Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32216 Publications
¹⁰Be exposure dating on moraines in the Sayan Mountains, Siberia
Rauh, P.; Schweri, L.; Garcia Morabito, E.; Merchel, S.ORC; Rugel, G.; Zech, R.
Mountain glaciers are very sensitive to (past) climate changes. Paleoglaciation of the Tibetan Plateau and the Himalaya received plenty of attention for the reconstruction of past climate and environmental conditions, whereas few studies have been conducted so far in the adjacent Altai and Sayan Mountains in Siberia, although they promise a complex history.
The investigated Sayan Mountains in the Russian Altai indicate extensive glacial activity during the Pleistocene and a shifting of the local Last Glacial Maximum (LGM). Rich glacial residues in terms of moraine ridges and erratic boulders in the region provide excellent opportunities to establish a detailed age chronology using in-situ cosmogenic ¹⁰Be surface exposure dating and derive information about paleoclimatic conditions.
We present 28 ¹⁰Be surface exposure ages from the Ergaki Range and Tuva Uplands in the western Sayan Mountains. Distinct lateral moraines document the extents of former glaciation during a last glacial maximum. Several recessional moraines in the Ergaki Range additionally record stand stills or readvances during the last glacial termination.
The prominent lateral moraine in the Ergaki Range yields three exposure ages of ~19 ka, indicating a MIS 2 glaciation. The maximum advances correlate with the end of the global LGM. Concluding, glaciers in the Ergaki Range existed continuously during the late Pleistocene only varying in their extent. The well-clustered ages of the Ergaki Range provide a robust deglaciation chronology. The readvances/ stand stills consistently date to ~18 ka (three boulders), ~17.5 ka (two boulders), ~17 ka (three boulders), and ~16 ka (two boulders), with a deglaciation starting after 16 ka. The valley is not elevated enough to record younger, less extensive glaciation, e.g. during the Younger Dryas and the Holocene. Exposure ages from the Tuva Uplands are more difficult to interpret: The lateral moraine documenting the most extensive glaciation yields two exposure ages of ~22 ka. The immediately adjacent inner lateral moraine has two slightly younger and stratigraphically consistent ages of ~21 ka, yet three more boulders from that moraine are ~27 and 43 ka. At this point, we suspect these older boulders to have inheritance, but we cannot confidently exclude a much older deposition age for both moraines. Planned are analyzes of other cosmogenic nuclides, such as ²⁶Al and/or in situ ¹⁴C, which might help to more robustly identify inheritance and complex exposure histories.
Keywords: AMS, glaciation, moraine, LGM
  • Poster
    INQUA 2019 (International Union for Quaternary Research), 25.-31.07.2019, Dublin, Ireland

Publ.-Id: 28728 - Permalink


Perforating Freestanding Molybdenum Disulfide Monolayers with Highly Charged Ions
Kozubek, R.; Tripathi, M.; Ghorbani-Asl, M.ORC; Kretschmer, S.; Madauß, L.; Pollmann, E.; O'Brien, M.; Mcevoy, N.; Ludacka, U.; Susi, T.; Duesberg, G. S.; Wilhelm, R. A.; Krasheninnikov, A. V.ORC; Kotakoski, J.; Schleberger, M. Y.
Porous single-layer molybdenum disulfide (MoS2) is a promising material for applications such as DNA sequencing and water desalination. In this work, we introduce irradiation with highly charged ions (HCIs) as a new technique to fabricate well-defined pores in MoS2. Surprisingly, we find a linear increase of the pore creation efficiency over a broad range of potential energies. Comparison to atomistic simulations reveals the critical role of energy deposition from the ion to the material through electronic excitation in the defect creation process, and suggests an enrichment in molybdenum in the vicinity of the pore edges at least for ions with low potential energies. Analysis of the irradiated samples with atomic resolution scanning transmission electron microscopy reveals a clear dependence of the pore size on the potential energy of the projectiles, establishing irradiation with highly charged ions as an effective method to create pores with narrow size distributions and radii between ca. 0.3 and 3 nm.
Keywords: ion irradiation, highly charged ions, molybdenum disulfide, 2D material, STEM, MD simulation, perforation

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  • Secondary publication expected from 15.01.2020

Publ.-Id: 28727 - Permalink


Study of the influence of water gaps between fuel assemblies on the activation of an aeroball measurement system (AMS)
Konheiser, J.; Mueller, S. E.; Seidl, M.;
The aeroball measuring system (AMS) at Siemens/KWU built pressurized water reactors (PWR) is an important part of the in-core instrumentation to determine in detail the local power distribution. Simulations were carried out with the help of the MCNP6 Monte Carlo program to determine the possible impact of an additional the water gap between the fuel assemblies with regard to the 51V(n,γ)52V reaction rate in the AMS. A simplified geometric model in a 3x3 matrix of identical fuel assemblies was used and four AMS lances were simulated in the central fuel assembly. By shifting the outer 8 fuel assemblies, different water gaps were created and the effects on the reaction rate of the AMS were calculated for different burn-up values and boron contents in the cooling water. It was found that the change of reaction rates can reach up to 10% for an assumed gap maximum of 1cm. The changes are largest for burn-up values at 30 and 45 GWd/t and slowly increase with decreasing boron concentration. The results are an important piece of information to assess the possibility of detecting non-nominal water gaps during reactor operation.
Keywords: AMS, PWR, MCNP6, in-core instrumentation

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  • Secondary publication expected from 09.09.2020

Publ.-Id: 28726 - Permalink


Site-controlled Si Nanodot Formation for a RT-SET via Ion Beam Mixing and Phase Separation
Xu, X.; Prüfer, T.; Wolf, D.; Hübner, R.; Bischoff, L.; Engelmann, H.-J.; Gharbi, A.; Heinig, K.-H.; Hlawacek, G.; von Borany, J.;
CMOS-compatible formation of Si nanodots (NDs) as Coulomb islands is a prerequisite for an RT Single Electron Transistor operation. In this work, Si NDs are formed via ion beam mixing and thermally stimulated phase separation. Broad-beam Si+ and Ne+ beams followed by a rapid thermal annealing treatment were utilized to create a layer of NDs and visualized by Energy-Filtered Transmission Electron Microscopy (EFTEM). The conditions for ND formation are optimized based on an extensive survey of the parameter space. The work is guided by TRIDYN simulations during the ion beam mixing and 3D Kinetic Monte-Carlo simulation for the phase separation during the thermal treatment. To tailor towards a single Si ND, the focused Ne+ beam from the Helium Ion Microscope (HIM) is utilized to create patterns of NDs in planar layer stacks. The formation of site-controlled single NDs with a diameter of 2.2 nm is confirmed by comparing the EFTEM Si plasmon-loss intensity with simulated intensity.
  • Lecture (Conference)
    HeFIB2018 Helium and emerging Focused Ion Beams, 11.06.2018, Dresden, Deutschland

Publ.-Id: 28724 - Permalink


Avoiding Amorphization Related Shape Changes of Nanostructures during Medium Fluence Ion Beam Irradiation of Semiconductor Materials
Xu, X.; Hlawacek, G.; Engelmann, H.-J.; Heinig, K.-H.; Möller, W.; Gharbi, A.; Tiron, R.; Bischoff, L.; Prüfer, T.; Hübner, R.; Facsko, S.; von Borany, J.;
We present an approach to mitigate the ion beam induced damage inflicted on semiconductor nano-structures during ion beam irradiation. Nanopillars (with diameter a of 35 nm and height of 70 nm) have been irradiated with both, a 50 keV Si+ broad beam and a 25 keV focused Ne+ beam from a helium ion microscope (HIM). Upon irradiation of the nanopillars at room temperature with a medium fluence (2e16 ions/cm2), strong plastic deformation has been observed which hinders further device integration. This differs from predictions made by the Monte-Carlo based simulations using the TRI3DYN. However, irradiation at elevated temperatures with the same fluence would preserve the shape of the nanopillars.
It is well known that a critical temperature exists for silicon above which it will recrystallize during ion beam irradiation. This prevents the amorphization of the target material independent of the applied fluence. At high enough temperatures and not for too high flux this prevents the ion beam hammering and viscous flow of the nano-structures. These two effects are responsible for the shape change observed at low temperature. This has been observed previously mainly for swift heavy ions and energies higher than 100 keV. We used HIM and transmission electron microscopy to follow the morphological evolution of the pillars and their crystallinity. While irradiation at room temperature results in amorphization and the related destruction of the nanopillars, irradiation above 650 K preserves the crystalline nature of the pillars and prevents viscous flow. This effect has been observed previously mainly for swift heavy ions and energies higher than 100 keV. Such high-temperature irradiation, when carried out on a nanopillar with Si/SiO2/Si layer stack, would induce ion beam mixing without suffering from the plastic deformation of the nanostructure. Due to a limited mixing volume, single Si-NCs would form in a subsequent rapid thermal annealing process via Oswald ripening and serve as a basic structure of a gate-all-around single electron transistor device.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.
  • Lecture (Conference)
    AVS 65th International Symposium & Exhibition, 22.10.2018, Long Beach, USA

Publ.-Id: 28723 - Permalink


Tuneable vortex dynamics with ion implantation
Ramasubramanian, L.; Kákay, A.; Fowley, C.; Yildirim, O.; Matthes, P.; Lindner, J.; Deac, A. M.;
The fundamental oscillation mode of magnetic vortices in thin-film elements has been proposed as working principle for spin-torque-driven nano-oscillators [Nat. Phys., 3:498, 2007].
Commercial applications require tuning of the output frequency by external parameters, such as spin-polarized currents. The tunability of vortex-based devices is limited, since the gyrotropic frequency is specific to the individual sample design. The fundamental frequency is determined by the saturation magnetisation, Ms, as well as the geometrical confinement of the magnetisation i.e. the diameter and height of a magnetic disk. Our micromagnetic simulations have shown that if regions with different Ms can be induced in a magnetic disk, multiple precession frequencies can be generated. Here, we show that ion implantation [Phys. Rev. B 73, 184410, 2006] is a novel route to fabricate such devices.
Permalloy (Py) disks of various diameters and thicknesses were patterned and contacted to study the interaction of an applied AC current with the magnetic vortex. Using a conventional lock-in technique, the resonance frequencies are measured based on the anisotropic magnetoresistance (AMR) effect. Regions of different Ms are induced in single disks by ion implantation, yielding different resonance frequencies corresponding to the specific area where the core is precessing. The work represents a novel way to obtain multiple oscillation frequencies from a single disk.
Keywords: magnetic vortex, ion implantation, frequency tunability
  • Lecture (Conference)
    9th JEMS Conference 2018, 03.-07.09.2018, Mainz, Germany

