.; Gerking, C.; Lindow, S.; Almousli, A.

Six carbon atoms of graphite of lithium ion battery (LIB) anodes can store one lithium atom, whereas one Si atom can store nearly four lithium atoms.
Theoretically, the replacement of graphite by silicon could reduce the weight of the anode by a factor of nearly 10. However, due to the strong swelling of silicon upon lithiation, Si anodes suffer from pulverization which reduces drastically the life cycle of LIBs. It has been shown that nanostructured silicon with structure sizes <200nm can withstand pulverization. There are many activities to develop an economic large-scale fabrication of such nanosilicon. We form Si nanostructures by phase separation during quenching of AlSi alloy droplets. At atomization of the AlSi melt the microdroplet solidify extremely fast which results in nanoscale Si pattern. Subsequently the Al is removed by selective etching leading to nanoporous Si microspheres.
We show that the structure depends strongly on the AlSi composition, the particle sizes and impurities. Promising nanosilicon for LIB anodes with a good cycling have been found.

This work is supported by the German federal ministry for economic affairs and climate protection under grant number 01221755/1.

Keywords: Lithium Ion Battery; Anode material; Nanosilicon; AlSi alloy melt quenching

Related publications

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

Permalink: https://www.hzdr.de/publications/Publ-36469
Publ.-Id: 36469


Magnetic Control of Flow and Mass Transfer in Weakly Conducting Fluids

Mutschke, G.

This talk summarizes work I was involved over the past 20 years to utilize magnetic
fields for controlling flow and mass transfer in weakly conducting fluids. It will mainly
focus on applications in aqueous solutions, e.g. electrolytes or sea water, with a typical
electrical conductivity of about 1...10 S/m. I will cover aspects of flow control and electrochemical
processes, including metal deposition and gas evolution.

Keywords: flow control; magnetic field; mass transfer; electrochemical processes; Lorentz force; Kelvin force; gas evolution; metal deposition

  • Invited lecture (Conferences)
    MAMI Workshop Magnetic Microhydrodynamics - An Emerging Research Field, 13.-17.06.2022, Mittelwhir, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-36468
Publ.-Id: 36468


CMOS-compatible Manufacturing of Room-Temperature Single Electron Transistors

Heinig, K.-H.; von Borany, J.; Engelmann, H.-J.; Hlawacek, G.; Hübner, R.; Klüpfel, F.; Möller, W.; Pourteau, M.-L.; Rademaker, G.; Rommel, M.; Baier, L.; Pichler, P.; Tiron, R.

Low-power logic and memory circuits remain a main task for the next generations of energy-efficient electronic devices. Single Electron Transistors (SETs) are extremely low energy dissipation devices. However, SETs operate usually at cryogenic temperatures and have some serious drawbacks. Fortunately, Field Effect Transistors (FETs) and SETs are
complementary: The SET is the champion of low-power consumption while FETs advantages, like high-speed, driving, voltage gain and input impedance can compensate exactly for SET's intrinsic drawbacks. To overcome the drawback of cryogenic temperature operation, each SET has to be manufactured with a quantum dot of a size of just a few nanometers, and this dot has to be located not more than about one nanometer apart from the electrodes. The large-scale implementation of SETs in room-temperature electronics is hampered by its unresolved manufacturability because such requirements are beyond the limits of present lithography. We employed self-organization to overcome the present-day limits of lithography. On 5…8nm thick SiO2 layers of (001)Si wafers about 30nm thick a-Si layers have been deposited and subsequently irradiated with 50 keV Si+ ions. The irradiation leads to ion beam mixing at the upper and lower Si/SiO2 interfaces and transforms the buried SiO2 layer to SiOx with x~1. Then, pillar arrays have been fabricated from such layer stacks using electron beam lithography and plasma etching. Arrays of pillars with different diameters from 100nm down to less than 20nm have been produced, where the smallest pillar diameters have been further reduced to ~10nm by plasma oxidation and selective oxide etching (sacrificial oxidation). In this manner we manufactured SiOx disks of ~10nm diameter and 5nm thickness sandwiched between the Si of the pillars. During Rapid Thermal Processing (RTP) of such pillars at 1050°C for 60s, phase separation SiOx  (1-x/2)Si + x/2SiO2 occurs via formation of Si nuclei and Ostwald ripening. Close to the SiO2/Si interfaces the Si excess of SiOx condensates on the upper/lower Si of the pillar, i.e. no Si nuclei can form there. The nucleation rate at the rim of the disk is reduced too, especially if there are traces of oxygen in the ambient. Thus, in nanopillars of ~10nm diameter a single Si dot of ~3nm forms in the ~5nm thick SiO2 disk, whereas in thicker pillars a few dots are found. From such nanopillars vertical nanowire Gate-All-Around SETs (nw GAA-SETs) are fabricated by gate oxide formation using plasma oxidation and gate layer deposition followed by contact formation. The nw GAA-SETs can be combined with nw GAA FETs to fabricate integrated hybrid SET/FET devices, where the FETs are responsible for current amplification.
The funding from the European Union’s Horizon 2020 research and innovation program under grand agreement Nº 688072 (project acronym: Ions4SET) is gratefully acknowledged.

