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Linear and nonlinear THz spectroscopy at HZDR
In this talk I have presented some experiments on linear and nonlinear THz spectroscopy at HZDR
Keywords: terahertz spectroscopy; free-electron laser
Seminarvortrag, Harbin Institute of Technology, 22.07.2019, Harbin, China
Nonlinear dressing of excitons, polaritons, and intersubband transitions using a terahertz free-electron laser
This talk reports some recent experiments making use of intense, spectrally narrow terahertz(THz) pulses from a free-electron laser (FEL) as a unique tool for nonlinear dressing of elementary transitions in the THz range.
Keywords: terahertz; free-electron laser; exciton; dressed state
VII International Conference “Frontiers of Nonlinear Physics”, 28.06.-04.07.2019, Nizhny Novgorod, Russian Federation
Nonlinear terahertz spectroscopy of III-V semiconductor quantum wires and quantum wells using a free-electron laser
This talk reviews some recent experiments using intense narrow-band terahertz (THz) fields from a free-electron laser for exploring electronic properties in semiconductor nanostructures. In n-type III-V semiconductor nanowires (NW), intense THz excitation causes a nonlinear plasmonic response, which manifests itself by a strong red shift of the plasma resonance. This nonlinearity is investigated by scattering-type scanning near-field infrared microscopy. For the NWs under study, a spectrally sharp plasma resonance, located at a photon energy of 125 meV for weak excitation, undergoes a power-dependent redshift to about 95 meV. We attribute this nonlinearity to an increase of the effective mass caused by transient carrier heating. In another experiment, we use strong narrowband THz excitation to dress the 2-3 intersubband transition in a 40 nm wide GaAs quantum well (QW). The resulting nonlinearities are explored by THz time-domain spectroscopy using synchronous broadband THz probe pulses and electro-optic sampling. Tuning the THz pump beam into resonance with the 2-3 intersubband transition, we have investigated the induced coherent signatures in the vicinity of the 1-2 intersubband transition and found evidence for mixed light-matter states in the QW giving rise to a THz Autler-Townes effect.
The presented work was conducted in collaboration with D. Lang and J. Schmidt (HZDR) who did most experiments, L. Balaghi, E. Dimakis, M. Helm, R. Hübner, D. Lang, A. Pashkin, S. Winnerl (HZDR), and S.C. Kehr, L.M. Eng (TU Dresden, Germany).
Keywords: terahertz; free-electron laser; nonlinear spectroscopy; quantum wire; quantum well
Invited lecture (Conferences)
Light Conference 2019, 16.-18.07.2019, Changchun, China
Gamma, neutron and muon background in the new Felsenkeller underground accelerator laboratory
Astrophysically relevant nuclear reactions between charged particles usually occurring in stars at deep sub-Coulomb energies. A direct experimental study of such reactions in the laboratory requires high luminosity coupled with low background in the detectors to compensate for the tiny reaction yield to be measured. The new Felsenkeller underground accelerator laboratory is equipped with a high current particle accelerator and has very low background.
This contribution will report about the experimental study of the muon flux and angular distribution of the muons in the new laboratory, which is required to optimize the veto detector arrangements. In addition, the measured neutron flux and energy spectrum at Felsenkeller will be reported. Finally, the actual γ background in muon vetoed HPGe detectors will be presented. The measured background and known ion beam current will allow the study many astrophysically relevant reactions direct in their stellar energy range.
Keywords: Nuclear astrophysiscs; Underground; Felsenkeller; Laboratory background
Nuclear Physics in Astrophysics IX, 15.-20.09.2019, Castle Waldthausen; Frankfurt, Germany
Background studies with actively vetoed germanium gamma-ray detector in Felsenkeller tunnels VIII and IX
A new underground accelerator facility is being built in tunnels VIII and IX of the Dresden Felsenkeller. Previous gamma-ray background measurements in another part of the tunnelsystem showed suitable conditions for in-beam nuclear astrophysics experiments [1, 2] using germanium detectors with active veto against the cosmic-ray muons. These stableion beam experiments are of high importance to understand the reactions of the stellar burning phases, and in particular the solar fusion reactions.
The new laboratory is now ready to host measurements mapping the background conditions. This work reports on the measured background in actively vetoed gamma-ray detectorat the place of the target station in the laboratory used for the upcoming experiments.
 T.Szücs et al., Eur. Phys. Jour. A 48 (2012) 8.  T.Szücs et al., Eur. Phys. Jour. A 51 (2015) 33.
Keywords: Nuclear astrophysics; underground; Felsenkeller; Gamma-background
XV International Symposium on Nuclei in the Cosmos (NIC XV), 24.-29.06.2018, Assergi, Italy
5th International Solar Neutrino Conference, 11.-14.06.2018, TU Dresden, Germany
Resonance strengths in the 14N(p,γ)15O astrophysical key reaction measured with activation
Background: The 14N(p ,γ )15O reaction plays a vital role in various astrophysical scenarios. Its reaction rate must be accurately known in the present era of high precision astrophysics. The cross section of the reaction is often measured relative to a low energy resonance, the strength of which must therefore be determined precisely. Purpose: The activation method, based on the measurement of 15O decay, has not been used in modern measurements of the 14N(p ,γ )15O reaction. The aim of the present work is to provide strength data for two resonances in the 14N(p ,γ )15O reaction using the activation method. The obtained values are largely independent from previous data measured by in-beam γ spectroscopy and are free from some of their systematic uncertainties. Method: Solid state TiN targets were irradiated with a proton beam provided by the Tandetron accelerator of Atomki using a cyclic activation. The decay of the produced 15O isotopes was measured by detecting the 511 keV positron annihilation γ rays. Results: The strength of the Ep=278 keV resonance was measured to be ω γ278=(13.4 ±0.8 ) meV while for the Ep=1058 keV resonance ω γ1058=(442 ±27 ) meV . Conclusions: The obtained Ep=278 keV resonance strength is in fair agreement with the values recommended by two recent works. However, the Ep=1058 keV resonance strength is about 20% higher than the previous value. The discrepancy may be caused in part by a previously neglected finite target thickness correction. As only the low energy resonance is used as a normalization point for cross section measurements, the calculated astrophysical reaction rate of the 14N(p ,γ )15O reaction and therefore the astrophysical consequences are not changed by the present results.
Keywords: Nuclear Astrophysics
Physical Review C 100(2019), 015805
Contribution to WWW
Magnetic Nanoparticle Chains in Gelatin Ferrogels: Bioinspiration from Magnetotactic Bacteria
Sturm, S.; Siglreitmeier, M.; Wolf, D.; Vogel, K.; Gratz, M.; Faivre, D.; Lubk, A.; Büchner, B.; Sturm, E.; Cölfen, H.
Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic magnetite NC chain-like assemblies is reported. An easy green synthesis route in a thermoreversible gelatin hydrogel matrix is used. The structure of these magnetite chains prepared with and without gelatin is characterized by means of transmission electron microscopy, including electron tomography (ET). These structures indeed bear resemblance to the magnetite assemblies found in MTB, known for their mechanical flexibility and outstanding magnetic properties and known to crystallographically align their magnetite NCs along the strongest <111> magnetization easy axis. Using electron holography (EH) and angular dependent magnetic measurements, the magnetic interaction between the NCs and the generation of a magnetically anisotropic material can be shown. The electro- and magnetostatic modeling demonstrates that in order to precisely determine the magnetization (by means of EH) inside chain-like NCs assemblies, their exact shape, arrangement and stray-fields have to be considered (ideally obtained using ET).
Keywords: bioinspiration; electron holography; electron tomography; gelatin; magnetite
Advanced Functional Materials 29(2019), 1905996
Online First (2019) DOI: 10.1002/adfm.201905996
Layer Rotation-Angle-Dependent Excitonic Absorption in van der Waals Heterostructures Revealed by Electron Energy Loss Spectroscopy
Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.
Keywords: 2D materials; EELS; TEM; electronic structure calculations
ACS Nano 13(2019), 9541-9550
- Final Draft PDF 1,5 MB Secondary publication
Enhanced sensitivity of MoSe2 monolayer for gas adsorption induced by electric field
Ai, W.; Kou, L.; Hu, X.; Wang, Y.; Krasheninnikov, A.; Sun, L.; Shen, X.
According to recent studies, gas sensors based on MoSe2 have better detection performance than graphene-based sensors, especially for N-based gas molecules, but the reason for that is not fully understood at the microscopic level. Here, we investigate the adsorption of CO, CO2, NH3, NO and NO2 gas molecules on MoSe2 monolayer by the density functional theory calculations. Our results reveal that indeed MoSe2 monolayer is more sensitive to adsorption of N-containing gas molecules than C-containing, which can be attributed to the distinct charge transfer between the gas molecules and MoSe2. The conductance was further calculated using the nonequilibrium Green's function (NEGF) formalism. The reduced conductance was found for NH3 and NO2 adsorbed MoSe2, consistent with the high sensitivity of MoSe2 for NH3 and NO2 molecules in the recent experiments. In addition, the adsorption sensitivity can significantly be improved by an external electric field, which implies the controllable gas detection by MoSe2. The magnetic moments of adsorbed NO and NO2 molecules can also be effectively modulated by the field-sensitive charge transfer. Our results not only give microscopic explanations to the recent experiments, but also suggest using MoSe2 as a promising material for controlled gas sensing.
Keywords: 2D materials; first-principles calculations
Journal of Physics: Condensed Matter 31(2019), 445301
- Final Draft PDF 5,7 MB Secondary publication
Fluctuation electron microscopy on silicon amorphized at varying self ion-implantation conditions
The medium range order of self-ion-implanted amorphous silicon was studied by variable resolution fluctuation electron microscopy and characterized by the normalized variance V(k, R). The ion-implantation was conducted at sequentially increasing ion energies ranging from 50 keV to 300 keV. Two silicon-on-insulator wafers were amorphized at different implantation conditions. From each material, one as-prepared and one ex situ annealed specimen were chosen for analysis. Fluctuation electron microscopy on cross-sectional prepared samples confirms the presence of medium range order due to the amorphization process. We propose three explanations on how the observed medium range order is created by silicon ion-implantation. Two of these suggestions involve paracrystals formed by thermal spikes while a third explanation assumes a medium range order due to nanoscale regions unaffected by the amorphization. Although the two amorphized silicon samples reveal different local structures due to the ion-implantation process, no difference in the self-diffusion behavior is evident, which demonstrates that self-diffusion mainly proceeds within the amorphous phase.
Keywords: fluctuation electron microscopy; amorphous silicon, ion implantation
Journal of Applied Physics 126(2019), 095707
Spatial Coefficient of Variation of Arterial Spin Labeling MRI as a Cerebrovascular Correlate of Carotid Occlusive Disease
Clinical interpretation of arterial spin labeling (ASL) perfusion MRI in cerebrovascular disease remains challenging mainly because of the method’s sensitivity to concomitant contributions from both intravascular and tissue compartments. While acquisition of multi-delay ASL images can differentiate between the two contributions, the prolonged acquisition is prone to artifacts and not practical for clinical research. Here, we evaluated the utility of the spatial coefficient of variation (sCoV) of a single-delay ASL image as a marker of the intravascular contribution. We tested the hypothesis that sCoV is more sensitive than CBF to the intravascular signal, and therefore will be a better predictor of the side of occlusion. To this end, we compared the hemispheric lateralization of sCoV and CBF ASL images obtained from 28 patients (age 73.9 ± 10.2 years, 8 women) with asymptomatic unilateral carotid occlusion. The results showed that sCoV lateralization predicted the occluded side with 96.4% sensitivity, missing only 1 patient out of the 28. In contrast, the sensitivity of the CBF lateralization was 71.4% with 8 patients showing no difference in CBF between the ipsi- and contra-lateral hemispheres. The findings demonstrate the potential clinical utility of sCoV as a cerebrovascular correlate of large vessel disease. Using sCoV in tandem with CBF, vascular information can be obtained in image processing without the need for additional scanning time.
PLOS ONE 15(2020)2, e0229444
Ultrafast metallization in NbO2 studied by pump-probe THz spectroscopy
Rana, R.; Klopf, J. M.; Grenzer, J.; Schneider, H.; Helm, M.; Pashkin, A.
Niobium dioxide (NbO2) is an isovalent counterpart of VO2 with considerably higher transition temperature (Tc = 1080 K). We have performed time-resolved optical pump – THz probe measurements on NbO2 epitaxial thin film at room temperature. Notably, the pump energy required for the switching into a metastable metallic state is smaller than the energy necessary for heating NbO2 up to TC providing strong evidence for the non-thermal character of the photoinduced insulator-to-metal transition.
44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2019), 02.-06.09.2019, Paris, France
Contribution to proceedings
44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2019), 01.-06.09.2019, Parin, France
44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2019), 8873838
Ultrafast neutralization dynamics of highly charged ions upon impact on 2D materials
Heavy ions in high charge states carry a large amount of potential energy in addition to their kinetic energy. The potential energy can amount to several 10keV and is released upon neutralization . We recently showed that neu- tralization of slow highly charged Ar and Xe ions proceeds on a sub-10fs time scale, i.e. during transmission through the very first monolayers of a solid . This feat makes highly charged ions an intriguing tool for efficient modification of 2D materials preventing significant damage to a substrate at the same time. Here we present data on the neutralization dynamics of slow highly charged ions in freestanding single layer graphene and freestanding single layer MoS2. Special emphasise is put on charge exchange of the ions, their kinetic energy loss, and the emission of secondary electrons/photons from the interaction pro- cess.