Publ.-Id: 28722 - Permalink


Phase transition lowering in dynamically compressed silicon
Mcbride, E. E.; Krygier, A.; Ehnes, A.; Galtier, E.; Harmand, M.; Konôpková, Z.; Lee, H. J.; Liermann, H.-P.; Nagler, B.; Pelka, A.; Rödel, M.; Schropp, A.; Smith, R. F.; Spindloe, C.; Swift, D.; Tavella, F.; Toleikis, S.; Tschentscher, T.; Wark, J. S.; Higginbotham, A.;
Silicon, being one of the most abundant elements in nature, attracts wide-ranging scientific and technological interest. Specifically, in its elemental form, crystals of remarkable purity can be produced. One may assume that this would lead to silicon being well understood, and indeed, this is the case for many ambient properties, as well as for higher-pressure behaviour under quasi-static loading. However, despite many decades of study, a detailed understanding of the response of silicon to rapid compression—such as that experienced under shock impact—remains elusive. Here, we combine a novel free-electron laser-based X-ray diffraction geometry with laser-driven compression to elucidate the importance of shear generated during shock compression on the occurrence of phase transitions. We observe lowering of the hydrostatic phase boundary in elemental silicon, an ideal model system for investigating high-strength materials, analogous to planetary constituents. Moreover, we unambiguously determine the onset of melting above 14 GPa, previously ascribed to a solid–solid phase transition, undetectable in the now conventional shocked diffraction geometry; transitions to the liquid state are expected to be ubiquitous in all systems at sufficiently high pressures and temperatures.
Keywords: compressed silicon, shock, LCLS, x-ray diffraction, XFEL, phase transition, MEC, high energy density

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Publ.-Id: 28721 - Permalink


Magnetic vortex dynamics and frequency tunability in Cr-implanted permalloy disks
Ramasubramanian, L.; Kákay, A.; Fowley, C.; Yildirim, O.; Matthes, P.; Böttger, R.; Lindner, J.; Fassbender, J.; Gemming, S.; Schulz, S. E.; Deac, A. M.;
The fundamental oscillation mode of magnetic vortices in thin-film elements has recently been proposed for designing spin-torque-driven nano-oscillators [1]. Commercial applications require tuning of the output frequency by external parameters, such as applied fields or spin-polarized currents. However, the tunability of vortex-based devices is limited, since the gyrotropic frequency is specific to the individual sample design. Indeed, the fundamental frequency is known to be determined by the saturation magnetisation, M_s , as well as the geometrical confinement of the magnetisation, i.e. the diameter and height of the magnetic disk [2, 3]. Micromagnetic simulations [4] have shown that if regions with different saturation magnetisation can be induced in a magnetic disk, multiple precession frequencies can be generated. We show that ion implantation [5] is a novel route to fabricate such devices.
Permalloy (Py) disks of various diameters and thicknesses were prepared using electron beam lithography followed by electron beam evaporation. Individual disks were contacted by gold leads to study the interaction of spin-polarized current with the magnetic vortex. The presence of vortex is verified by magneto optic Kerr effect (MOKE), X-ray magnetic circular dichroism (XMCD) and magnetotransport measurements. The magnetic field dependence of the vortex position can be tuned by the disk size as shown by XMCD (Figure 1 (a)). Higher magnetic stability due to larger annihilation fields can be achieved by smaller disk diameters, whereas larger field sensitivity is present in larger disks (Figure 1 (b)). Magnetotransport measurements on electrically contacted disks show the presence of anisotropic magnetoresistance (AMR) in different disks with varying thickness (Figure 1 (c)).
Using a conventional lock-in technique, the resonance frequencies are measured for disks with different radii as shown in Figure 2 (a), with the inset showing the scanning electron microscope image of an electrically contacted disk. In order to modify the magnetisation within a single disk and to achieve two different oscillation frequencies, we implant chromium in different regions of the disk (inner and outer). Cr-implantation leads to a decrease in the Curie temperature and thus a reduction in the magnetic moment [6]. The reduction of M_s as a function of Cr fluence was optimised on extended Py films using a vibrating sample magnetometer – superconducting quantum interference device (VSM-SQUID), see figure 2 (b). A clear drop in M_s with increasing the chromium ion fluence is observed. Concentric donut-like structures were then implanted with Cr and the modification of dynamics as a function of magnetic field was investigated. An example of Cr implantation in a 3 µm radius disk at 30 keV with a fluence of 1.2×〖10〗^16 ions/cm^2 is shown in Figure 2 (c). The vortex core is shifted between the two different magnetisation regions by applying an external in-plane field. The vortex nucleates in the irradiated region at – 2.281 mT, leading to a resonance frequency of 30.2 MHz (shown in orange in Figure 2 (c)). Further increasing the external field pushes the vortex core to the non-irradiated region where the resonance frequency is 42.3 MHz (shown in green), corresponding to a field of + 1.597 mT. The results show that ion implantation is a novel way to obtain multiple frequencies from a single disk.
Keywords: magnetic vortex, ion implantation, frequency tunability
  • Lecture (Conference)
    INTERMAG 2018 - The IEEE International Magnetics Conference (INTERMAG, 23.-27.04.2018, Singapore, Singapore

Publ.-Id: 28720 - Permalink


Effect of insertion layer on the properties of Mn₂RuₓGa in magnetic tunnel junctions
Titova, A.; Fowley, C.; Clifford, E.; Lau, Y.-C.; Borisov, K.; Betto, D.; Atcheson, G.; Hübner, R.; Xu, C.; Stamenov, P.; Coey, M.; Rode, K.; Lindner, J.; Fassbender, J.; Deac, A. M.;
The choice of proper materials for magnetic tunnel junctions (MTJs) for storage and communication applications (like MRAM or spin-transfer-torque nano-oscillators (STNOs)) is always an issue. On the one hand, the magnetic layers should exhibit as little stray field as possible and be mostly insensitive to the external magnetic field. On another hand, in order to maximize the tunneling magnetoresistance (TMR) ratio, these materials should provide high spin polarization, or even ideally possess half-metallic properties. An option which satisfies both criteria are the compensated half metallic ferrimagnets (CHFMs) — a class of materials predicted in 1995 by van Leuken and de Groot. CHFMs are materials which behave as antiferromagnets (AFMs) with respect to external magnetic fields, since the magnetic moments of the two sublattices compensate, while simultaneously exhibiting half-metal behavior from the point of view of magnetotransport. Experimentally, the first identified zero-moment half-metal was Mn₂RuₓGa (MRG) in 2014. It was already known that Mn-based Heusler compounds possess huge uniaxial anisotropy fields (exceeding tens of teslas); this, together with their vanishing magnetization, lead to resonance frequencies of several hundred GHz in such materials, making them very attractive candidates for STNOs in the sub-THz range. Such devices, due to the much higher bandwidth accessible, are expected to open the way for remote hospitals, 3-D remote meetings and much more.
Earlier MRG studies have already shown that these materials exhibit tunable magnetic properties. Indeed, the compensation temperature varies between 2 and 450K, depending on the Ru concentration. They also yield giant spontaneous Hall angle (7.7%). MRG has also been successfully integrated into perpendicular MRG/MgO/CoFeB MTJs, with low-bias TMR reaching up to 40 % at 10 K and 7 % at 300 K.
As the low value of TMR was attributed to diffusion of Mn atoms inside the MgO barrier, here, we investigate the effect of different insertion layers introduced between MRG and MgO on the magnetic properties and transport of MTJs. Mn₂Ruₓ Ga (23)/insertion layer(t)/MgO(1.7)/CoFeB(1)/Ta(0.3)/CoFeB(0.9)MgO(0.7)/Ta(3)/Ru(4) multilayers were deposited using a “Shamrock” fully automated sputter deposition tool (thickness given in nm). Mn₂RuₓGa was grown by co-sputtering from a Mn₂Ga and a Ru target. Different MRG compositions (Mn₂Ru1.1Ga, Mn₂Ru0.9Ga, Mn₂Ru0.75Ga, and Mn₂Ru0.65Ga) have been obtained by varying the sputtering power of Mn₂Ga while keeping the sputtering power of Ru constant. Changing Ru concentration in MRG allows adjusting the compensation temperature Tcomp from 2 to 450 K.
We fabricated MTJs without insertion layers, as well as stacks with Ta (0.3 nm, 0.6 nm, 0.9 nm) and Al (0.3 nm, 0.6 nm, 0.9 nm) insertion layers. The switching properties of MTJs were analyzed through magnetotransport measurements as a function of applied bias voltage at room temperature. Al 0.6 nm acts as the best diffusion barrier. Magnetic properties of the multi-layers were characterized by the quantum design superconducting quantum interference device (SQUID) with a maximal applied field of 7n T at the range of temperatures from 60 K to 300 T.
The magnetometry data was extracted from the typical out-of-plane hysteresis loop of the investigated MTJs (Fig.1). As the magnetic field is swept from +7 T to – 7 T, the magnetic moment of CoFeB starts to rotate first and switches close to 0 T. The sharp jump observed at -0.4 T is attributed to the reversal of MRG magnetization. With conducting the same measurements at different temperatures, it is possible to detect the compensation temperature of MRG, which will lead to a decrease of its magnetic moment and a divergence of the coercive field. The temperature with zero magnetic moment and extremely high Hc corresponds to the compensation point of MRG. In Fig.2 the temperature dependence of magnetic properties of MTJs with the same MRG composition, but different diffusion barriers, is presented. For different insertion layers, Tcomp can shift over a large range, showing that the choice of insertion layer can have a dramatic effect on the properties of MRG. For instance, in MTJs with no insertion layer 100 K < Tcomp < 160 K; the shift to the higher temperatures is observed for Ta 0.3 nm insertion (140 K < Tcomp < 200 K), and to the lower temperatures with Al 0.6 nm insertion (Tcomp < 120 K). Moreover, we demonstrate that Tcomp can also be altered by post-annealing, as a 20 K shift is observed after annealing at 325°C for 1 hour.
Mn₂RuₓGa integrated into MTJs demonstrates a low magnetic moment, high coercivity, and thereby high immunity to the applied magnetic field over a broad temperature range (60 K – 300 K). At the same time, these MTJs show TMR even at the compensation temperature, highlighting a fundamental difference between an AFM and a CHFM. All these make MRG extremely attractive for spintronics applications, and for the excitation of magnetic resonances in STNOs.
Keywords: Ferrimagnetism, Half-metals, Magnetic Tunnel Junctions, Heusler Alloy
  • Lecture (Conference)
    The IEEE International Magnetics Conference (INTERMAG), 23.-27.04.2018, Singapore, Singapore

