Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Electron transport through NiSi2-Si contacts and their role in reconfigurable field-effect transistors

Fuchs, F.; Gemming, S.; Schuster, J.

A model is presented which describes reconfigurable field-effect transistors (RFETs) with metal contacts, whose switching is controlled by manipulating the Schottky barriers at the contacts. The proposed modeling approach is able to bridge the gap between quantum effects on the atomic scale and the transistor switching. We apply the model to transistors with a silicon channel and NiSi2 contacts. All relevant crystal orientations are compared, focusing on the differences between electron and hole current, which can be as large as four orders of magnitude. Best symmetry is found for the < 110 > orientation, which makes this orientation most advantageous for RFETs. The observed differences are analyzed in terms of the Schottky barrier height at the interface. Our study indicates that the precise orientation of the interface relative to a given transport direction, perpendicular or tilted, is an important technology parameter, which has been underestimated during the previous development of RFETs. Most of the conclusions regarding the studied metal-semiconductor interface are also valid for other device architectures.

Keywords: density functional; nanowire; nanoelectronics; NanoNet; device modeling; interface; silicide; silicon

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Permalink: https://www.hzdr.de/publications/Publ-29427
Publ.-Id: 29427


Organic Iron Complexes Enhance Iron Transport Capacity along Estuarine Salinity Gradients

Herzog, S. D.; Kvashnina, K.; Persson, P.; Kritzberg, E.

Rivers discharge a notable amount of Fe (1.5 x 109 mol yr−1) to coastal waters, but are still not considered important sources of bioavailable Fe to open marine waters. The reason is that the vast majority of riverine Fe is considered to be lost to the sediment due to aggregation during estuarine mixing. Recently however, several studies demonstrate relatively high stability of riverine Fe to salinity induced aggregation, and it has been proposed that organically complexed Fe (Fe-OM) can “survive” the salinity gradient, while Fe (oxy)hydroxides are prone to aggregation and selectively removed. In this study, we directly identified, by X-ray absorption spectroscopy, the occurrence of these two Fe phases across eight boreal rivers and confirmed a significant but variable contribution of Fe-OM in relation to Fe (oxy)hydroxides among river mouths. We further found that that Fe-OM was more prevalent at high flow conditions in spring than at low flow conditions during autumn, and that Fe-OM was more dominant in low-order streams in a catchment than at the river mouth. The stability of Fe to increasing salinity correlated well to the relative contribution of Fe-OM, i.e. confirming that organic complexes promote Fe transport capacity. This study suggests that boreal rivers may provide significant amounts of potentially bioavailable Fe to marine waters beyond the estuary, due to organic matter complexes

Permalink: https://www.hzdr.de/publications/Publ-29426
Publ.-Id: 29426


Dual-time-point 64Cu-PSMA-617-PET/CT in patients suffering from prostate cancer

Hoberück, S.; Wunderlich, G.; Michler, E.; Hölscher, T.; Walther, M.; Seppelt, D.; Platzek, I.; Zöphel, K.; Kotzerke, J.

Regardless of its high positron energy, 68Ga-labeled PSMA ligands have become standard of care in metabolic prostate cancer imaging. 64Cu, a radionuclide with a much longer half-life (12.7 h), is available for PSMA labeling allowing imaging much later than 68Ga. In this study, the diagnostic performance of 64Cu-labeled PSMA was compared between early and late scans. Sixteen men (median age: 70 y) with prostate cancer in different stages underwent 64Cu-PSMA-617-PET/CT 2 and 22 hours post tracer injection. Pathologic and physiologic uptakes were analyzed for both points of time. Pathologic tracer accumulations occurred in 12 patients. Five patients presented with pathologic uptake in 17 different lymph nodes, two patients showed pathologic bone uptake in nine lesions, and seven patients had pathologic PSMA uptake in eight prostatic lesions. Physiologic uptake of the renal parenchyma, urine bladder, and salivary glands decreased over time, while the physiologic uptake of liver and bowel increased. In the present study, 64Cu-PSMA-617-PET demonstrated to be feasible for imaging prostate cancer for both the primary tumor site and metastases. Later imaging showed no additional, clinically relevant benefit compared with the early scans. At least the investigated time points we chose did not vindicate the additional expenditure.

Keywords: 64Cu; dual time; PET; prostate cancer; PSMA

  • Journal of Labelled Compounds and Radiopharmaceuticals 62(2019)8, 523-532
    DOI: 10.1002/jlcr.3745

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Permalink: https://www.hzdr.de/publications/Publ-29425
Publ.-Id: 29425


Spin textures and spin waves as seen by x-ray microscopy

Wintz, S.

The investigation of spin-wave phenomena, also referred to as magnonics, plays an important role in present condensed matter research. This holds true, in particular, as spin waves are seen as signal carriers for future spintronic information processing devices, with a high potential to outperform present charge-based technologies in terms of energy efficiency and device miniaturization. Yet a successful implementation of magnonic technology will require the usage and control of spin waves with nanoscale wavelengths. Here, I will show that ferromagnetic spin textures in metallic systems can be used as nanoscale spin-wave emitters and wave guides. In particular, topological spin vortex cores prove to act as efficient and tunable generators for sub-100 nm waves, while domain walls can be utilized as quasi one-dimensional channels for spin-wave propagation and routing. The underlying spin dynamic processes were directly imaged by using time-resolved x-ray microscopy.

  • Invited lecture (Conferences)
    NAP 2019, 15.-20.09.2019, Odessa, Ukraine
  • Invited lecture (Conferences)
    Challenges & Opportunities in X-Ray Microscopy, 11.-15.02.2019, Kreuth (Schloss Ringberg), Deutschland
  • Invited lecture (Conferences)
    SpinS-2019, 02.-04.10.2019, Duisburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29424
Publ.-Id: 29424


ExploreASL: a collaborative effort to process and explore multi-center ASL data

Mutsaerts, H. J.; Petr, J.; Groot, P.; Ingala, S.; Robertson, A.; Vaclavu, L.; Groote, I.; Kuijf, H.; O'Daly, O.; Zelaya, F.; Vandemaele, P.; Wink, A. M.; Kant, I.; Caan, M.; Morgan, C.; de Bresser, J.; Lysvik, E.; Schrantee, A.; Shirzadi, Z.; Kuijer, J. P. A.; Anazodo, U.; Richard, E.; Bokkers, R.; Reneman, L.; Masellis, M.; Achten, E.; Günther, M.; Macintosh, B.; Golay, X.; Hendrikse, J.; Chapell, M.; van Osch, M.; Thomas, D.; de Vita, E.; Bjornerud, A.; Nederveen, A.; Asllani, I.; Barkhof, F.

Arterial spin labeling (ASL) has undergone significant development since its inception; yet, standardized images processing procedures remain elusive. We present ExploreASL, a robust open source ASL image processing pipeline for clinical studies. Initiated through the European COST action ASL network, this joint effort provides integration and analysis of both single- and multi-center datasets across different operating systems. ExploreASL is optimized for both native- and standard-space analyses, and provides visual and automatic quality control on all intermediate and final images, allowing exploration of ASL datasets from multiple perspectives.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 2705
  • Poster
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-29422
Publ.-Id: 29422


Hemodynamic impairments in asymptomatic unilateral carotid artery stenosis are increased within individual watershed areas

Kaczmarz, S.; Goettler, J.; Petr, J.; Hansen, M. B.; Kufer, J.; Hock, A.; Sorg, C.; Zimmer, C.; Mouridsen, K.; Hyder, F.; Preibisch, C.

Internal carotid-artery stenosis (ICAS) causes complex and not yet well understood physiological impairments, which currently limits treatment decisions. We present multimodal perfusion and oxygenation-related MRI-data from unilateral asymptomatic ICAS-patients and age-matched healthy controls. The major aim was to investigate hemodynamic impairments in ICAS within individually defined watershed areas (iWSA’s) to account for individual vascular configurations. We found statistically significant lateralization of hemodynamic parameters within iWSA’s - strongest in WM of iWSA’s. Therefore, our iWSA-based approach facilitates detection of even subtle hemodynamic changes in ICAS. Furthermore, we detected spatially widespread capillary flow heterogeneity increases which are promising future treatment indicators.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 3246
  • Poster
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-29421
Publ.-Id: 29421


Recovery of cerebrovascular reactivity after asymptomatic carotid artery stenosis treatment is assessable by Breathhold-fMRI within global watershed areas

Kaczmarz, S.; Goettler, J.; Sollmann, N.; Kufer, J.; Hansen, M. B.; Hock, A.; Sorg, C.; Zimmer, C.; Mouridsen, K.; Hyder, F.; Preibisch, C.; Petr, J.

Asymptomatic unilateral internal carotid-artery stenosis (ICAS) causes complex and currently poorly understood hemodynamic impairments which could possibly improve treatment decisions. Cerebrovascular reactivity (CVR) is an important biomarker of vascular health and can potentially serve to evaluate ICAS-treatment efficacy. We present perfusion MRI-data from a longitudinal study in 16 asymptomatic ICAS-patients before and after treatment plus 17 age-matched healthy controls. We hypothesize that CVR impairments in ICAS and their recovery after treatment can be assessed by Breathhold-fMRI analyzed by a data-driven approach. Our results demonstrate statistically significant CVR impairments within global watershed areas before treatment and significant CVR recovery after treatment.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 0739
  • Lecture (Conference)
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-29420
Publ.-Id: 29420


Cerebral hypometabolism measured with intravascular T2-prepared tissue relaxation with inversion recovery (T2-TRIR) and pCASL in adults with sickle cell disease

Vaclavu, L.; Petersen, E. T.; Mutsaerts, H. J.; Petr, J.; Majoie, C. B.; Wood, J. C.; Vanbavel, E. T.; Biemond, B. J.; Nederveen, A. J.

Cerebral metabolic rate of oxygen (CMRO2) quantifies the amount of oxygen consumed by the brain, and relies on continuous delivery of nutrients and oxygen via cerebral blood flow (CBF). In sickle cell disease (SCD), CBF is elevated to compensate for chronic anaemia. This study investigates CMRO2 in adults with SCD using T2-prepared tissue relaxation with inversion recovery (T2-TRIR). CBF increased after acetazolamide-induced vasodilation in both groups but CMRO2 reduced even further in SCD patients while it remained stable in controls. Our results suggest that cerebral shunting is exacerbated by high flow conditions.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 0291
  • Lecture (Conference)
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-29419
Publ.-Id: 29419


A multi-site round robin assessment of ASL using a perfusion phantom

Oliver-Taylor, A.; Hampshire, T.; Mutsaerts, H.-J.; Clement, P.; Warnert, E.; Kuijer, J. P. A.; Baas, K.; Petr, J.; Siero, J. C. W.; Marques, J. P.; Sunaert, S.; Borra, R. J. H.; van Osch, M. J. P.; Golay, X.; Achten, E.

Arterial Spin Labelling shows great promise for perfusion measurements; however, despite numerous volunteer reproducibility studies, comparisons have not been made using a phantom to establish differences due to the acquisition hardware and pulse sequences. We present data from a multi-site study using a perfusion phantom, targeting 3T MRI systems from a single vendor running the same software version.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 2653
  • Poster
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-29418
Publ.-Id: 29418


Extra-neurite Perfusion Measurement with Combined Arterial Spin Labeling and Diffusion Weighted MRI

Asllani, I.; Petr, J.; Mutsaerts, H.-J.; Bozzali, M.; Cercignani, M.

Introduction:
Arterial Spin Labeling (ASL) is an MRI method that uses magnetically labeled endogenous water as a tracer for measuring cerebral perfusion in vivo1. The arterial water that is usually 'labeled' at a plane positioned at the base of the brain, perpendicular to the carotids. A post-labeling delay (PLD) is introduced prior to acquisition to allow labeled water to cross the vasculature and perfuse into the tissue1. Because of signal decay due to T1 relaxation, fast acquisition schemes are employed to ensure optimal SNR. Consequently, the spatial resolution of ASL is relatively low (~ 3 x 3 x 6 mm3). As such, the measured blood flow from a given voxel reflects a mixture of signals from gray matter (GM), white matter (WM), and CSF, a phenomenon known as partial voluming (PV)2. To correct for the confounding effects of PV in ASL imaging, an algorithm (PVC) has been developed and already used by several studies2,3. The algorithm is based on GM and WM volume data obtained from the segmentation of the T1w image2, and makes no further distinction between different compartments within the same tissue type. Here, we investigated the potential of PVC ASL to map blood perfusion in the extra-neurite compartment (e.g., soma, glial cells4) and the intra-neurite (comprised of axons and axon terminals4) within the same tissue, independently. We applied the PVC algorithm using compartmental data from a diffusion weighted imaging (DWI) model, referred to as NODDI4. The underlying hypothesis was that the blood flow in the extra- and intra-neurite compartments would vary with the PLD; a short PLD acquisition would increase the flow in the extra-neurite compartment compared to the long PLD for which there should be an increased flow in the intra-neurite compartment instead.
Methods:
Theory
At any given voxel, the blood flow (fT) is given as:
fT=VFIn•fIn+VFEn•fEn+VFIso•fIs
where, VFIn, VFEn, VFIso represent respectively: the intra-neurite, extra-neurite, and non-tissue compartments obtained from NODDI4. By assuming that for each compartment blood flow is constant over a 'kernel', the equation can be re-written in vectorial form to reflect the flow at the voxel in the center of the kernel2, from which then each compartmental flow can be computed using linear regression as detailed in Asllani et al.2..

MRI protocol & image analysis
T1w (MPRAGE), NODDI, and ASL MRI images were obtained on 4 healthy participants (mean age = 44.5 ± 7.4 y, 2 men) a Siemens 3T system. To test the hypothesis that a shorter PLD would increase the signal in the extra-neurite GM compartment, ASL was acquired with a short (200ms) and long PLD (1800ms). Only results from voxels with GM content > 80% are presented.
Results:
Fig.1 shows the raw images that were used by the PVC algorithm to extract the flow from each compartment within the GM. For the long-PLD acquisition, average CBF in the extra- and intra-neurite compartments was 76 ± 10 mL/100g*min and 59 ± 8 mL/100g*min, respectively. As hypothesized, for the short-PLD, the CBF signal was contained primarily in the extra-neurite department (118 ± 17 mL/100g*min) with the intra-neurite compartment flow being essentially zero (-0.9 ± 0.6 mL/100g*min). Results from one participant are shown in Fig.2.
Supporting Image: Fig1.jpg
·Fig.1: ‘Raw’ NODDI and ASL images used by the PVC algorithm from one subject. Top row: MPRAGE and VFIn images; middle row: VFEn and VFISO; bottom row: CBF for short PLD (left) and long PLD (right).
Supporting Image: Fig2.jpg
·Fig.2: Top: Extra-neurite GM CBF from short (left) & long (right) PLD acquisitions. Bottom: axial and sagittal views of Intra-neurite CBF for long PLD with areas in blue indicating ~zero signal.

Conclusions:
We combined NODDI with PVC ASL MRI to distinguish between blood flow in the extra- and intra-neurite compartments within GM. While these initial results look promising, more work is needed to test the sensitivity of this method and its feasibility for clinical applications. For example, a larger PLD range is needed to test whether the method can be used to detect inter-neurite subcortical flow. If successful, this method could prove invaluable in mapping blood flow with high spatial specificity.

Keywords: Cerebral Blood Flow; Data analysis; fMRI CONTRAST MECHANISMS; MRI

  • Open Access Logo Contribution to proceedings
    Organization for Human Brain Mapping Annual Meeting 2019, 09.-13.06.2019, Rome, Italy
  • Open Access Logo Poster
    Organization for Human Brain Mapping Annual Meeting 2019, 13.06.2019, Rome, Italy

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Permalink: https://www.hzdr.de/publications/Publ-29417
Publ.-Id: 29417


Photoelectrocatalytic degradation of emerging contaminants at WO₃/BiVO₄ photoanodes in aqueous solution

Cristino, V.; Pasti, L.; Marchetti, N.; Berardi, S.; Bignozzi, C. A.; Molinari, A.; Passabi, F.; Caramori, S.; Amidani, L.; Orlandi, M.; Bazzanella, N.; Piccioni, A.; Kesavan, J. K.; Boscherini, F.; Pasquini, L.

WO3/BiVO4 films obtained by electrochemical deposition of BiVO4 over mesoporous WO3 were applied to the photoelectrochemical degradation of selected emerging contaminants (ketoprofen and levofloxacine) in aqueous solutions. The WO3/BiVO4 films in this work are characterized by a mesoporous morphology with a maximum photoconversion efficiency >40% extending beyond 500 nm in Na2SO4 electrolytes.
Oxygen was found to be the dominant water oxidation product (ca. 90% faradaic yield) and no evidence for the photogeneration of OH radicals was obtained. Nevertheless, both 10 ppm levofloxacine and ketoprofen could be degraded at WO3/BiVO4 junctions upon a few hours of illumination under visible light. However, while levofloxacine degradation intermediates were progressively consumed by further oxidation at the WO3/BiVO4 interface, ketoprofen oxidation byproducts, being stable aromatic species, were found to be persistent in aqueous solution even after 15 hours of solar simulated illumination. This indicates that, due to the lower oxidizing power of photogenerated holes in BiVO4 and a different water oxidation mechanism, the employment of WO3/BiVO4 in photoelectrochemical environmental remediation processes is much less universal than that possible with wider band gap semiconductors such as TiO2 and WO3.

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-29416
Publ.-Id: 29416


NH₃‑SCR over V−W/TiO₂ Investigated by Operando X‑ray Absorption and Emission Spectroscopy

Doronkin, D. E.; Benzi, F.; Zheng, L.; Sharapa, D. I.; Amidani, L.; Studt, F.; Roesky, P. W.; Casapu, M.; Deutschmann, O.; Grunwaldt, J.-D.

V−W/TiO2-based catalysts, which are used for the removal of NOx from the exhaust of diesel engines and stationary sources via selective catalytic reduction with NH3 (NH3-SCR), were studied by operando X-ray absorption spectroscopy (XAS) and emerging photon-in/photon-out techniques. In order to minimize the influence of highly X-ray absorbing tungsten and the fluorescence of titanium, we used a high-energyresolution fluorescence setup that is able to separate efficiently the V Kβ1,3 emission lines and additionally allows to record valence-to-core (vtc) X-ray emission lines. High-energy resolution fluorescence-detected XAS (HERFD-XAS) and vtc X-ray emission spectroscopy (vtc-XES) proved to be the only way to perform an operando V K edge X-ray spectroscopic study on industrially relevant V−W/TiO2 catalysts so far. The V−W/TiO2 and V/TiO2 samples synthesized by incipient wetness impregnation and grafting exhibited high activity toward NH3-SCR. Raman spectroscopy showed that they mainly contained highly dispersed, isolated, and polymeric V-oxo species. HERFD-XAS and XES identified redox cycling of vanadium species between V4+ and V5+. With respect to most of the potential NH3 adsorption complexes, density functional theory calculations further showed that vtc-XES is more limited than surface-sensitive techniques such as infrared spectroscopy; hence, a combination of X-ray techniques with IR or similar spectroscopies is required to unequivocally identify the mechanism of NH3-SCR over vanadia-based catalysts.

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Permalink: https://www.hzdr.de/publications/Publ-29415
Publ.-Id: 29415


Synthesis and Characterization of an Epidermal Growth Factor Receptor selective Ru(II) Polypyridyl-Nanobody Conjugate as a Photosensitizer for Photodynamic Therapy

Karges, J.; Jakubaszek, M.; Mari, C.; Zarschler, K.; Goud, B.; Stephan, H.; Gasser, G.