Invited lecture (Conferences)
Towards Reality in Nanoscale Materials X, 12.-14.02.2019, Levi, Finnland
Interaction of highly charged ions with 2D materials
Slow highly charged ions (HCI) provide an efficient toolkit for surface modifications at the nanoscale . Due to the potential energy of HCIs, nanoscale surface melting or atom sputtering can be ob- served in susceptible materials with an efficiency of about 100% (one surface feature per ion). The neutralization of the HCIs driving the potential energy deposition is typically considered to be finished in ’a shallow region’ in the surface, i.e. ’on the first nanometers’. To further quantify the HCI neutral- ization dynamics we recently took a new approach and used freestanding 2D materials as the target. Due to the atomic thickness of the materials, ions are not stopped in the materials and are available for spectroscopic analysis. At the same time the 2D materials are available for post-irradiation microscopic analysis, which finally al- lows us to determine (1) the kinetic and potential energy lost by the ion, (2) the energy dissipated by emission of secondary particles (electrons and photons), and (3) the en- ergy spend in the nanostructure formation process.
By applying our ion beam spectroscopy, we performed charge state and kinetic energy analysis of ions transmit- ted through freestanding single layer graphene (SLG) , amorphous 1nm thick Carbon Nanomembranes (CNM) , freestanding single layer MoS2, SLG/MoS2 het- erostructures and others. As a first result we found an ultrafast (sub-10 fs ∼ 1 monolayer) neutralization taking place, much faster than established models would have an- ticipated . Furthermore, kinetic energy loss is signifi- cantly enhanced compared to the value of singly charged ions under the same conditions.
To facilitate a comprehensive understanding of the plethora of observed phenomena and their interplay, we use an en- ergy, angle, and charge state resolved spectroscopy in co- incidence with yield and energy resolved measurement of emitted secondary particles . We further developed an exchange and electronic decay taking the time-dependent atomistic model for ion stopping, charge ion charge state explicitly into account .
In this contribution I will give an overview about our recent progress in the field of ion scattering from 2D materials and put the results in perspective to nanostructure formation.
Invited lecture (Conferences)
Nanopatterning Workshop, 07.-10.07.2019, Guildford, United Kingdom
Ion Beam Spectroscopy with 2D Materials
The spectroscopic analysis of ions transmitted or backscat- tered through/from a solid is a standard procedure in ion beam analysis and reveals material composition, crystallog- raphy, surface roughness and other properties. The infor- mation on material properties is typically gained through the determination of the ion energy (or energy of emitted secondary particles) and thus from the ion stopping. Addi- tionally, the ion charge state may change upon interaction with the solid material, which is typically considered as a ’complication’ in experiment, e.g. in the context of charge fractionization when using charge state selective detectors (magnetic spectrometers or electrostatic analyzers). How- ever, charge exchange is also determined by material prop- erties and can yield additional information in conjunction with kinetic energy loss analysis. In this contribution I will show that charge exchange and stopping of highly charged ions (and ions in general) are closely coupled, which implies that nuclear and electronic energy loss are coupled as well. Our results in combina- tion with a quantitative model for impact parameter depen- dent charge exchange and stopping can serve as an addi- tional tool for material structure determination on the sub- nm scale for 2D materials, especially in cases where elec- tron microscopy may not yield atomically resolved data. In our experiments we use slow (v < v0) highly charged Ar and Xe ions with charge states of 1 − 18 and 1 − 40, respec- tively. We transmit the ions through freestanding layers of 2D materials, i.e. single-, bi-, and tri-layer graphene, single- layer hBN, carbon nanomembranes, single-layer MoS2, and other transition metal dichalcogenides . Secondary elec- trons emitted from the interaction process are recorded in a high voltage biased surface barrier detector serving as a start signal for time-of-flight measurements and also allow- ing us to determine the absolute amount of emitted elec- trons. Ions are detected by a position sensitive MCP detec- tor using a delay line anode. Utilizing a set of slits and parallel deflection plates we relate the impact position at the MCP to the scattering angle and charge state of the ions. The timing signal from the impact serves as the stop trigger for the ion’s time-of-flight. Thus, we obtain angle- resolved, energy-resolved charge exchange spectra in coin- cidence with the number of emitted electrons for each individual ion.
Comparing our highly differential data with an atomistic model for time-dependent charge redistribution between the ion and the target atoms allows us to link structural proper- ties and defects to the observed charge state pattern. Our model is based on the statistical description of atoms and an interatomic distance dependent ion de-excitation rate adapted from the Interatomic Coulombic Decay process [2, 3].
Fig. 1 shows a sketch of the ion transmission process in- volving the emission of secondary particles on the time scale of only femtoseconds. Thus, ion transmission studies with atomically thin materials not only are useful for materials science, but also to study inelastic ion-surface interaction on the femtosecond time scale simply by varying the ion velocity or tilting the sample.
Invited lecture (Conferences)
International Workshop on Inelastic Ion Surface Collisions, 17.-22.11.2019, Matsue, Japan
Collisions of highly charged ions with 2D materials - What we learn from ion transmission spectroscopy -
Slow ions in high charge states impacting a solid surface represent a far-from-equilibrium system. Upon impact, the ions capture dozens of electrons and these electrons decay into the atomic ground state already during the collision driven by non-radiative de-excitation processes such as Interatomic Coulombic Decay . The neutralization and electronic decay of the ion leads to the release of its potential energy, which amounts up to several 10 keV facilitating nanostructure formation in suscep- tible materials (mainly insulators with strong electron-phonon coupling).
When a freestanding 2D material is used as a solid target, the ions are still available for spectroscopic measurements after the ion-surface interaction. We performed charge state and kinetic energy analy- sis of ions transmitted through freestanding single layer graphene (SLG) , amorphous 1 nm thick Carbon Nanomembranes (CNM) , freestanding single layer MoS2, SLG/MoS2 heterostructures and others. As a first result we found an ultrafast (sub-10 fs) neutralization taking place, much faster than established models would have anticipated. Further, kinetic energy loss is significantly en- hanced over the expected value from singly charged ions under the same conditions. We are able to find charge exchange patterns, utilizing angle-resolved charge exchange spectroscopy . To facilitate a comprehensive understanding of the plethora of observed phenomena and their interplay, we developed an atomistic model for ion stopping, charge exchange and electronic decay taking the time-dependent ion charge state explicitly into account .
In this contribution I will show that charge exchange pattern together with an atomistic and local model for charge exchange can be used to determine the structure of 2D materials on a sub-nm level, especially important for amorphous materials where atomically-resolved microscopy is hard to perform.
Invited lecture (Conferences)
XXXI International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC), 23.-30.07.2019, Deauville, Frankreich
Development of a framework for generalized modelling of multiphase flow in OpenFOAM
Liao, Y.; Hänsch, S.; Meller, R.; Lehnigk, R.; Schlegel, F.; Lucas, D.