Keywords: Single Electron Transistor; Nanoelectronics; Ion Beam Processing

Related publications

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

Permalink: https://www.hzdr.de/publications/Publ-36467
Publ.-Id: 36467


Transport properties of systematically disordered Cr2AlC films

Salgado Cabaco, J.; Kentsch, U.; Lindner, J.; Faßbender, J.; Leyens, C.; Bali, R.; Boucher, R.

Nano-lamellar composite materials, known as MAX-phases, can possess a combination of ceramic and metallic properties. A prototype compound is Cr2AlC, formed from a unit cell of Cr2C sandwiched between atomic planes of Al. In this work we study the modifications to the structural, transport and magnetic behavior of 500 nm thick Cr2AlC after irradiation with Co+ ions, and Ar+ noble gas ions as control. X-ray diffraction shows that ion-irradiation induces a suppression of the 0002 reflection, indicating a deterioration of the crystal structure. Increasing the ion fluence leads to an increase of the saturation magnetization at 1.5 K, whereby both Ar+ and Co+ cause an increased magnetization,
respectively to 150 kA.m−1 and 190 kA.m−1, for the highest fluences used. At Co+ fluences of 5E13 ions.cm−2 the magnetoresistance (MR) shows a 2-order of magnitude increase, up to 3% (10 T) at 100 K. A similar effect also occurs for 5E12 ions.cm−2 Ar+ irradiated films, however, with a smaller MR-increase. The disordering of MAX phase films may reveal interesting spin-related trans-
port phenomena.

Keywords: Ion Irradiation; MAX phases; Disorder

Related publications

  • Open Access Logo Poster
    DPG-Tagung 2022, 04.-09.09.2022, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-36465
Publ.-Id: 36465


Metabolic regulation of prostate cancer heterogeneity and plasticity

Peitzsch, C.; Gorodetska, I.; Klusa, D.; Shi, Q.; Alves, T. C.; Pantel, K.; Dubrovska, A.

Metabolic reprogramming is one of the main hallmarks of cancer cells. It refers to the metabolic adaptations of
tumor cells in response to nutrient deficiency, microenvironmental insults, and anti-cancer therapies. Metabolic
transformation during tumor development plays a critical role in the continued tumor growth and progression
and is driven by a complex interplay between the tumor mutational landscape, epigenetic modifications, and
microenvironmental influences. Understanding the tumor metabolic vulnerabilities might open novel diagnostic
and therapeutic approaches with the potential to improve the efficacy of current tumor treatments. Prostate
cancer is a highly heterogeneous disease harboring different mutations and tumor cell phenotypes. While the
increase of intra-tumor genetic and epigenetic heterogeneity is associated with tumor progression, less is known
about metabolic regulation of prostate cancer cell heterogeneity and plasticity. This review summarizes the
central metabolic adaptations in prostate tumors, state-of-the-art technologies for metabolic analysis, and the
perspectives for metabolic targeting and diagnostic implications.

Keywords: Prostate cancer; Metabolic reprogramming; Metabolic heterogeneity; Metabolic biomarkers; Metabolic therapies; Metabolomics; Cancer stem cells; Circulating tumor cells; Disseminated tumor cells

Permalink: https://www.hzdr.de/publications/Publ-36464
Publ.-Id: 36464


Properties of systematically disordered Cr2AlC thin films

Salgado Cabaco, J.; Kentsch, U.; Lindner, J.; Faßbender, J.; Leyens, C.; Bali, R.; Boucher, R.

MAX phases are nano-lamellar composite materials of the form Mn+1AXn, where n is 1, 2 or 3; M an early transition metal; A is an A-group element and X is carbon or nitrogen[1,2]. An interesting combination of metallic and ceramic properties as well as potential applications in spintronics [1,3] led to significant research interest in MAX phases. Literature on the effect of systematic disordering of the nano-laminar structure on the magnetic and transport properties is still limited. In particular, MAX phase systems doped with magnetic ions via ion-irradiation may result in large variations of the magneto-transport properties.Here we observe the magneto-transport properties and attempt to separate the contributions of structural changes due to the irradiation and magnetic effects due to the doping on the magneto-transport. A prototype material is Cr2AlC, formed from a unit cell of Cr2C sandwiched between atomic planes of Al. In this work, we study 50 nm and 500 nm thick thin films of Cr2AlC grown on Si(111) by sputtering and subsequent annealing.Structural characterization using X-ray Diffraction in Bragg-Brentano geometry shows a pronounced MAX phase, confirmed by the occurrence of the 002 superstructure reflection. The films were irradiated with Co+ at 450 (50) keV for the 500 (50) nm thick films. The Co+ fluence varied between 1E12-1E15 ions.cm-2, in full order steps. The Co+ irradiation led to a gradual suppression of the 002 superstructure reflection, while preserving the fundamental peaks, implying the intermixing of the nano-laminar MAX phase structure. The magnetic properties are characterized using vibrating sample magnetometry at low temperatures (Fig.1a), showing an increasing paramagnetic behavior as the Co+ fluence increases. In comparison, magneto-resistance measurements (Fig.1b-c) show that for the 500 nm film thickness, the magnetoresistance reaches up to 3 % (10 T) for 100 K, at an optimized Co+ fluence of 5E13 ions.cm-2. The above results suggest that in the low-fluence regime, the irradiation induced disorder remains sufficiently low to obtain pronounced magneto-resistance values.Understanding the defect state in the optimized MAX phase films will shed light on the magneto-transport mechanisms in these nano-laminated materials.

