Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf
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Pulse- and Field-resolved THz-diagnostics at 4th Generation Lightsources
Multi-color pump-probe techniques utilizing modern accelerator-based 4th generation light sources such as X-ray free electron lasers or superradiant THz facilities have become important science drivers over the past 10 years. In this type of experiments the precise knowledge of the properties of the involved accelerator-based light pulses crucially determines the achievable sensitivity and temporal resolution. In this work we demonstrate and discuss the powerful role pulse- and field-resolved- detection of superradiant THz pulses can play for improving the precision of THz pump - femtosecond laser probe experiments at superradiant THz facilities in particular and at 4th generation light sources in general. The developed diagnostic scheme provides real-time information on the properties of individual pulses from multiple accelerator based THz sources and opens a robust way for sub femtosecond timing. Correlations between amplitude and phase of the pulses emitted from different superradiant THz sources furthermore provide insides into the properties of the driving electron bunches and is of general interest for the ultra-fast diagnostics at 4th generation light sources.
Keywords: Terahertz; Synchronization; ultrafast; diagnostics; accelerator
Optics Express 27(2019)22, 32360-32369
Modelling heat and mass transport in Liquid Metal Batteries
Personnettaz, P.; Weber, N.; Weier, T.
Liquid metal batteries (LMBs) are a promising electrical energy storage (EES) technology. An LMB is an electrochemical cell made of three stably stratified liquid layers. Two liquid metal electrodes are separated by a molten salt electrolyte. The high operating temperatures limit experimental studies to few measurable quantities. Numerical studies based on continuum mechanics are required to understand the relevant physical mechanisms. Simultaneous charge, heat, mass and momentum transfer together with chemical and electrochemical reactions takes place in the bulk fluids and at the liquid interfaces. These processes affect the electrochemical behavior of LMBs and the cell efficiency. In the initial presentation we have presented the study of heat and mass transport in a three layer liquid metal battery developed with a segregated multi-region approach. In the final presentation we have presented the study of thermal convection in a three layer liquid metal battery developed with a coupled single-region approach.
Keywords: Liquid metal batteries; transport phenomena; mass trasnport; heat transfer; openFOAM
NUMAP-FOAM Summer School 2019, 19.-30.08.2019, Zagreb, Hrvatska
Temperature‒dependent luminescence spectroscopic and mass spectrometric investigations of U(VI) complexation with aqueous silicates in the acidic pH‒range
In this study the complexation of U(VI) with orthosilicic acid (H4SiO4) between pH 3.5 and 5 with electrospray ionization mass spectrometry (ESI‒MS) and laser‒induced luminescence spectroscopy was comprehensively characterized. The ESI‒MS experiments performed at a total silicon concentration of 5∙10‒5 M (exceeding the solubility of amorphous silica at both pH‒values) revealed the formation of oligomeric sodium‒silicates in addition to the UO2OSi(OH)3+ species. For the luminescence spectroscopic experiments (25 °C), the U(VI) concentration was fixed at 5∙10‒6 M, the silicon concentration was varied between 1.3∙10‒4 ‒ 1.3∙10‒3 M (reducing the formation of silicon oligomers) and the ionic strength was kept constant at 0.2 M NaClO4. The results confirmed the formation of the aqueous UO2OSi(OH)3+ complex. The conditional complexation constant at 25 °C, log *β = ‒0.31± 0.24, was extrapolated to infinite dilution using the Davies equation, which led to log *β0 = ‒0.06 ± 0.24. Further experiments at different temperatures (1 – 25 °C) allowed the calculation of the molal enthalpy of reaction ΔrHm0 = 45.8 ± 22.5 kJ∙mol‒1 and molal entropy of reaction ΔrSm0 = 152.5 ± 78.8 J∙K‒1∙mol‒1 using the van’t Hoff equation, corroborating an endothermic and entropy driven complexation process.
Keywords: luminescence; silicates; Uranium(VI); complexation; thermodynamic constants; temperature dependent
Environment International 135(2020), 105425
Defect-Driven Magnetization Configuration of Isolated Linear Assemblies of Iron Oxide Nanoparticles
The magnetization state of 1D magnetic nanoparticle (NP) chains plays a key role in a wide range of applications ranging from diagnosis and therapy in medicine to actuators, sensors, and quantum recording media. The interplay between the exact particle orientation and the magnetic anisotropy is in turn crucial for controlling the overall magnetization state with high precision. Here, a 3D description of the magnetic structure of one-NP-wide chains is reported. Here, two complementary experimental techniques are combined, magnetic force microscopy (MFM) and electronic holography (EH) which are sensitive to out-of-plane and in-plane magnetization components, respectively. The approach to micromagnetic simulations is extended, which provides results in good agreement with MFM and EH. The findings are at variance with the known results on unidirectional NP assemblies, and show that magnetization is rarely strictly collinear to the chain axis. The magnetic structure of one-NP-wide chains can be interpreted as head-to-head magnetic domain structures with off-axis magnetization components, which is very sensitive to morphological defects in the chain structure such as minute size variation of NPs, tiny misalignment of NPs, and/or crystal orientation with respect to easy magnetization axis.
Keywords: AFM/MFM; e-holography; HR-TEM; magnetization states; micromagnetic simulations; one-NP-wide chains
Advanced Functional Materials 29(2019)45, 1903927
- Secondary publication expected
Dendritic structure formation of magnesium alloys for the manipulation of corrosion properties: Part 2-corrosion
Lakoma, P.; Ditze, A.; Scharf, C.
In pure magnesium and aluminum-containing magnesium alloys, the microstructure also plays a role in the corrosion properties. In Part 1, the grain sizes, secondary dendrite arm spacings (SDAS) and precipitates of b phase were determined by casting samples with 0, 3, 6, 9 and 12% aluminum (all compositions in mass percentage) at different cooling rates. These samples were tested for corrosion properties by immersion and salt spray tests. The modeling of the corrosion process enables establishing a mathematical link between the microstructure and corrosion properties of an alloy. The results show an increase in the corrosion rate with increasing aluminum contents and the cooling rate.
The precipitations at the grain boundaries have a relevant impact on corrosion properties of the magnesium-aluminum alloys. A random comparison using the salt spray test tends to confirm the results.
International Journal of Materials Research 110(2019)8, 703-714
Development of an in-situ cryo high resolution instrument for multimodal analysis in nano-toxicology
Nowadays many consumer products contain nanoparticles in order for them to have certain desired properties. However, with the addition of nanoparticles these products can have potentially unknown health risks to humans, animal and plant species, and to the environment in general. The nanomaterial risk identification involves their physico-chemical characterization currently employing a variety of techniques and separate instruments. This makes the characterization an expensive and time-consuming process.
In the framework of the Horizon2020 project npSCOPE, we are developing a new integrated instrument for the characterization of nanoparticles. The aim is to improve the efficiency of the nanomaterial characterization workflow by integrating several techniques in one single instrument. The npSCOPE instrument is equipped with the ultra-high resolution Gas Field Ion Source (GFIS) technology  allowing the sample to be irradiated with very finely focused He+ and Ne+ ion beams at the nano-scale. Furthermore, the instrument incorporates detectors for secondary electron imaging, a secondary ion mass spectrometer (SIMS) for chemical analysis [2-4] and a detector allowing the detection of transmitted ions/atoms to obtain in-situ structural/3D visualisation data. The instrument will allow the characterization of nanoparticles in their native state as well as embedded in complex matrices (e.g. biological tissue, liquid, etc.). A further key feature of the instrument is cryo-capability, including a 5 axis cryo-stage, in order to perform analyses of biological samples in a frozen-hydrated state and thus avoid artefacts caused by classical sample preparation (e.g. chemical fixation) used for HV or UHV imaging of biological specimens at room temperature.
Here, we will present the instrument, report on the instrument’s performance and discuss the correlative microscopy capabilities. We will present first results obtained with the npSCOPE instrument on different kinds of nano-particle samples relevant in the field of nano-toxicology.
Beside analyses of nano-toxicological samples we are planning to use this instrument in different material science fields as well as other life science domains that require high resolution imaging in cryo-conditions (e.g. lipid research) .
Keywords: Helium Ion Microscopy; Scanning transmission helium ion microscopy; secondary ion mass spectrometry; cryo microscopy
MRS Fall Meeting 2019, 01.-06.12.2019, Boston, United States of America
Terahertz excitations in α-RuCl3: Majorana fermions and rigid-plane shear and compression modes
Reschke, S.; Tsurkan, V.; Do, S.-H.; Choi, K.-Y.; Lunkenheimer, P.; Wang, Z.; Loidl, A.
Spin liquids may host emergent quasiparticles, collective excitations of the spin degrees of freedom with characteristic features of Majorana fermions, which experimentally are detectable by broad excitation continua due to spin fractionalization. The latter is predicted for the Kitaev spin liquid, an exactly solvable model with bond-dependent interactions on a two-dimensional honeycomb lattice. Here we report on detailed terahertz experiments in α-RuCl3, identifying these characteristic fingerprints of Majorana fermions. The continuum intensity decreases and finally vanishes on increasing temperature. It partly overlaps with phonon modes, representing characteristic sliding and compression modes of the van der Waals bonded molecular layers.
Physical Review B 100(2019), 100403
A comparative evaluation of calixarene-1,3-crown-6 as a ligand for selected divalent cations of radiopharmaceutical interest
Radionuclides of divalent metals like lead-203, lead-212 and the radionuclides of alkaline earth metals barium-131 and strontium 89 are promising candidates for a radiopharmaceutical application. In addition, the heavy homologues radium-223 and radium-224 – with similar properties to barium - are suitable alpha-emitters for the targeted alpha-particle therapy. However, there is a lack of suitable chelation agents, especially for heavy group 2 metals. The macrocycle calixarene-1,3-crown-6 seems to strongly interact with these metals. Therefore, this ligand and its coordination to the divalent cations of barium, strontium, and lead have been investigated. The complex formation was analyzed by NMR and UV/Vis titration experiments in acetonitrile, and stability constants were determine with both methods. It was found that the stability of these complexes increase in the order of strontium, barium, and lead. Additional to these investigations, X-ray crystallography, solvent-dependent 1H-NMR, and 207Pb NMR measurements were performed to deliver a deeper insight into the coordination chemistry of this ligand.
Keywords: Calixarene; Radium; Barium; X-ray
RSC Advances 7(2019)55, 32357-32366
Electroforming-free resistive switching in yttrium manganite thin films by cationic substitution
Rayapati, V. R.; Bürger, D.; Du, N.; Patra, R.; Skorupa, I.; Blaschke, D.; Stöcker, H.; Matthes, P.; Schulz, S. E.; Schmidt, H.
We report unipolar resistive switching in polycrystalline, hexagonal yttrium manganite thin films grown on unpatterned Pt metal coated SiO2/Si substrates with circular Al top electrodes. Electroforming-free or electroforming-based resistive switching is observed, depending on the chemical composition (Y1Mn1O3, Y0.95Mn1.05O3, Y1Mn0.99Ti0.01O3, and Y0.94Mn1.05Ti0.01O3). The number of loading cycles measured at room temperature for samples with Y1Mn1O3 and Y0.95Mn1.05O3 composition is larger than 103. The dominant conduction mechanism of the metal-insulator-metal structures between 295 K and 373 K in the high resistance state is space charge limited conduction and in the low resistance state is ohmic conduction. Activation energies in Ohm's law region in the high resistance state are calculated from the Arrhenius equation and are evaluated to be 0.39 ± 0.01 eV (Y1Mn1O3), 0.43 ± 0.01 eV (Y0.95Mn1.05O3), 0.34 ± 0.01 eV (Y1Mn0.99Ti0.01O3), and 0.38 ± 0.02 eV (Y0.94Mn1.05Ti0.01O3).
Journal of Applied Physics 126(2019)7, 074102
Liquid flow visualization in packed-bed multiphase reactors: Wire-mesh sensor design and data analysis for rotating fixed beds
Wire-mesh sensors are increasingly used for flow imaging in packed-beds. In this study, a capacitance wire-mesh sensor is applied to measure the cross-sectional liquid phase distribution in a rotating fixed bed reactor. The liquid filling level is derived as a crucial parameter defining the operational window of the reactor concept. Contrary to the standard sensor configuration, wireless data transfer and autonomous power supply is integrated. Furthermore, appropriate data processing is required to visualize the liquid flow of the three-phase system (nitrogen, cumene and γ-Al2O3 particles).
Keywords: Gas-liquid flow; Process intensification; Rotating fixed bed; Sensor design; Wire-mesh sensor
Chemie Ingenieur Technik 91(2019)12, 1812-1821
Droplet retention time and pressure drop in SiSiC open-cell foams used as droplet separation devices – A numerical approach
Open-cell foams are a promising alternative for the separation of liquid droplets suspended in gas flows at comparably low pressure drop. The separation in such ceramic foams is investigated using the residence time distribution of droplets derived from pore-scale CFD-simulations. 20 and 45 pores per inch (ppi) silicon-infiltrated silicon carbide (SiSiC) open-cell foams samples are considered. The foam structure was reconstructed from micro-computed tomography (µCT) images. To track the droplets, a Lagrangian discrete-phase model was used. The effect of pore size and pore density on the droplet retention time was studied. The flow pressure drop showed a remarkable agreement with the in-house experimental measurements. The droplet separation efficiency within the foam structure was found to generally increase with the inlet gas velocity and the droplet inertia.
Keywords: Ceramic foams; liquid droplet entrainment; gas-droplet flow; resolved pore-scale CFD simulations; droplet residence time; droplet separator device
Industrial & Engineering Chemistry Research (2020)
Online First (2019) DOI: 10.1021/acs.iecr.9b04247
An expanding view on actinide oxide nanoparticles
Understanding the mechanisms of different chemical reactions with actinides at the atomic level is a key step towards safe disposal of nuclear wastes and towards the identification of physical-chemical processes of radionuclides in the environment. This contribution will provide an overview of the recently performed studies on Uranium, Thorium, Plutonium and Cerium oxide nanoparticles at the Rossendorf Beamline (ROBL) of the European Synchrotron in Grenoble (France). This innovative, recently upgraded, world-wide unique experimental station, funded and operated by HZDR in Dresden (Germany) was used to study actinide systems by by X-ray absorption spectroscopy in high energy resolution fluorescence detection (HERFD) mode and resonant inelastic X-ray scattering (RIXS) at the An/Ln L3 and An M4 edge. The experimental results have been analysed using a number of theoretical methods based on density functional theory and atomic multiplet theory. This research has received funding from European Research Council (ERC) under grant agreement 759696.
the 43d Symposium on Scientific Basis for Nuclear Waste Management, 21.-24.10.2019, Vienna, Austria
Alkyne-based cysteine cathepsin inhibitors as basis for PET tracer development
Among the intertwined processes leading to cancer progression, protease activity plays an important role. Various attempts to develop molecular imaging probes have been made, as such probes can allow functional imaging and thus improve the understanding of tumour progression mechanisms and enable personalised cancer treatment. PET and SPECT tracers are particularly suitable for such applications. However, novel tracers have to overcome challenges such as stability, target efficiency and off-target effects.
Multiple members of the cathepsin family have been demonstrated to be involved in tumour invasion, metastasis, and angiogenesis. Especially high expression levels of the cysteine cathepsins B, K, L, S, and X are correlated with an increased metastatic potential and poor prognosis . Due to their high expression in a multitude of tumours, those enzymes represent promising targets for the therapy and imaging of tumours.
Despite being virtually chemically inert, alkynes were shown to be able to irreversibly inhibit cysteine proteases: Both EKKEBUS et al. and SOMMER et al. independently described the unexpected inactivation of de-ubiquitinating enzymes by ubiquitin or ubiquitin-like modifiers bearing propargylamine in place of C-terminal glycine [2, 3]. We aimed to take advantage of those findings for designing alkyne-based cysteine cathepsin inhibitors suitable for radiolabelling with PET nuclides. The probes thus obtained would irreversibly bind to the target molecule without showing indiscriminate thiol reactivity.
Based on a potent, highly selective dipeptidyl nitrile-based cathepsin B inhibitor reported by GREENSPAN et al. (left structure) , we designed dipeptide alkynes by isoelectronic replacement of the nitrile nitrogen atom by a methine group. To avoid partial enantiomerisation during the formation of the C-C triple bond as observed for the open-chain serine-derived alkyne, the synthesis was performed via Garner’s aldehyde. This ensured high stereochemical purity of the final compounds. The inhibitory potential was investigated against cathepsin B, S, L and K. To optimise the inhibitory potential and selectivity, we consecutively varied all moieties attached to the dipeptidic scaffold.
We identified potent alkyne-based inhibitors for all tested cathepsins, with inactivation constants (kinact/KI) up to 10133 M-1s-1 and distinct selectivity profiles. We demonstrated irreversibility in a “jump-dilution” experiment and inhibitor reactivity in cell lysates and on living cells was exemplarily verified for cathepsin B. During our research, MONS et al. successfully demonstrated irreversible cathepsin K inhibition by alkyne-based small molecule inhibitors with no indiscriminate thiol reactivity , which indicates the viability of our concept.
Among the tested inhibitors we identified two promising radiotracer candidates which are selective for cathepsin S and L. We successfully radiolabelled the cathepsin S-selective inhibitor with N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB). Radiopharmacological characterisation of the activity-based probe obtained by that approach is in progress.
 Löser, R; Pietzsch, J.: Front. Chem., 2015, 3: 37.
 Ekkebus et al.: J. Am. Chem. Soc., 2013, 135(8): 2867-2870.
 Sommer et al.: Bioorg. Med. Chem., 2013, 21(9): 2511-2517.
 Greenspan et al.: J. Med. Chem., 2001, 44(26): 4524-4534.
 Mons et al.: J. Am. Soc. 2019, 141(8): 3507-3514.