Publ.-Id: 28719 - Permalink


Running Status of SRF Gun-II at ELBE Center
Xiang, R.; Arnold, A.; Lu, P.; Murcek, P.; Schaber, J.; Teichert, J.; Vennekate, H.; Zwartek, P.;
As a new electron source with higher brilliance, the second version of the superconducting RF photoinjector (SRF Gun-II) has been successfully commissioned at the ELBE Center for high power radiation sources since 2014. SRF Gun-II features an improved 3.5-cell niobium cavity as well as a superconducting solenoid in the same cryomodule. With Mg photocathode SRF Gun-II can provide high current beam with bunch charge up to 300 pC at 100 kHz repetition rate. For user operation the SRF Gun-II successfully generated stable beam with 200 pC in CW mode and sub-ps bunch length. In this presentation the gun's status and beam parameters will be presented.
Keywords: photoinjector, SRF Gun, Mg photocathode, CW mode, sub-ps
  • Open Access LogoContribution to proceedings
    29th Linear Accelerator Conference, 16.-21.09.2018, Beijing, China
    Proceedings of the 29th Linear Accelerator Conference, ISBN 978-3-95450-194-6

Publ.-Id: 28718 - Permalink


Robust Cs2Te and Mg photocathodes in SRF gun at ELBE center successful for CW IR FEL and THz radiation
Xiang, R.; Teichert, J.;
Quality of photocathodes is one of the critical issues for the stability and reliability of the light source facility. In 2014, SRF gun-I with Cs2Te provided stable electron beams successfully for IR FEL at HZDR. Cs2Te worked in SRF gun for more than one year without degradation. Currently, Mg photocathodes with QE up to 0.5% are applied in SRF Gun II, which is able to generate e- beam with bunch charges up to 200 pC in CW mode with sub-ps bunch length for the high power THz radiation facility for the ELBE users.
Keywords: Photocathode, SRF gun
  • Lecture (Conference)
    Photocathode Physics for Photoinjectors 2018, 15.-17.10.2018, Santa Fe, NM, USA

Publ.-Id: 28717 - Permalink


Development and characterization of novel anti-GD2 target modules for retargeting of Universal CAR T cells toward GD2 expressing tumors
Mitwasi, N.; Feldmann, A.; Bergmann, R.; Berndt, N.; Rössig, C.; Bachmann, M.;
Although chimeric antigen receptor (CAR) engineered T cells demonstrated promising therapeutic effect against cancer, they are still associated with adverse side effects which could be life threatening in some cases. Therefore, in our group we have developed a switchable universal CAR T cell platform “UniCAR”, which can be repeatedly switched on and off. This system consists of CAR T cells that cannot bind tumor antigens directly but instead they are redirected with a target module (TM). Such TMs are mainly composed of an epitope on one side, which is recognized by the UniCAR T cells, and on the other side a tumor antigen-binding domain. Once the TM is eliminated, the UniCAR T cells are no more activated. Disialoganglioside GD2 was shown previously to be a very promising target for several tumors such as neuroblastoma and Ewing’s sarcomas. Therefore, anti-GD2 TMs were developed and evaluated regarding their functionality. They were shown to be functional in activating the UniCARs to secrete important pro-inflammatory cytokines and to kill GD2+ tumor cells both in vivo and in vitro. To further characterize the anti-GD2 TM with PET imaging, it was labeled with radioactive Cu64 . The TM showed a specific enrichment at the site of the GD2+ growing tumor, and it was mainly eliminated through the kidneys within half an hour due to its small size. Such short half-life, provides the UniCAR system with the fast safety switch in case any complications occurred in patients treated with the UniCAR T cells.
  • Poster
    The International Conference on Lymphocyte Engineering, 13.09.2018, Madrid, Spain
  • Abstract in refereed journal
    Human Gene Therapy 29(2018)11, A9

Publ.-Id: 28716 - Permalink


Automated Target Model Determination from MEIS Spectra Utilizing an Evolutionary Algorithm
Heller, R.;
To extract chemical compositions and layer thicknesses of layered samples from back scattering spectra experimentalists usually have to take the following approach: Simulation of a theoretical spectrum for an initial target configuration and comparison to the measured data followed by the successive re-adjustment of the target model iteratively, until simulation result and experimental spectrum fit together. For multi-layer samples this procedure can get rather time consuming, especially when a series of similar samples with varying layer thickness and/or stoichiometry has to be analyzed.

Although modern IBA spectrum simulation software like SimNRA[1] or WINDF[2] have become quite powerful and handy tools, the analysis of the spectra consumes still a significant fraction of an IBA scientist’s working time. SimNRA offers therefore the opportunity to partially fit layer thicknesses and/or elemental ratios for a given layer within a certain region of a spectrum. WINDF goes a step further and implements an automated spectrum fitting based on a simulated annealing algorithm. However, it takes the user quite some time to set up the boundary conditions and fit parameters until the actual fit procedure can be initiated. Furthermore, the outcome of the fit procedure in some cases contains non-physical artifacts and requires multiple re-adjustments of the boundary conditions / fit parameters.

An approach that came up in the past (and is still being applied for particular tasks) is the application of artificial neural networks (ANN) to derive sample information from IBA spectra [3,4]. In a nut-shell this method basically trains an algorithm how the shape of a spectrum is correlated to the sample’s target model without introducing any physics (numerical calculations) to the code. Therefore, the ANN is fed with many (typically several 10 thousand) training spectra with a known target model. After this training procedure (which can be quite time consuming) the ANN spits out the target model of any unknown spectra in almost zero time. However, the spectra must be of the same type as all the training spectra since an ANN can only interpolate and not extrapolate, which is for sure one of the mayor drawbacks of this approach. However, all these efforts are justified in some special scenarios e.g. if a large series of spectra of similar type has to be evaluated.

In this contribution, we present a new approach of automated IBA spectra fitting applying an evolutionary algorithm (EA). We show that EA is well suited and robust for complete and fast IBA spectrum fitting with minimum input of boundary conditions. The benefits of this algorithm and the particular differences to simulated annealing and ANN are pointed out. Special emphasis is put on the adoption of this algorithm to the analysis of MEIS spectra, since there is a couple of differences to classical IBA methods that needs to be considered.

Based on this algorithm a platform independent software package has been developed that comprises a clean and easy-to-use graphical user interface. We will introduce this software in a basic overview.
Keywords: Ion beam analysis, evaluation software, evolutionary algorithm
  • Invited lecture (Conferences)
    9th International Workshop on High-Resolution Depth Profiling (HRDP-9), 25.-29.06.2018, Uppsala, Schweden

Publ.-Id: 28715 - Permalink


Structural and magnetic properties of epitaxial Mn–Ge films grown on Ir/Cr buffered MgO(0 0 1)
Dash, S.; Schleicher, B.; Schwabe, S.; Reichel, L.; Heller, R.; Fähler, S.; Neu, V.; Patra, A. K.;
Epitaxial Mn–Ge films with varying composition have been prepared on Ir/Cr buffered MgO(0 0 1) substrates using DC magnetron sputtering. The effect of composition on phase formation, texture and magnetic properties of Mn–Ge films has been investigated. These films grow epitaxially on Ir/Cr buffered MgO(0 0 1) with a tetragonal D022 type structure. From the pole figure analysis the epitaxial relationship is determined to be: D022 Mn–Ge [1 0 0] (0 0 1)||Ir [1 0 0] (0 0 1)||Cr [1 1 0] (0 0 1)||MgO [1 0 0] (0 0 1). Mn–Ge films close to stoichiometric composition (Mn77.5Ge22.5) exhibit perpendicular magnetic anisotropy with crystallographic c-axis being the easy axis of magnetization. The room temperature measured values of coercivity µ 0 H c, saturation magnetization M S and anisotropy field µ 0 H A for Mn77.5Ge22.5 are 2.86 T, 90 kA m−1 and 9.6 T, respectively. Mn–Ge films with low and high Mn concentration possess high coercivity but extremely low magnetization and that can be ascribed to the presence of secondary phases of non-magnetic/low magnetic nature, possible interdiffusion, and especially partial substitution of excess Mn atoms into the Ge site.
Keywords: epitaxial growth, magnetron sputtering, ion beam analysis, Mn, Ge, magnetic propoerties

Publ.-Id: 28714 - Permalink


Hydrogen storage in Mg2FeSi alloy thin films depending on the Fe-to-Si ratio measured by conversion electron Mössbauer spectroscopy
Trinh, T. T.; Asano, K.; Heller, R.; Reuther, H.; Grenzer, J.; Schreuders, H.; Dam, B.; Potzger, K.;
Sputter deposited Mg2FexSi1-x films of 250 nm thickness have been investigated by means of Mössbauer spectroscopy. While non-hydrogenated films are characterized by a quadrupole split doublet, hydrogenated regions show a singlet with reduced isomer shift. The relative areas of the spectra reflect the relation between loaded and unloaded regions prepared at the same loading conditions.
Keywords: Hydrogen storage, MgFe, Mössbauer

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  • Secondary publication expected