Keywords: Magnetism; Ion Irradiation; Disorder; MAX phases

Related publications

  • Lecture (Conference)
    The Joint European Magnetic Symposia, 24.-29.07.2022, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-36462
Publ.-Id: 36462


Qualification of Image-Based Measurement Systems for Characterization of Sprays

Schunk, C.; Schulz, J.; Schleicher, E.; Bart, H.-J.

This repository contains the measurement and calibration data used in the CIT article 'Qualification of Image‐Based Measurement Systems for Characterization of Sprays'.

The data set contains three archives:

  • MTF.zip : The USAF target to calculate the Modulation Transfer Function.
  • Reference Particles.zip: The reference particles used for the comparison.
  • Checker Calib.zip: C++ based program to calculation the camera distortion and the checker calibration images for both cameras.

Keywords: Droplet detection; Image analysis; Optical measurement; Particle analysis; Spray analysis

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Publ.-Id: 36460


Qualification of Image–Based Measurement Systems for Characterization of Sprays

Schulz, J.; Schunk, C.; Schleicher, E.; Bart, H.-J.

Image-based measurement techniques become increasingly popular and expedite digitalization in chemical engineering. This article demonstrates their potential by testing two inline probes, namely modified optical multimode online probe (OMOP) and process microscope. Validations are performed with static monodisperse standards (9.2 µm to 406 µm) and fast-moving droplets (68.6 µm to 860.7 µm; 24.5 m s−1 to 11 m s−1). Screening of a lithography attests both probes great distortion-free image quality. A 1951 USAF chart attests a low optical resolution of 8 µm or 7 µm with respect to the OMOP or process microscope, respectively. The modified OMOP and process microscope reaches accuracies of 7.6 % or 5.9 % for particles and 8.2 % or 6.8 % for droplets.

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Permalink: https://www.hzdr.de/publications/Publ-36459
Publ.-Id: 36459


Data publication: Cu3N/Cu2O core–shell nanowires: growth and properties

Mavridou, K.; Katsikini, M.; Othonos, A.; Florini, N.; Komninou, P.; Zervos, M.

Raman, XRD and TEM characterization of Cu3N/Cu2O nanowires

Keywords: Cu3N; nanowires; oxidation

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Publ.-Id: 36457


Flexible, printable and self-healable magnetic field sensors for soft robotics and human-machine interfaces

Makarov, D.

Composites consisting of magnetic fillers in polymers and elastomers enable new types of applications in soft robotics, reconfigurable actuation and sensorics. In particular, soft-bodied robots emerge as the closest synthetic system analogous to living organisms mimicking their mechanical behavior and going beyond in performance. We will introduce lightweight, durable, untethered and ultrafast soft-bodied robots performing large amplitude of deformations at high frequencies of up to 100 Hz and exhibit high specific energy density [1]. Our soft-bodied robots can walk, swim, levitate, and transport cargo being driven using external magnetic fields. This inspires new classes of soft robots that impact biosensorics, biological tissue engineering, confined and high-speed mechanical (tissue) manipulation, and serve as working models to study fast biomechanical processes like hydro- and aero- dynamics of fast-moving organisms.

These mechanically active structures are typically designed to work in a specific prior defined parameter range and can malfunction when the conditions are changed. Specifically for magnetic soft robots, the change of the intrinsic magnetic properties due to temperature activations or time relaxation can lead to modifications in the actuation pattern. We present ultrathin and reconfigurable magnetic origami actuators based on a composite consisting of shape memory polymers and magnetic microparticles [2]. Self-sensing is achieved by laminating ultrathin magnetosensitive e-skins [3] on soft origami actuators. The sensor assesses the magnetic state of the actuator (magnetized vs. non-magnetized) and decides on its actuation pattern even before the actual actuation is done experimentally. Furthermore, the sensor enables communication of the actuator with external devices (rotation stage, electromagnets) for self-guided assembly of an initially flat layout and provides the possibility to control the sequentiality and quality of the folding process.

Magnetic composites can be readily used to realise not only actuators but also magnetic field sensors. We demonstrate that printed magnetoelectronics can be stretchable, skin-conformal, capable of detection in low magnetic fields and withstand extreme mechanical deformations [4,5]. We feature the potential of our skin-conformal sensors in augmented reality settings [6,7], where a sensor-functionalized finger conducts remote and touchless control of virtual objects manageable for scrolling electronic documents and zooming maps under tiny permanent magnet.
Furthermore, we put forth technology to realise magnetic field sensors, which can be printed and self-heal upon mechanical damage [8]. This opens exciting perspectives for magnetoelectronics in smart wearables, interactive printed electronics. Furthermore, this research motivates further explorations towards the realisation of 3D printed magnetic field sensors.