There is currently a surge for the development of novel photosensitizers (PSs) for photodynamic therapy (PDT) since those currently approved are not completely ideal. Among the tested compounds, we have previously investigated the use of Ru(II) polypyridyl complexes with a [Ru(bipy)2(dppz)]2+ and [Ru(phen)2(dppz)]2+ scaffold (bipy = 2,2'-bipyridine; dppz = dipyrido[3,2-a:2′,3′-c]-phenazine, phen = 1,10-phenanthroline). These complexes selectively target DNA. However, since DNA is ubiquitous, it would be of great interest to increase the selectivity of our PDT PSs by linking them to a targeting vector in view of targeted PDT. Herein, we present the synthesis, characterization and in-depth photophysical evaluation of a nanobody containing Ru(II) polypyridyl conjugate selective for the epidermal growth factor receptor (EGFR) in view of targeted PDT. Using ICP-MS and confocal microscopy, we could demonstrate that our conjugate had a high selectivity for the EGFR receptor, which is a crucial oncological target as it is overexpressed and/or deregulated in a variety of solid tumors. However, contrary to expectations, this conjugate was found to not produce reactive oxygen species (ROS) in cancer cells and to be therefore not phototoxic.

Keywords: Bioinorganic Chemistry; Medicinal Inorganic Chemistry; Metal-based drugs; Metals in Medicine; Photodynamic Therapy

Permalink: https://www.hzdr.de/publications/Publ-29412
Publ.-Id: 29412


Carrier Flotation: State of the Art and its Potential for the Separation of Fine and Ultrafine Mineral Particles

Eckert, K.; Schach, E.; Gerbeth, G.; Rudolph, M.

Critical raw materials (CRMs) are of primary importance for energy storage systems as needed for electromobility. Many mineral deposits which contain CRMs are low-grade ores. To liberate the CRMs, a grinding of the mineral ores to very fine sizes below 20 µm particle size is necessary. However, the present class of industrial flotation plants fail to extract such fine and ultrafine particles. To improve the recovery in fine particle flotation, techniques have been developed which attempt to agglomerate the fine valuable particles into larger aggregates which subsequently can be separated by established technologies such as froth flotation. Carrier flotation is one of these techniques. The present work reviews the state of the art of this technique for the recovery of fines and ultrafines.

Keywords: Flotation; Fine particles; Carrier Flotation

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-29411
Publ.-Id: 29411


Multidimensional characterization of separation processes – Part 1: Introducing kernel methods and entropy in the context of mineral processing using SEM-based image analysis

Schach, E.; Buchmann, M.; Tolosana Delgado, R.; Leißner, T.; Kern, M.; van den Boogaart, K. G.; Rudolph, M.; Peuker, U. A.

An alternative method for the particle tracking approach for scanning electron microscopy-based image analysis is introduced, using kernel density estimates instead of discrete bins. This allows for information that is more robust. Uncertainties of the data are assessed using the bootstrap resampling method. The presented methodology enables the calculation of multidimensional partition curves, which can be used for a detailed analysis of separation processes. It has been found that the statistical entropy is a helpful tool to evaluate the separation efficiency of these partition maps. The methodology was applied to a density separation process of a cassiteritebearing skarn ore from the Hämmerlein deposit in the Erzgebirge region in Germany, which serves as a case study. A Sepro™ Falcon concentrator was utilized for the density separation.

Keywords: Multidimensional characterization; Partition curve; Separation process; Mineral processing; Kernel density estimation; Entropy; Bootstrap resampling

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-29410
Publ.-Id: 29410


Uncertainty assessment in particle tracking processing models of cassiterite in complex skarn ores

Schach, E.; Buchmann, M.; Tolosana Delgado, R.; Kern, M.; Leißner, T.; Möckel, R.; van den Boogaart, K. G.; Rudolph, M.; Peuker, U. A.

An alternative method for the particle tracking approach for SEM-based image analysis is introduced, using kernel density estimates instead of discrete bins. This allows to obtain more robust information. Therefore, the bandwidth adjustment for the kernels is of special importance. Uncertainties of the data are assessed using the bootstrap resampling method. The mentioned methodology enables for the calculation of multidimensional partition curves, which can be used for a detailed analysis of separation processes. The measure of the entropy is used to evaluate the separation efficiency of the partition maps. A density separation process, using a falcon separator and a dry magnetic separation process, using a drum type separator serve as case studies for the described methodology. As feed material for the separation processes a cassiterite bearing skarn ore from the Pöhla deposit in the Erzgebirge region in Germany is used.

  • Lecture (Conference)
    Procemin-Geomet 2018, 28.-30.11.2018, Santiago, Chile

Permalink: https://www.hzdr.de/publications/Publ-29409
Publ.-Id: 29409


Oil assisted column flotation of a cassiterite-bearing complex skarn ore from the ore mountains, Germany

Schach, E.; Buchmann, M.; Leistner, T.; Kern, M.; Peuker, U. A.; Rudolph, M.

In this study, the flotation characteristics of a cassiterite-bearing fine-grained and complex skarn ore from a deposit in the Ore Mountains is investigated. The tests are performed using an oil-assisted column flotation approach to process very fine ore fractions and avoid losses of cassiterite into the tailings. First, process parameters are obtained for a finely ground artificial mixture of quartz, magnetite and cassiterite, simulating the real ore. Thereby, magnetite is used, as iron oxides can have a detrimental effect on the flotation due to a similar flotation behavior. In addition, they can act as a source of multivalent ions, which are known to reduce the concentration of collector molecules, active for flotation. Based on the results, selected parameters are further tested for cassiterite skarn ore from the Hämmerlein deposit including a pre-conditioning and a water exchange step to remove ionic contaminants. The process response is analyzed in detail by XRF (X-ray fluorescence) and MLA (mineral liberation analysis) to get a better understanding of the behavior of the single ore components. Sulfosuccinamate type surfactant is utilized as the collector, emulsifier and to reduce the froth destabilization through nonpolar oil. Sodium hexafluorosilicate is added as the depressant.

Keywords: Complex cassiterite-bearing skarn ore; Oil-assisted column flotation; Sulfosuccinamate collector; Water exchange

  • Lecture (Conference)
    IMPC 2018 - 29th International Mineral Processing Congress, 17.-21.11.2018, Moscow, Russian Federation

Permalink: https://www.hzdr.de/publications/Publ-29408
Publ.-Id: 29408


Density and Susceptibility: Geometallurgical Characterization of a Cassiterite Bearing Complex Skarn Ore From the Ore Mountains, Germany

Buchmann, M.; Schach, E.; Leißner, T.; Tolosana-Delgado, R.; Kern, M.; Krupko, N.; Rudolph, M.; Peuker, U. A.

In mineral processing, density and magnetic susceptibility are two very fundamental properties. For the beneficiation of valuables to saleable concentrates a detailed understanding of these properties is essential. Especially when it comes to the processing of cassiterite, which is the main mineral for tin production, they become highly prominent. Due to the chemically inert character of cassiterite towards most industrial applied leaching agents, density and magnetic separation processes are mainly applied for its beneficiation. To guarantee an optimized utilization of the different operations not only cassiterite but also the different gangue minerals have to be considered.
In this study, a skarn ore is characterized by density and magnetic susceptibility. Therefore, the material was first split into different density classes by heavy liquid separation. The obtained classes were further separated by their susceptibility to finally obtain a density-susceptibility matrix. For this purpose, an isodynamic separator was used. A more detailed characterization of the materials is done via gas pycnometer, magnetic susceptibility balance and vibrating sample magnetometer to estimate the characteristics of density and susceptibility for the various classes. Further, the determination of the chemical assay and the mineral intergrowth by mineral liberation analysis helps to generate a three dimensional data base for detailed characterization of the present ore.
The objective of this study is to estimate potential material streams for a modular processing plant via characterization of the material for the entire deposit by the two afore mentioned characteristic properties. The established multidimensional data matrix, enables predictions for the separation properties of the material and contributes to the characterization of the deposit within the context of geometallurgy.

Keywords: Geometallurgy; susceptibility; density; skarn ore; cassiterite

  • Lecture (Conference)
    MPC 2018 - 29th International Mineral Processing Congress, 15.-21.09.2018, Moscow, Russian Federation

Permalink: https://www.hzdr.de/publications/Publ-29407
Publ.-Id: 29407


Flotationscharakteristika eines zinnhaltigen Skarnerzes aus der Lagerstätte Hämmerlein im Erzgebirge

Schach, E.; Buchmann, M.; Astoveza, J.; Bremerstein, I.; Kern, M.; Peuker, U. A.; Rudolph, M.

Im Rahmen des AFK-Projektes beschäftigt sich das Helmholtz-Institut Freiberg mit der Aufbereitung feinster Fraktionen eines zinnhaltigen Skarnerzes. Dazu wird in einer gemeinsamen Studie mit der UVR-FIA GmbH und dem Institut für Mechanische Verfahrenstechnik und Aufbereitungstechnik der TU Bergakademie Freiberg die Flotationscharakteristika des Erzes in Abhängigkeit verschiedener, vorhergehender Aufbereitungsmethoden untersucht, um erste Erkenntnisse über geeignete Flotationsreagenzien und Prozessparameter zu erlangen. Bei diesen Methoden handelt es sich um die Dichtetrennung, Magnetscheidung, Sulfidflotation und die Entschlämmung des Aufgabematerials. Da das Aufgabematerial für die Kassiteritflotation noch sehr grobkörnig ist (x80,3 < 250 µm) wurde ebenfalls der Einfluss eines weiteren Zerkleinerungsschrittes zur Verbesserung des Aufschlussgrades betrachtet.
Als Ergänzung zu der von der UVR-FIA GmbH untersuchten Styrolphosphonsäure wurde für die Flotationsversuche, welche im Rahmen dieses Beitrages durchgeführt wurden, das anionaktive Sulfosuccinamat (Aerosol22®) als Sammler verwendet. Zusätzlich wurde MIBC als Schäumer und Natriumhexafluorosilicat als Drücker eingesetzt. Die Flotation erfolgte bei pH 3 in einer Flotationszelle der Firma Outotec® (GTK LabCell™).
Die Proben wurden sowohl mit Röntgenfluoreszenzanalyse als auch mit „Mineral Liberation Analysis“ (MLA) untersucht. Somit war es möglich, das Verhalten der einzelnen Minerale während der verschiedenen Aufbereitungsschritte genauer zu charakterisieren. Besonderes Augenmerk wurde dabei auf die für die Flotation problematische Bestandteile wie zum Beispiel die Chloritgruppenminerale und die Eisenoxide gelegt.
Um den Einfluss von störenden Metallionen auf die Flotation zu bestimmen, wurde für einige Versuche ein Wasserwechsel nach einer Vorkonditionierung mit Natriumhexafluorsilicat durchgeführt. Weiterhin wurden Wasserproben der Versuche entnommen und hinsichtlich der Ionengehalte mittels ICP-OES analysiert.
Im letzten Schritt wurden die einzelnen Aufbereitungsschritte miteinander kombiniert, um Möglichkeiten für ein Fließbild zur Aufbereitung vergleichbarer Erze aufzuzeigen.

  • Lecture (Conference)
    Tagung "Aufbereitung und Recycling", 08.-09.11.2017, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29406
Publ.-Id: 29406


The smaller the valuables, the poorer the recovery – Is that always true?

Schach, E.; Leistner, T.; Rudolph, M.

The recovery of valuables in a flotation process is known to depend on the particle size and to drop for very small particles. The lack of floatability of such particle fractions is often objected to poor particle-bubble collision efficiencies due to low inertial energies. We recently showed that very fine valuable particles do float well and that the overall flotation performance depends more on the size of the gangue particles. Those findings are in contradiction to many classic collision models in which the influence of fine gangue particles is neglected. In this study the effect of the fine gangue particles on the flotation process is investigated and discussed in more detail. Therefore flotation tests with different solid concentrations, particle size fractions and different hydrodynamic conditions are conducted, measuring the energy dissipation and analysing the obtained flotation products. In addition, the wettability of the valuables and the gangue particles is characterized.

  • Poster
    Flotation '17, 13.-16.11.2017, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-29405
Publ.-Id: 29405


Floatation characteristics of a cassiterite bearing complex skarn ore from the Ore Mountains, Germany

Buchmann, M.; Schach, E.; Astoveza, J.; Kern, M.; Urs. A., P.; Rudolph, M.

The flotation characteristics of a cassiterite bearing fine grained and complex skarn ore from the Ore Mountain region is investigated. A sulfosuccinamate type collector is used and sodium hexafluorosilicate is added as depressant. The objective of the experiments is a better understanding of the cassiterite flotation performance as influenced by different pre-processing operations as magnetic separation, gravity separation, sulphide flotation and desliming. Therefore, structure and composition of the feed, the different concentrates and the tailings of each process are analysed in detail by XRF and MLA to get a better understanding of the behaviour of the single ore components in the different processing steps. Problematic minerals (e.g. chlorites) have a negative effect on the selectivity of cassiterite flotation. Therefore, particular attention is payed to the behaviour of these minerals during flotation. Furthermore, the effect of the particle size due to the change in liberation on the flotation process is investigated. Three critical factors are found to greatly influence the flotation performance, namely: (1) particle size; (2) Fe oxides content; and (3) ions in the solution.

Keywords: cassiterite flotation; magnetic separation; density separation; fine grinding; desliming; water exchange

  • Poster
    Flotation, 13.11.2017, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-29404
Publ.-Id: 29404


Assessment of flotation kinetics modeling using information criteria; Case studies of elevated-pyritic copper sulfide and high-grade carbonaceous sedimentary apatite ores

Hassanzadehmahaleh, A.; Hoang, D. H.; Stockmann, M.

Despite flotation kinetic modeling is well discussed in the literature, its evaluation from overfitting, the number of model parameters and model complexities have not been adequately addressed. Flotation kinetic behavior of two deposits including an elevated-pyritic (Cu/S=0.21) complex copper sulfide ore and a high-grade carbonaceous sedimentary apatite (P2O5≥25%) ore were investigated. The flotation kinetic experiments were carried out in a mechanically agitated batch flotation cell. Different flotation kinetic models including seven common empirical and initially four mathematical models were applied to the experimental data. In addition to assessment of the goodness of fit (GOF) for each model, a factor of model complexity was considered using advanced statistical techniques (i.e. Bayesian information (BIC), low of iteratedn logarithm (LILC) and Akaike information (AIC) indices). The results confirmed that flotation kinetic modeling significantly depends on the feed type. The empirical models were found more sensitive than the mathematical ones to the ore properties and the mineral types. Furthermore, the mathematical models demonstrated relatively favorable results than the practical models concerning the variation of ore properties due to the consideration of more parameters in the modeling. Finally, it was concluded that the IC indices must be applied to the process of model selection owing to consideration of GOF, the complexity of a model and model consistency. The IC was introduced as a more reliable indicator than the common regression approach for evaluating, sequential ordering and selecting the suitable flotation kinetic models. Further studies are required for model’s generalizability from a statistical point of view.

Keywords: Flotation kinetic modeling; goodness of fit; information criteria; flotation rate constant; Bayesian information

Permalink: https://www.hzdr.de/publications/Publ-29403
Publ.-Id: 29403


Lift Forces on Solid Spherical Particles in Unbounded Flows

Shi, P.; Rzehak, R.

The present work is concerned with the lift forces acting on particles immersed in an unbounded fluid. Both mechanisms due to rotation of the particle and vorticity of the fluid flow are considered. Focus is on solid spherical particles at Reynolds numbers up to 103 which are relevant for particulate flows in chemical and minerals engineering. A comprehensive review of existing results from analytical, numerical, and experimental studies is given. In particular in the simulation area many new data have appeared in the past 10 years since the earlier review of Loth [AIAA Journal 46 (2008), 801–809]. The available correlations are critically assessed by comparison to data from experiment and direct numerical simulation. Based on the comparison new correlations are proposed and gaps or inconsistencies in the data are identified. The case of wall-bounded flows will be considered in a sequel.

Keywords: lift force; particles; shear flow; particle rotation; correlation

Permalink: https://www.hzdr.de/publications/Publ-29402
Publ.-Id: 29402


Nanoscale n++-p junction formation in GeOI probed by tip-enhanced Raman spectroscopy and conductive atomic force microscopy

Prucnal, S.; Berencen, Y.; Wang, M.; Georgiev, Y.; Erbe, A.; Khan, M. B.; Böttger, R.; Hübner, R.; Schönherr, T.; Kalbacova, J.; Vines, L.; Facsko, S.; Engler, M.; Zahn, D. R. T.; Knoch, J.; Helm, M.; Skorupa, W.; Zhou, S.

Ge-on-Si and Ge-on-insulator (GeOI) are the most promising materials for the next-generation nanoelectronics that can be fully integrated with silicon technology. To this day, the fabrication of Ge-based transistors with a n-type channel doping above 5 × 1019 cm−3 remains challenging. Here, we report on n-type doping of Ge beyond the equilibrium solubility limit (ne ≈ 6 × 1020 cm−3) together with a nanoscale technique to inspect the dopant distribution in n++-p junctions in GeOI. The n++ layer in Ge is realized by P+ ion implantation followed by millisecond-flashlamp annealing. The electron concentration is found to be three times higher than the equilibrium solid solubility limit of P in Ge determined at 800 °C. The millisecond-flashlamp annealing process is used for the electrical activation of the implanted P dopant and to fully suppress its diffusion. The study of the P activation and distribution in implanted GeOI relies on the combination of Raman spectroscopy, conductive atomic force microscopy, and secondary ion mass spectrometry. The linear dependence between the Fano asymmetry parameter q and the active carrier concentration makes Raman spectroscopy a powerful tool to study the electrical properties of semiconductors.
We also demonstrate the high electrical activation efficiency together with the formation of ohmic contacts through Ni germanidation via a single-step flashlamp annealing process.

Keywords: GeOI; ion implantation; flash lamp annealing; doping; TERS

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Permalink: https://www.hzdr.de/publications/Publ-29401
Publ.-Id: 29401


PIConGPU: Predictive Simulations of Laser-Particle Accelerators with Manycore Hardware

Huebl, A.

The presented thesis establishes simulations on modern massively parallel computing hardware to investigate relativistic laser-driven plasmas. The latter are of special interest as they may provide a compact source for energetic ion beams. Computer simulations provide valuable insight into ultrafast plasma processes, evolving in the ultrahigh intensity (I0 ≫ 1018 W/cm2) focus of the ultrashort (𝜏0=30-500 fs) laser pulses driving the interaction. Such simulations require high numerical resolution and full geometric treatment for reliable predictions, which can only be addressed with high-performance computing. The open source particle-in-cell code PIConGPU, which is developed in the framework of this thesis, answers these demands, providing speed and scalability to run on the world's largest supercomputers. PIConGPU is designed with a modular and extensible implementation, allowing to compute on current and upcoming hardware from a single code base. Furthermore, challenges arising for generated data rates, reaching 1 PByte per simulation, are resolved with scalable data reduction techniques and novel workflows, such as interactive simulations.

Numerical studies are performed on two novel targets for laser-proton acceleration with near-critical and mass-limited properties. A micrometer-scale spherical target is explored with realistic temporal laser contrast, providing an interpretation for experimental results collected at the PW-class laser system PHELIX (𝜏0=500 fs pulse length). In this study, 3D modeling with the GPU supercomputer Titan enabled the identification of pre-expansion to near-critical target conditions, which uncovers a regime of volumetric laser-electron interaction generating a highly directed proton beam. Furthermore, a novel cryogenic hydrogen jet target is researched in close collaboration to experiments at the laser system DRACO (𝜏0=30 fs). This target system provides a unique setup for the isolated investigation of multi-species effects and their influence on the generated ion energy distribution. A novel analytical model provides a link between characteristic modulations in the ion energy spectra and ensemble properties of the microscopic electron distribution. In view of a potential experimental realization, parametric scans are performed confirming the feasibility of the proposed setup.

