Publication database - Helmholtz-Zentrum Dresden-Rossendorf

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26408 Publications
Carrier-induced ferromagnetism in the insulating Mn-doped III-V semiconductor InP
Bouzerar, R.; May, D.; Löw, U.; Machon, D.; Melinon, P.; Zhou, S.; Bouzerar, G.
Abstract: Although InP and GaAs have very similar band structure their magnetic properties appear to drastically differ. Critical temperatures in (In,Mn)P are much smaller than those of (Ga,Mn)As and scale linearly with Mn concentration. This is in contrast to the square-root behavior found in (Ga,Mn)As. Moreover the magnetization curve exhibits an unconventional shape in (In,Mn)P contrasting with the conventional one of well-annealed (Ga,Mn)As. By combining several theoretical approaches, the nature of ferromagnetism in Mn-doped InP is investigated. It appears that the magnetic properties are essentially controlled by the position of the Mn acceptor level. Our calculations are in excellent agreement with recent measurements for both critical temperatures and magnetizations. The results are only consistent with a Fermi level lying in an impurity band, ruling out the possibility to understand the physical properties of Mn-doped InP within the valence band scenario. The quantitative success found here reveals a predictive tool of choice that should open interesting pathways to address magnetic properties in other compounds. Registration No. 24230 - Permalink

Loch an Loch und hält doch – Die Sprödbruchneigung genieteter Konstruktionen aus alten Baustählen
Sieber, L.; Stroetmann, R.; Viehrig, H.-W.; Houska, M.
Abstract: Zahlreiche erhaltene Stahlbauwerke des 19. und frühen 20. Jh. werden heute noch genutzt und haben somit ihre geplante Nutzungsdauer von 60 bis 80 Jahren deutlich überschritten. Aus wirtschaftlichen und oft auch denkmalpflegerischen Gründen besteht ein großes Inte-resse, die Nutzung dieser Bauwerke auch weiterhin sicherzustellen. Bedingt durch Schadensfälle infolge Sprödbruchversagen bei Altstahlkonstruktionen (z.B. an Stahlgeschossbauten und Stahlgittermasten) gewinnt neben der Tragsicherheit die Frage der Sprödbruchgefährdung alter Stahlkonstruktionen zunehmend an Bedeutung. Alte Stahlkonstruktionen bestehen überwiegend aus genieteten oder geschraubten Flachstählen, I-, L- und U-Profilen mit wiederkehrenden Konstruktionsprinzipien. Besonders sprödbruchgefährdet sind Bereiche in höher zugbeanspruchten Bauteilen aus stickstoffreichen Stählen, die durch gestanzte Löcher geschwächt sind.
Zur Beurteilung der Sprödbruchsicherheit stehen im Stahlbau verschiedene, unterschiedlich aufwendige und aussagefähige Methoden zur Verfügung, die in mehr oder weniger engem Zusammenhang mit dem eigentlichen Phänomen des Sprödbruchs stehen.

Keywords: basic oxygen steel, steel structure, rivet connection, fracture mechanics, Master Curve, integrity assessment
  • Lecture (Conference)
    7. Fachtagung Bemessung und Konstruktion, 07.03.2017, Halle/Saale, Deutschland
Registration No. 24226 - Permalink

Physical properties of the candidate quantum spin-ice system Pr2Hf2O7
Anand, V. K.; Opherden, L.; Xu, J.; Adroja, D. T.; Islam, A. T. M. N.; Herrmannsdörfer, T.; Hornung, J.; Schönemann, R.; Uhlarz, M.; Walker, H. C.; Casati, N; Lake, B
Abstract: Physical properties of a pyrohafnate compound Pr2Hf2O7 have been investigated by ac magnetic susceptibility χac(T ), dc magnetic susceptibility χ(T ), isothermal magnetization M(H), and heat-capacity Cp(T )measurements on polycrystalline as well as single-crystal samples combined with high-resolution synchrotron x-ray diffraction (XRD) for structural characterization and inelastic neutron scattering (INS) to determine the crystal-field energy-level scheme and wave functions. Synchrotron XRD data confirm the ordered cubic pyrochlore (Fd¯3m) structure without any noticeable site mixing or oxygen deficiency. No clear evidence of long-range magnetic ordering is observed down to 90 mK, however the χac(T ) evinces slow spin dynamics revealed by a frequency dependent broad peak associated with spin freezing. The INS data reveal the expected five well-defined magnetic excitations due to crystal-field splitting of the J = 4 ground-state multiplet of the Pr3+. The crystal-field parameters and ground-state wave function of Pr3+ have been determined. The Ising anisotropic nature of the magnetic ground state is inferred from the INS as well as χ(T) and M(H) data. Together these properties make Pr2Hf2O7 a candidate compound for quantum spin-ice behavior. Registration No. 24224 - Permalink

In-Situ Analysis and Experiment Regulation at HZDR
Frust, T.; Kelling, J.; Juckeland, G.
Abstract: A number of experiments at HZDR require in-situ evaluation of the experiment data of the results for automated responses by the experiment control systems. This talk presents two such examples and their current implementations.
  • Invited lecture (Conferences)
    PADC Annual Workshop 2016, 17.-18.10.2016, Jülich, Deutschland
Registration No. 24222 - Permalink

PIConGPU: First Experiences on Minski
Widera, R.; Hübl, A.; Juckeland, G.
Abstract: PICOnGPU is a highly scalable GPU accelerated particle-in-cell code. This talk presents the first experiences on running this code on IBM Minski (Power8+ with NVIDIA P100 GPUs).
  • Invited lecture (Conferences)
    PADC Annual Workshop 2016, 17.-18.10.2016, Jülich, Deutschland
Registration No. 24221 - Permalink

DFT study on the contribution of phonon and electron excitations to the free energy of embedded defect clusters
Posselt, M.; Devaraj, M.
Abstract: Modeling of nanostructure evolution in solids requires the knowledge of comprehensive data on the properties of point defects and defect clusters. Since most processes occur at elevated temperatures not only the energetics of the defects in the ground state but also their temperature-dependent free energy must be known. The determination of the contribution of phonon and electron excitations to the free binding energy of small embedded defect clusters is illustrated in the case of bcc-Fe. The fundamentals of the first-principles calculation method have been recently described [1]. First of all, the ground state properties of the clusters are determined under zero pressure (ZP) conditions. Second, the phonon contribution to the free energy is calculated within the harmonic approximation using the equilibrium atomic positions determined in the ground state. The application of a quasi-harmonic correction to the ZP-based data does not modify the results significantly. Therefore the obtained data are valid under zero-pressure conditions at higher temperatures than in the framework of the purely harmonic approach. These conditions are usually realized in experiments. Third, the contribution of electron excitations to the defect free energy is calculated. The electron excitations can lead to an additional deviation of the total free energy from the ground state value or can compensate the deviation caused by the phonon contribution. Depending on the examples considered the free binding energy of a defect cluster can differ significantly from the ground state value.
[1] D. Murali, M. Posselt, M. Schiwarth, Phys. Rev. B 92, 064103 (2015).

Keywords: DFT, defect clusters, free energy
  • Lecture (Conference)
    8th Int. Conf. on Multiscale Materials Modeling (MMM 2016), 09.-14.10.2016, Dijon, France
Registration No. 24218 - Permalink

Formation and properties of high-dose nitrogen implanted epitaxially grown Gd2O3 on silicon
Joseph, A.; Tetzlaff, D.; Schmidt, J.; Böttger, R.; Wietler, T. F.; Osten, H. J.
Abstract: The effects of nitrogen incorporation by high-dose ion implantation in epitaxial Gd2O3 films on Si(111) followed by annealing have been investigated. Nitrogen incorporation is believed to occur by filling the oxygen vacancies or by removing hydroxyl group ions in gadolinium oxide (Gd2O3). The nitrogen content in the oxide layer has been altered by changing the implantation dose. The impact of nitrogen incorporation on Gd-O bonding is studied using X-ray photoelectron spectroscopy. A shift in the Gd and O peak positions indicate the presence of nitrogen in the layer. Raman spectroscopy reveals heavy structural changes. The newly appearing structure is crystalline, but not in agreement with either the known bixbyite (Gd2O3) or rocksalt (GdN) structure. Electron microscopic investigations reveal the formation of cracks and small areas with lower densities or even voids. That structure exhibits similarities with transmission electron microscopy images of gadolinium nitride (GdN) layers. The electronic band gap of Gd2O3 estimated from O1s plasmon energy loss measurements was found to decrease significantly by the incorporation of nitrogen. Reduction in the valence band and conduction band offset is obtained as a function of implantation dose.
Keywords: Band gap, Crystal structure, Gadolinium, X-ray photoelectron spectroscopy, Transmission electron microscopy


Registration No. 24208 - Permalink

Hydrophilic Nd3+-Sensitized Upconverting Core-Shell Nanoparticles for Biomedical Applications
Hesse, J.; Sgarzi, M.; Stephan, H.
Abstract: Currently, there is a widespread interest to use neodymium containing upconverting nanophosphors (UCNPs) for bioimaging applications. The fascination of these nanoparticles derives from their capacity for excitation in the biologically transparent window (650-950 nm), exceptional ability to convert near infrared radiation into visible light (upconversion), which prevents autofluorescence and over-heating effect of biological tissues, capability for deep tissue, and high contrast imaging [1]. Despite the fast progress in lanthanide-doped upconversion nanoparticles, the preparation of ultrasmall, monodisperse and hydrophilic UCNPs that display intense luminescence is still a challenging issue. Only a few examples of ultrasmall and hydrophilic UCNPs have been reported [2-3]. Established strategies for synthesizing UCNPs yield mainly hydrophobic particles[1]. Here, we report the, synthesis and surface modification of sub-10 nm UCNPs with an excitation wavelength of 795 nm, which are composed of a host lattice of crystalline hexagonal phased NaYF4 doped with Nd3+ and Yb3+ as sensitizers, and Er3+, Ho3+ or Tm3+ as emitter ions. Surface passivation by coating with a shell of active and also inert host material is used to enhance the overall upconversion efficiency. We also report the conversion of these into hydrophilic, colloidally-stable, and biocompatible by using mainly ligand exchange strategies and the influence of the coating on the UCNPs’ photophysical properties will also be discussed. Finally, this study will also allow establishing information about biodistribution, pharmacokinetics and formation of protein corona for ultrasmall UCNPs.
Keywords: Upconversion, lanthanide, Sub 10nm particles, surface functionalization, Bio imaging
  • Poster
    6th EuCheMS Chemistry Congress, 11.-15.09.2016, Seville, Spain
Registration No. 24204 - Permalink

Soft matter nanoparticles based on polyglycerols as efficient multimodal imaging agents for EGF-receptor tumor targeting
Pant, K.; Zarschler, K.; Neuber, C.; Pufe, J.; Pietzsch, J.; Stephan, H.; Haag, R.
Abstract: Nano-constructs based on macromolecules have become increasingly interesting in the recent years owing to their unique properties like high aqueous stability, biocompatibility etc. in the field of drug delivery, nanomedicine as well as for multi modal imaging. Having multiple modalities on a single carrier molecule obviate the need to administer several compounds with different pharmacokinetics. In this regard, dendritic polyglycerols (dPG) are globular macromolecules with a nano-size (5-20 nm), narrow size distribution (PDI >1.26), high degree of branching and high end group functionalities which makes them amenable to a wide range of chemical modifications.[1] This great versatility allows dendritic polyglycerols to be fine-tuned with respect to various physico-chemical parameters such as particle size, water solubility, surface charge, chemical functionalities, etc, that are relevant for the successful preparation of theranostic systems. Previous studies done on 3H and 64Cu radiolabeled anionic and neutral dPG shows their great potential as platforms for various applications.[2] The presented work here deals with the development of a dendritic polyglycerol derivative as a dual-modal agent for epidermal growth factor receptor (EGFR) specific tumor targeting. In this respect, in a one pot reaction, simultaneously maleimido- bearing fluorescent labels (dye) for in vitro or vivo imaging (cy3/cy7) and macrocyclic chelators for 64Cu (PET tracer) were attached to thiol anchoring groups of the polymeric scaffold. For an EGFR specific targeting, a small camelid single-domain antibody (sdAb) representing a potential recognition agent for EGFR was attached via a PEG linker. For a controlled purification, an affinity chromatography procedure was used which selectively separates the antibody conjugated multimodal conjugates. This leads to a higher affinity and selectivity of the dual modal conjugates on the tumor cells. 64Cu radiolabeling was done under ambient temperature and physiological pH. Binding and uptake studies were performed using A431 and FaDu cell lines using 64Cu-labeled bioconjugates. Confocal laser scanning microscopy was used to study the receptor-mediated cellular uptake as well as scavenger receptor studies which show a selective affinity of dPG conjugates to the tumor cells. Antibody-dPG multimodal conjugates were injected intravenously to mouse xenografted models for in vivo studies using PET imaging as well as optical imaging which reveal a good tumor targeting of the conjugates. These results reveal an excellent potential of dendritic polyglycerols as multimodal platforms for various biomedical applications.
Keywords: Radiolabeled, nanoparticles, diagnostics, receptor-mediated
  • Lecture (Conference)
    6th European Chemical Society Congress, Seville, Spain, 11.-15.09.2016, English, Spain
Registration No. 24202 - Permalink

Nuclear and Optical Dual-labelled Imaging Agents
Stephan, H.
Abstract: For the past decade, nuclear and optical dual-labelled imaging agents have attracted enormous attention 1. Applied to cancer imaging, tumours can be tracked down by nuclear techniques such as SPECT and PET, and subsequently resected using image-guided surgery with the appropriate fluorophores. Moreover, the high spatial resolution of fluorescence imaging permits the elucidation of cell-biological events and thereby gaining a deeper insight into in vitro and in vivo processes. The development of dual imaging probes can be achieved using sophisticated low-molecular compounds that combine moieties for the desired imaging modalities, e.g. dyes for fluorescence optical imaging, and appropriate bifunctional chelator agents (BFCAs) for radiometals enabling SPECT or PET. We have developed BFCAs based on bis(2-pyridylmethyl)-1,4,7-triazacyclononane (DMPTACN) and 3,7-diazabicyclo[3.3.1]nonane (bispidine) that rapidly form stable 64CuII complexes under mild conditions. These BFCAs are well-suited for in vivo application in cancer imaging 2, 3. Since they are also relatively easy to functionalize with multiple modalities, they are ideal chelators for the design of targeted dual-labelled imaging agents (PET, fluorescence imaging) 4, 5.
Here, important features of 64CuII-labelled DMPTACN and bispidine complexes, e.g. stabilities, coordination geometry, ligand exchange kinetics, serum stability, partition coefficients (n-octanol/water), photophysical properties of dye-labelled compounds and biodistribution data will be reported.

1 A. Azhdarinia et al., Mol. Imag. Biol. 2012, 14, 261. 2 S. Juran et al., Bioconjugate Chem. 2009, 20, 347.
3 R. Bergmann et al., Eur. J. Med Chem. 2013, 70, 434. 4 K. Viehweger et al., Bioconjugate Chem. 2014, 25, 1011. 5 H. Stephan et al., Chem. Eur. J. 2014, 20, 17011.
  • Lecture (Conference)
    6th EuCheMS Chemistry Congress, 11.-15.09.2016, Seville, Spain
Registration No. 24198 - Permalink

Implementing High-Order FIR Filters in FPGAs
Födisch, P.; Bryksa, A.; Lange, B.; Enghardt, W.; Kaever, P.
Abstract: Contemporary field-programmable gate arrays (FPGAs) are predestined for the application of finite impulse response (FIR) filters. Their embedded digital signal processing (DSP) blocks for multiply-accumulate operations enable efficient fixed-point computations, in cases where the filter structure is accurately mapped to the dedicated hardware architecture. This brief presents a generic systolic structure for high-order FIR filters, efficiently exploiting the hardware resources of an FPGA in terms of routability and timing. Although this seems to be an easily implementable task, the synthesizing tools require an adaptation of the straightforward digital filter implementation for an optimal mapping. Using the example of a symmetric FIR filter with 90 taps, we demonstrate the performance of the proposed structure with FPGAs from Xilinx and Altera. The implementation utilizes less than 1% of slice logic and runs at clock frequencies up to 526 MHz. Moreover, an enhancement of the structure ultimately provides an extended dynamic range for the quantized coefficients without the costs of additional slice logic.
Keywords: digital filters, field-programmable gate arrays, FIR filters, fixed-point arithmetic


Registration No. 24197 - Permalink

Digital high-pass filter deconvolution by means of an infinite impulse response filter
Födisch, P.; Wohsmann, J.; Lange, B.; Schönherr, J.; Enghardt, W.; Kaever, P.
Abstract: In the application of semiconductor detectors, the charge-sensitive amplifier is widely used in front-end electronics. The output signal is shaped by a typical exponential decay. Depending on the feedback network, this type of front-end electronics suffers from the ballistic deficit problem, or an increased rate of pulse pile-ups. Moreover, spectroscopy applications require a correction of the pulse-height, while a shortened pulse-width is desirable for high-throughput applications. For both objectives, digital deconvolution of the exponential decay is convenient. With a general method and the signals of our custom charge-sensitive amplifier for cadmium zinc telluride detectors, we show how the transfer function of an amplifier is adapted to an infinite impulse response (IIR) filter. This paper investigates different design methods for an IIR filter in the discrete-time domain and verifies the obtained filter coefficients with respect to the equivalent continuous-time frequency response. Finally, the exponential decay is shaped to a step-like output signal that is exploited by a forward-looking pulse processing.
Keywords: Cadmium zinc telluride (CdZnTe,CZT) detector; Charge-sensitive amplifier; Digital pulse processing; Digital filter; Deconvolution; Field-programmable gate array (FPGA)