[1] X. Wang et al., Untethered and ultrafast soft-bodied robots. Communications Materials 1, 67 (2020).
[2] M. Ha et al., Reconfigurable magnetic origami actuators with on-board sensing for guided assembly. Adv. Mater. 33, 2008751 (2021).
[3] G. S. Canon Bermudez et al., Magnetosensitive e-skins for interactive devices. Adv. Funct. Mater. 31, 2007788 (2021).
[4] M. Ha et al., Printable and Stretchable Giant Magnetoresistive Sensors for Highly Compliant and Skin-Conformal Electronics. Adv. Mater. 33, 2005521 (2021).
[5] E. S. Oliveros Mata et al., Dispenser printed bismuth-based magnetic field sensors with non-saturating large magnetoresistance for touchless interactive surfaces. Adv. Mater. Technol. 7, 2200227 (2022).
[6] J. Ge et al., A bimodal soft electronic skin for tactile and touchless interaction in real time. Nature Communications 10, 4405 (2019).
[7] G. S. Canon Bermudez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).

Keywords: flexible magnetic field sensors; printable magnetic field sensors; magnetic soft robots

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  • Invited lecture (Conferences)
    LokoAssist Symposium, 20.-21.04.2023, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-36456
Publ.-Id: 36456


Focused ion beam applications using gas field and liquid metal alloy ion sources

Hlawacek, G.

Focused ion beams are often considered as tools required for the sample preparation for
other techniques such as transmission electron microscopy. However, in this presentation I
would like to convince you that by using other sources than ubiquitous Gallium liquid metal
ion source a wide range of interesting and challenging problems can be addressed in a very
flexible way. I will focus on applications enabled by the usage of gas field (GFIS) [1–3] and
liquid metal alloy ion sources (LMAIS) [4]. Among other examples I want to present some
recent results obtained using Ne and He GFIS based helium ion microscopy (HIM). I will
show how the HIM can be used to create arbitrary shaped ferromagnets using Fe60 Al40 [5]
as well as anti-ferromagnets in Co/Pt/Ru multilayers [6]. Using in-situ probing I will show
how to tune the spin torque interaction in a Pt/Co/W multilayer sample such that current
switchable magnetization patterns can be created[7]. Finally, I’d like to present recent results
related to the epitaxial overgrowth of tin spheres driven and observed by HIM [8].
In the second part of my talk I want to present results obtained using LMAIS based FIBs.
This includes our recent effort to create single photon emitters (SPE) in Si. We use LMAIS
based Si irradiation to create single W and G centers in two different Si base materials. The
obtained yield for the G-centers is more than 50% and the lateral precision is ≈100 nm. I
will also show how this process can be scaled up to avoid the flexible but serial FIB approach
and switch to broad beam irradiation [9]. Finally, I want to show that also LMAIS based
FIB can be used to control magnetic properties on the nanometer scale with high precision.
Examples include the implantation of up to 10% of Co into permalloy with a lateral resolution
of 30 nm and the control the Gilbert damping of the magnetization dynamics by four orders
of magnitude using a Dy LMAIS. An outlook on new sources currently under development
will conclude the talk.

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  • Invited lecture (Conferences)
    CAARI, 31.10.-03.11.2022, Denton, USA

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Adding "color" to Helium Ion Microscopy images

Hlawacek, G.

Helium Ion Microscopy (HIM) is well known for its high resolution imaging and nano
fabrication capabilities [1–3]. However, the created images are black and white images
presenting a mixture of material and topography contrast. While these images are beautiful
and of high importance for several research fields they do not include all the information that
could in principle be harvested from the specimen using HIM.
Here, I want to summarize the attempts of my group over the last decade to add “color”
to HIM images. In this context I will show how we exploit primary and secondary particles
generated during the ion solid interaction to obtain elemental and structural information
from the sample. The key element here is that the information is always collected as a map
and in this way can be combined with the high resolution surface image to gain additional
insight.
I will briefly cover results obtained using ionoluminescence [4], back scatter spectroscopy [5],
secondary ion mass spectrometry [6] and channeling of electrons and ions in backward [7] and
forward direction [8]. All methods have advantages and drawbacks but can achieve lateral
resolutions between 10 nm to 100 nm.

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  • Invited lecture (Conferences)
    CAARI, 31.10.-03.11.2022, Denton, USA

Permalink: https://www.hzdr.de/publications/Publ-36453
Publ.-Id: 36453


Cu3N/Cu2O core-shell nanowires: growth and properties

Mavridou, K.; Katsikini, M.; Othonos, A.; Florini, N.; Komninou, P.; Zervos, M.