Keywords: laser-plasma acceleration; modeling; HPC; GPU; laser-ion acceleration; exascale computing; open source; open data

  • Doctoral thesis
    TU Dresden, 2019
    Mentor: Prof. Dr. Ulrich Schramm
    171 Seiten
    DOI: 10.5281/zenodo.3266820
  • Lecture (others)
    Dissertationsverteidigung, 25.06.2019, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-29400
Publ.-Id: 29400


Joint project: Umwandlungsmechanismen in Bentonitbarrieren - Subproject B: Einfluss von mikrobiellen Prozessen auf die Bentonitumwandlung

Matschiavelli, N.; Drozdowski, J.; Kluge, S.; Arnold, T.; Cherkouk, A.

Concerning the deep geological disposal of high-level radioactive waste (HLW), bentonite can be used because of its high swelling capacity and its low hydraulic conductivity as geo-technical barrier and buffering material in between the waste-containing canister (technical barrier) and the surrounding host rock (geological barrier). There are still many gaps in process understanding of bentonite transformations, especially in dependence of different temperatures and pore waters. Within the joint-project UMB (“Umwandlungsmechanismen in Bentonitbarrieren”), the co-operation partner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Repository Safety Analysis), the University of Greifswald (Institute for Geography and Geology), the Federal Institute for Geosciences and Natural Resources (BGR, section of technical mineralogy), the Technical University of Munich (TUM; chair of theoretical chemistry, quantum chemistry) and the Helmholtz-Center Dresden-Rossendorf (HZDR, Institute of Resource Ecology) are supposed to define criteria which facilitate the selection of suitable bentonites in order to use them in the deep geological repository of high-level radioactive waste. HZDR analyzed two different bentonites (B36 and SD80) regarding their microbial diversity and potential microbial activity. In dependence of repository-relevant parameters (temperature, pore water, presence of substrates), microcosm experiments were set up at the GRS, containing the respective bentonites and Opalinus Clay pore water or cap rock solution, respectively. The long-term batches were incubated one year and two years at different temperatures (25 °C, 60 °C and 90 °C) in gastight bottles. Additionally, HZDR set up B36 short-term microcosms with Opalinus Clay pore water, which incubated for three month at 30 °C with six sampling points monitoring the microbial diversity and geochemical parameters.
After one and two years of incubation at 25 °C, respectively, supplemented SD80 microcosms containing Opalinus Clay pore water showed the formation of black precipitates and fissures as well as the dominance of sulfate-reducing and spore-forming bacteria. The detected genera are able to reduce the present sulfate in order to form hydrogen sulfide. XRF spectroscopy analysis, done at the University of Greifswald, showed a decrease in sulfate concentration in the respective SD80 microcosms, supporting this surveillance. Similar observations were made for the two-year incubations. The microbial diversity of the B36 bentonite raw material is much different from the SD80 bentonite raw material. Similar to the diversity of SD80 bentonite, the microbial community of the B36 bentonite long-term incubations changed with respect to the applied pore water. Spore-forming organisms dominated the set ups which were supplied with Opalinus Clay pore water solution whereas halophilic microorganisms were found in set ups containing diluted cap rock solution. We were also successful in showing the dominance of thermophilic bacteria in Opalinus clay pore water-containing microcosms that incubated at 60 °C for two years. Additionally, we were able to enrich microorganism from Opalinus Clay pore water of both, B36 and SD80 bentonite long-term incubations. Similar to the long-term analysis, substrate-containing B36 short-term microcosms, containing Opalinus Clay pore water, showed also the dominance of spore-forming bacteria after three months of incubation. Furthermore, a slight decrease in lactate-concentration as well as an increase in ferrous iron and acetate-concentration was observed in the respective B36 microcosms. The presence of substrates and mesophilic incubation temperatures of 25 °C or 30 °C, respectively, promoted the growth of “microbial generalists” that are able to exist in a vegetative state. Extreme environmental conditions as elevated temperatures (60 °C) or high-salt concentrations promote the dominance of highly specialized microorganisms. Our data show, that the microbial diversity in the analyzed bentonites and, furthermore, the evolution of the respective microbial communities differs significantly from each other. Since not that much is known about intrinsic extremophilic microorganisms (metabolic activity and potential influence on the bentonite barrier material), our data stress the importance of further microbial investigations in order to prevent and reduce potential risks (e.g. corrosion, mineralogical changes), due to microbial activity within the repository.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-103 2019
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-29398
Publ.-Id: 29398


Making a cool choice: the materials library of magnetic refrigeration

Gottschall, T.; Skokov, K. P.; Fries, M.; Taubel, A.; Radulov, I.; Scheibel, F.; Benke, D.; Riegg, S.; Gutfleisch, O.

The phase-down scenario of conventional refrigerants used in gas-vapor compressors and the demand for environmentally friendly and efficient cooling makes the search for alternative technologies more important than ever. Magnetic refrigeration utilizing the magnetocaloric effect of magnetic materials could be that alternative. However, there are still several challenges to be overcome before we have devices that are competitive with those based on the conventional gas-vapor technology. In this paper we present a rigorous assessment of the most relevant examples of 14 different magnetocaloric material families and compare them in terms of their adiabatic temperature and isothermal entropy change under cycling in magnetic-field changes of 1 and 2 T, criticality aspects and the amount of heat that they can transfer per cycle. The work is based on magnetic, direct thermometric and calorimetric measurements made under similar conditions and in the same devices. Such a wide-ranging study has not been carried out before. This data sets the basis for more advanced modelling and machine learning approaches in the near future.

Permalink: https://www.hzdr.de/publications/Publ-29397
Publ.-Id: 29397


Multiferroic spin-superfluid and spin-supersolid phases in MnCr2S4

Ruff, A.; Wang, Z.; Zherlitsyn, S.; Wosnitza, J.; Krohns, S.; Krug Von Nidda, H.-A.; Lunkenheimer, P.; Tsurkan, V.; Loidl, A.

Spin supersolids and spin superfluids reveal complex canted spin structures with independent order of longitudinal and transverse spin components. This work addresses the question whether these exotic phases can lead to spin-driven ferroelectricity. Here we report the results of dielectric and pyrocurrent measurements of MnCr2S4 as function of temperature and magnetic field up to 60 T. This sulfide chromium spinel exhibits a Yafet-Kittel type spin structure at low temperatures. As function of external magnetic field, the manganese spins undergo a sequence of ordering patterns of the transverse and longitudinal spin components, which can be mapped onto phases as predicted by lattice-gas models including solid, liquid, super-fluid, and supersolid phases. By detailed dielectric and pyrocurrent measurements, we document a zoo of multiferroic phases with sizable ferroelectric polarization strongly varying from phase to phase. Using lattice-gas terminology, the title compound reveals multiferroic spin-superfluid and spin-supersolid phases, while the antiferromagnetic solid is paraelectric.

Permalink: https://www.hzdr.de/publications/Publ-29396
Publ.-Id: 29396


Biologische Wege zur Rohstoffsicherung – vom Nobelpreis zum Recycling

Lederer, F.

Im Jahr 1985 entwickelte der Wissenschaftler George P. Smith eine Methode zur Identifizierung von kurzen Eiweißbruchstücken, die gezielt und selektiv ein Zielmaterial binden können. Für diese Methode der Evolution im Reagenzglas, welche auf der Verwendung von Bakteriophagen basiert, erhielt er im Jahr 2018 den Chemienobelpreis. Damals half ihm die Methode, Antikörper für bestimmte Krebszellen zu identifizieren. Die Wissenschaftler des Helmholtz-Instituts Freiberg für Ressourcentechnologie nutzen die Phage Surface Display genannte Methode für die Entwicklung hochspezifischer Bioangeln zum seletiven Recycling von Seltenen Erden aus Elektroschrott.

Keywords: Biotechnologie; Phage Surface Display; Bioangeln

  • Lecture (others)
    Lange Nacht der Wissenschaften 2019 in Dresden, 14.06.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29395
Publ.-Id: 29395


Metallgewinnung durch Mikrobiologie – Biologisch assistierte Prozesse in der Rohstofftechnologie

Lederer, F.

Präsentation der Arbeitsbereiche Bioflotation, Biosorption und Biolaugung, die in der Abteilung Biotechnologie des HIF Schwerpunktmäßig untersucht werden. Vorstellung der Nachwuchsgruppe BioKollekt

Keywords: Phage Surface Display; BioKollekt; Bioflotation; Biolaugung; Biosorption

  • Lecture (others)
    Lehrveranstaltung Industrielle Mikrobiologie im Fachbereich Technische Mikrobiologie, 24.06.2019, Senftenberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29394
Publ.-Id: 29394


Fermi surface investigation of the semimetal TaAs2

Butcher, T.; Hornung, J.; Förster, T.; Uhlarz, M.; Klotz, J.; Sheikin, I.; Wosnitza, J.; Kaczorowski, D.

The transversal magnetoresistance associated with the semimetal TaAs2 shows a parabolic field dependence that rises unrestrictedly to 2800 at 14 T and 1.8 K. Here, we report the results of a comprehensive quantum-oscillation study. Angular-dependent de Haas–van Alphen (dHvA) data were obtained with the method of cantilever-torque magnetometry. These were compared with the results of density-functional theory calculations, which predict a Fermi surface with two kinds of electron pockets, as well as two types of hole pockets. Only the electron pockets could be xperimentally verified, whereas no evidence for the hole pockets is present in the measured dHvA frequencies.

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Permalink: https://www.hzdr.de/publications/Publ-29393
Publ.-Id: 29393


Fermi surface studies of the skutterudite superconductors LaPt4Ge12 and PrPt4Ge12

Bergk, B.; Klotz, J.; Förster, T.; Gumeniuk, R.; Leithe-Jasper, A.; Lorenz, V.; Schnelle, W.; Nicklas, M.; Rosner, H.; Grin, Y.; Wosnitza, J.

We report on comprehensive de Haas–van Alphen (dHvA) and electronic band-structure studies of the superconducting skutterudites LaPt4Ge12 (Tc = 8.3 K) and PrPt4Ge12 (Tc = 7.9 K). Both materials show very rich spectra of dHvA oscillations with similar and only slightly varying angular-dependent frequencies. The spectral richness can partly be rationalized by the elaborated electronic band structures resulting in several Fermi surfaces built by six different bands. The effective cyclotron masses of both superconductors lie between about 0.5 and 1.1 times the free-electron mass. Although these values are small, we find moderate mass enhancements between about 2 and 4 when comparing to the calculated masses. Our results evidence the localized character of the 4f electrons in the Pr compound and are in line with an electron-phonon mediated multiband superconductivity, largely identical for both compounds.

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Permalink: https://www.hzdr.de/publications/Publ-29392
Publ.-Id: 29392


Hole compensation effect in III-Mn-V dilute ferromagnetic semiconductors

Xu, C.; Wang, M.; Yuan, Y.; Larkin, G.; Helm, M.; Zhou, S.

A systematic study of hole compensation effect on magnetic properties, which is controlled by defect compensation through ion irradiation, in (Ga,Mn)As, (In,Mn)As and (Ga,Mn)P is represented in this work. In all materials, both Curie temperature and magnetization decrease upon increasing the hole compensation, confirming the description of hole mediated
erromagnetism according to the p -d Zener model. The material dependence of Curie temperature and magnetization versus hole compensation reveals that the manipulation of magnetic properties in III-Mn-V dilute ferromagnetic semiconductors by ion irradiation is strongly influenced by the energy level location of the produced defect relative to the band edges in
emiconductors.

Keywords: dilute ferromagnetic semiconductors; the Curie temperature; magnetization; compensation effect; ion irradiation

Permalink: https://www.hzdr.de/publications/Publ-29391
Publ.-Id: 29391


Presenting Non-Invasive and Fully Acceptable Exploration Technologies - The INFACT Project

Viezzoli, A.; Roffey, S.; Wijns, C.; Fernandez, I.; Blanco Gonzalez, J. M.

Despite its rich history of mining and residual mineral wealth, current conditions within the EU present a number of social, political, legislative, cost, technical and physical obstacles to raw material exploration: obstacles to be overcome by innovation, dialogue, and reform. The Innovative, Non-invasive and Fully Acceptable Exploration Technologies (INFACT) project, within the Horizon 2020 program, will work to mitigate each and every one of these obstacles.
Specific to exploration geophysics, the project will facilitate the development of innovative airborne geophysical and remote sensing technologies (less-invasive than classical exploration methods) that promise to penetrate to new depths, reach new sensitivities and resolve new parameters. The project will also set the EU as a leader on the world stage by establishing permanent infrastructure (reference sites) to drive innovation in the next generation of exploration tools: tools that are cost-effective, designed for EU conditions and its raw materials strategy, and high-performing in terms of minimum environmental impact, social acceptability, and technical performance. These reference sites will provide long-term targets over which successive new technologies can be tested against previous ones.

  • Poster
    2nd Conference on Geophysics for Mineral Exploration and Mining, 09.-12.09.2018, Porto, Portugal
    DOI: 10.3997/2214-4609.201802752

Permalink: https://www.hzdr.de/publications/Publ-29390
Publ.-Id: 29390


Investigations on potential methods for the long-term monitoring of the state of fuel elements in dry storage casks: recent results

Hampel, U.; Wagner, M.; Schmidt, S.; Fiß, D.; Reinicke, S.; Kratzsch, A.

Until a repository is available in deep geological formations, there is a need in Germany for the safe interim storage of spent fuel elements at the power plant sites. It is assumed that considerable periods of more than 50 years will have to be taken into account. Spent fuel elements are stored in Germany in transport and storage casks of the CASTOR type.
A material-scientific question currently being investigated in depth internationally concerns the long-term integrity of the fuel rod cladding tubes during dry storage and thus the safety during transport to the final repository and during secondary packaging. The absorption of hydrogen in the cladding tube during reactor operation leads to the precipitation of hydrides. If the cladding tube temperature increases during reloading or dry storage, a radial reorientation of the hydrides is conceivable due to the tangential stresses caused by the internal rod pressure. This type of hydride arrangement considerably reduces the brittle fracture toughness. A long-term cladding tube failure is conceivable due to a long-term increase in the internal rod pressure (production of gaseous fission products) and a long-term decrease in the cladding tube temperature (reduction of brittle fracture toughness).
Due to the existing uncertainties with regard to the concrete physical processes, the question arises as to the possibility of monitoring the cask contents. Invasive procedures, such as internal probes, are mainly ruled out for reasons of licensing. On the other hand, the massive construction of the containers with a wall thickness of at least 47 cm on all sides limits the spectrum of non-invasive testing and condition monitoring procedures that can be used. Within the DCS-Monitor project, four non-invasive measuring methods are investigated with regard to their suitability for the condition monitoring of the cask inventory by simulations and experiments. For this purpose, damage scenarios of the cask inventory were assumed in a CASTOR V/19, which were identified on the basis of investigations on damage mechanisms. In the following, the recent investigation results of the project are presented.

  • Contribution to proceedings
    3rd Workshop on Safety of Extended Dry Storage of Spent Nuclear Fuel, 05.-07.06.2019, Garching, Deutschland
  • Lecture (Conference)
    3rd Workshop on Safety of Extended Dry Storage of Spent Nuclear Fuel, 05.-07.06.2019, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29389
Publ.-Id: 29389


Role of the hydroxo group in the coordination of citric acid toward trivalent americium

Tamain, C.; Bonato, L.; Aupiais, J.; Dumas, T.; Guillaumont, D.; Barkleit, A.; Berthon, C.; Solari, P. L.; Ikeda-Ohno, A.; Guilbaud, P.; Moisy, P.

The molecular characterization based on multi-technique approach has led to major highlights on revealing the coordination environment of americium (Am) surrounded by citric acid (H3CitH). The structure of the different complexes at pH 1 and 3 are described. These characterizations are made possible by the comparison of the americium-citric acid system with the americium-tricarballylic acid (one analogue of the citric acid without the alpha-hydroxo group). The structural analyses (Vis spectrophotometry, NMR, EXAFS, TRLFS and capillary electrophoresis) were carried out after the establishment of the speciation distribution diagrams so that the complex percentages in solution are known, allowing to take into account the species repartition for structural analysis data treatment. With this combination of means, it was proved for the 1:1 complex that the hydroxo group is counter intuitively deprotonated and coordinated to the Am(III) at pH 1 as well as two carboxylate functions, whereas at pH 3 the hydroxo is not coordinated and stays protonated allowing the three carboxylate functions to coordinate the metallic cation. Therefore, the hydroxo group affects the Am complexation differently depending on the pHs: the complexation is favored by inductive effect at pH 3, and by direct coordination at pH 1.

Keywords: Americium; citric acid; tricarballylic acid; complexation constants; alpha-hydroxycarboxylate; structure; coordination sphere; EXAFS; NMR; capillary electrophoresis; TRLFS; speciation

Permalink: https://www.hzdr.de/publications/Publ-29388
Publ.-Id: 29388


Identification of Prime Factors to Maximize the Photocatalytic Hydrogen Evolution of Covalent Organic Frameworks

Ghosh, S.; Nakada, A.; Springer, M.; Kawaguchi, T.; Suzuki, K.; Kaji, H.; Baburin, I.; Kuc, A. B.; Heine, T.; Suzuki, H.; Abe, R.; Seki, S.

Visible-light-driven hydrogen (H2) production from water is a promising strategy to convert and store solar energy as chemical energy. Covalent organic frameworks (COFs) are front runners among different classes of organic photocatalysts. The photocatalytic activity of COFs depends on numerous factors such as the electronic band gap, crystallinity, surface area, exciton migration, stability of transient species, charge separation and transport, etc. However, it is challenging to fine tune all of these factors simultaneously to enhance the photocatalytic activity. Hence, in this report, an effort has been made to understand the interplay of these factors and identify the key factors for efficient photocatalytic H2 production through a structure−property−activity relationship. Careful molecular engineering allowed us to optimize all of the above plausible factors impacting the overall catalytic activities of a series of isoreticular COFs. The present study determines three prime factors: light absorption, charge carrier generation, and its transport, which influence the photocatalytic H2 production of COFs to a much greater extent than the other factors.

Permalink: https://www.hzdr.de/publications/Publ-29387
Publ.-Id: 29387


Phase Transition Induced Carrier Mass Enhancement in 2D Ruddlesden-Popper Perovskites

Baranowski, M.; Zelewski, S. J.; Kepenekian, M.; Traoré, B.; Urban, J. M.; Surrente, A.; Maude, D. K.; Kuc, A. B.; Booker, E. P.; Stranks, S. D.; Plochocka, P.

The variety of possible ways to tune the optical properties of 2D perovskites is their huge advantage, while at the same time, the mutual dependence between different tuning parameters hinder our fundamental understanding of their properties. In this work, we attempt to address this issue for (CnH2n+1NH3)2PbI4 (with n=4,6,8,10,12) using optical spectroscopy in high magnetic fields up to 67T. Our experimental results, supported by DFT calculations, clearly demonstrate that the reduced mass of the exciton increases by around 30% in the low temperature phase. This is reflected by a 2-3 fold decrease of the diamagnetic coefficient. Our studies shows that the effective mass which is essential parameter for optolectronic device operation can be tuned by the variation of organic spacers and/or moderate cooling achievable using Peltier coolers. Moreover, we show that the complex absorption features visible in absorption/transmission specta track each other in magnetic field providing strong evidence for the phonon related nature of the observed side bands.