Annual Meeting of the German Pharmaceutical Society - DPhG, 01.-04.09.2019, Heidelberg, Deutschland
Radiotherapy Beamline Design for Laser-driven Proton Beams
Motivation: Radiotherapy is an important modality in cancer treatment commonly using photon beams from compact electron linear accelerators. However, due to the inverse depth dose profile (Bragg peak) with maximum dose deposition at the end of their path, proton beams allow a dose escalation within the target volume and reduction in surrounding normal tissue. Up to 20% of all radiotherapy patients could benefit from proton therapy (PT). Conventional accelerators are utilized to obtain proton beams with therapeutic energies of 70 – 250 MeV. These beams are then transported to the patient via magnetic transferlines and a rotatable beamline, called gantry, which are large and bulky. PT requires huge capex, limiting it to only a few big centres worldwide treating much less than 1% of radiotherapy patients. The new particle acceleration by ultra-intense laser pulses occurs on micrometer scales, potentially enabling more compact PT facilities and increasing their widespread. These laser-accelerated proton (LAP) bunches have been observed recently with energies of up to 90 MeV and scaling models predict LAP with therapeutic energies with the next generation petawatt laser systems.
Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-104 2019
ISSN: 2191-8708, eISSN: 2191-8716
A multi-environmental tracer study to determine groundwater residence times and recharge in a structurally complex multi-aquifer system
Despite being the main drinking water resource for over five million people, the water balance of the Eastern Mountain Aquifer system on the western side of the Dead Sea is poorly understood. The regional aquifer consists of fractured and karstified limestone — aquifers of Cretaceous age and can be separated in Cenomanian aquifer (upper aquifer) and Albian aquifer (lower aquifer). Both aquifers are exposed along the mountain ridge around Jerusalem, which is the main recharge area. From here, the recharged groundwater flows in a highly karstified aquifer system towards the east, to discharge in springs in the Lower Jordan Valley and Dead Sea region. We investigated the Eastern Mountain Aquifer system on groundwater flow, groundwater age and potential mixtures, and groundwater recharge. We combined ³⁶Cl/Cl, tritium and the anthropogenic gases SF₆, CFC-12 and CFC-11, CFC-113 as “dating” tracers to estimate the young water components inside the Eastern Mountain Aquifer system. By application of lumped parameter models, we verified young groundwater components from the last 10 to 30 years and an admixture of a groundwater component older than about 70 years. Concentrations of nitrate, Simazine® (Pesticide), Acesulfame K® (artificial sweetener) and Naproxen® (drug) in the groundwater were further indications of infiltration during the last 30 years. The combination of multiple environmental tracers and lumped parameter modelling helped to understand the groundwater age distribution and to estimate recharge despite scarce data in this very complex hydrogeological setting. Our groundwater recharge rates support groundwater management of this politically difficult area and can be used to inform and calibrate ongoing groundwater flow models.
Hydrology and Earth System Sciences 24(2020), 249-267
Implantable highly compliant devices for heating of internal organs: towards cancer treatment
Cañón Bermudez, G. S.; Kruv, A.; Voitsekhivska, T.; Hochnadel, I.; Lebanov, A.; Potthoff, A.; Fassbender, J.; Yevsa, T.; Makarov, D.
Flexible electronics have a strong potential to revolutionize the health care sector. Numerous flexible diagnostic or therapeutic devices have been successfully demonstrated. However, tumor treatment remains rather unexplored in the field of flexible electronics. Here, we demonstrate that the electrical and mechanical properties of highly compliant electronics are advantageous for targeting tumor sites at internal organs. This kind of electronics could be implanted to heat and thereby render the treated tissue susceptible to chemotherapy, radiation or other available treatments. Our method relies on the implantation directly at the tumor site of an ultra-thin flexible device comprising a resistive heater and temperature sensor. The device consists of a 6 µm thick polymeric foil hosting the heater and sensor, capped with a 5 µm thick encapsulation layer. Due to its ultrathin nature, it seamlessly conforms to the very soft liver tissue and allows for precisely controlled thermal treatment. Its high mechanical compliance provides stable readings even upon severe mechanical deformations, enabling a temperature accuracy of 0.1°C at bending radii of 2.5 mm, characteristic for mouse liver tissues. We demonstrate a proof-of-concept prototype and evaluate its electrical and mechanical performance when applied to murine cancer models. The presented highly compliant device paves the way for handling of exophytic (located at the organ surface) tumor nodules via thermal destruction of tissue, targeted drug release, or enhancement of anti-tumor immune responses. In addition, it raises the possibility to further study the effects of thermal treatment in enhancing the development of the new cancer therapies, especially for severe malignancies as liver cancer.
Keywords: flexible electronics; cancer
Advanced Engineering Materials 21(2019)9, 1900407
A bimodal soft electronic skin for tactile and touchless interaction in real time
Ge, J.; Wang, X.; Drack, M.; Volkov, O.; Liang, M.; Cañón Bermúdez, G. S.; Illing, R.; Wang, C.; Zhou, S.; Fassbender, J.; Kaltenbrunner, M.; Makarov, D.
The emergence of smart electronics, human friendly robotics and supplemented or virtual reality demands electronic skins with both tactile and touchless perceptions for the manipulation of real and virtual objects. Here, we realize bifunctional electronic skins equipped with a compliant magnetic microelectromechanical system able to transduce both tactile - via mechanical pressure - and touchless - via magnetic fields - stimulations simultaneously. The magnetic microelectromechanical system separates electric signals from tactile and touchless interactions into two different regions, allowing the electronic skins to unambiguously distinguish the two modes in real time. Besides, its inherent magnetic specificity overcomes the interference from non-relevant objects and enables signal-programmable interactions. Ultimately, the magnetic microelectromechanical system enables complex interplay with physical objects enhanced with virtual content data in augmented reality, robotics, and medical applications.
Keywords: flexible electronics; magnetic field sensors
Nature Communications 10(2019), 4405
Interplay Between Relaxation and Resonance in Ultrasound Attenuation by the Cubic Crystal ZnSe:Cr
Baryshnikov, K.; Averkiev, N.; Bersuker, I.; Gudkov, V.; Zhevstovskikh, I.; Sarychev, M.; Zherlitsyn, S.; Yasin, S.; Korostelin, Y.
Resonance ultrasound attenuation, albeit broadened, is observed in doped cubic crystal ZnSe with a part of the Zn ions substituted by magnetic anisotropic Cr2+ ions. In the tetrahedral selenium environment the latter form a T term Jahn–Teller (JT) center with a T⊗e JT problem and three equivalent distortions along the three tetragonal axes. In sufficiently strong magnetic fields (B > 4 T) applied along the  direction the degeneracy of the ground state is removed, and the ultrasound wave propagating along  and polarized along  (at T = 1.3 K) does not interact with the center, its impurity attenuation being reduced to zero. By comparison, this allows to estimate the contribution of the Cr centers to the attenuation of ultrasound in the ZnSe:Cr crystal in zero magnetic field. The experimental data revealed a strong dependence of the attenuation on the ultrasound frequency, evidencing for the resonance nature of the attenuation: there is no frequency dependence in relaxational attenuation with the relaxation time much larger than the period of the ultrasonic wave. The resonance attenuation is attributed to transitions between the ground state energy levels, split by spin-orbital interaction. The high sensitivity of the resonance absorption on the ultrasound power is also discussed.
Physica Status Solidi (B) 256(2019), 1800635
Diffusion of Phosphorus and Boron from Atomic Layer Deposition Oxides into Silicon
Beljakowa, S.; Pichler, P.; Kalkofen, B.; Hübner, R.
Oxides containing group III or group V elements (B2O3/Sb2O5 and P2O5/Sb2O5) are grown by plasma-assisted atomic layer deposition (ALD) on single-crystalline silicon and serve as dopant sources for conformal and shallow doping. Transport phenomena in ALD-oxide–Si structures during rapid thermal annealing (RTA) are investigated subsequently by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). The XPS and TEM analyses of the annealed ALD oxide–Si structures demonstrate that the ALD oxide converts to a silicon oxide and partially evaporates during annealing. In addition, dopant-containing, spherical, and partially crystalline particles form in the oxide, and Si-P precipitates at the oxide–Si interface. After diffusion annealing at 1000 °C, the SIMS analyses reveal phosphorus and boron concentration profiles in the silicon substrate with maximum concentrations exceeding their solid solubility limits by roughly one order of magnitude. Experimental doping profiles of phosphorus and boron in silicon are compared with simulation results, considering a slight injection of self-interstitials and dynamical defect clustering.
Physica Status Solidi (A) 216(2019), 1900306
Gettering and Defect Engineering in Semiconductor Technology XVIII, GADEST 2019, 22.-27.09.2019, Zeuthen, Germany
PIConGPU simulation settings for TWEAC
The input sets of the simulations as used in the publication "Circumventing the Dephasing and Depletion Limits of Laser-Wakefield Acceleration" by A. Debus et al. .
The input sets include TWEAC scenarios, the LWFA scenario and the laser-propagation scenario of Appendix D. The src-directories include custom additions to the PIConGPU source code.
The simulations were run using the beta-rc6, 0.3.1, and 0.4.0 releases of PIConGPU (see DOI: 10.5281/zenodo.591746). The input sets are shown according to the respective PIConGPU version used in the original simulation. However, for running the simulations we recommend adapting the input sets to the 0.4.0 release.
Keywords: Optics; Photonics; Plasma Physics
- Circumventing the dephasing and depletion limits of … (Id 25244) is documented by this (Id 29625) publication
Reseach data in the HZDR data repository RODARE
Publication date: 2019-09-04
Vapor-liquid equilibrium data for efficiency estimation of tray columns
Vapor-liquid equilibrium data are the prerequisites for determining column efficiencies. For this purpose, industrial binary distillation operations are selected from the literature. At representative column pressures, high resolution data are obtained for the mixtures using suitable thermodynamic models in Aspen Plus (v10).
Keywords: column efficiency; vapor-liquid equilibrium; thermodynamic model
- Efficiency estimation of tray columns based on flow … (Id 29618) has used this (Id 29624) publication of HZDR-primary research data
Reseach data in the HZDR data repository RODARE
Publication date: 2019-09-02
The influence of microstructural anisotropy on secondary cracking in ferritic ODS steels
ODS steels are known to exhibit anisotropic fracture behaviour owing to their anisotropic microstructure and form secondary cracks. Secondary cracks are observed more often in hot-rolled than in hot-extruded ODS steels. They tend to absorb energy and help in stabilizing primary crack propagation at low temperatures but initiate at lower loads than primary cracks. In this work, a correlation is made between the microstructural anisotropy of three ferritic ODS steels and the secondary cracking induced in these materials. Better understanding of these factors can lead to tailoring of improved ODS steels. Fracture toughness testing of three batches of ferritic ODS steels, one hot-rolled and two hot-extruded, were carried out using small C(T) specimens. The fracture behaviour of secondary cracks was investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Crystallographic texture and grain morphology play a dominant role in the formation of secondary cracks in hot-rolled ODS steels. Secondary crack initiation at low loads in hot-rolled material is predominantly due to anisotropic grain morphology. At lower temperatures, secondary cracks occur via transgranular cleavage while at higher temperatures, the fracture mode changes to ductile and intergranular.
Keywords: secondary cracking; ODS steels; fracture; microstructure
Fifth International Workshop on Structural Material for Innovative Nuclear Systems (SMINS-5), 08.-11.07.2019, Kyoto, Japan
Drone-borne spectral monitoring of post-mining areas
Mining always played a decisive role in achieving modern technology standards, influencing raw material driven aspects of today’s societies. During the last decade, more focus is put towards environmental protection in developed countries. This progression is not yet implemented in many mining sites all over the world. In those cases, mining and post-mining management represents a negative intervention in ecosystems. We take the example of acid mine drainage (AMD) accompanied by high concentrations of dissolved metal ions, which influence characteristics of soils and water bodies. This poses a hazardous situation not only to nature, but also to agriculture and food production. Monitoring of post mining-related contamination hot-spots is one step to detect problem sand take fast responsive actions. Environmental screening basically depends on geochemical analyses, gathered from sampling points, distributed over the investigated area. Even though this kind of investigation provides very detailed information about concentrations of various elements and compounds, that information is only available for sampled spots. Furthermore, some areas are inaccessible due to various reasons (risks of rockfall, cliffs, in-accessible terrain). We present two case studies with test-areas from the coal-mining districts of Sokolov in the Czech Republic and from eastern Saxony in Germany. The acquisitions in the German test sites are part of the EU-founded project “VitaMin”. The use of unmanned aerial systems (UAS) provides the possibility of detailed surface mapping, using sensors that are light enough to be mounted on a UAS. We carried out several studies in post mining areas, including drone-borne multi- and hyperspectral acquisitions, along with ground-based validation data. This approach allows the generation of high-resolution surface maps, containing information about the distribution of certain elements, mineral proxies and chemical compounds. The sensor wavelength-ranges and spectral resolution determine the substances that can be detected. Among the spectral detectable substances, iron is of key importance. By analysing the spectra in the visible to near infrared region of the electromagnetic spectrum, we distinguish between Fe(II)- and Fe(III)-compounds. Furthermore, iron bearing minerals are a suitable indicator for the distribution and severity of acid mine drainage. A rough estimation about the predominant pH-value can be made. Hyperspectral imagery is one solution to enhance the quality of classical geochemical analyses and increase the overall amount of information during efficient environmental monitoring. We highlight the potential of UAS hyperspectral mapping to provide a highly efficient way of precisely mapping superficial indicative compounds. We explore the potential in combining drone-borne hyperspectral imaging with geochemical analyses.
Keywords: UAS; hyperspectral; multispectral; geochemistry; groundwater; vegetation; post-mining
EGU General Assembly 2019, 09.04.2019, Vienna, Austria
Drone-Borne Hyperspectral and Magnetic Data Integration: Otanmäki Fe-Ti-V Deposit in Finland
The technical evolution of unmanned aerial systems (UAS) for mineral exploration advances rapidly. Recent sensor developments and improved UAS performance open new fields for research and applications in geological and geophysical exploration among others. In this study, we introduce an integrated acquisition and processing strategy for drone-borne multi-sensor surveys combining optical remote sensing and magnetic data. We deploy both fixed-wing and multicopter UAS to characterise an outcrop of the Otanmäki Fe-Ti-V deposit in central Finland. The lithology consists mainly of gabbro intrusions hosting ore bodies of magnetite-ilmenite. Large areas of the outcrop are covered by lichen and low vegetation. We use two drone-borne multi- and hyperspectral cameras operating in the visible to near-infrared parts of the electromagnetic spectrum to identify dominant geological features and the extents of ore bodies via iron-indicating proxy minerals. We apply band ratios, unsupervised and supervised image classifications on the spectral data, from which we can map surficial iron-bearing zones. We use two setups with three-axis fluxgate magnetometers deployed both by a fixed-wing and a multi-copter UAS to measure the magnetic field at various flight altitudes (15 m, 40 m, 65 m). The total magnetic intensity (TMI) computed from the individual components is used for further interpretation of ore distribution. We compare to traditional magnetic ground-based survey data to evaluate the UAS-based results. The measured anomalies and spectral data are validated and assigned to the outcropping geology and ore mineralisation by performing surface spectroscopy, portable X-ray fluorescence (pXRF), magnetic susceptibility and traditional geologic mapping. Locations of mineral zones and magnetic anomalies correlate with the established geologic map. The integrated survey strategy allowed a straightforward mapping of ore occurrences. We highlight the efficiency, spatial resolution and reliability of UAS surveys. Acquisition time of magnetic UAS surveying surpassed ground surveying by factor of twenty with a comparable resolution. The proposed workflow possibly facilitates surveying particularly in areas with complicated terrain and of limited accessibility, but highlights the remaining challenges in UAS mapping.
Keywords: UAS; hyperspectral; multispectral; magnetic; mineral exploration; iron minerals; Otanmäki
Remote Sensing 11(2019)18, 2084
Eu2+: a suitable substituent for Pb2+ in CsPbX3 perovskite nanocrystals?
Europium is used to replace toxic lead in metal halide perovskite nanocrystals. They are synthesized by injecting cesium oleate in a solution of europium (II) bromide at an experimentally determined optimum temperature of 130°C. The obtained CsEuBr3 NCs exhibit bright blue emission at 413 nm (FWHM: 30 nm) with a room temperature photoluminescence (PL) quantum yield of 39%. The emission originates from the Laporte allowed 4f7 – 4f65d1 transition of Eu2+ and shows a PL decay time of 263 ns. Under optimized synthesis conditions long-term stability of the optical properties without any sign of oxidation to Eu3+ is achieved, making the fully inorganic lead-free CsEuBr3 NCs promising deep blue emitters for optoelectronics.
Journal of Physical Chemistry C 151(2019), 231101
- Secondary publication expected from 17.12.2020
Modulated Rotating Waves in the Magnetised Spherical Couette System
We present a study devoted to a detailed description of modulated rotating waves (MRW) in the magnetised spherical Couette system. The set-up consists of a liquid metal confined between two differentially rotating spheres and subjected to an axially applied magnetic field. When the magnetic field strength is varied, several branches of MRW are obtained by means of three-dimensional direct numerical simulations. The MRW originate from parent branches of rotating waves and are classified according to Rand’s (Arch Ration Mech Anal 79:1–37, 1982) and Coughling and Marcus (J Fluid Mech 234:1–18, 1992) theoretical description. We have found relatively large intervals of multistability of MRW at low magnetic field, corresponding to the radial jet instability known from previous studies. However, at larger magnetic field, corresponding to the return flow regime, the stability intervals of MRW are very narrow and thus they are unlikely to be found without detailed knowledge of their bifurcation point. A careful analysis of the spatio-temporal symmetries of the most energetic modes involved in the different classes of MRW will allow in the future a comparison with the HEDGEHOG experiment, a magnetised spherical Couette device hosted at the Helmholtz-Zentrum Dresden-Rossendorf.