Registration No. 24196 - Permalink

Charge-sensitive front-end electronics with operational amplifiers for CdZnTe detectors
Födisch, P.; Berthel, M.; Lange, B.; Kirschke, T.; Enghardt, W.; Kaever, P.
Abstract: Cadmium zinc telluride (CdZnTe, CZT) radiation detectors are suitable for a variety of applications, due to their high spatial resolution and spectroscopic energy performance at room temperature. However, state-of-the-art detector systems require high-performance readout electronics. Though an application-specific integrated circuit (ASIC) is an adequate solution for the readout, requirements of high dynamic range and high throughput are not available in any commercial circuit. Consequently, the present study develops the analog front-end electronics with operational amplifiers for an 8x8 pixelated CZT detector. For this purpose, we modeled an electrical equivalent circuit of the CZT detector with the associated charge-sensitive amplifier (CSA). Based on a detailed network analysis, the circuit design is completed by numerical values for various features such as ballistic deficit, charge-to-voltage gain, rise time, and noise level. A verification of the performance is carried out by synthetic detector signals and a pixel detector. The experimental results with the pixel detector assembly and a 22Na radioactive source emphasize the depth dependence of the measured energy. After pulse processing with depth correction based on the fit of the weighting potential, the energy resolution is 2.2% (FWHM) for the 511 keV photopeak.
Keywords: Analogue electronic circuits; Front-end electronics for detector readout; Gamma detectors (scintillators, CZT, HPG, HgI etc)


Registration No. 24194 - Permalink

HASEonGPU—An adaptive, load-balanced MPI/GPU-code for calculating the amplified spontaneous emission in high power laser media
Eckert, C. H. J.ORC; Zenker, E.ORC; Bussmann, M.ORC; Albach, D.
Abstract: We present an adaptive Monte Carlo algorithm for computing the amplified spontaneous emission (ASE) flux in laser gain media pumped by pulsed lasers. With the design of high power lasers in mind, which require large size gain media, we have developed the open source code HASEonGPU that is capable of utilizing multiple graphic processing units (GPUs). With HASEonGPU, time to solution is reduced to minutes on a medium size GPU cluster of 64 NVIDIA Tesla K20m GPUs and excellent speedup is achieved when scaling to multiple GPUs. Comparison of simulation results to measurements of ASE in Yb3+ : YAG ceramics show perfect agreement.
Keywords: Amplified spontaneous emission CUDA GPU cluster Massively parallel Monte Carlo integration High power laser


Registration No. 24191 - Permalink

Extending the truncated Dyson-Schwinger equation to finite temperatures
Dorkin, S. M.; Viebach, M.; Kaptari, L. P.; Kämpfer, B.
Abstract: In view of the properties of mesons in hot strongly interacting matter the properties of the solutions of the truncated Dyson-Schwinger equation for the quark propagator at finite temperatures within the rainbow-ladder approximation are analysed in some detail. In Euclidean space within the Matsubara imaginary time formalism the quark propagator is not longer a O(4) symmetric function and possesses a discrete spectra of the fourth component of the momentum. This makes the treatment of the Dyson-Schwinger and Bethe-Salpeter equations conceptually different from the vacuum and technically much more involved. The question whether the interaction kernel known from vacuum calculations can be applied at finite temperatures remains still open. We find that, at low temperatures, the model interaction with vacuum parameters provides a reasonable description of the quark propagator, while at temperatures higher than a certain critical value Tc the interaction requires stringent modifications. The general properties of the quark propagator at finite temperatures can be inferred from lattice QCD calculations. We argue that, to achieve a reasonable agreement of the model calculations with that from lattice QCD, the kernel is to be modified in such a way as to screen the infra-red part of the interaction at temperatures larger than Tc. For this, we analyse the solutions of the truncated Dyson-Schwinger equation with existing interaction kernels in a large temperature range with particular attention on high temperatures in order to find hints to an adequate temperature dependence of the interaction kernel to be further implemented in to the Bethe-Salpeter equation for mesons. This will allow to investigate the possible in medium modifications of the meson properties as well as the conditions of quark deconfinement in hot matter.


Registration No. 24190 - Permalink

Analysis of C/E results of fission rate ratio measurements in several fast lead VENUS-F cores
Kochetkov, A.; Krása, A.; Baeten, P.; Vittiglio, G.; Wagemans, J.; Bécares, V.; Bianchini, G.; Fabrizio, V.; Carta, M.; Firpo, G.; Fridman, E.ORC; Sarotto, M.
Abstract: During the GUINEVERE FP6 European project (2006-2011), the zero-power VENUS water-moderated reactor was modified into VENUS-F, a mockup of lead cooled fast spectrum system with solid components that can be operated in both critical and subcritical mode.
The Fast Reactor Experiments for hybrid Applications (FREYA) FP7 project was launched in 2011 to support the designs of the MYRRHA Accelerator Driven System (ADS) and the ALFRED Lead Fast Reactor (LFR). Three VENUS-F critical core configurations, simulating the complex MYRRHA core design and one configuration devoted to the LFR ALFRED core conditions were investigated in 2015. The MYRRHA related cores simulated step by step design peculiarities like the BeO reflector and in pile sections. For all of these cores the fuel assemblies were of a simple design consisting of 30 % enriched metallic uranium, lead rodlets to simulate the coolant and Al2O3 rodlets to simulate the oxide fuel.
Fission rate ratios of minor actinides such as Np-237, Am-241 as well as Pu-239, Pu-240, Pu-242 and U-238 to U-235 were measured in these VENUS-F critical assemblies with small fission chambers in specially designed locations, to determine the spectral indices in the different neutron spectrum conditions.
The measurements have been analyzed using advanced computational tools including deterministic and stochastic codes and different nuclear data sets like JEFF-3.1, JEFF-3.2, ENDF/B7.1, ENDF/B6.8, JENDL-4.0 and TENDL-2014. The analysis of the C/E discrepancies will help to improve the nuclear data in the specific energy region of fast neutron reactor spectra.
  • Contribution to proceedings
    ND2016 - International Conference on Nuclear Data for Science and Technology, 11.-16.09.2016, Bruges, Belgium
Registration No. 24183 - Permalink

Contactless inductive flow tomography: recent developments in its application to continuous casting with electromagnetic brakes
Ratajczak, M.; Wondrak, T.; Martin, R.; Stefani, F.; Jacobs, R.
Abstract: Measuring the velocity in hot and/or aggressive melts is a challenging task. Many applications, like continuous casting of steel, would benefit even from a rough knowledge of the global flow structure of the melt, because the flow structure has a direct impact on the quality of the final product. In continuous casting, electromagnetic brakes (EMBrs) are widely used to influence the flow in the mold, as they are expected to damp undesired flow oscillations that are associated with multiple kinds of defects. Yet, without direct feedback from the mold flow, a tailored process control with EMBrs is hardly possible.
The contactless inductive flow tomography (CIFT) could help to circumvent these problems. The method relies on the induction of a secondary magnetic field if the moving fluid is exposed to a primary magnetic field. From the measurement of the induced magnetic outside the melt, the global flow structure of the melt can be inferred by solving the associated linear inverse problem. A successful application of CIFT to EMBr-influenced mold flows could enable steel producers to cast high quality steel with less rejects. In this paper we will outline the efforts to adapt CIFT to a laboratory liquid-metal mold under the influence of an EMBr.

Keywords: Contactless inductive flow tomography, continuous casting, magnetic field measurement, gradiometric sensor, electromagnetic brake
  • Contribution to proceedings
    WCIPT8 - 8th World Congress on Industrial Process Tomography, 26.-29.09.2016, Foz do Iguacu, Brasilia
  • Lecture (Conference)
    WCIPT8 - 8th World Congress on Industrial Process Tomography,, 26.-29.09.2016, Foz do Iguacu, Brasilia
Registration No. 24182 - Permalink

Performance study of a Mosaic high rate MRPC
Wang, F.; Han, D.; Xie, B.; Wang, Y.; Lyu, P.; Guo, B.; Laktineh, I.; Naumann, L.; Kotte, R.; Dreyer, J.; Garcia, A. L.; Stach, D.; Fan, X.; Akindinov, A.
Abstract: A prototype of a large mosaic MRPC with low resistive glass for the future upgrade of CMS muon system is presented. This prototype is designed by jointing two pieces of glass together and separating them by fishing lines to prevent sparks. A simulation of the weighting field based on Maxwell shows that the efficiency is higher than 90% in the joint area. In a beam test at HZDR, the prototype achieved ~ 92% detection efficiency and about 60 ps time resolution in the joint area, and ~95% efficiency and 60 ps time resolution in the active area. A rate capability study shows this prototype can withstand 40 kHz/cm2 at least. Registration No. 24181 - Permalink

Use of ion irradiation to tune magnetic anisotropy
Osten, J.; Greene, P.; Lenz, K.; Fassbender, J.; Jenkins, C.; Arenholz, E.; Endo, T.; Iwata, N.; Liu, K.
Abstract: Current challenges in magnetic storage media will be shortly discussed. In detail perpendicular magnetic recording media is addressed. Perpendicular magnetic recording media has the advantage of good data stability but the disadvantage of a high writing field. The writing field is also determined by the anisotropy of the material. To control the anisotropy ion irradiation of Co/Pd multilayers has been investigated. By adjusting the kinetic energy and fluence, the depth and lateral density of the local structural modification are controlled. First-order reversal curve analysis through X-ray magnetic circular dichroism and conventional magnetometry studies shows that the local structural damage weakens the perpendicular anisotropy near the surface, leading to a magnetization tilting towards the in-plane direction. The ion irradiation method is complementary to and may be used in conjunction with, other synthesis approaches to maximize the anisotropy gradient.
Keywords: anisotropy gradient PMR ion implantation
  • Invited lecture (Conferences)
    Ion Beams in Materials Engineering and Characterization (IBMEC), 28.09.-01.10.2016, New Dehli, Indien
Registration No. 24178 - Permalink

Shapeable magnetic sensorics
Makarov, D.
Abstract: The flourishing and eagerness of portable consumer electronics necessitates functional elements to be lightweight, flexible, and even wearable [1,2]. Next generation flexible appliances aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems. Such devices fulfill the needs of soft robotics [3], functional medical implants [4] as well as epidermal [5], imperceptible [6] and transient [7] electronics. Key building blocks of navigation and position tracking devices are the magnetic field sensors.
We developed the technology platform allowing us to fabricate high-performance shapeable magnetoelectronics [8] – namely, flexible [9-11], printable [12-14], stretchable [15-17] and even imperceptible [18] magnetosensitive elements. The technology relies on smart combination of thin inorganic functional elements prepared directly on flexible or elastomeric supports. The unique mechanical properties open up new application potentials for smart skins, allowing to equip the recipient with a “sixth sense” providing new experiences in sensing and manipulating the objects of the surrounding us physical as well as digital world [11,18].
Combining large-area printable and flexible electronics paves the way towards commercializing the active intelligent packaging, post cards, books or promotional materials that communicate with the environment and provide the respond to the customer. Realization of this vision requires fabrication of printable electronic components that are flexible and can change their properties in the field of a permanent magnet [13]. For this concept, we fabricated high performance magnetic field sensors relying on the giant magnetoresistive (GMR) effect, which are printed at pre-defined locations on flexible circuitry and remain fully operational over a temperature range from -10°C up to +95°C, well beyond the requirements for consumer electronics [14]. Our work potentially enables commercial use of high performance magneto-sensitive elements in conventional printable electronic industry, which, although highly demanded, had not yet been possible.
In this talk, I will review the recent advances in the field of shapeable magnetic sensorics and emergent applications of this novel technology.

Keywords: Shapeable magnetoelectronics, smart Skins, magnetic field sensors
  • Invited lecture (Conferences)
    Brazilian-German Frontiers of Science & Technology Symposium, 20.-23.09.2016, Campinas, Brazil
Registration No. 24174 - Permalink

Modification of semiconductor or metal nanoparticle lattices in amorphous alumina by MeV heavy ions
Bogdanović Radović, I.; Buljan, M.; Karlušić, M.; Jerčinović, M.; Dražič, G.; Bernstorff, S.; Boettger, R.
Abstract: In the present work we investigate effects ofMeVheavy ions (from 0.4 MeVXe to 15 MeVSi) on regularly ordered nanoparticle (NP) lattices embedded in amorphous alumina matrix. These nanostructures were produced by self-assembling growth using magnetron-sputtering deposition. From grazing incidence small-angle x-ray scattering measurements we have found that the usedMeV heavy ions do not change the NPsizes, shapes or distances among them. However, ions cause a tilt of the entire NP lattice in the direction parallel to the surface. The tilt angle depends on the incident ion energy, type and the applied fluence and a nearly linear increase of the tilt angle with the ion fluence and irradiation angle was found. This way,MeV heavy ion irradiation can be used to design custom-made NPlattices. In addition, grazing incidence small-angle x-ray scattering can be effectively used as a method for the determination of material redistribution/shift caused by the ion hammering effect. For the first time, the deformation yield in amorphous alumina was determined for irradiation performed at the room temperature.
Keywords: nanoparticles, MeV heavy ions, ion hammering, amorphous alumina, GISAXS


Registration No. 24166 - Permalink

Magnetization dynamics of a single Fe-filled carbon nanotube detected by ferromagnetic resonance
Lenz, K.; Narkowicz, R.; Reiche, C. F.; Kákay, A.; Mühl, T.; Büchner, B.; Suter, D.; Lindner, J.; Fassbender, J.
Abstract: Designing future spintronic devices or entities requires the knowledge of their static and dynamic properties. However, the precise magnetic characterization of a single nanostructure like a nanowire or dot, e.g. by ferromagnetic resonance, is still an experimental challenge.
Broadband ferromagnetic resonance (FMR) or cavity-based FMR usually lack the necessary sensitivity to measure single micron-sized or smaller structures. Measurements of arrays of such elements often might be no alternative due to inhomogeneity either.
Here we show that microresonator FMR [1] can overcome these limitations. By decreasing the resonator size the filling factor is increased, therefore boosting the FMR sensitivity by several orders of magnitude.
This allows for measuring even a single Fe-filled carbon nanotube (Fe-CNT) [2]. The Fe-filling inside the CNT has a diameter of 42 nm with an initial length of several micrometers (see Fig. 1). In order to understand the origin of the various resonance peaks, a focused ion beam was used to shorten little-by-little the length of the Fe-CNT after each FMR measurement.
Furthermore, angle-dependent FMR measurements were performed to extract the anisotropy contributions (like shape and magnetocrystalline anisotropy). In addition, the measured narrow linewidth suggests that the Fe-filling is a well ordered crystal, as confirmed by transmission electron microscopy. Therefore, besides the magnetic characterization of a single nanostructure, the microresonator FMR can also provide ‘indirectly’ information about the crystalline structure.

Keywords: ferromagnetic resonance, magnetization, nanostructures, microresonator, microwaves, carbon nanotubes, magnetism
  • Invited lecture (Conferences)
    5th International Conference on Microwave Magnetics, 05.-08.06.2016, Tuscaloosa, USA
Registration No. 24164 - Permalink

Melanoma targeting with [99mTc(N)(PNP3)]-labeled α-melanocyte stimulating hormone peptide analogs: Effects of cyclization on the radiopharmaceutical properties
Carta, D.; Salvarese, N.; Morellato, N.; Gao, F.; Sihver, W.; Pietzsch, H.-J.; Biondi, B.; Ruzza, P.; Refosco, F.; Carpanese, D.; Rosato, A.; Bolzati, C.
Abstract: The purpose of this study was to evaluate the effect of cyclization on the biological profile of a [99mTc(N)(PNP3)]-labeled α-melanocyte stimulating hormone peptide analog. A lactam bridgecyclized H-Cys-Ahx-Ala3-c[Lys4-Glu-His-D-Phe-Arg-Trp-Glu10]-Arg11-Pro-Val-NH2 (NAP―NS2) and the corresponding linear H-Cys-Ahx-Ala-Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH2 (NAP―NS1) peptide were synthetized, characterized by ESI-MS spectroscopy and their melanocortin-1 receptor (MC1R) binding affinity was determined in B16/F10 melanoma cells. The consistent [99mTc(N)(PNP3)]-labeled compounds were readily obtained in high specific activity and their stability and biological properties were assessed. As an example, the chemical identity of [99mTc(N)(NAP–NS1)(PNP3)]+ was confirmed by carrier added experiments supported by radio/UV HPLC analysis combined with ESI(+)-MS. Compared with the linear peptide, cyclization negatively affected the biological properties of NAP–NS2 peptide by reducing its binding affinity for MC1R and by decreasing the overall excretion rate of the corresponding [99mTc(N)(PNP3)]-labeled peptide from the body as well as its in vivo stability. [99mTc(N)(NAP–NS1)(PNP3)]+ was evaluated for its potential as melanoma imaging probe in murine melanoma model. Data from in vitro and in vivo studies on B16/F10 melanoma model of [99mTc(N)(NAP–NS1)(PNP3)]+ clearly evidenced that the radiolabeled linear peptide keeps its biological properties up on the conjugation to the [99mTc(N)(PNP3)]-building block. The progressive increase of the tumor-to-nontarget ratios over the time indicate a quite stable interaction between the radiocomplex and the MC1R.
Keywords: Tc-99m, alpha-MSH, melanoma, MC1R, peptides, SPECT, Imaging. Registration No. 24162 - Permalink

Probing high-intensity laser-matter interaction at the Helmholtz International Beamline for Extreme Fields at the European XFEL
Schramm, U.ORC
Abstract: Talk on Probing high-intensity laser-matter interaction at the Helmholtz International Beamline for Extreme Fields at the European XFEL
Keywords: Relativistic Laser Plasma, HIBEF
  • Invited lecture (Conferences)
    PWSC 8th Petawatt Scientific Committee and ICUIL 2016, 10.-16.09.2016, Montebello, Canada
Registration No. 24159 - Permalink