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Permalink: https://www.hzdr.de/publications/Publ-29386
Publ.-Id: 29386


Vacancy complexes in nonequilibrium germanium-tin semiconductors

Assali, S.; Elsayed, M.; Nicolas, J.; Liedke, M. O.; Wagner, A.; Butterling, M.; Krause-Rehberg, R.; Moutanabbir, O.

Depth-profiled pulsed low-energy positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy were combined to identify vacancy-related complexes and probe their evolution as a function of Sn content in GeSn epitaxial layers. Regardless of the Sn content in the 6.5-13.0 at.% range, all GeSn samples showed the same depth-dependent increase in the positron annihilation line broadening parameters, relative to that of epitaxial and bulk Ge references thus confirming the formation of open volume defects during growth. The measured average positron lifetimes were found to be the highest (380-395 ps) in the region near the surface and monotonically decrease across the analyzed thickness, but remain above 350 ps. All GeSn layers exhibit average lifetimes that are 20 to 160 ps higher than those recorded for the Ge reference. Surprisingly, these lifetimes were found to decrease as Sn content increases in GeSn layers. These measurements indicate that divacancies are the dominant defect in the as-grown GeSn layers. However, their corresponding lifetime was found to be shorter than in epitaxial Ge thus suggesting that the presence of Sn may alter the structure of divacancies. Additionally, GeSn layers were found to also contain a small fraction of vacancy clusters, which become less important as Sn concentration increases. The interaction and possible pairing between Sn and vacancies have been proposed to explain the reduced formation of larger vacancy clusters in GeSn when Sn content increases.

Keywords: GeSn semiconductor; positron annihilation lifetime spectroscopy; Doppler broadening spectroscopy; vacancy complexes; open volume defects divacancies vacancy clusters

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Permalink: https://www.hzdr.de/publications/Publ-29385
Publ.-Id: 29385


Towards reconfigurable electronics: silicidation of top down fabricated Silicon nanowires

Khan, M. B.; Deb, D.; Kerbusch, J.; Fuchs, F.; Löffler, M.; Banerjee, S.; Mühle, U.; Weber, W. M.; Gemming, S.; Schuster, J.; Erbe, A.; Georgiev, Y.

We present results of our investigations on nickel (Ni) silicidation of top-down fabricated silicon nanowires (SiNWs). Control over the silicidation process is important for the applications of SiNWs in reconfigurable field effect transistors (RFETs). Silicidation is performed using a rapid thermal annealing (RTA) process on the SiNWs fabricated by electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. The effect of variations in crystallographic orientations of SiNWs and different NW designs on the silicidation process is studied. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are done to study Ni diffusion, silicide phases and silicide-silicon interface. Control over the silicide phase is achieved together with atomically sharp interfaces between the silicide and silicon. We find that {111} interfaces are predominantly formed, which are energetically most favorable according to density functional theory calculations. However, control over the silicide length remains a challenge.

Keywords: Schottky junction; field effect transistors; nickel silicide; annealing

Permalink: https://www.hzdr.de/publications/Publ-29384
Publ.-Id: 29384


Tunable large field magnetoconductance of ZnO, ZnMnO, and ZnCoO thin films

Vegesna, S. V.; Bürger, D.; Patra, R. K.; Dellith, J.; Abendroth, B.; Skorupa, I.; Schmidt, O. G.; Schmidt, H.

Magnetoconductivity of ten ZnO, Zn1-x Cox O, and Zn1-x MnxO thin films with nominal concentrations of 2.0 at.% and 0.1 at.% of Co2+ and Mn2+ ions, respectively, has been analyzed in the temperature range from 5 K to 200 K in in-plane and out-of-plane magnetic fields up to 6 T. The formation of a highly conducting surface layer can be controlled during thin film deposition, leading to a large variation of the sheet resistance, namely, from 2 × 103 ω /□ to 1 × 10 5 ω/□ at room temperature. Depending on the thickness of the highly conducting surface layer, a single two-dimensional (2D), a single three-dimensional (3D), or a two-dimensional and three-dimensional (2D + 3D) parallel conducting model was chosen to analyze the measured magnetoconductivity of the magnetic ZnO thin films with different electron spins (S = 5 / 2 for Zn 1 - x Mn x O and S = 3 / 2 for Zn1-x Cox O) and with different Landé g -factors (isotropic for 3D Zn1-x Mnx O and 2D Zn1-x Cox O and anisotropic for 2D Zn1-x Mnx O and 3D Zn1-x Cox O).

Permalink: https://www.hzdr.de/publications/Publ-29383
Publ.-Id: 29383


Fundamentals and Applications of Hybrid LWFA-PWFA

Hidding, B.; Beaton, A.; Boulton, L.; Corde, S.; Doepp, A.; Habib, F. A.; Heinemann, T.; Irman, A.; Karsch, S.; Kirwan, G.; Knetsch, A.; Manahan, G. G.; Martinez De La Ossa, A.; Nutter, A.; Scherkl, P.; Schramm, U.; Ullmann, D.

Fundamental similarities and differences between laser-driven plasma wakefield acceleration (LWFA) and particle-driven plasma wakefield acceleration (PWFA) are discussed.
The complementary features enable the conception and development of novel hybrid plasma accelerators, which allow previously not accessible compact solutions for high quality electron bunch generation and arising applications. Very high energy gains can be realized by electron beam drivers even in single stages because PWFA is practically dephasing-free and not diffraction-limited.
These electron driver beams for PWFA in turn can be produced in compact LWFA stages. In various hybrid approaches, these PWFA systems can be spiked with ionizing laser pulses to realize tunable and high-quality electron sources via optical density downramp injection (also known as plasma torch) or plasma photocathodes (also known as Trojan Horse) and via wakefield-induced injection (also known as WII). These hybrids can act as beam energy, brightness and quality transformers, and partially have built-in stabilizing features. They thus offer compact pathways towards beams with unprecedented emittance and brightness, which may have transformative impact for light sources and photon science applications. Furthermore, they allow the study of PWFA-specific challenges in compact setups in addition to large linac-based facilities, such as fundamental beam–plasma interaction physics, to develop novel diagnostics, and to develop contributions such as ultralow emittance test beams or other building blocks and schemes which support future plasma-based collider concepts.

Keywords: plasma physics; accelerators; electron beams; light sources; photon science

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Permalink: https://www.hzdr.de/publications/Publ-29382
Publ.-Id: 29382


Simulación de una pila PEMFC "air-breathing" utilizando el código OpenFOAM

Weber, N.; Ferreira-Aparicio, P.; Chaparro, A.

The open-source CFD code OpenFOAM is being used to simulate the operation conditions of a proton exchange membrane fuel cell (PEMFC), with an 'air-breathing' cathode. The fuel cell operates with ambient air without additional convective elements. The anode works in dead-end mode using a static H2 pressure of 0.5bar, and with a hydrophilic membrane to allow for the evacuation of liquid water. This mode allows for 100% hydrogen consumption in the electrochemical reaction. This fuel cell type is being developed in CIEMAT and applied to small portable applications where extra weight and volume must be minimised, while maximizing hydrogen utilization. Being originally developed for solid oxide fuel cells, the openFuelCell model is extended to PEMFCs for the first time. It will provide basic knowledge of this special fuel cell configuration, essential characteristics of its performance reflected by the polarization curve, liquid water transport, temperature inhomogeneities, and heat transport.

  • Lecture (Conference)
    Congreso Iberoamericano de Hidrógeno y Pilas de Combustible, 23.10.2019, Madrid, Spanien

Permalink: https://www.hzdr.de/publications/Publ-29381
Publ.-Id: 29381


Which transition metal atoms can be embedded into two-dimensional molybdenum dichalcogenides and add magnetism?

Karthikeyan, J.; Komsa, H.-P.; Batzill, M.; Krasheninnikov, A. V.

As compared to bulk solids, large surface-to-volume ratio of two-dimensional (2D) materials may open new opportunities for post-synthesis introduction of impurities into these systems by, e.g., vapor deposition. However, it does not work for graphene or h-BN, as the dopant atoms prefer clustering on the surface of the material instead of getting integrated into the atomic network. Using extensive first-principles calculations, we show that counterintuitively most transition metal (TM) atoms can be embedded into the atomic network of the pristine molybdenum dichalcogenides (MoDCs) upon atom deposition at moderate temperatures either as interstitials or substitutional im- purities, especially in MoTe2, which has the largest spacing between the host atoms. We further demonstrate that many impurity configurations have localized magnetic moments. By analyzing the trends in energetics and values of the magnetic moments across the periodic table, we rationalize the results through the values of TM atomic radii and the number of (s + d) electrons available for bonding, and suggest the most promising TMs for inducing magnetism in MoDCs. Our results are in line with the available experimental data and should further guide the experimental effort towards a simple post-synthesis doping of 2D MoDCs and adding new functionalities to these materials.

Keywords: 2D materials; electronic structure calcualtions

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Permalink: https://www.hzdr.de/publications/Publ-29380
Publ.-Id: 29380


Analysing tumour growth delay data from animal irradiation experiments with deviations from prescribed dose

Karsch, L.; Beyreuther, E.; Eger Passos, D.; Pawelke, J.; Löck, S.

Abstract: The development of new radiotherapy technologies is a long-term process, which requires proving the general concept although clinical requirements with respect to beam quality and controlled dose delivery may not yet be fulfilled. Exemplarily, the necessary radiobiological experiments with laser-accelerated ion beams are challenged by fluctuating beam intensities. Based on tumour-growth data and dose values obtained in an in-vivo trial comparing the biological efficacy of laser-driven and conventional Linac electrons [2], different statistical approaches for analysis were compared. In addition to the classical averaging per dose point, which excludes animals with high dose deviations, multivariable linear regression, Cox regression and a Monte-Carlo-based approach were tested as alternatives that include all animals in statistical analysis. The four methods were compared based on experimental and simulated data. All applied statistical approaches revealed a comparable radiobiological efficacy of laser-driven and conventional Linac electrons, confirming the experimental conclusion. However, in the simulation study, significant differences in dose-response were observed by all methods except for the conventional method. Thereby, these statistical approaches may allow for reducing the total number of required animals in future pre-clinical trials.

Keywords: pre-clinical studies; statistical analysis; experimental beams; radiotherapy

Permalink: https://www.hzdr.de/publications/Publ-29379
Publ.-Id: 29379


Comparative effect of trivalent lanthanides and actinides on a rat kidney cell line

Heller, A.; Acker, M.; Barkleit, A.; Bok, F.; Wober, J.

Exposure to trivalent lanthanides (Ln) and actinides (An) poses a serious health risk to animals and humans. Since both Lan and An are mainly excreted with the urine, we investigated the effect of La, Ce, Eu, and Yb (as representatives of Ln) as well as Am (as representative of An) exposure on a rat renal cell line (NRK-52E) for 8, 24, and 48 h in vitro. Cell viability studies using the XXT assay and fluorescence microscopic investigations were combined with solubility and speciation studies using ICP-MS and time-resolved laser-induced fluorescence spectroscopy (TRLFS). Thermodynamic modeling was applied to predict the speciation of Ln and Am in cell culture medium.
All Ln show a concentration- and time-dependent effect on NRK-52E cells with Ce being the most potent element. Effective Ln concentrations reducing the cell viability to 50 % (EC50 values) range from 340 µM for Ce to 1.1 mM for Eu. In general, light and heavy Ln seem to exhibit a greater effect than middle Ln.
In cell culture medium with 10 % fetal bovine serum (FBS), the Ln are completely soluble and complexed with proteins from FBS. Ln speciation is time-independent. Comparative experiment with Am are ongoing and will reveal analogies and differences in the effect of trivalent Ln and An on rat kidney cells.
The results of this study underline the importance of combining biological, chemical, and spectroscopic methods in studying the effect of Ln and An on cells in vitro and may contribute to the improvement of the current risk assessment for Ln in the human body. Furthermore, they demonstrate that Ln seem to have no effect on rat renal cells in vitro at environmental trace concentrations. Nevertheless, especially Ce has the potential for harmful effects at elevated concentrations observed in mining and industrial areas.

References:
[1] A. Heller, Ecotox. Environ. Safe. 2019, 173.

  • Lecture (Conference)
    GDCh-Jahrestagung der Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29378
Publ.-Id: 29378


Calculation of neutron fluence distribution in components in the reactor vicinity and their validation on experiments as a basis for activity calculations

Barkleit, A.; Konheiser, J.

Due to the “German Energiewende”, all nuclear power plants (NPPs) in Germany will be shut down by the end of 2022. Consequently, the safe and sustainable decommissioning and dismantling of the NPPs will be an important challenge for the next decades.
The aim of the project EMPRADO (“Entwicklung einer Methode zur Pre-Aktivitäts- und Dosisleistungsberechnung von reaktornahen Bauteilen auf Basis von Neutronen-fluenzverteilungen” – “Development of a method for pre-activity and dose rate calculations of components in the reactor vicinity based on neutron fluence distributions”) is to develop a standardized method to calculate the specific and temporal progression of activation for reactor components and near-reactor concrete as well as construction elements based on the power history of a nuclear reactor. A non-destructive early radiological characterization in the region of the reactor core is thus possible, which is required for an optimal planning of the dismantling. This can make a significant contribution to minimize the radioactive waste and the radiation exposure of personnel during the decommissioning.
The exact 3D neutron fluence calculations are carried out by Monte-Carlo simulations using the international widely used program MCNP6. For validation of the calculation results neutron flux measurements on the basis of activation foils (monitors) are carried out at several German NPPs which are still in operation.
The monitors used in this project are thin metal foils (10 × 10 × 0.1 mm) of Ti, Fe, Ni, Cu, Zn, Nb, Pd, In, and Sn. They are placed during the annual revision of the NPP at different construction elements, for instance near the reactor pressure vessel and at the first concrete wall, the biological shield, at different heights. At these positions the monitors remain during one working cycle of the NPP; that is approximately one year. After recovery, the neutron activation products are analyzed qualitatively and quantitatively by gamma spectroscopy and liquid scintillation counting (LSC). The experimentally determined activities are compared with the calculated ones in order to optimize the simulation procedure.
First experimental results of a feasibility study carried out in NPP Grohnde will be presented and compared to the available literature.

  • Poster
    Jahrestagung der Fachgruppe Nuklearchemie, 25.-27.09.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29377
Publ.-Id: 29377


Curved magnetic thin films: fundamentals and applications

Makarov, D.

Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. We study 3D curved magnetic thin films and nanowires where new fundamental effects emerge from the interplay of the geometry of an object and topology of a magnetic sub-system [1,2]. On the other hand, we explore the application potential of these 3D magnetic architectures for the realization of mechanically shapeable magnetoelectronics [3] for automotive but also virtual and augmented reality appliances [4,5]. The balance between the fundamental and applied inputs stimulates even further the development of new theoretical methods and novel fabrication/characterization techniques [6-8].

[1] R. Streubel et al., Magnetism in curved geometries. J. Phys. D: Appl. Phys. (Review) 49, 363001 (2016).
[2] D. Sander et al., The 2017 magnetism roadmap. J. Phys. D: Appl. Phys. (Review) 50, 363001 (2017).
[3] D. Makarov et al., Shapeable Magnetoelectronics. Appl. Phys. Rev. (Review) 3, 011101 (2016).
[4] G. S. Cañón Bermúdez et al., Magnetosensitive e-skins with directional perception for augmented reality. Science Advances 4, eaao2623 (2018).
[5] G. S. Cañón Bermúdez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).
[6] R. Streubel et al., Retrieving spin textures on curved magnetic thin films with full-field soft X-ray microscopies. Nature Communications 6, 7612 (2015).
[7] T. Kosub et al., All-electric access to the magnetic-field-invariant magnetization of antiferromagnets. Phys. Rev. Lett. 115, 097201 (2015).
[8] T. Kosub et al., Purely antiferromagnetic magnetoelectric random access memory. Nature Communications 8, 13985 (2017).

Keywords: curvilinear magnetism; flexible magnetoelectronics

  • Invited lecture (Conferences)
    Joint European Magnetic Symposia (JEMS), 26.-30.08.2019, Uppsala, Sweden

Permalink: https://www.hzdr.de/publications/Publ-29376
Publ.-Id: 29376


Application of Magnetism on Curved Surfaces

Makarov, D.

Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. We study 3D curved magnetic thin films where new fundamental effects emerge from the interplay of the geometry of an object and topology of a magnetic sub-system. On the other hand, we explore the application potential of these 3D magnetic architectures for the realization of mechanically shapeable magnetoelectronics for automotive but also virtual and augmented reality appliances.

Keywords: flexible magnetoelectronics; virtual reality

  • Invited lecture (Conferences)
    European Forum for Science, Research and Innovation, 24.-25.06.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-29375
Publ.-Id: 29375


A series of tetravalent Pu, Np, U and Th complexes of a salen type ligand

Radoske, T.; Kaden, P.; Walter, O.; Kloditz, R.; Patzschke, M.; Stumpf, T.; März, J.

Fundamental actinide (An) coordination chemistry is still rather scarcely explored though it can provide a deep insight into the bonding situation and bonding trends across the An series. Characteristic of actinides is their huge variety of possible oxidation states, typically ranging from +II to +VII for early An. A suitable approach to explore fundamental physical-chemical properties of actinides is to study series of isostructural An compounds in which the An possesses the same oxidation state. Changes in e.g. the binding situation or magnetic effects among the An series allow insights into their unique electronic properties mainly originating from the 5f-electrons. The tetravalent actinides (An(IV)) are particularly suitable for this kind of systematic studies, as this is the largest accessible series within the early actinides.
Against this background, we performed the current study focusing on a systematic comparison of isostructural An(IV) complexes of Th, U, Np and Pu with a salen type ligand (H2L).
All syntheses and characterizations are conducted under inert, water-free nitrogen atmosphere. SC-XRD results prove that an isostructural complex series was achieved with a molecular unit where two ligands coordinate tetradentately to the An with all oxygen and nitrogen donor atoms. The resulting eightfold coordination environment exhibits a distorted square antiprismatic coordination geometry around the An center. Moreover, the relevant complexes are characterized in solution by NMR spectroscopy displaying characteristic paramagnetic effects according to the unpaired f-electrons. Interestingly, the paramagnetic contributions to the 1H and 13C NMR chemical shifts reach their maximum with [NpL2], and are drastically lower for [PuL2]. The acquired experimental results are further supported by quantum chemical calculations to study the electronic structure of the complexes.

Keywords: tetravalent actinide complexes; coordination chemistry; paramagnetic effects

  • Lecture (Conference)
    49èmes Journées des Actinides, 14.-18.04.2019, Erice, Italy

Permalink: https://www.hzdr.de/publications/Publ-29374
Publ.-Id: 29374


Cerebral Oxygen Metabolism Measurements with MRI in Adults with Sickle Cell Disease: PF742

Vaclavu, L.; Petersen, E.; Mutsaerts, H.; Petr, J.; Majoie, C.; Wood, J.; Vanbavel, E.; Nederveen, A.; Biemond, B.

MRI studies have demonstrated a high prevalence of silent cerebral infarcts (SCI) in both children and adults with sickle cell disease (SCD). SCI are associated with cognitive impairment and lesion progression in adults with SCD. Disrupted oxygen transport can contribute to cerebral ischemic lesions, despite the compensatory elevation in cerebral blood flow (CBF) in SCD. Investigating the cerebral metabolic rate of oxygen (CMRO2) may therefore give insight into the hemodynamic etiology of SCI in SCD patients. We hypothesized that CMRO2 is reduced in adult patients with SCD as a result of chronic anemia and that vasodilation can improve CMRO2 by generating an increase in blood and oxygen flow.