The multi-fluid CFD methodology is widely used in the simulation of multiphase flows. The numerical results are able to provide insight and knowledge on local phenomena, and frequently used to assist the design, optimization and safety analysis of industrial processes. However, current multi-fluid CFD simulations often suffer from two limitations. One is that the predictability for multiphase systems is not fully guaranteed. The transferability of a setup from its calibration case to other cases, where experimental data are not available, is not always reliable, and result-oriented tuning is often necessary. The deficiency is believed to be caused majorly by the imperfectness in the closure models that are required to reconstruct the processes occuring at the interface between phases. The other is that the state of the art multi-fluid model is usually limited to certain flow regimes. It fails to capture the transition between different flow regimes, e.g. bubbly flow to churn-turbulent flow, which are frequently encountered in the practice. This work aims to present a framework for generalized modelling of multiphase flow and the efforts made in the CFD department at HZDR towards closure model development. A new solver for the realization and validation of the framework is developed on the basis of the open source CFD code OpenFOAM. It is capable of capturing both dispersed and resolved gaseous structures in the liquid as well as the transfer between them.
Keywords: Multi-fluid model; baseline closure strategy; GENTOP model; OpenFOAM
Invited lecture (Conferences)
SG-FANS-3 Workshop, 25.-27.09.2019, Xi'an, China
Roadmap on photonic, electronic and atomic collision physics: III. Heavy particles: with zero to relativistic speeds
Aumayr, F.; Ueda, K.; Sokell, E.; Schippers, S.; Sadeghpour, H.; Merkt, F.; Gallagher, T. F.; Dunning, F. B.; Scheier, P.; Echt, O.; Kirchner, T.; Fritzsche, S.; Surzhykov, A.; Ma, X.; Rivarola, R.; Fojon, O.; Tribedi, L.; Lamour, E.; Crespo López-Urrutia, J. R.; Litvinov, Y. A.; Shabaev, V.; Cederquist, H.; Zettergren, H.; Schleberger, M.; Wilhelm, R. A.; Azuma, T.; Boduch, P.; Schmidt, H. T.; Stöhlker, T.
We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. Roadmap III focusses on heavy particles: with zero to relativistic speeds. Modern theoretical and experimental approaches provide detailed insight into the wide range of many-body interactions involving projectiles and targets of varying complexity ranging from simple atoms, through molecules and clusters, complex biomolecules and nanoparticles to surfaces and crystals. These developments have been driven by technological progress and future developments will expand the horizon of the systems that can be studied. This Roadmap aims at looking back along the road, explaining the evolution of the field, and looking forward, collecting nineteen contributions from leading scientists in the field.
Keywords: heavy particles; many-body interactions; clusters; complex biomolecules
Journal of Physics B 52(2019), 171003
Charge-Exchange-Driven Low-Energy Electron Splash Induced by Heavy Ion Impact on Condensed Matter
Low-energy electrons (LEEs) are of great relevance for ion-induced radiation damage in cells and genes. We show that charge exchange of ions leads to LEE emission upon impact on condensed matter. By using a graphene monolayer as a simple model system for condensed organic matter and utilizing slow highly charged ions (HCIs) as projectiles, we highlight the importance of charge exchange alone for LEE emission. We find a large number of ejected electrons resulting from individual ion impacts (up to 80 electrons/ion for Xe40+). More than 90% of emitted electrons have energies well below 15 eV. This “splash” of low-energy electrons is interpreted as the consequence of ion deexcitation via an interatomic Coulombic decay (ICD) process.
The Journal of Physical Chemistry Letters 2019(2019)10, 4805-4811
Ultrasonic Determination of the Jahn–Teller Effect Parameters in Impurity-Containing Crystals
Averkiev, N. S.; Bersuker, I. B.; Gudkov, V. V.; Zhevstovskikh, I. V.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Korostellin, Y. V.; Surikov, V. T.
A method is developed to determine the symmetry properties of strains and the type of Jahn–Teller effect in crystals with impurity ions in a triply degenerate electronic T state. This method is based on a calculation of the isothermal contribution of the impurity subsystem to the elastic moduli of a crystal and the absorption and velocity of normal modes for all three possible problems, namely, T ⊗ e, T ⊗ t2, and T ⊗ (e + t2). The calculation results are compared with experimental data. The efficiency of the method is demonstrated for a CdSe:Cr2+ crystal. The CrSe4 center is found to be described in terms of the problem T ⊗ e. The parameters of the ground-state adiabatic potential are determined.
Journal of Experimental and Theoretical Physics 129(2019), 72-80
Pronounced 2/3 magnetization plateau in a frustrated S = 1 isolated spin-triangle compound: Interplay between Heisenberg and biquadratic exchange interactions
Chattopadhyay, S.; Lenz, B.; Kanungo, S.; Sushila, S.; Panda, S. K.; Biermann, S.; Schnelle, W.; Manna, K.; Kataria, R.; Uhlarz, M.; Skourski, Y.; Zvyagin, S. A.; Ponomaryov, A.; Herrmannsdörfer, T.; Patra, R.; Wosnitza, J.
We report the synthesis and characterization of a new quantum magnet [2-[Bis(2-hydroxybenzyl) aminomethyl]pyridine]Ni(II)-trimer (BHAP-Ni3) in single-crystalline form. Our combined experimental and theoretical investigations reveal an exotic spin state that stabilizes a robust 2/3 magnetization plateau between 7 and 20 T in an external magnetic field. AC-susceptibility measurements show the absence of any magnetic order/glassy state down to 60 mK. The magnetic ground state is disordered and specific-heat measurements reveal the gapped nature of the spin excitations. Most interestingly, our theoretical modeling suggests that the 2/3 magnetization plateau emerges due to the interplay between antiferromagnetic Heisenberg and biquadratic exchange interactions within nearly isolated spin S = 1 triangles.
Physical Review B 100(2019), 094427
- Original PDF 1,9 MB Secondary publication
Chemical Shift and Exchange Interaction Energy of the 1s States of Magnesium Donors in Silicon. The Possibility of Stimulated Emission
Shastin, V. N.; Zhukavin, R. K.; Kovalevsky, K. A.; Tsyplenkov, V. V.; Rumyantsev, V. V.; Shengurov, D. V.; Pavlov, S. G.; Shuman, V. B.; Portsel, L. M.; Lodygin, A. N.; Astrov, Y. A.; Abrosimov, N. V.; Klopf, J. M.; Hübers, H.-W.
The results of experiments aimed at the observation of split 1s states in Mg-doped Si are reported. From the results, it is possible to determine the chemical shift and exchange interaction energy of a neutral Mg donor in Si. The position of the 1s(E), 1s(T2), and 2s(A1) parastates determines the possibility for attaining population inversion and the specific mechanism of stimulated Raman scattering. The energy of the 1s(T2) parastate is determined from the position of the Fano resonances in the photoconductivity spectrum of Si:Mg at T = 4 K, and the energies of the 1s(T2) and 1s(E) orthostates from the transmittance spectra at elevated temperatures. On the basis of the experimental data, the relaxation rates are estimated, and the possible mechanisms of stimulated emission are analyzed.