Temperature-Dependent Charge Transport through Individually Contacted DNA Origami-Based Au Nanowires
Teschome, B.; Facsko, S.; Schönherr, T.; Kerbusch, J.; Keller, A.; Erbe, A.
Abstract: DNA origami nanostructures have been used extensively as scaffolds for numerous applications such as for organizing both organic and inorganic nanomaterials, studying single molecule reactions, and fabricating photonic devices. Yet, little has been done toward the integration of DNA origami nanostructures into nanoelectronic devices. Among other challenges, the technical difficulties in producing well-defined electrical contacts between macroscopic electrodes and individual DNA origami-based nanodevices represent a serious bottleneck that hinders the thorough characterization of such devices. Therefore, in this work, we have developed a method to electrically contact individual DNA origami-based metallic nanowires using electron beam lithography. We then characterize the charge transport of such nanowires in the temperature range from room temperature down to 4.2 K. The room temperature charge transport measurements exhibit ohmic behavior, whereas at lower temperatures, multiple charge transport mechanisms such as tunneling and thermally assisted transport start to dominate. Our results confirm that charge transport along metallized DNA origami nanostructures may deviate from pure metallic behavior due to several factors including partial metallization, seed inhomogeneities, impurities, and weak electronic coupling among AuNPs. Besides, this study further elucidates the importance of variable temperature measurements for determining the dominant charge transport mechanisms for conductive nanostructures made by self-assembly approaches.
Keywords: DNA origami, gold nanoparticles, metallization, electrical contacting, charge transport Registration No. 24153 - Permalink

In situ bow change of Al-alloy MEMS micromirrors during 248-nm laser irradiation
Mai, A.; Bunce, C.; Hübner, R.; Pahner, D.; Dauderstädt, U.
Abstract: Micromirror based spatial light modulators (SLMs) developed by the Fraunhofer Institute for Photonic Microsystems are well established in microlithography applications. Serving, e.g., as reflective, programmable photomasks in deep-UV mask writers, they enable highly flexible pattern generation. During operation, the micromirror bow significantly impacts contrast and the resolvable feature size of generated patterns. In some situations, MEMS micromirrors tend to change their bow during laser irradiation. A test regime including a characterization unit for the in situ analysis of MEMS micromirror topology has been developed to measure the bow change under various irradiation conditions. Experiments in which SLMs were irradiated by a 1-kHz, 248-nm pulse laser revealed that mirror bowing can occur in both directions (concave and convex). The bowing direction is dependent upon the applied irradiation parameters such as pulse-energy density, pulse number, and the deposited energy. Sustained irradiation at energy densities exceeding a certain limit can potentially become a limiting factor for the resolvable feature sizes of the patterns generated and, therefore, for the usable SLM lifespan.
Keywords: spatial light modulator; micromirror array; micro-(opto)-electro-mechanical-system device; laser; UV; in situ Registration No. 24150 - Permalink

Generation of high charge electron beams by ionization injection
Couperus, J. P.; Köhler, A.; Zarini, O.; Krämer, J.; Pausch, R.; Debus, A.; Hübl, A.; Garten, M.; Bussmann, M.; Irman, A.; Schramm, U.
Abstract: One of the most challenging aspects in Laser wakefield acceleration (LWFA) is controlled injection of electrons into the correct phase of the accelerating field. In the ionization injection scheme this is addressed by adding a small fraction of high Z gas to the accelerating medium. Electrons in the K-shell possess a high ionization threshold which is only reached around the laser maximum, close to the center of the propagation axis. Compared to wave-breaking injection, ionization injection requires relatively low laser intensities and plasma densities, allowing us to drive the wakefield in a more stable way.
We present an extensive experimental parameter study, showing the influence of Nitrogen doping concentration on beam parameters: energy spread, charge & repeatability. We discuss the influence of laser energy and plasma density on maximum reachable energy and conversion efficiency.
We show a regime where our laser system (2.5J on target, 30 fs) generates stable electron beams (252 MeV, +/- 9% shot-to-shot) with narrow bandwidth (36 MeV +/- 11MeV FWHM) and high charge (292 pC +/- 59 pC within 1/e2) electron beams, while retaining a low background.

Keywords: Laser wakefield acceleration, LWFA
  • Poster
    Advanced Accelerator Concepts Workshop (AAC 2016), 02.08.2016, National Harbor, Maryland, USA
Registration No. 24149 - Permalink

High temperature stable TCOs as selective transmitter for solar thermal applications
Lungwitz, F.; Schumann, E.; Guillen, E.; Escobar-Galindo, R.; Gemming, S.; Krause, M.
Abstract: Materials used in the receiver tubes of a solar thermal power plant must exhibit several properties, e.g. high temperature stability, high absorption in the solar region and low thermal emittance. Nowadays, temperatures of up to 450°C and up to 550°C are reached using parabolic trough arrays and solar tower absorbers, respectively, whereas temperatures up to 800°C or higher could be reached if the receiver materials were stable enough. Previous R&D approaches for high temperature solar receiver materials include multilayer coatings deposited by PVD or sol-gel techniques. Here, a new concept for solar-selective coating is presented. A transparent conductive oxide (TCO) is deposited as a solar selective transmitter on a black body absorber to implement both, high absorption (from the black body) in the ultraviolet, visible and near infrared spectral range (300 nm – 2500 nm) as well as high reflectivity (from the TCO) in the infrared (> 2500 nm) in a relative simple material design. Therefore SnO2:Ta and TiO2:Ta thin films are reactively magnetron co-sputtered from tantalum doped and undoped metal targets at high temperatures (400°C - 700°C). By changing dopant concentration, oxygen flux, process pressure and deposition temperature the optical properties of these films can be tailored to meet the requirements of a solar selective transmitter coating. It is also shown that the electrical properties of the TCO, namely charge carrier concentration and mobility, determine the optical behavior. The correlation between structural, optical, and electrical properties is analyzed by Raman Spectroscopy and Spectroscopic Ellipsometry (SE) both at room- and especially (in situ) at hightemperatures simulating the conditions where the functional coating is supposed to operate. Additionally, Rutherford Backscattering Spectroscopy (RBS), X-ray Diffraction (XRD), UV-VIS spectrometry, and Hall Effect measurements are performed. Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged.
Keywords: solar thermal transparent conductive oxide
  • Lecture (Conference)
    15th International Conference on Plasma Surface Engineering, 14.09.2016, Garmisch-Partenkirchen, Deutschland
Registration No. 24146 - Permalink

In-Depth Performance Analysis for OpenACC/CUDA/OpenCL Applications with Score-P and Vampir
Juckeland, G.; Henschel, R.
Abstract: Participants will work with Score-P/Vampir to learn how to dive into the execution properties of CUDA and OpenACC applications. We'll show how to use Score-P to generate a trace file and how to study it with Vampir. Additionally, we'll use the newly established OpenACC tools interface to also present how OpenACC applications can be studied for performance bottlenecks. This lab utilizes GPU resources in the cloud, you are required to bring your own laptop.
Keywords: Score-P Vampir Tracing Performance-Analysis
  • Lecture (Conference)
    GTC Europe 2016, 28.-29.09.2016, Amsterdam, Nederland
Registration No. 24143 - Permalink

Introduction into Raman spectroscopy
Krause, M.
Abstract: Fundamentals and new developments in Raman spectroscopy
  • Invited lecture (Conferences)
    Friends2-Workshop: Advanced coating and characterization techniques, 19.-20.09.2016, Dresden-Rossendorf, Deutschland
Registration No. 24142 - Permalink

Comparative study of the deposition of highly reflectant metal thin films by ionized PVD techniques
Rincón Llorente, G.; Guillén Rodríguez, E.; Schumann, E.; Heras Pérez, I.; Mesko, M.; Munnik, F.; Krause, M.; Escobar Galindo, R.
Abstract: The degree of ionization during Physical Vapor Deposition (PVD) plays a critical role on the final surface quality of the deposited coatings. In this work a comparative study of metal thin films (Al, Cu, Ag) deposited by conventional DC-Magnetron Sputtering (DCMS) and highly ionized techniques such as Filtered Cathodic Vacuum Arc (FCVA) and high power impulse magnetron sputtering (HiPIMS) was performed. The final scope of the study is aimed to optimize the deposition parameters to achieve higher specular reflectance as this have a critical influence in the yield of solar plants based on concentrated solar power. In this regard, the optical constants of the deposited films were modeled departing from ellipsometry data. A comparison of the experimental reflectance with that obtained after optical simulation was also carried out. The achieved optical performance of the films was further compared to the structural properties resulting from different deposition techniques. Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA)was applied to explore the potential oxidation of the films during deposition. Surface morphological changes were explored by Scanning Electron Microscopy (SEM). In addition, Atomic Force Microscopy (AFM) measurements at different deposition times allowed exploring the dynamics of the growth mechanism of the films.
Keywords: PVD techniques, Optical properties, Simulation, RBS, AFM
  • Lecture (Conference)
    Plasma Surface Engineering 2016, 11.-16.09.2016, Garmisch-Partenkirchen, Deutschland
Registration No. 24140 - Permalink

Impurity suppression in sputtered metallic thin films using HiPIMS
Mesko, M.; Munnik, F.; Heller, R.; Grenzer, J.; Hübner, R.; Halanda, J.; Gemming, S.; Krause, M.
Abstract: Composition and microstructure of thin films deposited by PVD are often influenced by the presence of residual gas. Therefore, it would be desirable to enable thin film growth without residuals incorporation. Strategies to avoid impurities incorporation are substrate heating, applying substrate bias, and reduction of base pressure to ultra-high vacuum (UHV) conditions. Industrial demand for low temperature and low cost processes often precludes these approaches. More recently, a very important question has been raised regarding high power impulse magnetron sputtering (HiPIMS) to form pure metallic films at low deposition rates and high values of base pressure in the deposition chamber [1].

In this study, HiPIMS was applied for room-temperature deposition of pure metallic thin films of Al, Ti, and Cu. These metals are distinguished by their oxygen affinities and melting temperatures. Deposition of carbon top layers was used to differentiate between residual gas and post-deposition contamination. Elastic recoil detection analysis (ERDA) revealed that HiPIMS produces bulk-impurity-free metallic thin films. The growth of such high-purity metallic thin films can be partly explained by gas rarefaction and the self-cleaning effect of the bombarding ions. Moreover, densification effects presumably suppress post-deposition oxidation. Proposed deposition mechanism will be explained in sufficient detail. The compositional effects are correlated with differences in the film microstructure revealed by SEM, XRD, and TEM analyses.

[1] P. Pokorný et al., Plasma Processes Polym. 12, 416 (2015)

Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged. This work was also funded by the ERDF, Project CAMBO, ITMS: 2622022079, and by Slovak grant agency VEGA, project no. 1/0503/15

Keywords: HiPIMS, Room temperature PVD, High-purity metallic films, ERDA
  • Poster
    Plasma Surface Engineering 2016, 11.-16.09.2016, Garmisch-Partenkirchen, Deutschland
Registration No. 24139 - Permalink

In situ RBS, Raman, and ellipsometry studies of layered material systems at elevated temperatures
Wenisch, R.; Heras, I.; Lungwitz, F.; Janke, D.; Guillén, E.; Heller, R.; Gemming, S.; Escobar Galindo, R.; Krause, M.
Abstract: The detailed knowledge of composition and structure is essential for the understanding of processes and properties of functional materials at elevated temperatures. To ensure materials functionality under in operando conditions, new concepts for analysis and process monitoring are necessary. In this contribution, selected layered material systems were studied in situ at temperatures up to 830°C by Rutherford backscattering (RBS), Raman spectroscopy, and ellipsometry within a cluster tool. Metal induced crystallization (MIC) is a promising technique for hydrogen-free synthesis of two-dimensional materials. Here, Si/Ag bilayers are studied as model system. The Si/Ag layer stacks are annealed at temperatures of 380 to 700°C. simultaneously, depth profiles of the elements are investigated by RBS revealing the diffusion kinetics. The changes in the phase structure and the degree of crystallinity are analyzed by Raman spectroscopy. Both the quick initial nucleation and ensuing growth processes are investigated. MIC is observed for all temperatures under study, while layer exchange occurs only for optimized process conditions.
As an example for high-temperature functional coatings, AlTiOxN1-x thin films were investigated in order to understand the influence of the oxygen to nitrogen ratio on the optical properties and their failure mechanisms at high temperatures. Ellipsometry and RBS results showed the influence of the initial oxygen content in the sample, inward diffusion of oxygen into the coating, and the high temperature stability of AlTiOxN1-x thin films. The low emittance of AlTiOxN1-x, allowed performing in situ RBS analysis at temperature up to 830°C for the first time.
Financial support by the EU, grant No. 645725, project FRIENDS2, and the
HGF via the W3 program (S.G.) is gratefully acknowledged.

Keywords: cluster tool, in situ analysis, RBS, Raman
  • Lecture (Conference)
    Plasma Surface Engineering 2016, 11.-16.09.2016, Garmisch-Partenkirchen, Deutschland
Registration No. 24136 - Permalink

Growth and applications of III-V nanowires on Si substrates
Dimakis, E.
Abstract: III-V semiconductor nanowires have been a subject of intense research over the last 10 years and a plethora of exciting nanoscale phenomena has been unveiled. The peculiar strain relaxation mechanisms in nanowire heterostructures offer the possibility to integrate epitaxially materials with large mismatch of lattice parameters and thermal expansion coefficients. Thus, one can tailor the (opto)electronic properties of nanowire heterostructures using an extended palette of materials compared to traditional thin-film heterostructures. Furthermore, the epitaxial growth of III-V nanowires on lattice mismatched Si substrates is of great interest, because the two complementary technologies can thus be integrated on single multifunctional chips combining the superior electronic and optoelectronic properties of the former with the mature CMOS technology of the latter.
This seminar will be focusing on III-As nanowires grown on Si(111) substrates by molecular beam epitaxy. Starting from the basic description of the vapor-liquid-solid (self-induced) growth of GaAs (InAs) nanowires [1,2], the problem of structural polytypism and its effect on the nanowire optoelectronic and electrical properties will be discussed [3,4] and, finally, the droplet-confined alternate pulsed epitaxy will be proposed as a unique growth mode that offers compatibility with the Si-CMOS processing standards [5]. Finally, the growth and the structural properties of coaxial multishell (In,Al,Ga)As/GaAs nanowires will be discussed, and their application in light emitting diodes or modulation doped heterostructures will be demonstrated [6].

[1] E. Dimakis, J. Lähnemann, U. Jahn, S. Breuer, M. Hilse, L. Geelhaar, and H. Riechert, Cryst. Growth Des. 2011, 11, 4001–4008
[2] A. Biermanns, E. Dimakis, A. Davydok, T. Sasaki, L. Geelhaar, M. Takahasi, and U. Pietsch, Nano Lett. 2014, 14, 6878−6883
[3] P. Schroth, M. Köhl, and J.-W. Hornung, E. Dimakis, C. Somaschini, L. Geelhaar, A. Biermanns, S. Bauer, S. Lazarev, U. Pietsch, T. Baumbach, Phys. Rev. Lett. 2015, 114, 055504
[4] G. Bussone, H. Schäfer-Eberwein, E. Dimakis, A. Biermanns, D. Carbone, A. Tahraoui, L. Geelhaar, P. Haring Bolívar, T. U. Schülli, and U. Pietsch, Nano Lett. 2015, 15, 981−989
[5] L. Balaghi, T. Tauchnitz, R. Hübner, L. Bischoff, H. Schneider, M. Helm, and E. Dimakis, Nano Lett. 2016, 16, 4032−4039
[6] E. Dimakis, U. Jahn, M. Ramsteiner, A. Tahraoui, J. Grandal, X. Kong, O. Marquardt, A. Trampert, H. Riechert, and L. Geelhaar, Nano Lett. 2014, 14, 2604−2609
  • Invited lecture (Conferences)
    Seminar, Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (FORTH), 05.08.2016, Heraklion, Greece
Registration No. 24133 - Permalink

The double role of Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates
Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.
Abstract: We have investigated the in-situ surface modification of a SiOx/Si(111) substrate by Ga droplets and its effect on the subsequent self-catalyzed growth of GaAs nanowires. Using a procedure of Ga droplet formation and subsequent re-evaporation prior to the nanowire growth, we found that the number density of nanowires at a given growth temperature can be varied deliberately within four orders of magnitude without affecting the nanowire diameter. A detailed study of the Ga droplet formation in a wide range of substrate temperatures revealed the physical processes that control the number density and size of the droplets.
Keywords: Nanowire; Ga droplets; oxide etching; nanoholes; GaAs; Si substrate
  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy (MBE 2016), 04.09.2016, Montpellier, France
Registration No. 24131 - Permalink

Droplet-confined alternate pulsed epitaxy of GaAs nanowires on Si substrates: meeting the typical MBE standards
Tauchnitz, T.; Balaghi, L.; Bischoff, L.; Hübner, R.; Schneider, H.; Helm, M.; Dimakis, E.
Abstract: We introduce a growth scheme with alternate Ga and As4 pulses for the self-catalyzed growth of free-standing GaAs nanowires on Si(111) substrates. Unlike the conventional growth mode, our scheme offers a wide growth temperature window (450 – 600 °C), low growth rates (down to 1-2 monolayers per As4 pulse), and the ability for defect-free and abrupt growth interruptions, meeting the typical MBE standards. We demonstrate the possibility to grow defect-free zinc blende nanowires in the whole temperature window and to probe the growth dynamics in specially designed experiments.
Keywords: nanowire; self-catalyzed; alternate pulsed epitaxy; GaAs; Si substrate
  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy (MBE 2016), 04.09.2016, Montpellier, France
Registration No. 24130 - Permalink

Exciton recombination at crystal-phase quantum rings in GaAs/InxGa1−xAs core/multishell nanowires
Corfdir, P.; Lewis, R. B.; Marquardt, O.; Küpers, H.; Grandal, J.; Dimakis, E.; Trampert, A.; Geelhaar, L.; Brandt, O.; Phillips, R. T.
Abstract: We study the optical properties of coaxial GaAs/InxGa1-xAs core/multishell nanowires with x between 0.2 and 0.4 at 10K. The evolution of the photoluminescence energy of the InxGa1-xAs quantum well shell with x and shell thickness agrees with the result of 8-band k.p calculations, demonstrating that the shell growth is pseudomorphic. At low excitation power, the photoluminescence from the shell is dominated by the recombination of exciton states deeply localized within the shell. We show that these states are associated with crystal-phase quantum rings that form at polytype segments of the InxGa1-xAs quantum well shell. Registration No. 24129 - Permalink