  • Open Access Logo Poster
    24th Annual Congress of the European Hematology Association, 13.06.2019, Amsterdam, The Netherlands
  • Open Access Logo Contribution to proceedings
    24th Annual Congress of the European Hematology Association, 13.06.2019, Amsterdam, The Netherlands
    Hemasphere, 324-325
    DOI: 10.1097/01.HS9.0000561252.50212.c6

Permalink: https://www.hzdr.de/publications/Publ-29373
Publ.-Id: 29373


Using Agile Development Platforms for Continuous Integration, Code Review and Collaboration

Schlegel, F.

The reality of scientific software development is of a more or less agile nature. As such, modern code development platforms such as GitHub or GitLab are a great fit to support this process. With their components (issues, projects, continuous integration, etc.) they match the agile development components, merge request enforce a cross-check for all code changes. While a lot of other development workflows are possible, this talk will present the best practice established for large and small projects at HZDR for using these platforms for software development projects.

  • Lecture (Conference)
    Platform for Advanced Scientific Computing (PASC) Conference 2019, 12.-14.06.2019, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-29372
Publ.-Id: 29372


Synthesis and Reactivity of Tetravalent Actinide Amidinates

Schöne, S.; März, J.; Kaden, P.

A series of tetravalent actinide amidinates was synthesized and characterized in solution and in solid state. Quantum chemical calculations support findings based on bonding analysis. Furthermore the reactivity of the complexes is presented.

  • Lecture (others)
    FENABIUM Projekttreffen März 2019, 27.02.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29371
Publ.-Id: 29371


Enantiopure Tetravalent Actinide Amidinates – Synthesis and Reactivity

Schöne, S.; Kloditz, R.; März, J.; Kaden, P.; Patzschke, M.; Roesky, P. W.; Stumpf, T.

In contrast to the dominant trivalent state for the lanthanide series (Ln(III)), a wide variety of oxidation states (from II to VII) of actinides (An) makes their chemistry intricate but attractive. Especially the early An thorium (Th), uranium (U), neptunium (Np), and plutonium (Pu) form highly charged cations with the oxidation state +IV (An4+), which are of particular interest for coordination chemistry due to their strong interaction with ligands.
The focus of our investigations lies in the comprehensive characterization of An(IV) complexes with ligands bearing soft donor atoms, such as nitrogen (N), both in the solid state and in solution. The present study focuses particularly on the interaction of An(IV) (Th, U, Np) with N-donor ligands of amidinate type, which could be considered as a simplified model of naturally occurring N-donor organic compounds.
Recently, the trivalent lanthanide complexes with the chiral benzamidine, (S,S)-N,N‘-Bis-(1-phenylethyl)-benzamidine ((S)-HPEBA), have been successfully synthesized.[1,2] Mono- and bis-amidinate complexes of the later lanthanides (Er, Yb, Lu) were obtained using a salt metathesis approach. Only for the larger samarium(III) a homoleptic tris-amidinate was accessible.
We have extended this approach to the tetravalent An, and successfully synthesized the first transuranic amidinate complexes. Moreover, we have obtained the first enantiopure amidinate complexes of An(IV) [AnCl((S)-PEBA)3] (An = Th, U, and Np) as well as the analogous Ce(IV) compound, a chemical analog of An(IV). The tris-amidinate complexes have been structurally characterized in solid state and in solution showing a comparable complex geometry.
Due to the presence of a Cl- ligand in the An coordination sphere, it could be speculated that the complex should be reactive. Thus, the reactivity of the complexes has been demonstrated by successful reduction with potassium graphite to homoleptic trivalent actinide amidinates [An((S)-PEBA)3] (An = U, Np).

  • Lecture (Conference)
    Journées des Actinides 2019, 14.-18.04.2019, Erice, Italien

Permalink: https://www.hzdr.de/publications/Publ-29370
Publ.-Id: 29370


Comprehensive real space bonding analysis of tetravalent f-element complexes with Schiff-base ligands

Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.

The contribution of the f-orbitals to chemical bonding leads to the rich chemistry of the actinides. This is in contrast to the lanthanides, where it is known that this contribution is less important. Of special interest is the influence of these orbitals on the bonding character of actinides and lanthanides with organic ligands reflecting natural binding motifs.
This study compares the different bonding behavior of tetravalent actinides and lanthanides with the Schiff base salen (see Fig. 1, left) by means of real-space bonding analysis. Our approach makes use of the quantum theory of atoms in molecules (QTAIM), plots of the non-covalent interactions (NCI) and density differences complemented by natural population analysis (NPA). Especially the local properties at the bond critical points (Fig. 1, right), for instance charge, density, ellipticity and others, can be used to characterize a bond’s order, strength, and covalent contribution. In addition, thermodynamic calculations on the stability of these complexes are presented since the difference in stability is a direct consequence of the different interaction strengths of the f elements.
First results reveal a strong interaction of the actinides, i.e. Th to Pu, with the oxygen of salen characterized by a high electron density concentration between the atoms. In contrast, the interaction between the actinides and the nitrogen of salen is much weaker. The delocalization index, density and Laplacian reveal a significant increase of covalency for Pa to Pu compared to Th and Ce being an indicator of the contribution of the f-electrons. Tetravalent Ce as a lanthanide analogue of Th is expected to show a similar bonding behavior, but, surprisingly, this is not the case for all investigated bonding properties.
Such a detailed analysis of the electronic properties of actinide compounds will help to improve understanding of their behavior in the environment as well as in technical processes and leads to the possibility to predict properties of unknown complexes.

Keywords: Actinides; Quantum chemistry; DFT; Bonding; Covalency

  • Lecture (Conference)
    Journees des Actinides, 14.-18.04.2019, Erice, Italien

Permalink: https://www.hzdr.de/publications/Publ-29369
Publ.-Id: 29369


Hybrid LWFA–PWFA staging as a beam energy and brightness transformer: conceptual design and simulations

Martinez De La Ossa, A.; Assmann, R. W.; Bussmann, M.; Corde, S.; Couperus Cabadağ, J. P.; Debus, A.; Döpp, A.; Ferran Pousa, A.; Gilljohann, M. F.; Heinemann, T.; Hidding, B.; Irman, A.; Karsch, S.; Kononenko, O.; Kurz, T.; Osterhoff, J.; Pausch, R.; Schöbel, S.; Schramm, U.

We present a conceptual design for a hybrid laserdriven plasma wakefield accelerator (LWFA) to beam-driven plasma wakefield accelerator (PWFA). In this set-up, the output beams from an LWFA stage are used as input beams of a new PWFA stage. In the PWFA stage, a new witness beam of largely increased quality can be produced and accelerated to higher energies. The feasibility and the potential of this concept is shown through exemplary particle-in-cell simulations.
In addition, preliminary simulation results for a proof-of-concept experiment in Helmholtz-Zentrum Dresden-Rossendorf (Germany) are shown.

Keywords: laser plasma accelerator; LWFA; PWFA

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-29368
Publ.-Id: 29368


Dynamics of Charges in Superlong Blacklight-Emitting CaB2O4:Ce3+ Persistent Phosphor

Sharma, S. K.; Bettinelli, M.; Carrasco, I.; Beyer, J.; Gloaguen, R.; Heitmann, J.

The optical and persistent luminescence properties of CaB2O4:Ce3+ phosphor are presented. The optical emission for excitation in the 250–340 nm wavelength region is dominated by two bands at 365 and 460 nm. Lifetime measurements suggested that the 365 nm emission band is due to interconfigurational Ce3+ 5d → 4f transitions. Upon excitation with a 254 nm UV lamp, a superlong persistent luminescence in the UVA1 region (340–400 nm, blacklight) was observed, lasting for at least 15 h, and with excellent reproducibility, which is perfectly suitable for phototherapy application. The initial-rise method was applied on the thermoluminescence glow curves to determine the trap distribution and trap depth. The results suggest that one distinct trap, with an activation energy of ∼0.52 eV, was solely responsible for the persistent luminescence in the CaB2O4:Ce3+ phosphor. The other traps had a quasi-continuous distribution, with activation energies between 0.56 and 1.15 eV. The proposed persistent luminescence and the thermoluminescence mechanisms are elucidated using experimental parameters obtained from the optical and thermoluminescence results and the theoretically calculated electronic structure of the Ce3+ ion in CaB2O4. The lowest Ce3+ 5d1 level was found to be ∼0.97 eV below the conduction band, and the persistent luminescence/thermoluminescence emission was dominated by the radiative transitions between Ce3+ energy levels, 5d → 2F5/2,7/2.

Keywords: Rare earth luminescence; long persistence; photoluminescence; thermoluminescence; mechanism

Permalink: https://www.hzdr.de/publications/Publ-29367
Publ.-Id: 29367


Nanoscale modification of one-dimensional single-crystalline cuprous oxide

Das, P.; Raibhar, M. K.; Elliman, R. G.; Möller, W.; Facsko, S.; Chatterjee, S.

In this work we report for the first time a method to modify the surface of Cu2O nanowires in a controllable way and physically weld them into a network form, which contributes to higherelectrical conductivity as well as a strong water-repelling nature. We have used state-of-the-art theoretical calculations to support our experimental observations. We demonstrate how varying the irradiation fluence can modulate the surface and decorate the nanowire with a uniformdistribution of Cu8O nanocrystals due to referential sputtering. While several well studied joining techniques are available for carbon and metal-based nanowires, the same information forceramic nanowires is scarce at present. The current study sheds light into this and a state-of-the art 3D simulation technique predicts most of the modifications including surface modulation, oxygen depletion and welding. The welded network shows higher electrical conductivity than the unwelded assembly. With Cu2O being of p-type the current ion beam joining technique shows a novel path for fabricating p-i-n junctions or solar cell devices through bottom-up approach. Furthermore, we have explored the response of this network to moisture. Our calculation based on density functional theory predicts the hydrophilic nature of individual copper oxide nanowires both before and after irradiation. However, the network shows a strong water-repelling nature, which has been explained quantitatively using the Cassie–Baxter model.

Keywords: copper oxide; superhydrophobic; ion irradiation; nanowire; welding

Permalink: https://www.hzdr.de/publications/Publ-29366
Publ.-Id: 29366


Ab initio path integral Monte Carlo approach to the static and dynamic density response of the uniform electron gas

Groth, S.; Dornheim, T.; Vorberger, J.

In a recent Letter [T. Dornheim et al., Phys. Rev. Lett. 121, 255001 (2018)] we have presented ab initio results for the dynamic structure factor S(q,ω) of the uniform electron gas for conditions ranging from the warm dense matter regime to the strongly correlated electron liquid. This was achieved on the basis of exact path integral Monte Carlo data by stochastically sampling the dynamic local field correction G(q,ω). In this paper we introduce in detail this reconstruction method and provide several practical demonstrations. Moreover, we thoroughly investigate the associated imaginary-time density-density correlation function F(q,τ). The latter also gives us access to the static density-response function χ(q) and static local field correction G(q), which are compared to standard dielectric theories like the widespread random phase approximation. In addition, we study the high-frequency limit of G(q,ω) and provide extensive results for the dynamic structure factor for different densities and temperatures. Finally, we discuss the implications of our findings for warm dense matter research and the interpretation of experiments.

Keywords: electron gas; warm dense matter; response function; structure factor; local field correction; quantum Monte Carlo

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Permalink: https://www.hzdr.de/publications/Publ-29365
Publ.-Id: 29365


Investigations of the interactions of a Halobacterium isolate with uranium using different microscopic and spectroscopic methods

Hilpmann, S.; Bader, M.; Bachran, M.; Steudtner, R.; Schmidt, M.; Stumpf, T.; Cherkouk, A.

Rock salt formations can serve as potential host rocks for the long-term storage of high-level radioactive waste in a deep geological repository. Haloarchaea are widespread under these highly saline conditions. However, there exists a lack of knowledge about the interactions of these microorganisms with radionuclides especially concerning the chemical speciation. Therefore, the interactions of an extremely halophilic archaeon, Halobacterium sp. GP5 1-1 with uranium, one of the major radionuclides of concern, were investigated in detail. This haloarchaeon was isolated from a German rock salt sample. Different microscopic and spectroscopic techniques were used to get an overall image of the occurring processes on a molecular level.
Time-dependent association experiments with two different U(VI) concentrations were performed, to investigate the interaction kinetics of U(VI) with the cells of the haloarchaeon. The amount of bioassociated U(VI) increased with the incubation time at both concentrations. However, the association process at the lower concentration (10 µM) was much faster than at the higher U(VI) concentration (30 µM). Overall, the association process is not exclusively biosorption, being a passive process and normally finished after a short time of incubation (0 – 2 h) [1].
Scanning electron microscopy coupled with energy-dispersive X-ray absorption spectroscopy indicates different interaction mechanisms of the cells at different U(VI) concentrations. It was found that at a concentration of 10µM U(VI) preferentially biomineralization takes place, whereas biofilm-like structures are formed at a concentration of 30µM.
With the help of time-resolved laser-induced luminescence spectroscopy, different aqueous U(VI) species could be extracted from the supernatant. These species differ slightly in dependence of the U(VI) concentration. In general, the formation of a uranyl-carbonate-complex was observed. This could be the result of microbial released CO2 during the process. In contrast to the higher U(VI) concentration, a phosphate species was formed at a U(VI) concentration of 10 µM.
These findings offer new insights into the microbe-actinide interactions at highly saline conditions relevant to high-level radioactive waste disposal in rock salt formations.

[1] J. R. Lloyd, L. E. Macaskie (2002) in “Interactions of Microorganisms with Radionuclides” (Eds.: M.J. Keith-Roach, F. R. Livens), Elsevier, pp. 313-381

  • Poster
    Jahrestagung der Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29364
Publ.-Id: 29364


Selective leaching of rare earth elements (REEs) from eudialyte concentrate after sulfation and thermal decomposition of non-REE sulfates

Balinski, A.; Atanasova, P.; Wiche, O.; Kelly, N.; Reuter, M.; Scharf, C.

Eudialyte, a sodium rich zirconosilicate, is one of the promising sources for REEs, particularly for HREEs+Y. The key challenge by hydrometallurgical processing is the prevention of silica gel formation and REE separation from resulting multi-element leach solutions. This study deals with the selective leaching of REEs from eudialyte concentrate after sulfation and thermal decomposition of non-REE sulfates. We demonstrate how to select the parameters in each process stage to achieve high yields of REEs and to separate them from Zr⁴⁺(+Hf⁴⁺), Nb⁵⁺, Al³⁺ and Fe³⁺. The best result in terms of the separation and the REE yield was achieved with the following parameters: acid addition: 15 mmol/g; roasting temperature: 750 °C; roasting time: 2 h; pulp density: 25 kg/m³; leaching temperature: 20 °C; leaching time: 24 h; stirring speed: 300 rpm. For sufficient conversion of REEs into sulfates H₂SO₄ was added in excess, approximately twice as high as the acid consumption. Water leaching at high solid/liquid ratios caused decrease in the separation factor and REE losses resulting from formation of double sulfates and gypsum.

Keywords: eudialyte concentrate; rare earth elements; separation; sulfation; selective roasting; thermal stability of sulfates; leaching; silica stability during leaching

Permalink: https://www.hzdr.de/publications/Publ-29363
Publ.-Id: 29363


Effective Hexagonal Boron Nitride Passivation of Few-Layered InSe and GaSe to Enhance Their Electronic and Optical Properties

Arora, H.; Jung, Y.; Venanzi, T.; Watanabe, K.; Taniguchi, T.; Schneider, H.; Hone, J.; Helm, M.; Erbe, A.; Hübner, R.

Indium selenide (InSe) and gallium selenide (GaSe), members of the III–VI chalcogenide family, are emerging two-dimensional (2D) semiconductors with appealing electronic properties. However, their devices are still lagging behind because of their sensitivity to air and device fabrication processes which induce structural damage and hamper their intrinsic properties. Thus, in order to obtain high-performance and stable devices, effective passivation of these air-sensitive materials is strongly required. Here, we demonstrate a hexagonal boron nitride (hBN)-based encapsulation technique, where 2D layers of InSe and GaSe are covered entirely between two layers of hBN. To fabricate devices out of fully encapsulated 2D layers, we employ the lithography-free via-contacting scheme. We find that hBN acts as an excellent encapsulant and a near-ideal substrate for InSe and GaSe by passivating them from the environment and isolating them from the charge disorder at the SiO2 surface. As a result, the encapsulated InSe devices are of high quality and ambient-stable for a long time and show an improved two-terminal mobility of 30–120 cm2 V–1 s–1 as compared to mere ∼1 cm2 V–1 s–1 for unencapsulated devices. On employing this technique to GaSe, we obtain a strong and reproducible photoresponse. In contrast to previous studies, where either good performance or long-term stability was achieved, we demonstrate a combination of both in our devices. This work thus provides a systematic study of fully encapsulated devices based on InSe and GaSe, which has not been reported until now. We believe that this technique can open ways for fundamental studies as well as toward the integration of these materials in technological applications.

Keywords: indium selenide; gallium selenide; hexagonal boron nitride; encapsulation; photoluminescence; stable electronics; field-effect transistors; photodetectors

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  • Secondary publication expected from 25.10.2020

Permalink: https://www.hzdr.de/publications/Publ-29362
Publ.-Id: 29362


Interlayer Exciton Transport Modulated by Twist-Angle-Dependent Moiré Potentials in WS2-WSe2 Heterobilayers

Yuan, L.; Zheng, B.; Kunstmann, J.; Brumme, T.; Kuc, A. B.; Ma, C.; Deng, S.; Blach, D.; Pan, A.; Huang, L.

The nanoscale periodic potentials introduced by moiré patterns in semiconducting van der Waals heterostructures provide a new platform for designing exciton superlattices. T o realize these applications, a thorough understanding of the localization and delocalization of interlayer excitons in the moiré potentials is necessary. Here, we investigated interlayer exciton dynamics and transport modulated by the moiré potentials in WS2- WSe2 heterobilayers using experiments and theory. Experimental results verified the theoretical prediction of energetically favorable K-Q interlayer excitons and unraveled exciton-population dynamics that was controlled by the twist-angle-dependent energy difference between the K-Q and K-K excitons. Spatially- and temporally-resolved exciton- population imaging visualized exciton localization by twist-angle-dependent moiré potentials of ~100 meV and exciton delocalization by strong many-body interactions at densities >1012 cm-2.
The studied heterobilayers have two stacking orientations with twist angles of 𝜃 = 0° and 60°, which are energetically favorable in the modified two-step CVD growth. Both structures have type-II band aligment, resulting in the formation of spatially- indirect interlayer charge-transfer excitons, with electrons and holes residing in the WS2 and WSe2 layers, respectively. The lowest-energy transition is always K-Q and therefore K-Q interlayer excitons are expected to represent the ground state instead of the more commonly discussed K-K excitons. The spatial variations of the moiré potential for 0° are much stronger (deep potential)than for 60° (shallow potential). Thus, two predictionscan be made based on the DFT calculations: (i) the population dynamics of the K-K and K-Q excitons should be affected by the twist-angle-dependent energy difference between the two transitions; and (ii) the twist-angle- dependent moiré potentials should lead to different degrees of localization of the interlayer excitons in both systems. The validation of both predictions will be discussed in this presentation
The localization and delocalization of the interlayer excitons presented here have important implications for the potential applications of heterostructures; for long-range transport, more delocalized interlayer excitons are preferred and, therefore, deep moiré potentials should be avoided. On the other hand, for applications, such as, quantum emitters, deep moiré potential should be preferred, to localize excitons. We also stress that K-Q interlayer excitons are the ground state instead of the commonly assumed K-K excitons and should be considered when discussing interlayer excitons in the WS2-WSe2 systems.