Keywords: Magnetohydrodynamics; Nonlinear waves; Bifurcation theory; Symmetry breaking; Experiments; Astrophysics
Journal of Nonlinear Science 29(2019)6, 2735-2759
Efficiency estimation of tray columns based on flow profiles and vapor-liquid equilibrium characteristics of binary mixtures
A new systematic approach for estimating the section and column efficiencies based on flow profiles and vapor−liquid equilibrium (VLE) characteristics of binary mixtures exclusively for each tray is proposed. A novel iterative technique for approximating the slope of the VLE curve and the tray efficiency is also developed. For demonstrating the predictive capabilities of the new approach, two case studies are formulated in this work - one with a theoretical column processing selected binary mixtures at total reflux, and the other involving an industrial column whose performance data are acquired from the literature. An in-depth analysis of theoretical column study reveals the superiority of the new approach over the most applied method. In the case study of industrial column, the new approach predicts the section efficiency accurately, unlike the efficiency underestimation from the most applied method. Such an approach would allow a priori calculation of the section and column efficiencies in the tray and column design phase.
- Vapor-liquid equilibrium data for efficiency estimation of … (Id 29624) HZDR-primary research data are used by this (Id 29618) publication
Industrial & Engineering Chemistry Research 58(2019)51, 23347-23358
- Secondary publication expected from 27.11.2020
Melting behaviour of uranium-americium mixed oxides under different atmospheres
In the context of a comprehensive campaign for the characterisation of transmutation fuels for next generation nuclear reactors, the melting behaviour of mixed uranium-americium dioxides has been experimentally studied for the first time by laser heating, for Am concentrations up to 70 mol. % under different types of atmospheres. Extensive post-melting material characterisations were then performed by X-ray absorption spectroscopy and electron microscopy. The melting temperatures observed for the various compositions follow a markedly different trend depending on the experimental atmosphere. Uranium-rich samples melt at temperatures significantly lower (around 2700 K) when they are laser-heated in a strongly oxidizing atmosphere compressed air at (0.300 ± 0.005) MPa, compared to the melting points (beyond 3000 K) registered for the same compositions in an inert environment (pressurised Ar). This behaviour has been interpreted on the basis of the strong oxidation of such samples in air, leading to lower-melting temperatures. Thus, the melting temperature trend observed in air is characterized, in the purely pseudo-binary dioxide plane, by an apparent maximum melting temperature around 2850 K for 0.3 < x(AmO2) < 0.5. The melting points measured under inert atmosphere uniformly decrease with increasing americium content, displaying an approximately ideal solution behaviour if a melting point around 2386 K is assumed for pure AmO2. In reality, it will be shown that the (U, Am)-oxide system can only be rigorously described in the ternary U-Am-O phase diagram, rather than the UO2-AmO2 pseudo-binary, due to the aforementioned over-oxidation effect in air. Indeed, general departures from the oxygen stoichiometry (Oxygen/Metal ratios ≠ 2.0) have been highlighted by the X-ray Absorption Spectroscopy (XAS). Finally, to help interpret the experimental results, thermodynamic computations based on the CALPHAD method will be presented.
Keywords: Uranium americium dioxide; Melting; Transmutation targets; CALPHAD
The Journal of Chemical Thermodynamics 140(2020), 105896
- Secondary publication expected from 01.01.2021
Hydrodynamic correlations for bubble columns from complementary UXCT and RPT measurements in identical geometries and conditions
Many correlations have been developed to predict the hydrodynamics of bubble columns. Often, these studies are performed for incomparable systems in terms of column and sparger dimensions as well as physical fluid properties. In this work, a different approach is proposed comprising interrelated correlations for liquid velocity, gas holdup and bubble size. The correlations are developed on the basis of complementary experiments with non-invasive measurement techniques, namely, Ultrafast X-ray Computed Tomography (UXCT) and Radioactive Particle Tracking (RPT). The experimental setup consists of a bubble column equipped with a needle sparger. The developed correlations consider sparger dimensions, operating conditions and bubble size. The bubble size is applied as the characteristic length in the Reynolds and the Eötvös numbers, which are utilized for the gas holdup and liquid velocity correlations. In comparison with previous approaches, the developed correlations show better agreement with experimental data from this study as well as from the literature.
Keywords: Bubble columns; Hydrodynamic correlations; Radioactive particle tracking; Ultrafast X-ray computed tomography
Chemical Engineering Science 208(2019), 115099
- Fulltext from www.sciencedirect.com
- Secondary publication expected from 23.11.2020
The missing pieces of the PuO2 nanoparticles puzzle
Gerber, E.; Romanchuk, A.; Pidchenko, I.; Amidani, L.; Roßberg, A.; Hennig, C.; Vaughan, G.; Trigub, A.; Egorova, T.; Bauters, S.; Plakhova, T.; Hunault, M.; Weiß, S.; Butorin, S.; Scheinost, A.; Kalmykov, S.; Kvashnina, K.
The nanoscience field often produces results more mystifying than any other discipline. It has been argued that changes of the plutonium dioxide (PuO2) particle size from bulk to nano can have a drastic effect on PuO2 properties. Here we report a full characterization of PuO2 nanoparticles (NPs) at the atomic level, explore their stability and probe their local and electronic structure. The particles were synthesized from precursors with different oxidation states (Pu III, IV and V) under various environmentally and waste storage relevant conditions (pH 8 and pH 12). We demonstrate that well dispersed, crystalline NPs with a size of ~2.5 nm in diameter are always formed in spite of diverse chemical conditions. Identical crystal structures and the presence of only Pu(IV) oxidation state in all NPs indicate that their fundamental properties, rather than being fancy and exotic, are identical to those of the bulk PuO2.
A novel metastable pentavalent plutonium solid phase on the pathway from aqueous Pu(VI) to PuO2 nanoparticles
We report here experimental evidence that the formation of PuO2 nanoparticles from oxidized Pu(VI) under environmentally relevant conditions proceeds through the formation of an intermediate Pu(V) solid phase, similar to NH4PuO2CO3, which is stable over a period of several months. State-of-the-art experiments at Pu M4 and L3 absorption edges combined with theoretical calculations unambiguously allowed us to determine the oxidation state and the local structure of this intermediate phase
Angewandte Chemie - International Edition 58(2019)49, 17558-17562
A multi-technique study of altered granitic rock from the Krunkelbach Valley uranium deposit, Southern Germany
Herein, a multi-technique study was performed to reveal the elemental speciation and microphase composition in altered granitic rock collected from the Krunkelbach Valley uranium (U) deposit area near an abandoned U mine, Black Forest, Southern Germany. The former Krunkelbach U mine with 1–2 km surrounding area represents a unique natural analogue site with the rich accumulation of secondary U minerals suitable for radionuclide migration studies from a spent nuclear fuel (SNF) repository. Based on a micro-technique analysis using several synchrotron-based techniques such as X-ray fluorescence analysis, X-ray absorption spectroscopy, powder X-ray diffraction and laboratory-based scanning electron microscopy and Raman spectroscopy, the complex mineral assemblage was identified. While on the surface of granite, heavily altered metazeunerite–metatorbernite (Cu(UO2)2(AsO4)2−x(PO4)x·8H2O) microcrystals were found together with diluted coatings similar to cuprosklodowskite (Cu(UO2)2(SiO3OH)2·6H2O), in the cavities of the rock predominantly well-preserved microcrystals close to metatorbernite (Cu(UO2)2(PO4)2·8H2O) were identified. The Cu(UO2)2(AsO4)2−x(PO4)x·8H2O species exhibit uneven morphology and varies in its elemental composition, depending on the microcrystal part ranging from well-preserved to heavily altered on a scale of ∼200 μm. The microcrystal phase alteration could be presumably attributed to the microcrystal morphology, variations in chemical composition, and geochemical conditions at the site. The occurrence of uranyl-arsenate-phosphate and uranyl-silicate mineralisation on the surface of the same rock indicates the signatures of different geochemical conditions that took place after the oxidative weathering of the primary U- and arsenic (As)-bearing ores. The relevance of uranyl minerals to SNF storage and the potential role of uranyl-arsenate mineral species in the mobilization of U and As into the environment is discussed.
RSC Advances 10(2020), 25529-25539
Direct measurements of low-energy resonance strengths of the 23Na(p,γ)24Mg reaction for astrophysics
Boeltzig, A.; Best, A.; Pantaleo, F. R.; Imbriani, G.; Junker, M.; Aliotta, M.; Balibrea-Correa, J.; Bemmerer, D.; Broggini, C.; Bruno, C. G.; Buompane, R.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Deboer, R. J.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Kochanek, I.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; Munnik, F.; Paticchio, V.; Perrino, R.; Piatti, D.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.; Wiescher, M.; Zavatarelli, S.
The NeNa and the MgAl cycles play a fundamental role in the nucleosynthesis of asymptotic giant branch stars undergoing hot bottom burning. The 23Na (p , γ)24Mg reaction links these two cycles and a precise determination of its rate is required to correctly estimate the contribution of these stars to the chemical evolution of various isotopes of Na, Mg and Al. At temperatures of 50 ≲ T ≲ 110MK, narrow resonances at Ep = 140 and 251keV are the main contributors to the reaction rate, in addition to the direct capture that dominates in the lower part of the temperature range. We present new measurements of the strengths of these resonances at the Laboratory for Underground Nuclear Astrophysics (LUNA). We have used two complementary detection approaches: high efficiency with a 4π BGO detector for the 140 keV resonance, and high resolution with a HPGe detector for the 251 keV resonance. Thanks to the reduced cosmic ray background of LUNA, we were able to determine the resonance strength of the 251 keV resonance as ωγ = 482 (82) μeV and observed new gamma ray transitions for the decay of the corresponding state in 24Mg at Ex = 11931keV. With the highly efficient BGO detector, we observed a signal for the 140 keV resonance for the first time in a direct measurement, resulting in a strength of ωγ140 = 1.46-0.53+0.58 neV (68% CL). Our measurement reduces the uncertainty of the 23Na (p , γ)24Mg reaction rate in the temperature range from 0.05 to 0.1 GK to at most -35%+50% at 0.07 GK. Accordingly, our results imply a significant reduction of the uncertainties in the nucleosynthesis calculations.
Keywords: LUNA; Nuclear Astrophysiscs; Underground nuclear physics; Hydrogen burning; Stellar evolution
Physics Letters B 795(2019), 122-128
Direct observation of the attachment behavior of hydrophobic colloidal particles onto a bubble surface
The attachment of solid particles to the surface of immersed gas bubbles plays a fundamental role in surface science, and hence plays key roles in various engineering fields ranging from industrial separation processes to the fabrication of functional materials. However, detailed investigation from a microscopic view on how a single particle attaches to a bubble surface and how the particle properties affect the attachment behavior has been so far scarcely addressed. Here, we observed the attachment of a single particle to a bubble surface using a high-speed camera and systematically investigated the effects of the wettability and shape of particles. We found that hydrophobic particles abruptly “jumped into” the bubble while sliding down the bubble surface to eventually satisfy their static contact angles, the behavior of which induced a much stronger attachment to the bubble surface. Interestingly, the determinant factor for the attachment efficiency of spherical particles was not the wettability of the spherical particles but the location of the initial collision with the bubble surface. In contrast, the attachment efficiency of anisotropically-shaped particles was found to increase with the hydrophobicity caused by a larger contact area to the bubble surface. Last but not least, a simple formulation is suggested to recover the contact angle based on the jump-in.
Soft Matter 16(2020), 695
- Secondary publication expected from 03.12.2020
Electro-Hydro Dynamic ion sources and Focused ion Beam Machines
In this talk we will review and detail the current status of EHD ion sources, also commonly referred as Liquid Metal Ion Sources, their development perspectives and their ever present expanding applicative domains. We will review the roots of this technology born in the early 70’s, deriving from space propulsion research, when physicists applied EHD phenomena onto liquid metal meniscus to create high brightness ion sources. Since then the LMIS qualities based on a remarkable brightness, excellent emission stabilities (current emission and emitting area invariance), ease of operation, lifespan and compactness small size were at the origin of the focused ion beam (FIB).
As a deeply involved team in the pursuing quest aiming at investigating the full applied potential of the direct-write Focused Ion Beams technology since the mid-80’s, we will analyze and comment the never interrupted major effort invested around the world aiming at developing alternative ion sources. As a complement to the development of high current sources or atomic-sized emitters, we will show that high performance Liquid Metal Ion Sources and Liquid Metal Alloys Ion Sources exhibit definitive advantages at the prototyping level.
We will analyze, quantify and describe the potential gains still to be expected from the widely used gallium LMIS and other alloy ion sources, that add a large number of ion species and patterning schemes.
In conclusion we will summarize our vision on the future of FIB technology based on electro-Hydro Dynamically (EHD) driven emitters operating in the cone-jet mode, both in terms of performances, versatility and on the science frontiers these might help to push. My presentation will be an attempt to provide an overview on this FIB continuous evolution and future capabilities.
Keywords: EHD ion sources; direct-write Focused Ion Beam technology
Invited lecture (Conferences)
2019 MRS Fall Meeting, 01.-06.12.2019, Boston, USA
GaBiLi Liquid Metal Alloy Ion Sources for Advanced Nanofabrication
Nanofabrication requirements for FIB technologies are specifically demanding in terms of patterning resolution, stability and the support of new processing techniques. Additionally, the type of ion defines the nature of the interaction mechanism with the sample and thus has significant consequences on the resulting nanostructures . Therefore, we have extended the technology towards the stable delivery of multiple ion species selectable into a nanometer scale focused ion beam by employing a liquid metal alloy ion source (LMAIS) . This LMAIS provides single and multiple charged mon- as well as polyatomic ion species of different masses, resulting in significantly different interaction mechanisms. Nearly half of the elements of the periodic table are thus made available in the FIB technology as a result of continuous research in this area . This range of ion species with different mass or charge can be beneficial for various nanofabrication applications. Recent developments could make these sources to an alternative technology feasible for nanopatterning challenges. In this contribution, the operation principle, the preparation and testing process as well as prospective domains for modern FIB applications will be presented. As an example we will introduce the GaBiLi LMAIS. It enables high resolution imaging with light Li ions and sample modification with Ga or heavy polyatomic Bi clusters, all coming from one ion source. For sub-10 nm focused ion beam nanofabrication and microscopy, the GaBiLi-FIB or the AuSiGe-FIB could benefit of providing additional ion species in a mass separated FIB without changing the ion source.
 L. Bruchhaus, P. Mazarov, L. Bischoff, J. Gierak, A. D. Wieck, and H. Hövel, Comparison of technologies for nano device prototyping with a special focus on ion beams: A review, Appl. Phys. Rev. 4, 011302 (2017).
 L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Liquid Metal Alloy Ion Sources – An Alternative for Focused Ion Beam Technology, Appl. Phys. Rev. 3 (2016) 021101.
 J. Gierak, P. Mazarov, L. Bruchhaus, R. Jede, L. Bischoff, Review of electrohydrodynamical ion sources and their applications to focused ion beam technology, JVSTB 36 (2018).
 W. Pilz, N. Klingner, L. Bischoff, P. Mazarov, and S. Bauerdick, Lithium ion beams from liquid metal alloy ion sources, JVSTB 37(2), Mar/Apr (2019).
Keywords: Liquid Metal Alloy Ion Source; GaBiLi alloy; Focused Ion Beam
AVS International Symposium and Exhibition, 20.-25.10.2019, Columbus, Ohio, USA
New light and heavy ion beams from liquid metal alloy ion sources for advanced nanofabrication and ion implantation.
Focused Ion Beam (FIB) processing has been developed into a well established and still promising technique for direct patterning and proto-typing on the nm scale, high resolution imaging or high resolution ion lithography1. Exploring the Liquid Metal Alloy Ion Sources (LMAIS) potential represents a promising alternative to expand the global FIB application fields. Thanks to this, nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last fifty years2. Recent developments could make these sources to an alternative technology feasible for nanopatterning challenges.
Concerning ion beam resolution and minimization of unwanted damage, light ions like He or Li are preferred candidates. Liquid metal alloy ion sources (LMAIS) with a life time of more than 1000 µAh on the basis of Ga35Bi60Li5 and Sn95Li5 alloys were developed, characterized and finally applied in a commercial mass-separated VELION FIB-SEM system (Raith GmbH) 3. In the case of Li ions from the mass separated FIB a lateral resolution of 5.6 nm could be obtained in first experiments and the sputter yield was determined to 0.4 for 35 keV Li ions on Au. For reference, the helium ion microscope (HIM) has a lateral resolution of about 0.5 nm and 1.8 nm, for He and Ne respectively, He has a sputter yield of 0.14. For sub-10 nm focused ion beam nanofabrication and microscopy, the GaBiLi-FIB or the SnLi-FIB could therefore be considered alternatives to the HIM with the benefit of providing additional ion species in a mass separated FIB without changing the ion source.
In this contribution the operation principle, the preparation and testing process as well as prospective domains for modern FIB applications will be presented1,5. As an example we will introduce a GaBiLi LMAIS in detail. It enables high resolution imaging with light Li ions and sample modification with Ga or heavy polyatomic Bi clusters, all coming from one ion source. Moreover we will discuss the main properties of a modern LMAIS like long life-time, high brightness and stable ion current. The physical basics and experimental results of LMAIS, their physical properties (I-V characteristics, energy spread) and questions of the preparation technology using elementary as well as binary and ternary alloys as source material will be covered.