Keywords: neutral double donor; magnesium; spectroscopy; Fano resonance; photoconductivity; population inversion; stimulated Raman scattering
Contribution to proceedings
XXIII International Symposium "Nanophysics and Nanoelectronics", 11.-14.03.2019, Nizhny Novgorod, Russia
Semiconductors 53(9), 1234-1237
Characterization of suprathermal electrons inside a laser accelerated plasma via highly-resolved K⍺-emission
Suprathermal electrons are routinely generated in high-intensity laser produced plasmas via instabilities driven by non-linear laser-plasma interaction. Their accurate characterization is crucial for the performance of inertial confinement fusion as well as for performing experiments in laboratory astrophysics and in general high-energy-density physics. Here, we present studies of non-thermal atomic states excited by suprathermal electrons in kJ-ns-laser produced plasmas. Highly spatially and spectrally resolved X-ray emission from the laser-deflected part of the warm dense Cu foil visualized the hot electrons. A multi-scale two-dimensional hydrodynamic simulation including non-linear laser-plasma interactions and hot electron propagation has provided an input for ab initio non-thermal atomic simulations. The analysis revealed a significant delay between the maximum of laser pulse and presence of suprathermal electrons. Agreement between spectroscopic signatures and simulations demonstrates that combination of advanced high-resolution X-ray spectroscopy and non-thermal atomic physics offers a promising method to characterize suprathermal electrons inside the solid density matter.
Nature Communications 10(2019), 4212
Development of a plasma Faraday rotation calculator for an XFEL pulse
This thesis presents a computational tool for obtaining the Faraday rotation of an X-Ray pulse propagating through a plasma. The fields, needed for the calculation, can be obtained from either a three or a two-dimensional simulation. In the 2D case, a half turn rotational symmetry is assumed and a numerical implementation of the underlying Abel integral is implemented so the Faraday effect can be obtained from the radial distribution. A time-resolved calculation is introduced by integrating the effect over an X-ray pulse, with a specified temporal shape, and using multiple outputs from various iterations. The prototype is developed using Python/Cython and tested in a few simple, analytically solvable scenarios. The main motivation for this tool are planned experiments to study relativistic laser-matter-interactions with help of the ultra-bright XFEL pulses. Hence, examples of such interaction are simulated with the PIConGPU framework, and the developed prototype is used to examine the influence of Rayleigh-Taylor and Weibel-like instabilities on the Faraday rotation effect.
TU Dresden, 2019
Synthetic characterization of ultrashort electron bunches using transition radiation
This work describes the in-situ CTR plugin for the particle-in-cell code PIConGPU.
The C++ -plugin calculates coherent transition radiation (CTR) from millions to billions of macro-particles in a PIConGPU plasma simulation. In order to avoid excessive disk output of many GB to TB of data, as well as and extensive post-processing runtimes on only few CPUs, the plugin was parallelized on GPUs and implemented in-situ as part of PIConGPU.
The physics of this plugins was successfully implemented, tested and verified to agree with an initial python implementation, which again was verified using analytical CTR theory, with an average error of less than 1%. Additionally the plugin was benchmarked, resulting in typical time to solutions for complete transition radiation spectra on the scale of several minutes.
The CTR plugin was then used in several Laser-wakefield accelerator (LWFA) simulations, with self-injected and down-ramp injected electrons respectively. Mimicking the hypothetical placement of successive transition radiaton foils along the LWFA interaction length, the CTR plugin was used multiple times for observing how the electron bunch evolution leads to the characteristic features of transition radiation spectra. This new tool is a synthetic diagnostic, which enables direct comparison of experimentally measured transition radiation data to simulations. In future experiments this can provide insight into LWFA longitudinal electron pulse profiles on the fs-scale, required for future compact LWFA-driven free-electron laser applications.
Keywords: Transition Radiation; Coherent Transition Radiation; PIConGPU; Synthetic Analysis; Ultrashort electron bunches; Laser plasma accelerators; Laser wakefield accelerators; CTR
TU Dresden, 2019
Mentor: Prof. Dr. U. Schramm, Prof. Dr. T. Cowan
Experimental study on the air-side thermal-flow performance of additively manufactured heat exchangers with novel fin designs
Unger, S.; Beyer, M.; Gruber, S.; Willner, R.; Hampel, U.
We introduce novel fin designs for finned tube heat exchangers which enhance the conduction heat transfer within the fin and the convective heat transfer along the fin surface simultaneously. Oval tubes with circular plain fins (CPF), circular integrated pin fins (CIPF) and a serrated integrated pin fins (SIPF) were additively manufactured via Selective Laser Melting (SLM) and their heat transfer and flow characteristics studied in a flow channel for different Reynolds number between 1800 and 7800 as well as fin spacing values between 6 mm and 16 mm. From the experiments an improvement of Nusselt number and a reduction of friction factor was found for all fin designs when fin spacing increases. CIPF showed a higher Nusselt number compared to CPF at all Reynolds numbers and fin spacing values. The highest Nusselt number as well as moderate friction factor values were found for the SIPF design. However, for SIPF the fin efficiency of 30:3 % is lowest due to the high heat dissipation along the fin surface. In order to evaluate the thermal and flow performance three parameters were studied: the performance evaluation criterion, the volumetric heat flux density and the global performance. CIPF gives a higher performance evaluation criterion compared to CPF and SIPF performs best compared to the other fin designs. Highest volumetric heat flux density of 2:72 mkW3K was achieved with CIPF at lowest fin spacing. Small differences in the global performance criterion between the fin designs and for various fin spacing were observed.
The SIPF design is of advantage, if the required surface area, the material cost and the weight of the finned tube heat exchanger are relevant. From the experimental results a heat transfer correlation that includes Nusselt number, Reynolds number, Prandtl number, fin spacing and fin design has been derived.
Keywords: Finned tube heat exchanger; Novel fin designs; Heat transfer; Friction factor; Thermal-flow performance; Additive manufacturing; Selective laser melting
International Journal of Thermal Sciences 146(2019), 106074
Online First (2019) DOI: 10.1016/j.ijthermalsci.2019.106074
Two types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe1+yTe
Rößler, S.; Koz, C.; Wang, Z.; Skourski, Y.; Doerr, M.; Kasinathan, D.; Rosner, H.; Schmidt, M.; Schwarz, U.; Rößler, U. K.; Wirth, S.
A detailed experimental investigation of Fe1+yTe (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field–induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal
Proceedings of the National Academy of Sciences of the United States of America 116(2019)34, 16697-16702
Ion-irradiation induced hardening and defect evolution in CoCrFeMnNi
Heintze, C.; Eißmann, N.; Kieback, B.; Akhmadaliev, S.