  • Invited lecture (Conferences)
    XX Brazilian Symposium on Theoretical Chemistry, 10.-14.11.2019, Joao Pessoa, Brazil

Permalink: https://www.hzdr.de/publications/Publ-29361
Publ.-Id: 29361


Relation between topology and electronic structure of 2D polymers

Springer, M.; Kuc, A.; Heine, T.

New 2D materials open access to a whole new world of compounds and properties. Graphene monolayer is such a material, since it has special electron transport features due to its honeycomb topology. Apart from the honeycomb net, there are many more topologies, which promise a manifold of new properties, e.g. the kagomé or the Lieb lattice. As recently shown in the case of the kagomé net, 2D polymers (covalent organic frameworks) can be designed in a way, that their geometric and electronic structures match the desired topology.[1] Other nets, e.g. the Lieb lattice, can at the moment only be realized as optical lattices or via adsorption of molecules on a surface.[2]
In this project, we want to work out the relation between topology and electronic properties. For this purpose, we employ a tight-binding model. In Fig. 1, exemplary results for the aforementioned kagomé and Lieb lattices are shown. Based on these findings, we want to propose new 2D polymers with the desired structures and new properties using density- functional theory.
[1] Y. Jing, T. Heine, J. Am. Chem. Soc. 141, 2, 743 (2019)
[2] S. Mukherjee et al., Phys. Rev. Lett. 114, 245504 (2015); S. Taie et al., Sci. Adv. 1, e1500854 (2015); M. R. Slot et al., Nat. Phys. 13, 672 (2017)

  • Poster
    Flatlands Beyond Graphene 2019, Toulouse, 02.-06.09.2019, Toulouse, France
  • Poster
    European Conference On Chemistry Of Two-Dimensional Materials, 03.-06.09.2019, Dresden, Deutschland
  • Poster
    55th Symposium on Theoretical Chemistry, 22.-26.09.2019, Rostock, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29360
Publ.-Id: 29360


The clinically used PET radiopaharmaceutical s-(-)[18F]fluspidine offers potential for brain tumor imaging

Toussaint, M.; Kranz, M.; Deuther-Conrad, W.; Patt, M.; Wünsch, B.; Sabri, O.; Brust, P.

Overexpression of the sigma-1 receptor (S1R) in various cancers correlates with tumor grade, and drug binding decreases the proliferation of human glioblastoma cell lines. Thus, S1R characterization in glioblastoma could help to better understand its pathophysiology and improve diagnosis or treatment follow-up. Therefore, we aim to evaluate the potential of (S)-(−)-[18F]fluspidine, a highly specific S1R radioligand already applied in clinical studies, to characterize S1R expression in an orthotopic glioblastoma model in mouse with small-animal PET/MRI.
Female nude mice (24-30 g, 8 weeks old) underwent a stereotactic xenograft of U87 cells in the striatum. Healthy female nude mice (25-30 g) were used as control group.
(S)-(-)-[18F]fluspidine (5.6±2.5 MBq; Am: 140±50 GBq/µmol, EOS) was injected intravenously followed by 60 min dynamic PET scans (Mediso nanoScan®). 17 scans were performed and time-activity curves (TAC) from the tumor and the contralateral region were analyzed (PMOD v3.9).
TACs show a comparable profile for healthy mice and the contralateral tumor side. Lower initial uptake values and higher uptake values at the end of the scan were observed in the tumor compared to the contralateral side. Accordingly, the peak-to-end ratio of the tumor region is significantly different from the ratio of the contralateral region (1.65±0.49 vs. 2.19±0.59, p=0.0015)
The PET investigation revealed a significant difference in the pharmacokinetics of (S)-(-)-[18F]fluspidine between the tumor and the contralateral region, probably related to different S1R availability. These first results show the suitability of (S)-(-)-[18F]fluspidine for characterization of U87 S1R status in mice offering hints for brain tumor imaging in human.

Keywords: Sigma 1 receptor; glioblastoma; s-(-)-[18F]fluspidine; PET

  • Invited lecture (Conferences)
    2nd European Symposium on Physiopathology of sigma-1 receptors, 31.05.-02.06.2019, Latvian Institute of Organic Synthesis, Riga, Latvia

Permalink: https://www.hzdr.de/publications/Publ-29359
Publ.-Id: 29359


The Relevance of the Signal Integrator Lamellipodin for the Radiation Resistance and Invasiveness of Glioblastoma Cells

Moritz, S.; Cordes, N.; Krause, M.; Vehlow, A.

Fragestellung: Die Prognose von Patienten mit einem Glioblastom (GBM) ist trotz eines multimodalen Therapieansatzes schlecht, weshalb die zugrunde liegenden molekularen Resistenzmechanismen besser aufgeklärt werden müssen. Interaktionen von GBM-Zellen mit zellulären und nicht-zellulären Faktoren im Tumormikromilieu tragen dabei entscheidend zu Invasion und Therapieresistenz von GBM-Zellen bei. Die Kommunikation zwischen Zellen und dem Tumormikromilieu wird unter anderem vom Signaladapterprotein Lamellipodin (Lpd), dessen Funktion in GBM-Zellen unklar ist, vermittelt. In der vorliegenden Studie evaluieren wir die Rolle von Lpd für die GBM Invasion und Radioresistenz und charakterisieren den basierenden molekularen Mechanismus.
Methodik: Lpd Expression und Phosphorylierungsstatus (Y426, Y1226) wurden in acht GBM-Zelllinien vor und zu verschiedenen Zeitpunkten (0,5 24 h) nach Bestrahlung mit 6 Gy mittels Western Blot Analysen evaluiert. Die Quantifizierung der dreidimensionalen Kollagen Typ-1-abhängigen Invasion, des klonogenen Überlebens (2, 4, 6 Gy) und residualer DNA-Doppelstrangbrüche (6 Gy) erfolgte nach siRNA-vermittelten Lpd Knockdown. Direkte Lpd Interaktionspartner wurden mit Massenspektrometrie von Lpd Immunpräzipitaten nach Röntgenbestrahlung bestimmt und durch Datenbankanalysen ausgewertet (Reactome, Gene Ontology).
Ergebnis: Western Blot Analysen ergaben eine Zelllinien-abhängige basale Lpd Expression und Phosphorylierung. Eine Bestrahlung mit 6 Gy Röntgen führte zu einem Anstieg in der Lpd Phosphorylierung Y1226 nach 1 h bis 24 h, wohingegen die Lpd Expression unverändert blieb. Lpd Knockdown reduzierte in allen getesteten GBM Zelllinien die Invasionskapazität und führte zu einer signifikanten Strahlensensibilisierung in vier von acht GBM-Zelllinien. Dieser Effekt ging mit einer erhöhten Anzahl von γH2AX/53BP1-positiven residualen DNA-Doppelstrangbrüchen nach Lpd Depletion und Bestrahlung in den responsiven Zelllinien einher. Die massenspektrometrische Analyse der Lpd Immunpräzipitate ergab 56 potentielle Lpd Interaktionspartner, welche in den vesikulären Transport, Metabolismus und Signaltransduktion involviert sind.
Schlussfolgerung: Die Ergebnisse verdeutlichen eine zentrale Funktion von Lpd bei der Invasion und Radioresistenz von Glioblastomen. Nachfolgende Untersuchungen konzentrieren sich auf die Charakterisierung des zugrunde liegenden molekularen Signalweges.

  • Abstract in refereed journal
    Strahlentherapie und Onkologie 195(2019), S166-S166

Permalink: https://www.hzdr.de/publications/Publ-29358
Publ.-Id: 29358


Tetranuclear Cu(II)-chiral complexes: Synthesis, characterization and biological activity

Peewasan, K.; Merkel, M. P.; Zarschler, K.; Stephan, H.; Anson, C. E.; Powell, A. K.

Tetranuclear chiral Cu(II)-Schiff-base complexes S-1 and R-1, were synthesised using enantiomerically pure (S)-H2L and (R)-H2L ligand respectively in the ratio of 1:1 of Cu(NO3)2 to (S/R)-H2L in MeOH at room temperature. A pair of polynuclear chiral Cu(II)-cluster complexes were characterized using single-crystal X-ray diffraction, elemental analysis, infrared and CD spectroscopy. The results revealed the importance of these chiral ligands encouraging the arrangement of copper metal in non-centrosymmetric polar packing. The potential of the novel Cu(II)-H2L complexes as biologically active compounds was assessed in particular regarding their anti-proliferative and anti-microbial properties.

Keywords: Metal-based drugs; Polynuclear Cu(II)-cluster; Enantiomerically pure Schiff-base ligand; Cell viability; Single-crystal X-ray diffraction

Permalink: https://www.hzdr.de/publications/Publ-29357
Publ.-Id: 29357


Bakterien als Alleskönner

Lederer, F.

Bakterien sind Lebewesen, die unser tägliches Leben ganz entscheidend prägen. Ob Käse, Sauerkraut oder Wein - viele Delikatessen werden für uns durch diese kleinen Alleskönner produziert. Obwohl Bakterien häufig als Krankheitserreger verschrien sind, sind viele von ihnen wichtige Unterstützer unserer Gesundheit - was wir oft erst dann merken, wenn sie weg sind. Eine gesunde Darmflora aus Millionen von Bakterien ist entscheidend für die Produktion und Aufnahme vieler Vitamine in unserem Körper und für unser körperliches Wohlbefinden.
Auch in der Forschung werden Bakterien mit ihren vielen Eigenschaften gerne eingesetzt. Am Helmholtz-Zentrum Dresden-Rossendorf studiert man unter anderem ihre Fähigkeiten, sich fehlende Metalle aus der Umgebung zu besorgen und nutzt diese mikrobiellen Komplexbildner zur Rohstoffrückgewinnung aus Industrieabwässern.
Der Vortrag wird Bakterien als Alleskönner aus verschiednen Perspektiven beleuchten.

Keywords: Bakterien

  • Lecture (others)
    Seniorenakademie, 11.4.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29356
Publ.-Id: 29356


Gezieltes selektives Herauslösen von Substanzen aus Roh- und Reststoffen mit biologisch basierten Aufbereitungstechnologien

Lederer, F.

Gast-Vorlesung an der BTU Cottbus-Senftenberg in der Fakultät Umweltwissenschaften und Verfahrenstechnik im Modul "Stoffliche Nutzung nachwachsender Rohstoffe"

Keywords: Mikrobiologie; Phage Surface Display

  • Lecture (others)
    Vorlesung im Modul "Stoffliche Nutzung nachwachsender Rohstoffe", 17.01.2019, Cottbus, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29355
Publ.-Id: 29355


Ultrafast X-ray tomography raw-data of bubbly two-phase pipe flow around a ring-shaped constriction

Neumann-Kipping, M.; Hampel, U.

For the investigation of bubbly two-phase flow, which should serve as a future benchmark experiment for CFD code validation, an experimental study has been conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) using ultrafast electron beam X-ray tomography (UFXRAY). In this study, flow constrictions were installed into a pipe to create a generic three-dimensional flow field as an advanced test case for CFD codes. UFXRAY provide valueable data of the gas phase dynamics with high temporal and spatial resolution.

The provided data set contains tomography raw-data for the experimental series L30 that uses a ring shaped flow constriction with a blockage ratio of 0.5. 

For visualization, the data might be opend with Fiji. Therefore choose Import->Raw... In the following window specify "Image type" as 16-bit Unsigned, "Width" as 288 pixels and "Height" as 500 pixels for 2x1000Hz measurement or 200 pixels for 2x2500Hz measurement. Make sure that "Little-endian byte order" is checked. A data set contains image frames of both scanning planes in alternating order. Therefore, if only a single scanning plane is required, the offset and gap parameters need to be set to 288000 bytes for 2x1000Hz measurement or 115200 bytes for 2x2500Hz measurement.

Keywords: ultrafast X-ray computed tomography; bubbly two-phase flow; three-dimensional flow field; two-phase pipe flow

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-06-18
    DOI: 10.14278/rodare.124
    License: CC-BY-NC-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-29354
Publ.-Id: 29354


Ultrafast X-ray tomography raw-data of bubbly two-phase pipe flow around a semi-circular constriction

Neumann-Kipping, M.; Hampel, U.

For the investigation of bubbly two-phase flow, which should serve as a future benchmark experiment for CFD code validation, an experimental study has been conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) using ultrafast electron beam X-ray tomography (UFXRAY). In this study, flow constrictions were installed into a pipe to create a generic three-dimensional flow field as an advanced test case for CFD codes. UFXRAY provide valueable data of the gas phase dynamics with high temporal and spatial resolution.

The provided data set contains tomography raw-data for the experimental series L30 that uses a semi-circular flow constriction with a blockage ratio of 0.5. 

For visualization, the data might be opend with Fiji. Therefore choose Import->Raw... In the following window specify "Image type" as 16-bit Unsigned, "Width" as 288 pixels and "Height" as 500 pixels for 2x1000Hz measurement or 200 pixels for 2x2500Hz measurement. Make sure that "Little-endian byte order" is checked. A data set contains image frames of both scanning planes in alternating order. Therefore, if only a single scanning plane is required, the offset and gap parameters need to be set to 288000 bytes for 2x1000Hz measurement or 115200 bytes for 2x2500Hz measurement.

Keywords: ultrafast X-ray computed tomography; bubbly two-phase flow; three-dimensional flow field; two-phase pipe flow

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-06-26
    DOI: 10.14278/rodare.122
    License: CC-BY-NC-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-29353
Publ.-Id: 29353


Use of activated products as radiotracers for the development of environmental technologies

Jentsch, T.

Preserving the environment is essential for maintaining the quality of life on our planet. For this reason, efforts are being made in the world, and especially in Germany, to develop environmentally friendly and resource-saving production technologies.
This article uses two selected examples to show how activation products can be used as radiotracers for the development and optimization of such environmental technologies. The first example reports the use of Cu-64 and Zn-69 m for the investigation of heavy metal release during municipal solid waste incineration. The second one presents the use of Ar-41 for measuring the residence time distributions of gaseous phase in a reactor for the partial oxidation of hydrocarbon-containing fluids (gases, liquids, slurries) under high pressures.
Both examples show why only radionuclides obtained by neutron activation in a research reactor could solve the problems presented in this article.

Keywords: Cu-64; Zn-69m; Ar-41; radiotracer; environmental technologies; heavy metal release; municipal solid waste incineration; high pressure partial oxidation; industrial application of activation products

  • Open Access Logo Invited lecture (Conferences)
    15th International Conference on Modern Trends in Activation Analysis (MTAA-15), 17.-22.11.2019, Mumbai, India

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Permalink: https://www.hzdr.de/publications/Publ-29352
Publ.-Id: 29352


Scalable, Data Driven Plasma Simulations with PIConGPU

Huebl, A.; Widera, R.; Garten, M.; Pausch, R.; Steiniger, K.; Bastrakov, S.; Meyer, F.; Bastrakova, K.; Debus, A.; Kluge, T.; Ehrig, S.; Werner, M.; Worpitz, B.; Matthes, A.; Rudat, S.; Starke, S.; Bussmann, M.

PIConGPU is an open source, multi-platform particle-in-cell code scaling to the fastest supercomputers in the TOP500 list. We present the architecture, novel developments, and workflows that enable high-precision, fast turn-around computations on Exascale-machines. Furthermore, we present our strategies to handle extreme data flows from thousands of GPUs for analysis with in situ processing and open data formats (openPMD). PIConGPU is since recently furthermore natively controlled by a Python Jupyter interface and we research just-in-time kernel generation for C++ with our Cling-CUDA extensions.

Keywords: LPA; laser-plasma; particle-in-cell; HPC; manycore; GPU; simulation; interactive; big data

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-06-13
    DOI: 10.14278/rodare.130
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-29351
Publ.-Id: 29351


Scalable, Data Driven Plasma Simulations with PIConGPU

Huebl, A.; Widera, R.; Garten, M.; Pausch, R.; Steiniger, K.; Bastrakov, S.; Meyer, F.; Bastrakova, K.; Debus, A.; Kluge, T.; Ehrig, S.; Werner, M.; Worpitz, B.; Matthes, A.; Rudat, S.; Starke, S.; Bussmann, M.

PIConGPU is an open source, multi-platform particle-in-cell code scaling to the fastest supercomputers in the TOP500 list. We present the architecture, novel developments, and workflows that enable high-precision, fast turn-around computations on Exascale-machines. Furthermore, we present our strategies to handle extreme data flows from thousands of GPUs for analysis with in situ processing and open data formats (openPMD). PIConGPU is since recently furthermore natively controlled by a Python Jupyter interface and we research just-in-time kernel generation for C++ with our Cling-CUDA extensions.

Keywords: LPA; laser-plasma; particle-in-cell; HPC; manycore; GPU; simulation; interactive; big data

Related publications

  • Invited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference (PASC19), 12.-14.06.2019, Zürich, Schweiz
    DOI: 10.14278/rodare.131

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Permalink: https://www.hzdr.de/publications/Publ-29350
Publ.-Id: 29350


AMS measurements of cosmogenic nuclide concentrations resolve mountain landscape evolution and the glacial history in the Pamir, Central Asia

Stübner, K.; Bookhagen, B.; Merchel, S.; Rugel, G.; Lachner, J.

Secondary cosmic rays interact with terrestrial materials in the atmosphere and near the Earth's surface to produce cosmogenic radionuclides. The production and accumulation of cosmogenic ¹⁰Be and ²⁶Al in quartz allows geologists to investigate processes of landscape evolution such as erosion, landsliding, sediment transport and deposition on time scales of thousands to few millions of years. The Pamir mountains at the western end of the India-Asia collision zone have been in the focus of geologic research since the early 2000s. While the tectonic evolution of the Pamir is increasingly well understood, the drivers of Pamir landscape evolution remain elusive. The western Pamir is characterized by an extreme topographic relief with summit and valley elevations of 6-7 km and 2-3 km, respectively; the eastern Pamir is a low-relief plateau at ~4 km. This contrast may be attributed to higher precipitation in the western Pamir driving faster river incision and erosion compared to the arid east. Alternatively, the relief may be controlled by spatially variable, tectonically forced surface uplift. Field observations suggest that Pleistocene glaciation of the Pamir was much more extensive than modern glaciation, and that glaciation had a significant impact on the evolution of the Pamir landscape.

We use cosmogenic ¹⁰Be and ²⁶Al concentrations in moraine boulders, glacially polished bedrock and glacio-alluvial sediment deposits to determine the timing and extent of past glacial stages with the goal to better understand what controls landscape evolution in the Pamir. Our results indicate that early Holocene (~10 ka) glaciation was more extensive than previously thought, and that at that time the western Pamir was much more strongly glaciated than the east. The most widespread glaciation occurred at ≥200 ka covering most of the western Pamir and possibly also much of the east Pamir plateau. These results strengthen our hypothesis that the glacial history of the Pamir had a significant impact on its landscape evolution.

Keywords: AMS; tectonics; geomophology

  • Lecture (Conference)
    Heavy Ion Accelerator Symposium on Fundamental and Applied Science (HIAS), 09.-13.09.2019, Canberra, Australia

Permalink: https://www.hzdr.de/publications/Publ-29349
Publ.-Id: 29349


Mass transport induced asymmetry in charge/discharge behavior of liquid metal batteries

Personnettaz, P.; Landgraf, S.; Nimtz, M.; Weber, N.; Weier, T.