1 L. Bruchhaus et al. Appl. Phys. Rev. 4, 011302 (2017).
2 L. Bischoff et al. Appl. Phys. Rev. 3, 021101 (2016).
3 W. Pilz et al. J. Vac. Sci. Technol. B 37, 021802 (2019).
4 G. Hlawacek et al. J. Vac. Sci. Technol. B 32, 020801 (2014).
5 J. Gierak et al. J. Vac. Sci. Technol. B 36, 06J101(2018).
Keywords: Liquid Metal Alloy Ion Source; nanofabrication; focused ion beam
Invited lecture (Conferences)
2019 MRS Fall Meeting, 01.-06.12.2019, Boston, USA
Combined proton-photon treatments: How can limited proton slots be optimally distributed over a patient cohort?
Although rapidly growing, proton therapy is a limited resource, which is not available to all the patients who may benefit from it. In this study, we investigate if combined proton-photon treatments, in which some fractions are delivered with protons and the rest with photons, improve on single-modality treatments. Combined treatment can be motivated by the consideration that, on the convex part of the NTCP curve, the first proton fractions are the most beneficial. We assume a situation of limited proton slot availability and develop methods to distribute those limited slots over a patient cohort optimally in order to optimize the benefit of proton therapy at a population level.
Material and Methods:
We consider a cohort of 45 head and neck cancer patients for which IMRT and IMPT plans were previously created . NTCP models for relevant side effects (e.g. xerostomia) were used to calculate the NTCP values for all the plans. We investigate a 30 fraction simultaneous integrated boost (SIB) scheme (1.8 Gy to the PTV, 2.3 Gy to the GTV) and a sequential boost (SEQ) scheme with a 25 fraction base plan (2 Gy to the PTV) and a 10 fraction boost plan (2 Gy to the GTV). Under the assumption that, due to limited resources, only a small percentage of the total number of fractions can be delivered with protons, an integer programming algorithm was applied to determine the optimal number of proton fractions per patient that minimizes the total number of expected complications over the patient cohort.
Figure 1a shows the NTCP values for xerostomia in the IMRT and IMPT plans for the SIB scheme for all patients. Figures 1b shows the optimal allocation of proton slots for the situation where 20% of all fractions are delivered with protons. The patients with the highest ∆NTCP value (IMRT-IMPT) receive the largest number of proton fractions. The average xerostomia NTCP value from all 45 patients for the SIB scheme for combined treatment equals 13.0%. For the single-modality treatment, where the 20% of patients with the highest ∆NTCP are selected for proton therapy, the average NTCP equals 13.2%. For the SEQ scheme, the average NTCP values for xerostomia equal 13.6% and 14.2% for the combined and the single-modality treatment, respectively. Figure 1c shows the corresponding proton slot allocation for the SEQ scheme, indicating that only 3 patients receive proton slots for the boost plan whereas most proton slots are used for base plans. To achieve an average NTCP of 14.2%, combined treatment would require only 265 (16.8%) proton fractions instead of 315 (20%). Similar results were obtained for NTCP models for dysphagia and aspiration.
Combined proton-photon treatments with optimized allocation of proton slots increase the benefit of proton therapy on the population level compared to single-modality treatments with optimal proton patient selection. However, the benefit is small for the SIB scheme. A larger benefit is observed for the sequential boost scheme, where combined treatments can exploit that some patients benefit from proton boost plans and others from proton base plans.
Keywords: proton therapy; slot allocation; NTCP reduction
53rd SSRMP Annual Meeting, 21.-22.11.2019, Villigen, Schweiz
Untersuchung disperser Zweiphasenströmungen in komplexen Geometrien – Methodenentwicklung und Experimente
Das Gesamtziel des Vorhabens war die Verbesserung der methodischen experimentellen Basis für die Weiterentwicklung von CFD-Codes zur Berechnung dreidimensionaler zweiphasiger Strömungsvorgänge, wie sie im Kühlkreislauf von Kernkraftwerken auftreten. Es ordnet sich damit in das strategische Ziel der Reaktorsicherheitsforschung ein, wobei die nachhaltige Verbesserung der experimentellen Basis zur Validierung von CFD-Modellen für die Berechnung sicherheitsrelevanter Strömungsvorgänge in Kernkraftwerken im Fokus stand. Die erzielten Ergebnisse der experimentellen Studien liefern zudem wertvolle Grundlagenkenntnisse zu Zweiphasenströmungen sowie Validierungsdaten für zukünftige Weiterentwicklungen von CFD-Codes.
Wesentliche Bestandteile aktueller CFD-Code-Weiterentwicklung, speziell für den Reaktorkreislauf, sind die Turbulenzmodellierung und Zweiphasenströmungen. Hierfür werden räumlich und zeitlich hochaufgelöste experimentelle Validierungsdaten benötigt. In diesem Vorhaben wurden dafür zwei moderne Messverfahren für die Charakterisierung von zweiphasigen Strömungen eingesetzt. Mit diesen wurden die Phasenverteilung und Gasphasendynamik, sowie Flüssigphasengeschwindigkeit und Turbulenz in ausgewählten generischen Experimenten untersucht.
Weiterhin wurden in diesem Vorhaben ausgewählte experimentelle Ergebnisse mit CFD-Vorausrechnungen verglichen. Die zweiphasige Strömungssimulation wurde mit dem verfügbaren Simulationswerkzeug ANSYS-CFX durchgeführt, um für diesen Anwendungsfall bereits verfügbare Standardmodelle auf ihre Anwendbarkeit zu prüfen.
Keywords: ultrafast x-ray CT; hot-wire anemometry; two-phase flow; bubbly pipe flow; three-dimensional flow; obstacle; CFD
Dresden: Eigenverlag, 2019
Investigation of three-dimensional two-phase flow using combined ultrafast X-ray tomography and hot-film anemometry
Gas-liquid two-phase flow modelling is of highest relevance in nuclear safety analyses. This concerns e.g. the modelling of steam-water two-phase flow and heat transfer in the reactor core, the steam generators, the containment and the spent fuel pool under accident conditions. Prediction of flow conditions by Computational Fluid Dynamics (CFD) tools is of particular interest for supporting safety assessments. However, achieving physically correct simulations is quite challenging due to the complexity of the flow, which includes turbulence, highly deformable gas-liquid interfaces and heat, mass and momentum transfer across the interfaces. Today, two-phase flow models contain a large number of empirical correlations and closure models, which are derived from experimental data. The role of thermal hydraulics experiments nowadays still lies in the creation of such data but moreover they are also needed for model validation.
This contribution describes an experimental study of a generic three-dimensional two phase flow, which should serve as a future benchmark experiment for CFD code validation. The experiments were conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) and are a continuation of earlier studies, which were performed using a moveable flow obstacle and the wire-mesh sensor technique. Although these investigations already provided very good data for a generic two-phase flow, the intrusiveness of both sensor and obstacle motion unit lead to some non-idealities with respect to the fully undisturbed flow. With a new imaging technique, ultrafast electron beam X-ray tomography, we are now able to perform investigations fully non-intrusively and to study the gas phase dynamics with high temporal and spatial resolution in two planes simultaneously. Furthermore, the previous studies did not provide measurement data of liquid velocities, which are required for CFD code validation. Thus, for this study ultrafast X-ray tomography and hot-film anemometry was used in combination to extend the available experimental database. This paper presents selected results of this experimental study.
Keywords: ultrafast x-ray CT; hot-wire anemometry; two-phase flow; bubbly pipe flow; three-dimensional flow; obstacle; CFD
50th Annual Meeting on Nuclear Technology, 07.-08.05.2019, Berlin, Deutschland
Contribution to proceedings
50th Annual Meeting on Nuclear Technology, 07.-08.05.2019, Berlin, Dresden
Proceedings of the 50th Annual Meeting on Nuclear Technology
Investigation of three-dimensional two-phase flow using combined ultrafast X-ray tomography and hot-film anemometry
In vielen industriellen Prozessen und Apparaten treten Mehrphasenströmungen auf. Dies sind häufig Flüssigkeits-Gas-Strömungen, beispielsweise in der Kraftwerkstechnik, in Wärmetauschern, chemischen Reaktoren und Trennapparaten oder in Ölfördersystemen. Ein großes Ziel ist die Berechnung solcher Strömungen mittels computergestützter Simulationswerkzeuge (CFD Codes) zur Unterstützung der Auslegung, zur Optimierung, aber auch zur Sicherheitsbewertung. Die komplexe Physik von Zweiphasenströmungen erschwert dieses Vorhaben im Vergleich zu einphasigen Strömungen erheblich. Grund dafür ist die Komplexität der Transportprozesse über stark verformbare und sich verändernde Phasengrenzflächen in mehreren Zeit- und Längenskalen. Zudem werden durch anlagentechnische Komponenten, wie beispielsweise Krümmer, Ventile, T-Stücke oder querschnittsverändernde Einbauten, ausgeprägte dreidimensionale Strömungsfelder erzeugt, welche von aktuellen CFD-Codes nur sehr stark eingeschränkt berechnet werden können.
Der Beitrag beschäftigt sich mit der experimentellen Untersuchung von generischen dreidimensionalen Zweiphasenströmungen. Mit Hilfe neuartiger experimenteller Methoden wurde eine Datenbasis für die nachhaltige Validierung und Weiterentwicklung von CFD-Codes, speziell für dreidimensionale Strömungseffekte, generiert.
Keywords: ultrafast x-ray CT; hot-wire anemometry; two-phase flow; bubbly pipe flow; three-dimensional flow; obstacle; CFD
Jahrestreffen Reaktionstechnik 2019 gemeinsam mit der Fachgruppe Mehrphasenströmungen, 27.-29.05.2019, Würzburg, Deutschland
Experimental investigation of three-dimensional bubbly two-phase pipe flows
Modelling gas-liquid two-phase flow is a topic of constant relevance in nuclear thermal hydraulics. Gas-disperse two-phase flows occur in e.g. fuel elements in the reactor core, in pipes and components during pressure loss, sudden reflooding or other events. Due to the deformable gas-liquid interface and the complexity of heat, mass and momentum transfer across the interface, gas-liquid two-phase flow is very difficult to model and simulate. On the device scale it is common to use Euler/Euler multi-fluid approaches for CFD simulations, which require a good number of empirical correlations as closure models. Such models are commonly derived from experiments. Validation of the correctness of predictive simulations then also requires experiments, which must be simplified to a degree to allow provision of CFD-grade experimental data but complex enough to resemble real flow situations. The latter calls especially for investigations on flow fields in more complex three-dimensional domains, which are prototypical for e.g. bends, valves, T-junctions and rod bundles.
Keywords: ultrafast x-ray CT; two-phas flow; three-dimensional flow; obstacle
East German Centre of Competence in Nuclear Technology Workshop of Doctoral Candidates, 13.12.2018, Zittau, Deutschland
Mitigating Meniscus Instabilities in Solution-Sheared Polymer Films for Organic Field-Effect Transistors
Semiconducting donor−acceptor copolymers are considered to be a promising material class for solution-coated, large-scale organic electronic applications. A large number of works have shown that the best-performing organic field-effect transistors (OFETs) are obtained on low-surface-energy substrates. The meniscus instabilities that occur when coating on such surfaces considerably limit the effective deposition speeds. This represents a limiting factor for the upscaling of device fabrication for mass production, an issue that needs to be addressed if organic electronic devices are ever to become commercially relevant. In this work, we present a method to increase the accessible window of coating speeds for the solution shearing of donor−acceptor semiconductor polymers for the fabrication of OFETs. By incorporating a piezo crystal that is capable of producing high-frequency vibrations into the coating head, we are able to mitigate contact line instabilities due to the depinning of the contact line, thereby suppressing the commonly encountered “stick-and-slip” phenomenon.
Keywords: organic field-effect transistors; solution shearing; meniscus instabilities; vibration; large-area fabrication
ACS Applied Materials and Interfaces 11(2019), 30079-30088
- Secondary publication expected
p-type codoping effect in (Ga,Mn)As: Mn lattice location versus magnetic properties
In the present work, we perform a systematic investigation on p-type codoping in (Ga,Mn)As. Through gradually increasing Zn doping concentration, the hole concentration increases, which should theoretically lead to an increase of the Curie temperature (TC) according to the p-d Zener model. Unexpectedly, although the film keeps its epitaxial structure, both TC and the magnetization decrease. The samples present a phase transition from ferromagnetism to paramagnetism upon increasing hole concentration. In the intermediate regime, we observe a signature of antiferromagnetism. By using channeling Rutherford backscattering spectrometry and particle-induced x-ray emission, the substitutional Mn atoms are observed to shift to interstitial sites, while more Zn atoms occupy Ga sites, which explains the observed behavior. This is also consistent with first-principles calculations, showing that the complex of substitutional Zn and interstitial Mn has the lowest formation energy.
Physical Review Materials 3(2019), 084604
Background in γ-ray detectors and carbon beam tests in the Felsenkeller shallow-underground accelerator laboratory
The relevant interaction energies for astrophysical radiative capture reactions are very low, much below the repulsive Coulomb barrier. This leads to low cross sections, low counting rates in γ-ray detectors, and therefore the need to perform such experiments at ion accelerators placed in underground settings, shielded from cosmic rays. Here, the feasibility of such experiments in the new shallow-underground accelerator laboratory in tunnels VIII and IX of the Felsenkeller site in Dresden, Germany, is evaluated. To this end, the no-beam background in three diff erent types of germanium detectors, i.e. a Euroball/Miniball triple cluster and two large monolithic detectors, is measured over periods of 26-66 days. The cosmic-ray induced background is found to be reduced by a factor of 500-2400, by the combined eff ects of, first, the 140 meters water equivalent overburden attenuating the cosmic muon flux by a factor of 40, and second, scintillation veto detectors gating out most of the remaining muon-induced eff ects. The new background data are compared to spectra taken with the same detectors at the Earth’s surface and at other underground sites. Subsequently, the beam intensity from the cesium sputter ion source installed in Felsenkeller has been studied over periods of several hours. Based on the background and beam intensity data reported here, for the example of the 12 C(α,γ) 16 O reaction it is shown that highly sensitive experiments will be possible.
Keywords: Nuclear Astrophysiscs; Underground experiment, sputter source, Felsenkeller
European Physical Journal A 55(2019)10, 174
Contribution to WWW
- Secondary publication expected from 17.10.2020
Photodecarbonylation and in vitro studies of dicarbonyl ruthenium complexes
Carbon monoxide has been demonstrated to exhibit several beneficial effects on biological targets (anti-inflammatory, anti-proliferative, anti-apoptotic effects, causes vasodilation, etc.). Consequently, the development of CO releasing molecules (CORMs) that allows a controlled release of CO under physiological conditions has therefore become a major field of scientific and medical interest. Considerable research interest has been drawn on light-activated CORMs (photoCORMs) which only release CO upon radiation with certain wavelengths. However, despite a large number of photoCORMs reported, relatively little information is available on the precise mechanism of CO release from most photoCORMs and even less compounds have been tested as anti-cancer agents in cells so far. Herein, we report the synthesis of ruthenium(II) carbonyl complexes functionalized with (fluorescent) bidentate pyridyl (1) and tridentate diquinolyl ligands (2) and investigate the mechanism of CO release in aqueous media (before and after light-activation). The photo-induced CO release kinetics of the Ru(II) photoCORMs, as well as in vitro studies in cancerous and healthy cell lines will be presented .
 R. Motterlini, L. E. Otterbein, Nat. Rev. Drug Discov. 9 (2010) 728-743.
 U. Schatzschneider, Br. J. Pharmacol. 172 (2015) 1638-1650.
 M. Kubeil, R. R. Vernooij, C. Kubeil, B. R. Wood, B. Graham, H. Stephan, L. Spiccia, Inorg. Chem.
56 (2017) 5941-5952.
 M. Kubeil, T. Joshi, B. R. Wood, H. Stephan, ChemistryOpen (2019) accepted.
19th International Conference on Biological Inorganic Chemistry, 11.-16.08.2019, Interlaken, Schweiz
None is like the other: the interaction of selected fungi with radionuclides
Not only since Chernobyl and Fukushima is it well known that fungi can accumulate large amounts of heavy metals and radionuclides. Although there are many publications describing this phenomenon and naming transfer factors, almost nothing is known about the underlying molecular processes being responsible for the binding, uptake and accumulation in the cell or even transport inside the organism for elements like uranium, americium and other heavy radio-metals. However, knowing this is crucial if one wants to understand the influence of fungi on the migration behavior of radionuclides in the environment. It is all the more important to know the underlying biochemical processes and to know how environmental influences affect the radionuclide-cell interaction, if one considers using these extraordinary properties to biologically immobilize radionuclides in contaminated soil or even to remove radionuclides from it. As part of the BioVeStRa project, various fungi have been studied to determine their potential for precautionary radiation protection and the remediation of contaminated soils. Therefore, two fungi were selected based on published transfer factor and a known rapid growth on complex media, namely Schizophyllum commune and Leucoagaricus naucinus. Additionally, two further fungi metabolically related to S. commune or L. naucinus were included also in the studies to determine if similar fungi behave similarly or not. To study the fungi, a combination of growth and binding experiments, mass spectrometry, fluorescence spectroscopy and electron microscopy was used. In summary, it can be stated, that S. commune is not only the most robust fungus that prevails even in the test field against autochthonic soil microbes and fungi, but also shows the highest accumulation rates for uranium and europium, the latter as a substitute for trivalent actinides such as americium. Furthermore, it could be shown that fungi behave very differently depending on the investigated elements.
Keywords: fungi; radinuclides; spectroscopy; microscopy
Invited lecture (Conferences)
18. Jenaer Sanierungskolloquium, 01.-02.10.2019, Jena, Deutschland
Carbon nanotubes for mechanical sensor applications
This article features the evolution of carbon nanotubes as functional material in nano and microelectromechanical systems. Introducing materials morphologies for the CNTs in a homologue series (single CNTs - bundles, fibers, yarns - networks and thin films), different concepts for mechanical sensors based on the intrinsic and extrinsic properties of the CNT material are introduced (piezoresistive effect, strain-induced band bending, charge tunneling).