Publ.-Id: 28713 - Permalink


Interaction of hydrogen with hafnium dioxide grown on silicon dioxide by the atomic layer deposition technique
Kolkovsky, V.; Scholz, S.; Kolkovsky, V.; Schmidt, J. U.; Heller, R.;
The electrical and structural properties of thin hafnia films grown by the atomic layer deposition technique were investigated before and after different annealing steps as well as after a dc H plasma treatment. By using the nuclear reaction analysis, the authors demonstrated that high concentrations of hydrogen (about 1–2 at. %) could be observed even in as-grown hafnia layers. An additional hydrogenation of the samples with atomic H led to a significant shift of the flatband voltage. This shift could be explained by the introduction of positively charged H-related defects which were found to be stable at room temperature. By comparing the experimental findings with the theory and the data from muon spin spectroscopy, they tentatively ascribed these defects to interstitial H in HfO2.
Keywords: hafnium oxide, ion beam analysis, nuclear reaction analysis, hydrogen depth profiling

Publ.-Id: 28712 - Permalink


Untersuchung an Meteoriten mittels INAA am FRM II
Li, X.; Lierse Von Gostomski, C.; Merchel, S.ORC; Leister, N.
Im Rahmen eines Schülerprogrammes (TUM-Kolleg) der TU München wurden drei gewöhnliche Chondrite aus Deutschland (Cloppenburg (Fund 2017) [1,2], Oldenburg (Bissel), Benthullen) und drei Achondrite der Gruppe der HEDs (Howardite-Eukrite-Diogenite) aus dem Oman und aus Nord-West-Afrika (Dhofar 1675, NWA 2690, NWA 2698) sowie ein Mond-, ein Marsmeteorit (NWA 7986, NWA 4925) und zwei potentielle Mikrometeorite mit Probengewichten von je 38 µg und 22 µg mittels der INAA im radiochemischen Labor der Radiochemie analysiert. Die Mikrometeoriten wurden einmal 24 h lang in der Hochflussposition (>1E14 cm-2s-1) und die anderen größeren Proben mit einem Gewicht von je ca. 20 mg jeweils für 3 min bzw. 5 min und 45 min in der Rohrpostanlage bestrahlt. Durch den hohen und reinen thermischen Neutronenfluss am FRM II konnten insgesamt bis zu 45 Elemente in den Proben bestimmt werden.
Anhand der Elementzusammensetzung konnten die beiden Meteoritengruppen eindeutig unterschieden werden, und damit die Klassifizierung der Meteoriten bestimmt bzw. bestätigt werden [Abb. 1 & 2].
Der Marsmeteorit konnte mit seinem hohen Eisenanteil von 17,2 % von den anderen Achondriten unter-schieden werden. Das Ergebnis vom Mondmeteorit zeigte hingegen zwar einen höheren Gehalt von Elementen seltener Erden, aber keine deutliche KREEP-Signatur. Eine negative Europium-Anomalie konnte aber auch nicht zweifelfrei festgestellt werden [Tab. 1].
Bei den beiden potentiellen Mikrometeoriten konnten trotz geringer Probenmassen bis zu 14 Elemente detektiert werden. Beide haben einen hohen Fe-Gehalt von 65 Gew.% bzw. 55 Gew.%, aber für Ni wurde nur eine Nachweisgrenze von 0,3 Gew.% bzw. 0,45 Gew.% fest-stellt, so dass ein extraterrestrischer Ursprung kaum möglich ist.
Danksagung: Wir danken A. Muszynski und M. Szyszko (Poznan, PL), A. Bischoff (U Münster), D. Heinlein, J. Feige (TU Berlin) und A. Gärtner (Senckenberg Dresden) für die Bereitstellung der Meteoritenproben.

[1] www.dlr.de/dlr/desktopdefault.aspx/tabid-10081/151_read-24638/#/gallery/28819 (Jan. 2019)
[2] J. Storz et al., (Jan. 2019) www.paneth.eu/PanethKolloquium/2017/0075.pdf.
[3] A. Palme et al., GCA 55 (1991) 3105-3122.
[4] H. Binder, Lexikon der chemischen Elemente, ISBN 3-7776-0736-3 (1999).
[5] J.A. Barrat et al., Geochim. Cosmochim. Acta 83 (2012) 79–92.
Keywords: INAA, meteorite, cosmic rays
  • Lecture (Conference)
    27th Seminar on Activation Analysis and Gamma Spectrometry (SAAGAS 27), 24.-27.02.2019, München, Deutschland

Publ.-Id: 28711 - Permalink


Immune Monitoring of Cancer Patients Prior to and During CTLA-4 or PD-1/PD-L1 Inhibitor Treatment
Tunger, A.; Kießler, M.; Wehner, R.; Temme, A.; Meier, F.; Bachmann, M.; Schmitz, M.;
Targeting the immune checkpoint receptors cytotoxic T lymphocyte antigen 4 (CTLA-4), programmed cell death protein 1 (PD-1), or programmed cell death 1 ligand 1 (PD-L1) represents a very attractive treatment modality for tumor patients. The administration of antibodies against these receptors can promote efficient antitumor effects and can induce objective clinical responses in about 20–40% patients with various tumor types, accompanied by improved survival. Based on their therapeutic efficiency, several antibodies have been approved for the treatment of tumor patients. However, many patients do not respond to checkpoint inhibitor therapy. Therefore, the identification of biomarkers is required to guide patient selection for this treatment modality. Here, we summarize recent studies investigating the PD-L1 expression or mutational load of tumor tissues as well as the frequency and phenotype of immune cells in tumor patients prior to and during CTLA-4 or PD-1/PD-L1 inhibitor treatment.

Publ.-Id: 28710 - Permalink


Multimodal PET/MRI Imaging Results Enable Monitoring the Side Effects of Radiation Therapy.
Kovács, N.; Szigeti, K.; Hegedűs, N.; Horváth, I.; Veres, D. S.; Bachmann, M.; Bergmann, R.; Máthé, D.;
Radiotherapy is one of the most frequently applied treatments in oncology. Tissue-absorbed ionizing radiation damages not only targeted cells but the surrounding cells too. The consequent long-term induced oxidative stress, irreversible tissue damage, or second malignancies draw attention to the urgent need of a follow-up medical method by which personalized treatment could be attained and the actually dose-limiting organ could be monitored in the clinical practice. We worked out a special hemisphere irradiation technique for mice which mimics the radiation exposure during radiotherapy. We followed up the changes of possible brain imaging biomarkers of side effects, such as cerebral blood flow, vascular endothelial function, and cellular metabolic processes for 60 days. BALB/c mice were divided into two groups (n=6 per group) based on the irradiation doses (5 and 20 Gy). After the irradiation procedure arterial spin labeling (ASL), diffusion-weighted imaging (DWI) in magnetic resonance modality and [18F]fluoro-deoxy-D-glucose positron emission tomography (FDG-PET) scans of the brain were obtained at several time points (3, 7, 30, and 60 days after the irradiation). Significant physiological changes were registered in the brain of animals following the irradiation by both applied doses. Elevated standard uptake values were detected all over the brain by FDG-PET studies 2 months after the irradiation. The apparent diffusion coefficients from DWI scans significantly decreased one month after the irradiation procedure, while ASL studies did not show any significant perfusion changes in the brain. Altogether, our sensitive multimodal imaging protocol seems to be an appropriate method for follow-up of the health status after radiation therapy. The presented approach makes possible parallel screening of healthy tissues and the effectiveness of tumor therapy without any additional radiation exposure.

Publ.-Id: 28709 - Permalink


Late-Stage Preclinical Characterization of Switchable CD123-Specific CAR-T for Treatment of Acute Leukemia
Loff, S.; Meyer, J.-E.; Dietrich, J.; Spehr, J.; Riewaldt, J.; von Bonin, M.; Gründer, C.; Franke, K.; Feldmann, A.; Bachmann, M.; Ehninger, G.; Ehninger, A.; Cartellieri, M.;
Application of autologous T cells genetically engineered to express CD19-specific chimeric antigen receptors (CAR-T) is highly effective in the treatment of B cell malignancies. To this date, application of CAR-T therapy beyond CD19 remains challenging due to the inability to control CAR-T reactivity in patients and the lack of tumor-associated antigens exclusively expressed by malignant cells. The interleukin-3 receptor alpha chain (CD123) is a promising immunotherapeutic target and associated with leukemia-initiating compartments in myeloid- or lymphoid derived diseases. However, in contrast to CD19, CD123 is a precarious target due to its prevalent expression on healthy hematopoietic stem and progenitor cells (HSPC) as well as endothelial cells. Thus, CAR-T lacking any fine-tuned control mechanisms are at risk to cause life threatening toxicities or can only act as bridging therapy to an allogeneic stem cell transplantation. To extend application of CAR-T therapy and safely redirect CAR engineered T cells to challenging targets such as CD123, a switch-controllable universal CAR T platform (UniCAR) was recently introduced. The UniCAR system consists of two components: (1) a non-reactive inducible second generation CAR with CD28/CD3ζ stimulation for an inert manipulation of T cells (UniCAR-T) and (2) soluble targeting modules (TM) enabling UniCAR-T reactivity in an antigen-specific manner.
Here we provide late stage pre-clinical data for UniCAR-T in combination with a CD123 specific TM (TM123) for treatment of acute leukemia. Primary patient-derived CD123-positive leukemic blasts were efficiently eradicated by TM123-redirected clinical grade manufactured UniCAR-T in vitro and in vivo. Activation, cytolytic responses and cytokine release were proven to be strictly switch-controlled. Moreover, anti-leukemic responses of UniCAR-T were demonstrated to be comparable to conventional CD123 specific CAR-T in vitro. In contrast to conventional CD123 CAR-T, TM123-redirected UniCAR-T discriminate between CD123high malignant cells and CD123lowhealthy cells with negligible toxicity towards HSPC in vivo. As 4-1BB mediated co-stimulation is known to enhance CAR-T activity in vivo, a novel CD123-specific targeting module bearing a covalently bound trimeric 4-1BB ligand (4-1BBL) was developed and characterized for co-stimulation at the leukemic site in trans. Specific binding of TM123 4 1BBL was demonstrated against native 4-1BB as well as CD123-positive leukemic blasts. In long-term tumor eradication models, TM123 4 1BBL ameliorated the killing capability of UniCAR-T in vitro. Additionally, the increased hydrodynamic radius of trimeric 4-1BBL-coupled TM123 prolonged plasma half-life and enhanced bioavailability in vivo. In conclusion, UniCAR-T maintain high anti-leukemic efficacy, while adding a sophisticated mechanism for immediate control to improve safety and versatility of CD123-directed CAR-T therapy. Moreover, switching between several TMs from short to moderate plasma half-life allows for an individualized treatment of various leukemic settings while minimizing potential adverse effects.