CuO nanowires with diameters between 100 and 200 nm, lengths up to ∼10 μm and a uniform distribution have been grown at 600 °C under 100 mL min−1 O2 on 15 mm × 30 mm Cu foils. The CuO nanowires have a monoclinic crystal structure, grow by a vapor–solid mechanism and can be reduced to Cu under H2 at 300 °C but they are shortened, contain residual Cu2O and are eliminated above 400 °C. We develop a strategy to preserve their integrity via the deposition of Cu over the CuO in order to convert them into Cu3N under NH3:H2. The Cu3N nanowires obtained in this way are curly and have a cubic anti-ReO3 crystal structure but are surrounded by a surface shell of Cu2O with a thickness of a few tens of nm as shown by transmission electron microscopy. We find that the CuO NWs coated with Cu having a thickness greater than 200 nm are not fully converted into Cu3N and have an inner core of CuO. The Cu3N nanowires exhibited four maxima in differential transmission at 2.41, 2.17, 1.9 and 1.8 eV, using ultrafast absorption-transmission spectroscopy, corresponding to the M and R direct energy band gaps of Cu3N in good agreement with theory but we find no evidence for quantization. In addition, we observed two minor peaks at 1.69 and 1.67 eV that may be related to transitions between states in the Cu2O shell or Cu3N under compression. Despite the fact that Cu3N has no mid-gap states the photogenerated carriers have lifetimes less than 100 ps, so its potential as a defect tolerant semiconductor for energy conversion is discussed along with its perspective for energy storage.

Keywords: Cu3N; nanowires; surface oxidation

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Permalink: https://www.hzdr.de/publications/Publ-36452
Publ.-Id: 36452


Applications of focused ion beams for semiconductor and quantum technology

Hlawacek, G.

Non-Ga focused ion beams (FIB) are often applied in the development of future quantum
and nano-electronic applications. GFIS based Helium Ion Microscopy (HIM) is providing
best resolution Nobel gas FIB based imaging and nanofabrication capabilities [1, 2]. I will
present how Ne based HIM has been used for the accelerated development of an irradiation
protocol for the fabrication of CMOS compatible Si based single electron transistors [3]. We
used ion beam mixing of Si and SiO2 to form individual Si nanoscrystals with a size of 2 nm
to 3 nm embedded in an SiO2 matrix. In addition I will present a method to reduce the
diameter of individual Si nanopillars by ion beam irradiation by 50 %.
In an second example I will show how we can use GFIS based spatially resolved ion beam
irradiation to locally tune the magnetic landscape. These type of applications pave the way
for various fundamental studies as well as applications based on standing and propagating
spin waves.
I will end my presentation with a presentation of the FIT4NANO network and a preview
of the FIB roadmap which is currently designed by this COST network.
Part of this work has been performed in the framework of COST Action FIT4NANO
(CA19140) and the European Commission H-2020 programme under grant agreement No.
688072.

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  • Lecture (Conference)
    RAISIN workshop, 05.-08.09.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-36451
Publ.-Id: 36451


Influence of crystal structure on helium induced tendril formation in an FeCoCrNiV high-entropy alloy

Hlawacek, G.; Lohmann, S.; Hübner, R.; Gandy, A. S.; Goodall, R.; Ma, L.

High-entropy alloys (HEAs) are a relatively new class of metal alloys composed of several principal elements, usually at (near) equiatomic ratios. It has previously been reported that some HEAs display superior radiation damage resistance, with composition and microstructure being cited as contributing factors, though the precise mechanism is still unknown. To study the influence of the crystal structure on the response to radiation, we have chosen FeCoCrNiV as a model system. While FeCoCrNi has a face-centred cubic (fcc) structure, adding V leads to a structural transformation towards a body-centred tetragonal (bct) structure with both phases present at near-stochiometric composition [1].
The as-cast sample was characterised by energy-dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM) confirming the presence of both phases. Irradiations were performed with a focussed He beam provided by a helium ion microscope (HIM) at temperatures between room temperature and 500°C. The irradiation fluence was varied between 6x1017 ions/cm2 and 1x1020 ions/cm2. High-resolution images of the irradiated areas were taken with the same HIM, and an example is shown in Fig. 1a. Selected irradiated areas were additionally studied by transmission electron microscopy (TEM) in combination with EDXS.
Under irradiation, pores start to be generated in the material with pore sizes differing significantly between the two phases. At higher fluences and above a critical temperature, a tendril structure as exemplary shown for the bct phase in Fig. 1a forms in both phases. We have found that the critical temperature depends on the phase and is lower for fcc. TEM images reveal that the tendrils span the whole depth of the irradiated area and are accompanied by bubbles of various sizes as shown in Fig. 1b for the bct phase. Scanning TEM-based EDXS of these structures indicates a He-induced change in composition.
A.G. acknowledges support by the Royal Academy of Engineering and the Leverhulme Trust.

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    ÖPG, 26.-30.09.2022, Leoben, Österreich

Permalink: https://www.hzdr.de/publications/Publ-36450
Publ.-Id: 36450


On demand spatially controlled fabrication of single photon emitters in Si

Hlawacek, G.; Klingner, N.; Kentsch, U.; Erbe, A.; Jagtap, N.; Fowley, C.; Abrosimov, N.; Helm, M.; Berencen, Y.; Hollenbach, M.; Astakhov, G.