Functional behavior of the anomalous magnetic relaxation observed in melt-textured YBa2Cu3O7- δ samples showing the paramagnetic Meissner effect
Dias, F. T.; Vieira, V. N.; Garcia, E. L.; Wolff-Fabris, F.; Kampert, E.; Gouvea, C. P.; Schaf, J.; Obrados, X.; Puig, T.; Roa, J. J.
Abstract: We have studied the functional behavior of the field-cooled (FC) magnetic relaxation observed in melt- textured YBa2Cu3O7- δ(Y123) samples with 30 wt% of Y2Ba1Cu1O5 (Y211) phase, in order to investigate anomalous paramagnetic moments observed during the experiments. FC magnetic relaxation experiments were performed under controlled conditions, such as cooling rate and temperature. Magnetic fields up to 5T were applied parallel to the ab plane and along the c-axis. Our results are associated with the para-magnetic Meissner effect (PME), characterized by positive moments during FC experiments, and related to the magnetic flux compression into the samples. After different attempts our experimental data could be adequately fitted by an exponential decay function with different relaxation times. We discuss our results suggesting the existence of different and preferential flux dynamics governing the anomalous FC paramagnetic relaxation in different time intervals. This work is one of the first attempts to interpret this controversial effect in a simple analysis of the pinning mechanisms and flux dynamics acting during the time evolution of the magnetic moment. However, the results may be useful to develop models to explain this interesting and still misunderstood feature of the paramagnetic Meissner effect. Registration No. 24128 - Permalink

Magneto-acoustic study near the quantum critical point of the frustrated quantum antiferromagnet Cs2CuCl4
Cong, P. T.; Postulka, L.; Wolf, B.; van Well, N.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M.
Abstract: Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs2CuCl4 were performed for the longitudinal modes c11 and c33 in magnetic fields along the a axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at TN. Isothermal measurements at T < TN of the sound attenuation a reveal two closely spaced features of different characters on approaching the material’s quantum-critical point (QCP) at Bs = 8.5 T for B II a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature TN(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material’s spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/kB = 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality. Registration No. 24127 - Permalink

A monomeric copper-phosphoramide complex: Synthesis, structure, and electronic properties
Henriques, M. S.; Gorbunov, D. I.; Ponomaryov, A. N.; Saneei, A.; Pourayoubi, M.; Dusek, M.; Zvyagin, S.; Uhlarz, M.; Wosnitza, J.
Abstract: We report on a novel phosphoramide complex with formula Cu(NO3)2([C5H10N]3PO)2. This complex is the first example of a copper monomeric phosphoric triamide having an octahedral Cu[O]6 coordination environment. Cu(NO3)2([C5H10N]3PO)2 crystallizes in the monoclinic space group P21/n with the Cu atom located at an inversion center, as determined by single-crystal X-ray diffraction. Magnetic measurements along the principal crystallographic directions of the single crystal indicate that the complex is a paramagnet with very low magnetic anisotropy. Electron paramagnetic resonance spectra reveal the presence of two Cu2+ sites and make it possible to extract the hyperfine coupling. Registration No. 24126 - Permalink

Evaluation of E-Waste Processing through Secondary Copper Smelting
Rhamdhani, M. A.; Ghodrat, M.; Brooks, G.; Masood, S.; Corder, G.; Haque, N.; Reuter, M.
Abstract: Wastes of electronics and electrical equipment (WEEE) or simply e-wastes contain many valuable elements that include base metals (Cu, Fe, Pb, Al), precious metals (Au, Ag, Pt, Pd), other metals (Sn, Se, Te, Ta, Co, In, Ru, etc); as well as hazardous elements. Sustainable extraction of the valuable elements from e-waste is challenging due to the complexities of the materials and associated processing routes. There have been a number of processing and extraction techniques developed at laboratory level and few are implemented in industrial practices [1]. The processes implemented at industrial scale are mainly based on an improved combination of traditional extractive metallurgy processes (for example a combined pyrometallurgy, hydrometallurgy and electrometallurgy processes). Although practiced at industry scale, these processes and processing routes are far from optimised. Development of new technologies and/or improvement of the existing practices are still needed. Some of the barriers for improvement include: lack of fundamental knowledge (behaviour of all of these elements, which are governed by their solution thermodynamics); limited sound technoeconomic analyses; as well as limited understanding on the environmental impact of the different processing routes.
Keywords: E-Waste, E-Waste processing, WEEE recycling, precious metals, secondary copper
  • Lecture (Conference)
    8th Annual High Temperature Processing Symposium 2016, 01.-02.02.2016, Melbourne, Australien


Registration No. 24125 - Permalink

Recycling Indices Visualizing the Performance of the Circular Economy
Reuter, M.; van Schaik, A.
Abstract: The EU has adopted an ambitious Circular Economy (CE) package. This action plan aims to "close" the loop of product lifecycles through improved product design, improved collection, recycling, remanufacture and re-use. Through this the EU envisages to bring benefits both environmentally as well as economically. Recycling forms the heart of the CE system; metal and material recycling and metallurgical processing are key enablers. Maximizing the recovery of materials from End-of-Life (EoL) products, while simultaneously lowering the environmental footprint, is a vital outcome. Therefore, designing greener products while also optimizing organisational and technology infrastructures of industrial recycling processing flow sheets are vital. This enables the maximal recovery of materials and also especially strategic elements from EoL products, requiring a deep understanding of the fundamental opportunities and limits and the dynamics of the evolving and agile system. In order to inform the consumer, this paper presents the developed Recycling Index (RI) (analogous to the EU Energy Labels) that includes a new Material-RI.These are based on simulation models that have their roots in minerals and metallurgical processing. It builds on previous work by the authors that visualises and communicate the recycling performance of a product as well as of the individual materials in a clear, easy and transparent manner. It will help to empower the consumer to make informed purchasing decisions. Furthermore, RIs are essential for communicating greener design and efforts to improve resource efficiency by producers and state-of-the art recycling and (metallurgical) processing technology by industry. The RI is an excellent tool to provide insight into possibilities and improvements as well as barriers and limits for CE to policy makers and to close the missing links in the CE.
Keywords: Recycling – Design for Recycling – Recycling Index – Simulation – Calculation methods for recycling rates – Circular Economy
  • World of Metallurgy 69(2016)4, 201-216
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Registration No. 24124 - Permalink

Strategic metal recycling: adaptive metallurgical processing infrastructure and technology are essential for a Circular Economy
Reuter, M.; van Schaik, A.
Abstract: Recycling forms the heart of the Circular Economy (CE) system. Ultimately all products will have to be recycled at their End-of-Life (EoL). Maximizing the recovery of materials and also especially strategic elements from EoL products requires a deep understanding of the fundamental limits and the dynamics of the evolving system, thus an adaptive processing and metallurgical infrastructure is critical to recover all metals and materials. Paramount is the quantification of the “mineralogy”, the complex and interlinked composition of products, to trace and quantify specifically all the losses of materials, metals, alloys, etc. due to thermodynamic and other non-linear interactions. We named this product centric recycling. The recycling potential and performance must be quantified and demonstrated for products, collection systems, waste separation and recovery technologies, and material supply. Emphasis is also placed on informing the consumer through iRE i.e. informing Resource Efficiency in an easy-to-understand way. System Integrated Metal Processing (SIMP) using big-data, multi-sensors, simulation models, metallurgy, etc. links all stakeholders through Circular Economy Engineering (CEE), an important enabler to maximize Resource Efficiency and thus iRE.
Keywords: EoL, CE, CEE
  • Annales des Mines - Responsiabilité & Environnement (2016)82, 62-66
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Registration No. 24123 - Permalink

Digitalizing the Circular Economy: Circular Economy Engineering Defined by the Metallurgical Internet of Things
Reuter, M.
Abstract: Metallurgy is a key enabler of a circular economy (CE), its digitalization the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitalization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated. The true boundaries of sustainability can be determined in addition to the techno-economic evaluation of RE. The integration of me tallurgical reactor technology and systems digitally, not only on one site but linking different sites globally via hardware, is the basis for describing CE systems as dynamic feedback control loops, i.e., the m-IoT.
Keywords: digitalization the metallurgical Internet of Things (m-IoT)


Registration No. 24121 - Permalink

Fast neutron-induced fission at the time-of-flight facility nELBE
Kögler, T.; Beyer, R.; Junghans, A. R.; Müller, S.
Abstract: The fast neutron-induced fission cross section of Pu(242) was determined the range of 0.5 MeV and in 10 MeV relative to U(235)(n,f) at the neutron time-of-flight facility nELBE. Using the high spontaneous fission rate of Pu(242) to determine the number of target atoms makes the cross section independent from the detection. Sophisticated neutron transport simulations with Geant 4 and MCNP 6 are used to correct the neutron scattering. The determined relative cross section is in good agreement with current experimental and evaluated data sets.
Keywords: neutron-induced fission cross section, neutron scattering corrections, fast neutrons, nELBE
  • Lecture (Conference)
    ND2016 - International Conference on NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, 11.-16.09.2016, Bruges, Belgien
Registration No. 24120 - Permalink

The case of a rough potential energy surface: Discrepancies between results of NEB and MD calculations
Posselt, M.
Abstract: Vacancy migration is studied in a silicon crystal with atomic interactions described by the Kumagai potential [1]. The basic functional form of this potential is very similar to the Tersoff potential. The main improvements concern the values of the elastic constants and the melting temperature. However, the potential energy surface is as rough as in the case of the Tersoff potential. In the ground state the vacancy has the “normal” tetrahedral configuration. The migration in the rugged potential energy landscape leads to peculiarities. Extensive Molecular Dynamics (MD) calculations show that the atomic mechanism of the migration process depends on temperature. The vacancy migration energy changes at about 1000 K: At lower and higher temperatures it is about 0.71 and 0.41 eV, respectively. Investigations on the dominating defect structure show that below about 1000 K the tetrahedral vacancy prevails whereas at higher temperature a modified version of the tetrahedral vacancy, the split vacancy and other configurations become dominant.
Applying the Nudged Elastic Band (NEB) method to the potential energy surface in the ground state, the transition between neighboring tetrahedral vacancy structures was studied. A number of intermediate metastable states were found, amongst them the modified version of the tetrahedral vacancy and the split vacancy. The maximum barrier for the migration between one ground state configuration to another is about 0.9 eV, whereas a barrier of about 0.3 eV is found for the transition from the split to the modified tetrahedral structure. Comparing with the results of MD simulations one may assume that in the high temperature range the vacancy moves mainly between high-energy configurations such as the split and the modified tetrahedral structure. The reason why the vacancy is not very often found in the ground state is not completely clear. Obviously, the free energy landscape at elevated temperature differs strongly from the ground-state energy landscape. Vibrational degrees of freedom may lead to the narrowing of the path to the tetrahedral state while the path between the high energy states may become much broader.
[1] T. Kumagai et al., Comput. Mater. Sci. 39, 457 (2007)

Keywords: molecular dynamics, nudged elastic band method, potential energy surface
  • Poster
    Int. Focus Workshop on Bridging-Time Scale Techniques and their Application in Atomistic Computational Science, 12.-15.09.2016, Dresden, Germany
Registration No. 24117 - Permalink

Local Scale-Invariance of the 2+1 dimensional Kardar-Parisi-Zhang model
Kelling, J.; Ódor, G.; Gemming, S.
Abstract: Local Scale-Invariance theory is tested by extensive dynamical simulations of the driven dimer lattice gas model, describing the surface growth of the 2+1 dimensional Kardar–Parisi–Zhang surfaces. Very precise measurements of the universal autoresponse function enabled us to perform nonlinear fitting with the scaling forms, suggested by local scale-invariance (LSI). While the simple LSI ansatz does not seem to work, forms based on logarithmic extension of LSI provide satisfactory description of the full (measured) time evolution of the autoresponse function.
Keywords: Kardar-Parisi-Zhang, Local Scale-Invariance, Monte-Carlo, GPU Registration No. 24116 - Permalink

Rohstoffe für die Energieversorgung der Zukunft
Angerer, G.; Buchholz, P.; Gutzmer, J.; Hagelten, C.; Herzig, P.; Little, R.; Trauer, R. K.; Welker, F.-W.
  • Book (Authorship)
    München: Acatech, 2016
    198 Seiten
Registration No. 24112 - Permalink

Self-Supporting Hierarchical Porous PtAg Alloy Nanotubular Aerogels as Highly Active and Durable Electrocatalysts
Liu, W.; Haubold, D.; Rutkowski, B.; Oschatz, M.; Hübner, R.; Werheid, M.; Ziegler, C.; Sonntag, L.; Liu, S.; Zheng, Z.; Herrmann, A.-K.; Geiger, D.; Terlan, B.; Gemming, T.; Borchardt, L.; Kaskel, S.; Czyrska-Filemonowicz, A.; EychmüLler, A.
Abstract: Developing electrocatalysts with low cost, high activity, and good durability is urgently demanded for the wide commercialization of fuel cells. By taking advantage of nanostructure engineering, we fabricated PtAg nanotubular aerogels (NTAGs) with high electrocatalytic activity and good durability via a simple galvanic replacement reaction between the in situ spontaneously gelated Ag hydrogel and the Pt precursor. The PtAg NTAGs have hierarchical porous network features with primary networks and pores from the interconnected nanotubes of the aerogel and secondary networks and pores from the interconnected thin nanowires on the nanotube surface, and they show very high porosities and large specific surface areas. Due to the unique structure, the PtAg NTAGs exhibit greatly enhanced electrocatalytic activity toward formic acid oxidation, reaching 19 times higher metal-based mass current density as compared to the commercial Pt black. Furthermore, the PtAg NTAGs show outstanding structural stability and electrochemical durability during the electrocatalysis. Noble metal-based NTAGs are promising candidates for applications in electrocatalysis not only for fuel cells, but also for other energy-related systems. Registration No. 24111 - Permalink

Downscaling Effect on the Superconductivity of Pd3Bi2X2 (X = S or Se) Nanoparticles Prepared by Microwave-Assisted Polyol Synthesis
Roslova, M.; Opherden, L.; Veremchuk, I.; Spillecke, L.; Kirmse, H.; Herrmannsdörfer, T.; Wosnitza, J.; Doert, T.; Ruck, M.
Abstract: PdBi2S2 and Pd3Bi2Se2 have been successfully prepared in the form of nanoparticles with diameters of ∼50 nm by microwave-assisted modified polyol synthesis at low temperatures. The composition and morphology of the samples have been studied by means of powder X-ray diffraction as well as electron microscopy methods, including X-ray intensity mapping on the nanoscale. Superconducting properties of the as-prepared samples have been characterized by electrical resistivity measurements down to low temperatures (∼0.2 K). Deviations from the bulk metallic behavior originating from the submicrometer nature of the samples were registered for both phases. A significant critical-field enhancement up to 1.4 T, i.e., 4 times higher than the value of the bulk material, has been revealed for Pd3Bi2Se2. At the same time, the critical temperature is suppressed to 0.7 K from the bulk value of ∼1 K. A superconducting transition at 0.4 K has been observed in nanocrystalline Pd3Bi2S2. Here, a zero-temperature upper critical field of ∼0.5 T has been estimated. Further, spark plasma-sintered Pd3Bi2S2 and Pd3Bi2Se2 samples have been investigated. Their superconducting properties are found to lie between those of the bulk and nanosized samples. Registration No. 24109 - Permalink

Field-stepped broadband NMR in pulsed magnets and application to SrCu2(BO3)2 at 54 T
Kohlrautz, J.; Haase, J.; Green, E. L.; Zhang, Z. T.; Wosnitza, J.; Herrmannsdörfer, T.; Dabkowska, H. A.; Gaulin, B. D.; Stern, R.; Kühne, H.
Abstract: Pulsed magnets generate the highest magnetic fields as brief transients during which the observation of NMR is difficult, however, this is the only route to unique insight into material properties up to the regime of 100 T. Here, it is shown how rather broad NMR spectra can be assembled in a pulsed magnet during a single field pulse by using the inherent time dependence of the field for the recording of field-stepped free induction decays that cover a broad frequency range. The technique is then applied to 11B NMR of the spin-dimer system SrCu2(BO3)2, a magnetic insulator known to undergo a series of field-driven changes of the magnetic ground state. At peak fields of about 54 T at the Dresden High Magnetic Field Laboratory, 11B NMR spectra spanning a total of about 9 MHz width are reconstructed. The results are in good accordance with a change from a high-temperature paramagnetic state to a low-temperature commensurate superstructure of field-induced spin-dimer triplets. Registration No. 24108 - Permalink

Quantum phase transitions and multicriticality in Ta(Fe1-xVx)2
Brando, M.; Kerkau, A.; Todorova, A.; Yamada, Y.; Khuntia, P.; Förster, T.; Burkhard, U.; Baenitz, M.; Kreiner, G.
Abstract: We present a comprehensive study of synthesis, structure analysis, transport and thermodynamic properties of the C14 Laves phase Ta(Fe1-xVx)2. Our measurements confirm the appearance of spin-density wave (SDW) order within a dome-like region of the x-T phase diagram with vanadium content 0.02 < x < 0.3. Our results indicate that on approaching TaFe2 from the vanadium-rich side, ferromagnetic (FM) correlations increase faster than the antiferromagnetic (AFM) ones. This results in an exchange-enhanced susceptibility and in the suppression of the SDW transition temperature for x < 0.13 forming the dome-like shape of the phase diagram. This effect is strictly related to a significant lattice distortion of the crystal structure manifested in the c / a ratio. At x = 0.02 both FM and AFM energy scales have similar strength and the system remains paramagnetic down to 2 K with an extremely large Stoner enhancement factor of about 400. Here, spin fluctuations dominate the temperature dependence of the resistivity ρ ∝ T3/2 and of the specific heat C/T ∝-log(T) which deviate from their conventional Fermi liquid forms, inferring the presence of a quantum critical point of dual nature. Registration No. 24107 - Permalink

Structure, composition and magnetism in FeAl alloys
Menendez, E.; Surinach, S.; Baro, M. D.; Liedke, M. O.; Fassbender, J.; Nogues, J.; Sort, J.
Abstract: Fe1–xAlx alloys with x ranging from roughly 0.35 to 0.5 at. % show an interesting combination of room temperature magnetic and structural properties. Atomically ordered Fe1–xAlx (0.35 ≤ x ≤ 0.5 at. %) alloys are paramagnetic, while atomically disordered Fe1–xAlx (0.35 ≤ x ≤ 0.5 at. %) alloys become ferromagnetic [1]. The transition from the paramagnetic to the ferromagnetic state can be accomplished by different means (e.g., deformation or ion irradiation) and, remarkably, fully reversed upon thermal treatment [2]. Fabrication of Fe1–xAlx (0.35 ≤ x ≤ 0.5 at. %) thin films with controlled microstructure, composition and thickness would turn them into potential candidates to be magnetically patterned for the functioning of devices, such as magnetic storage media or magnetoresistive random access memories [3]. An overwiew of this order-disorder transition by either deformation or ion irradiation in bulk samples will be presented. Particular emphasis will be given to magnetic patterning routes by both local deformation and selective ion irradiation. Finally, our recent results on the preparation of thin films with controlled microstructure, composition and thickness will be outlined.