In a rigorous theoretical treatment, the limits of the achievable sensor performance (i.e., gauge factor) are derived and discussed in the context of applications. A careful literature survey shows that highest sensitivity is reached for devices exploiting the intrinsic transport properties of single CNTs. For reliability tests of such sensor systems made from nanomaterials and classical MEMS, a specimen-centered approach is introduced to give viable insights into the structure-property relationships and failure modes.
Keywords: carbon nanotubes (CNTs); sensors; micro- and nano electromechanical systems (MEMS; NEMS); strain; reliability
Physica Status Solidi (A) 216(2019)19, 1900584
Interlayer excitons in van-der-Waals heterostructures: MoS2 on GaSe
Hybrid van-der-Waals heterostructures of two-dimensional nanomaterials are a vibrant field of study: The (weak) electronic interaction between two layers is often reasonably described by a perturbation of the physical effects of the isolated layers, such as electrostatic doping and increased screening of intralayer excitons. However, it turns out that this picture of the weak interaction is not exhaustive in terms of all optical properties: the formation of bound excitons from electrons of one layer and holes from the other layer yields the formation of interlayer excitons. These mixed states are measured experimentally by photoluminescence and photocurrents and predicted by theory. Examples are of MoS2 or MoSe2 on WSe2, MoS2 or GaSe due to type-II band alignment [1-3].
The conditions for the formation of interlayer excitons are elucidated from a first-principles point of view. For this, first-principles studies of a minimal test system of MoS2 on GaSe is conducted .
This work envisions to predict the interlayer states as a function of the heterostack in order to specifically tailor efficient photon absorption.
Keywords: 2D materials; DFT; Bethe-Salpeter; Density-functional perturbation theory; MoS2; GaSe; bilayer; van-der-Waals heterostructure; interlayer exciton
Chem2DMat, 03.-06.09.2019, Dresden, Deutschland
Order/disorder processes and electromechanical properties of monoclinic GdCa4O(BO3)3
Münchhalfen, M.; Schreuer, J.; Reuther, C.; Möckel, R.; Götze, J.; Mehner, E.; Stöcker, H.; Meyer, D.
Large single crystals of GdCa₄O(BO₃)₃ (space group Cm) were grown by the Czochralski method. Dielectric, piezoelectric and elastic coefficients at room temperature as well as specific heat capacity, thermal expansion and cation disorder were studied employing a variety of methods including resonant ultrasound spectroscopy, differential scanning calorimetry, dilatometry and X-ray diffraction techniques. The electromechanical parameters (4 dielectric, 10 piezoelectric and 13 elastic stiffness coefficients) obtained on different samples are in excellent agreement indicating high internal consistency of our approach, whereas the values reported in literature differ significantly. The elastic behaviour of GdCa₄O(BO₃)₃ resembles the one of structurally related fluorapatite, i.e. the elastic anisotropy is relatively small and the longitudinal effect of the deviations from Cauchy-relations exhibit a pronounced minimum along the direction of the dominating chains of cation polyhedra. GdCa₄O(BO₃)₃ exhibits a maximum longitudinal piezoelectric effect of 7.67 × 10−12 CN−10, a value in the order of that of langasite-type materials. Significant changes of the calcium/gadolinium distribution on the 3 independent cation sites accompanied by characteristic anomalies of heat capacity and thermal expansion suggest processes of nonconvergent cation ordering above about 900 K in GdCa₄O(BO₃)₃.
Keywords: elasticity; GdCa₄O(BO₃)₃; heat capacity; nonconvergent cation ordering; piezoelectricity; thermal expansion
Zeitschrift für Kristallographie 234(2019)11-12, 707-724
One-step radiosynthesis of the MCTs imaging agent [18F]FACH by aliphatic 18F-labelling of a methylsulfonate precursor containing an unprotected carboxylic acid group
Monocarboxylate transporters 1 and 4 (MCT1 and MCT4) are involved in tumour development and progression. Their level of expression is particularly upregulated in glycolytic cancer cells and accordingly MCTs are considered as promising drug targets for treatment of a variety of human cancers. The non-invasive imaging of these transporters in cancer patients via positron emission tomography (PET) is regarded to be valuable for the monitoring of therapeutic effects of MCT inhibitors. Recently, we developed the first 18F-radiolabelled MCT1/MCT4 inhibitor [18F]FACH and reported on a two-step one-pot radiosynthesis procedure. We herein describe now a unique one-step radiosynthesis of this radiotracer which is based on the approach of using a methylsulfonate (mesylate) precursor bearing an unprotected carboxylic acid function. With the new procedure unexpected high radiochemical yields of 43 ± 8% at the end of the radiosynthesis could be obtained in a strongly reduced total synthesis time. Moreover, the radiosynthesis was successfully transferred to a TRACERlab FX2 N synthesis module ready for future preclinical applications of [18F]FACH.
Keywords: monocarboxylate transporters (MCTs); [18F]FACH; PET; aliphatic nucleophilic 18F-labelling; unprotected precursor
Scientific Reports 9(2019), 18890
Sample preparation for AMS astrophysics projects – Size does (not) matter
The determination of long-lived radionuclides by means of accelerator mass spectrometry (AMS) is usually outstandingly successful when an interdisciplinary team comes together. The “heart” of AMS research is of course an accelerator equipped with sophisticated ion sources, analytical tools and detectors run by experienced and ambitious physicists [e.g. 1-3]. Setting-up and further developing AMS systems is one of the most interesting and challenging topics. The reputation to be reached here is the greatest uniqueness of analysis possible, lowest detection levels, and/or most reliable data world-wide.
For sure, another primary pillar of AMS research is based on the questions addressed within fundamental and applied research. “How have supernovae explosions influenced Earth, our solar system and beyond?” [e.g. 4] or “How does the Earth’s surface and environment respond to earthquakes, climate change and anthropogenic influences?” [e.g. 5] are just two examples of high-quality studies.
However, somehow in-between there are groups of hidden figures like people developing software for data analysis or performing the required chemical sample preparation for AMS. These often unacknowledged individuals do crucial work for the overall outcome of the studies.
Chemists can spend weeks and months trying (and failing) on sample preparation before they find a “safe way” and start the actual work on the most valuable sample material, repeat all over again the same “recipe” for hundreds of samples, or train non-chemists the secrets of their successful recipes. Nevertheless, interdisciplinary AMS work can also be very exciting for a chemist: touching (and destroying) samples from outer space, the deep ocean or (currently) frozen places like Antarctica is quite thrilling. But at the end of the day, the whole AMS chemist’s work can be described as “reducing the sample matrix, other impurities and especially isobars to a level the AMS machine can handle while enriching the radionuclide of interest”.
Starting materials for applications such as astrophysical research can be “orders of magnitude” different: a neutron-irradiated sample of 1 g tungsten powder , over 40 g of clay-rich material from the Cretaceous–Tertiary (K-T) boundary, 100 g of ultra-pure sodium iodide, or 500 kg of snow from Antarctica  can cause totally different and sometimes unexpected problems in the chemistry lab. In general, smaller samples are not always easier to handle for example if they are chemically rather resistant or reactive. The cream of the crop of failure and success in a few AMS chemistry labs will be presented.
 P. Steier et al., Int. J. Mass Spectr. 444, 116175 (2019).
 G. Rugel et al., Nucl. Instr. Meth. B 370, 94 (2016).
 D. Koll et al., Nucl. Instr. Meth. B 438, 180 (2019).
 D. Koll et al., Phys. Rev. Lett. 123, 072701 (2019) and this meeting.
 W. Schwanghart et al., Science 351, 147 (2016).
 M. Martschini et al., this meeting.
Keywords: AMS; long-lived radionuclides
Heavy Ion Accelerator Symposium on Fundamental and Applied Science (HIAS), 09.-13.09.2019, Canberra, Australia
Lanthanide–induced conformational change of methanol dehydrogenase involving coordination change of cofactor pyrroloquinoline quinone
There is emerging interests to the role of lanthanides as cofactor in XoxF-type methanol dehydrogenase (MHD). Here, classical molecular dynamics simulations combined with fragment molecular orbital calculations were employed to rationalize enzymatic activities of MHD (both XoxF- and MxaF- types) carrying different lanthanides. In XoxF–type MDH, lanthanide binding to cofactor pyrroloquinoline quinone was found to switch from tridentate to unidentate fashion as it switches from lighter to heavier lanthanide. This fact possibly plays crucial role to the enzymatic activity exclusive to XoxF–type MDH incorporating lighter lanthanides.
Physical Chemistry Chemical Physics 21(2019), 21979-21983
17th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (Migration 2019), 15.-20.09.2019, Kyoto, Japan
A theranostic PSMA ligand for PET imaging and retargeting of T cells expressing the universal chimeric antigen receptor UniCAR
Arndt, C.; Feldmann, A.; Koristka, S.; Schäfer, M.; Bergmann, R.; Metwasi, N.; Berndt, N.; Bachmann, D.; Kegler, A.; Schmitz, M.; Puentes-Cala, E.; Soto, J. A.; Ehninger, G.; Pietzsch, J.; Liolios, C.; Wunderlich, G.; Kotzerke, J.; Kopka, K.; Bachmann, M.
Chimeric antigen receptor (CAR) T cells have shown impressive therapeutic potential. Due to the lack of direct control mechanisms, therapy-related adverse reactions including cytokine release- and tumor lysis syndrome can even become life-threatening. In case of target antigen expression on non-malignant cells, CAR T cells can also attack healthy tissues. To overcome such side effects, we have established a modular CAR platform termed UniCAR: UniCAR T cells per se are inert as they recognize a peptide epitope (UniCAR epitope) that is not accessible on the surface of living cells. Bifunctional adapter molecules termed target modules (TM) can cross-link UniCAR T cells with target cells. In the absence of TMs, UniCAR T cells automatically turn off. Until now, all UniCAR TMs were constructed by fusion of the UniCAR epitope to an antibody domain. To open up the wide field of low-molecular weight compounds for retargeting of UniCAR T cells to tumor cells, and to follow in parallel the progress of UniCAR T cell therapy by PET imaging we challenged the idea to convert a PET tracer into a UniCAR-TM. For proof of concept, we selected the clinically used PET tracer PSMA-11, which binds to the prostate-specific membrane antigen overexpressed in prostate carcinoma. Here we show that fusion of the UniCAR epitope to PSMA-11 results in a low-molecular weight theranostic compound that can be used for both retargeting of UniCAR T cells to tumor cells, and for non-invasive PET imaging and thus represents a member of a novel class of theranostics.
Keywords: PSMA ligand; UniCAR; prostate cancer; immunotherapy; PET imaging
OncoImmunology 8(2019)9, 1659095
Interactions of halophilic microorganisms with radionuclides
For the final storage of radioactive waste in a deep geological formation rock salt is a potential host rock. Indigenous microorganisms and its interactions with radionuclides have to be considered for the safety performance of the repository in terms of a worst case scenario, where radionuclides are potentially released from the storage site.
The kinetics of uranium bioassociation onto cells of the extreme halophilic archaeon Halobacterium noricense DSM 15987 and the moderate halophilic bacterium Brachybacterium sp. G1 were investigated in detail in batch experiments. For the understanding on a molecular level, a combination of spectroscopic, microscopic and molecular biological methods was used.
Invited lecture (Conferences)
Jahrestagung der Fachgruppe Nuklearchemie, 25.-27.09.2019, Dresden, Deutschland
1,4,7-Triazacyclononane ligands as bifunctional radiocoppper chelating agents
Stephan, H.; Joshi, T.
design of tailor-made bifunctional chelating agents (BFCAs) for radioactive transition metals in view of nuclear medical applications as well as acquisition of reliable information about the biodistribution of different materials represents an intensive and rapidly developing field of research . In this context, the tridentate macrocycle 1,4,7-triazacyclononane (TACN) is of special interest since it forms stable complexes with transition metal ions particularly with Cu(II) . Further, the introduction of donor groups, such as pyridyl units, on the TACN scaffold, significantly enhances the thermodynamic stability as well as the kinetic inertness of the Cu(II) complexes formed. Furthermore, the ligand structure offers various possibilities to introduce biological vectors and suitable linkers for tuning the lipophilicity, overall charge and aqueous solubility of the final bioconjugates. For example, TACN ligands with two pyridylmethyl side-arms (DMPTACN derivatives) rapidly chelate copper(II) radionuclides under ambient conditions and the resulting complexes show high in vivo stability. One such derivative, 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (DMPTACN-COOH), containing two coordinating picoline groups, not only exhibits excellent in vivo stability after 64Cu radiolabeling, but also allows for direct attachment of vector molecules as well as easy introduction of bioconjugatable functionalities (e.g., maleimide, isothiocyanate) via the carboxylate pendant. This makes DMPTACN-COOH and its derivatives promising BFCAs for radiocopper (DMPTACN-based BFCAs), facilitating the preparation of radiolabeled targeting molecules and bio(nano)materials.
Examples of target-specific peptides and bio(nano)materials equipped with DMPTACN ligands for labeling with 64Cu as an ideal positron emitter are discussed. This enables tumor imaging and the biodistribution of the materials to be studied over a period of days via positron emission tomography (PET).
 E. Boros, A. B. Packard, Chem. Rev. 119 (2019) 870-901.
 T. Joshi, M. Kubeil, A. Nsubuga, G. Singh, G. Gasser, H. Stephan, ChemPlusChem 83 (2018) 554-564.
19th International Conference on Biological Inorganic Chemistry, 11.-16.08.2019, Interlaken, Schweiz
CMOS-compatible Single Si Quantum Dot fabrication in a SiO2 layer sandwiched in a Si nanopillar for a Room Temperature Single Electron Transistor
Heinig, K.-H.; Hlawacek, G.; Engelmann, H.-J.; Prüfer, T.; Xu, X.; Möller, W.; Bischoff, L.; Gharbi, A.; Tiron, R.; Rommel, M.; von Borany, J.
The transistor pathway predicts an evolution from lateral MOSFETs via FinFETs to vertical nanowire gate-all-around FETs (vNW GAA-FET). Aiming at low-power electronics we replace the channel of the vNW GAA-FET by a SiO2 layer with an embedded Si Quantum Dot (QD), thus manufacturing a Single Electron Transistor (SET). To achieve room temperature (RT) operation of the vNW GAA-SET, Si QDs of ~3 nm diameter and tunneling distances of < 1 nm have to be manufactured. This is far beyond the present possibilities of lithography.
The challenge of such tiny structures has been solved in the framework of our European project IONS4SET  by means of a controlled self-organization and self-alignment process. Nanopillars with diameters down to ~20nm have been fabricated from Si/SiO2/Si layer stacks by Electron Beam Lithography and Reactive Ion Etching (RIE), a further diameter reduction to ~10nm has been achieved by sacrificial plasma oxidation. Before RIE the SiO2 layer is transferred to SiOx by Si+ ion beam mixing, which allows a controlled self-organization of a Si QD during thermally activated phase separation using RTA. During phase separation the Si QD becomes also self-aligned with respect of the upper and lower Si, thus forming the tunnel distances of ~1nm.
 This work has received funding from the European Unions Horizon 2020 research and innovation programme under grant agreement No 688072 (www.ions4set.eu).
Keywords: Ion Irradiation; Single Electron Transistor; SiOx Phase Separation
European Materials Research Society 2019 Fall Meeting, 16.-19.09.2019, Warsaw, Poland
Dramatic SiO2 Thickness Reduction by Reactive Ion Etching of Nanopillars from Si/SiO2/Si layer stacks
Heinig, K.-H.; Engelmann, H.-J.; Gharbi, A.; Tiron, R.; Prüfer, T.; von Borany, J.
The transistor pathway predicts an evolution from lateral MOSFETs via FinFETs to vertical nanowire gate-all-around FETs (vNW GAA-FET). Our European project IONS4SET  goes a step further: Aiming at low-power electronics, the principle of operation of transistors will be changed from field effects to single electron tunneling via a Si quantum dot (QD) in SiO2. Room temperature (RT) operation of Single Electron Transistors (SETs) requires Si QDs of ~3 nm and tunneling distances of < 1 nm. The SiO2 with the embedded Si QD has to be ~ 5nm thick. To fabricate vNW GAA-SETs, Si nanopillars with ~5nm SiO2 have to be fabricated by Electron Beam Lithography and Reactive Ion Etching (RIE).
Here we report on a dramatic SiO2 thickness reduction in the Si/SiO2/Si layer stack by RIE of nanopillars. It is strongly pillar diameter dependent: In 100 nm pillars the thickness remains almost unchanged, but for < 20nm it shrinks from 8nm to ~3nm as shown by Energy-Filtered Transmission Electron Beam Microscopy (EFTEM). Modeling, computer simulation and dedicated experiments reveal that it is due to a huge number of electric breakdowns during RIE. A breakdown forms a SiOx filament which emits O in SiO2. Each O atom of the SiO2 becomes many times an O interstitial, which in most cases recombines with an O vacancy. Depending on diameter, some O will emanate from the edge of the SiO2 disk leading to the dramatic oxide thinning.
 This work has received funding from the European Unions Horizon 2020 research and innovation programme under grant agreement No 688072 (www.ions4set.eu).
Keywords: Nanoelectronics; Ion Irradiation; Single Electron Transistor; Reactive Ion Etching
European Materials Research Society 2019 Fall Meeting, 16.-19.09.2019, Warsaw, Poland
PIConGPU simulation setup for L|PWFA simulation
The input set of the L|PWFA simulation as used in the publication "Demonstration of a compact plasma wakefield accelerator powered by laser-accelerated electron beams" by T.Kurz et al. .
To run the simulation use PIConGPU 0.4.2 (see DOI: 10.5281/zenodo.1491926).