Single photon emitters (SPE) are fundamental building blocks for
future quantum technology applications. However, many ap-
proach lack the required spatial placement accuracy and Si tech-
nology compatibility required for many of the envisioned applica-
tions. Here, we present a method to fabricate at will placed single
or few SPEs emitting in the telecom O-band in Silicon [1] . The
successful integration of these telecom quantum emitters into
photonic structures such as micro-resonators, nanopillars and
photonic crystals with sub-micrometer precision paves the way to-
ward a monolithic, all-silicon-based semiconductor-supercon-
ductor quantum circuit for which this work lays the foundations.
To achieve our goal we employ home built AuSi liquid metal alloy
ion sources (LMAIS) and an Orsay Physics CANION M31Z+ focused
ion beam (FIB). Silicon-on-insulator substrates from different fabri-
cation methods have been irradiated with a spot pattern. 6 to 500
Si2+ ions have been implanted per spot using an energy of 40 keV.
For the analysis and confirmation of the fabrication of true SPEs a
home build photo luminescence setup has been used. G-centers
formed by the combination of two carbon atoms and a silicon
atom are confirmed by measurements of zero phonon lines (ZPL)
at the expected wave length of 1278 nm for the case of carbon
rich SOI wafers. In the case of ultra clean SOI wafers and high ion
fluxes emission from tri-interstitial Si complexes is observed. The
SPE nature of these so called W-centers has also been confirmed
by ZPL measurements at 1218 nm. The achieved lateral SPE
placement accuracy is below 100 nm in both cases and the
success rate of SPE formation is more than 50%. After a discus-
sion of the formation statistic we also present an approach how
our FIB based approach can be upscaled to wafer-scale
nanofabrication of telecom SPEs compatible with complementary
metal oxide semiconductor (CMOS) technology for very large
scale integration (VLSI).

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  • Lecture (Conference)
    Eu-F-N workshop, 31.08.-02.09.2022, Hamburg, Deutschland
  • Lecture (Conference)
    ÖPG, 26.-30.09.2022, Leoben, Österreich
  • Lecture (Conference)
    AVS, 06.-11.11.2022, Pittsburgh, USA

Permalink: https://www.hzdr.de/publications/Publ-36449
Publ.-Id: 36449


Beyond Gallium: FIB based local materials property tuning with advanced ion sources

Hlawacek, G.

Gas Field Ion Source (GFIS) based Helium Ion Microscopy (HIM) is providing best
resolution Nobel gas focused ion beam (FIB) based imaging and nanofabrication capabilities [1,
2]. Liquid Metal Alloy Ion Source (LMAIS) based FIBs, on the other hand enable the nanoscale
modification of the morphology and the elemental composition of materials [3]. I will address
in particular low on fluence modification of materials properties with only negligible material
removal. Examples in the part will include the modification magnetic, superconducting,
electrical and optical properties in metals, semiconductors and 2D materials. I will show how
the HIM can be used to create arbitrary shaped nano-magnets [4] and tailor their magnetic
properties, with minimal morphological modifications. We use a set of in-situ probes to follow
the change of the magnetic properties during irradiation to allow optimized fluence delivery [5].
Similarly, we can use the probes to characterize transistors build from 2D materials and
follow the change of their electrical properties during ion beam irradiation. However, also
beams of other elements are useful for crating new functionality on the nanometer scale. I
will present very recent results on the application of Dy and Co LMAIS FIB to tune the spin
transport properties of magnetic materials.
Part of this work has been performed in the framework of COST Action FIT4NANO
(CA19140) and the BMBF projects ZF4330905AB9 and ZF4330902DF7.

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  • Invited lecture (Conferences) (Online presentation)
    2022 Spring Meeting, 30.05.-03.06.2022, Strassbourg, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-36448
Publ.-Id: 36448


Spatially resolved materials property tuning using GFIS and LMAIS based FIBs

Hlawacek, G.

Introduction
Gas Field Ion Source (GFIS) based Helium Ion Microscopy (HIM) is providing best resolu-
tion Nobel gas focused ion beam (FIB) based imaging and nanofabrication capabilities [1,2].
Liquid Metal Alloy Ion Source (LMAIS) based FIBs, on the other hand enable the nanoscale
modification of the morphology and the elemental composition of materials [3]. Both meth-
ods allow going beyond classical Ga-FIB based material removal.
Description of the Work or Project
I will address in particular low ion fluence modification of materials properties with only
negligible material removal. Examples will include the modification of magnetic, supercon-
ducting, electrical and optical properties in metals, semiconductors and 2D materials. I will
show how the HIM can be used to create arbitrary shaped nano-magnets [4] and tailor their
magnetic properties, with minimal morphological modifications. We use a set of in-situ
probes to follow the change of the magnetic properties during irradiation to allow optimized
fluence delivery [5]. Similarly, we can use the probes to characterize transistors build from
2D materials and follow the change of their electrical properties during ion beam irradiation.
A more fundamental investigation, based on focussed He irradiation of tin spheres, looks at
the importance of interstitial formation and diffusion. However, also beams of other elements
are useful for creating new functionality on the nanometer scale. I will present very recent re-
sults on the application of Dy and Co LMAIS FIB to tune the spin transport properties of
magnetic materials.
Conclusions
Beyond Ga-FIB instruments such as HIM and LMAIS-FIB offer an unprecedented flexibility
for research and development applications. Using in-situ and in-operando techniques further
accelerates the throughput and versatility of FIB based materials research.
Part of this work has been performed in the framework of COST Action FIT4NANO
(CA19140) and the BMBF projects ZF4330905AB9 and ZF4330902DF7.

