Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39129 Publications

References, Data publication: Review of Photocathodes for electron beam sources in particle accelerators

Schaber, J.; Xiang, R.; Gaponik, N.

Bib. tex Datei mit allen Referenzen die im Review Artikel zitiert wurden

Keywords: photocathodes; electron source; particle accelerator; quantum efficiency

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Permalink: https://www.hzdr.de/publications/Publ-36504
Publ.-Id: 36504


Data publication : Open- and closed-loop data taken at ELBE for the development of a beam-based feedback regulator

Maalberg, A.; Kuntzsch, M.; Zenker, K.; Petlenkov, E.

Open- and closed-loop data traces taken during measurements at the linear accelerator ELBE.

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Permalink: https://www.hzdr.de/publications/Publ-36503
Publ.-Id: 36503


Data publication: Parallel Algorithm for Connected-Component Analysis using CUDA

Windisch, D.

Benchmark results used in the associated publication. These were generated by profiling a set of pre-configured RISA-pipelines with nsys.

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Permalink: https://www.hzdr.de/publications/Publ-36498
Publ.-Id: 36498


Evaluation of experimental constraints on the 44Ti(α,p)47V reaction cross section relevant for supernovae

Chipps, K. A.; Adsley, P.; Couder, M.; Hix, W. R.; Meisel, Z.; Schmidt, K.

Due to its importance as an astronomical observable in core-collapse supernovae (CCSNe), the reactions producing and destroying 44Ti must be well constrained. Generally, statistical model calculations such as Hauser-Feshbach are employed when experimental cross sections are not available, but the variation in such adopted rates can be large. Here, data from the literature is compared with statistical model calculations of the 44Ti(α,p)47V reaction cross section and used to constrain the possible reaction rate variation over the temperatures relevant to CCSNe. Suggestions for targeted future measurements are given.

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Permalink: https://www.hzdr.de/publications/Publ-36492
Publ.-Id: 36492


Studying the impact of electron bunch characteristics on plasma wakefield performance using particle-in-cell simulations

Wrobel, N.

The submitted version of my bachelor thesis + tex files and notebooks used for data evaluation.

Abstract

The accessibility of plasma-based accelerators was greatly expanded by the realization of laser wakefield accelerator (LWFA)-driven plasma wakefield accelerators (PWFA). This development speeds up research on PWFA significantly. In this thesis, 3D particle-in-cell-simulations were used to analyze driver parameters for a PWFA to achieve maximal energy gain for a hypothetical witness beam. Only small increases in witness energy were found when drivers with high kinetic energy were compared. In contrast, great witness energy increases result when the divergence of the driver gets reduced. The transformation of a driver in plasma is analyzed, and the influence of the wakefield on it is discussed. Additionally, evidence for non-constant peak energy is presented, with energy losses in the MeV scale independent from driver characteristics. This could require adjustments to the charge reconstruction of the LWFA bunch after the PWFA stage.

Keywords: PWFA; PIConGPU; Plasma Accelerator

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Permalink: https://www.hzdr.de/publications/Publ-36490
Publ.-Id: 36490


Investigation of the Σ0 Production Mechanism in p(3.5 GeV)+p Collisions

Abou Yassine, R.; Arnold, O.; Becker, M.; Kämpfer, B.; Kotte, R.; Naumann, L.; HADES Collaboration

The production of Σ0 hyperons in proton proton collisions at a beam kinetic energy of 3.5 GeV impinging on a liquid hydrogen target was investigated using data collected with the HADES setup. The total production cross section is found to be σ(pK+Σ0)[μb]=17.7±1.7(stat)±1.6(syst). Differential cross section distributions of the exclusive channel pp→pK+Σ0 were analyzed in the center-of-mass, Gottfried-Jackson and helicity reference frames for the first time at the excess energy of 556 MeV. The data support the interplay between pion and kaon exchange mechanisms and clearly demonstrate the contribution of interfering nucleon resonances decaying to K+Σ0. The Bonn-Gatchina partial wave analysis was employed to analyse the data. Due to the limited statistics, it was not possible to obtain an unambiguous determination of the relative contribution of intermediate nucleon resonances to the final state. However nucleon resonances with masses around 1.710 GeV/c2 (N∗(1710)) and 1.900 GeV/c2 (N∗(1900) or Δ∗(1900)) are preferred by the fit.