Software in the HZDR data repository RODARE
Publication date: 2019-08-19
Neurocognitive function and quality of life after proton beam therapy for brain tumour patients
Dutz, A.; Agolli, L.; Bütof, R.; Valentini, C.; Baumann, M.; Lühr, A.; Löck, S.; Krause, M.
Neurocognitive function of adult patients with brain tumours may deteriorate after radiotherapy. Proton beam therapy (PBT) reduces the volume of irradiated healthy brain tissue and could potentially preserve neurocognition and quality of life (QoL). As present data are still limited, the impact of clinical factors and dosimetric parameters on neurocognitive function and QoL during recurrence-free follow-up after PBT is investigated.
The current study includes 62 brain tumour patients treated with PBT between 2015 and 2017. Neurocognition and QoL were assessed at baseline and every 3 months after PBT using the Montreal Cognitive Assessment (MoCA) test together with EORTC-QLQ-C30 and BN20 questionnaires, respectively. Objective and self-reported measures of neurocognitive functions were correlated. During two years of follow-up, the impact of clinical co-factors as well as dosimetric parameters of several brain structures were analysed using a mixed-model approach.
At baseline, mean MoCA total score was 24.8/30 and self-reported cognitive function was 68.9/100. Both remained stable over time. Patients with impaired neurocognition on the MoCA test reported significantly lower global health status, cognitive, physical and role function as well as more fatigue, pain, headache and communication deficits compared to normal performing patients. For most follow-up time points, the majority of MoCA subitems correlated significantly to QoL items regarding neurocognition. Slight deterioration of the MoCA score was associated with tumours located in the left hemisphere and with an increase in relative volume of the anterior cerebellum that received doses of 30 to 40 Gy(RBE).
Self-reported and objectively measured neurocognition and most other QoL domains remained largely stable over time during recurrence-free follow-up for brain tumour patients treated with PBT.
The association between reduced cognitive function and irradiated volume of the anterior cerebellum requires validation in larger studies and comparison to patients treated with photon therapy.
Keywords: brain tumours; neurocognitive function; quality of life; proton beam therapy
Radiotherapy and Oncology 143(2020), 108-116
Coherent control of qudit modes in SiC at room temperature
We present room-temperature coherent control of high-dimensional quantum bits, the so-called qudits, associated with vacancy-related spins in silicon carbide enriched with nuclear spin-free isotopes. In addition to the excitation of a spectrally narrow qudit mode at the pump frequency, several other modes are excited in the electron spin resonance spectra whose relative positions depend on the external magnetic field.
Invited lecture (Conferences)
4th International Conference on Metamaterials and Nanophotonics METANANO 2019, Special Symposium QuantuMetanano, 14.-19.07.2019, Saint Petersburg, Russia
Coherent control of qudit modes in SiC
We demonstrated coherent manipulation of spin qudit modes in isotopically purified SiC at room temperature. We also developed a theory describing the excitation and detection of these modes in inhomgeneously broadened systems and showed that qudits are characterized by multiple relaxation times. These findings can lead to dipole-coupled networks, unconditional electron-nuclear spin registers and spectral selection of highly coherent individual spins, particularly in nanocrystals. Our results hence open new possibilities to improve the sensitivity of quantum sensors and execute nontrivial quantum protocols in dense spin ensembles.
Invited lecture (Conferences)
Invited colloquium at TU Dortmund, 13.06.2019, Dortmund, Germany
Effect of irradiation on defect coherence properties in silicon carbide
We have thoroughly investigated the irradiation impact on the room-temperature spin coherence properties of silicon vacancies in SiC. We have measured the spin-lattice relaxation time and the spin coherence time depending on the irradiation particle (electron, neutron and proton), irradiation fluence and irradiation energy.
Invited lecture (Conferences)
Ion Beam for future Technologies 2019, 01.-03.04.2019, Dubrovnik, Croatia
Influence of irradiation on defect spin coherence in silicon carbide
Irradiation-induced lattice defects in silicon carbide (SiC) have already exceeded their previous reputation as purely performance-inhibiting. With their remarkable quantum properties, such as long room-temperature spin coherence and the possibility of downscaling to single-photon source level, they have proven to be promising candidates for a multitude of quantum information applications. One of the most crucial parameters of any quantum system is how long its quantum coherence can be preserved. By using the pulsed optically detected magnetic resonance (ODMR) technique, we investigate the spin-lattice relaxation time (T1) and spin coherence time (T2) of silicon vacancies in 4H-SiC created by neutron, electron and proton irradiation in a broad range of fluences. We also examine the effect of irradiation energy and sample annealing. We establish a robustness of the T1 time against all types of irradiation and reveal a universal scaling of the T2 time with the emitter density. Our results can be used to optimize the coherence properties of silicon vacancy qubits in SiC for specific tasks.
Keywords: Spin coherence; quantum applications; SiC
Physical Review Applied 13(2020), 044054
UFXCT data of silo discharge of hydrogel spheres
The outflow of hydrogel spheres from a cylindrical storage container with narrow outlet of two different sizes is imaged by means of ultrafast X-ray computed tomography (UFXCT) at different heights above the outlet. Sequences of cross-sectional images were recorded over 30 s with a frame rate of 1000 fps in dual plane mode.
Keywords: ultrafast measurement; X-ray CT; silo discharge
- UFXCT data of silo discharge of airsoft balls (Id 29573) is a supplement to this (Id 29575) publication
- High-speed X-ray tomography of silo discharge (Id 29464) is supplemented by this (Id 29575) publication
Reseach data in the HZDR data repository RODARE
Publication date: 2019-08-16
An integrative analysis of image segmentation and survival of brain tumour patients
Starke, S.; Eckert, C.; Zwanenburg, A.; Speidel, S.; Löck, S.; Leger, S.
Our contribution to the BraTS 2019 challenge consisted of a deep learning based approach for segmentation of brain tumours from MR images using cross validation ensembles of 2D-UNet models. Furthermore, different approaches for the prediction of patient survival time using clinical as well as imaging features were investigated.
A simple linear regression model using patient age and tumour volumes outperformed more elaborate approaches like convolutional neural networks or Radiomic-based analysis with an accuracy of 0.55 on the validation set.
Keywords: UNet; Segmentation; Radiomic; Linear regression; Deep-learning; Ensemble; Survival analysis
Contribution to proceedings
MICCAI BrainLes 2019, 5th International Workshop, 17.10.2019, Shenzhen, China
Brainlesion: Glioma, Multiple Sclerosis, Stroke and Traumatic Brain Injuries
UFXCT data of silo discharge of airsoft balls
The outflow of airsoft bullets from a cylindrical storage container with narrow outlet is imaged by means of ultrafast X-ray computed tomography (UFXCT) at different heights above the outlet. Sequences of cross-sectional images were recorded over 30 s with a frame rate of 1000 fps in dual plane mode.
Keywords: ultrafast measurement; X-ray CT; silo discharge
- UFXCT data of silo discharge of hydrogel spheres (Id 29575) is supplemented by this (Id 29573) publication
- High-speed X-ray tomography of silo discharge (Id 29464) is supplemented by this (Id 29573) publication
Reseach data in the HZDR data repository RODARE
Publication date: 2019-08-16
Biomaterials in repairing rat femoral defects: in vivo insights from small animal positron emission tomography/computed tomography (PET/CT) studies
Biomaterials coated with artificial extracellular matrices (aECM) are intended to support the healing of critical size bone defects. This pilot study investigated (i) the feasibility of dual tracer PET/CT imaging for functional characterization of biomaterial-assisted bone healing in a rat femoral defect model and (ii) the bone healing ability of polycaprolactone-co-lactide (PCL) scaffolds, coated with various aECM consisting of collagen type I (Col) and glycosaminoglycans (GAGs) such as chondroitin sulfate (CS) or polysulfated hyaluronan (sHA3). [18F]FDG and [18F]fluoride PET 4 and 8 weeks after implantation of aECM-coated PCL scaffolds, which provide an in vivo measure of cellular activation and bone mineralization, respectively, combined with CT imaging (in vivo/ex vivo) and histologic/immunohistochemical investigations (ex vivo) showed that coating with CS in particular is beneficial for bone healing. The possible involvement of COX-2 and TGase 2, key enzymes of inflammation and ECM remodeling, in these processes offers starting points for targeted adjuvant therapy in the course of various bone healing phases. Our investigations show the feasibility of the selected dual tracer approach for PET/CT imaging. In principle, this approach can be extended by further PET tracers for the functional characterization of physiological processes such as hypoxia/reperfusion or selected molecular players.
Keywords: Artificial extracellular matrices; bone healing; [18F]fluorodeoxyglucose; [18F]fluoride; glycosaminoglycans; inflammation; metabolism; molecular imaging; revascularization
Clinical Hemorheology and Microcirculation 73(2019), 177-194
- Final Draft PDF 2,6 MB Secondary publication
More than 15 Years of CW SRF Operation at ELBE
Arnold, A.; Freitag, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schneider, C.; Teichert, J.; Xiang, R.
ELBE is a compact, accelerator-driven photon and particle source. Since 2001 it is operated as a user facility, providing more than 5500 hours of beam time each year. The electron accelerator is based on four superconducting 9-cell TESLA cavities that are driven in full CW operation to accelerate an average current of 1 mA up to beam energies of 40 MeV. The first part of the talk will summarize our experiences of operating TESLA cavities in CW. In detail, this includes their performance and attempts to improve it, as well as investigations on limitations. Additionally, we will discuss several issues that are related to the high average RF as well as beam power and we will present appropriate measures to protect the machine. In this regard, a resonant ring for RF component tests up to 100 kW was set up. The second part of the talk will focus on the development and operation of our SRF guns that are designed to produce short bunches with high charges and repetition rates of 1 MHz and beyond. Recently, SRF gun II was successfully transferred into routine user operation and delivers now more than 200 pC at 100 kHz to the experiment. First convincing results will be presented.
Keywords: ELBE; electron accelerator; SRF; cryomodule; high RF power; high average current
Invited lecture (Conferences)
19th International Conference on RF Superconductivity, SRF2019, 30.06.-05.07.2019, Dresden, Germany
Single bubble dynamics during nucleate flow boiling on a vertical heater: Experimental and theoretical analysis of the effect of surface wettability,roughness and bulk liquid velocity
Sarker, D.; Ding, W.; Schneider, C.; Hampel, U.
The present study reports the mutual effect of heater surface wettability, roughness and bulk liquid velocity on the bubble dynamics and departure in nucleate boiling. Boiling experiments were conducted at atmospheric pressure with degassed-deionized water at low subcooling (1.9 ± 0.25 K) for vertically oriented stainless steel heaters. Self-assembled monolayer (SAM) coating and wet-etching technique were used to alter the heater surface wettability and roughness. Liquid contact angle hysteresis ("θ" _"hys" ) and root mean square roughness (Sq) of the heater surfaces were adjusted between "42.32° "≤ "θ" _"hys" ≤ "68.56°" and roughness "0.01" µm≤"Sq"≤"0.549" µm. High resolution optical shadowgraphy has been used to record the bubble life cycle. Experimental results show that higher bulk liquid velocity yields smaller bubble departure diameters for all heater surface characteristics. Bubble departure diameters are greater for low wetting surfaces. The bubble growth rate and departure diameter were found maximum for an intermediate surface roughness Sq between 0.108 and 0.218 m. The corresponding roughness height is referred to as the ‘optimal roughness height’ in this study. Eventually, a bubble departure criterion was derived from the expressions of forces which act on a nucleating bubble throughout its growth cycle. 90% of the departing bubbles satisfy the bubble departure criterion with ± 25% deviation.
Keywords: Bubble growth; bubble departure; surface wettability; roughness; flow boiling
International Journal of Heat and Mass Transfer 142(2019), 118481
- Final Draft PDF 954 kB Secondary publication
A Two-Parameter Model for Colloidal Particles with an Extended Magnetic Cap
Neumann, M.; Strobel, A.; Al-Saadawi, Y.; Steinbach, G.; Erbe, A.; Gemming, S.
Self-assembly of magnetic colloidal particles in solution has succesfully been simulated by hard- or soft-sphere models with a set of embedded magnetic point dipoles, and the position and orientation of each dipole are adapted to mimic the magnetization distribution. The present study introduces a conceptually simpler approach for magnetically capped colloidal particles, which replaces the set of dipoles by the magnetization distribution of a single conductive loop. Only two parameters are required to characterize the magnetization distribution: the diameter of the loop and its radial off-center shift within the sphere. This approach reflects the radial symmetry and the spatial extension of the magnetic cap. In the far-field and in the limit of very small loops the model exactly reproduces the magnetization distribution and the particle arrangements obtained with the single, radially shifted dipole model. For larger loop radii additional stable assembly patterns are obtained, which occur in experiments, but can not be simulated with a single shifted dipole model.
Keywords: colloids; colloidal suspensions; magnetic colloidal particles; 2D assembly; self-assembly; effective Hamiltonians; theory; mesoscopic materials; soft-sphere potential; shifted-dipole model
Physica Status Solidi (A) 216(2019)19, 1900506
A new particle-based approach to process modelling and diagnostics
For a long time, the mining and minerals processing communities have developed process models based on the bulk chemical compositions of ores and processing products. Recently, the emergence of the geometallurgy field and the advent of new characterization techniques have shifted the focus to mineralogical composition and certain particle-based properties (e.g. mineral liberation). Automated mineralogy systems based on scanning electron microscope platforms, such as the Mineral Liberation Analyzer or TIMA-X, were essential for this advance. They are capable of producing large data sets with detailed information on the sizes, shapes and compositions of individual ore particles in a sample.
Methodologies that use this particle-based information to model the outcomes of a specific processing unit or an entire operation are summarized as “particle tracking”. This is a useful diagnostic technique for mineral separation processes. However, limitations in the statistical methods applied in existing approaches mean that users are required to summarize considerably the information contained in the particle datasets by pre-selecting explanatory variables (expert input) and binning particles. This means that a distinct recipe, including specific assumptions, is required for each new case. It also makes the resultant models liable to human bias.
This work describes a new method for particle tracking that combines automated mineralogy data with machine learning to automate the variable selection process and eliminate the need for particle binning. In doing so, it maximizes the utilization of detailed particle data, minimizes the effects of human input, and provides the flexibility to assess different cases with minimal prior adjustments. Its utility is demonstrated using data from both a flotation and a magnetic separation units of an operating niobium mine. In both cases, the method is able to accurately predict the mineralogical compositions of the concentrate and tailings streams. It clearly has the potential to be extended as a diagnostic tool for the optimization and operation of processing plants.
Keywords: Machine learning; predictive geometallurgy; particle tracking
Procemin Geomet, 20.-22.11.2019, Santiago, Chile
Opportunities and challenges for spintronics in the microelectronic industry
Dieny, B.; Prejbeanu, I. L.; Garello, K.; Gambardella, P.; Freitas, P.; Lehndorff, R.; Raberg, W.; Ebels, U.; Demokritov, S. O.; Akerman, J.; Deac, A.; Pirro, P.; Adelmann, C.; Anane, A.; Chumak, A. V.; Hiroata, A.; Mangin, S.; Cengiz Onbaşlı, M.; D’Aquino, M.; Prenat, G.; Finocchio, G.; Lopez Diaz, L.; Chantrell, R.; Chubykalo-Fesenko, O.; Bortolotti, P.
Spin-based electronics has evolved into a major field of research that broadly encompasses different classes of materials, magnetic systems, and devices. This review describes recent advances in spintronics that have the potential to impact key areas of information technology and microelectronics. We identify four main axes of research: nonvolatile memories, magnetic sensors, microwave devices, and beyond-CMOS logic. We discuss state-of-the-art developments in these areas as well as opportunities and challenges that will have to be met, both at the device and system level, in order to integrate novel spintronic functionalities and materials in mainstream microelectronic platforms.
Keywords: magnetism; spintronics; microelectronics; non-volatile memory; microwave devices
Nature Electronics 3(2020)8, 446-459
- Secondary publication expected from 01.02.2021
Effect of materials heterogeneities on microstructure and mechanical properties at irradiated state
This talk summarizes the new insight accumulated in the work package 3 of the European Horizon 2020 project SOTERIA on the effects of materials heterogeneities on microstructure and mechanical properties at the irradiated state.
Keywords: Reactor pressure vessel steels; irradiation effects; microstructure; mechanical properties
Open SOTERIA Final Workshop, 25.-27.06.2019, Miraflores de la Sierra, Spanien
Transient Characteristics of Interdigitated GaAs Photoconductive Semiconductor Switch at 1-kHz Excitation
Xu, M.; Liu, X.; Li, M.; Liu, K.; Qu, G.; Wang, V.; Hu, L.; Schneider, H.
To explore the stability of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSSs) with avalanche multiplication mechanism, an interdigitated electrodestructure is presented at 1-kHz excitation by a femtosecond laser. The influences of optical excitation and bias electric field on switching characteristics are investigated. The transient current density and the distribution of electric field are demonstrated by the Monte Carlo simulation. The repetitive switching indicates that the avalanche multiplication mechanism could persist stably at 1-kHz repetition rate operation with this specific electrode structure.
Keywords: Gallium arsenide; GaAs; high gain; photoconductive semiconductor switch; avalanche multiplication; repetition rate
IEEE Electron Device Letters 40(2019)7, 1136-1138
Computer Modeling of Single-layer Nanocluster Formation in a Thin SiO2 Layer Buried in Si by Ion Mixing and Thermal Phase Decomposition
Prüfer, T.; Möller, W.; Heinig, K.-H.; Wolf, D.; Engelmann, H.-J.; Xu, X.; von Borany, J.
