Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41356 Publications

Energy Flexibility Potential and Costs of the Materials- and Recycling Industry

Parvez, A. M.; van den Boogaart, K. G.; Sajjad, M.

Renewable Electricity production will strongly vary over time in the
Energy System of 2045. Simultaneously the raw materials industry
needs to have its own transition towards a more local circular economy
and from fossil carbon based energy sources to renewables. As a major
and increasingly important energy consumer, this industry might need
to adapt energy consumption to current energy availability.

In this contribution we discuss four major technical possibilities on
different time scales (Inner Energy variation, throughput variation,
scheduled production pauses, and dual power options) for power
flexibility in this sector, their characteristics with regard to grid
service and power market, and with respect to economic and
environmental impacts generated by providing and by using these
flexibility options. The contribution provides generic formulas to
compute such impacts from LCA and LCC results for stationary operation
conditions plus direct impacts of certain actions, and shows how they
depend on market conditions. It also discusses the need for energy
system models to provide predictions of flexibility requirements early
on, to allow the industry to take the right investment decisions with
respect to flexibility.

The contribution shows that while technically major flexibility
potentials exist, considerable investment is required to make them
practically available for the future energy system. It also shows that
Germany needs a considerable local hydrogen infrastructure
(production, distribution and storage) in order to sustain such
industry.

Keywords: Energy Transition; Recycling; Flexibility; LCA

  • Lecture (Conference)
    Helmholtz Energy Conference 2023, 12.-13.06.2023, Koblenz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36564
Publ.-Id: 36564


Transfer printing of GMR sensing elements for curved electronics

Bezsmertna, O.; Xu, R.; Oliveros Mata, E. S.; Voigt, C.; Mosch, S.; Faßbender, J.; Vinnichenko, M.; Makarov, D.

In the post-covid era, touchless interaction between human beings and environments is attracting more and more attentions. Sensors based on giant magnetoresistance (GMR) effect are widely considered as a workhorse to address this demand. However, the fabrication of GMR
multi-layer elements face many limitations (e.g., inappropriate to substrates with curved and/or rough surfaces) due to the layer thickness
dependence of performance. Here, we propose a transfer technique to overcome the aforementioned limitations. With the assistance of two
sacrificial layers, a large scale and wrinkle-free coverage is realized on
various substrates (of different materials, roughness, and curvatures) with little loss of GMR performance. Notably, such technique is easy
processing, without the need of any substrate deformation, temporary carriers or high-temperature processing. The transferred sensors are
integrated into skin-mountable electronics, successfully functioning as a human-machine interface.

  • Lecture (Conference)
    DPG Spring Meeting 2023, 26.-31.03.2023, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36563
Publ.-Id: 36563


Supervised folding of magnetic origami actuators using highly compliant magnetic field sensors

Oliveros Mata, E. S.; Ha, M.; Cañón Bermúdez, G. S.; Liu, J. A.-C.; Evans, B. A.; Tracy, J. B.; Makarov, D.

Soft actuators are mechanically active functional systems. Magnetic polymeric composites have been used as grippers, rollers, and walkers responding to applied magnetic fields. Flexible, light and conformal sensory systems are still under research to have on-board control of actuation of soft systems. We show electronic skins with magnetic field sensors that provides awareness of the folding state to origami-like magnetic foils.
[1] M. Ha, et al. Adv. Mater. 33, 2008751 (2021)

  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie 2023, 26.-31.03.2023, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36562
Publ.-Id: 36562


Printed magnetic field sensors based on bismuth showing large non-saturating magnetoresistance

Oliveros Mata, E. S.; Voigt, C.; Cañón Bermúdez, G. S.; Zabila, Y.; Illing, R.; Fritsch, M.; Mosch, S.; Kusnezoff, M.; Faßbender, J.; Vinnichenko, M.; Makarov, D.

The development of functional inks allows to create novel printed electronics with unconventional form factors. Here, we show the fabrication of printed magnetic field sensors based on bismuth microparticles. Sensors showed non-saturating large magnetoresistance (146%, 5T, at room temperature), and resilience to mechanical bending (2000 cycles). We demonstrated large area magnetically sensitive interfaces as smart lock and interactive wallpapers.[1]
[1] E.S. Oliveros-Mata, C. Voigt, et al. Adv. Mater. Technol.2200227 (2022)

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie 2023, 23.-31.03.2023, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36561
Publ.-Id: 36561


The morphology adaptive multifield solver OpenFOAM-Hybrid and its application to multiphase flow problems in nuclear safety

Krull, B.; Lucas, D.; Meller, R.; Schlegel, F.; Tekavcic, M.

A typical feature of nuclear safety facilities are multiphase flows with coexisting morphologies, i.e. with phases which occur both in a continuous form (such as in a stratified flow) and in a disperse form (bubbles or droplets). Established simulation methods are usually suitable for either resolved structures (e.g., Volume-of-Fluid) or dispersed structures (e.g., Euler-Euler). We propose a morphology adaptive multifield two-fluid model, which is able to handle both disperse and resolved interfacial structures coexisting in a common computational domain, covered by a unified set of equations. This requires (A) a careful selection of closure models. On the continuous side, the interfacial drag formulation of Štrubelj and Tiselj (Int J Numer Methods Eng, 2011, 85, 575-590) is used to describe large interfacial structures in a volume-of-fluid-like manner. For the dispersed structures, the HZDR baseline model is applied. Meller et al. (Int J for Numer Method Fluid, 2021, 93, 748-773) and Tekavčič et al. (Nucl Eng Des, 379, 111223) presented several test cases to prove that the numerical consistent coexistence of different morphologies is ensured. The interaction of the morphologies is only controlled by the aforementioned closure models without being disturbed by numerical effects. A second requirement is (B) a reliable transition between continuous and disperse states, depending on the size of the structures and the degree of spatial resolution. This is subject of the current work. A prerequisite for reliable transitions is the stable coverage of intermediate situations, where bubbles are either over- or under-resolved for Euler-Euler or Volume-of-Fluid (Fig. 1). An adaptive interfacial drag model and a filtering technique are applied for stable and robust handling of the transition regions. Two morphology transfer models are established, allowing large resolved structures to disintegrate into small unresolved fluid particles and, vice versa, the accumulation of disperse fluid particles to continuous large-scale structures. This is applied to generic verification and validation test cases, representing typical sub-problems relevant in safety facilities. The model is applied to a cyclic separator (Fig. 2), which can only be simulated with methods allowing the transition from a disperse to a continuous morphology. This is particularly challenging because the gas core must exhibit a stable behavior in the highly rotating flow while gas and liquid are moving in opposite directions along the rotational axis.

Related publications

  • Contribution to proceedings
    Workshop on Experimental Validation and Application of CFD and CMFD codes to Nuclear Reactor Safety Issues (CFD4NRS-9), 20.-22.02.2023, College Station, USA
    Proceedings of the CFD4NRS-9
  • Lecture (Conference)
    Workshop on Experimental Validation and Application of CFD and CMFD codes to Nuclear Reactor Safety Issues (CFD4NRS-9), 20.-22.02.2023, College Station, USA

Permalink: https://www.hzdr.de/publications/Publ-36560
Publ.-Id: 36560


Realisierung von neuronalen Netzwerken mit hls4ml auf einer Alveo Accelerator Card

Ufer, R.

Für die Lösung von komplexen Problemen können neben Algorithmen auch künstliche neuronale Netzwerke verwendet werden. Mit maschinellem Lernen werden diese Netzwerke standardmäßig auf CPU und GPU erstellt und ausgeführt. Zur Verwendung von trainierten Netzwerken auf FPGAs gibt es jedoch keine direkte Umsetzung innerhalb der bekannten Machine Learning Frameworks. Um dieses Problem zu beheben wurde für Xilinx und Intel FPGA die Portierungs-Software hls4ml entwickelt. Diese Open-Source Software ermöglicht eine Übersetzung von trainierten Netzwerken die mit etablierten Machine Learning Frameworks erstellt wurden in eine High-Level Synthese Sprache.

Innerhalb dieses Projekts erfolgt die Implementierung eines neuronalen Netzwerks für die MNIST-Datensatz Klassifikation, welches anschließend mit hls4ml für die Xilinx Alveo U200 Data Center Accelerator Card portiert wird. Die Portierung erfolgt mit verschiedenen Konfigurationen, um unterschiedlich optimierte Implementierungen zu generieren. Der gesamte Prozess vom Erstellen des Netzwerks bis zur Ausführung der Implementierung und Auswertung der Ergebnisse wird mithilfe von Continous Integration automatisiert.

Die Evaluation zeigt, dass eine Portierung des Netzwerks auf die Xilinx Alveo U200 Data Center Accelerator Card möglich ist. Es sollte jedoch dabei beachtet werden das nicht mit allen Konfigurationen eine ausführbare Implementierung erstellt werden kann.

Keywords: FPGA; hls4ml; MNIST; ML; CI

  • Other
    TU Dresden, 2023
    Mentor: Seniorprofessor Dr.-Ing. habil. Rainer G. Spallek, Dr.-Ing. Oliver Knodel
    27 Seiten

Permalink: https://www.hzdr.de/publications/Publ-36559
Publ.-Id: 36559


Reproducibility in Data Science and Machine Learning: How far should we go to enable products?

Steinbach, P.

Machine Learning is becoming ubiquitous in many scientific domains. However, practitioners struggle to apply every new addition to the Machine Learning market on their data with comparable effects than published. In this talk, I'd like to present recent observations on reproducibility of Machine Learning results and how the community strives to tackle related challenges.

Keywords: machine learning; reproducibility; replication; generalisation

Permalink: https://www.hzdr.de/publications/Publ-36556
Publ.-Id: 36556


Data publication: Impedimetric Nanobiosensor for the Detection of SARS-CoV-2 Antigens and Antibodies

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.; Tonn, T.; Bachmann, M.; Baraban, L.

This publication includes datasets of electrical impedance spectroscopy measurements of the response of functionalized gold nanowires when interacting with antigens and antibodies related to SARS-CoV-2 in physiological conditions and in human plasma samples.

Keywords: impedimetric sensing; point-of-care testing; SARS-CoV-2; gold nanowires; impedance model; reliability; electrochemical impedance spectroscopy (EIS); surface plasmon resonance (SPR)

Related publications

Downloads

Permalink: https://www.hzdr.de/publications/Publ-36555
Publ.-Id: 36555


Energy response and spatial alignment of the perturbed electron gas

Dornheim, T.; Tolias, P.; Moldabekov, Z.; Vorberger, J.

We present extensive new \emph{ab initio} path integral Monte Carlo (PIMC) simulations of the harmonically perturbed uniform electron gas (UEG) for different densities and temperatures. This allows us to study the linear response of the UEG with respect to different contributions to the total energy for different wave numbers. We find that the induced change in the interaction energy exhibits a non-monotonic behaviour, and becomes negative for intermediate wave numbers. This effect is strongly dependent on the coupling strength and can be traced back to the spatial alignment of electrons introduced in earlier works [T.~Dornheim \emph{et al.}, Communications Physics \textbf{5}, 304 (2022)]. The observed quadratic dependence on the perturbation amplitude in the limit of weak perturbations and the quartic dependence of the perturbation amplitude corrections are consistent with linear and non-linear versions of the density stifness theorem. All PIMC simulation results are freely available online and can be used to benchmark new methods, or as input for other calculations.