Permalink: https://www.hzdr.de/publications/Publ-36489
Publ.-Id: 36489


Production of hydrogen isotopes and charged pions in p (3.5 GeV) + Nb reactions

Abou Yassine, R.; Arnold, O.; Becker, M.; Kämpfer, B.; Kotte, R.; Naumann, L.; HADES Collaboration

The double differential production cross sections, d2σ/dΩdE, for hydrogen isotopes and charged pions in the reaction of p + Nb at 3.5 GeV proton beam energy have been measured by the High Acceptance DiElectron Spectrometer (HADES). Thanks to the high acceptance of HADES at forward emission angles and usage of its magnetic field, the measured energy range of hydrogen isotopes could be significantly extended in comparison to the relatively scarce experimental data available in the literature. The data provide information about the development of the intranuclear cascade in the proton-nucleus collisions. They can as well be utilized to study the rate of energy/momentum dissipation in the nuclear systems and the mechanism of elementary and composite particle production in excited nuclear matter at normal density. Data of this type are important also for technological and medical applications. Our results are compared to models developed to describe the processes relevant to nuclear spallation (INCL++) or oriented to probe either the elementary hadronic processes in nuclear matter or the behavior of compressed nuclear matter (GiBUU).

Permalink: https://www.hzdr.de/publications/Publ-36488
Publ.-Id: 36488


Hadron Production and Propagation in Pion-Induced Reactions on Nuclei

Abou Yassine, R.; Adamczewski-Musch, J.; Arnold, O.; Kämpfer, B.; Kotte, R.; Naumann, L.; HADES Collaboration

Hadron production (π±, proton, Λ, K0S, K±) in π−+C and π−+W collisions is investigated at an incident pion beam momentum of 1.7 GeV/c. This comprehensive set of data measured with HADES at SIS18/GSI significantly extends the existing world data on hadron production in pion induced reactions and provides a new reference for models that are commonly used for the interpretation of heavy-ion collisions. The measured inclusive differential production cross-sections are compared with state-of-the-art transport model (GiBUU, SMASH) calculations. The (semi-) exclusive channel π−+A→Λ+K0S+X, in which the kinematics of the strange hadrons are correlated, is also investigated and compared to a model calculation. Agreement and remaining tensions between data and the current version of the considered transport models are discussed

Permalink: https://www.hzdr.de/publications/Publ-36487
Publ.-Id: 36487


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

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


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

Ge, Y.; Lünser, K.; Fink, L.; Ganss, F.; 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, Lukas Fink, Fabian Ganss, and Sebastian Fähler. The raw data will be for the first time online published here in Rodare. The raw data order matches the order of the Figures of the so-called final draft which will be together uploaded with the raw data folders.

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


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


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

  • Open Access Logo International Journal of Molecular Sciences 24(2023)1, 666
    Online First (2022) DOI: 10.3390/ijms24010666

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


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


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

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  • 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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Permalink: https://www.hzdr.de/publications/Publ-36460
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.

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


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

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


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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Permalink: https://www.hzdr.de/publications/Publ-36445
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

Related publications

  • Lecture (Conference)
    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

Related publications

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

Permalink: https://www.hzdr.de/publications/Publ-36441
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


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


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


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"

Downloads

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


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


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


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 from 13.09.2023

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


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


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

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

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  • 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


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


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


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


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


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™).