A single sheet of Si nanoclusters with an average diameter of about 2 nm has been formed in a 30 nm Si / 7 nm SiO2 / Si layer stack by 50 and 60 keV Si+ ion-beam mixing at room temperature and fluences between 8.51015 and 2.61016 ions/cm2, and subsequent thermal annealing at a temperature above 1000°C. Computer modelling of the process is accomplished by TRIDYN dynamic ballistic simulation of ion mixing and subsequent lattice kinetic Monte Carlo simulation of the phase decomposition of sub-stoichiometric silicon oxide into Si nanoclusters in a SiO2 matrix. The simulation algorithms are briefly described with special emphasis on the choice of governing parameters for the present system. In comparison to the experimental results it is concluded that the predicted ion mixing profiles overestimate the interface broadening. This discrepancy is attributed to the neglect of chemical driving forces in connection with thermal-spike induced diffusion, which tends to re-constitute the Si/SiO2 interfaces. With a corresponding correction and a suitable number of Monte Carlo steps, the experimentally obtained areal densities and average diameters of the nanoclusters are successfully reproduced.
Keywords: Ion Beam Mixing; SiO2; Silicon; Thermal Spikes
Journal of Applied Physics 125(2019), 225708
- Final Draft PDF 1,3 MB Secondary publication
The efficiency of sequential accident management measures for a German PWR under prolonged SBO conditions
In this paper, the results of ATHLET-CD simulations of an SBO accident for a German Siemens KWU type PWR are reported. The developed model is used in a series of calculations to evaluate SBO coping time provided by a set of countermeasures relevant to the defense-in-depth Level 4. The analysed accident management measures cover a sequence of the bleed and feed procedures, starting/ending with secondary/primary side depressurization followed by the feeding of SGs in the passive (AMM-1) or active (AMM-2) mode and coolant injection from hydro-accumulators (HA) to the primary system (AMM-3).
A sequential implementation of the first two measures with almost equal efficiency (AMM-1 and AMM-2) delays the core degradation onset (CDO) by 21.5 hours compared to the case without AMMs, extending SBO coping time to 24 hours. This time window can be further extended (more than twice) through sequential feeding of a single SG from the four emergency feedwater tanks of the plant. The third measure (AMM-3) is significantly inferior to AMM-1 and/or AMM-2 in contributing to the coping time, since it delays CDO by less than 1 hour.
Keywords: Accident management measures; Station Black Out; PWR; ATHLET-CD
Nuclear Engineering and Design 363(2020), 110663
- Secondary publication expected from 04.05.2021
Cancer Stem Cells and Radioresistance: DNA Repair and Beyond
Schulz, A.; Meyer, F.; Dubrovska, A.; Borgmann, K.
The current preclinical and clinical findings demonstrate that, in addition to the conventional clinical and pathological indicators that have a prognostic value in radiation oncology, the number of cancer stem cells (CSCs) and their inherent radioresistance are important Parameters for local control after radiotherapy. In this review, we discuss the molecular mechanisms of CSC radioresistance attributable to DNA repair mechanisms and the development of CSC-targeted therapies for Tumor radiosensitization. We also discuss the current challenges in preclinical and translational CSC research including the high inter- and intratumoral heterogeneity, plasticity of CSCs, and microenvironment-stimulated tumor cell reprogramming.
Keywords: cancer stem cells; DNA repair; radioresistance; 5Rs of radiation biology
Cancers 11(2019), 862
Interference of tumour mutational burden with outcome of patients with head and neck cancer treated with definitive chemoradiation: a multicentre retrospective study of the German Cancer Consortium Radiation Oncology Group
Eder, T.; Hess, A.; Konschak, R.; Stromberger, C.; Johrens, K.; Fleischer, V.; Hummel, M.; Balermpas, P.; von der Grun, J.; Linge, A.; Lohaus, F.; Krause, M.; Baumann, M.; Stuschke, M.; Zips, D.; Grosu, A.; Abdollahi, A.; Debus, J.; Belka, C.; Pigorsch, S.; Combs, E.; Budach, V.; Tinhofer, I.
Background: Tumour mutational burden (TMB) estimated from whole exome sequencing or comprehensive gene panels has previously been established as predictive factor of response to immune checkpoint inhibitors (ICIs).
Its predictive value for the efficacy of concurrent chemoradiation (cCRTX), a potential combination partner of ICI, remains unknown.
Methods: The accuracy of TMB estimation by an in-house 327-gene panel was established in the Cancer Genome Atlas (TCGA) head and neck squamous cell carcinoma (HNSCC) data set. Interference of TMB with outcome after cCRTX was determined in a multicentre cohort of patients with locally advanced HNSCC uniformly treated with cCRTX. Targeted next-generation sequencing was successfully applied in 101 formalin-fixed, paraffin-embedded pretreatment tumour samples. In a subset of cases (n = 40), tumour RNA was used for immune-related gene expression profiling by the nanoString platform. TMB was correlated with TP53 genotype, human papilloma virus (HPV) status, immune expression signatures and survival parameters. Results were validated in the TCGA HNSCC cohort.
Results: A high accuracy of TMB estimation by the 327-gene panel was established. High TMB was significantly associated with an increased prevalence of TP53 mutations and immune gene expression patterns unrelated to T cell-inflamed gene expression profiles. Kaplan-Meier analysis revealed significantly reduced overall survival in the patient group with high TMB (hazard ratio for death: 1.79, 95% confidence interval: 1.02-3.14; P = 0.042) which remained significant after correcting for confounding factors in the multivariate model. The prognostic value of TMB was confirmed in the TCGA HNSCC cohort.
Conclusion: High TMB identifies HNSCC patients with poor outcome after cCRTX who might preferentially benefit from CRTX-ICI combinations.
European Journal of Cancer 116(2019), 67-76
⁵³Mn and ⁶⁰Fe in iron meteorites - new data and model calculations
We measured specific activities of the long-lived cosmogenic radionuclides ⁶⁰Fe in 28 and ⁵³Mn in 41 iron meteorites. Accelerator mass spectrometry was applied at the 14-MV Heavy Ion Accelerator Facility at ANU Canberra for all samples but two which were measured at the Maier-Leibnitz Laboratory, Munich. For the large iron meteorite Twannberg (IIG) we measured six samples for ⁵³Mn. This work doubles the number of existing individual ⁶⁰Fe data and quadruples the number of iron meteorites studied for ⁶⁰Fe. We also significantly extended the entire ⁵³Mn database for iron meteorites. The ⁵³Mn data for the iron meteorite Twannberg vary by more than a factor of 30, indicating a significant shielding dependency. In addition, we performed new model calculations for the production of ⁶⁰Fe and ⁵³Mn in iron meteorites. While the new model is based on the same particle spectra as the earlier model, we no longer use experimental cross sections but instead use cross sections that were calculated using the latest version of the nuclear model code INCL. The new model predictions differ substantially from results obtained with the previous model: Predictions for the ⁶⁰Fe activity concentrations are about a factor of two higher and for ⁵³Mn they are ~30% lower compared to the earlier model, which gives a better agreement with experimental data.
Keywords: ⁵³Mn; ⁶⁰Fe; cosmogenic production rates; iron meteorites; Accelerator Mass Spectrometry
Meteoritics & Planetary Science 55(2020), 818-831
Cancer Stem Cells in Head and Neck Squamous Cell Carcinoma: Identification, Characterization and Clinical Implications
Peitzsch, C.; Nathansen, J.; Schniewind, S.; Schwarz, F.; Dubrovska, A.
Head and neck squamous cell carcinoma (HNSCC) is the sixth most commonly diagnosed cancer worldwide. Despite advances in the treatment management, locally advanced disease has a poor prognosis, with a 5-year survival rate of approximately 50%. The growth of HNSCC is maintained by a population of cancer stem cells (CSCs) which possess unlimited self-renewal potential and induce tumor regrowth if not completely eliminated by therapy. The population of CSCs is not only a promising target for tumor treatment, but also an important biomarker to identify the patients at risk for therapeutic failure and disease progression.
This review aims to provide an overview of the recent pre-clinical and clinical studies on the biology and potential therapeutic implications of HNSCC stem cells.
Keywords: head and neck squamous cell carcinoma; HNSCC; cancer stem cells; therapy resistance; biomarkers
Cancers 11(2019), 616
Mineral Precipitation in Fractures and Nanopores within Shale Imaged Using Time-Lapse X-ray Tomography
Da Assuncao Godinho, J. R.; Ma, L.; Chai, Y.; Storm, M.; Burnett, T. L.
Barite precipitation in fractures and nanopores within a shale sample is analysed in situ, in 3D, and over time. Diffusion of barium and sulphate from opposite sides of the sample creates a supersaturated zone where barium sulphate crystals precipitate. Time-lapse synchrotron-based computed tomography was used to track the growth of precipitates over time, even within the shale’s matrix where the nanopores are much smaller than the resolution of the technique. We observed that the kinetics of precipitation is limited by the type and size of the confinement where crystals are growing, i.e., nanopores and fractures. This has a major impact on the ion transport at the growth front, which determines the extent of precipitation within wider fractures (fast and localised precipitation), thinner fractures (non-localised and slowing precipitation) and nanopores (precipitation spread as a front moving at an approximately constant velocity of 10 ± 3 µm/h). A general sequence of events during precipitation in rocks containing pores and fractures of different sizes is proposed and its possible implications to earth sciences and subsurface engineering, e.g., fracking and mineral sequestration, are discussed.
Keywords: time-lapse imaging; 3D imaging; shale; barite; mineral precipitation; scale; formation damage; porous media; fracking
Minerals 9(2019)8, 480
Study of process water recirculation in a flotation plant by means of process simulation
Michaux, B.; Hannula, J.; Rudolph, M.; Reuter, M. A.
One of the biggest challenges with water in the mining industry is the need for water management systems that consider production-related issues when the quality of process water is subject to variations. Part of the work required to tackle this challenge is the development of simulation platforms that correlates the quality of the process water to the processing plant performance. In this paper, the application of a previously developed simulation-based approach to include the impact of process water chemistry on the performance of a flotation plant is presented. The water chemistry-dependent plant simulation is then used to investigate the implementation of a water-saving strategy to reduce fresh water requirements without impairing process performance, thus demonstrating the applicability of the previously developed approach for the simulation of large scale industrial plants.
Keywords: Flotation plant simulation; flotation kinetics; process water chemistry; water-saving strategies
Minerals Engineering 148(2020), 106181
- Secondary publication expected from 20.01.2021
R as an environment for data mining of process mineralogy data: A case study of an industrial rougher flotation bank
Through a series of in-house routines of R, an open source programming language for statistical computing, statistical analysis is applied to automated process mineralogy data in order to describe the performance of an industrial scheelite rougher flotation bank. These routines allow: 1) exploring all particles properties over residence time, not only particle size or surface liberation but also mineral association and a wealth of other particle properties, 2) to free the user from the limitations of the menu-driven built-in mineralogy software or spreadsheets, for calculation, data plotting or predictive model fitting, in particular for the parallel analysis of several streams; and 3) a more flexible manipulation of the data, both class and particle wise, for instance allowing for data mining across streams.
In an illustration case study, these functions are used to show the separation efficiency shift over residence time and over particle size; to indicate which associated minerals have a greater influence on the flotation of scheelite; to determine which gangue minerals are more impacted by entrainment; and finally to link said entrainment to particle shape. In general, the Helmholtz Institute Freiberg for Resource Technology intends to use such a programming platform on automated mineralogy data as a routine to understand processes better, as a potential diagnostic tool for process troubleshooting, and also for predictive model building within the frame of geometallurgy.
Keywords: rougher flotation; R; automated mineralogy; statistical analysis
Minerals Engineering 146(2020), 106111
- Secondary publication expected from 15.01.2021
Spin Hall magnetoresistance in heterostructures consisting of noncrystalline paramagnetic YIG and Pt
Lammel, M.; Schlitz, R.; Geishendorf, K.; Makarov, D.; Kosub, T.; Fabretti, S.; Reichlova, H.; Huebner, R.; Nielsch, K.; Thomas, A.; Goennenwein, S. T. B.
The spin Hall magnetoresistance (SMR) effect arises from spin-transfer processes across the interface between a spin Hall active metal and an insulating magnet. While the SMR response of ferrimagnetic and antiferromagnetic insulators has been studied extensively, the SMR of a paramagnetic spin ensemble is not well established. Thus, we investigate herein the magnetoresistive response of the as-deposited yttrium iron garnet/platinum thin film bilayers as a function of the orientation and the amplitude of an externally applied magnetic field. Structural and magnetic characterization shows no evidence for the crystalline order or spontaneous magnetization in the yttrium iron garnet layer. Nevertheless, we observe a clear magnetoresistance response with a dependence on the magnetic field orientation characteristic for the SMR. We propose two models for the origin of the SMR response in paramagnetic insulator/platinum heterostructures. The first model describes the SMR of an ensemble of noninteracting paramagnetic moments, while the second model describes the magnetoresistance arising by considering the total net moment. Interestingly, our experimental data are consistently described by the net moment picture, in contrast to the situation in compensated ferrimagnets or antiferromagnets.
Keywords: spin Hall magnetoresistance; antiferromagnetic insulators
Applied Physics Letters 114(2019), 252402
Exploring enhanced low-energy magnetic dipole strength in photon scattering
Schwengner, R.; Rusev, G.
Strengths of M1 transitions depopulating high-lying 1+ states and of subsequent transitions in cascades populating the first excited state were determined on the basis of large-scale shell-model calculations for the nuclide 54Fe. The results reveal that the spectra of primary M1 transitions from 1+ states only as well as the subsequent cascade M1 transitions show an enhancement of strength toward small energy, similar to that found for a huge number of transitions between states of a wide spin range as observed in light-ion induced reactions. This allows in principle the study of low-energy M1 strength using photon scattering. Based on these results, intensities of M1 transitions under experimental conditions are estimated.
Keywords: Strength functions; M1 transitions; shell model; photon scattering
Physical Review C 100(2019), 054320
Tuning the interactions in the spin-ice materials Dy2Ge2−xSixO7 by silicon substitution
Stöter, T.; Antlauf, M.; Opherden, L.; Gottschall, T.; Hornung, J.; Gronemann, J.; Herrmannsdörfer, T.; Granovsky, S.; Schwarz, M.; Doerr, M.
We report that the lattice constant of Dy2Ge2−xSixO7 (x = 0, 0.02, 0.08, 0.125) can be systematically reduced by substituting the nonmagnetic germanium ion in the cubic pyrochlore oxide with silicon. A multianvil high-pressure synthesis was performed up to 16 GPa and 1100 °C to obtain polycrystalline samples in a solid-state reaction. Measurements of magnetization, ac susceptibility, and heat capacity reveal the typical signatures of a spin-ice phase. From the temperature shift of the peaks, observed in the temperature-dependent heat capacity, we deduce an increase in the strength of the exchange interaction. In conclusion, the reduced lattice constant leads to a changed ratio of the competing exchange and dipolar interaction. This puts the new spin-ice compounds closer towards the phase boundary of a short-range spin-ice arrangement and antiferromagnetic long-range order consistent with an observed reduction in the energy scale of monopole excitations.
Physical Review B 100(2019), 054403
- Original PDF 1,3 MB Secondary publication
Controlling Chiral Spin States of a Triangular-Lattice Magnet by Cooling in a Magnetic Field
Deng, S.; Fischer, G.; Uhlarz, M.; Wosnitza, J.; Bohnen, K.-P.; Heid, R.; Wang, C.; Sürgers, C.
Magnetic materials with a non-collinear and non-coplanar arrangement of magnetic moments hosting a nonzero scalar spin-chirality exhibit unique magnetic and spin-dependent electronic transport properties. The spin chirality often occurs in materials where competing exchange interactions lead to geometrical frustrations between magnetic moments and to a strong coupling between the crystal lattice and the magnetic structure. These characteristics are particularly strong in Mn-based antiperovskites where the interactions and chirality can be tuned by substitutional modifications of the crystalline lattice. This study presents evidence for the formation of two unequal chiral spin states in magnetically ordered Mn3.338Ni0.651N antiperovskite based on density functional theory calculations and supported by magnetization measurements after cooling in a magnetic field. The existence of two scalar spin-chiralities of opposite sign and different magnitude is demonstrated by a vertical shift of the magnetic-field dependent magnetization and Hall effect at low fields and from an asymmetrical magnetoresistivity when the applied magnetic field is oriented parallel or antiparallel to the direction of the cooling field. This opens up the possibility of manipulating the spin chirality for potential use in the emerging field of chiral spintronics.
Advanced Functional Materials 29(2019), 1900947
Evidence for the Single-Site Quadrupolar Kondo Effect in the Dilute Non-Kramers System Y1−xPrxIr2Zn20
Yanagisawa, T.; Hidaka, H.; Amitsuka, H.; Zherlitsyn, S.; Wosnitza, J.; Yamane, Y.; Onimaru, T.
Acoustic signatures of the single-site quadrupolar Kondo effect in Y0.966Pr0.034Ir2Zn20 are presented. The elastic constant (C11 − C12)/2, corresponding to the Γ3(E)-symmetry electric-quadrupolar response, reveals a logarithmic temperature dependence of the quadrupolar susceptibility in the low-magnetic-field region below ∼0.3 K. Furthermore, the Curie-type divergence of the elastic constant down to ∼1 K indicates that the Pr ions in this diluted system have a non-Kramers ground-state doublet. These observations evidence the single-site quadrupolar Kondo effect, as previously suggested based on specific-heat and electrical-resistivity data.
Physical Review Letters 123(2019), 067201
High magnetic field phase diagram and failure of the magnetic Grüneisen scaling in LiFePO4
Werner, J.; Sauerland, S.; Koo, C.; Neef, C.; Pollithy, A.; Skourski, Y.; Klingeler, R.