Related publications

Permalink: https://www.hzdr.de/publications/Publ-36554
Publ.-Id: 36554


Impedimetric Nanobiosensor for the Detection of SARS-CoV-2 Antigens and Antibodies

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.; Tonn, T.; Bachmann, M.; Baraban, L.

Detection of antigens and antibodies (Abs) is of great importance in determining the infection and immunity status of the population, as they are key parameters guiding the handling of pandemics. Current point-of-care (POC) devices are a convenient option for rapid screening; however, their sensitivity requires further improvement. We present an interdigitated gold nanowire-based impedance nanobiosensor to detect COVID-19-associated antigens (receptor-binding domain of S1 protein of the SARS-CoV-2 virus) and respective Abs appearing during and after infection. The electrochemical impedance spectroscopy technique was used to assess the changes in measured impedance resulting from the binding of respective analytes to the surface of the chip. After 20 min of incubation, the sensor devices demonstrate a high sensitivity of about 57 pS·sn per concentration decade and a limit of detection (LOD) of 0.99 pg/mL for anti-SARS-CoV-2 Abs and a sensitivity of around 21 pS·sn per concentration decade and an LOD of 0.14 pg/mL for the virus antigen detection. Finally, the analysis of clinical plasma samples demonstrates the applicability of the developed platform to assist clinicians and authorities in determining the infection or immunity status of the patients.

Keywords: impedimetric sensing; point-of-care testing; SARS-CoV-2; gold nanowires; impedance model; reliability; electrochemical impedance spectroscopy (EIS); surface plasmon resonance (SPR)

Related publications

Permalink: https://www.hzdr.de/publications/Publ-36553
Publ.-Id: 36553


A thermodynamic database for the solution chemistry and solubility of europium(III) inorganic species: recent developments

Jordan, N.; Thoenen, T.; Starke, S.; Spahiu, K.; Brendler, V.

Performance assessments of geological repositories for the underground disposal of high-level radioactive waste require a deep understanding of the phenomena influencing the mobility of radionuclides, e.g. sorption, redox immobilization, surface precipitation, incorporation, etc. Reliable thermodynamic databases (TDB) are essential in order to generate speciation calculations, surface complexation and reactive transport models to predict the aforementioned mechanisms. In this work, the focus was set on europium (Eu), a lanthanide used for decades as a chemical analogue of trivalent actinides (Pu, Am). However, a consolidated and internationally recognized Eu TDB does currently not exist.

Several reviews and reports [1-4] on the aqueous chemistry/geochemistry of europium were published, but had various drawbacks, for example:

→ Insufficient transparency about the selection procedure,

→ Lack of systematic screening to gather primary literature sources,

→ No original data but rather analogue values from other REE or compilations from secondary references,

→ Postulation of species not independently evidenced by means of advanced spectroscopic techniques,

→ Too high reliance on the analogy with trivalent actinides,

→ For weak complexes such as chloride and nitrate, changes in the activity coefficients due to the replacement of up to 100 % of the background electrolyte anion by Cl⁻ or NO₃⁻ was either completely overlooked or, if recognized, not handled properly,

→ Too high reliance on the charge analogy for the estimation of missing ion interaction coefficients when the Specific ion Interaction theory was applied.

This study aims at significantly improving the situation by carefully addressing all aforementioned issues in order to provide a reliable, robust, and internally consistent TDB for europium. For this, an extensive data survey of more than 350 peer-reviewed publications from around 1900 until June 2021 was performed. Furthermore, technical reports, scientific books, collected editions as well as various thermodynamic databases (Nagra/PSI [2], Thermochimie [5], etc.) were surveyed to identify their original Eu(III) data sources and references used therein. Data up to 90 °C and 5 M ionic strength were selected for screening, but all data dealing with hydrothermal conditions were out of the scope of this review. Thermodynamic data determined in non-aqueous solvents were explicitly not considered either. For the three ligands (SO₄²⁻, Cl⁻, PO₄³⁻) to which our attention was focused on in a first step, the result of the screening together with the number of selected data for aqueous complexation constants is shown in Table 1.

Table 1. Summary of the aqueous inorganic Eu complexation data records
System #total #selected
Eu – sulphate 244 34
Eu – chloride 186 0
Eu – phosphate 40 8

The complexation of Eu(III) with sulphate was investigated by ion exchange, solvent extraction, spectrophotometry, electrophoresis, and time resolved laser-induced fluorescence spectroscopy [6]. Despite the broad variety of methods used for the determination of the conditional complexation constants of the Eu(III) sulphate species in the literature, a consistent set of data was obtained for both EuSO₄⁺ and Eu(SO₄)₂⁻ aqueous complexes at 25 °C.
Chloride complexes with Eu(III) are very weak, and high chloride concentrations are required to form them. Related experiments (up to 4 mol∙L⁻¹ Cl⁻ at 25 °C) need to be considered with extra care because the perchlorate ion was systematically substituted by the chloride ion by more than 10 %, and in some cases even completely. However, the resulting changes in the activity coefficients due to such large compositional modifications of the background electrolyte were simply ignored. All our recalculations [7] based on the exclusive consideration of changes in activity coefficients without considering the formation of Eu-chloro complexes as proposed in the original studies, are able to describe the experimental data of the literature [6]. This means that the formation of Eu(III)-chloro complexes postulated in the literature was an artefact [6].
Unfortunately, very little is known concerning the complexation of Eu(III) with phosphate ions. The only experimental study was performed recently [8], by means of laser-induced luminescence spectroscopy at 25 °C and at different ionic strengths (0.6 – 3.1 mol∙L⁻¹) imposed by NaClO₄. The impact of temperature up to 80 °C on the formation of the EuH₂PO₄²⁺ complex was also investigated [8].

Recently, results of our critical evaluation for the chloride, sulphate, and phosphate ligands were published [6]. The recommended complexation constants and solubility products for further inorganic ligands, e.g. hydroxide and carbonate, will also be presented [9].

[1] Brown, P.L. and Ekberg, C. (2016) Hydrolysis of Metal Ions. Vol. 1, Wiley-VCH, Weinheim.
[2] Hummel, W. et al. (2002) Nagra/PSI Chemical Thermodynamic Data Base 01/01, Technical Report 02-16.
[3] Rard, J.A. (1985). Chemistry and thermodynamics of europium and some of its simpler inorganic compounds and aqueous species. Chem. Rev. 85(6): 555-582.
[4] Spahiu, K. and Bruno, J. (1995) A selected thermodynamic database for REE to be used in HLNW performance assessment exercises, SKB Technical Report.
[5] Giffaut, E, et al. (2014). Andra thermodynamic database for performance assessment: ThermoChimie. Appl. Geochem. 49: 225–236.
[6] Jordan, N. et al. (2022). A critical review of the solution chemistry, solubility, and thermodynamics of europium: recent advances on the Eu3+ aqua ion and the Eu(III) aqueous complexes and solid phases with the sulphate, chloride, and phosphate inorganic ligands. Coord. Chem. Rev. 473, 214608.
[7] Spahiu, K. and Puigdomènech, I. (1998). On weak complex formation: re-interpretation of literature data on the Np and Pu nitrate complexation. Radiochim. Acta 82: 413-419.
[8] Jordan, N. et al. (2018). Complexation of trivalent lanthanides (Eu) and actinides (Cm) with aqueous phosphates at elevated temperatures. Inorg. Chem. 57(12): 7015-7024.
[9] Jordan, N. et al. (2023). Coord. Chem. Rev. (in preparation).

Keywords: thermodynamic database; europium

  • Contribution to proceedings
    Migration 2023, 24.-29.09.2023, Nantes, France
  • Poster
    Migration 2023, 24.-29.09.2023, Nantes, France

Permalink: https://www.hzdr.de/publications/Publ-36552
Publ.-Id: 36552


Data publication: A shallow hybrid classical-quantum spiking feedforward neural network for noise-robust image classification

Konar, D.; Sarma, A. D.; Bhandary, S.; Bhattacharyya, S.; Cangi, A.; Aggarwal, V.

The PyTorch implementation of SQNN is available on Github at https://github.com/darthsimpus/ASOC

Keywords: Quantum machine learning; Spiking neural networks; Variational quantum circuit; Hybrid classical-quantum neural networks

Related publications

  • Reseach data in external data repository
    Publication year 2023
    License: Common
    Hosted on Github: Link to location

Permalink: https://www.hzdr.de/publications/Publ-36551
Publ.-Id: 36551


Establishment of a thermodynamic database for the solution chemistry and solubility of Eu(III) inorganic species

Jordan, N.; Thoenen, T.; Starke, S.; Spahiu, K.; Brendler, V.

Performance assessments of geological repositories for the underground disposal of high-level radioactive waste require a deep understanding of the phenomena influencing the mobility of radionuclides, e.g. sorption, redox immobilization, surface precipitation, incorporation, etc. Reliable thermodynamic databases (TDB) are required in order to generate speciation calculations, surface complexation and reactive transport models to predict the aforementioned mechanisms. In this work, the focus was set on europium (Eu), a lanthanide used for decades as a chemical analogue of trivalent actinides (Pu, Am). Indeed, a consolidated and internationally recognized Eu TDB does currently not exist.

Several reviews and reports [1-4] on the aqueous chemistry/geochemistry of europium were published, but had several drawbacks, for example:

→ Insufficient transparency about the selection procedure,

→ Lack of systematic screening to gather primary literature sources,

→ Too high reliance on the analogy with trivalent actinides,

→ For weak complexes such as chloride and nitrate, changes in the activity coefficients due to the replacement of up to 100 % of the background electrolyte anion by Cl⁻ or NO₃⁻ was either completely overlooked or, if recognized, not handled properly,

→ Too high reliance on the charge analogy for the estimation of missing ion interaction coefficients when the Specific ion Interaction theory was applied.

This study aims at significantly improving the situation by carefully addressing all aforementioned issues in order to provide a reliable, robust, and internally consistent TDB for europium. Recently, results of our critical evaluation for the chloride, sulphate, and phosphate ligands were published. The recommended complexation constants and solubility products for further inorganic ligands, e.g. hydroxide and carbonate, will also be presented [6].

[1] P.L. Brown, C. Ekberg, Hydrolysis of Metal Ions. Vol. 1, Wiley-VCH, Weinheim, 2016.
[2] W. Hummel, et al., Nagra/PSI Chemical Thermodynamic Data Base 01/01, Technical Report 02-16, 2002.
[3] J.A. Rard, Chemical Reviews, 85(6) (1985) 555-582.
[4] K. Spahiu, J. Bruno, A selected thermodynamic database for REE to be used in HLNW performance assessment exercises, SKB Technical Report, 1995.
[5] N. Jordan et al., Coordination Chemistry Reviews, 473, 214608 (2022).
[6] N. Jordan et al., Coordination Chemistry Reviews, (2023) (in preparation).

Keywords: thermodynamic database; europium; SIT

  • Contribution to proceedings
    Goldschmidt2023, 09.-14.07.2023, Lyon, France
  • Poster
    Goldschmidt2023, 09.-14.07.2023, Lyon, France

Permalink: https://www.hzdr.de/publications/Publ-36550
Publ.-Id: 36550


Reliable europium thermodynamic database: uses and needs in the energy field

Jordan, N.; Thoenen, T.; Starke, S.; Spahiu, K.; Brendler, V.