Mass and charge transport in liquid metal batteries are closely intertwined because of the fully liquid interior of the cells. We found that charging and discharging cycles may show pronounced asymmetries. They are caused by the presence (charge) or absence (discharge) of solutal convection. While the direction of thermal gradients in the positive electrode of a liquid metal battery depend on boundary conditions and thermodynamics in a non-trivial manner, the solutal gradient predictably changes direction from charge to discharge. The unstable density distribution during charge drives a flow strong enough to prevent any concentration polarization. In contrast, during discharge, the stable density gradient suppresses convection and leads to a substantial mass transport overvoltage. We illustrate this scenario by experimental data, numerical simulations and a physical model.

Keywords: electrorefining; liquid electrode; liquid metal batteries; mass transport; overvoltage; solutal convection

Permalink: https://www.hzdr.de/publications/Publ-29348
Publ.-Id: 29348


Round Robin: Composition And Thickness of Nitride and Oxide Thin Films Grown by Atomic Layer Deposition

Julin, J.; Sajavaara, T.

A round robin characterization of the elemental composition and thickness of Al₂O₃ and TiN thin films using IBA methods was organized. The samples were grown by atomic layer deposition (ALD) on 200 mm Si wafers. The Al₂O₃ films with different thicknesses (10–100 nm) were deposited using Al(CH₃)₃ and water as precursors at low temperatures, known to produce films with high impurity concentrations and non-stoichiometric O/Al ratio. The TiN films, sandwiched between thinner ALD-Al₂O₃ films, were grown using TiCl₄ and NH₃ precursors. The samples were chosen to represent a typical thin film analysis problem with real-world applications.

The participating institutes were mainly using heavy ion elastic recoil detection analysis (HI-ERDA) as a single measurement technique capable of providing all the requested information. Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA) were employed as multi-technique complementary analysis (so called Total-IBA) or to give partial results. In addition, X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were employed as complementary techniques.

The main goal of this study was not to promote the HI-ERDA technique but to identify the possible weaknesses and limitations of different analysis techniques and approaches, and thereafter improve the accuracy and reliability of the results given by the ion beam analysis community. A special emphasis was put on transparency of the results obtained – all the raw measurement data are publicly available for e.g. comparison and educational use via open data portal.

  • Lecture (Conference)
    IBA2019 - 24th International conference on Ion Beam Analysis, 13.-18.10.2019, Antibes, France

Permalink: https://www.hzdr.de/publications/Publ-29347
Publ.-Id: 29347


Heavy ion irradiation damage in Zr2AlC MAX phase

Qarra, H. H.; Knowles, K. M.; Vickers, M. E.; Akhmadaliev, S.; Lambrinou, K.

Zr2AlC MAX phase-based ceramic material with 33 wt% ZrC has been irradiated with 22 MeV Au7+ ions between room temperature and 600 °C, achieving a maximum nominal midrange dose of 3.5 displacements per atom. The response of the material to irradiation has been studied using scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Under room temperature irradiation, the ions caused a partial amorphisation of the MAX phase. At high temperatures, irradiated Zr2AlC remained crystalline, but developed an increased density of dislocations and stacking faults in the (0001) basal planes. The irradiated material also exhibited a temperature-dependent microcracking phenomenon similar to that previously reported in other MAX phase materials.

Permalink: https://www.hzdr.de/publications/Publ-29346
Publ.-Id: 29346


Advanced characterization methods for electrical and sensoric components and devices at the micro and nanoscale

Sheremet, E.; Meszmer, P.; Blaudeck, T.; Hartmann, S.; Wagner, C.; Ma, B.; Hermann, S.; Wunderle, B.; Schulz, S. E.; Hietschold, M.; Rodriguez, R. D.; Zahn, D. R. T.

This feature article covers the nano-analysis methods for four key material characteristics: electrical and electronic properties, optical, stress and strain, and chemical composition. With the downsizing of the geometrical dimensions of electronic, optoelectronic, and electromechanical devices from the micro to the nanoscale at the one hand and the increase of functionality density at the other, the previous generation of micro-analysis methods is no longer sufficient. Therefore, the metrology of materials’ properties with nanoscale resolution has become prerequisite in materials research and development. The article shortly reviews the standard analysis methods and focuses on advanced methods with a nanoscale spatial resolution based on atomic force microscopy (AFM): current-sensing AFM (CSAFM), Kelvin probe force microscopy (KPFM), and hybrid optical techniques coupled with AFM including tip-enhanced Raman spectroscopy (TERS), photothermal-induced resonance (PTIR) characterization methods (nano-Vis, nano-IR), photo-induced force microscopy (PIFM) and photothermal microspectroscopy (PTMS). The simultaneous acquisition of multiple parameters (topography, charge and conductivity, stress and strain, chemical composition) at the nanoscale is a key for exploring new research on structure-property relationships of nanostructured materials such as carbon nanotubes (CNTs) and nano/microelectromechanical systems (N/MEMS). Advanced nanocharacterization techniques foster the design and development of new functional materials for flexible hybrid and smart applications.

Keywords: Scanning probe microscopy; Kelvin probe force microscopy; nanoanalysis; Raman spectroscopy; atomic force microscopy

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-29345
Publ.-Id: 29345


RF Controls Towards Femtosecond and Attosecond Precision

Zenker, K.; Ludwig, F.; Branlard, J.; Butkowski, L.; Czwalinna, M. K.; Hoffmann, M.; Killenberg, M.; Lamb, T.; Mavric, U.; Mueller, J. M.; Pfeiffer, S.; Schlarb, H.; Schmidt, C.; Springer, L.; Kuntzsch, M.; Hierholzer, M.; Marjanovic, J.

In the past two decades, radio-frequency (RF) controls have improved by two orders in magnitude achieving meanwhile sub-10 fs phase stabilities and 0.01% amplitude precision. Advances are through improved field detection methods and extensive usage of digital signal processing on very powerful field programmable gate arrays (FPGAs). The question rises, what can be achieved in the next 10 years? In this paper, a review is given of existing systems and strategies, current stability limitations of RF control systems and new technologies with the potential to achieve attosecond resolutions.

  • Open Access Logo Contribution to proceedings
    10th International Particle Accelerator Conference, 19.-24.05.2019, Melbourne, Astralia: JACoW, 978-3-95450-208-0, 3414-3418
    DOI: 10.18429/JACoW-IPAC2019-THYYPLM2

Permalink: https://www.hzdr.de/publications/Publ-29344
Publ.-Id: 29344


Super-SIMS at HZDR - first steps: measurements on halogens

Rugel, G.; Renno, A. D.; Wiedenbeck, M.; Ziegenrücker, R.

The integration of an ion source with very high spatial resolution with a tandem accelerator is a long-standing concept for improving analytical selectivity and sensitivity by orders of magnitude [1-3]. Translating this design concept to reality has its challenges [e.g. 4-6]. Supporting a strong focus on natural, metallic and mineral resources the Helmholtz Institute Freiberg for Resource Technology installed such a system at the Ion Beam Centre at HZDR. This so-called Super-SIMS will be at the core of a comprehensive pallet of micro-analytical methods devoted to the characterization of minerals and ores. Secondary ion beam from a CAMECA IMS 7f-auto are injected into the pre-existing 6MV Dresden Accelerator Mass Spectrometry facility [7,8], which quantitatively eliminates isobaric molecular species from the ion beam.
Our SIMS component can function as either a stand-alone device or can be used to inject the negatively charged secondary ions at energies of up to 40 keV (to match the acceptance conditions) into the accelerator.
We will present the current status of this initiative and will report first results from halogen determinations (F – I) in sphalerite and galena. These data demonstrate a systematic and significant change in the counting rates of all halogens in mineralogically clearly distinguishable areas of both minerals. Furthermore first attempts on quantification with reference materials are given in [8].

[1] K. Purser et al. Surface and Interface Analysis 1(1), 1979, 12.
[2] J. M. Anthony, D. J. Donahue, A. J. T. Jull, MRS Proceedings 69 (1986) 311-316.
[3] S. Matteson, Mass Spectrom. Rev., 27 (2008) 470.
[4] Ender et al. NIMB 123 (1997) 575.
[5] C. Maden, PhD thesis, ETH Zurich 2003.
[6] A. J. Fahey et al. Analytical Chemistry 88(14), 2016, 7145.
[7] Sh. Akhmadaliev et al., NIMB 294 (2013) 5. [8] G. Rugel et al. NIMB 370 (2016) 94.
[8] R. Ziegenrücker et al., this conference.

Keywords: SIMS; Super-SIMS; AMS; accelerator; Beschleuniger; Flur; Flourine; Sphalerit; sphalerite

  • Poster
    Ion Beam Physics Workshop 2019, 24.-26.06.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29342
Publ.-Id: 29342


The association of intra-therapeutic heterogeneity of somatostatin receptor expression with morphological treatment response in patients undergoing PRRT with [177Lu]-DOTATATE

Wetz, C.; Genseke, P.; Apostolova, I.; Furth, C.; Ghazzawi, S.; Rogasch, J.; Schatka, I.; Kreissl, M.; Hofheinz, F.; Grosser, O.; Amthauer, H.

Aim

Purpose of this study was to evaluate the association of the spatial heterogeneity (asphericity, ASP) in intra-therapeutic SPECT/ CT imaging of somatostatin receptor (SSR) positive metastatic gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN) for morphological treatment response to peptide receptor radionuclide therapy (PRRT). Secondly, we correlated ASP derived form a pre-therapeutic OctreoScan (ASP[In]) and an intra-therapeutic [177Lu]-SPECT/CT (ASP[Lu]).

Materials and methods

Data from first therapy cycle [177Lu-DOTA0-Tyr3]octreotate ([177Lu]-DOTATATE)-PRRT was retrospectively analyzed in 33 patients (m = 20; w = 13; median age, 72 [46–88] years). The evaluation of response to PRRT was performed according to RECIST 1.1 in responding lesions [RL (SD, PR, CR), n = 104] and non-responding lesions [NRL (PD), n = 27]. The association of SSR tumor heterogeneity with morphological response was evaluated by Kruskal-Wallis test and receiver operating characteristic curve (ROC). The optimal threshold for separation (RL vs. NRL) was calculated using the Youden-index. Relationship between pre- and intra-therapeutic ASP was determined with Spearman’s rank correlation coefficient (ρ) and Bland-Altman plots.

Results

A total of 131 lesions (liver: n = 59, lymph nodes: n = 48, bone: n = 19, pancreas: n = 5) were analyzed. Lesions with higher ASP values showed a significantly poorer response to PRRT (PD, median: 11.3, IQR: 8.5–15.5; SD, median: 3.4, IQR: 2.1–4.5; PR, median 1.7, IQR: 0.9–2.8; CR, median: 0.5, IQR: 0.0–1.3); Kruskal-Wallis, p<0.001). ROC analyses revealed a significant separation between RL and NRL for ASP after 4 months (AUC 0.85, p<0.001) and after 12 months (AUC 0.94, p<0.001). The optimal threshold for ASP was >5.45% (sensitivity 96% and specificity 82%). The correlation coefficient of pre- and intra-therapeutic ASP revealed ρ = 0.72 (p <0.01). The mean absolute difference between ASP[In] and ASP[Lu] was -0.04 (95% Limits of Agreement, -6.1–6.0).

Conclusion

Pre- and intra-therapeutic ASP shows a strong correlation and might be an useful tool for therapy monitoring.

Permalink: https://www.hzdr.de/publications/Publ-29341
Publ.-Id: 29341


Continuous Documentation for Users, Developers and Maintainers

Frust, T.

This talk covers the often neglected and “hated” aspect of software documentation that is indispensable in a sustainable research software development process. A good, up-to-date and easily accessible software documentation lays the foundation for broader usage and collaboration. Software documentation usually covers three different components: user documentation, instructions how to modify and contribute to the software and a low-level API documentation. When starting developing a new research software, the documentation should be considered from the very beginning. Maintaining an up-to-date software documentation with good coverage in an exascale ready scientific software stack is only achievable, if the contribution process clearly includes a check for documentation adding or updates. This check can only be automated partially and usually requires a manual review process. All contributions must be made with the understanding, that documentation is a key aspect of any contribution. Things get never cleaned up later. Recurrent tasks should be automated wherever possible to reduce the impact of manual errors, e.g. the deployment of software documentation. This talk provides a set of best practices for software documentation in science combined with concrete examples from real-world scientific software solutions.

Keywords: Documentation; Software; Best Practices; CI; CD; Continuous Integration; API

  • Open Access Logo Invited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference 2019, 12.-14.06.2019, Zürich, Schweiz
    DOI: 10.5281/zenodo.3247324

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Permalink: https://www.hzdr.de/publications/Publ-29338
Publ.-Id: 29338


Smart Kd-concept for a realistic description of sorption processes in repository safety assessment

Stockmann, M.; Becker, D.-A.; Noseck, U.; Brendler, V.

A key component of safety assessment for radioactive waste repositories in deep geological formations is the simulation of potential radionuclide release scenarios and the transport of radionuclides through the repository system. The realistic modelling of (hydro-)geochemical processes is of high relevance for assessing the migration of radionuclides in groundwater systems. There, one important retardation process is sorption onto mineral surfaces of the host rock / sediments. Most often conventional concepts with constant sorption coefficients (Kd values) are applied in reactive transport simulations. Such an approach has the advantage to be simple and computationally fast but cannot reflect changes in geochemical conditions that will occur during the evolution of the repository system, e.g. due to climatic changes. Due to the German safety criteria with an assessment period of 1 million years it is necessary to consider the impact of such geochemical changes on the radionuclide transport and retardation. For this, we developed a new approach, the smart Kd concept (www.smartkd-concept.de) [1]. It is considering competitive sorption on different minerals (bottom-up approach) based on mechanistic sorption models and has been implemented in reactive transport codes [2, 3]. Possible migration scenarios for repository-relevant radionuclides (isotopes of Am, Cm, Cs, Ni, Np, Pu, Ra, Se, Th and U) through a typical sedimentary rock system covering potential repository host rocks, namely salt and clay formations in Northern Germany as natural geological barrier, were developed. The resulting smart Kd-values (for U(VI) in Fig. 1) and their associated sensitivities and uncertainties are presented for a wide range of important geochemical input parameters / boundary conditions such as pH value, ionic strength, concentration of competing cations and complexing ligands, e.g. dissolved inorganic carbon (DIC) and calcium (Ca).

  • Poster
    GDCh-Jahrestagung der Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-29337
Publ.-Id: 29337


Entwicklung induktiver Strömungs- und Füllstandssensoren für flüssige Metalle

Krauter, N.

In dieser Arbeit werden die Weiterentwicklung bestehender und die Entwicklung neuer Sensoren für die induktive Strömungs- und Füllstandsmessung in flüssigen Metallen sowie die zugehörigen Simulations- und Messergebnisse vorgestellt: Dabei handelt es sich um die Entwicklung und Charakterisierung eines miniaturisierten Eddy Current Flow Meters, das z.B. als Bestandteil der Sicherheitstechnik in flüssigmetallgekühlten Reaktoren zur Überwachung der Kühlmittelströmung bei hohen Umgebungstemperaturen eingesetzt werden kann. Außerdem wird das im Rahmen dieser Arbeit entwickelte Immersed Transient Eddy Current Flow Meter vorgestellt, welches eine direkte und kalibrierungsfreie Fließgeschwindigkeitsmessung ermöglicht und damit einen entscheidenden Vorteil gegenüber herkömmlichen induktiven Strömungssensoren besitzt. Anschließend werden neue Konzepte und ein Sensor für die Füllstandsüberwachung bei industriellen Prozessen, hier am Beispiel der Aluminium-Elektrolyse bei Temperaturen bis zu 1000 °C und der Titanherstellung vorgestellt.

Keywords: Induktive Messverfahren; Fließgeschwindigkeitsmessung; Füllstandsmessung

  • Doctoral thesis
    TUDpress, 2019
    Mentor: Prof. Dr. Uwe Hampel und Dr. Frank Stefani
    248 Seiten

Permalink: https://www.hzdr.de/publications/Publ-29336
Publ.-Id: 29336


Local inductive flow measurements

Krauter, N.; Stefani, F.

An overview of current research on inductive local flow rate measurement techniques in liquid metals at the HZDR.

Keywords: Inductive Flow Measurements; Eddy Current Flow Meter; Immersed Transient Eddy Current Flow Meter

  • Lecture (Conference)
    ESFR-SMART European Workshop on Instrumentation for the Safety of Liquid Metal Facilities, 10.-12.04.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29335
Publ.-Id: 29335


Inductive Level Sensors

Krauter, N.; Stefani, F.; Zürner, T.; Wondrak, T.; Ratajczak, M.

An overview of current research on inductive level measurement techniques in liquid metals at the HZDR.

Keywords: Eddy Current Level Sensor; Free Surface Detection; Look-Up-Table Method

  • Lecture (Conference)
    ESFR-SMART European Workshop on Instrumentation for the Safety of Liquid Metal Facilities, 10.-12.04.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29334
Publ.-Id: 29334


Simultaneous determination of flow velocity and electrical conductivity of a liquid metal using an eddy current flow meter in combination with a look-up-table method

Krauter, N.; Stefani, F.

Eddy Current Flow Meters (ECFM) are inductive sensors that are commonly used to measure the local flow rate or flow velocity of liquid metals in the vicinity of the sensor. One disadvantage of the ECFM is, that the measured voltage signals depend on the magnetic Reynolds number i.e. they are not only depending on the flow velocity but also on the electrical conductivity of the liquid metal. For applications where the temperature (and therefore also the electrical conductivity) is fluctuating significantly, the ECFM has to be calibrated in order to be able to distinguish between the influence of the flow velocity and the temperature on the measured signals. In this paper we present a method that allows the simultaneous measurement of electrical conductivity and flow velocity by using a so called Look-Up-Table method. When using this method, there is no need to calibrate the ECFM.

Keywords: Eddy current; inductive flow measurement; look-up-table

  • Contribution to proceedings
    11th Pamir International Conference Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich
  • Lecture (Conference)
    11th Pamir International Conference Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-29333
Publ.-Id: 29333


I-BEAT: Ultrasonic method for online measurement of the energy distribution of a single ion bunch

Haffa, D.; Yang, R.; Bin, J.; Lehrack, S.; Brack, F.-E.; Ding, H.; Englbrecht, F.; Gao, Y.; Gaus, L.; Gebhard, J.; Gilljohann, M.; Götzfried, J.; Hartmann, J.; Herr, S.; Hilz, P.; Kraft, S.; Kreuzer, C.; Kroll, F.; Lindner, F. H.; Metzkes-Ng, J.; Ostermayr, T. M.; Ridente, E.; Rösch, T. F.; Schilling, G.; Schlenvoigt, H.-P.; Speicher, M.; Taray, D.; Würl, M.; Zeil, K.; Schramm, U.; Karsch, S.; Parodi, K.; Bolton, P.; Schreiber, J.; Assmann, W.

the shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens’ principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. this novel method, which we refer to as Ion-Bunch energy Acoustic tracing (I-BeAt), is a refinement of the ionoacoustic approach. With its capability of completely monitoring a single, focused proton bunch with prompt readout and high repetition rate, I-BeAt is a promising approach to meet future requirements of experiments and applications in the field of laser-based ion acceleration. We demonstrate its functionality at two laser-driven ion sources for quantitative online determination of the kinetic energy distribution in the focus of single proton bunches

Keywords: laser ion acceleration; ion spectrometer

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Permalink: https://www.hzdr.de/publications/Publ-29332
Publ.-Id: 29332


Direct Observation of Plasma Waves and Dynamics Induced by Laser-Accelerated Electron Beams

Gilljohann, M. F.; Ding, H.; Döpp, A.; Götzfried, J.; Schindler, S.; Schilling, G.; Corde, S.; Debus, A.; Heinemann, T.; Hidding, B.; Hooker, S. M.; Irman, A.; Kononenko, O.; Kurz, T.; Martinez De La Ossa, A.; Schramm, U.; Karsch, S.