Publ.-Id: 28708 - Permalink


Low-energy carrier dynamics in graphene and other 2D materials
Winnerl, S.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Venanzi, T.; Schneider, H.; Helm, M.;
Phonons in graphene and interexcitonic transition in transition metal dichalcogenides are examples for low-energy excitations in 2D materials. Free-electron lasers such as FELBE deliver tunable short mid-infrared pulses that are ideally suited to study the carrier dynamics in 2D materials in the energy range of these low-energy excitations. We present results on the carrier dynamics in graphene and MoSe2.
Keywords: free-electron laser, ultrafast dynamics, low energy excitations, 2D materials
  • Invited lecture (Conferences)
    18th International Conference on Laser Optics (ICLO 2018), 04.-08.06.2018, St. Petersburg, Russland

Publ.-Id: 28707 - Permalink


Ultrafast Carrier Dynamics in Hybrid Plasmonic Nanostructured metal/graphene
Huang, X.; Winnerl, S.; Schneider, H.;
Graphene plasmonic circuits critically depend on convertingincident light into propagating graphene plasmons (GPs), and on controlling their propagation and focusing to enhance light-matter interactions. Here, the theoretical analysis and experimental studies are mainly focused on the GP induced hot-carrier generation and injection on graphene when energy transferred at different SPP interference states. We characterize the ultrafast carrier dynamics in the hybrid metal/graphene nanostructures using ultrafast pump-probe spectroscopy in the mid-inferred range. The renormalized plasmon dispersions in the interface of the metal/graphene nanostructures are investigated. And, the characterization of nonlinearity phase of the high order harmonic generation signals of the hybrid nanostructures are also demonstrated.
Keywords: graphene, plasmonics, hybride graphene-metal nanostructure
  • Poster
    Graphene 2018, 26.-29.06.2018, Dresden, Deutschland

Publ.-Id: 28706 - Permalink


ESUO - The European Synchrotron and FEL User Organisation: Aims and activities
Arčon, I.; Arikan, P.; Bittencourt, C.; Boscherini, F.; Braz Fernandes, F. M.; Brooks, N.; Buljan, M.; Casu, B.; D'Angelo, M.; D'Astuto, M.; Feiters, M.; Froideval, A.; Gross, S.; Gutt, C.; Hase, T.; Huotari, S.; Jablonska, K.; Jergel, M.; Kajander, T.; Khan, A.; Kirm, M.; Kokkinidis, M.; Kövér, L.; Lamba, D.; Larsen, H. B.; Lechner, R. T.; Logan, D. T.; López, O.; Lorentz, K.; Lüning, J.; Mariani, C.; Marinkovic, B.; Mc Guinness, C.; Meedom Nielsen, M.; Mickevicius, S.; Mikulík, P.; Petukhov, A.; Pietsch, U.; Pokroy, B.; Purans, J.; Renault, L.; Santoro, G.; Shivachev, B.; Stangl, J.; Tromp, M.; Vankó, G. A.; Blasetti, C.; Górkiewicz, A.; Grobosch, M.; Helm, M.; Schramm, B.; Seidlhofer, B. K.; van Daalen, M.; Vollmer, A.;
The European Synchrotron and free-electron laser User Organisation (ESUO) established in 2010 today represents about 30.000 users. We aim at representing the users from all European countries. Each country is represented within ESUO by one up to four national delegate(s), depending on the size of the user community in the respective country. The ESUO aims and activities are shown in this poster.
Keywords: European synchrotron and FEL user organisation (ESUO), European projects, scientific collaborations, European synchrotron and FEL radiation facilities
  • Poster
    10th Joint BER II and BESSY II User Meeting, 05.-07.12.2018, Berlin, Deutschland

Publ.-Id: 28705 - Permalink


Rotation-Free Scattered-Radiation Imaging with a Radiotherapy X-Ray Linac
Simoes, H.; Ferreira Marques, R.; Rachinhas, P. J. B. M.; Wagner, A.ORC; Crespo, P.ORC
The OrthoCT (acronym for orthogonal computed tomography) concept, based on orthogonal ray imaging, is a new low-dose imaging technique under investigation to potentially assist external-beam radiation therapy treatments. It consists in detecting radiation scattered in the patient and emitted at approximately 90 degrees with respect to the direction of the incoming beam. Such radiation can be collected by a 1D-detector system with a multi-sliced collimator positioned parallel to the incident beam axis. This system can be potentially useful for on-board imaging with the patient positioned and ready for treatment, or for real-time treatment monitoring. In this work, a multi-pixel, small OrthoCT detector prototype was developed and tested experimentally. This system is based on gadolinium orthosilicate crystals coupled to photomultiplier tubes and a collimator made of lead slices. The experimental measurements were performed with a heterogeneous phantom of acrylic with an air cavity inside, using a TrueBeam linac operated at 6MV in the flattening-filter-free modality. The results allow concluding that this new imaging technique is capable to provide, in 1.3 s, morphological images of the phantom without the need to rotate the X-ray source around the object to be irradiated, showing the feasibility of such system.
Keywords: Low-dose imaging for radiotherapy, Rotationfree megavoltage tomography, X-ray detection, Image-guided radiotherapy (IGRT)
  • Lecture (Conference)
    IEEE Nuclear Science Symposium and Medical Imaging Conference, 10.-17.11.2018, Sydney, Australien

Publ.-Id: 28704 - Permalink


Double-bended saturation of optically induced bleaching in graphene
Winnerl, S.; Winzer, T.; Mittendorff, M.; Mittenzwey, H.; Jago, R.; Schneider, H.; Helm, M.; Malic, E.; Knorr, A.;
Saturable absorption due to Pauli blocking is a fundamental optical phenomenon that can be described fully analytically for a two-level system. In solids, the related carrier dynamics is typically much more complex. Nevertheless, the fluence dependence of the induced bleaching is typically qualitatively similar to the behaviour of a two-level system. Saturable absorbers are important photonic devices for realizing short laser pulses.
We present a joint theory-experiment study, where the bleaching of graphene is studied in a wide range of fluences. In pump-probe experiments utilizing 30 fs near-infrared (wavelength 800 nm) pulses the pump-induced transmission is measured. The study reveals an unusual double-bended saturation behaviour. For fluences in the mJ/cm2 range the induced transmission saturates due to Pauli blocking. Interestingly, a qualitatively similar behaviour is found at fluences that are 1000 times smaller. In this range one would expect a linear fluence dependence of the induced transmission. Microscopic theory based on the density matrix formalism shows that the unexpected saturation at low fluences is related to intensity dependent many-particle scattering. The crucial point is the balance between in- and out-scattering of electrons from the optically excited k-space regions. The occupation of this region determines the observed transmission [1].
Full understanding of the saturation behaviour in graphene is of relevance for graphene-based saturable absorbers. Graphene is an interesting material for this purpose as it can be applied in a very broad spectral range from THz to UV [2,3]. Also the high damage threshold, which is verified in our experiments, is an attractive feature.

[1] T. Winzer et al., Nature Commun. 8 (2017) 15042
[2] V. Bianchi et al., Nature Commun. 8 (2017) 15763
[3] D. G. Purdie et al., Appl. Phys. Lett. 106 (2015) 253101
Keywords: graphene, ultrafast dynamics, saturable absorption
  • Poster
    Graphene 2018, 26.-29.06.2018, Dresden, Deutschland

Publ.-Id: 28703 - Permalink


Unusual Coulomb effects in graphene
Winnerl, S.;
In many semiconductors Coulomb scattering plays an essential role in the thermalization process of a non-equilibrium carrier distribution. Here we discuss three surprising and fascinating manifestations of Coulomb scattering in graphene. All phenomena are explored both experimentally and by manybody theory. The experimental techniques for time-resolved studies at rather low photon energy (mi-infrared and terahertz range) are introduced and we explain why epitaxial graphene samples are particularly well suited for our experiments.
The first observation concerns a double-bended saturation behavior of bleaching induced by near-infrared radiation. The second phenomenon is the optically induced anisotropy in k-space for excitation with linearly polarized radiation and its relaxation to a Fermi-Dirac distribution. The third set of experiments tackles the dynamics of graphene in a magnetic field perpendicular to the graphene layer. Here evidence for strong Auger scattering is found. We discuss the possibility to apply Landau quantized graphene as a gain medium in a tunable laser and as a tunable nonlinear optical material.
Keywords: graphene, ultrafast dynamics, Coulomb scattering
  • Invited lecture (Conferences)
    Tianjin International Symposium on Epigraphene (TISEG), 22.-27.07.2018, Tianjin, China

Publ.-Id: 28702 - Permalink


Low energy relaxation dynamics in graphene and MoSe2
Winnerl, S.;
Time-resolved investigations of 2D materials such as graphene and transition metal dichalcogenides (TMDs) in the energetic vicinity of their low-energy excitations provide deep insights into the physical processes involved in the carrier relaxation dynamics. We show results of pump-probe experiments in the mid-infrared and terahertz rage using a free-electron laser as a source. They allow one to disentangle the role of carrier-carrier and carrier-phonon scattering. As an application, an ultra-broadband fast photodetector is demonstrated. Furthermore we present very recent results on monolayer MoSe2. Here, fairly slow carrier cooling is observed. At the overlap of the terahertz pump pulse with the near-infrared probe pulse we see a red-shift of both the exciton and trion peak. This signal may stem from either the Franz-Keldysh or the AC-Stark effect.
  • Lecture (others)
    Seminar of Physics Departmern, Chalmers University, 14.11.2018, Göteborg, Schweden

Publ.-Id: 28701 - Permalink


Pump-probe spectroscopy in the infrared
Winnerl, S.;
We discuss infrared pump-probe spectroscopy experiments, where both tabletop lasers and a free-electron laser are applied as radiation sources covering the inire infrared range from the near infrared to terahertz.The focus of the talk is on the basic principle of the experiment and related techniques like four-wave mixing, and on the experimental capabilities in our labs at HZDR. Electronic transitions in semiconductor quantum wells, interband transitions in graphene, plasmonic excitations in graphene ribbons will serve as examples for low-energy excitations that can be investigated in a time-resolved manner. In particular, examples for excitations with different polarization states will be discussed. Finally we will show the strength of probing with terahertz time-domain spectroscopy.
Keywords: Pump-Probe spectroscopy
  • Lecture (others)
    Leibniz-Institut für Polymerforschung, 18.12.2018, Dresden, Deutschland