For hydrometallurgy, mining and ore processing, disposal of chemotoxic and radioactive waste as well as for remediation of polluted areas, scientists and engineers from various disciplines need reliable thermodynamic data. Researchers from HZDR, together with colleagues from Sweden and Switzerland, developed a respective database for europium, one of the most important rare earth elements (REE). The result is the first comprehensive, self-consistent, transparent, and openly accessible database of chemical and thermodynamic aspects of that element. Basis is a state-of-the-art critical, internally consistent, and thorough evaluation of all data previously published for europium worldwide. This new compilation of high-quality data will now render extraction, separation, and recycling processes more efficient for europium as well as other rare earth elements. An increased recycling rate of REE, currently lower than 5 %, could decrease the need for exploitation of new primary deposits, reduce environmental impacts, and minimize the overall energy consumption. Further fields of application concern fundamental geological aspects, e.g. relevant for chemical evolutions and alterations of sedimentary rocks and deposits. Eventually, it will also significantly improve mobility predictions of trivalent actinides in nuclear waste disposals where europium serves as a chemical analogue. Thus, the new data will serve both industrial and ecological applications in Germany and many other countries depending on high-technology metals such as europium.

Keywords: europium; thermodynamic database

  • Poster
    Helmholtz Energy Conference 2023, 12.-13.06.2023, Koblenz, Germany

Permalink: https://www.hzdr.de/publications/Publ-36549
Publ.-Id: 36549


Data publication: Assessing the accuracy of hybrid exchange-correlation functionals for the density response of warm dense electrons

Moldabekov, Z.; Lokamani, M.; Vorberger, J.; Cangi, A.; Dornheim, T.

This repository contains the DFT simulation results presented in the article "Assessing the accuracy of hybrid exchange-correlation functionals for the density response of warm dense electrons". The minimal dataset that would be necessary to interpret, replicate and build upon the findings reported in the article.

Keywords: warm dense matter; hybrid functionals; Hartree-Fock

Related publications

Downloads

Permalink: https://www.hzdr.de/publications/Publ-36547
Publ.-Id: 36547


A shallow hybrid classical-quantum spiking feedforward neural network for noise-robust image classification

Konar, D.; Sarma, A. D.; Bhandary, S.; Bhattacharyya, S.; Cangi, A.; Aggarwal, V.

Deep Convolutional Neural Network (CNN)-based image classification systems are often susceptible to noise interruption, i.e., minor image noise may significantly impact the outcome. On the contrary, classical Spiking Neural Network (SNN) is known for handling noisy data due to the stochastic and temporal behaviour of the spiking neuron signals. However, it is not always feasible to train the weights of the classical SNN due to stochastic and non-differentiable spiking signals. Recent applications of quantum machine learning to stochastic modelling have predicted that quantum computing would prove to be a significant advantage, hence catapulting the study of quantum and neuromorphic computing to a new level of development. Motivated by these observations, this paper introduces a shallow hybrid classical-quantum spiking feedforward neural network referred to as Spiking Quantum Neural Network (SQNN) for dealing with a robust image classification task in the presence of noise and adversarial attacks. The proposed SQNN offers the inherent capabilities of processing unforeseen noisy test images due to its spatial and temporal information. An efficient variational quantum circuit training with the help of a standard back-propagation algorithm obviates the classical Spiking Time-Dependent Plasticity (STDP) and Spike-Prop algorithms, which are often found inefficient in training the feedforward SNN. The proposed SQNN is extensively tested and benchmarked on the PennyLane Quantum Simulator. Experimental results show that the proposed SQNN model supersedes the feedforward SNN (SFNN), Random Quantum Neural Networks (RQNN), AlexNet and ResNet-18 on unseen test images with added noise from the FashionMNIST, MNIST, KMNIST, CIFAR10, and ImageNet datasets.

Keywords: Quantum machine learning; Spiking neural networks; Variational quantum circuit; Hybrid classical-quantum neural networks

Related publications

Permalink: https://www.hzdr.de/publications/Publ-36546
Publ.-Id: 36546


The Effect of Macroscopic Particle Features on Mineral Dissolution

Winardhi, C. W.; Da Assuncao Godinho, J. R.; Gutzmer, J.

Mineral dissolution is a dynamic process in which kinetics depend on the reactive surface area, orientation, and geometry of the dissolving mineral grain. Dissolution rate is, thus, not represented by a single value, but rather, by a spectrum that is affected by the reactivity of different types of surface features. Such dissolution rate spectra are usually obtained by very detailed studies of perfectly cleaved surfaces by atomic force microscopy or in situ studies, such as flow-through experiments. This study visualizes dissolution progress by repeated X-ray computed tomography scans of a single particle. This allows studying the influence of larger particle features, such as corners and edges, at the interception of macroscopic faces of particles, as well as the influence of those macroscopic features on the dissolution rate spectra. As a suitable case study, the dissolution of a monomineralic galena (PbS) particle in ethaline is studied. The observed changes in particle geometry are evaluated using a newly developed empirical model in order to break down the rate spectra as a function of the particle geometry. Results illustrate that dissolution rates are exponentially correlated with the distance to crystal corners and edges. The reactivity map generated from these exponential relations shows a linear trendline with the dissolution rates over the entire surface of the studied galena particle. The empirical reactivity map developed here opens the possibility of predicting the dissolution rate of particulate materials based on computed tomography and the optimal geometrical properties of the particles that maximize the dissolution, e.g., size and shape.

Keywords: computed tomography (CT); corners and edges; dissolution; dissolution rate spectra; reactivity map

Related publications

Permalink: https://www.hzdr.de/publications/Publ-36545
Publ.-Id: 36545


Herausforderungen in der Radiopharmazie aus europäischer Sicht

Kiß, O.

6th Life Sciences Forum Sachsen

  • Invited lecture (Conferences)
    6th Life Sciences Forum Sachsen, 01.12.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36543
Publ.-Id: 36543


EANM perspective on Health/Pharmaceutical Regulations

Kiß, O.; Patt, M.

Technical Meeting

  • Invited lecture (Conferences)
    Technical Meeting on Health/Pharmaceutical Regulations for Radiopharmaceuticals, 06.-10.03.2023, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-36542
Publ.-Id: 36542


A short history of the Heidelberg PSMA compounds – what will tomorrow bring?

Kiß, O.

New Horizons in Imaging and Therapy

  • Invited lecture (Conferences)
    2nd 180°N Conference, 25.-27.04.2023, Bergen, Norwegen

Permalink: https://www.hzdr.de/publications/Publ-36541
Publ.-Id: 36541


Planungsschritte und Antragsstellung im Rahmen von prospektiven Studien

Kiß, O.

Young DGN Fortbildung

  • Invited lecture (Conferences)
    NuklearMedizin 2023, 19.-22.04.2023, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36540
Publ.-Id: 36540


Data publication: 3D gas distribution in lab-scale zero-gap water electrolysers measured by 3D X-ray computed microtomography

Dung, O.-Y.; Boden, S.

Postprocessed 3D raw attenuation data of lab-scale zero-gap water electrolysers at different operating conditions.

Keywords: X-ray computed tomography; Microtomography; Zero-gap electrolyser; Fluid Dynamics

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Permalink: https://www.hzdr.de/publications/Publ-36539
Publ.-Id: 36539


Modelling water circulation and solute transport at a former french uranium mining site

Katz, A.; Veilly, E.; Lévrier, L.; Pérez-Sànchez, D.; Arnold, T.; Bok, F.; Montavon, G.; Bertin, C.; Urso, L.; Chardon, P.; Sarramia, D.; Vaudelet, P.; Mallet, C.

Within the frame of the RadoNorm project (https://www.radonorm.eu/), the goal is to better understand the importance of hydrogeochemical and chemical processes for radionuclides’ transfer in the environment with a focus on Naturally Occurring Radioactive Material (NORM). In that context, a wetland in a downstream area of a former uranium mine tailing, i. e. the Rophin site, has been selected and the following water flows and solute transport models, in 1, 2 or 3 D could be used: HYTEC [1], HYDRUS [2], CIEMAT model [3], and MELODIE [4]. This application should allow to understand the fate of uranium and radium observed in the wetland area, the link between radionuclides’ concentration in the wetland and in the crossing stream and also to highlight a possible transfer of radionuclides to the groundwater.
The Rophin site located in the department of Puy-de-Dôme of the region Auvergne-Rhone-Alpes (France) where measured dose rates are 20 to 30 times higher than the background along the Gourgeat stream and in a so-called “wetland area”. A source of contamination is present due to successive discharges from settling ponds during the operational phase of the mine and located in the whitish layer of the wetland, where three different soil horizons are identified (an organic-rich surface layer, a whitish layer, and a paleosol layer).
The watershed has been equipped since 2019 with piezometers and surface sensors to monitor the water (electrical conductivity, temperature and water flow). Metereological data is available to identify patterns for precipitation regimes for the wet and dry seasons. First results from measuring campaigns in 2021 and 2022 confirm the presence of a groundwater table in the wetland, which is rather close to the surface and varies depending on meterological conditions. To characterise the different horizons in the wetland, a field study was carried out in October 2022 which provides information about geophysical parameters. In parallel, parameters such as soil permeability, soil porosity, diffusion coefficients and dispersivity are going to be obtained by laboratory measurements in spring 2023. Surface mapping data (dose rates and gamma-ray spectroscopy analysis) and Light Detection and Ranging (LiDaR) data are available as well as information about water chemical composition and soil/sediment mineralogy both in the wetland and in the Gourgeat stream. To evaluate radionuclides sorption onto the various soil layers and partition of radionuclides between solid and liquid phases, distribution coefficients are determined either experimentally (Kd) or modelled with the mechanistic "Smart Kd" approach [5].
A description of water flows and soil layers to be modelled is presented. In a first approach assuming a saturated zone, modelling of the three layers system will be performed in 1D and 2D. Two types of simulation are considered, one with a low flux regime when the stream and the wetland seems to be disconnected and the other with a high flux regime when the stream and the wetland should be hydraulically connected. The aim is to evaluate the evolution of uranium and radium concentration within the layers of the wetland and also to quantify the concentrations of those radionuclides released into the environment, i.e. groundwater and Gourgeat stream.

References
[1] Van Der Lee, J., De Windt, L., Lagneau, V., & Goblet, P. (2003). Module-oriented modeling of reactive transport with HYTEC. Computers & Geosciences, 29(3), 265-275.
[2] Simunek, J., Jacques, D., van Genuchten, M. T., & Mallants, D. (2006). Multicomponent geochemical transport modeling using HYDRUS-1 D and HP 1. Journal of the American water resources Association, 42(6), 1537-1547.
[3] Pérez-Sánchez, D., & Thorne, M. C. (2014). Modelling the behaviour of uranium-series radionuclides in soils and plants taking into account seasonal variations in soil hydrology. Journal of environmental radioactivity, 131, 19-30.
[4] Mathieu, G., Dymitrowska, M., & Bourgeois, M. (2008). Modeling of radionuclide transport through repository components using finite volume finite element and multidomain methods. Physics and Chemistry of the Earth, Parts A/B/C, 33, S216-S224.
[5] Stockmann, M. & Schikora, J. & Becker, D.-A. & Flügge, J. & Noseck, U. & Brendler, V. (2017). Smart Kd-values, their uncertainties and sensitivities - Applying a new approach for realistic distribution coefficients in geochemical modeling of complex systems. Chemosphere. 187. 10.1016/j.chemosphere.2017.08.115.
Acknowledgments

The RadoNorm project has received funding from the Euratom research and training programme 2019-2020 under grant agreement No 900009.