The operating conditions of future nuclear reactors, both fission and fusion, still pose a number of materials challenges. In this context, the novel class of high-entropy alloys (HEA) attracts attention due to good mechanical properties and corrosion resistance as well as an - mostly hypothesized -improved irradiation resistance. In the present work the single-phase fcc HEA CoCrFeMnNi, produced by means of powder metallurgy, was ion-irradiated with Fe ions at RT, 300°C and 410°C up to 0.6 and 1 dpa, respectively, along with the austenitic stainless steel 316 serving as a benchmark. Transmission electron microscopy and nanoindentation were applied to study the irradiation-induced hardening and the evolution of the microstructure. While similar hardening is observed for the HEA compared to the benchmark material 316 at RT and 410°C, substantially higher hardening was observed at 300°C. The origin of the hardening will be discussed based on the microstructural evidence.
Keywords: High entropy alloys; Irradiation tolerance; TEM; Nanoindentation
EUROMAT 2019, 01.-05.09.2019, Stockholm, Schweden
Cross section of the reaction 18O(p,γ)19F at astrophysical energies: The 90 keV resonance and the direct capture component
Best, A.; Pantaleo, F. R.; Boeltzig, A.; Imbriani, G.; 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.; Junker, M.; Kochanek, I.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; 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 observation of oxygen isotopes in giant stars sheds light on mixing processes operating in their interiors. Due to the very strong correlation between nuclear burning and mixing processes it is very important to reduce the uncertainty on the cross sections of the nuclear reactions that are involved. In this paper we focus our attention on the reaction . While the channel is thought to be dominant, the (p,γ) channel can still be an important component in stellar burning in giants, depending on the low energy cross section. So far only extrapolations from higher-energy measurements exist and recent estimates vary by orders of magnitude. These large uncertainties call for an experimental reinvestigation of this reaction. We present a direct measurement of the cross section using a high-efficiency 4π BGO summing detector at the Laboratory for Underground Nuclear Astrophysics (LUNA). The reaction cross section has been directly determined for the first time from 140 keV down to 85 keV and the different cross section components have been obtained individually. The previously highly uncertain strength of the 90 keV resonance was found to be 0.53 ± 0.07 neV, three orders of magnitude lower than an indirect estimate based on nuclear properties of the resonant state and a factor of 20 lower than a recently established upper limit, excluding the possibility that the 90 keV resonance can contribute significantly to the stellar reaction rate.
Keywords: Experimental nuclear astrophysics; Underground nuclear physics; Hydrogen burning; Stellar evolution
Physics Letters B 797(2019), 134900
Dataset on Relationships between primary radiation damage, irradiation-induced microstructure and hardening of ion-irradiated Fe-Cr and ODS Fe-Cr alloys
Dataset on Relationships between primary radiation damage, irradiation-induced microstructure and hardening of ion-irradiated Fe-Cr and ODS Fe-Cr alloys including SRIM calculations, nanoindentation, TEM and modelling.
- Relationships between depth-resolved primary radiation … (Id 30720) has used this (Id 29653) publication of HZDR-primary research data
Reseach data in the HZDR data repository RODARE
Publication date: 2019-09-11
Binding, uptake and transport of radionuclides and their analogues by the fungus Schizophyllum commune under natural conditions
Radionuclides occur naturally and can be released into nature through anthropogenic effects. Through leaching and migration, also the anthropogenically released radionuclides can enter the groundwater and endanger the environment, animals and humans. However, the microbial community living in the soil may influence the mobility and thus the migration behaviour of radionuclides.
Since the Chernobyl accident at the latest, it became clear that various fungi are able to accumulate considerable amounts of heavy metals and radionuclides in their fruiting bodies [1-3]. However, it has not yet been determined, which processes lead to this significant accumulation in the fungal fruiting body.
For this reason, the interaction of a model fungus, namely Schizophyllum commune, with various radionuclides was studied in detail in the steps of binding and uptake by the fungal cells and transport within the mycelium.
For the visualization of the radionuclide and heavy metal transport through the hyphae, TEM and STEM imaging in combination with Energy-dispersive X-ray spectroscopy analysis were used to locate accumulation sites within the cells and to identify the formed species. The first results with uranium show that it is accumulated in form of phosphate minerals mainly on the cell membrane. Furthermore, microcosm experiments were conducted in which the bidirectional growth of the fungus was exploited: parts of the mycelium were growing upwards, while the other parts were growing into the contaminated soil. In order to check the transport of soil contaminants through the hyphae, the part of the mycelium that has no direct contact with the soil was sampled and analysed by ICP-MS. First results show that uranium could be detected in the samples, suggesting transport through the hyphae.
In addition to the transport of uranium, the experiments also investigate the transport of europium as an analogue for trivalent actinides, as well as the transport of inactive caesium and strontium within the mycelium.
Keywords: Fungi; Uranium; Transport; Uptake
17th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 15.-20.09.2019, Kyoto, Japan
Investigation of the potential of fungi for precautionary radiation protection in soil
Due to the multifaceted use of radionuclides in research, medicine and industry, there is an increased risk of a release into the environment during the extraction and use of radioactive materials, but also during the storage of the resulting radioactive waste. If radionuclides are released into the soil, they can migrate through soil layers to the groundwater or can be absorbed by crops. In any case, it endangers the environment, animals and humans. For this reason, an effective precautionary radiation protection method must be found which can limit the mobility of possible released radionuclides in the environment.
Since the Chernobyl accident at the latest, it became clear, that fungi influence the migration behavior of radionuclides in the soil by accumulating them in large quantities. Due to other positive properties of fungi, such as the spread of one organism over several square kilometers and their high life expectancy, they provide a good basis for a bio-based precautionary radiation protection. Nevertheless, previous studies have also shown, that the effectiveness of radionuclide accumulation depends on the respective fungal strain [1-3].
For this reason, the molecular interactions of four different fungi with uranium were investigated and compared.
First TEM and STEM images of the fungus Schizophyllum commune, which is widely used as a model organism, show mineralization of uranium in form of needles at the cell membrane. Energy-dispersive X-ray spectroscopy analysis and time-resolved laser-induced fluorescence spectroscopy (TRLFS) have shown, that uranium is mineralized with phosphate. A second fungus, called Leucoagaricus naucinus, shows a different form of mineralization and localization of uranium in the cell. However, first TRLFS experiments suggest that it is a phosphate mineral as well. Together with two other fungi, Pleurotus ostreatus and Macrolepiota procera, a better understanding of the interactions of different fungi with radionuclides will be generated in order to evaluate the potential of fungi for the precautionary radiation protection of soils and to lay the basis for the development of a practicable process.