Publ.-Id: 28700 - Permalink


Application of electromagnetic fields in material processing, metallurgy, casting and crystal growth
Eckert, S.;
Basic and applied research on Liquid Metal Technologies and Magnetohydrodynamics represents a surprising bandwidth ranging from high-temperature energy conversion, new kinds of liquid metal batteries, the production of solar-grade silicon, carbon dioxide free production of hydrogen, liquid metal targets in modern neutron sources and transmutation systems, casting of steel and light metals, welding and soldering processes, to basic laboratory experiments with relevance to liquid metal cooled systems, materials processing as well as to geo- and astrophysics.
Most of the metallurgical and crystal growth processes comprise phases with liquid metals (or liquid semiconductors with very similar properties). The application of diverse electromagnetic fields has proven to be a very effective tool of influencing and controlling such liquid metal flows and the corresponding heat and mass transport. For instance, most of the problems in casting of metal alloys affecting the product quality are associated with an improperly conditioned fluid flow during the process. Small improvements in the flow pattern can achieve therefore large effects in terms of quality assurance and energy savings.
This presentation gives an overview of the research activities at the HZDR with respect to the use of magnetic fields in metallurgy, casting and crystal growth. The experimental work is based on model experiments for the detailed investigation of flow processes under the influence of magnetic fields. This presentation presents a number of examples and discusses corresponding results in the light of the respective technologies considered.
Keywords: Magnetohydrodynamics, crystal growth, metallurgy, metal casting
  • Invited lecture (Conferences)
    The Third Russian Conference on Magnetohydrodynamics, 18.-21.06.2018, Perm, Russia

Publ.-Id: 28699 - Permalink


Flow structures in liquid metal Rayleigh-Benard convection under the influence of DC magnetic fields
Vogt, T.; Schindler, F.; Zürner, T.; Schumacher, J.; Tasaka, Y.; Yanagisawa, T.; Eckert, S.;
One of the classical problems in fluid dynamics is the Rayleigh-Bénard convection (RBC) where a fluid layer is exposed to a temperature difference ΔT between a colder lid and a warmer bottom. RBC under the influence of a steady magnetic field is of particular interest in geo- and astrophysics, but has also some relevance for technical applications such as the use of liquid metals for new type of batteries or heat removals in fusion blankets. In this paper we present flow measurements conducted in various geometries and magnetic field configurations. Systematic flow measurements were performed by means of the ultrasound Doppler velocimetry (UDV). Experiments were carried out in GaInSn using a cylindrical fluid vessel in a vertical magnetic field and a rectangular container exposed to a horizontal magnetic field. Various flow regimes have been identified by the velocity measurements, in particular, we studied the transition from a quasi-two-dimensional state towards a three-dimensional flow occurring with decreasing magnetic field strength.
Keywords: Rayleigh, Benard convection, liquid metals, magnetoconvection, flow measurements, ultrasound Doppler velocimetry
  • Lecture (Conference)
    9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Awaji Island, Japan

Publ.-Id: 28698 - Permalink


A material experiment for small satellites to characterise the behaviour of carbon nanotubes in space – development and ground validation
Abbe, E.; Renger, T.; Sznajder, M.; Klemmed, B.; Sachse, E.; Hübner, R.; Schüler, T.; Bärtling, Y.; Muchow, B.; Tajmar, M.; Schmiel, T.;
Over the last years, Carbon Nanotubes (CNT) drew interdisciplinary attention. Regarding space technologies a variety of potential applications were proposed and investigated. However, no complex data on the behaviour and degradation process of carbon nanotubes under space environment exist. Therefore, it is necessary to investigate the performance of these new materials in space environment and to revaluate the application potential of CNTs in space technologies. Hence, CiREX (Carbon Nanotubes – Resistance Experiment) was developed as a part of a student project. It is a small and compact experiment, which is designed for CubeSat class space satellites. These are a class of nanosatellites with a standardized size and shape. The CiREX design, electrical measurements and the satellites interfaces will be discussed in detail. CiREX is the first in-situ space material experiment for CNTs. To evaluate the data obtained from CiREX, ground validation tests are mandatory. As part of an extensive test series the behaviour of CNTs under solar ultra violet light (UV) and vacuum ultraviolet light (VUV) was examined. Single-walled carbon nanotubes (SWNT), multi-walled carbon nanotubes (MWNT) and MWNT/resin composite (ME) were exposed to different light sources. After the exposure, the defect density was investigated with Raman spectroscopy. There is a clear indication that UV and VUV light can increase the defect density of untreated CNTs and influence the electrical behaviour.
Keywords: Carbon nanotubes, CubeSat, Electrical behavior, Material experiment, Solar light, Space environment

Publ.-Id: 28697 - Permalink


Nanocomposite thin film research using ion beams and in situ techniques
Krause, M.;
Lecture about research activities on "Nanocomposite thin film research using ion beams and in situ techniques"
  • Invited lecture (Conferences)
    Institutsseminar in der Veranstaltungsreihe - Doctorado en Nanociencia y Tecnologías de Materiales Facultad de Ciencias, 19.10.2018, Puerto Real, Cadiz, Spanien

Publ.-Id: 28696 - Permalink


Zr and Mo thin films with reduced residual impurities’ uptake under high vacuum conditions at room temperature
Meško, M.; Bohovičová, J.; Munnik, F.; Grenzer, J.; Hübner, R.; Čaplovič, Ľ.; Čaplovičová, M.; Vančo, Ľ.; Vretenár, V.; Krause, M.;
In recent years, transition (refractory) metals such molybdenum (Mo) and zirconium (Zr) have been studied as infrared (IR) reflector in solar absorber applications. The sputter process parameters are very important for depositing a high quality thin film achieving the necessary low emittance. IR reflectance of the metal film is influenced by the film microstructure, presence of residual impurities and surface roughness. The main objective of the present study is to prepare Mo and Zr metallic thin films with improved optical properties by high power impulse magnetron sputtering at room temperature under high vacuum conditions. In comparison to the Mo and Zr thin films deposited by direct current magnetron at the same average power, thin films deposited by HiPIMS exhibits dense microstructure without voids, grown preferentially along c-axis, have smooth surface and are free of residual contaminants. Compared to the dcMS films we observed an element specific reduction of impurities measured by elastic recoil detection analysis (ERDA) by a factor 4/8 for N, 3/4 for H and 9/14 for O for Mo/Zr thin films respectively. The compositional effects are correlated with differences in the film morphology microstructure revealed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis.
  • Poster
    16th International Conference on Plasma Surface Engineering, 16.-21.09.2018, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 28695 - Permalink


Vacuum and in-air thermal stability studies of SnO2-based TCO for concentrated solar power applications
Mendez, A.; Lungwitz, F.; Schumann, E.; Janke, D.; Guillén, E.; Escobar Galindo, R.; Gemming, S.; Fernández-Martínez, I.; Krause, M.;
In concentrated solar power plants, the receiver tubes are one of the key components to increase the solar-thermal conversion efficiency. Absorber materials of those tubes have to exhibit high-temperature and air stability, high optical absorption in the solar region and low thermal emittance. In state of the art central tower plants black paints (i.e. Pyromark 2500) are used as absorber material. However, the high emissivity of those paints leads to high radiative energy losses. Moreover, these paints undergo a temporal degradation and performance loss during the lifetime of the plant.
Here, an alternative concept for high-temperature stable solar-selective coatings is presented. It consists of a transparent conductive oxide (TCO) deposited as solar-selective transmitter on a black body absorber. For this purpose, SnO2:Ta thin films were reactively sputtered on fused quartz substrates. Their vacuum and in-air stability up to 800°C were studied by in situ Rutherford backscattering spectrometry (RBS), Raman spectroscopy and spectroscopic ellipsometry (SE). The correlation between structural, optical and electric transport properties was analyzed by RBS, SE, UV-Vis spectrometry, and Hall effect measurements. Solar selective properties are demonstrated as proof of concept for the TCO deposited on a silicon substrate.
Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged.
  • Lecture (Conference)
    16th International Conference on Plasma Surface Engineering, 16.-21.09.2018, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 28694 - Permalink


Design and high-temperature durability tests of solar-selective coatings based on aluminium titanium oxynitrides AlyTi1-yOxN1-x
Escobar-Galindo, R.; Guillén, E.; Heras, I.; Lungwitz, F.; Munnik, F.; Rincon-Llorente, G.; Alcon-Camas, M.; Schumann, E.; Azcona, I.; Krause, M.;
Aluminium titanium oxynitrides were studied as candidate materials for high temperature absorbers in solar-selective coatings (SSC) due to their excellent stability and their tuneable optical behaviour. A set of individual AlyTi1-y(OxN1-x) layers with different oxygen content was prepared by cathodic vacuum arc (CVA) deposition. A comprehensive analysis of the sample microstructure and morphology allowed an accurate modelling of the optical constants in the whole wavelength range of solar interest (190 nm - 25 μm). The optical properties of these films can be controlled from metallic to dielectric character by adjusting the oxygen content. Complete multilayer SSC, including a TiN layer as IR reflector, were designed by applying optical simulations, obtaining excellent optical selective properties (α = 94.0% and εRT = 4.8%). The design concepts were validated by an excellent agreement between simulated and experimental stacking order, composition and optical properties. The durability of two multilayers was studied under conditions simulating realistic operation of central receiver power plants. Both SSC stacks were stable in single stage tests of 12 h at 650°C in air. During cyclic tests, the coarser microstructure of multilayer 1, was found to be more resistant against oxidation than multilayer 2 constituted of four oxynitride layers with a graded oxygen content. Multilayer 1 fulfilled the performance criterion of PC ≤ 5% for 300 symmetric, 3 h long cycles at 600°C in air confirming that the designed SSCs are exciting candidate material for concentrated solar power applications at high temperature. Financial support by the EU, grant No. 645725, project FRIENDS22, is gratefully acknowledged.
Keywords: Solar-selective coatings, CSP, Optical simulation, Thermal test
  • Lecture (Conference)
    16th International Conference on Plasma Surface Engineering, 16.-21.09.2018, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 28693 - Permalink