Keywords: RadoNorm; Modelling; Smart Kd; Naturally Occurring Radioactive Material

  • Lecture (Conference)
    Migration, 24.-29.09.2023, Nantes, France

Permalink: https://www.hzdr.de/publications/Publ-36538
Publ.-Id: 36538


Quantum version of the integral equation theory based dielectric scheme for strongly coupled electron liquids

Tolias, P.; Lucco Castello, F.; Dornheim, T.

A novel dielectric scheme is proposed for strongly coupled electron liquids that handles quantum mechanical effects beyond the random phase approximation level and treats electronic correlations within the integral equation theory of classical liquids. The self-consistent scheme features a complicated dynamic local field correction functional and its formulation is guided by ab initio path integral Monte Carlo simulations. Remarkably, our scheme is capable to provide unprecedently accurate results for the static structure factor with the exception of the Wigner crystallization vicinity, despite the absence of adjustable or empirical parameters.

Permalink: https://www.hzdr.de/publications/Publ-36537
Publ.-Id: 36537


Impact of various cleaning procedures on p-GaN surfaces

Schaber, J.; Xiang, R.; Arnold, A.; Ryzhov, A.; Teichert, J.; Murcek, P.; Zwartek, P.; Ma, S.; Michel, P.

This work discusses the influence of different cleaning procedures on p-GaN grown on sap-phire by metal-organic chemical vapor deposition. The cleaned p-GaN surface was trans-ferred into an ultra-high vacuum chamber and studied by an X-ray photoelectron spectrome-ter, revealing that a cleaning with a so-called „piranha“ procedure results in low carbon and oxygen concentrations on the p-GaN surface. Contrary, a cleaning that solely uses ethanol represents a simple cleaning, but leads to an increase of carbon and oxygen contaminations on the surface. Afterward, the cleaned p-GaN samples underwent a subsequential vacuum thermal cleaning at various temperatures to achieve an atomically clean surface. XPS meas-urements revealed residual oxygen and carbon on the p-GaN surface. Thus, a thermal treat-ment under a vacuum did not entirely remove these organic contaminations, although the thermal cleaning reduced their peak intensities. The complete removal of carbon and oxygen contaminants was only achieved by argon ion sputtering, which is accompanied by a strong depletion of the nitrogen on the p-GaN surface. The treatments cause a large number of sur-face defects preventing the formation of a negative electron surface when the p-GaN is acti-vated with a thin layer of cesium.

Keywords: p-GaN; photocathode; sputtering damage; surface cleaning; damage effects

Related publications

  • Open Access Logo Surface and Interface Analysis 55(2023), 507-514
    Online First (2023) DOI: 10.1002/sia.7207

Permalink: https://www.hzdr.de/publications/Publ-36534
Publ.-Id: 36534


Boosting complex Systems Research through RSE Collaboration

Kelling, J.; Tripathi, R.; Calabrese, J.

Stochastic simulations of complex systems from domains including physics, biology, ecology or economics often require large system sizes, long time scales, and numerous replications
to fully explore model behavior. The simple rules defining many models can lead researchers
to prefer familiar but inefficient programming techniques, which severely hinder progress
by creating computational bottlenecks. While such studies often benefit from combined
domain-specific, statistical, and programming knowledge, few individual researchers span
the full range of necessary skills. Here, we present a collaboration on the neutral model
of biodiversity in dendritic river networks, where the goal is to analyze biodiversity data
across the world’s major river systems. We show how we achieved large performance gains
by engaging the problem at its foundations and thereby enabled research at a new scale.

Keywords: performance; GPU; complex systems; computational science

Permalink: https://www.hzdr.de/publications/Publ-36533
Publ.-Id: 36533


The self-assembly process of helical molecules

Thi, N. H. N.; Günther, F.; Preis, K.; Kelling, J.; Tegenkamp, C.; Gemming, S.

Helical polyalanine (PA) molecules gathered a lot of interest as the propagation of electrons along the helical backbone structure comes along with spin polarization. Via liquid and solid scanning tunneling microscopy (STM) we studied the ordering of physisorbed and chemisorbed PA molecules on HOPG and Au surfaces. While enantiopure PA molecules adsorb in a hexagonally close-packed structure, we found heterochiral dimers with a rectangular unit cell for DL-PA. Despite the steric hindrance, the packing density of the DL-PA heterophase is increased by 25% compared to the enantiopure PA structure. Apparently, this is achieved by shifting D- and L-PA along their helical axis. Moreover, the alpha-helix structure of the PA molecules seems to be preserved; thus, electrostatic forces indeed play an important role for the formation and stabilization of the helical structure. In parallel, the interactions between PA homo- and heterochiral pairs were analyzed by van-der-Waals-corrected DFT-based tight binding calculations. Denser packing geometries can be reached by heterochiral PA pairs. Second, coarse-grained classical potentials were derived from the DFTB data, and the different PA phases seen in STM were also successfully obtained from Monte-Carlo simulations.

Keywords: self-assembled monolayer; chiral organic molecules; scanning tunneling microscopy

  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 26.-31.03.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36532
Publ.-Id: 36532


Efficient integration of short-range models on complex networks

Kelling, J.; Ódor, G.; Barancsuk, L.; Deng, S.; Hartmann, B.; Gemming, S.

Complex, hierarchical or random network topolgies can give rise to unique behavior in many physical models. We study dynamical synchronization behavior in Kuramoto models on power grids and brain connectomes with millons of connections and O(100k) nodes. At these scales it is crucial to use the sparsity when computing derivatives, which, due to the random network structure, makes employing modern parallel hardware tricky. Here, we present our approach to numerically solving large systems ordinary differential equations on random directed graphs, where we focus on the computationally expensive task of computing derivatives and leave the common integration step to the boost::odeint library. Our application can utilize both parallel CPUs and GPUs. We also provide an overview of our results on human and fly brain connectomes as well as failure cascades in power grids and provide a measure of the advantage gained from our computational optimization efforts.

Keywords: synchronization; networks; brain; power grids; GPU

Permalink: https://www.hzdr.de/publications/Publ-36531
Publ.-Id: 36531


Simulating neutral biodiversity in large-scale networks

Kelling, J.; Tripathi, R.; Calabrese, J.

The neutral model of biodiversity describes a Markov process of death and replacement of neutral individuals constituting the species occupying an ecosystem. It predicts a number macroscopic ecosystem observables, including local and global abundances, and can serve as advanced null-hypothesis for more complex models. We present a massively parallel approach to simulating the neutral model which both enables simulations on large networks, to, e.g., capture fine details of real river networks, and efficiently produces averages results to enable comparisons with empirical data or other models at high statistical significance or accurately compute correlations or responses.

Keywords: biodiversity; GPU; research software engineering; networks

  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 26.-31.03.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36530
Publ.-Id: 36530


U(VI) retention on bentonite and cementitious materials: Effect of increased ionic strengths and presence of organics

Schmeide, K.; Philipp, T.; Huittinen, N. M.; Shams Aldin Azzam, S.; Kretzschmar, J.

The safe disposal of radioactive waste from operation and decommissioning of nuclear power plants in geological repositories requires the application of multiple barriers to isolate the waste from the biosphere. Most disposal concepts consider the extensive use of bentonite and cementitious materials in the geoengineered barrier as buffer and borehole sealing material as well as to enforce mechanical stability of disposal facilities. To evaluate the radionuclide retention potential of these barrier materials, it is necessary to examine the effects of various repository-relevant conditions that are expected to develop over time, such as altered pH, increased ionic strengths or temperatures, or the release of organic constituents.
Pore waters of the North German clay deposits are characterized by high ionic strengths up to 4 M [1,2]. The contact of such saline formation waters with concrete will result in an enhanced corrosion of concrete and to the evolution of highly alkaline cement pore waters (10 < pH < 13), which in turn, can react with the bentonite buffer as well as with the clay host rock, changing their retention potential towards radionuclides. Moreover, the role of organics (as admixtures in cement-based materials or waste constituents [3]) on actinide retention has to be studied.
The U(VI) retention on Ca-bentonite in mixed electrolyte solutions (‘diluted Gipshut solution’, I = 2.6 M) was found to be very effective at pH>10, even in the presence of carbonate and despite the prevalence of anionic aqueous uranyl species [4]. By means of luminescence and X-ray absorption spectroscopy, two dominating U(VI) surface species at hyperalkaline conditions were identified: (i) a ternary U(VI) complex, where U(VI) is bound to the surface via bridging Ca cations with the configuration surface ≡Ca–OH–U(VI) and, (ii) U(VI) sorption into the interlayer space of calcium (aluminum) silicate hydrates (C-(A-)S-H), which form as secondary phases in the presence of Ca due to partial dissolution of alumosilicates at hyperalkaline conditions (Figs. 1 and 2) [5]. Citrate and 2 phosphonobutane-1,2,4,-tricarboxylate (PBTC) were found to reduce U(VI) retention only when present at high concentrations.
The U(VI) retention by C-A-S-H, formed due to Al-rich additives in cement formulations, was studied applying samples with Ca/Si molar ratios of 0.8, 1.2 and 1.6, representing different alteration stages of concrete, and with increasing Al/Si molar ratios of 0, 0.06 and 0.18 in each series. Furthermore, the impact of temperature (25°C, 100°C, 200°C) on both the C-A-S-H structure and the U(VI) retention mechanism was studied. Solid-state 27Al and 29Si NMR spectroscopy along with XRD revealed that enhanced temperatures increase the crystallinity of the material with the appearance of neoformed crystalline phases. Surface-sorbed and interlayer-sorbed U(VI) species were detected by luminescence spectroscopy. U(VI) mobilization due to high ionic strengths or presence of organics (gluconate or PBTC) was very low [6,7].
The results show that both bentonite and cementitious material constitute an important geoengineered retention barrier for U(VI) under hyperalkaline conditions at increased ionic strengths and in presence of organics. Thus, both bentonite and cementitious material strongly contribute to the safe confinement of radionuclides in a repository to isolate radiotoxic contaminants from the hydrosphere and biosphere.

Keywords: uranium; bentonite; cement; organics; ionic strength; retention; geotechnical barrier

Related publications

  • Lecture (Conference)
    18th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere - Migration 2023, 24.-29.09.2023, Nantes, France

Permalink: https://www.hzdr.de/publications/Publ-36529
Publ.-Id: 36529


Cement-based materials in the multi-barrier system of nuclear waste repositories – impact on radionuclide retention

Gaona, X.; Ait Mouheb, N.; Altmaier, M.; Bosbach, D.; Deissmann, G.; Geckeis, H.; Kretzschmar, J.; Schmeide, K.; Stumpf, T.