We report the magnetic phase diagram of single-crystalline LiFePO4 in magnetic fields up to 58 T and present a detailed study of magnetoelastic coupling by means of high-resolution capacitance dilatometry. Large anomalies at TN in the thermal-expansion coefficient α imply pronounced magnetoelastic coupling. Quantitative analysis yields the magnetic Grüneisen parameter γmag = 6.7(5) × 10−7 mol/J. The positive hydrostatic pressure dependence dTN/dp = 1.46(11) K/GPa is dominated by uniaxial effects along the a axis. Failure of Grüneisen scaling below ≈40K, i.e., below the peak temperature in the magnetoelectric coupling coefficient , implies several competing degrees of freedom. A broad and strongly magnetic field dependent anomaly in α in this temperature regime highlights the relevance of structure changes. Upon application of the magnetic field B||b axis, a pronounced jump in the magnetization implies spin reorientation at BSF = 32 T as well as a precursing phase at 29 T and T = 1.5K. In a two-sublattice mean-field model, the saturation field Bsat,b = 64(2) T enables assessing the effective antiferromagnetic exchange interaction Jaf = 2.68(5)meV as well as anisotropies Db = −0.53(4)meV and Dc = 0.44(8)meV.
Physical Review B 99(2019), 214432
High Temperature and Ion Implantation-Induced Phase Transformations in Novel Reduced Activation Si-Fe-V-Cr (-Mo) High Entropy Alloys
Gandy, A. S.; Jim, B.; Coe, G.; Patel, D.; Hardwick, L.; Akhmadaliev, S.; Reeves-Mclaren, N.; Goodall, R.
For fusion to be realized as a safe, sustainable source of power, new structural materials need to be developed which can withstand high temperatures and the unique fusion radiation environment. An attractive aspect of fusion is that no long-lived radioactive wastes will be produced, but to achieve this structural materials must comprise reduced activation elements. Compositionally complex alloys (CCAs) (also called high entropy alloys, HEAs) are promising candidates for use in extreme environments, including fusion, but few reported to date have low activation. To address these material challenges, we have produced novel, reduced activation, HEAs by arc-melting, and investigated their thermal stability, and radiation damage resistance using 5 MeV Au2+ ion implantation. Whilst the alloys were designed to form single phase BCC, using room temperature and non-ambient in situ X-ray diffraction we have revealed the thermodynamically stable structure of these alloys is in fact a sigma phase. We propose that a BCC phase is formed in these alloys, but at high temperatures (>1000°C). A BCC phase was also formed during heavy ion implantation, which we propose to be due to the rapid heating and cooling that occurs during the thermal spike, effectively freezing in the BCC phase produced by an implantation induced phase transformation. The BCC phase was found to have high hardness and a degree of ductility, making these new alloys attractive in the development of reduced activation HEAs for nuclear applications.
Keywords: high entropy alloy (HEA); reduced activation; phase transformation; ion implantation; thermal stability; nuclear; radiation damage
Frontiers in Materials 6(2019), 146
Not all Neoproterozoic iron formations are glaciogenic: Sturtian-aged non-Rapitan exhalative iron formations from the Arabian–Nubian Shield
Abd El-Rahman, Y.; Gutzmer, J.; Li, X.-H.; Seifert, T.; Li, C.-F.; Ling, X.-X.; Li, J.
Neoproterozoic iron formations are exposed in the Wadi Hamama area (Egypt) in the northwestern part of the Arabian–Nubian Shield. Mafic and felsic volcanic and volcaniclastic rocks of an intra-oceanic island-arc setting host multiple, thin iron-formation units. Major element compositions of the iron formation confirm a low detrital input, whereas the rare-earth elements and Y data suggest deposition related to an influx of low-temperature hydrothermal fluids. Unlike most Neoproterozoic banded iron formations, but similar to other iron-formation occurrences from the Arabian–Nubian Shield, the Nd isotopic compositions of the Wadi Hamama iron formations are predominantly mantle-like. SIMS U–Pb zircon ages of the host volcaniclastic units indicate that the age of iron-formation deposition is ca. 695 Ma, which is within the Sturtian epoch that is presumed to be a glacial event of global extent. Nevertheless, there is no robust evidence of any influence of Sturtian glaciation in the Arabian–Nubian Shield. Our results rather suggest that the iron formations in the area may have formed as low-temperature exhalites on the floor of an island-arc basin. The iron formations were deposited during periods of volcanic quiescence, with metals having been derived during low-temperature pervasive hydrothermal alteration of volcanic and volcaniclastic rocks exposed at the seafloor–seawater interface. Precipitation took place due to mixing of metal-bearing hydrothermal fluids and cold, oxygenated seawater. There is no need to invoke possible effects of global glaciation to explain the origin of the Sturtian-aged iron formations in the shield. Our study thus suggests that not all Neoproterozoic iron formations are necessarily linked to glacial events as the Hamama deposit represents a non-Rapitan exhalative iron formation.
Keywords: Cryogenian; Exhalite; Hydrothermal; Iron formations; Island arc; Sturtian glaciation
Mineralium Deposita (2020)
Online First (2019) DOI: 10.1007/s00126-019-00898-0
High temperature plasma immersion ion implantation using hollow cathode discharges in small diameter metal tubes
Ueda, M.; Silva, C.; de Souza, G. B.; Pichon, L.; Reuther, H.
High temperature nitrogen plasma immersion ion implantation (HT-NPIII) method was used to treat the internal walls of small diameter metal tubes made of SS304 and of Ti6-Al4-V (TAV). Using a lid in one side of the tubes was essential to reach high temperatures of 700-900 °C, necessary for high thermal diffusion of nitrogen in Ti alloy samples placed inside the metal tubes for monitoring the HT-NPIII process. The used metal tubes also reached such high temperatures. New phases of TiN and Ti2N were successfully attained in the TAV samples with the treated layer thickness of more than 1.3 μm for all the tested cases. For tubes made of SS304, HT-NPIII treatments resulted in redeposition of FeN thick layers with high hardness on the surfaces of the internal walls of the tubes and on the monitoring samples. Obtaining such HT-NPIII conditions in these small metallic tubes was possible by achieving high plasma density through hollow cathode discharges inside those tubes. These results were compared to the ones obtained on the nitrogen implantation treatments of TAV samples in moderate to high temperatures carried out previously in the laboratory which indicated the superior performance of the presently reported method of surface modification.
Journal of Vacuum Science & Technology B 37(2019)4, 042902
Structure–Affinity Relationships of Fluorinated Spirocyclic Sigma2 Receptor Ligands with an Exocyclic Benzylamino Moiety
Bergkemper, M.; Kronenberg, E.; Schepmann, D.; Ludwig, F.-A.; Brust, P.; Wünsch, B.
To identify a potent and selective σ2 receptor ligand appropriate for development as a positron emission tomography (PET) tracer, several fluorinated analogues of the spirocyclic lead compounds trans- and cis-6 (N-(2,4-dimethylbenzyl)-3-methoxy-3,4-dihydrospiro[benzopyran-1,1′-cyclohexan]-4′-amine) were designed. In multistep syntheses, a fluorine atom was introduced directly or as a 2-fluoroethoxy moiety on the 2-benzopyran scaffold, on the dimethylbenzylamino moiety, or on the central amino moiety. The σ1 and σ2 receptor affinity was determined in receptor binding studies with radioligands. With respect to σ2 affinity and σ2/σ1 selectivity, cis-N-(2,4-dimethylbenzyl)-5-fluoro-3-methoxy-3,4-dihydrospiro[benzopyran-1,1′-cyclohexan]-4′-amine (cis-15 c, Ki(σ2)=51 nm) and cis-N-[4-(fluoromethyl)-2-methylbenzyl]-3-methoxy-3,4-dihydrospiro[benzopyran-1,1′-cyclohexan]-4′-amine (cis-28 e, Ki(σ2)=57 nm) are the most promising ligands. The combination of both structural elements in one molecule, cis-N-[4-(fluoromethyl)-2-methylbenzyl]-5-fluoro-3-methoxy-3,4-dihydrospiro[benzopyran-1,1′-cyclohexan]-4′-amine (cis-28 c: Ki(σ2)=874 nm), resulted in decreased σ2 and σ1 affinity. Methylation of secondary amines led to three tertiary methylamines with moderate affinity for both σ receptor subtypes.
Keywords: cis–trans configuration; fluorinated PET tracers; receptor selectivity; spirocyclic ligands; structure–affinity relationships; σ receptors
ChemMedChem 14(2019), 1392-1402
Mikroorganismen und deren Relevanz in einem Endlager
Der Vortrag dient der Weiterbildung von Lehrkräften und gibt Einblicke in die Endlager-Problematik von hoch-radioaktiven Abfällen. Im speziellen soll hier die Relevanz von Mikroorganismen dargestellt und erleutert werden.
Radioaktivität - Forschung, Schule, Praxis, 09.10.2019, Schülerlabor DeltaX, HZDR, Dresden, Deutschland
Opportunities for measurements of astrophysical‐relevant alpha‐capture reaction rates at CRYRING@ESR
The heavy‐ion storage ring CRYRING@ESR has recently been installed and commissioned at GSI as one of the first installations of the upcoming Facility for Antiproton and Ion Research (FAIR). It is designed to store highly charged ions in the energy range between 300 keV/u and about 10 MeV/u. It will incorporate a gas‐jet target providing high‐density jets of, among other gases, hydrogen and helium. This will allow to study alpha‐capture reaction rates of astrophysical interest in the energy range of the Gamow window for core‐collapse supernovae. Special interest comes from the long‐lived radio‐isotope 44Ti (t1/2 = 58.9 years), which is supposed to be produced in the alpha‐rich freeze‐out during such an event. The nucleosynthesis of this isotope is of great interest, as the amount of material produced can be estimated by direct observation in remnants of recent supernovae. The disagreements between the observations and the estimations from astrophysical models show the need of more experimental data for the production and consumption reactions in the energy range of a core‐collapse supernova. In this article, we will describe the proposed method of injecting beams of 44Ti into CRYRING@ESR and performing the actual reaction rate measurements.
Keywords: 44Ti; core-collapse supernova; alpha-capture
X-Ray Spectrometry 49(2020)1, 129-132
Deutschlands Ausstieg aus der Atomkraft - Was passiert mit dem Müll und welche Rolle spielen dabei Mikroorganismen
Zur Zeit werden in Deutschland noch 7 Kernkraftwerke zur Stromerzeugung betrieben. Bis 2022 soll das letzte Kernkraftwerk abgeschaltet werden – Deutschlands Ausstieg aus der Atomkraft. Der Atomausstieg ist ein wichtiger Schritt für die Energiewende, nicht nur in Deutschland, sondern in vielen Ländern Europas. Ziel ist eine langfristige und vollständige Umstellung auf erneuerbare Energien wie z. B. Wasserkraft, Sonnen- und Windenergie.
Der Ausstieg aus der Kernenergie bringt auch einige Konsequenzen mit sich, für welche wir Verantwortung übernehmen müssen. Eine der größten Herausforderungen ist dabei die sichere und langfristige Lagerung des Atommülls. Allein in Deutschland entstanden im Jahr 2015 15 Tonnen an abgebrannten Brennelementen. Dieser Atommüll ist hoch radioaktiv und wird erst nach einer Dauer von etwa 200.000 bis 500.000 Jahren als „ungefährlich“ eingestuft. Das Endlager für die Brennelemente muss also über diesen langen Zeitraum stabil und sicher sein. Weltweit hat sich hierbei das Konzept einer tiefen-geologischen Lagerung – etwa 500 m bis 1000 m unter der Erde – durchgesetzt. Hierbei soll ein Multi-Barrieren-Konzept Anwendung finden, welches aus folgenden Elementen bestehen wird:
1) technische Barriere – Metall-Behälter, welcher die Brennelemente beherbergt (Gusseisen, Stahl, oder Kupfer)
2) geo-technische Barriere – Puffer- und Abdichtungsmaterial (Bentonit oder Salzgrus)
3) geologische Barriere – Wirtsgestein (Steinsalz, Granit oder Tongestein)
In Deutschland starten wir von einer „weißen Landkarte“. Die unterschiedlichen Materialien und Gesteine werden momentan auf ihre Eignung für das Endlager in Deutschland untersucht. Viele verschiedene Fachdisziplinen sind dafür relevant: Geologie, Mineralogie, (Radio-)Chemie, Physik, Mathematik, Materialwissenschaften, Architektur – um hier nur einige zu nennen. Interessanterweise spielt auch die Biologie bei der Planung des Endlagers eine Rolle. Lebewesen können auf verschiedene Art und Weise mit den hier verwendeten Materialien – sogar mit dem Atommüll selbst – interagieren. Zu den hauptsächlich hier betrachteten Lebewesen zählen Pflanzen, Pilze und Mikroorganismen (Bakterien, Archaeen). Mikroorganismen sind ubiquitär auf dem Planeten Erde verbreitet und werden auch im Endlager für Atommüll anwesend sein. Bedingt durch ihren Stoffwechsel, welcher sich von dem des Menschen zum Teil stark unterscheidet, sind Mikroorganismen in der Lage, Materialien und deren Eigenschaften zu verändern. Da die Lagerung des Atommülls sicher und langfristig sein muss, ist es wichtig zu erforschen, inwiefern Mikroorganismen hierfür genutzte Barriere-Materialien verändern und deren Eigenschaften beeinflussen können. Im ungünstigsten Fall könnte dadurch die langfristige Sicherheit des Endlagers stark reduziert werden.
Der Vortrag gibt einen Einblick in die faszinierende Welt der Mikroorganismen und zeigt zugleich deren Relevanz für die sichere und langfristige Lagerung des Atommülls.
Keywords: hoch-radioaktiver Abfall; Endlager; Mikroorganismen
Veranstaltung der Dresdner Seniorenakademie, 08.10.2019, Deutsches Hygienemuseum, Deutschland
Crystal structure and dehydration behaviour of Ag+-exchanged levyne
Cametti, G.; Churakov, S. V.; Scheinost, A.
Levyne is a natural zeolite Ca2.53Na0.72K0.23(Al6.26Si11.8O36)·17.58H2O with LEV framework type. The structure can be described by a sequence of single six-membered rings (S6R) and double six-membered rings (D6R) stacked along the c axis with AABCCABBCAA sequence [1,2]. This sequence originates columns along  of  polyhedra (levyne cages) alternating with  polyhedra (double six-rings). Two-dimensionally interconnected channels (free diameters 3.6 × 4.8 Å) confined by eight-membered rings run perpendicular to . In this study we investigated the crystal structure and thermal stability of a Ag-exchanged levyne by using a multimethodological approach.
Keywords: zeolite; levyne; Ag-doping; XAFS
32nd European Crystallographic Meeting (ECM 32), 18.-23.08.2019, Wien, Austria
Magnetization Dynamics of an Individual Single-Crystalline Fe-Filled Carbon Nanotube
The magnetization dynamics of individual Fe-filled multiwall carbon-nanotubes (FeCNT), grown by chemical vapor deposition, are investigated by microresonator ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) microscopy and corroborated by micromagnetic simulations. Up to now, only static magnetometry measurements are available. They suggest that the FeCNTs consist of a single-crystalline Fe nanowire throughout the length. The number and structure of the FMR lines and the abrupt decay of the spin-wave transport seen in BLS indicate, however that the Fe filling is not a single straight piece along the length. Therefore a stepwise cutting procedure was applied in order to investigate the evolution of the ferromagnetic resonance lines as a function of the nanowire length. Our results show that the FeCNT is indeed not homogeneous along the full length but is built from 300-400 nm long single-crystalline segments. These segments consist of magnetically high quality Fe nanowires with almost the bulk values of Fe and with a similar small damping in relation to thin films, promoting the FeCNTs as appealing candidates for spin-wave transport in magnonic applications.
Keywords: ferromagnetic nanotubes; ferromagnetic resonance; carbon nanotubes; Brillouin light scattering; micromagnetism
Small 15(2019)49, 1904315
IAEA Photonuclear Data Library 2019
Kawano, T.; Cho, Y. S.; Dimitriou, P.; Filipescu, D.; Iwamoto, N.; Plujko, V.; Tao, X.; Utsunomiya, H.; Varlamov, V.; Xu, R.; Capote, R.; Gheorghe, I.; Gorbachenko, O.; Jin, Y. L.; Renström, T.; Stopani, K.; Tian, Y.; Tveten, G. M.; Wang, J. M.; Belgya, T.; Firestone, R.; Goriely, S.; Kopecky, J.; Krticka, M.; Schwengner, R.; Siem, S.; Wiedeking, M.
Photo-induced reaction cross section data are of importance for a variety of current or emerging applications, such as radiation shielding design and radiation transport analyses, calculations of absorbed dose in the human body during radiotherapy, physics and technology of fission reactors (influence of photo-reactions on neutron balance) and fusion reactors (plasma diagnostics and shielding), activation analyses, safeguards and inspection technologies, nuclear waste transmutation, medical isotope production and astrophysical applications. To address these data needs the IAEA Photonuclear Data library was produced in 2000, containing evaluated photo-induced cross sections and neutron spectra for 164 nuclides which were deemed relevant for the applications. Since the release of the IAEA Photonuclear Data Library however, new experimental data as well as new methods to assess the reliability of experimental cross sections have become available. Theoretical models and input parameters used to evaluate photo-induced reactions have improved significantly over the years. In addition, new measurements of partial photoneutron cross sections using mono-energetic photon beams and advanced neutron detection systems have been performed allowing for the validation of the evaluations and assessments of the experimental data. Furthermore, technological advances have led to the construction of new and more powerful gamma-beam facilities, therefore new data needs are emerging.
We report our coordinated efforts to address these data needs and present the results of the new evaluations of more than 200 nuclides included in the new updated IAEA Photonuclear Data Library, where the photon energy goes up to 200 MeV. We discuss the new assessment method and make recommendations to the user community in cases where the experimental data are discrepant and the assessments disagree. In addition, in the absence of experimental data, we present model predictions for photo-induced reaction cross section on nuclides of potential interest to medical radioisotope production.
Keywords: Photonuclear reactions; cross sections; data library
Nuclear Data Sheets 163(2020), 109-162
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