Keywords: Fungi; Radionuclide; TRLFS; precautionary radiation protection
Jahrestagung der Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Deutschland
Research and Implementation of Efficient Parallel Processing of Big Data at TELBE User Facility
In recent years, improvements in high-speed Analog-to-Digital Converters (ADC) and sensor technology has encouraged researchers to improve the performance of Data Acquisition (DAQ) systems for scientific experiments which require high speed and continuous data measurements — in particular, measuring the electronic and magnetic properties of materials using pump-probe experiments at high repetition rates. Experiments at TELBE are capable of acquiring almost 100 Gigabytes of raw data every ten minutes. The DAQ system used at TELBE partitions the raw data into various subdirectories for further parallel processing utilizing the multicore structure of modern CPUs.
Furthermore, several other types of processors that accelerate data processing like the GPU and FPGA have emerged to solve the challenges of processing the massive amount of raw data. However, the memory and network bottlenecks become a significant challenge in big data processing, and new scalable programming techniques are needed to solve these challenges. In this contribution, we will outline the design and implementation of our practical software approach for efficient parallel processing of our large data sets at the TELBE user facility.
Keywords: Big Data; Data Processing Pipeline; Data Acquisition Systems; Signal Processing; Data analytics
Contribution to proceedings
2019 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS), 22.07.2019, Berlin, Deutschland
2019 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS): IEEE, 978-1-5108-8479-3
Novel High Affinity Histone Deacetylase Inhibitors as Potential Radiotracers for PET
Epigenetics investigates heritable phenotype changes that do not involve alterations in the DNA sequence. The related phenomena play a key role in gene expression by enzyme-mediated post-translational modifications (PTMs) of proteins. One of the most relevant modifications is the process of deacetylation of the lysine side chains on histones, which are regulated by histone deacetylases (HDACs). The catalyzed deacetylation of lysine residues on histones modulates the chromatin and thus influences the gene expression and transcription. The class I histone deacetylases 1, 2 and 3 are overexpressed in several types of cancer, neurodegenerative diseases and inflammation. Inhibition of those zinc-dependent HDACs relaxes the chromatin structure and can result in transcriptional activation and anticancer effects, e.g. cell cycle arrest and induced differentiation. Consequently, radiolabeled HDAC inhibitors have emerged as a potential tool for the diagnostic imaging of tumors by positron emission tomography (PET). 
The aim of this work is the development of novel highly affine and selective fluorine-containing derivatives of a class I selective HDAC inhibitor to obtain the corresponding 18F-labeled PET radiotracers with an ortho-aminoanilide as zinc-binding motif for targeting class I HDACs in tumors. Recently, we discovered a new highly affine HDAC 1 ligand LSH-A30 with an IC50 for HDAC 1 inhibition of 4.4 ± 0.1 nM. In this connection, the structure of LSH-A30 serves as lead for the development of a series of fluorinated reference compounds, which are currently synthesized. The binding affinities and selectivities towards the class I HDAC isoforms will be determined. Our strategy is mainly focused on the medicinal chemistry of fluorine-containing derivatives, which are suitable for direct and indirect nucleophilic radiofluorination. For the most promising compounds, precursors for radiolabeling will be synthesized, the evaluation of physicochemical properties, e.g. stability and lipophilicity of the radiolabeled compounds will be assessed and further in vitro and in vivo investigations will be performed.
Keywords: HDAC inhibitors; PET tracer development; ortho-aminoanilides
GDCh Wissenschaftsforum Chemie 2019, 15.-18.09.2019, Aachen, Deutschland
Terahertz Nonlinear Optics of Graphene: From Saturable Absorption to High-Harmonics Generation
Graphene has long been predicted to show exceptional nonlinear optical properties, especially in the technologically important terahertz (THz) frequency range. Recent experiments demonstrated that this atomically-thin material indeed exhibits possibly the largest nonlinear coefficients of any material known to date. These findings in particular pave ways for practical graphene-based applications in ultrafast electronics and optoelectronics operating at THz rates. Here we report on the advances in the booming field of nonlinear THz optics of graphene, and describe the state-of-the-art understanding of the nature of the nonlinear interaction of electrons in graphene with intense THz fields based on the thermodynamic model of electron transport in graphene. We also provide a comparison between different mechanisms of nonlinear interaction of graphene with light fields in THz, infrared and visible frequency ranges.
We conclude the report with the perspectives for the expected technological applications of graphene based on its extraordinary THz nonlinear properties. This report covers the evolution of the field of THz nonlinear optics of graphene from the very pioneering to the state-of-the-art works. It also serves as a concise overview of the current understanding of THz nonlinear optics of graphene, and as a compact reference for researchers entering the field, as well as for the technology developers.
Keywords: Graphene; High Harmonics Generation; Terahertz; ultrafast
Advanced Optical Materials 8(2020)3, 1900771
Online First (2019) DOI: 10.1002/adom.201900771
Phase-resolved Higgs response in superconducting cuprates
Chu, H.; Kim, M.-J.; Katsumi, K.; Kovalev, S.; Dawson, R. D.; Schwarz, L.; Yoshikawa, N.; Kim, G.; Putzky, D.; Li, Z. Z.; Raffy, H.; Germanskiy, S.; Deinert, J.-C.; Awari, N.; Ilyakov, I.; Green, B. W.; Chen, M.; Bawatna, M.; Christiani, G.; Logvenov, G.; Gallais, Y.; Boris, A. V.; Keimer, B.; Schnyder, A.; Manske, D.; Gensch, M.; Wang, Z.; Shimano, R.; Kaiser, S.
In high energy physics, the Higgs field couples to gauge bosons and fermions and gives mass to their elementary excitations. Experimentally, such couplings can be verified from the decay product of the Higgs boson, the scalar (amplitude) excitation of the Higgs field. In superconductors, Cooper pairs bear a certain analogy to the Higgs field. Coulomb interactions between the Cooper pairs give mass to the electromagnetic field, which leads to the Meissner effect. Additional coupling with other types of interactions or collective modes is foreseeable, and even highly probable for high-Tc superconductors, where multiple degrees of freedom are intertwined4. The superconducting Higgs mode may reveal such couplings spectroscopically and uncover interactions directly relevant to Cooper pairing. To this end, we investigate the Higgs mode of several cuprate thin films using phase-resolved terahertz third harmonic generation (THG) to. In addition to the heavily damped Higgs mode itself, we observe a universal jump in the phase of the driven Higgs oscillation as well as a non-vanishing THG above Tc. These findings indicate coupling of the Higgs mode to other collective modes and a nonzero pairing amplitude above Tc. Our study demonstrates a new approach for investigating unconventional superconductivity. We foresee a fruitful future for phase-resolved spectroscopy in various superconducting systems.