The safe disposal of long-lived nuclear waste is a grand societal challenge and part of the current energy transition in Germany. Safety concepts regarding nuclear waste disposal in underground repositories generally rely on a combination of engineered and geological barriers, which minimize the potential release of radionuclides out of the containment providing rock zone or even the transport into the biosphere. Cementitious materials are very important in this context. They are used for conditioning of certain nuclear waste types, as components of waste containers and overpacks as well as constituents of structural materials at the interface between backfill and host-rocks in some repository concepts. In order to assess the potential impact of cement-based materials on the (geo)chemical behaviour of radionuclides in a repository system, targeted studies on the interaction of radionuclides with cementitious materials are required.
In the event of water interacting with cementitious materials, pore water solutions characterized by (highly) alkaline pH conditions will form. These boundary conditions define the chemical response of the radionuclides, but also influence the behaviour of neighbouring components of the multi-barrier system, e.g. bentonitic or argillaceous backfill and host-rocks, respectively. Hardened cement pastes are considered to be the main sorbing materials present in the near field of repositories for low and intermediate level waste. Hence, interactions of radionuclides with cementitious materials represent a very important mechanism retarding their mobility and potential migration from the near field. In addition to a robust quantitative description of the sorption processes (usually in terms of sorption coefficients, i.e. Kd values), the detailed mechanistic analysis and understanding of sorption phenomena provide additional scientific arguments and important process understanding and thus enhance both the quality of safety arguments and the overall confidence in the safety assessment process.
The NUSAFE partners KIT, HZDR and FZJ have contributed to a significantly improved understanding on various processes related to the retention of radionuclides on cement-based materials. Within the framework of the EU project EURAD (https://www.ejp-eurad.eu/), NUSAFE partners are contributing to and coordinating the workpackage (WP) Cement Organic Radionuclide Interactions - CORI, providing new insights into the role of organic molecules with respect to radionuclide mobility. With a focus on the elevated ionic strength conditions expected for the north German clay formations, NUSAFE partners likewise collaborate within the GRAZ II project, funded by the Federal Ministry for the Environment, Nature Conservation, Nuclear Safety, and Consumer Protection (BMUV). Further work is performed within bilateral international contracts or cooperations. Apart from the frequently studied actinide elements, long-lived fission and activation products receive specific attention. The combination of classical experimental (wet-chemistry) methods, advanced spectroscopic techniques, and theoretical calculations provides both an accurate quantitative evaluation and a fundamental understanding of the sorption processes. The present state-of-knowledge as well as main remaining uncertainties affecting the retention processes of radionuclides in cementitious environments under different conditions will be critically discussed.

Keywords: cement; concrete; actinide; organic ligands; ionic strength; geotechnical barrier; nuclear waste management

  • Lecture (Conference)
    Helmholtz Energy Conference 2023, 12.-13.06.2023, Koblenz, Germany

Permalink: https://www.hzdr.de/publications/Publ-36528
Publ.-Id: 36528


Regulating oxygen ion transport at the nanoscale to enable highly cyclable magneto-ionic control of magnetism

Tan, Z.; Ma, Z.; Fuentes-Rodriguez, L.; Liedke, M. O.; Butterling, M.; Elsherif, A. G. A.; Hirschmann, E.; Wagner, A.; Abad, L.; Casañ-Pastor, N.; Lopeandia, A.; Menéndez, E.; Sort, J.

Magneto-ionics refers to the control of magnetic properties of materials through voltage-driven ion motion. To generate effective electric fields, either solid or liquid electrolytes are utilized,
which also serve as ion reservoirs. Thin solid electrolytes have difficulties to (i) withstand high electric fields without electric pinholes and (ii) maintain stable ion transport during long-term
actuation. In turn, the use of liquid electrolytes can result in poor cyclability, thus limiting their applicability. Here we propose a nanoscale-engineered magneto-ionic architecture (comprising a thin solid electrolyte in contact with a liquid electrolyte), that drastically enhances cyclability while preserving sufficiently high electric fields to trigger ion motion. Specifically, we show that the insertion of a highly nanostructured (amorphous-like) Ta layer (with suitable thickness and electric resistivity) between a magneto-ionic target material (i.e., Co3O4) and the liquid electrolyte, increases magneto-ionic cyclability from < 30 cycles (when no Ta is inserted) to more than 800 cycles. Transmission electron microscopy together with variable energy positron annihilation spectroscopy reveal the crucial role of the generated TaOx interlayer as a solid-electrolyte (i.e., ionic conductor) that improves magneto-ionic endurance by proper tuning of the types of voltage driven structural defects. The Ta layer is very effective in trapping oxygen and hindering O2– ions from moving into the liquid electrolyte, thus keeping O2– motion mainly restricted between Co3O4 and Ta when voltage of alternating polarity is applied. We demonstrate that this approach provides a suitable strategy to boost magneto-ionics by combining the benefits of solid and liquid electrolytes in a synergetic manner.

Keywords: magnetoelectricity; voltage control of magnetism; magneto-ionics; transition metal oxide; ion diffusion; positron annihilation spectroscopy; defects

Related publications

Permalink: https://www.hzdr.de/publications/Publ-36527
Publ.-Id: 36527


Effect of citric acid and malic acid on the uranium uptake into Brassica napus plants in hydroponic culture

John, W. A.; Jessat, J.; Steudtner, R.; Hübner, R.; Sachs, S.

The transport and transfer of radionuclides in the environment is an important aspect with regard to the health risk assessment of sites contaminated with naturally occurring radionuclides. In addition, this knowledge is highly relevant for the long-term safety assessment of future nuclear waste repositories. Radionuclides such as uranium are non-essential elements for plants. However, when present in contaminated soil, they can be taken up by plants and thus enter the food chain, posing a health risk to humans. Plants exude organic acids such as citric acid, malic acid, and/or oxalic acid into the rhizosphere. Under deficiency conditions, this can induce the dissolution of previously unavailable insoluble compounds, e.g., iron and phosphate minerals [1]. However, these processes can lead to the acquisition not only of essential nutrients, but also of non-essential ones, such as uranium. Therefore, plants may influence the mobility and bioavailability of radionuclides in the environment.
In the present work, we investigated the effect of citric acid and malic acid, both characteristic plant exudates, on the solubility of uranium in hydroponic plant culture medium as well as on the uranium uptake by Brassica napus (canola) plants in hydroponic culture. Prior to plant exposure, the solubility and speciation of 20 µM uranium(VI) in a phosphate reduced hydroponic solution (HRred, [2]) in the absence and presence of citric acid or malic acid was studied. After 24 h equilibration of uranium(VI) in HRred solution in the absence of citric acid or malic acid, a part of the uranium (~50%) precipitated, most probably in form of a uranyl(VI) phosphate. The control samples without organic acids stayed at the minimum concentration of dissolved uranium for 72 h, whereas those with citric acid or malic acid showed a re-solubilisation to the maximum uranium concentration of 20 µM within the first 24 h after addition of the respective organic acid. Following the uranium speciation in the hydroponic solutions during the exposure period by time-resolved laser-induced fluorescence spectroscopy (TRLFS) indicated the formation of uranium(VI) citrate and malate complexes, whereas in the organic-acid-free solution, the UO2(CO3)34- complex predominated.
B. napus plants were cultivated according to Jessat et al. [2]. To study the influence of the two organic acids on uranium exposure to B. napus, 20 µM U(VI) were added to HRred solution and allowed to equilibrate for 24 h in a plant growth chamber. After pre-equilibration, citric acid or malic acid (100 and 1000 µM) were added to the solutions. Immediately after that, the plants were inserted for exposure to uranium. For comparison, control samples were studied under the same conditions, however, without addition of citric acid or malic acid. The uranium concentration of the solutions was regularly determined by inductively coupled mass spectrometry (ICP-MS) within 72 h. After 72 h, the uranium content in the roots, stems, and leaves was analyzed by ICP-MS after drying and incineration. Furthermore, scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX) was used to qualitatively confirm the presence of uranium in the roots.
The time-dependent bioassociation experiments showed a strong immobilization of uranium by the B. napus plants either in the absence or in the presence of organic acids. However, in the presence of citric acid and malic acid, this process seems to be retarded due to the re-dissolution of the uranium precipitate by the organic acids. Using TRLFS, uranium(VI) citrate and malate complexes were identified in the hydroponic solutions in the presence of the plants at the beginning of exposure. After longer exposure times, however, their contribution decreased and the UO2(CO3)34- complex dominated the speciation. For all conditions, STEM/EDX results verified the uptake of uranium into the whole root tissue. After 72 h of uranium exposure in the presence of citric acid or malic acid, more uranium was found in the leaves of B. napus compared to the control samples, indicating a stronger translocation of uranium in the plants. Despite that, in the presence of 1000 µM malic acid, a significantly lower amount of uranium was observed in the roots. These results demonstrate the ability of plant metabolites to dissolve hardly soluble uranium precipitates and shed more light on the speciation dependent uranium uptake into and translocation in canola plants.
The results of this study may contribute to a more pronounced process understanding on the uranium uptake into plants and their impact on the uranium mobility in the environment. This knowledge is required for the improvement of radioecological models to assess the migration and transfer of radionuclides in the environment, to develop efficient and cost-effective remediation technologies for contaminated sites, and to perform reliable dose predictions for humans and environment.

Acknowledgement
This work was performed within the RadoNorm project. This project has received funding from the Euratom research and training programme 2019-2020 under grant agreement No. 900009.

References
[1] Jones, D. L. (1998). Organic acids in the rhizosphere - a critical review. Plant and Soil 205: 25-44.
[2] Jessat, J., John, W.A., Moll, H., Vogel, M., Steudtner, R., Drobot, B., Hübner, R., Stumpf, T., Sachs, S. (2023), Ecotox. Environ. Saf., under review.

Keywords: Radioecology; Naturally occurring radionuclides; NORM; Uranium; Plants; Transport; Transfer; Environment; Speciation; Localization; Organic acids

  • Poster
    18th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere - Migration 2023, 24.-29.09.2023, Nantes, France

Permalink: https://www.hzdr.de/publications/Publ-36526
Publ.-Id: 36526


Strahlenschutzmaßnahmen bei der Anwendung von PET-Nukliden in der Krebsforschung

Wendler, M.; Kowe, S.

Der Strahlenschutz bei der Erzeugung, Verarbeitung und Forschung an PET-Nukliden wird betrachtet. Es werden die verschiedenen Abläufe im Herstellungsprozess - vom Zyklotron bis zur Auslieferung - betrachtet. Darüber hinaus wird auch auf die speziellen Berührungspunkte und Kompromissfindung mit z. B. dem Tierschutz verwiesen und an einem Beispiel die Lösung eines konkreten Problems geschildert.

Keywords: Strahlenschutz; Radiation Protection; Betrieblicher Strahlenschutz; PET

  • Strahlenschutz-Praxis 2(2023), 27-29
    ISSN: 0947-434 X

Downloads

  • Secondary publication expected from 26.05.2024

Permalink: https://www.hzdr.de/publications/Publ-36525
Publ.-Id: 36525


Element Distributions in Bimetallic Aerogels

Wang, C.; Herranz, J.; Hübner, R.; Schmidt, T. J.; Eychmüller, A.