Plasma wakefield acceleration (PWFA) is a novel acceleration technique with promising prospects for both particle colliders and light sources. However, PWFA research has so far been limited to a few large-scale accelerator facilities worldwide. Here, we present first results on plasma wakefield generation using electron beams accelerated with a 100-TW-class Ti:sapphire laser. Because of their ultrashort duration and high charge density, the laser-accelerated electron bunches are suitable to drive plasma waves at electron densities in the order of 1019  cm−3. We capture the beam-induced plasma dynamics with femtosecond resolution using few-cycle optical probing and, in addition to the plasma wave itself, we observe a distinctive transverse ion motion in its trail. This previously unobserved phenomenon can be explained by the ponderomotive force of the plasma wave acting on the ions, resulting in a modulation of the plasma density over many picoseconds. Because of the scaling laws of plasma wakefield generation, results obtained at high plasma density using high-current laser-accelerated electron beams can be readily scaled to low-density systems. Laser-driven PWFA experiments can thus act as miniature models for their larger, conventional counterparts. Furthermore, our results pave the way towards a novel generation of laser-driven PWFA, which can potentially provide ultralow emittance beams within a compact setup.

Keywords: laser wakefield; plasma wakefield electron acceleration; high power laser; advanced accelerator

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Permalink: https://www.hzdr.de/publications/Publ-29331
Publ.-Id: 29331


A new method for the production of CeO2-base nanograined high capacity absorbent

Bonani, W.; Walter, O.; Cologna, M.; Prieur, D.; Beck, A.; Vitova, T.; Martin, P.; Störmer, H.; Popa, K.

Due to the broad range of applications (e.g.: catalyst, polishing agents, in fuel cells, pollutant adsorbed, in medicine), ceria is one of the most engineered oxides at nano- and micro-scale. The present research demonstrates highly reactive, nearly mono-dispersed metal oxides NPs with very large specific surface area (>300 m /g). The size of the NPs can be tailored by controlling the temperature and the pressure of the process. This research project explores applications of high quality CeO nanomaterials towards safe management of liquid radioactive wastes contributing to the environmental protection, resources, energy consumption optimisation, and circular economy.

  • Poster
    Nano Today Conference, 17.-21.06.2019, Lisbon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-29330
Publ.-Id: 29330


How do actinyls interact with hyperphosphorylated yolk protein Phosvitin ?

Kumar, S.; Creff, G.; Hennig, C.; Rossberg, A.; Steudtner, R.; Raff, J.; Vidaud, C.; Oberhaensli, F. R.; Bottein, Y.; Den Auwer, C.

We carried out a multi-techniques spectroscopic investigation to reveal the coordination geometry of actinyl ions (U(VI), Np(V)) in speciation with phosvitin protein. Like other protein molecules, phosvitin has carboxylic, phosphoryl and amide functional groups, but it has clustered serine residues and all the serine residues are phosphorylated to make it a hyperphosphorylated protein. IR spectroscopic study revealed phosphoryl groups as the main functional group interacting with uranyl ions. This was confirmed in the U(VI)-phosvitin fluorescence spectroscopic investigation and Np(V)-phosvitin UV-visible studies. Further, the existence of U(VI)-phosvitin system in a single speciation was found by the analysis of uranyl ion fluorescence decay data. Interestingly, X-ray absorption fine structure spectroscopic data for U/Np LIII edge revealed small contribution of bidentate binding present along with predominantly monodentate binding of phosphoryl groups in speciation of Uranyl ions with phosvitin protein. Signature of only bidentate binding was found in speciation of Np(V)-phosvitin system. In view of (de)phosphorylation as an important step of functional expression of various human body proteins, this study adds significant details to the molecular description of the toxicity of actinyl ions in biosphere.

Permalink: https://www.hzdr.de/publications/Publ-29329
Publ.-Id: 29329


Instant kit preparation of 68Ga-radiopharmaceuticals via the hybrid chelator DATA: clinical translation of [68Ga]Ga-DATA-TOC

Sinnes, J. P.; Nagel, J.; Waldron, B. P.; Maina, T.; Nock, B. A.; Bergmann, R. K.; Ullrich, M.; Pietzsch, J.; Bachmann, M.; Baum, P. B.; Rösch, F.

PURPOSE:
The widespread use of 68Ga for positron emission tomography (PET) relies on the development of radiopharmaceutical precursors that can be radiolabelled and dispensed in a simple, quick, and convenient manner. The DATA (6-amino-1,4-diazapine-triacetate) scaffold represents a novel hybrid chelator architecture possessing both cyclic and acyclic character that may allow for facile access to 68Ga-labelled tracers in the clinic. We report the first bifunctional DATA chelator conjugated to [Tyr3]octreotide (TOC), a somatostatin subtype 2 receptor (SST2)-targeting vector for imaging and functional characterisation of SSTR2 expressing tumours.

METHODS:
The radiopharmaceutical precursor, DATA-TOC, was synthesised as previously described and used to complex natGa(III) and 68Ga(III). Competition binding assays of [natGa]Ga-DATA-TOC or [natGa]Ga-DOTA-TOC against [125I-Tyr25]LTT-SS28 were conducted in membranes of HEK293 cells transfected to stably express one of the hSST2,3,5 receptor subtypes (HEK293-hSST2/3/5 cells). First in vivo studies were performed in female NMRI-nude mice bearing SST2-positive mouse phaeochromocytoma mCherry (MPC-mCherry) tumours to compare the in vivo SST2-specific tumour-targeting of [68Ga]Ga-DATA-TOC and its overall pharmacokinetics versus the [68Ga]Ga-DOTA-TOC reference. A direct comparison of [68Ga]Ga-DATA-TOC with the well-established PET radiotracer [68Ga]Ga-DOTA-TOC was additionally performed in a 46-year-old male patient with a well-differentiated NET (neuroendocrine tumour), representing the first in human administration of [68Ga]Ga-DATA-TOC.

RESULTS:
DATA-TOC was labelled with 68Ga with a radiolabelling efficiency of > 95% in less than 10 min at ambient temperature. A molar activity up to 35 MBq/nmol was achieved. The hSST2-affinities of [natGa]Ga-DATA-TOC and [natGa]Ga-DOTA-TOC were found similar with only sub-nanomolar differences in the respective IC50 values. In mice, [68Ga]Ga-DATA-TOC was able to visualise the tumour lesions, showing standardised uptake values (SUVs) similar to [68Ga]Ga-DOTA-TOC. Direct comparison of the two PET tracers in a NET patient revealed very similar tumour uptake for the two 68Ga-radiotracers, but with a higher tumour-to-liver contrast for [68Ga]Ga-DATA-TOC.

CONCLUSION:
[68Ga]Ga-DATA-TOC was prepared, to a quality appropriate for in vivo use, following a highly efficient kit type process. Furthermore, the novel radiopharmaceutical was comparable or better than [68Ga]Ga-DOTA-TOC in all preclinical tests, achieving a higher tumour-to-liver contrast in a NET-patient. The results illustrate the potential of the DATA-chelator to facilitate the access to and preparation of 68Ga-radiotracers in a routine clinical radiopharmacy setting.

Keywords: DATA-TOC; DOTA-TOC; Gallium-68; Molecular imaging; NET; PET-CT; Somatostatin receptor

Permalink: https://www.hzdr.de/publications/Publ-29328
Publ.-Id: 29328


High-field magnetoresistance of graphite revised

Barzola-Quiquia, J.; Esquinazi, P. D.; Precker, C. E.; Stiller, M.; Zoraghi, M.; Förster, T.; Herrmannsdörfer, T.; Coniglio, W. A.

A detailed magnetoresistance (MR) study of bulk and microflake samples of highly oriented pyrolytic graphite in a broad temperature 240 ≳ T ≳ 1 K and magnetic field μ0H ≼ 62 T range, reveals the existence of three independent phenomena, the contributions of which are observed at different temperatures and fields. The identification of the three phenomena was possible by studying the MR of samples with thickness of 25 μm to 23 nm. At temperatures T ≳ 100 K the MR is mainly given by the semiconducting stacking order regions. At lower temperatures the contribution of the internal interfaces of graphite to its MR is clearly observable. These interfaces are the origin of the commonly observed electronic phase transitions at fields 35 ≲ μ0H ≲ 55 T at T ≲ 10 K as well as a background MR in the whole field range that resembles the MR measured in granular superconductors.

Permalink: https://www.hzdr.de/publications/Publ-29327
Publ.-Id: 29327


Bedtime stories from space - Cosmogenic nuclides investigated by accelerator mass spectrometry

Merchel, S.; Rugel, G.; Wallner, A.; DREAMS-Friends/Users

High-energy particles as part of the cosmic ray spectrum are constantly bombarding Earth and induce nuclear reactions in the atmosphere and the Earth’s surface. The reaction products can be determined by sophisticated analytical methods such as mass spectrometry (noble gases), radioactivity counting (short-lived radionuclides) or accelerator mass spectrometry (long-lived radionuclides). Their concentrations allow us to date and quantify geomorphological processes like Earth quakes, rock avalanches, glacier movements, volcanic eruptions, tsunamis, and meteoroid impacts, which have happened hundred to million years ago. Combined with stable isotope data, we can reconstruct the Sun’s activity, the Earth’s magnetic field and temperature of the past.

Additionally, meteorites found on Earth also contain the same nuclear reaction products induced mainly by the galactic cosmic radiation but at much higher concentrations as they have not been shielded by the Earth’s atmosphere and magnetic field while irradiated. These data provide information about the exposure history of the individual meteorite and the cosmic radiation itself.

Last but not least, terrestrial archives from the deep-sea or from remote areas like Antarctica contain traces of cosmic events like supernovae explosions or stellar collisions. Identifying those long-lived radionuclides, produced not only long-time ago but also at a far-distance in the interstellar space, gives hints about these amazing astrophysical events.

For many of these interdisciplinary research areas accelerator mass spectrometry (AMS) being able to determine long-lived radionuclides at the ultra-trace level, i.e. isotopic ratios (radioactive/stable) as low as 10-16, is nowadays the analytical method-of-choice. Thus, DREsden AMS (DREAMS) and other European AMS facilities offer external users free measurements via a Trans-National-Access proposal program (www.ionbeamcenters.eu) and also national access (www.hzdr.de/ibc; DREAMS only).

Keywords: AMS; cosmic radiation

  • Invited lecture (Conferences)
    Colloquium Analytische Atomspektroskopie 2019 (canas 2019), 23.-26.09.2019, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29326
Publ.-Id: 29326


Extremely high conductivity observed in the triple point topological metal MoP

Kumar, N.; Sun, Y.; Nicklas, M.; Watzmann, S. J.; Young, O.; Leermakers, I.; Hornung, J.; Klotz, J.; Gooth, J.; Manna, K.; Süß, V.; Guin, S. N.; Förster, T.; Schmidt, M.; Muechler, L.; Yan, B.; Werner, P.; Schnelle, W.; Zeitler, U.; Wosnitza, J.; Parkin, S. S. P.; Felser, C.; Shekhar, C.

Weyl and Dirac fermions have created much attention in condensed matter physics and materials science. Recently, several additional distinct types of fermions have been predicted. Here, we report ultra-high electrical conductivity in MoP at low temperature, which has recently been established as a triple point fermion material. We show that the electrical resistivity is 6 nΩ cm at 2 K with a large mean free path of 11 microns. de Haas-van Alphen oscillations reveal spin splitting of the Fermi surfaces. In contrast to noble metals with similar conductivity and number of carriers, the magnetoresistance in MoP does not saturate up to 9 T at 2 K. Interestingly, the momentum relaxing time of the electrons is found to be more than 15 times larger than the quantum coherence time. This difference between the scattering scales shows that momentum conserving scattering dominates in MoP at low temperatures.

Permalink: https://www.hzdr.de/publications/Publ-29325
Publ.-Id: 29325


Ultrafast Response of Photoexcited Carriers in Transition Metal Oxides under High Pressure

Braun, J. M.

In this work, optical pump – near-infrared probe and near-infrared pump – mid-infrared probe spectroscopy are used for the investigation of pressure-induced insulator-tometal transitions in transition metal oxide compounds. The materials under study are a-Fe₂O₃, also known as hematite, and VO₂. Both materials undergo pressureinduced metallization. However, the physical mechanisms of this phase transition are very different for these systems and have not been fully understood up to now. Using ultrafast pump-probe spectroscopy we obtain an insight into the evolution of the band structure and electron dynamics across the insulator-to-metal transition.
In the case of VO₂, our near-infrared pump – mid-infrared probe experiments reveal a non-vanishing pumping threshold for photo-induced metallization even at our highest pressures around 20 GPa. This demonstrates the existence of localized charge carriers and the corresponding persistence of a band gap. Besides the threshold behaviour for photo-induced metallization, the carrier relaxation time scale, and the linear reflectivity and transmissivity have been studied under pressure increase. An anomaly in the threshold behaviour as well as the linear reflectivity and transmissivity at a critical pressure around 7 GPa indicates band gap filling under pressure. This is further supported by results obtained under decompression, where the changes of the linear reflectivity turned out to be almost fully reversible. The observations on VO₂ are highly reproducible and can be explained in terms of a pressure-induced bandwidth-driven insulator-to-metal transition.
Fe₂O₃ has been studied via optical pump – near-infrared probe spectroscopy up to pressures of 60 GPa. In the pressure range up to 40 GPa, the changes of the response can be explained by photo-induced absorption and bleaching. The pressure-dependent study of the relaxation dynamics allows to identify cooling of the electron system as origin of the picosecond relaxation process. A sharp anomaly found in the response of Fe₂O₃ at 40 GPa indicates a strong rearrangement of the electronic band structure which could be explained by an insulator-to-metal phase transition induced by pumping.
The successful demonstration of pump-probe experiments in diamond anvil cells using pulses from optical to mid-infrared wavelengths and reaching pressures of several tens of GPa is a good basis for further experimental high-pressure studies. Our results obtained on VO₂ and Fe₂O₃ can serve as a benchmark for the development of advanced material models.

Keywords: metal-insulator transition; high-pressure; ultrafast spectroscopy; correlated oxides

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-101 2019
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-29324
Publ.-Id: 29324


Cytocompatible, Injectable, and Electroconductive Soft Adhesives with Hybrid Covalent/Noncovalent Dynamic Network

Xu, Y.; Patsis, P. A.; Hauser, S.; Voigt, D.; Rothe, R.; Günther, M.; Cui, M.; Yang, X.; Wieduwild, R.; Eckert, K.; Neinhuis, C.; Akbar, T. F.; Minev, I. R.; Pietzsch, J.; Zhang, J.

Synthetic conductive biopolymers have gained increasing interest in tissue engineering, as they can provide a chemically defined electroconductive and biomimetic microenvironment for cells. In addition to low cytotoxicity and high biocompatibility, injectability and adhesiveness are important for many biomedical applications but have proven to be very challenging. Recent results show that fascinating material properties can be realized with a bioinspired hybrid network, especially through the synergy between irreversible covalent crosslinking and reversible noncovalent self-assembly.
Herein, a polysaccharide-based conductive hydrogel crosslinked through noncovalent and reversible covalent reactions is reported. The hybrid material exhibits rheological properties associated with dynamic networks such as self-healing and stress relaxation. Moreover, through fine-tuning the network dynamics by varying covalent/noncovalent crosslinking content and incorporating electroconductive polymers, the resulting materials exhibit electroconductivity and reliable adhesive strength, at a similar range to that of clinically used fibrin glue. The conductive soft adhesives exhibit high cytocompatibility in 2D/3D cell cultures and can promote myogenic differentiation of myoblast cells. The heparin-containing electroconductive adhesive shows high biocompatibility in immunocompetent mice, both for topical application and as injectable materials. The materials could have utilities in many biomedical applications, especially in the area of cardiovascular diseases and wound dressing.

Keywords: 3D cell culture; adhesion; biocompatibility; PEDOT; small animal magnetic resonance imaging

Permalink: https://www.hzdr.de/publications/Publ-29323
Publ.-Id: 29323


PANAS- Project: Heat Transfer Model Development for Passive Safety Systems

Leyer, S.; Hampel, U.; Schuster, C.; Lippmann, W.; Walther, M.; Kosowski, K.

The Project PANAS (acronym for the German “PAssive Nachzerfallswärme-AbfuhrSysteme” = passive residual heat removal systems) deals with the assessment of the heat transfer mechanisms and the operational stability of passive residual heat removal systems applied in GENERATION III and III + nuclear reactors. The project is funded by the German Federal Ministry of Education and Research and executed by a consortium consisting of the German Partners: Technische Universität Dresden (TUD), Technische Hochschule Deggendorf (THD), Helmholtz Zentrum- Dresden- Rossendorf (HZDR), Framatome GmbH and PreussenElektra GmbH. Based on experimental data recorded during the course of the project at the high-pressure test facility COSMEA at HZDR and the low-pressure test facility GENEVA at TUD state of the art heat transfer models are examined. The test facilities are equipped with innovative two-phase-flow instrumentations and heat transfer probes. At the COSMEA test facility the angular resolved radial heat transfer measurement is combined with a 2D image of the liquid/vapor phase distribution inside a heat exchanger pipe. Since drastic deviations between experimentally obtained and calculated heat transfer have been detected depending on the operational conditions, available heat transfer models are modified or new models are proposed. This model adaptation and development process is supported by 3D CFD modeling of the flow inside the tubes. In addition, the operational stability of low-pressure natural circulation systems has been assessed applying RAM-ROM methodology. The paper gives an overview of the first project phase recently being completed and outlines the objectives of the subsequent project phase, which is planned to be completed until end of 2020.

Keywords: Passive Safety Systems; Heat Transfer; Two-Phase-Flow; Natural Convection

  • Contribution to proceedings
    18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-23.08.2019, Portland, Oregon, USA
    Proceedings of the 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 1332-1345
  • Lecture (Conference)
    18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-23.08.2019, Portland, Oregon, USA

Permalink: https://www.hzdr.de/publications/Publ-29322
Publ.-Id: 29322


Exciton localization in MoSe₂ monolayer induced by adsorbed gas molecules

Venanzi, T.; Arora, H.; Erbe, A.; Pashkin, O.; Winnerl, S.; Helm, M.; Schneider, H.

Lattice defects and dielectric environment play a crucial role for 2D materials. Gas molecules can get physisorbed easily on the surface through van der Waals forces and can modify dramatically the electronic and optical properties. In this work we investigate the impact of the physisorbed gas molecules on the optical properties of MoSe₂ monolayers by means of low-temperature photoluminescence (PL). More specifically we focus on the physics of excitons localized by gas molecules. The associated PL peak is observed to show a systematic and large red-shift with temperature and a blue-shift with laser irradiation. Both energy shifts are explained in terms of thermal instability of the localization in combination with hopping effects. Finally a model is presented which can reproduce the experimental data with excellent agreement.

Keywords: MoSe2; photoluminescence; localized excitons; TMD; physisorption

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Permalink: https://www.hzdr.de/publications/Publ-29321
Publ.-Id: 29321


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