Keywords: Superconductors; terahertz; Higgs; Nonlinear dynamics; ultrafast
- Phase-resolved Higgs response in superconducting cuprates (Id 30902) HZDR-primary research data are used by this (Id 29647) publication
Nature Communications 11(2020)1, 1793
Non-perturbative high-harmonic generation in the three-dimensional Dirac semimetal Cd₃As₂
Harmonic generation is a general characteristic of driven nonlinear systems, and serves as an efficient tool for investigating the fundamental principles that govern the ultrafast nonlinear dynamics. In atomic gases, high-harmonic radiation is produced via a three-step process of ionization, acceleration, and recollision by strong-field infrared laser. This mechanism has been intensively investigated in the extreme ultraviolet and soft X-ray regions, forming the basis of attosecond research, e.g. real-time observation of electron dynamics and sub-atomic tomography of molecular orbitals. In solid-state materials, which are characterized by crystalline symmetry and strong interactions, yielding of harmonics has just recently been reported. The observed high-harmonic generation was interpreted with fundamentally different mechanisms, such as interband tunneling combined with dynamical Bloch oscillations, intraband thermodynamics and nonlinear dynamics, and many-body electronic interactions. Here, in a distinctly different context of three-dimensional Dirac semimetal, we report on experimental observation of high-harmonic generation up to the seventh order driven by a strong-field terahertz pulse. The observed non-perturbative high-harmonic generation is interpreted as a generic feature of terahertz-field driven nonlinear intraband kinetics of Dirac fermions. We anticipate that our results will trigger great interest in detection, manipulation, and coherent control of the nonlinear response in the vast family of three-dimensional Dirac and Weyl materials.
Keywords: Dirac semimetals; High Harmonic Generation; Tehahertz; Nonlinear dynamics
- Research data: Non-perturbative high-harmonic generation … (Id 32144) HZDR-primary research data are used by this (Id 29646) publication
Nature Communications 11(2020)1, 2451
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
- Preprint PDF 7,2 MB Secondary publication
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
Online First (2019) DOI: 10.1002/cite.201900117
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 59(2020)9, 4093-4107
Online First (2019) DOI: 10.1021/acs.iecr.9b04247
- Fulltext from pubs.acs.org
- Secondary publication expected
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
A Kinetic Study On Grinding And Flotation Of Untreated And Microwave-Treated Copper Sulfide Ore
Gholami, H.; Rezai, B.; Hassanzadeh, H.; Mehdilo, A.; Yarahmadi, M. R.; Rudolph, M.
The present work aims to study the impact of microwave irradiation on grinding and flotation kinetics of a porphyry copper ore. For this purpose, the kinetic trails were carried out on the samples (d80=1.5mm) pretreated in the absence and presence of microwave irradiation varying the exposure time from 15 to 150s. Semi-quantitative X-ray diffraction technique (SQ-XRD), energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) techniques were used for elemental, surface and mineralogical analyses. Breakage and selection functions were determined using the top-size-fraction method. Commonly used first-order flotation kinetic model and Berube model were utilized for estimating the related parameters. The results disclosed that the ore’s breakage rate constant monotonically increased by increasing the exposure time particularly for the coarsest fraction size (400µm) owing to the creation of thermal stress fractures alongside grain boundaries. Chalcopyrite’s flotation rate constant and infinitive recovery of pyrite improved while samples irradiated to the shorter exposure time (<60s) in comparison with the untreated ones. We finally concluded that the MW-treated copper ore was ground faster and floated similarly compared to the untreated one. Further fundamental studies are required for profound understanding of these phenomena from analytical points of view.
Keywords: Kinetic; microwave; grinding; flotation; copper sulfide ore
Contribution to proceedings
IMPC - EURASIA 2019, 30.10.-02.11.2019, Antalya, Turkey
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
Online First (2019) DOI: 10.1002/adem.201900407
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
Online First (2019) DOI: 10.1002/pssa.201900306
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
- Final Draft PDF 651 kB Secondary publication
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
Online First (2019) DOI: 10.1007/s00332-019-09557-0
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
Online First (2019) DOI: 10.1021/acs.iecr.9b04915
- Final Draft PDF 1,3 MB Secondary publication
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
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
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.
Nanoscale 12(2020)35, 18039-18048
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
Online First (2019) DOI: 10.1016/j.physletb.2019.05.044
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
- Final Draft PDF 1,7 MB Secondary publication
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
Numerical methods for plasma accelerators
Computer simulations have had a profound impact on the design and understanding of past and present plasma-based particle acceleration experiments, and will be a key component for turning plasma-based accelerators from a promising technology into a mainstream scientific tool.
Keywords: LPA; computer simulation; PIC
Contribution to external collection
in: 2020 Roadmap on Plasma Accelerators, Bristol: Institute of Physics: New Journal of Physics, 2021, 031101
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
Online First (2019) DOI: 10.1021/acsami.9b07832
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; Felsenkeller; sputter source
European Physical Journal A 55(2019)10, 174
Contribution to WWW
- Final Draft PDF 5,1 MB Secondary publication
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.
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 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
Online First (2019) DOI: 10.1002/pssa.201900584
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
Radioligand development for PET imaging of the vesicular acetylcholine transporter (VAChT) in brain
Nowadays, it is general consensus that the cholinergic transmission system in brain is heavily involved in the development, progress and therapy of certain neurodegenerative diseases. In particular cholinergic presynaptic components such as the acetylcholinesterase (AChE) or the vesicular acetylcholine transporter (VAChT) are considered to be affected by early changes in neuropathological processes as observed e.g. in Alzheimer's disease (AD). The VAChT is a transmembrane protein located at synaptic vesicles and responsible for the transport and storage of the neurotransmitter acetylcholine (ACh) into the vesicles. Therefore, the VAChT is regarded as a potential target for neuroimaging of cholinergic alterations with positron emission tomography. To date, the development of PET radioligands for this transporter is based on a single known lead compound named vesamicol. A challenge was arising due to the finding that vesamicol also binds to the sigma receptors which are partly co-localized with the VAChT in several cholinergic brain regions. In the last three decades a multitude of structural diverse vesamicol analogs have been designed resulting in a considerable number of 11C- and 18F-labeled PET as well as a few 123/125I-labeled SPECT tracers which were mainly preclinically evaluated. However, only very few of them had the potential for translation to human studies. Therefore, a routinely used VAChT PET imaging could not be established in the clinics so far. However, just recently published studies using the potent candidate [18F]FEOBV in patients with neuropathologies are very promising and probably a breakthrough within this field.
This review addresses the efforts in ligand design and PET radioligand developments for the VAChT with a special view on the difficulties arising from the lead compound vesamicol and its low selectivity.
Rudi Dierckx, Andreas Otte, Erik de Vries, Adriaan Lammertsma and Aren van Waarde: PET and SPECT of Neurobiological Systems, Berlin-Heidelberg: Springer, 2021, 978-3-030-53176-8
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
Online First (2019) DOI: 10.1515/zkri-2019-0026
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
Online First (2019) DOI: 10.1039/C9CP03953H
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
Online First (2019) DOI: 10.1080/2162402X.2019.1659095
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
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