Metal aerogels assembled from nanoparticles have captured grand attention because they combine the virtues of metals and aerogels and are regarded as ideal materials to address current environmental and energy issues. Among these aerogels, those composed of two metals not only display combinations (superpositions) of the properties of their individual metal components but also feature novel properties distinctly different from those of their monometallic relatives. Therefore, quite some effort has been invested in refining the synthetic methods, compositions, and structures of such bimetallic aerogels as to boost their performance for the envisaged application(s). One such use would be in the field of electrocatalysis, whereby it is also of utmost interest to unravel the element distributions of the (multi)metallic catalysts to achieve a ratio of their bottom-to-up design. Regarding the element distributions in bimetallic aerogels, advanced characterization techniques have identified alloys, core-shells, and structures in which the two metal particles are segregated (i.e., adjacent but without alloy or core-shell structure formation). While an almost infinite number of metal combinations to form bimetallic aerogels can be envisaged, the knowledge of their formation mechanisms and the corresponding element distributions is still in its infancy. The evolution of the observed musters is all but well understood, not to mention the positional changes of the elements observed in operando or in beginning- vs end-of-life comparisons (e.g., in fuel cell applications).
With this motivation, in this Account we summarize the endeavors made in element distribution monitoring in bimetallic aerogels in terms of synthetic methods, expected structures, and their evolution during electrocatalysis. After an introductory chapter, we first describe briefly the two most important characterization techniques used for this, namely, scanning transmission electron microscopy (STEM) combined with element mapping (e.g., energy-dispersive X-ray spectroscopy (EDXS)) and X-ray absorption spectroscopy (XAS). We then explain the universal methods used to prepare bimetallic aerogels with different compositions. Those are divided into one-step methods in which gels formed from mixtures of the respective metal salts are coreduced and two-step approaches in which monometallic nanoparticles are mixed and gelated. Subsequently, we summarize the current state-of-knowledge on the element distributions unraveled using diverse characterization methods. This is extended to investigations of the element distributions being altered during electrochemical cycling or other loads. So far, a theoretical understanding of these processes is sparse, not to mention predictions of element distributions. The Account concludes with a series of remarks on current challenges in the field and an outlook on the gains that the field would earn from a solid understanding of the underlying processes and a predictive theoretical backing.

Related publications

Permalink: https://www.hzdr.de/publications/Publ-36524
Publ.-Id: 36524


Terahertz harmonic generation from graphite pencil drawings

Arshad, A.; Koyun, H. N.; Salikhov, R.; Gensch, M.; Ilyakov, I.; Ponomaryov, O.; Prajapati, G. L.; Mavridou, K.; Lindner, J.; Deinert, J.-C.; Ünlü, C.; de Oliveira, T.; Kovalev, S.

We study the third harmonic generation (THG) of graphite layers on paper substrate upon excitation with intense (up to 100 kV/cm) narrowband terahertz (THz) pulses. Highest THG efficiencies are comparable with those of CVD-grown single-layer graphene. Samples were hand-drawn, using commercially available pencils. The THG response showed a high sensitivity regarding the hatching direction relative to the THz polarization orientation. Using Raman spectroscopy, we confirmed the occurrence of graphene-like structures in the samples. Our findings demonstrate the feasibility of virtually no cost and easy to fabricate materials for THz nonlinear optics.

Keywords: Graphite; terahertz harmonic generation; Dirac materials; nonlinear terahertz optics; Raman Spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-36523
Publ.-Id: 36523


Biomedical research with laser-driven ion sources

Metzkes-Ng, J.

Biomedical research with laser-driven ion sources

  • Invited lecture (Conferences)
    Special Laser Symposium "The path from chirped pulse amplification to applications of laser plasma accelerators and x-ray probing of extreme states of matter”, 06.-07.02.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36522
Publ.-Id: 36522


High energy proton acceleration at DRACO-PW and radiobiological applications

Metzkes-Ng, J.

Exploiting the strong electromagnetic fields that can be supported by a plasma, high-power laser driven compact plasma accelerators can generate short, high-intensity pulses of high energy ions with special beam properties. By that they may expand the portfolio of conventional machines in many application areas. The maturating of laser-driven ion accelerators from physics experiments to turn-key sources for these applications will rely on breakthroughs in both, generated beam parameters (kinetic energy, flux), as well as increased reproducibility, robustness and scalability to high repetition rate.
Recent developments at the high-power laser facility DRACO-PW enabled the production of polychromatic proton beams with unprecedented stability [1]. This allowed the first in vivo radiobiological study to be conducted using a laser-driven proton source [2]. Yet, the ability to achieve energies beyond the 100 MeV frontier is matter of ongoing research, mainly addressed by exploring advanced acceleration schemes like the relativistically induced transparency (RIT) regime.
In this talk, we report on experimental proton acceleration studies at the onset of relativistic transparency using pre-expanded plastic foils. Combined hydrodynamic and 3D particle-in-cell (PIC) simulations helped to identify the most promising target parameter range matched to the prevailing laser contrast conditions carefully mapped out in great detail beforehand. A complex suite of particle and optical diagnostics allowed characterization of spatial and spectral proton beam parameters and the stability of the regime of best acceleration performance, yielding cut-off energies larger than 100 MeV in the best shots.
The reported progress for proton acceleration directly feeds into our program on ultra-high dose rate radiobiology. We operate a fully-equipped beamline including beam monitoring and dosimetry adapted to ultra-high dose rate proton pulses at DRACO-PW with the future perspective of a dedicated beamline at our high-power laser facility PENELOPE within the ATHENA project.

References
[1] Ziegler, T. et al. Proton beam quality enhancement by spectral phase control of a PW-class laser system. Sci Rep 11, 7338 (2021)
[2] Kroll, F. et al. Tumour irradiation in mice with a laser-accelerated proton beam. Nat. Phys. 18, 316–322 (2022)

  • Invited lecture (Conferences)
    43rd Workshop on High-Energy-Density Physics with laser and Ion beams, 26.02.-03.03.2023, Hirschegg, Österreich
  • Invited lecture (Conferences)
    6th European Advanced Accelerator Concepts workshop, 17.09.-22.10.2023, La Biodola, Elba, Italien
  • Invited lecture (Conferences)
    ELI-NP 10 YEAR ANNIVERSARY SYMPOSIUM, 24.-25.10.2023, Magurele, Rumänien

Permalink: https://www.hzdr.de/publications/Publ-36521
Publ.-Id: 36521


High energy proton acceleration at DRACO-PW and radiobiological applications

Metzkes-Ng, J.

Exploiting the strong electromagnetic fields that can be supported by a plasma, high-power laser driven compact plasma accelerators can generate short, high-intensity pulses of high energy ions with special beam properties. By that they may expand the portfolio of conventional machines in many application areas. The maturating of laser-driven ion accelerators from physics experiments to turn-key sources for these applications will rely on breakthroughs in both, generated beam parameters (kinetic energy, flux), as well as increased reproducibility, robustness and scalability to high repetition rate.
Recent developments at the high-power laser facility DRACO-PW enabled the production of polychromatic proton beams with unprecedented stability [1]. This allowed the first in vivo radiobiological study to be conducted using a laser-driven proton source [2]. Yet, the ability to achieve energies beyond the 100 MeV frontier is matter of ongoing research, mainly addressed by exploring advanced acceleration schemes like the relativistically induced transparency (RIT) regime.
In this talk, we report on experimental proton acceleration studies at the onset of relativistic transparency using pre-expanded plastic foils. Combined hydrodynamic and 3D particle-in-cell (PIC) simulations helped to identify the most promising target parameter range matched to the prevailing laser contrast conditions carefully mapped out in great detail beforehand. A complex suite of particle and optical diagnostics allowed characterization of spatial and spectral proton beam parameters and the stability of the regime of best acceleration performance, yielding cut-off energies larger than 100 MeV in the best shots.
The reported progress for proton acceleration directly feeds into our program on ultra-high dose rate radiobiology. We operate a fully-equipped beamline including beam monitoring and dosimetry adapted to ultra-high dose rate proton pulses at DRACO-PW with the future perspective of a dedicated beamline at our high-power laser facility PENELOPE within the ATHENA project.

References
[1] Ziegler, T. et al. Proton beam quality enhancement by spectral phase control of a PW-class laser system. Sci Rep 11, 7338 (2021)
[2] Kroll, F. et al. Tumour irradiation in mice with a laser-accelerated proton beam. Nat. Phys. 18, 316–322 (2022)

  • Invited lecture (Conferences)
    43rd International Workshop on High- Energy-Density Physics with Intense Ion and Laser Beams, 29.01.-03.02.2023, Hirschegg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-36520
Publ.-Id: 36520


Electron-Beam- and Thermal-Annealing-Induced Structural Transformations in Few-Layer MnPS₃

Storm, A.; Köster, J.; Ghorbani Asl, M.; Kretschmer, S.; Gorelik, T. E.; Kinyanjui, M. K.; Krasheninnikov, A.; Kaiser, U.

Quasi-two-dimensional (2D) manganese phosphorus trisulfide, MnPS₃, which exhibits antiferromagnetic ordering, is a particularly interesting material in the context of magnetism in a system with reduced dimensionality and its potential technological applications. Here, we present an experimental and theoretical study on modifying the properties of freestanding MnPS₃ by local structural transformations via electron irradiation in a transmission electron microscope and thermal annealing in vacuum. In both cases we find that phases with the net formula MnS₁₋ₓPₓ in the α- or γ-MnS crystal structure can be formed. The phase transformations can be locally and precisely controlled by the total applied electron dose and explored at the atomic scale. For the MnS structures generated in this process, our ab-initio calculations indicate that their electronic and magnetic properties strongly depend on both in-plane crystallite orientation and thickness. Moreover, the electronic properties of the MnS phases can be further tuned by alloying with phosphorus, suggesting a novel route toward the design of lateral heterostructures. Therefore, our results may enable pathways for the controlled growth of new phases with distinct properties embedded in freestanding quasi-2D MnPS₃.

Keywords: Structural transformations; MnPS3; α-MnS; γ-MnS; 3D electron diffraction; thermal annealing; modification

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-36519
Publ.-Id: 36519


A new ultra low-level HPGe activity counting setup in the Felsenkeller shallow-underground laboratory

Turkat, S.; Bemmerer, D.; Boeltzig, A.; Domula, A. R.; Koch, J.; Lossin, T.; Osswald, M.; Schmidt, K.; Zuber, K.

A new ultra low-level counting setup has been installed in the shallow-underground laboratory Felsenkeller in Dresden, Germany. It includes a high-purity germanium detector (HPGe) of 163\% relative efficiency within passive and active shields. The passive shield consists of 45m rock overburden (140 meters water equivalent), 40 cm of low-activity concrete, and a lead and copper castle enclosed by an anti-radon box. The passive shielding alone is found to reduce the background rate to rates comparable to other shallow-underground laboratories. An additional active veto is given by five large plastic scintillation panels surrounding the setup. It further reduces the background rate by more than one order of magnitude down to 116±1 kg−1 d−1 in an energy interval of 40-2700 keV. This low background rate is unprecedented for shallow-underground laboratories and close to deep underground laboratories.

Keywords: Nuclear astrophysics; Low-background physics; Underground physics; Radioactivity Measurements

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Permalink: https://www.hzdr.de/publications/Publ-36518
Publ.-Id: 36518


Data publication: Bottom-up Fabrication of FeSb₂ Nanowires on Crystalline GaAs Substrates with Ion-induced Pre-patterning

Weinert, T.; Erb, D.; Hübner, R.; Facsko, S.

Bei dem Datensatz handelt es sich um die Daten für die Abscheidung von FeSb₂ Nanodrähten auf GaAs-Substraten mit ioneninduzierter Vorstruckturierung. Der Datensatz beinhaltet die AFM-Aufnahme der verwendeten Substratoberfläche und die TEM-Aufnahmen mit den EDXS- udn FFT-Ergebnisse.