[1] E. Menéndez et al. New J. Phys. 10 (2008) 103030
[2] E. Menéndez et al. Small 5 (2009) 229
[3] R. Bali et al. Nano Lett. 14 (2014) 435

Keywords: magnetism, FeAl, binary alloys
  • Invited lecture (Conferences)
    Frontiers in Materials Processing Applications, Research and Technology, 09.-12.07.2017, Bordeaux, Frankreich
Registration No. 24104 - Permalink

Magnetic anisotropy peculiarities of high-temperature ferromagnetic MnxSi1−x (x ≈ 0.5) alloy films
Drovosekov, A. B.; Kreines, N. M.; Savitsky, A. O.; Kapelnitsky, S. V.; Rylkov, V. V.; Tugushev, V. V.; Prutskov, G. V.; Novodvorskii, O. A.; Cherebilo, E. A.; Kulatov, E. T.; Wang, Y.; Zhou, S.
Abstract: Thin films of Mn x Si1−x alloys with different Mn concentration $x\approx0.44\text{--}0.63$ grown by the pulsed-laser deposition (PLD) method onto the Al2O3 (0001) substrate were investigated in the temperature range 4–300 K using ferromagnetic resonance (FMR) measurements in the wide range of frequencies $(f = 7\text{--}60\ \text{GHz})$ and magnetic fields $(H = 0\text{--}30\ \text{kOe})$ . For samples with $x\approx0.52\text{--}0.55$ , FMR data show clear evidence of ferromagnetism (FM) with high Curie temperatures $T_\mathrm{C} \sim 300\ \text{K}$ . These samples demonstrate the complex and unusual character of magnetic anisotropy described in the frame of phenomenological model as a combination of the essential second-order easy-plane anisotropy contribution and the additional fourth-order anisotropy contribution with the easy direction normal to the film plane. We explain the obtained results by a polycrystalline (mosaic) structure of the films caused by the film-substrate lattice mismatch. Registration No. 24100 - Permalink

Formation of silicon nanocrystals in silicon carbide using flash lamp annealing
Weiss, C.; Schnabel, M.; Prucnal, S.; Hofmann, J.; Reichert, A.; Fehrenbach, T.; Skorupa, W.; Janz, S.
Abstract: During the formation of Si nanocrystals (Si NC) in SixC1-x layers via solid-phase crystallization, the unintended formation of nanocrystalline SiC reduces the minority carrier lifetime and therefore the performance of SixC1-x as an absorber layer in solar cells. A significant reduction in the annealing time may suppress the crystallization of the SiC matrix while maintaining the formation of Si NC. In this study, we investigated the crystallization of stoichiometric SiC and Si-rich SiC using conventional rapid thermal annealing (RTA) and nonequilibrium millisecond range flash lamp annealing (FLA). The investigated SixC1-x films were prepared by plasma-enhanced chemical vapor deposition and annealed at temperatures from 700 C to 1100C for RTA and at flash energies between 34 J/cm2 and 62 J/cm2 for FLA. Grazing incidence X-ray diffraction and Fourier transformed infrared spectroscopy were conducted to investigate hydrogen effusion, Si and SiC NC growth, and SiC crystallinity. Both the Si content and the choice of the annealing process affect the crystallization behavior. It is shown that under certain conditions, FLA can be successfully utilized for the formation of Si NC in a SiC matrix, which closely resembles Si NC in a SiC matrix achieved by RTA. The samples must have excess Si, and the flash energy should not exceed 40 J/cm2 and 47 J/cm2 for Si0.63C0.37 and Si0.77C0.23 samples, respectively. Under these conditions, FLA succeeds in producing Si NC of a given size in less crystalline SiC than RTA does. This result is discussed in terms of nucleation and crystal growth using classical crystallization theory. For FLA and RTA samples, an opposite relationship between NC size and Si content was observed and attributed either to the dependence of H effusion on Si content or to the optical absorption properties of the materials, which also depend on the Si content.
Keywords: solar cells, flash lamp annealing, Si, SiC Registration No. 24099 - Permalink

Untersuchungen zu magnetohydrodynamischen Instabilitäten in Flüssigmetallen
Seilmayer, M.
Abstract: This dissertation, “Studies on magnetohydrodynamic instabilities in liquid metal flows”, focuses on two different experiments in a cylindrical Taylor-Couette (TC) geometry. This fundamental set-up consists of an inner and an outer cylinder, which are mounted concentrically. The different radii are defined by the parameters and . The rotation of both cylinders can be set independently by their angular frequencies and . The gap between them is filled with the fluid whose flow is to be investigated. For an ideal non-viscous fluid, Rayleigh’s criterion states that the flow between two concentric cylinders with infinite length is stable against small perturbations as long as the angular momentum increases outward, [1]. Rayleigh’s criterion can be interpreted in a way that an ideal TC-flow remains laminar if the pressure and centrifugal forces are in a stable equilibrium state.
A more general setting is now introduced with an azimuthal magnetic field being applied to the electrical conducting fluid. For this different situation Michael [2] and Chandrasekhar [3] derived an extended stability criterion only for axisymmetric perturbations which is valid for an ideally conducting and non-viscous fluid. The first experiment described in the present dissertation consists of a TC-setup using the eutectic alloy Ga67In20,5Sn12,5 as working fluid. In addition to the common installation an insulated current on the rotation axis with up to 20 kA generates the necessary magnetic field . Michael’s criterion indicates in that case that the flow is stable with respect to axisymmetric perturbations. However, this does not apply for non-axisymmetric perturbations. It was shown theoretically by Rüdiger et al. [4, 5] that the interaction of an azimuthal magnetic field with a laminar rotational flow may become unstable against non-axisymmetric disturbances. This phenomenon is called Azimuthal Magnetorotational Instability (AMRI). The present work gives the first experimental evidence for AMRI in a liquid metal TC-experiment. It is shown that a hydrodynamically stable flow can be disturbed by an applied current free azimuthal magnetic field . The instability itself is then identified as a travelling wave co-rotating with the cylinders.
The second configuration investigated in this work is characterized by a magnetic field profile proportional to the radius. The basis for such an experiment is the remarkable stability criterion from Tayler [6, 7]. It tells that even an ideal fluid at rest can become unstable against non-axisymmetric disturbances. The Tayler instability (TI) in liquid metals can be considered as the incompressible version of the kink instability that is widely known in plasma physics. The TI-experiment confirms the numerical results given by Rüdiger et al. [8, 9] who calculated the onset for the instability in an incompressible liquid metal column with finite conductivity at round about 3 kA.
Both observed phenomena are strongly related to astrophysical processes in which angular momentum transport plays an essential role. What was missing so far was a clear experimental evidence for the described interaction mechanisms between a rotational flow and a magnetic field. The submitted dissertation reports the analysis and results of the first experiments on the two fundamental instabilities AMRI and TI.

[1] Rayleigh, Proc. R. Soc. London, Ser. A, 93(648), 148‑154, 1917.
[2] D. H. Michael, Mathematika, 1, 45‑50, 1954.
[3] S. Chandrasekhar, Proc.Roy.Soc.-A, 216(1126), 293‑309, 1953.
[4] G. Rüdiger et al. MNRAS, 377(4), 1481‑1487, 2007.
[5] G. Rüdiger et al. Astron. Nachr., 328, 1158‑1161, 2007.
[6] R. J. Tayler, Proc. R. Soc. London, Ser. B, 70(1), 31‑48, 1957.
[7] R. J. Tayler, MNRAS, 161(4), 365‑380, 1973.
[8] G. Rüdiger et al., Astron. Nachr., 332(1), 17‑23, 2011.
[9] G. Rüdiger et al., Astrophys. J., 755(2), 181, 2012.

Keywords: MRI, magnetohydrodynamic instabilities, Azimuthal Magnetorotational Instability,Tayler instability
  • Book (Authorship)
    Dresden: TUDpress, 2016
    261 Seiten
Registration No. 24097 - Permalink

Cm3+ incorporation in La1-xGdxPO4 monazites: a TRLFS and XAFS study
Huittinen, N.; Scheinost, A. C.; Wilden, A.; Arinicheva, Y.
Abstract: Crystalline ceramic materials show promise as potential waste forms for immobilization of high-level radioactive wastes. Especially for the immobilization of trivalent minor actinides (MA) and plutonium, some ceramic materials such as the lanthanide phosphates (LnPO4) crystallizing in the monazite structure have been envisioned as host materials due to their thermal stability, high radiation tolerance, and chemical durability [1]. Thus, for a reliable long-term safety assessment of nuclear waste repositories for conditioned radioactive waste, a fundamental understanding of the MA incorporation process in these envisioned ceramic matrices is required.
In the present study, the incorporation of the minor actinide Cm3+ in a series of La1-xGdxPO4 (x = 0, 0.2, 0.5, 0.8, 1) monazite solid solutions has been investigated using time-resolved laser fluorescence- (TRLFS) and Cm L3-edge x-ray absorption fine-structure spectroscopy (XAFS).
The Cm3+ excitation spectra obtained with the TRLFS method of the pure LaPO4 and GdPO4 end-members (Figure 1) show four well-resolved peaks corresponding to the 4-fold splitting of the Cm3+ ground state. The highly resolved ground-state splitting indicates the presence of only one, very well-defined, crystalline environment for the incorporated Cm3+ cation in the La and Gd monazite end-members. The situation changes when examining the solid solution compositions (La0.8Gd0.2PO4, La0.5Gd0.5PO4, and La0.2Gd0.8PO4) where the complete loss of the splitting fine-structure and the broadening of the excitation peaks indicate a decrease of the short-range order in these solid solutions.
The fitting of the first coordination shell of our Cm L3 XAFS data (Figure 2) for LaPO4, La0.5Gd0.5PO4, and GdPO4, indicate a contraction of the Cm-O distance when going from the larger LaPO4 monazite toward GdPO4 (see Table 1). In addition the Debye-Waller (DW, σ2) factor (which is an indicator for thermal and structural disorder) decreases substantially from 0.0079 Å2 in LaPO4 to 0.004 Å2 in GdPO4, while an increase is observed for the solid-solution composition (0.0112 Å2). The shortening of the Cm···O bond distance can be understood by the decreasing size of the monazite unit cell when going from the larger La3+-bearing host toward the smaller GdPO4. The differences in the DW factors between the monazite end-members can be explained when examining our previously obtained results for Eu3+ incorporation in LnPO4 monazites [2]. Here we could show that a larger mismatch between host and dopant radii causes a larger distortion of the monazite crystal lattice around the trivalent dopant. The cation radii of nine-fold coordinated La3+, Cm3+, and Gd3+ are 121.6 Å [3], 114.6 Å [4], and 110.7 Å [3], respectively. Thus, the larger mismatch of host and dopant radii in Cm3+-doped LaPO4 could explain the larger DW factor than obtained for Cm3+ incorporation in GdPO4. The large DW factor obtained for La0.5Gd0.5PO4 in comparison to the monazite end-members is in concordance with the excitation line broadening observed for the monazite solid solutions in our Cm3+ excitation spectra (Figure 1), implying an increasing disordering of the monazite crystal structure. In our previous work investigating the incorporation of Eu3+ in La1-xGdxPO4 monazites [5], the systematic excitation line broadening could be attributed to and increasing broadening of the Eu∙∙∙O bond distance distribution in the synthetic solid solution series when going from the pure end-members with very well-defined Eu∙∙∙O distances toward the La0.5Gd0.5PO4 composition.

Our spectroscopic results obtained in the present study show that Cm3+ is substituted for the host cation sites in all investigated monazites. Although the spectroscopic data suggest a disordering of the monazite solid solution series due to less explicit Ln∙∙∙O bond distances in the mixed solids, the spectroscopic investigations also imply that no preferential incorporation of dopants on host cation sites with similarly sized cation radii occurs, which is of great importance when considering the performance of monazite materials as immobilization matrices for highly radioactive actinide compounds.

[1] G. R. Lumpkin (2006) “Ceramic waste forms for actinides.” Elements 2: 365-372.
[2] N. Huittinen et al. (submitted) Using Eu3+ as an atomic probe to investigate the local environment in LaPO4 GdPO4 monazite end-members.
[3] R. D. Shannon (1976) Revised effective ionic radii and systematic studies of interatomic distances
in halides and chalcogenides. Acta Cryst. A32, 751–767.
[4] F. H. David and V. Vokhmin (2003) Thermodynamic properties of some tri- and tetravalent actinide aquo ions. New J. Chem., 27, 1627–1632.
[5] N. Huittinen et al. (submitted) Structural incorporation of Eu3+ in La1-xGdxPO4 monazite solid solutions: A combined spectroscopic and computational study.
  • Poster
    9th international conference on nuclear and radiochemistry (NRC9), 29.08.-02.09.2016, Helsinki, Finland
Registration No. 24096 - Permalink

Using Eu3+ as an atomic probe to investigate the local environment in LaPO4–GdPO4 monazite end-members
Huittinen, N.; Arinicheva, Y.; Schmidt, M.; Neumeier, S.; Stumpf, T.
Abstract: In the present study, we have investigated the luminescent properties of Eu3+ as a dopant in a series of synthetic lanthanide phosphates from the monazite group. Systematic trends in the spectroscopic properties of Eu3+ depending on the size of the host cation and the dopant to ligand distance have been observed. Our results show that the increasing match between host and dopant radii when going from Eu3+-doped LaPO4 toward the smaller GdPO4 monazite decreases both the full width at half maximum of the Eu3+ excitation peak, as well as the 7F2/7F1 emission band intensity ratio. The decreasing Ln-O bond distance within the LnPO4 series causes a systematic bathochromic shift of the Eu3+ excitation peak, showing a linear dependence of both the host cation size and the Ln-O distance. The linear relationship can be used to predict the energy band gap for Eu3+-doped monazites for which no Eu3+ luminescent data is available. Finally, mechanisms for metal-metal energy transfer between host and dopant lanthanides have been explored based on recorded luminescence lifetime data. Luminescence lifetime data for Eu3+ incorporated in the various monazite hosts clearly indicated that the energy band gap between the guest ion emission transition and the host ion absorption transition can be correlated to the degree of quenching observed in these materials with otherwise identical geometries and chemistries.
Keywords: Eu3+, Monazite, Incorporation, TRLFS, Luminescence, Quenching Registration No. 24093 - Permalink

Rotational friction of dipolar colloids measured by driven torsional oscillations
Steinbach, G.; Gemming, S.; Erbe, A.
Corresponding author: Steinbach, Gabi
Corresponding author: Erbe, Artur
Abstract: Despite its prominent role in the dynamics of soft materials, rotational friction remains a quantity that is difficult to determine for many micron-sized objects. Here, we demonstrate how the Stokes coefficient of rotational friction can be obtained from the driven torsional oscillations of single particles in a highly viscous environment. The idea is that the oscillation amplitude of a dipolar particle under combined static and oscillating fields provides a measure for the Stokes friction. From numerical studies we derive a semi-empirical analytic expression for the amplitude of the oscillation, which cannot be calculated analytically from the equation of motion. We additionally demonstrate that this expression can be used to experimentally determine the rotational friction coefficient of single particles. Here, we record the amplitudes of a field-driven dipolar Janus microsphere with optical microscopy. The presented method distinguishes itself in its experimental and conceptual simplicity. The magnetic torque leaves the local environment unchanged, which contrasts with other approaches where, for example, additional mechanical (frictional) or thermal contributions have to be regarded.