On the Effect of Thin Film Growth Mechanisms on the Specular Reflectance of Aluminium Thin Films Deposited via Filtered Cathodic Vacuum Arc
Rincón-Llorente, G.; Heras, I.; Guillén Rodríguez, E.; Schumann, E.; Krause, M.; Escobar-Galindo, R.;
The optimisation of the specular reflectance of solar collectors is a key parameter to increase the global yield of concentrated solar power (CSP) plants. In this work, the influence of filtered cathodic vacuum arc deposition parameters, particularly working pressure and deposition time, on the specular and diffuse reflectance of aluminium thin films, was studied. Changes in specular reflectance, measured by ultraviolet–visible and near-infrared spectroscopy (UV-vis-NIR) spectrophotometry, were directly correlated with thin film elemental concentration depth profiles, obtained by Rutherford backscattering spectrometry (RBS), and surface and cross-sectional morphologies as measured by scanning electron microscopy (SEM) and profilometry. Finally, atomic force microscopy (AFM) provided information on the roughness and growth mechanism of the films. The two contributions to the total reflectance of the films, namely diffuse and specular reflectance, were found to be deeply influenced by deposition conditions. It was proven that working pressure and deposition time directly determine the predominant factor. Specular reflectance varied from 12 to 99.8% of the total reflectance for films grown at the same working pressure of 0.1 Pa and with different deposition times. This transformation could not be attributed to an oxidation of the films as stated by RBS, but was correlated with a progressive modification of the roughness, surface, and bulk morphology of the samples over the deposition time. Hence, the evolution in the final optical properties of the films is driven by different growth mechanisms and the resulting microstructures. In addition to the originally addressed CSP applications the potential of the developed aluminium films for other application rather than CSP, such as, for example, reference material for spectroscopic diffuse reflectance measurements, is also discussed.
Keywords: filtered cathodic vacuum arc; total and specular reflectance; thin film deposition conditions; structural characterisation

Publ.-Id: 28692 - Permalink


Statistical entropy analysis as tool for circular economy: Proof of concept by optimizing a lithium-ion battery waste sieving system
Reuter, M. A.; van den Boogaart, K. G.; Lundströma, M.; Santasalo-Aarnioa, A.; Velázquez Martíneza, O.; Serna-Guerreroa, R.;
With the concept of circular economy gaining strength as an alternative for the sustainable production of raw materials, there is an inherent need to develop methods capable of quantifying the efficiency of recycling systems, provide guidelines for optimization of existing technologies, and support the design of new products based on sound, scientific and engineering principles. The work hereby presented proposes the use of statistical entropy coupled with material flow analysis as a basis for the optimization of separation and purification processes. Unlike other efficiency parameters, this approach provides an analysis of component concentration or dilution from a systemic perspective, taking into consideration products, by-products and waste streams. As a proof-of-concept, a sieving process for waste lithium-ion batteries (LIB) was chosen. It is demonstrated that using this approach it is possible to determine the stages that do not contribute to the concentration of components thus offering guidelines for process optimization. In the present case, the total number of sieving stages can be decreased with a minimum impact on the concentration of the products. In comparison, it is also shown that the widely accepted exergy analysis is not able to identify the opportunities for optimization due to the particular characteristics of this exemplary system, i.e., negligible change in energy consumption as a function of sieving stages and absence of chemical changes. Finally, the experimental results suggest that Al and Cu can be concentrated using a simple sieving pre-processing step, perhaps in preparation for a subsequent refining stage.
Keywords: Circular economy, Material flow analysis, Relative statistical entropy, Lithium-ion batteries, Process simulation, Process optimization

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  • Secondary publication expected from 15.12.2019

Publ.-Id: 28691 - Permalink


FPGAs and the Cloud – An Endless Tale of Virtualization, Elasticity and Efficiency
Knodel, O.ORC
The flexible use of reconfigurable devices within a cloud context requires abstraction from the actual hardware through virtualization to offer these resources to service providers. In this talk, we present our Reconfigurable Common Computing Frame (RC2F) approach – inspired by system virtual machines – for the profound virtualization of reconfigurable hardware in cloud services. Using partial reconfiguration, our framework abstracts a single physical FPGA into multiple independent virtual FPGAs (vFPGAs). A user can request vFPGAs of different size for optimal resource utilization and energy efficiency of the whole cloud system. To enable such flexibility, we create homogeneous partitions on top of an inhomogeneous FPGA fabric abstracting from physical locations and static areas. On the host side our Reconfigurable Common Cloud Computing Environment (RC3E) offers different service models and manages the allocation of the dynamic vFPGAs.
Keywords: Reconfigurable Hardware; FPGA; Cloud; Virtualization
  • Invited lecture (Conferences)
    13th HiPEAC Workshop on Reconfigurable Computing (WRC'2019), 21.01.2019, Valencia, Spain

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Publ.-Id: 28690 - Permalink


Magnetically Induced Cavitation for the Dispersion of Particles in Liquid Metals
Sarma, M.; Grants, I.; Bojarevics, A.; Gerbeth, G.;
A contactless excitation of cavitation is possible by superposition of induction heating with a static axial magnetic field. This creates an alternating electromagnetic body force in a liquid metal which in turn produces pressure oscillations. Using this method, the onset of cavitation has been clearly observed in various liquid metals (tin, zinc, aluminum, steel SAE 304) at pressure oscillations in the range of 28…50 kPa. The present study aims to extend the previous work by producing steel metal matrix composites (MMC) and assessing the feasibility of the proposed method for particle dispersion in steel. Stainless steel (SAE 316L) samples with different ceramic inclusions, e.g. TiN, Al2O3, TiB2 as well as others, have been created. It has been demonstrated that the cavitation onset in the liquid steel varies extensively and depends on the cavitation nuclei rather than the strength of acoustic pressure. The microstructure of the produced samples has been analyzed using SEM and EDS.
Keywords: MMC production; Steel composites; Cavitation treatment
  • Contribution to proceedings
    TMS 2018, 11.-15.03.2018, Phoenix, Arizona, United States of America
    Magnetically Induced Cavitation for the Dispersion of Particles in Liquid Metals: Springer, Cham, 978-3-319-72852-0
    DOI: 10.1007/978-3-319-72853-7_12

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Publ.-Id: 28687 - Permalink


Dendritic structure formation of magnesium alloys for the manipulation of corrosion properties: Part 1 – microstructure
Lakoma, P.; Ditze, A.; Scharf, C.;
Besides impurities in magnesium alloys containing aluminum, the microstructure also plays a role in the corrosion properties of the alloy. By targeted manipulation of grain size, secondary dendrite arm spacings and segregation in terms of amount and position, the corrosion properties are expected to be improved. For this, experiments were carried out by casting alloys with 0, 3, 6, 9, and 12%aluminum into a mold with different applied cooling rates. The samples were analyzed regarding microstructure and composition, and the grain size and secondary dendrite arm spacings, as a function of aluminum content and cooling rate, were modeled. The results show a decrease in grain size and secondary dendrite arm spacings with an increased cooling rate. The segregated b phase was predominantly situated at the grain boundaries as divorced eutectic and in lamellar form. The assumed influences on the corrosion properties will be examined in Part 2.
Keywords: Magnesium alloy; Microstructure; Corrosion behavior; SDAS
  • International Journal of Materials Research 109(2018)12, 1081-1091
    DOI: 10.3139/146.111708

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  • Secondary publication expected from 10.01.2020

Publ.-Id: 28686 - Permalink


Novel magnetite-biocomposites for clean-up of highly diluted Ga and As containing industrial wastewaters
Vogel, M.; Matys, S.; Hübner, R.; Pollmann, K.;
Gallium is an essential element in many semi-conducting products, electronic devices and opto-electronic components. It is mostly applied as GaAs and GaN. Despite it’s growing demand it is currently not recycled. The development of novel biocomposites based on magnetite and biopolymers for the selective binding of Ga and As from diluted flushing solutions of the semi-conducting industry offers a promising concept for the efficient, economical and sustainable recycling of these metal(loids).

In this study several magnetite based-biocomposites for an efficient and easy separation in magnetic field were developed and optimized regarding an effective sorption behavior for Ga and As from complex but highly diluted industrial wastewaters (each 4 mg/L, pH 8.4). Combinations of magnetite nanoparticles and S-layer proteins removed up to 100% of both elements depending on the used amount of material. Additionally, the S-layer-magnetite-composites showed a better stability compared to pure magnetite during the sorption process. The materials showed a preferred sorption of Ga compared to As. An optimization of (selective) sorption and stability of the materials was achieved by addition of a second biomolecule (bovine serum albumin, phosvitin, chitosan) to S-layer-magnetite-composites. Raman spectroscopy and transmission electron microscopy with electron diffraction of the biocomposites revealed pure magnetite particles with size between 5-10 nm surrounded by the biocomponent. The zeta-potential of the biocomposites is negative which favors the binding of Ga3+ compared to negatively charged As species. Sustainability of the biocomposites is given as bound Ga and As could be completely removed from the composites with EDTA, so that the biocomposites could be reused for several sorption-desorption cycles.