Keywords: Ion irradiation; Focused ion Beams

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  • Invited lecture (Conferences)
    4th International Conference on Radiation and Emission in Materials, 06.-08.04.2022, Pattaya, Thailand

Permalink: https://www.hzdr.de/publications/Publ-36446
Publ.-Id: 36446


Data publication: Terahertz control of photoluminescence emission in few-layer InSe

Venanzi, T.; Selig, M.; Pashkin, O.; Winnerl, S.; Katzer, M.; Arora, H.; Erbe, A.; Patanè, A.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.; Baldassarre, L.; Knorr, A.; Helm, M.; Schneider, H.

streak camera data, meta data

Keywords: 2D materials; InSe; photoluminescence; hot carrier response

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Publ.-Id: 36445


Exploring mid-infrared transient gain in graphene

Mavridou, K.; Seidl, A.; Rana, R.; Pashkin, O.; Helm, M.; Winnerl, S.

In our study we employ a powerful method, namely a three-pulse pump-probe technique, that was first suggested by Kim et al.1, to explore the possibility to achieve transient gain photon energies below the optical phonon energy (∼ 200 meV) in graphene. Intriguingly, this technique is not widely established and to our knowledge has never been used in the mid- or far-infrared spectral range. The principle behind this method relies on the effect of a strong pre-pump pulse of 1.55 eV photons, which can cause a transient population inversion at lower energies. This population inversion is evidenced by a sign flip of the mid-infrared (86 meV photon energy) pump-probe signal that is related to either absorption or stimulated emission of mid-infrared photons of the pump beam. We present the results on multilayer graphene obtained under various experimental configurations. Our findings shed light into the completion of rapid thermalization via Coulomb scattering and carrier cooling via optical phonons.

1. Kim, K.; Urayama, J.; Norris, T.; Singh, J.; Phillips, J.; Bhattacharya, P. Appl. Phys. Lett., 2002, 81, 670-672.

Keywords: graphene; transient gain

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    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 04.-09.09.2022, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36443
Publ.-Id: 36443


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.

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 average 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 photoexcited carriers has been investigated with 10 nm and 10 fs spatial and temporal resolution [2].
Time-resolved studies are still missing in both far-field and near-field spectroscopy for doped nanowires excited by THz radiation via intraband excitation. Here we report on THz-pump MIR-probe s SNOM studies on highly-doped GaAs/InGaAs core-shell NWs utilizing intense narrowband THz 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 an 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 an s-SNOM setup from Neaspec GmbH equipped with a broadband difference-frequency generation (DFG) source (5 – 15 µm; 20 – 60 THz). For the pump-probe measurements the laser oscillator of the DFG source was synchronized to the FEL and the time delay between the pulses was varied by an optical delay line. A low-pass filter suppresses the scattered THz FEL radiation from the nano-FTIR unit (Fig 1a).
In the unpumped case, a sharp plasma edge around 130 meV is observed. Upon intraband pumping with 13THz FEL radiation (pulse duration 2 – 5 ps, average power 15 mW), the near-field response of the 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 time constant (1/e) of ≈ 7 ps (Fig. 1b, insert). The nano FTIR studies reveal strong red shift (black curve) and then flattening (red curve) of the plasma resonance (Fig. 1b). 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 nanoimaging pump-probe studies will be 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.
References
[1] P. Parkinson, et al., Nano Lett. 7, 2162 (2007).
[2] M. Eisele, et al., Nature Photon. 8, 841 (2014).
[3] D. Lang, et al., Nanotechnology 30, 084003 (2019).

Keywords: Nanospectroscopy; Core-shell nanowires; SNOM; GaAs-InGaAs

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  • Poster
    2nd International Nanoscale Analytics Workshop, 18.05.2022, Munich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36442
Publ.-Id: 36442


Terahertz free carrier absorption to modulate the optical properties of nanometer-thick van der Waals semiconductors

Venanzi, T.; Selig, M.; Pashkin, O.; Winnerl, S.; Katzer, M.; Arora, H.; Erbe, A.; Patane, A.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.; Baldassarre, L.; Knorr, A.; Helm, M.; Schneider, H.