Registration No. 24091 - Permalink

MIR and THz spectroscopy of condensed matter
Helm, M.
Abstract: MIR and THz spectroscopy of condensed matter
Keywords: infrared, THz, condensed matter
  • Invited lecture (Conferences)
    Summer School NanoTech Tera-Mir, 29.08.-01.09.2016, Porquerolles, Hyeres, France
Registration No. 24090 - Permalink

Common methods of spectral data analysis
Seilmayer, M.
Abstract: Fourier and Hilbert transforms are utilized to perform several types of spectral analysis on the supplied data. Also gapped and irregularly spaced data can be processed. A user friendly interface helps to interpret the results.
Keywords: spectral analysis Fourier transform Hilbert transform R
  • Software
    Publication year 2016
    Programming language: R
    System requirements: Windows, Linux, MacOS, R (>= 2.15.0)
    License: GPL-2 (Link to license text)
    Hosted on CRAN: Link to location
Registration No. 24082 - Permalink

Seilmayer, M.
Abstract: This is a wrapper function for image(), which makes reasonable raster plots with nice axis and other useful features.
Keywords: plot function R
  • Software
    Publication year 2016
    Programming language: R
    System requirements: Windows, Linux, MacOS, R (>= 2.15.0)
    License: GPL-2 (Link to license text)
    Hosted on CRAN: Link to location
Registration No. 24081 - Permalink

Progress of the Felsenkeller shallow-underground accelerator for nuclear astrophysics
Bemmerer, D.; Cavanna, F.; Cowan, T. E.; Grieger, M.; Hensel, T.; Junghans, A. R.; Ludwig, F.; Müller, S. E.; Rimarzig, B.; Reinicke, S.; Schulz, S.; Schwengner, R.; Stöckel, K.; Szücs, T.; Takács, M. P.; Wagner, A.; Wagner, L.; Zuber, K.
Abstract: Low-background experiments with stable ion beams are an important tool in order to put the understanding of stellar hydrogen, helium, and carbon burning on a solid experimental foundation. The pioneering work in this regard has been done by the LUNA collaboration at Gran Sasso, using a 0.4 MV accelerator. In the present contribution, the status of the project for a higher-energy underground accelerator is reviewed. Two tunnels of the Felsenkeller underground site in Dresden, Germany, are currently being refurbished for the installation of a 5 MV high-current Pelletron accelerator. Construction work is on schedule and expected to complete in August 2017. The accelerator will provide intense, 50μA, beams of 1H+, 4He+, and 12C+ ions, enabling research on astrophysically relevant nuclear reactions with unprecedented sensitivity.
Keywords: Felsenkeller underground nuclear astrophysics Registration No. 24079 - Permalink

High resolution x-ray Thomson scattering measurements from cryogenic hydrogen jets using the linac coherent light source
Fletcher, L. B.; Zastrau, U. B.; Galtier, E. A.; Gamboa, E. J. A.; Goede, S. A.; Schumaker, W. A.; Ravasio, A. A.; Gauthier, M. A.; Macdonald, M. J. A.; Chen, Z. A.; Granados, E. A.; Lee, H. J. A.; Fry, A. A.; Kim, J. B. A.; Roedel, C. A.; Mishra, R. A.; Pelka, A. F.; Kraus, D. F.; Barbrel, B. G.; Döppner, T. H.; Glenzer, S. H. A.
Abstract: We present the first spectrally resolved measurements of x-rays scattered from cryogenic hydrogenjets in the single photon counting limit. The 120 Hz capabilities of the LCLS, together with a novelhydrogen jet design [J. B. Kimet al., Rev. Sci. Instrum. (these proceedings)], allow for the ability torecord a near background free spectrum. Such high-dynamic-range x-ray scattering measurementsenable a platform to study ultra-fast, laser-driven, heating dynamics of hydrogen plasmas. Thismeasurement has been achieved using two highly annealed pyrolytic graphite crystal spectrometers tospectrally resolve 5.5 keV x-rays elastically and inelastically scattered from cryogenic hydrogen andfocused on Cornell-SLAC pixel array detectors [S. Herrmannet al., Nucl. Instrum. Methods Phys.Res., Sect. A718, 550 (2013)]. Registration No. 24077 - Permalink

Phase Shift and Reflection of Spin Waves at Magnetic Domain Walls in Thin Films
Körber, L.; Wagner, K.; Lindner, J.; Fassbender, J.; Schultheiß, H.
Abstract: Investigating the transmission of magneto-static surface waves through 180° Néel walls using micromagnetic simulations.
Keywords: spin waves, phase shift, micromagnetic simulation, reflection, domain wall
  • Poster
    Spin, Waves and Interactions, 31.08.-02.09.2016, Greifswald, Deutschland
Registration No. 24076 - Permalink

Magnetic domain walls as reconfigurable spin-wave nano-channels
Wagner, K.; Kakay, A.; Schultheiß, K.; Henschke, A.; Sebastian, T.; Lindner, J.; Fassbender, J.; Schultheiß, H.
Abstract: Use of magnetic domains as nano channels for spin wave propagation
  • Lecture (Conference)
    Spin, Waves and Interaction, 31.08.-02.09.2016, Greifswald, Deutschland
Registration No. 24075 - Permalink

Modern Measurement Methods of Brillouin Light Scattering
Osten, J.; Schultheiß, H.; Wagner, K.; Körber, L.; Wehrmann, F.; Hula, T.
Abstract: Explanation of different measurement methods of BLS: phase, time, wavevector, frequency and spacial resolved
Keywords: BLS
  • Poster
    Spins, Waves and Interactions, 31.08.-02.09.2016, Greifswald, Deutschland
Registration No. 24074 - Permalink

An Electrochemical and Photoelectron Spectroscopy Study of a Low Temperature Liquid Metal Battery Based on an Ionic Liquid Electrolyte
Lalau, C.-C.; Dimitrova, A.; Himmerlich, M.; Ispas, A.; Weier, T.; Krischok, S.; Bund, A.
Abstract: We report the design of a low-temperature liquid metal battery (LMB). Li and Ga as the negative and positive electrode, respectively, are used in combination with a room temperature ionic liquid as an electrolyte. 1 mol/L lithium bis(trifluoromethylsulfonyl)imide (Li[TFSI]) in 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl)imide ([BMP][TFSI]) is chosen as electrolyte. The battery operates at 220 °C which is a relatively low temperature for a LMB and shows good electrochemical performance at low current density. The cells were cycled for more than 600 h and achieved a round-trip Coulombic efficiency close to 100% and an average voltage efficiency of 66% resulting in an overall energy efficiency of 65%. At higher current densities, however, the system showed up to 75% irreversible capacity loss after three cycles. To understand the origin of this strong deterioration, we characterized the surface and the bulk properties of the Ga cathode using X-ray Photoelectron Spectroscopy. Especially at higher current densities a decomposition of the electrolyte was found. The chemical changes that occurred and the elemental distribution at the Ga cathode are analyzed based on XPS measurements at different stages of the battery charge/discharge cycling.
Keywords: liquid metal battery, ionic liquids Registration No. 24072 - Permalink

Resistive switching behavior in single crystal SrTiO3 annealed by laser
Pan, X.; Shuai, Y.; Wu, C.; Luo, W.; Sun, X.; Yuan, Y.; Zhou, S.; Ou, X.; Zhang, W.
Abstract: Single crystal SrTiO3 (STO) wafers were annealed by XeCl laser (λ = 308 nm) with different fluences of 0.4 J/cm2, 0.6 J/cm2 and 0.8 J/cm2, respectively. Ti/Pt electrodes were sputtered on the surface of STO wafer to form co-planar capacitor-like structures of Pt/Ti/STO/Ti/Pt. Current-Voltage measurements show that the leakage current is enhanced by increasing laser fluence. Resistive switching behavior is only observed in the sample annealed by laser with relatively high fluence after an electro-forming process. The X-ray photoelectron spectroscopy measurements indicate that the amount of oxygen vacancies increases with the increase of laser fluence. This work indicates resistive switching appears when enough oxygen vacancies are generated by the laser, which form conductive filaments under an external electric field.
Keywords: Resistive switching; Laser annealing; SrTiO3 Registration No. 24069 - Permalink

Direct measurement of low-energy 22Ne(p,γ)23Na resonances
Depalo, R.; Cavanna, F.; Aliotta, M.; Anders, M.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Ciani, G. F.; Corvisiero, P.; Davinson, T.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Piatti, D.; Prati, P.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.
Abstract: Background: The 22Ne(p,γ)23Na reaction is the most uncertain process in the neon-sodium cycle of hydrogen burning. At temperatures relevant for nucleosynthesis in asymptotic giant branch stars and classical novae, its uncertainty is mainly due to a large number of predicted but hitherto unobserved resonances at low energy.
Purpose: A new direct study of low energy 22Ne(p,γ)23Na resonances has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA), in the Gran Sasso National Laboratory, Italy.
Method: The proton capture on 22Ne was investigated in direct kinematics, delivering an intense proton beam to a 22Ne gas target. γ rays were detected with two high-purity germanium detectors enclosed in a copper and lead shielding suppressing environmental radioactivity.
Results: Three resonances at 156.2 keV (ωγ = (1.48 ± 0.10) · 10−7 eV), 189.5 keV (ωγ = (1.87±0.06)·10−6 eV) and 259.7 keV (ωγ = (6.89±0.16)·10−6 eV) proton beam energy, respec- tively, have been observed for the first time. For the levels at Ex = 8943.5, 8975.3, and 9042.4 keV excitation energy corresponding to the new resonances, the γ-decay branching ratios have been precisely measured. Three additional, tentative resonances at 71, 105 and 215 keV proton beam energy, respectively, were not observed here. For the strengths of these resonances, experimental upper limits have been derived that are significantly more stringent than the upper limits reported in the literature.
Conclusions: Based on the present experimental data and also previous literature data, an updated thermonuclear reaction rate is provided in tabular and parametric form. The new reaction rate is significantly higher than previous evaluations at temperatures of 0.08-0.3 GK.
Registration No. 24067 - Permalink

Scalable, multi-GPU photon tracing for the interaction of X-Rays with solid density plasmas
Grund, A.; Huebl, A.ORC; Kluge, T.; Widera, R.; Fortmann-Grote, C.; Bussmann, M.
Abstract: We present the scientific workflow using our performance portable, open source, 3D3V particle-in-cell (PIC) code PIConGPU and its X-Ray tracing prototype ParaTAXIS to model the interaction of XFEL type X-Rays with solid density plasmas. With an open and modern software environment, our infrastructure is already suited for the largest available supercomputers today and key numerical and methodical challenges have been solved towards first simulations of upcoming pump-probe experiments at the European XFEL.
Keywords: EUCALL, SIMEX, XFEL, GPU, photon beamline, ParaTAXIS, PIConGPU, x-ray scattering
  • Poster
    EUCALL Annual Meeting 2016, 31.08.-02.09.2016, Dresden, Deutschland
Registration No. 24065 - Permalink

Plasmas, Photons, Open Standards: PIConGPU meets simex_platform through openPMD
Huebl, A.ORC; Kluge, T.; Grund, A.; Fortmann-Grote, C.; Widera, R.; Bussmann, M.
Abstract: Technische Aspekte des Datenaustauschs SIMEX XFEL Wavefronts -> XRT/PIConGPU via openPMD, die wir zusammen erstellt haben und aktueller Stand der Photon-Plasma Streuung der dann anschließenden HPC Simulation auf unserer Seite.

- SIMEX Platform: Short intro functional parts, PIConGPU = interaction
- SIMEX Platform: Wavefronts to Photon Picture
- openPMD: why, what, how
- status XRT (PIConGPU photon scattering code prototype)
- typical HPC size of a PIConGPU simulation for dense targets
- continuous integration (simex platform & PIConGPU)
- maybe some future ideas such as successful docker-ization of
PIConGPU for our "relatively fixed" beamline

  • Lecture (Conference)
    EUCALL Annual Meeting, 31.08.-02.09.2016, Dresden, Deutschland
Registration No. 24064 - Permalink

Induced conductivity in sol-gel ZnO films by passivation or elimination of Zn vacancies
Winarski, D. J.; Anwand, W.; Wagner, A.; Saadatkia, P.; Selim, F. A.; Allen, M.; Wenner, B.; Leedy, K.; Allen, J.; Tetlak, S.; Look, D. C.
Abstract: Undoped and Ga- and Al- doped ZnO films were synthesized using sol-gel and spin coating methods and characterized by X-ray diffraction, high-resolution scanning electron microscopy (SEM), optical spectroscopy and Hall-effect measurements. SEM measurements reveal an average grain size of 20 nm and distinct individual layer structure. Measurable conductivity was not detected in the unprocessed films; however, annealing in hydrogen or zinc environment induced significant conductivity (~10^-2 Ohm cm) in most films. Positron annihilation spectroscopy measurements provided strong evidence that the significant enhancement in conductivity was due to hydrogen passivation of Zn vacancy related defects or elimination of Zn vacancies by Zn interstitials which suppress their role as deep acceptors. Hydrogen passivation of cation vacancies is shown to play an important role in tuning the electrical conductivity of ZnO, similar to its role in passivation of defects at the Si/SiO2 interface that has been essential for the successful development of complementary metal–oxide–semiconductor (CMOS) devices. By comparison with hydrogen effect on other oxides, we suggest that hydrogen may play a universal role in oxides passivating cation vacancies and modifying their electronic properties.
Keywords: ZnO conductivity sol-gel hydrogen passivation defects positron annihilation


Registration No. 24063 - Permalink

Magnetic functionalities for flexible interactive electronics
Makarov, D.
Abstract: The flourishing and eagerness of portable consumer electronics necessitates functional elements to be lightweight, flexible, and even wearable [1,2]. Next generation flexible appliances aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems. Such devices fulfill the needs of soft robotics [3], functional medical implants [4] as well as epidermal [5], imperceptible [6] and transient [7] electronics. Key building blocks of navigation and position tracking devices are the magnetic field sensors.
We developed the technology platform allowing us to fabricate high-performance shapeable, namely, flexible [8-10], printable [11-13], stretchable [14-16] and even imperceptible [17] magnetic sensorics. The technology relies on smart combination of thin inorganic functional elements prepared directly on flexible or elastomeric supports. The unique mechanical properties open up new application potentials for smart skins, allowing to equip the recipient with a “sixth sense” providing new experiences in sensing and manipulating the objects of the surrounding us physical as well as digital world [10,17].
Combining large-area printable and flexible electronics paves the way towards commercializing the active intelligent packaging, post cards, books or promotional materials that communicate with the environment and provide the respond to the customer. Realization of this vision requires fabrication of printable electronic components that are flexible and can change their properties in the field of a permanent magnet [12]. For this concept, we fabricated high performance magnetic field sensors relying on the giant magnetoresistive (GMR) effect, which are printed at pre-defined locations on flexible circuitry and remain fully operational over a temperature range from -10°C up to +95°C, well beyond the requirements for consumer electronics [13]. Our work potentially enables commercial use of high performance magneto-sensitive elements in conventional printable electronic industry, which, although highly demanded, had not yet been possible.
In this talk, I will review the recent advances in the field of shapeable magnetic sensorics and emergent applications of this novel technology.

Keywords: flexible electronics, magnetic field sensorics
  • Invited lecture (Conferences)
    Special seminar, Institute of Physics, Johannes Gutenberg-Universität Mainz, 29.08.2016, Mainz, Germany
Registration No. 24062 - Permalink

Evidence of trivalent Am substitution into U3O8
Caisso, M.; Roussel, P.; Den Auwer, C.; Picart, S.; Hennig, C.; Scheinost, A. C.; Delahaye, T.; Ayral, A.
Abstract: U3O8 is considered to be the most stable phase for uranium oxide. Its structural properties must be accurately understood in order to foresee and manage aspects such as its leaching behavior when spent nuclear fuel is stored in an oxidative environment. Moreover, as fuel irradiation causes the formation of fission products and activation products such as plutonium and minor actinides, it is probable that U3O8 will be mixed with other chemical elements under real conditions of oxidation. The storage issue can be extended to americium transmutation, where the irradiated compounds are mixed oxides composed of uranium and americium. This study thus focused on determining the structural properties of a solid solution containing uranium and trivalent americium (U/Am ratio = 90/10), and synthetized so as to obtain conventional U3O8 oxide. This paper presents the possibility of combining trivalent americium with uranium in a U3O8 mixed oxide for the first time, despite the high valence and atomic ratio differences, and proposes novel structural arrangements. XRD measurements reveal americium substitution in U3O8 uranium cationic sites, leading to phase transformation into a U3O8 high temperature structure and general lattice swelling. XANES and EXAFS experiments highlight an excess of U+VI organized in uranyl units as the main consequence of accommodation.
Keywords: americium transmutation U3O8 Registration No. 24061 - Permalink

In-situ X-ray observations of dendritic solidification under the influence of natural and forced convection
Eckert, S.; Shevchenko, N.; Kepplinger, O.; Sokolova, O.
Abstract: The directional solidification of Ga–25wt%In alloys within a Hele-Shaw cell was investigated by means of X-ray radioscopy. This diagnostic technique offers a visual access to opaque metal alloys and enables a basic, intuitional understanding of the complex interplay between melt flow and dendritic growth. Natural convection occurs during a bottom up solidification because lighter solute is rejected at the solid-liquid interface leading to an unstable density stratification. Forced convection was produced by a rotating wheel with two parallel disks containing at their inner sides a set of permanent NdFeB magnets with alternating polarization. The direction of forced melt flow is almost horizontal at the solidification front whereas local flow velocities in the range between 0.1 and 1.0 mm/s were achieved by controlling the rotation speed of the magnetic wheel.
Melt flow induces various effects on the grain morphology primarily caused by the convective transport of solute. Our observations show a facilitation of the growth of primary trunks or lateral branches, suppression of side branching, dendrite remelting and fragmentation. The manifestation of all phenomena depends on the dendrite orientation, local direction and intensity of the flow.
The forced flow eliminates the solutal plumes and damps the local fluctuations of solute concentration. It provokes a preferential growth of the secondary arms at the upstream side of the primary dendrite arms, whereas the high solute concentration at the downstream side of the dendrites can inhibit the formation of secondary branches completely. Moreover, the flow changes the inclination angle of the dendrites and the angle between primary trunks and secondary arms.