  • Open Access Logo 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


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

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

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

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

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


Electrical characterization of highly doped germanium nanowires using Hall bar configuration

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

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

Related publications

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

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


Size-dependent electrical characteristics of highly doped Germanium nanowires

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

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

Related publications

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

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


Developing a Hall Bar Configuration for semiconducting Nanowires

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

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

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

Related publications

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

Permalink: https://www.hzdr.de/publications/Publ-36363
Publ.-Id: 36363


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

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

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

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

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


Axial p–n junction photodetectors based on single germanium nanowires

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

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

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

Related publications

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

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


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

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

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

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

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

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

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

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


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

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

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

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

Related publications

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

Permalink: https://www.hzdr.de/publications/Publ-36357
Publ.-Id: 36357


Characterization of Tri- and Tetravalent Actinide Complexes with Amidinate Ligands

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

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

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

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

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

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


Coordination Chemistry of Tri- and Tetravalent Actinides with Benzamidinate Ligands

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

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

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

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

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

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


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

Höhne, T.

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

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

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


Synthesis and Characterization of Tetravalent Actinide Amidinate Halide Complexes

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

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

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

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

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

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Particle based characterization of lithium ion battery recycling using automated mineralogy

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

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

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

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Publ.-Id: 36351


Synthesis and complexation of nitrogen donor ligands with tetravalent uranium

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

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

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

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


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

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

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

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

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

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

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

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


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

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

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

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

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

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


Coordination chemistry of N-Donor Ligands with early Actinides

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

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

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

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


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

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

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

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

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


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

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

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

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

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


Drill Core Scanning using MLA - Micro Methods for Macro Samples

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

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

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

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

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

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


Towards Atmospheric Radical Sensing: Fabrication of Junctionless Transistors

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

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

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

Keywords: Juntionless transistors; nanowires; Radical sensing

Related publications

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

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


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

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

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

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

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


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

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

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

Keywords: antiferromagnetism; curvilinear spin chains

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

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


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

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

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

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

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


Production of 67Cu at the TR-FLEX Cyclotron

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

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

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

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


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

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

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

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

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


β Decay of 61V and its Role in Cooling Accreted Neutron Star Crusts

Ong, W.-J.; Brown, E. F.; Browne, J.; Ahn, S.; Childers, K.; Crider, B. P.; Dombos, A. C.; Gupta, S. S.; Hitt, G. W.; Langer, C.; Lewis, R.; Liddick, S. N.; Lyons, S.; Meisel, Z.; Möller, P.; Montes, F.; Naqvi, F.; Pereira, J.; Prokop, C.; Richman, D.; Schatz, H.; Schmidt, K.; Spyrou, A.

The interpretation of observations of cooling neutron star crusts in quasipersistent x-ray transients is affected by predictions of the strength of neutrino cooling via crust Urca processes. The strength of crust Urca neutrino cooling depends sensitively on the electron-capture and β-decay ground-state-to-ground-state transition strengths of neutron-rich rare isotopes. Nuclei with a mass number of A=61 are predicted to be among the most abundant in accreted crusts, and the last remaining experimentally undetermined ground-state-to-ground-state transition strength was the β decay of 61V. This Letter reports the first experimental determination of this transition strength, a ground-state branching of 8.1+4.0−3.1%, corresponding to a log ft value of 5.5+0.2−0.2. This result was achieved through the measurement of the β-delayed γ rays using the total absorption spectrometer SuN and the measurement of the β-delayed neutron branch using the neutron long counter system NERO at the National Superconducting Cyclotron Laboratory at Michigan State University. This method helps to mitigate the impact of the pandemonium effect in extremely neutron-rich nuclei on experimental results. The result implies that A=61 nuclei do not provide the strongest cooling in accreted neutron star crusts as expected by some predictions, but that their cooling is still larger compared to most other mass numbers. Only nuclei with mass numbers 31, 33, and 55 are predicted to be cooling more strongly. However, the theoretical predictions for the transition strengths of these nuclei are not consistently accurate enough to draw conclusions on crust cooling. With the experimental approach developed in this work, all relevant transitions are within reach to be studied in the future.

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Permalink: https://www.hzdr.de/publications/Publ-36325
Publ.-Id: 36325


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