Keywords: bottom-up nanofabrication; ion-induced nanopatterning; physical vapor deposition; transmission electron microscopy; energy-dispersive X-ray spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-36517
Publ.-Id: 36517


Curvilinear magnetism: from fundamentals to applications

Makarov, D.

Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics, superconductivity and magnetism [1,2]. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape of magnetic thin films and nanowires [2,3]. In this talk, we will address fundamentals of curvature-induced effects in magnetism and review current application scenarios. In particular, we will demonstrate that curvature allows tailoring fundamental anisotropic and chiral magnetic interactions [4] and enables fundamentally new non-local chiral symmetry breaking effect [5]. Application potential of geometrically curved magnetic architectures is currently being explored as mechanically reshapeable magnetic field sensors for automotive applications, memory, spin-wave filters, high-speed racetrack memory devices as well as on-skin interactive electronics relying on thin films [6,7] as well as printed magnetic composites [8,9].

[1] P. Gentile et al., Electronic materials with nanoscale curved geometries. Nature Electronics (Review) 5, 551 (2022).
[2] D. Makarov et al., New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures. Advanced Materials (Review) 34, 2101758 (2022).
[3] D. Makarov et al., Curvilinear micromagnetism: from fundamentals to applications (Springer, Zurich, 2022).
[4] O. Volkov et al., Experimental observation of exchange-driven chiral effects in curvilinear magnetism. Physical Review Letters 123, 077201 (2019).
[5] D. D. Sheka et al., Nonlocal chiral symmetry breaking in curvilinear magnetic shells. Communications Physics 3, 128 (2020).
[6] J. Ge et al., A bimodal soft electronic skin for tactile and touchless interaction in real time. Nature Communications 10, 4405 (2019).
[7] G. S. Canon Bermudez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).
[8] M. Ha et al., Printable and Stretchable Giant Magnetoresistive Sensors for Highly Compliant and Skin-Conformal Electronics. Advanced Materials 33, 2005521 (2021).
[9] R. Xu et al., Self-healable printed magnetic field sensors using alternating magnetic fields. Nature Communications 13, 6587 (2022).

Keywords: curvature effects in magnetism; curvilinear magnetism; magnetic field sensing

Related publications

  • Lecture (others)
    Colloquia in the frame of the CRC/TRR 270 - Hysteresis design of magnetic materials for efficient energy conversion, 14.02.2023, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-36515
Publ.-Id: 36515


Magnetic soft robots from macro- to nanoscale

Pylypovskyi, O.

The talk will be about theoretical description of magnetic soft robots at different scales starting from the macroscopic actuators based on polymer membranes to properties of nanoscaled mechanically soft exchange-coupled systems.

Keywords: soft robots

  • Invited lecture (Conferences)
    Bio Meets Magnetism, 10.02.2023, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36514
Publ.-Id: 36514


Tailoring of thermomagnetic properties in Ni-Mn-Ga films through Cu addition

Fink, L.; Nielsch, K.; Fähler, S.

Thermomagnetic generators enable the conversion of low-grade waste heat into electric energy. The performance of a generator is intimately connected with the active thermomagnetic material used. Heusler alloys had been proposed as ideal systems for thermomagnetic microsystems, as they comprise a tuneable transition temperature just above room temperature, a steep change of magnetization within a narrow temperature change, a low heat capacity, and are easily processable by common deposition techniques.
In this work, we present a path to optimize Heusler films for thermomagnetic applications, which need different properties compared to magnetocaloric applications. We focus on the key thermomagnetic properties like 1) the thermomagnetic working temperature T* and 2) the change of magnetization with the change of temperature ∆M/∆T and correlate them with common properties like 3) crystal structure, 4) martensitic transition temperature, 5) Curie temperature and 6) spontaneous magnetization M0073. We systematically examine all these properties on polycrystalline Ni-Mn-Ga-Cu films prepared by combinatorial sputter deposition and subjected to a heat treatment. Our analysis allows disentangling the effects in changing the number of valence electrons trough the addition of Cu and the alteration of chemical order before and after heat treatment.

Keywords: Heusler alloys; Curie temperature; Magnetic films; Thermomagnetic material; Energy harvesting

Permalink: https://www.hzdr.de/publications/Publ-36512
Publ.-Id: 36512


Sorption of Ba onto Gibbsite: a batch and modeling study

Dück, V.; Jordan, N.; Brendler, V.; Stumpf, T.; Bok, F.

Exposure of radium as an example for NORM (Naturally Occurring Radioactive Material) must be avoided to protect people and the environment and minimize uncertainties in all steps of radiation risk management. For this purpose, Surface Complexation Models (SCM) are used in reactive transport modeling to describe sorption behavior as a function of geochemical parameters. These models help to understand the dynamics of sorption-desorption reactions in soils. When combined with site-specific data predictions for Kd can be made. Currently, the SCM data on the sorption of radium onto naturally occurring aluminosilicates (especially feldspar) is unsatisfactory and often handled by using barium or strontium as chemical analogues for Ra [1-3]. However, there is evidence in the literature that the sorption behavior within the series of alkaline earth metal cations is not as similar as expected [4], which renders the application of the chemical analogy questionable.
To implement surface complexation model for earth alkaline metal ion sorption on natural alumosilicate phases, sorption experiments of Ba onto gibbsite were performed as representatives of a mineral with aluminol binding sites, in the first phase of the project. Later, Ba sorption experiments onto quartz will also be conducted. The derived surface complexation parameters describing Ba sorption onto gibbsite and quartz will then be used to generate synthetic SCM for Ba onto natural occurring minerals with both aluminol and silanol binding site types, namely feldspar. This bottom-up approach will be extended to Sr and Ra as well to evaluate the limitations of the alkaline earth metals chemical analogy in the context of sorption. The models obtained will help to better predict the spread of NORM and reduce conservatism.

Keywords: RadoNORM; Barium; Sorption; Gibbsite; Surface Complexation Modelling

  • Poster
    Goldschmidt2023, 09.-14.07.2023, Lyon, France

Permalink: https://www.hzdr.de/publications/Publ-36511
Publ.-Id: 36511


Aromatic and aliphatic hydrocarbon hydroxylation via a formally Ni(IV)=O oxidant

Heim, P.; Gericke, R.; Spedalotto, G.; Lovisari, M.; Farquhar, E. R.; McDonald, A. R.

The reaction of (NMe₄)₂[Ni(II)(LPh)(OAc)] (1[OAc], LPh = 2,2’,2’’-nitrilo-tris-(N-phenylacetamide); OAc = acetate) with 3-chloroperoxybenzoic acid (m-CPBA) resulted in the formation of a self-hydroxylated Ni(III)- phenolate complex, 2, where one of the phenyl groups of LPh underwent hydroxylation. 2 was characterised by UV-Vis, EPR, and XAS spectroscopies and ESI-MS. 2 decayed to yield a previously characterised Ni(II)-phenolate complex, 3. We postulate that self-hydroxylation was mediated by a formally Ni(IV)=O oxidant, formed from the reaction of 1[OAc] with m-CPBA, which undergoes electrophilic aromatic substitution to yield 2. This is supported by an analysis of the kinetic and thermodynamic properties of the reaction of 1[OAc] with m-CPBA. Addition of exogenous hydrocarbon substrates intercepted the selfhydroxylation process, producing hydroxylated products, providing further support for the formally Ni(IV)=O entity. This study demonstrates that the reaction between Ni(II) salts and m-CPBA can lead to potent metal-based oxidants, in contrast to recent studies demonstrating carboxyl radical is a radical free-chain reaction initiator in Ni(II)/m-CPBA hydrocarbon oxidation catalysis.

Keywords: hydrocarbon hydroxylation; nickel; XANES/EXAFS; electron paramagnetic resonance; quantum chemical calculation

Permalink: https://www.hzdr.de/publications/Publ-36510
Publ.-Id: 36510


Raw data for: Probing shock dynamics inside micro-wire targets after high-intensity laser irradiation using small angle x-ray scattering of a free-electron laser

Kluge, T.

Raw data for: Probing the dynamics of solid density micro-wire targets after ultra-intense laser irradiation using a free-electron laser

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Permalink: https://www.hzdr.de/publications/Publ-36509
Publ.-Id: 36509


Data publication: Code for performing simulations on the evolutionary stability of territorial retention strategies.

Saraiva De Menezes, J. F.; Oliveira-Santos, L. G. R.

This is the supplementary material for the submission of "Heterogenous and continuous resource distribution promote diversity in territorial behavior." to the journal "Ecological modelling". In this dataset, one can find the simulation code used to determine the evolutionary stability of 4 territorial strategies: cautious, common-sense, paradoxical, and daring. Strategies varied in their space utilization after losing or winning a conflict. Simulations.r contains the code for running the simulation and generating the data files presented in data/paper II. However, for the simulation to run, it needs acessory functions which are coded in Library/simulation library.r. Figures.r is the code used to generate the figures 1-7 in the paper. Analysis on number of conflicts.r contains figure 8 and the analysis that lead to it.

Keywords: game theory; fluid dynamics; movement ecology; evolutionary stable strategy; modelling; simulation

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Permalink: https://www.hzdr.de/publications/Publ-36508
Publ.-Id: 36508


The ELBE infrared and THz facility at Helmholtz-Zentrum Dresden Rossendorf

Helm, M.; Winnerl, S.; Pashkin, O.; Klopf, J. M.; Deinert, J.-C.; Kovalev, S.; Evtushenko, P.; Lehnert, U.; Xiang, R.; Arnold, A.; Wagner, A.; Schmidt, S. M.; Schramm, U.; Cowan, T.; Michel, P.

The coherent infrared and THz sources driven by the superconducting electron accelerator ELBE are described. The present status of the facility is summarized and a few scientific highlights are mentioned. Finally plans for a successor facility (Dresden Advanced Light Infrastructure, DALI) are outlined along with the most important scientific and technological challenges.

Keywords: terahertz source; infrared source; ELBE; DALI; electron accelerator

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Permalink: https://www.hzdr.de/publications/Publ-36505
Publ.-Id: 36505


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


Regulation of electron bunch arrival time for a continuous-wave linac: Exploring the application of the H2 mixed-sensitivity problem

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

Regulating the arrival time of electron bunches is a crucial step to improve the temporal resolution
of accelerator-based pump-probe experiments. In this regard, an electron beam regulation method,
called beam-based feedback, has been shown to work well for stabilizing longitudinal beam properties
on pulsed accelerator machines. Essentially, the method resembles a typical design of a proportional
regulator, where the plant is represented by an electron beam response matrix, and where the
inversion of such matrix produces the regulator. In recent years, however, linear accelerators (linacs)
that operate in a continuous-wave (CW) mode have received increasing attention. One of the key
features of such machines is the improved statistics of measured data, which enables a high-resolution
spectral analysis of the noise acting on the electron beam. This new insight allows to reinterpret the
electron beam regulation as a disturbance rejection goal, where the disturbance is based on measured
frequency data. In this work, we show that the proportional beam-based feedback method has a
principal performance limitation that becomes apparent by analyzing CW data. To improve this
situation, we propose a regulator design that incorporates a dynamical disturbance model formulated
in the context of the so-called H2 mixed-sensitivity problem. The designed regulator demonstrated
excellent agreement between the model and measurements carried out at the CW linac ELBE and
showed a potential to improve the proportional regulator approach.