Keywords: solidification, melt flow, dendritic growth, fragmentation, segregation
  • Invited lecture (Conferences)
    16th International Conference on Liquid and Amorphous Metals (LAM-16), 05.-09.09.2016, Bonn-Bad Godesberg, Deutschland
Registration No. 24060 - Permalink

Reactive transport modelling based on velocity fields obtained on drill core scale
Lippmann-Pipke, J.; Karimzadeh, L.; Blanc, P.; Eichelbaum, S.; Schymura, S.; Rogóż, T.; Frühwirt, K.; Kulenkampff, J.
Abstract: The objective of the EU project BioMOre is the development of new technological concepts for in situ recovering metals from deep European Kupferschiefer deposits using controlled stimulation of pre-existing fractures in combination with in-situ bioleaching. Considerable parts of the project are leaching experiments on lab scale and on small field scale at a selected location in an existing copper mine, as well as the related reactive transport odelling tasks including the required backcoupling from chemical reactions on the hydrodynamics as well as the upscaling. These tasks shall assist in the optimization of the bio-leaching efficiency, stimulating processes, as well as the environmental impact and sustainability assessment. Here we introduce our most recent technical advancement. It allows us to accomplish two tasks in one line of action: The extraction of effective hydrodynamic parameters in 3D for downstram modelling, and the upscaling from molecular process observations to reactive transport simulations on drill core scale.
For more than a decade a spatiotemporal visualization tool for transport process observations in dense material by means of PET (positron emission tomography) was developed [1-5]. Such quantitative GeoPET images are xceptionally sensitive to displacements of pico molar tracer quantities detected within 1 mm grids on laboratory/drill core scale. Now we reached a strategic milestone: A custom made image analysis algorithm is capable of quantitatively extracting velocity and porosity fields from such GeoPET image time series, even if the 4D image information includes discontinuous flow patterns (due to bottle neck effect related detection limits) and localized image artifacts. We present our approach with the aid of a) the data set with which the algorithm was validated, and b) provide an outlook for its application in the context of this EU project: the bio-leaching of Kupferschiefer.
From an observed fluid flow process in a dense core material by means of GeoPET (Fig. 1 left) the effective porosity and velocity field is extracted by our image analyis algorithm and this data is used in a forward numerical transport simulation and compared with the original fluid flow process (Fig. 1 right). Next steps will be the evaluation of non-reactive flow process observations in fractured calciferous sandstone from the Kupferschiefer ore deposit (Fig. 2), and the respective porosity and velocity field extraction for 3D reactive transport modelling in fracture and porous matrix by means of iCP [6] - an interface coupling the finite element based code COMSOL Multiphysics® with the geochemical code PhreeqC.
  • Lecture (Conference)
    IMWA 2016 - Annual Conference of the International Mine Water Association, 14.07.2016, Leipzig, Germany
  • Contribution to proceedings
    IMWA 2016 - Annual Conference of the International Mine Water Association, 14.07.2016, Leipzig, Germany
    Mining Meets Water – Conflicts and Solutions, Freiberg: Medienzentrum of TU Bergakademie Freiberg, 978-3-86012-533-5, 1219-1220
Registration No. 24059 - Permalink

Analysis of the characteristics of hot particles related to environmental fate and interaction with living organisms
Johansen, M. P.; Child, D. P.; Collins, R. N.; Hotchkis, M. A. C.; Howell, N. A.; Payne, T. E.; Mokhber-Shahin, L.; Ikeda-Ohno, A.
Abstract: The radiological residues at the former British weapons testing sites at Maralinga, Emu and the Monte Bello Islands often occur in particulate form (so called hot particles). Large numbers of these particles were emitted from nuclear and non-nuclear tests. For example each square meter in a plume that extends for tens of kilometres at the Taranaki site (Maralinga) can contain more than 3000 readily identifiable particles. The physical and chemical characteristics of these particles affect their mobility and availability for uptake into living organisms. When they contain long-lived radionuclides (e.g. 239Pu) these particles may slowly weather, and thus provide a persistent source of ionic forms, or smaller particles, for many thousands of years.

Here we present a status on a range of methods being used at ANSTO to evaluate the physical and chemical characteristics of particles gathered from Australian sites. Methods include gamma spectrometry, autoradiography, high sensitivity Accelerator Mass Spectrometry analysis (AMS), leaching studies, and synchrotron-based X-ray fluorescence microscopy/spectroscopy. We focus on some of the practical issues involved when gathering and working with hot particles, as well as challenges in determining speciation and its influence on radioecological outcomes. We discuss data gaps and recommendations for current and future use of analysis methods in radioecological studies in Australia and the wider international community.

Keywords: Actinides, plutonium, environmental fate, bioavailability, nuclear weapons tests, Australia
  • Lecture (Conference)
    The South Pacific Environmental Radioactivity Association (SPERA) Conference 2016, 07.09.2016, Sanur, Indonesia
Registration No. 24058 - Permalink

Improved direct measurement of the 64.5 keV resonance strength in the 17O(p,alpha)14N reaction at LUNA
Bruno, C. G.; Scott, D. A.; Aliotta, M.; Formicola, A.; Best, A.; Boeltzig, A.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Cavanna, F.; Ciani, G. F.; Corvisiero, P.; Davinson, T.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; GyÜrky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Piatti, D.; Prati, P.; Somorjai, E.; Straniero, O.; Strieder, F.; SzÜcs, T.; Takács, M. P.; Trezzi, D.
Abstract: The 17O(p,α)14N reaction plays a key role in various astrophysical scenarios, from asymptotic giant branch stars to classical novae. It affects the synthesis of rare isotopes such as 17O and 18F, which can provide constraints on astrophysical models. A new direct determination of the ER = 64.5 keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics accelerator has led to the most accurate value to date, ωγ = 10.0 ± 1.4stat ± 0.7syst neV, thanks to a significant background reduction underground. The (bare) proton partial width of the corresponding state at Ex = 5672 keV in 18F is Γp = 35±5stat ±3syst neV. This width is about a factor of 2 higher than previously estimated thus leading to a factor of 2 increase in the 17O(p,α)14N reaction rate at astrophysical temperatures relevant to shell hydrogen-burning in red giant and asymptotic giant branch stars. The new rate implies lower 17O/16O ratios, with important implications on the interpretation of astrophysical observables from these stars. Registration No. 24057 - Permalink

A mineral liberation study of grain boundary fracture based on measurements of the surface exposure after milling
Leißner, T.ORC; Hoang, D.; Rudolph, M.ORC; Heinig, T.; Bachmann, K.; Gutzmer, J.; Schubert, H.; Peuker, U. A.
Abstract: Minerals can be liberated by random fracture of particles into smaller fragments or by detachment along phase boundaries. These two mechanisms represent borderline cases. When ores get comminuted the liberation of minerals is achieved to some extent by both mechanisms. This article describes a method to determine the extent of transgranular and intergranular fracture based on 2-dimensional analysis of surface exposure of minerals.
The approach uses the unbiased surface information like of phase specific surface area (PSSA), phase specific free surface (PSFS) and phase specific locked surface (PSLS) of minerals and their change with comminution. The parameters are discussed related to the normalized grain size, which is the ratio of mineral grain size in the product to mineral grain size in the unbroken material. Finally, the amount of transgranular and intergranular fracture on surface exposure can be calculated using the phase specific surface parameters.
A sedimentary rock (apatite ore), an igneous rock (nepheline-syenite) and an artificial material (copper slags) were ground to different fineness. Based on the mineral liberation analysis (MLA) of feed and products, the extent of phase boundary fracture on the surface exposure of the minerals is studied.

Keywords: Mineral liberation Analysis; preferential breakage; transgranular fracture; intergranular fracture; random fracture; grain boundary fracture Registration No. 24056 - Permalink

Tuning the fabrication of nanostructures by low-energy highly charged ions
El-Said, A. S.; Wilhelm, R. A.ORC; Heller, R.; Sorokin, M.; Facsko, S.; Aumayr, F.
Abstract: Slow highly charged ions were utilized recently for the creation of monotype surface nanostructures (craters, calderas or hillocks) in different materials. In the present study, we report on the ability of slow highly charged xenon ions (129XeQ+) to form three different types of nanostructures on LiF (100) surface. By increasing the charge state from Q = 15 to Q = 36, the shape of the impact induced nanostructures changes from craters to hillocks crossing an intermediate stage of caldera structures. The dimensional analysis of the nanostructures reveals an increase of the height up to 1.5 nm as a function of the potential energy of the incident ions. Based on the evolution of both the geometry and size of the created nanostructures, defect-mediated desorption and the development of a thermal spike are utilized as creation mechanisms of the nanostructures at low and high charge states, respectively. Registration No. 24053 - Permalink

ZnO Luminescence and scintillation studied via photoexcitation, X-ray excitation, and gamma-induced positron spectroscopy
Ji, J.; Colosimo, A. M.; Anwand, W.; Boatner, L. A.; Wagner, A.; Stepanov, P. S.; Trinh, T. T.; Liedke, M. O.; Krause-Rehberg, R.; Cowan, T. E.; Selim, F. A.
Abstract: The luminescence and scintillation properties of ZnO single crystals were studied by photoluminescence and X-ray-induced luminescence (XRIL) techniques. XRIL allowed a direct comparison to be made between the near-band emission (NBE) and trap emissions providing insight into the carrier recombination efficiency in the ZnO crystals. It also provided bulk luminescence measurements that were not affected by surface states. The origin of a green emission, the dominant trap emission in ZnO, was then investigated by gamma-induced positron spectroscopy (GIPS) - a unique defect spectroscopy method that enables positron lifetime measurements to be made for a sample without contributions from positron annihilation in the source materials. The measurements showed a single positron decay curve with a 175 ps lifetime component that was attributed to Zn vacancies passivated by hydrogen. Both oxygen vacancies and hydrogen-decorated Zn vacancies were suggested to contribute to the green emission. By combining scintillation measurements with XRIL, the fast scintillation in ZnO crystals was found to be strongly correlated with the ratio between the defect luminescence and NBE. This study reports the first application of GIPS to semiconductors, and it reveals the great benefits of the XRIL technique for the study of emission and scintillation properties of materials.
Keywords: luminescence scintillation ZnO photoluminescence X-ray-induced luminescence XRIL gamma-induced positron spectroscopy GIPS defect spectroscopy


Registration No. 24051 - Permalink

Activation cross sections of longer-lived radionuclides produced in germanium by alpha particle irradiation
Takács, S.; Takács, M. P.; Ditrói, F.; Aikawa, M.; Haba, H.; Komori, Y.
Abstract: The cross sections of alpha particles induced nuclear reactions on natural germanium were investigated by using the standard stacked foil target technique, the activation method and high resolution gamma spectrometry. Targets with thickness of about 1 μm were prepared from natural Ge by vacuum evaporation onto 25 μm thick polyimide (Kapton) backing foils. Stacks were composed of Kapton-Ge-Ge-Kapton sandwich target foils and additional titanium monitor foils with nominal thickness of 11 μm to monitor the beam parameters using the natTi(α,x)51Cr reaction. The irradiations were done with Eα = 20.7 and Eα = 51.25 MeV, Iα = 50 nA alpha particle beams for about 1 h. Direct or cumulative activation cross sections were determined for production of the 72,73,75Se, 71,72,74,76,78As, and 69Ge radionuclides. The obtained experimental cross sections were compared to the results of theoretical calculations taken from the TENDL data library based on the TALYS computer code. A comparison was made with available experimental data measured earlier. Thick target yields were deduced from the experimental cross sections and compared with the data published before.
Keywords: Alpha particle irradiation; Natural germanium target; Cross sections; 72,73,75Se, 71,72,74,76,78As and 69Ge excitation functions; TENDL comparison Registration No. 24042 - Permalink

Thermodynamics Behavior of Germanium During Equilibrium Reactions between FeOx-CaO-SiO2-MgO Slag and Molten Copper
Reuter, M. A.; Shuva, M. A. H.; Rhamdhani, M. A.; Brooks, G. A.; Masood, S.
Abstract: The distribution ratio of germanium (Ge), (Formula presented.) during equilibrium reactions between magnesia-saturated FeOx-CaO-SiO2 (FCS) slag and molten copper has been measured under oxygen partial pressures from 10−10 to 10−7 atm and at temperatures 1473 to 1623 K (1200 to 1350 °C). It was observed that the Ge distribution ratio increases with increasing oxygen partial pressure, and with decreasing temperature. It was also observed that the distribution ratio is strongly dependent on slag basicity. The distribution ratio was observed to increase with increasing optical basicity. At fixed CaO concentration in the slag, the distribution ratio was found to increase with increasing Fe/SiO2 ratio, tending to a plateau at (Formula presented.) = 0.8. This behavior is consistent with the assessment of ionic bond fraction carried out in this study, and suggested the acidic nature of germanium oxide (GeO2) in the slag system studied. The characterisation results of the quenched slag suggested that Ge is present in the FeOx-CaO-SiO2-MgO slag predominantly as GeO2. At 1573 K (1300 °C) and (Formula presented.) = 10−8 atm, the activity coefficient of GeO2 in the slag was calculated to be in the range of 0.24 to 1.50. The results from the current study suggested that less-basic slag, high operating temperature, and low oxygen partial pressure promote a low Ge distribution ratio. These conditions are desired for maximizing Ge recovery, for example, during pyrometallurgical processing of Ge-containing e-waste through secondary copper smelting. Overall, the thermodynamics data generated from this study can be used for process modeling purposes for improving recovery of Ge in primary and secondary copper smelting processes.
Keywords: Engineering controlled terms: Copper; Germanium; Germanium oxides; Iron oxides; Magnesia; Oxygen; Partial pressure; Pyrometallurgy; Secondary recovery; Slags; Temperature; Thermodynamics Distribution ratio; Equilibrium reactions; High operating temperature; Low oxygen partial pressure; Oxygen partial pressure; Pyrometallurgical processing; Secondary copper smelting; Thermodynamics data Registration No. 24040 - Permalink

Hydrodynamic modeling of a pure-glue initial scenario in high-energy hadron and heavy-ion collisions
Vovchenko, V.; Pang, L.-G.; Niemi, H.; Karpenko, I. A.; Gorenstein, M. I.; Satarov, L. M.; Mishustin, I. N.; Kämpfer, B.; Stoecker, H.
Abstract: Partonic matter produced in the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, and quarks and antiquarks are produced at later times. The comparable hydrodynamic simulations of heavy-ion collisions for (2+1)-flavor and Yang-Mills equations of state performed by using three different hydrodynamic codes are presented. Assuming slow chemical equilibration of quarks, the spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy of √sNN=2.76 TeV. It is shown that a suppression of quarks at early times leads to a significant reduction of the yield of the thermal dileptons, but only to a rather modest suppression of the pT-distribution of direct photons. It is demonstrated that an enhancement of photon and dilepton elliptic flows might serve as a promising signature of the pure-glue initial state. Calculations based on Bjorken hydrodynamics suggest that collisions of small systems at intermediate energies available at RHIC or future FAIR facilities may show stronger effects associated with initial pure gluodynamic evolution.


Registration No. 24039 - Permalink

Vacuum particle-antiparticle creation in strong fields as a field induced phase transition
Smolyansky, S. A.; Panferov, A. D.; Blaschke, D. B.; Juchnowski, L.; Kämpfer, B.; Otto, A.
Abstract: The features of vacuum particle creation in an external classical field are studied for simplest external field models in 3+1 dimensional QED. The investigation is based on a kinetic equation that is a nonperturbative consequence of the fundamental equations of motion of QED. The observed features of the evolution of the system apply on the qualitative level also for systems of other nature and therefore are rather general. Examples from cosmology and condensed matter physics illustrate this statement. The common basis for the description of these systems are kinetic equations for vacuum particle creation belonging to the class of integro-differential equations of non-Markovian type with fastly oscillating kernel. This allows to characterize processes of this type as belonging to the class of field induced phase transitions.


Registration No. 24038 - Permalink

Holographically emulating sequential versus instantaneous disappearance of vector mesons in a hot environment
Zöllner, R.; Kämpfer, B.
Abstract: Descent extensions of the soft-wall model are used to accommodate two variants of Regge trajectories of vector meson excitations. At non-zero temperatures, various options for either sequential or instantaneous disappearance of vector mesons as normalisable modes are found, thus emulating deconfinement at a certain temperature in the order of the (pseudo-) critical temperature of QCD. The crucial role of the blackness function, which steers the thermodynamic properties of the considered system, is highlighted.


Registration No. 24037 - Permalink

Magnetic properties and giant reversible magnetocaloric effect in the GdCoC2 compound
Meng, L.; Xu, C.; Yuan, Y.; Qi, Y.; Zhou, S.; Li, L.
Abstract: The crystal structure, magnetic properties and magnetocaloric effect (MCE) of GdCoC2 have been studied. The compound crystallizes in an orthorhombic CeNiC2-type structure which belongs to Amm2 space group. A giant reversible MCE is observed in GdCoC2 accompanied by a second-order paramagnetic to ferromagnetic (PM-FM) phase transition around the Curie temperature ~15 K. For the magnetic field change of 0-5 T, the maximum values of the magnetic entropy change (-ΔSMmax), relative cooling power (RCP), and refrigerant capacity (RC) are 28.4J/kg K, 566 J/kg and 369 J/kg, respectively. The present results indicate that the GdCoC2 compound is a promising candidate for low temperature magnetic refrigeration.
Keywords: GdCoC2 compound; magnetocaloric effect; magnetic properties; magnetic refrigeration. Registration No. 24034 - Permalink

Raman scattering at terahertz frequencies enabled by an infrared free electron laser
Pavlov, S.; Dessmann, N.; Zhukavin, R. K.; Shastin, V.; Hübers, H.-W.; Pohl, A.; Redlich, B.; van der Meer, A. F. G.; Winnerl, S.; Schneider, H.; Ortega, J.-M.; Prazeres, R.; Abrosimov, N. V.
Abstract: In the last decade the use of infrared free electron laser facilities enabled observation of inelastic light (Raman) scattering in THz frequency range. Raman-active intracenter donor transitions in silicon fall into the THz range and serve as outgoing resonances in electronic Stokes scattering. At photon fluxes above 1E24 photon/cm2/s donor-related Raman stimulated emission occurs in the range 4.2-6.5 THz from natural and isotopically enriched silicon crystals with various dopants while the free electron laser wavelength was varied between 18 and 41 mkm (7.5-16.5 THz). Study of dynamics of the observed emission shows a transient picosecond-micropulse mode that indicates on significantly larger Raman gain realized in THz Raman silicon lasers. This research has been partly supported by the EC CALIPSO project for the Transnational access to the European FELs and Synchrotron facilities as well as joint German-Russian program "Research on technological advances of radiation sources of photons and neutrons based on accelerators and neutron sources in cooperation with research organizations and universities of the Federal Republic of Germany" (InTerFEL project, BMBF No. 05K2014 and the Russian Ministry of Science and Education (No. RFMEFl61614X0008).
Keywords: terahertz, infrared, free-electron laser, Raman scattering
  • Lecture (Conference)
    2016 International Conference "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2016), 04.-07.07.2016, Novosibirsk, Russia
Registration No. 24033 - Permalink

Exciton dynamics in semiconductor quantum wells and single quantum dots studied with a THz free-electron laser
Schneider, H.; Stephan, D.; Zybell, S.; Winnerl, S.; Bhattacharyya, J.; Eßer, F.; Helm, M.
Abstract: Excitons in III-V semiconductors are Coulomb-bound electron-hole pairs which are analogous to two-dimensional hydrogen atoms with terahertz (THz) binding energies. In semiconductor quantum wells (QW), confinement into the plane of the QW gives rise to essentially two-dimensional excitons, thus giving rise to a different symmetry and higher binding energy. In quantum dots (QD), three-dimensional confinement leads to discrete electronic and excitonic states, such that the system becomes similar to a trapped atom.
Using intense, spectrally narrow terahertz (THz) pulses from the free-electron laser (FEL) facility FELBE in Dresden, Germany, we have investigated the population dynamics between exciton states in III-V QWs and single QDs. To this end, carriers are optically injected by picosecond near-infrared optical pulses, which leads to a population of the lowest excitonic level. Using narrowband THz pulses provided by the free-electron laser at HZDR, excitons are resonantly excited into higher levels. Time-dependent photoluminescence (TDPL) measurements based on a streak camera system and on time-correlated photon counting, respectively, then allow us to study the transient population of dipole-allowed higher excitonic levels and to access the relaxation dynamics of these quasi-particles.
In QWs, the most prominent transition is from the 1s ground state into the 2p excited state (using hydrogen notation). While the 2p state is "optically dark", rapid scattering from the 2p into the 2s state occurs. TDPL originating from the 1s and 2s exciton states thus provides a unique signature which allows us to explore the relaxation dynamics involving 1s, 2s, and 2p excitons. Now turning to QDs, single QDs rather than QD ensembles should be investigated in order to prevent strong inhomogeneous broadening. We have therefore developed a micro-TDPL setup with a probe volume significantly below 1 µm^3 and high quantum efficiency to become sensitive to one single QD. In particular, we investigate the dynamics of the s-to-p inter-sublevel transition, which occurs in the range 13-20 meV for the QDs under study. Resonant excitation with a THz pulse, which is applied at about 0.7 ns time delay after interband excitation, causes an instantaneous reduction of the ground state TDPL. The signal recovers within about 100 ps towards a value which depends on the near-infrared excitation energy. In particular, qualitatively different behavior has been observed and analyzed using a phenomenological rate equation for interband excitation of the GaAs matrix, the InGaAs wetting layer, and quasi-resonant excitation of the QD.
Acknowledgements: We thank L. Schneebeli, C.N. Böttge, M. Kira, and S.W. Koch (Marburg, Germany) for fruitful discussions and collaboration.