Free carriers in doped semiconductors absorb terahertz radiation when the frequency of the electromagnetic field is lower or comparable to the plasma frequency of the system. This phenomenon can be used to manipulate the optical response of the material. We present here the results of two different experiments performed at the infrared free-electron laser FELBE on atomically-thin van der Waals semiconductors. In MoSe2 monolayers, we observe a terahertz-induced redshift of the trion resonance. Terahertz absorption induces an average high momentum to the carriers and this momentum gets transferred during the trion formation, resulting in a net redshift in the absorption. In few-layer InSe, the terahertz pulses induce a transient quenching of the photoluminescence emission. In both cases, a microscopic study of the hot carrier distribution cooling is also presented.

Keywords: 2D materials; photoluminescence; terahertz; MoSe2; InSe

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  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 04.-09.09.2022, Regensburg, Deutschland

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Publ.-Id: 36441


Nonequelibrium carrier dynamics in Landau quantized graphene and mercury cadmium telluride

Winnerl, S.

The narrow-gap semiconductor mercury cadmium telluride (MCT) is used for decades as a material for applications in the mid- and far infrared, in particular for detectors. Graphene, on the other hand, has been explored in recent years regarding THz detection, modulation, generation and harmonic generation [1]. In magnetic fields, both materials exhibit strongly non-equidistant Landau-level (LL) systems. Here we present an overview that sheds light into the carrier dynamics of in Landau-quantized Dirac electrons in graphene and Kane electrons in 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. [2]. 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 [3]. 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 [4]. 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.

REFERENCES
[1] M. Mittendorff, S. Winnerl, and T.E. Murphy, Advanced Optical Materials, 9 2001500 (2021).
[2] E. Gornik, G. Strasser und K. Unterrainer, Nature Photonics 15, 875 (2021).
[3] 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).
[4] 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; Landau quantization

Related publications

  • Invited lecture (Conferences)
    Advanced Properties and Processes in Optoelectronic Materials and Systems (APROPOS 18), 05.-07.10.2022, Vilnius, Litauen

Permalink: https://www.hzdr.de/publications/Publ-36440
Publ.-Id: 36440


Auger scattering in massless Dirac and Kane materials

Winnerl, S.

Overview of results on time resolved experiemnts on Landau quantized graphene and HgCdTe.

Keywords: graphene; HgCdTe; Landau quantization

Related publications

  • Lecture (others)
    Dirac3D, 14.-15.11.2022, Orsay, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-36439
Publ.-Id: 36439


Auger scattering in massless Dirac and Kane materials

Winnerl, S.

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

Related publications

  • 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
Publ.-Id: 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.

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

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
Publ.-Id: 36437


Pump-induced terahertz anisotropy in graphene

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

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

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
Publ.-Id: 36436


Photoconductive THz emitters: a brief history and recent advances

Winnerl, S.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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

Related publications

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

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

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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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Downloads

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

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
Publ.-Id: 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.

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
Publ.-Id: 36421


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

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

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
Publ.-Id: 36420


Gold nanoparticle-enhanced flexible electrochemical glucose biosensors

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

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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

Related publications

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

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

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 36409


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

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

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

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

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

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.

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

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.

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


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

Schramm, U.

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

  • 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
Publ.-Id: 36404


How martensitic transitions make materials smart

Lünser, K.

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
Publ.-Id: 36402


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

Schramm, U.

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

  • 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
Publ.-Id: 36400


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

Schramm, U.

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

  • 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
Publ.-Id: 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.

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

  • Open Access Logo Journal of the American Chemical Society 145(2023)3, 1826-1834
    Online First (2023) DOI: 10.1021/jacs.2c11331

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

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

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
Publ.-Id: 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.

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).

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

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.

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

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
Publ.-Id: 36393


Homogenization and Chemical Ordering in Co-Pt Thin Films

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

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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

Related publications

  • 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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Permalink: https://www.hzdr.de/publications/Publ-36390
Publ.-Id: 36390


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.

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
Publ.-Id: 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.

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

Related publications

  • 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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Permalink: https://www.hzdr.de/publications/Publ-36388
Publ.-Id: 36388


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.

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
Publ.-Id: 36387


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

Liao, Y.

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

  • Lecture (Conference)
    34th German CFD Network of Competence Meeting, 14.-15.03.2023, Garching bei München, Germany

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


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

Liao, Y.

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
Publ.-Id: 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.

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

Related publications

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

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.

Related publications

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


Group IV Nanowires for Reconfigurable Field Effect Transistors

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

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.

Related publications

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

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


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

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

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.

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
Publ.-Id: 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.

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.

Related publications

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

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

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
Publ.-Id: 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.

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.

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
Publ.-Id: 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.

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

Related publications

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

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


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

Georgiev, Y.

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
Publ.-Id: 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.

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

Related publications

Downloads

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

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).

Related publications

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

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

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 36370


Domain walls in Cr2O3

Pylypovskyi, O.

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
Publ.-Id: 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.

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
Publ.-Id: 36368


Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.] [331.] [332.] [333.] [334.] [335.] [336.] [337.] [338.] [339.] [340.] [341.] [342.] [343.] [344.] [345.] [346.] [347.] [348.] [349.]