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Permalink: https://www.hzdr.de/publications/Publ-36501
Publ.-Id: 36501


Unchanged perfusion in normal-appearing white and grey matter of glioma patients nine months after proton beam irradiation

Witzmann, K.; Raschke, F.; Löck, S.; Wesemann, T.; Krause, M.; Linn, J.; Troost, E. G. C.

Purpose: Radio(chemo)therapy is used as standard treatment for glioma patients. The surrounding normal tissue is inevitably affected by the
irradiation. The aim of this longitudinal study was to investigate perfusion alterations in the normal-appearing tissue after proton irradiation and assess the dose sensitivity of the normal tissue perfusion.
Methods: In 14 glioma patients, a sub-cohort of a prospective clinical trial (NCT02824731), perfusion changes in normal-appearing white matter (WM), grey matter (GM) and subcortical GM structures, i.e. caudate nucleus, hippocampus, amygdala, putamen, pallidum and thalamus, were evaluated before treatment and at three-monthly intervals after proton beam irradiation. The relative cerebral blood volume (rCBV) was assessed with dynamic susceptibility contrast MRI and analysed as the percentage ratio between follow-up and baseline image (∆rCBV). Radiation-induced alterations were evaluated using Wilcoxon signed rank test. Dose and time correlations were investigated with univariate and multivariate linear regression models.
Results: No significant ∆rCBV changes were found in any normal-appearing WM and GM region after proton beam irradiation. A positive correlation with radiation dose was observed in the multivariate regression model applied to the combined ∆rCBV values of low (1-20Gy), intermediate (21-40Gy) and high (41-60Gy) dose regions of GM (p<0.001), while no time dependency was detected in any normal-appearing area.
Conclusion: The perfusion in normal-appearing brain tissue remained unaltered after proton beam therapy. In further studies, a direct comparison with changes after photon therapy is recommended to confirm the different effect of proton therapy on the normal-appearing
tissue.

Keywords: Dynamic susceptibility contrast; Relative cerebral blood volume; Normal- appearing brain tissue; Proton beam irradiation; Radio(chemo)therapy

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-36500
Publ.-Id: 36500


Wissenschaftler*in im Bereich Biologie

Matschiavelli, N.; Zarschler, K.

Wissenschaftler*innen aus der Ressourcenökologie und Radiopharmazeutischen Krebsforschung geben dir Einblicke in ihre aktuellen Forschungsarbeiten und berichten, welchen Einfluss Mikroorganismen bei der sicheren Lage¬rung von hoch-radioaktiven Brennelementen haben und wie wir Bakterien zur Herstellung von zielgerichteten radioaktiven Arzneimitteln nutzen können, um damit Krebszellen aufzuspüren und zu zerstören.

  • Lecture (others) (Online presentation)
    Girls`and Boys`Day 2023, 27.04.2023, Helmholtz-Zentrum Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36499
Publ.-Id: 36499


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


Accurate Temperature Diagnostics for Matter under Extreme Conditions

Dornheim, T.

The experimental investigation of matter under extreme densities and temperatures, as in astrophysical objects and nuclear fusion applications, constitutes one of the most active frontiers at the interface of material science, plasma physics, and engineering. The central obstacle is given by the rigorous interpretation of the experimental results, as even the diagnosis of basic parameters like the temperature T is rendered difficult at these extreme conditions. Here, we present a simple, approximation-free method to extract the temperature of arbitrarily complex materials in thermal equilibrium from X-ray Thomson scattering experiments, without the need for any simulations or an explicit deconvolution. Our paradigm can be readily implemented at modern facilities and corresponding experiments will have a profound impact on our understanding of warm dense matter and beyond, and open up a variety of appealing possibilities in the context of thermonuclear fusion, laboratory astrophysics, and related disciplines.

  • Lecture (Conference)
    43rd International Workshop on High- Energy-Density Physics with Intense Ion and Laser Beams, 29.01.-03.02.2023, Hirschegg, Austria

Permalink: https://www.hzdr.de/publications/Publ-36495
Publ.-Id: 36495


Data on gerbil distribution within a vivarium in the Negev desert

Mukherjee, S.; Menezes, J. F. S.; Berger-Tal, O.; Kotler, B. P.; Bouskila, A.; Brown, J. S.

Data on the distribution of gerbils in a an experiment conducted in the Ben Gurion University vivarium, with the purpose of testing whether these animals follow an ideal free distribution.

Keywords: giving-up density; quitting harvest-rate; foraging; habitat-selection; predation risk; predator-prey interaction

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Permalink: https://www.hzdr.de/publications/Publ-36494
Publ.-Id: 36494


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


Catch me if you can – understanding antimony geochemistry during Fe(II) oxidation

Wegner, L.; Peiffer, S.; Scheinost, A.; Hockmann, K.

The mobility of antimony (Sb), a toxic metalloid of increasing concern, is closely linked to the biogeochemical cycling of iron (Fe). For example, the microbial production of soluble Fe(II) under oxygen-free conditions has been shown to result in the release of co-associated Sb (occurring as Sb(V) and/or Sb(III)). In redox-dynamic environments, Fe(II) may be re-oxidized and precipitate as Fe(III) oxides. The extent to which Fe(III) precipitation by Fe(II) oxidation immobilizes Sb, however, is still poorly understood and likely depends on an array of factors such as pH, Sb species and the nature of the newly formed Fe(III) oxides.

This study aims at investigating the effect of Fe(II) oxidation on Sb sequestration and on the mineralogy of the resulting Fe(III) precipitates in a pH range typical of Sb-contaminated systems (i.e. pH 6 – 7). To initiate the oxidation reaction, 0.5 mmol L-1 Fe(II) are added to an oxygen-saturated electrolyte solution containing 0 – 50 µmol L-1 Sb(V) or Sb(III). Changes in aqueous Sb and Fe(II) concentration are monitored during the experiment. Resulting solid phase samples are collected and characterized using a combination of spectroscopic, microscopic, and wet chemical extraction techniques.

First results show that Fe(II) oxidation kinetics and Sb sequestration are highly pH-dependent. At circumneutral pH and in the absence of Sb, X-ray diffractometry revealed lepidocrocite as the only solid-phase product. In contrast, the presence of Sb(V) partially inhibited lepidocrocite precipitation, and additionally resulted in formation of feroxyhyte – a rarely reported FeOOH polymorph. Sb EXAFS analysis indicated the incorporation of Sb(V) into the Fe oxide structure.

Our results are important for a robust understanding of Sb geochemistry in redox-dynamic environments as they demonstrate that Sb itself influences the pathways of secondary Fe oxide formation. This study also provides important information for the development of adequate remediation practices of Sb-contaminated soils under changing redox conditions.

Keywords: Antimony; Iron; Redox; Soils; EXAFS

Related publications

  • Lecture (Conference)
    ICOBTE & ICHMET, 1st Joint International Conference, 06.-10.09.2023, Wuppertal, Germany

Permalink: https://www.hzdr.de/publications/Publ-36491
Publ.-Id: 36491


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).

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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


movedesign: Shiny R app to evaluate sampling design for animal tracking movement studies

Simoes Silva, I. M.; Fleming, C. H.; Noonan, M. J.; Fagan, W. F.; Calabrese, J.

Projects focused on movement behavior and home range are commonplace, but beyond a focus on choosing appropriate research questions, there are no clear guidelines for such studies. The estimation of space-use and movement properties is often necessary to answer basic movement ecology questions, but designing an animal tracking study to produce reliable estimates is often done in an ad hoc manner. We developed 'movedesign', a user-friendly Shiny application, which can be utilized to investigate the precision of three estimates regularly reported in movement and spatial ecology studies: home range area, speed, and distance traveled. Conceptually similar to statistical power analysis, this application enables users to assess the degree of estimate precision that may be achieved with a given sampling design. Leveraging the 'ctmm' R package, we utilize two methods proven to handle many common biases in animal movement datasets: autocorrelated Kernel Density Estimators (AKDE) and continuous-time speed and distance (CTSD) estimators. Longer sampling durations are required to reliably estimate home range areas via the detection of a sufficient number of home range crossings. In contrast, speed and distance estimation requires a sampling interval short enough to ensure that a statistically significant signature of the animal's velocity remains in the data. This application addresses key challenges faced by researchers when designing tracking studies, including the trade-off between long battery life and high resolution of GPS devices, which may result in a compromise between reliably estimating home range or speed and distance. 'movedesign' has broad applications for researchers and decision-makers, supporting them to focus efforts and resources in achieving the optimal sampling design strategy for their research questions, prioritizing the correct deployment decisions for insightful and reliable outputs, while understanding the trade-off associated with these choices.

Keywords: ecology; conservation; experimental design; biologgers; GPS sampling; GPS tracking; trajectory; home range; space use

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Permalink: https://www.hzdr.de/publications/Publ-36485
Publ.-Id: 36485


Influence of 73Rb on the ashes of accreting neutron stars

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

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

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


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

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

´Objectives:

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

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

Results

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

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

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


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

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

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

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

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


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

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

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

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

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


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

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

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

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

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


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

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

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

Keywords: martensitic transformation; epitaxial film; ferromagnetism

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


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

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

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

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

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

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

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

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


Growth and Dynamics of Hydrogen Bubbles at Microelectrodes

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

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

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

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

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


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

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

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

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

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

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


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

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

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

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

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


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

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

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

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

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


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

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

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

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

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


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

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

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

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

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

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

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


Magnetic Control of Flow and Mass Transfer in Weakly Conducting Fluids

Mutschke, G.

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

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

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

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


CMOS-compatible Manufacturing of Room-Temperature Single Electron Transistors

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

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

Keywords: Single Electron Transistor; Nanoelectronics; Ion Beam Processing

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

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


Transport properties of systematically disordered Cr2AlC films

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

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

Keywords: Ion Irradiation; MAX phases; Disorder

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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

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  • 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.

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


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

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

Raman, XRD and TEM characterization of Cu3N/Cu2O nanowires

Keywords: Cu3N; nanowires; oxidation

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Permalink: https://www.hzdr.de/publications/Publ-36457
Publ.-Id: 36457


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

Makarov, D.

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

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

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

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

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

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

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


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

Hlawacek, G.

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

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

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Permalink: https://www.hzdr.de/publications/Publ-36455
Publ.-Id: 36455


Adding "color" to Helium Ion Microscopy images

Hlawacek, G.

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

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

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


Cu3N/Cu2O core-shell nanowires: growth and properties

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

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

Keywords: Cu3N; nanowires; surface oxidation

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


Applications of focused ion beams for semiconductor and quantum technology

Hlawacek, G.

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

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

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


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

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

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

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  • Lecture (Conference)
    ÖPG, 26.-30.09.2022, Leoben, Österreich

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


On demand spatially controlled fabrication of single photon emitters in Si

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

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

Related publications

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

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


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

Hlawacek, G.

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

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

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


Spatially resolved materials property tuning using GFIS and LMAIS based FIBs

Hlawacek, G.

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

Keywords: Ion irradiation; Focused ion Beams

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

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


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

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

streak camera data, meta data

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

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Publ.-Id: 36445


Exploring mid-infrared transient gain in graphene

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

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

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

Keywords: graphene; transient gain

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

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


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

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

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

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

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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

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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

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    Dirac3D, 14.-15.11.2022, Orsay, Frankreich

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


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