Keywords: quantum well, exciton, terahertz, free-electron laser
  • Invited lecture (Conferences)
    International Workshop on "Terahertz Science, Nanotechnologies and Applications", 16.-22.07.2016, Erice, Italien
Registration No. 24032 - Permalink

Semiconductor spectroscopy with infrared and THz free-electron lasers
Schneider, H.
Abstract: This talk reviews some recent spectroscopic studies on semiconductor structures carried out using the mid-infrared and terahertz (THz) free-electron laser facility FELBE in Dresden, Germany. Its intense, nearly transform-limited picosecond pulses, which can also be combined with synchronous pico- or femtosecond pulses from near-infared tabletop lasers, provide unique research opportunities to advance our knowledge on the interaction of intense mid-infrared and THz fields with materials and devices.
Keywords: Semiconductor spectroscopy, infrared, terahertz, free-electron laser
  • Invited lecture (Conferences)
    2016 International Conference on "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2016), 04.-07.07.2016, Novosibirsk, Russia
Registration No. 24031 - Permalink

Overcoming the diffraction limit with a GaAs-based plasmonic superlens
Fehrenbacher, M.; Winnerl, S.; Döring, J.; Kehr, S. C.; Eng, L. M.; Huo, Y. H.; Schmidt, O. G.; Yao, K.; Liu, Y.; Helm, M.; Schneider, H.
Abstract: We report a semiconductor-based superlens for sub-diffraction-limited near-field imaging at mid-infrared wavelengths. The superlens is based on a sequence of intrinsic and doped GaAs layers. Resonant enhancement of evanescent waves is accomplished here by exploiting the Drude response of a highly doped n-GaAs layer. Operation as a near-field superlens is validated by utilizing an aperture-less scattering near-field optical microscope (s-SNOM), which allows us to probe the image plane of the superlens with sub-wavelength resolution.
In our experiments, gold stripes underneath the GaAs superlens are imaged by the s-SNOM. The s-SNOM comprises an atomic-force microscope (AFM), the tip of which is illuminated by mid-infrared radiation from a free-electron laser (FEL). Imaging results reveal sub-wavelength resolution better than λ/6 at the resonant wavelength of λ = 22.0 µm. In excellent accordance with the Drude-Lorentz model, the resonant wavelength for superlensing can easily be adjusted by changing the doping concentration. Our approach thus reveals a simple and versatile superlens implementation for infrared nanospectroscopy. Detector issues specific for s-SNOM will also be addressed.
[1] M. Fehrenbacher, S. Winnerl, H. Schneider, J. Döring, S. C. Kehr, L. M. Eng, Y. Huo, O. G. Schmidt, K. Yao, Y. Liu, M. Helm, Nano Lett. 15, 1057 (2015)

Keywords: Scattering near-field optical microscopy, s-snom, superlens, GaAs, sub-diffraction-limited
  • Lecture (Conference)
    Quantum Structured Infrared Photodetector International Conference (QSIP 2016), 12.-17.06.2016, Tel Aviv, Israel
Registration No. 24030 - Permalink

The South Um Mongul Cu-Mo-Au prospect in the Eastern Desert of Egypt: From a mid-Cryogenian continental arc to Ediacaran post-collisional appinite-high Ba-Sr monzogranite
Abd El-Rahman, Y.; Gutzmer, J.; Said, A.; Hofmann, M.; Gärtner, M.; Linnemann, U.
Abstract: The South Um Mongul prospect is a Cu-Mo-Au porphyry system. It is covered by porphyritic dacite and hornblende gabbro. Both units are intruded by monzogranite, which encloses xenoliths of both units. Using LA-ICP-MS U-Pb zircon method, the dacite is dated at ca. 773 ± 6.9 Ma, while the gabbro and the monzogranite are dated at 603 ± 3.5 and 558 ± 4.6 Ma, respectively. The dacite age is consistent with the mid-Cryogenian subduction-related magmatic stage and the gabbro-monzogranite age is comparable to the Ediacaran post-collisional magmatic stage during the evolution of the Arabian-Nubian Shield. The dacite is akin to high-K I-type granitoids and its primitive mantle-normalized trace element patterns show negative Nb anomalies and enrichment in LILE (large ion lithophile elements), Th and U over HFSE. These geochemical characteristics are similar to those of felsic magma formed in a subduction-related tectonic setting. The high La/Ybcn (7.2–30.9), Nb/Yb (2.63–4.41) and Th/Yb (2.07–3.04) ratios of the dacite are comparable to continental rather than oceanic arc systems. Its low Sm/Yb ratios (1.84–3.13) support the primitive nature of the crust beneath the continental arc and derivation from a garnet-free lower crustal source. The dacite has low Sr/Y ratios (5–9) and its Eu/Eu⁎ ratios range from 0.66 to 0.83. Similar to dacite, the primitive mantle-normalized trace element patterns of the post-collisional suite show a subduction-related geochemical signature. However, the gabbro is characterized by Th/Ta ratios (3.4–14.8), which are comparable with the within-plate tectonic setting. The subduction-related geochemical signature is inherited from long subduction history beneath the Arabian-Nubian Shield. Both the gabbro and monzogranite are characterized by high Ba (404–590 ppm and 936–1590 ppm, respectively) and Sr (611–708 ppm and 624–793 ppm, respectively) contents, which make them analogous to the Caledonian appinite-high Ba-Sr granite assemblage. The formation of these rocks is related to the Ediacaran lithospheric erosion accompanying slab break-off. This process induced asthenospheric upwelling, which led to partial melting of the lithosphere previously metasomatised by subducted sediments involving carbonates impregnated by hydrothermal barite. Melting of this lithosphere led to the formation of the hornblende gabbro. Underplating by the mafic magma led to melting of the lower crust and the formation of high Ba-Sr monzogranite in the area. The high Sm/Yb (2.94–4.19) and Sr/Y (52–74) ratios of the monzogranite may indicate the presence of garnet in the melted amphibolitic lower crust. The higher Sr/Y ratios, lower HFSE (high field strength elements) contents and the absence of pronounced Eu anomalies in monzogranite relative to dacite suggest the productive nature of the post-collisional magma relative to the continental arc magma in this prospect.
Keywords: Appinite; Arabian-Nubian Shield; Continental arc; High Ba-Sr granite; Neoproterozoic; Post-collisional porphyry copper Registration No. 24029 - Permalink

Dynamics of nonequilibrium electrons on neutral center states of interstitial magnesium donors in silicon
Pavlov, S. G.; Deßmann, N.; Pohl, A.; Shuman, V. B.; Portsel, L. М.; Lodygin, А. N.; Astrov, Y. A.; Winnerl, S.; Schneider, H.; Stavrias, N.; van der Meer, A. F. G.; Tsyplenkov, V. V.; Kovalesky, K. A.; Zhukavin, R. K.; Shastin, V. N.; Abrosimov, N. V.; Hübers, H.-W.
Abstract: Subnanosecond dynamics of optically excited electrons bound to excited states of neutral magnesium donor centers in silicon has been investigated. Lifetimes of nonequilibrium electrons have been derived from the decay of the differential transmission at photon energies matching the intracenter and the impurity–to–conduction band transitions. In contrast to hydrogen-like shallow donors in silicon, significantly longer lifetimes have been observed. This indicates weaker two-phonon and off-resonant interactions dominate the relaxation processes in contrast to the single-intervalley-phonon assisted impurity-phonon interactions in the case of shallow donors in silicon.
Keywords: Extrinsic semiconductors, dynamics of electrons from impurities, magnesium doping of silicon Registration No. 24025 - Permalink

Volumetrical Laser Ion Acceleration of Spherical Mass Limited Solid Density Targets
Huebl, A.; Hilz, P.; Schreiber, J.; Kluge, T.; Widera, R.; Bussmann, M.
Abstract: Invited presentation at the LMU group of Jörg Schreiber about the results of the large scale 3D3V simulations for their experiments.
Keywords: Mass Limited Target, Paul Trap, PIConGPU, Simulation, 3D3V, GPGPU, OpenSource
  • Invited lecture (Conferences)
    LMU/MPI QO Munich: Prof. Schreiber Group Meeting (Laser-driven ion acceleration), 18.-20.07.2016, München, Deutschland
Registration No. 24023 - Permalink

Test of Lorentz invariance in β decay of polarized 20Na
Sytema, A.; van den Berg, J. E.; Böll, O.; Chernowitz, D.; Dijck, E. A.; Grasdijk, J. O.; Hoekstra, S.; Jungmann, K.; Mathavan, S. C.; Meinema, C.; Mohanty, A.; Müller, S. E.; Noordmans, J. P.; Nunez Portela, M.; Onderwater, C. J. G.; Pijpker, C.; Timmermans, R. G. E.; Vos, K. K.; Willmann, L.; Wilschut, H. W.
Abstract: Background: Lorentz invariance is key in our understanding of nature, yet relatively few experiments have tested Lorentz invariance in weak interactions.

Purpose: Our goal is to obtain limits on Lorentz-invariance violation in weak interactions, in particular rotational invariance in β decay.

Method: We search for a dependence of the lifetime of 20Na nuclei on the nuclear spin direction. Such directional dependence would be evidence for Lorentz-invariance violation in weak interactions. A difference in lifetime between nuclei that are polarized in the east and west direction is searched for. This difference is maximally sensitive to the rotation of the Earth, while the sidereal dependence is free from most systematic errors.

Results: The experiment sets a limit of 2×10-4 at 90% C.L. on the amplitude of the sidereal variation of the relative lifetime differences, an improvement by a factor 15 compared to an earlier result.

Conclusions: No significant violation of Lorentz invariance is found. The result sets limits on parameters of theories describing Lorentz-invariance violation.

Keywords: Lorentz violation, beta-decay


Registration No. 24020 - Permalink

Laser proton acceleration from liquid crystal films of different thicknesses with ultra-high laser contrast
Obst, L.; Poole, P.; Metzkes, J.; Zeil, K.; Cochran, G.; Kluge, T.; Schlenvoigt, H.-P.; Kraft, S.; Prencipe, I.; Rehwald, M.; Schumacher, D.; Schramm, U.
Abstract: We present results of our experimental campaign on laser proton acceleration, in which liquid crystal film targets of tunable thickness were irradiated with plasma mirror cleaned laser pulses. The data show a significant increase in proton cut-off energy up to 25 MeV for a target thickness of 10 nm as compared to the few- micron scale reference for this target configuration yielding roughly 12 MeV.

The performance of laser based ion acceleration strongly depends on the laser temporal contrast and its effect on the target plasma scale length. Plasma mirror setups have proven to be a valuable tool to improve the temporal contrast by several orders of magnitude, reducing the intensity of pre-pulses that emanate from the laser chain and steepening the rising edge of the main laser pulse. We present recent results obtained at the Titanium Sapphire laser system Draco, delivering 30 fs long laser pulses at an intensity exceeding 10^20 W/cm^2. Our recently commissioned single plasma mirror improves the contrast by four orders of magnitude while reflecting 80% of the initial pulse energy. Its influence on the laser proton acceleration process was studied in a campaign in collaboration with the High Energy Density Physics Group of Ohio State University using their tunable liquid crystal film target source. This device allows an on-demand variation of the target thickness from tens of micrometers down to 10 nm while keeping the target composition constant. The target was positioned under 45 degrees with respect to the incoming laser beam while accelerated protons and ions were monitored in both laser- and target normal direction by means of Thomson Parabolas and Radiochromic Film stacks. Hence, being sensitive to the identification of acceleration regimes beyond the well-known Target Normal Sheath Acceleration, preliminary results display a significant increase in proton cut-off energy when reaching thin targets. Up to 25 MeV could be observed for an optimum target thickness of 10 nm as compared to the few- micron scale reference for this target configuration yielding roughly 12 MeV.

Keywords: laser-driven proton acceleration, high-intensity lasers
  • Lecture (Conference)
    Advanced Accelerator Concepts Workshop 2016, 2.8.2016, National Harbor, Maryland, USA
Registration No. 24018 - Permalink

Superconductivity in Weyl semimetal candidate MoTe2
Qi, Y.; Naumov, P. G.; Ali, M. N.; Rajamathi, C. R.; Schelle, W.; Barkalov, O.; Hanfland, M.; Wu, S.-C.; Shekhar, C.; Sun, Y.; Süß, V.; Schmidt, M.; Schwarz, U.; Pippel, E.; Werner, P.; Hillebrand, R.; Förster, T.; Kampert, E.; Parkin, S.; Cava, R. J.; Felser, C.; Yan, B.; Medvedev, S. A.
Abstract: Transition metal dichalcogenides have attracted research interest over the last few decades due to their interesting structural chemistry, unusual electronic properties, rich intercalation chemistry and wide spectrum of potential applications. Despite the fact that the majority of related research focuses on semiconducting transition-metal dichalcogenides (for example, MoS2), recently discovered unexpected properties of WTe2 are provoking strong interest in semimetallic transition metal dichalcogenides featuring large magnetoresistance, pressure-driven superconductivity and Weyl semimetal states. We investigate the sister compound of WTe2, MoTe2, predicted to be a Weyl semimetal and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that bulk MoTe2 exhibits superconductivity with a transition temperature of 0.10 K. Application of external pressure dramatically enhances the transition temperature up to maximum value of 8.2 K at 11.7 GPa. The observed dome-shaped superconductivity phase diagram provides insights into the interplay between superconductivity and topological physics.


Registration No. 24017 - Permalink

Commensurate and incommensurate magnetic order in spin-1 chains stacked on the triangular lattice in Li2NiW2O8
Ranjith, K. M.; Nath, R.; Majumder, M.; Kasinathan, D.; Skoulatos, M.; Keller, L.; Skourski, Y.; Baenitz, M.; Tsirlin, A. A.
Abstract: We report the thermodynamic properties, magnetic ground state, and microscopic magnetic model of the spin-1 frustrated antiferromagnet Li2NiW2O8, showing successive transitions at TN1 similar or equal to 18 K and TN2 similar or equal to 12.5 K in zero field. Nuclear magnetic resonance and neutron diffraction reveal collinear and commensurate magnetic order with the propagation vector k = (1/2,0,1/2) below TN2. The ordered moment of 1.8 µB at 1.5 K is directed along [0.89(9), - 0.10(5), - 0.49(6)] and matches the magnetic easy axis of spin-1 Ni2+ ions, which is determined by the scissor-like distortion of the NiO6 octahedra. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between TN2 and TN1. Density-functional band-structure calculations put forward a three-dimensional spin lattice with spin-1 chains running along the [01-1] direction and stacked on a spatially anisotropic triangular lattice in the ab plane. We show that the collinear magnetic order in Li2NiW2O8 is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy of Ni2+. Registration No. 24016 - Permalink

Spin transport in tantalum studied using magnetic single and double layers
Montoya, E.; Omelchenko, P.; Coutts, C.; Lee-Hone, N. R.; Hübner, R.; Broun, D.; Heinrich, B.; Girt, E.
Abstract: We report on spin transport in sputter-grown Ta films measured by ferromagnetic resonance. Spin diffusion length and spin mixing conductance are determined from magnetic damping measurements for a varying thickness of Ta layer 0 <= dTa <= 10 nm. The different boundary conditions of single- and double-magnetic-layer heterostructures Py|Ta and Py|Ta|[Py|Fe] allow us to significantly narrow down the parameter space and test various models.We showt hat a common approach of using bulk resistivity value in the analysis yields inconsistent spin diffusion length and spin mixing conductance values for magnetic single- and double-layer structures. X-ray diffraction shows that bulk Ta is a combination of β-Ta and bcc-Ta. However, in the region of significant spin transport, <~ 2 nm, there is an intermediate region of growth where the Ta lacks long-range structural order, as observed by transmission electron microscopy. Thickness-dependent resistivity measurements confirm that the bulk and intermediate regions have significantly different resistivity values. We find that the data can be well represented if the intermediate region resistivity value is used in the analysis. Additionally, the data can be fit if resistivity has the measured thickness dependence and spin diffusion length is restricted to be inversely proportional to resistivity. Finally, we rule out a model in which spin diffusion length is a constant, while the resistivity has the measured thickness dependence.
  • Physical Review B 94(2016), 054416
    Button zum Volltext
Registration No. 24015 - Permalink

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