In conclusion, these regenerative materials enable an efficient and selective removal of gallium and arsenic from highly diluted industrial wastewaters. The combination of magnetite with biomolecules provides a promising approach to improve metal recycling and contribute to environmentally friendly and sustainable processes.
Keywords: S-layer, magnetite, biosorption, gallium, arsenic
  • Lecture (Conference)
    4th Green & Sustainable Chemistry Conference, 05.-08.05.2019, Dresden, Germany

Publ.-Id: 28685 - Permalink


Factor Analysis, Monte Carlo Modeling and Landweber Iteration: advanced approaches to EXAFS analysis
Rossberg, A.; Scheinost, A. C.;
Factor analysis, monte carlo modeling and Landweber iteration are advanced EXAFS data analysis methods used for structurally complicated chemical systems for which common EXAFS shell fit analysis fails. Here we present the mathematical background of the advanced methods and their application.
Keywords: EXAFS, monte carlo simulation, Landweber iteration
  • Invited lecture (Conferences)
    Demi-journée de l'Atelier de l'OSUG sur le Traitement du Signal pour la Spectroscopie et l'imagerie Hyperspectrale, 25.01.2019, Grenoble, France

Publ.-Id: 28684 - Permalink


Spectral random masking: a novel dynamic masking technique for PIV in multiphase flows
Anders, S.ORC; Noto, D.; Seilmayer, M.ORC; Eckert, S.ORC
A novel masking technique for PIV-analysis of multiphase flows is presented. With this new approach, the velocity-field of an unmasked particle fraction (e. g. PIV-tracers) can be determined without the influence of a second (masked) particle fraction (e. g. bubbles or solid particles). Starting from a series of segmented grayscale images in which different particle fractions are determined for each frame, different masking techniques are compared. The problems caused by state of the art masking in case of dynamic masks (individual masks for each frame) are discussed. As a solution the novel spectral random masking algorithm is presented which replaces masked regions in the images by randomized intensity patterns in order to hide them from subsequent PIV-analysis. The advantages over conventional masking techniques are demonstrated for a model experiment of crystallizing ammonium-chloride solution.
Keywords: PIV; Dynamic Image Masking; Multiphase Flow; Particle Laden Flow; Optical Measurement Techniques; Image Processing; Double Diffusive Convection

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  • Secondary publication expected from 04.04.2020

Publ.-Id: 28683 - Permalink


Significance of the electrode widths in GaAs based Photoconductive Terahertz Emitters
Abhishek, S.; Winnerl, S.; Helm, M.; Schneider, H.;
Significance of the electrode widths in GaAs based Photoconductive Terahertz Emitters
Keywords: Terahertz emitter, stripline antenna, GaAs photoconductive THz emitter
  • Poster
    8th International Workshop on Terahertz Technology and Applications, 20.-21.03.2018, Kaiserslautern, Germany

Publ.-Id: 28682 - Permalink


Broadband THz emission from Ge photoconductive antenna
Singh, A.; Pashkin, A.; Winnerl, S.; Helm, M.; Schneider, H.;
We demonstrate THz emission from a Ge-based photoconductive antenna and compare its bandwidth with the GaAs-based analog. Due to its non-polar character, the Ge emitter demonstrates a broader THz spectrum reaching up to ~ 7.5 THz.
Keywords: Broadband terahertz emitter, Ge photoconductive emitter, Terahertz spectroscopy
  • Poster
    EOS Topical Meeting on Terahertz Science & Technology (TST 2018), 06.-09.05.2018, Berlin, Germany

Publ.-Id: 28681 - Permalink


Broadband Spectrum from a Photoconductive Emitter Spanning up to 13 THz
Singh, A.; Pashkin, A.; Winnerl, S.; Helm, M.; Schneider, H.;
We demonstrate here ultra-broadband THz emission from a Ge based photoconductive emitter with the gapless spectrum extending up to ~ 13 THz, twice as far as what has been previously achieved with other materials. THz emission properties of Ge based emitter are compared with that of GaAs based emitter.
Keywords: Terahertz emitter, Germanium (Ge) photoconductive switch, Broadband terahertz
  • Contribution to proceedings
    2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 09.-14.09.2018, Nagoya, Japan
    DOI: 10.1109/IRMMW-THz.2018.8510016

Publ.-Id: 28680 - Permalink


Impact of flash-lamp-annealing on the structure of TiO2-based films
Gago, R.; Prucnal, S.; Hübner, R.; Jiménez, I.; Palomares, J.;
Many applications of titanium dioxide (TiO2) partially rely on its good performance as solvent for impurities [1]. For example, metal (cation) dopants can functionalize or enhance TiO2 as catalyst [2], diluted magnetic semiconductor [3] or transparent conductor [4]. Special attention has been devoted to TiO2 photoactivity where doping has been extensively studied towards band-gap narrowing to achieve visible-light (VISL) response [2]. Here, the most common approach has relied on anion (B,C,N,F,S,…) dopants triggered by the work of Asahi et al. [5]. However, cation (Cr,V,Fe,Ni,Mo,…) doping can also effectively increase VISL absorption but introducing severe structural distortions that additionally result in carrier recombination centers [4].
Our interest is focused on improving the structural quality of metal (co-)doped TiO2 films by post-deposition rapid and non-contact thermal treatments such as flash-lamp-annealing (FLA). An additional objective is to do so with (single and mixed) phase selectivity. For example, the promotion of anatase would be preferable due to the superior photoactivity of this phase or phase mixtures with high anatase content [6]. In particular, in this paper we address the impact of FLA on pure and (co-)doped (Cr,N) TiO2 films produced by magnetron sputtering as relevant systems for VISL photoactivity. The results on monolithic films [7] will be presented as well as promising alternatives to promote anatase by the use of modulated film architectures. The interest of FLA processing can also be extended to other dopants in TiO2 for improving the photoactivity or any other functionality. Therefore, the reported methodology can be attractive for many industrial applications dealing with the synthesis of band-gap engineered TiO2-based materials.
[1] Sacerdoti et al., J. Solid State Chem. 177, 1781 (2004); [2] Henderson, Surf. Sci. Rep. 66, 185 (2011); [3] Matsumoto et al. Science 291, 854 (2001); [4] Serpone et al., J. Phys. Chem. B 110, 24287 (2006); [5] Asahi et al. Science 293, 269 (2001) [6] Scanlon et al., Nat. Mater. 12, 798 (2013); [7] R. Gago, S. Prucnal et al., J. Alloys & Compounds 729 (2017) 438.
  • Lecture (Conference)
    XV Congreso Nacional de Materiales / 1st Iberian Meeting on Materials Science, 04.-06.07.2018, Salamanca, Spain

Publ.-Id: 28679 - Permalink


An Algorithm for Maximum-Likelihood Estimation of the Timing Resolution in TOF-PET
Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.ORC; Maus, J.ORC; van den Hoff, J.ORC
INTRODUCTION
As is well known, utilization of time-of-flight (TOF) information can reduce noise and improve convergence rate in PET image reconstruction since it allows to incorporate the (Gaussian) probability density function (the ”TOF-kernel”) of the annihilation event position along the respective LOR into the image reconstruction process. In doing so, it is crucial to use the best possible estimate of the actually given timing resolution in order to achieve a realistic contrast recovery and minimize noise, see [1]. Moreover, it was recently recognized that using the correct timing resolution is necessary to avoid artifacts in Maximum-Likelihood reconstruction of Attenuation and Activity (MLAA), which is in agreement with our own experience. In this context, it is relevant to recognize that the timing resolution of a time-of-flight PET system is count rate dependent, see e.g. [2]. However, count rate dependent TOF-resolution calibration is usually not provided by the vendors. We, therefore, developed a procedure which is compatible with clinical routine and is also applicable retrospectively to existing data.

METHODS
We propose a novel Maximum-Likelihood Timing Resolution Estimation (MLTRE) algorithm that maximizes likelihood by updating activity image and TOF-kernel width alternately. For activity update, TOF-MLEM was used and quadratic surrogate based maximization of the likelihood was performed
to timing resolution update. The listmode version of the algorithm was used to exclude a possible influence of the TOF-binning procedure on the timing resolution estimation process. Ordered subsets optimization was applied in order to reduce computation time. The algorithm was integrated into our
previously developed Tube of response High resolution OSEM Reconstruction (THOR) [3]. THOR incorporates normalization, attenuation, dead-time, randoms corrections, as well as different options for TOF scatter correction including TOF-Single Scatter Simulation algorithm (TOF-SSS), see [4], and
two accelerated in-house algorithms. MLTRE was evaluated using phantom and patient studies covering a large range of count rates that were acquired with a Philips Ingenuity TF PET/MR scanner. Studies were grouped by imaging protocol (”brain” and ”whole-body”, covering different transaxial fields
of view). The iteration scheme of five timing resolution updates per single MLEM update was chosen to achieve convergence of the algorithm in all studies. Iteration was initialized with a timing resolution estimate of 700 ps. Performance of the algorithm was also investigated in the extreme high contrast
conditions that are typical for pelvis region investigations. A dedicated phantom was used for this purpose. Global convergence of MLTRE is not guaranteed. Therefore it is recommended to use a reasonable TOF-kernel width as the start value for the algorithm. In order to assess the stability of the algorithm regarding this start value, MLTRE reconstructions of the same phantom study with varying initial values for the TOF-kernel width in the range [500 − 1000] ps were performed.

RESULTS
Our evaluation yields a linear dependency of timing resolution on count rate which is in correspondence with the reports by other groups, see [2]. According to our results the scanner reaches 551 ps timing resolution at “zero” count rate. Resolution degrades by 146 ps for each ten millions of singles counts per second. Timing resolution degradation can exceed 150 ps ( 25% of initial TOF-kernel width) for clinical relevant count rates. No difference in estimated timing resolution between brain and whole-body protocal was encountered. However, scatter and attenuation correction errors can adversely affect timing resolution estimation. Therefore, using patient data for calibration purposes in PET/MR is not optimal. Dedicated phantom measurements are preferable. However, the procedure is still suitable for retrospective application to existing clinical data if TOF-scatter and attenuation correction
are reliable. Although global convergence of MLTRE algorithm is not guaranteed, no significant influence of the chosen start value for TOF-kernel width on estimated timing resolution was encountered in our data. The results are deviating from the mean by ∼ 4 ps (≈ 0.5%) at maximum whilst the initial values were varied between 500 and 1000 ps.

CONCLUSION
Our preliminary results indicate that the proposed algorithm is capable of realistic timing resolution estimation, while being convenient and easy to use in clinics. To the best of our knowledge, the dependency of timing resolution on singles rate of the Philips Ingenuity TF PET/MR scanner was never published before. According to our findings, the timing resolution of this scanner degrades rapidly with increasing count rate. This fact should be accounted for during image reconstruction.

REFERENCES
[1] S. Vandenberghe, S. Matej, M. E. Daube-Witherspoon, M. Guerchaft, J. Verhaeghe, A. Bol, L. Van Elmbt, I. Lemahieu, and J. S. Karp, “Determining timing resolution from TOF-PET emission data,” IEEE Nuclear Science Symposium Conference Record, vol. 4, pp. 2727–2731, 2007.
[2] S. Surti, A. Kuhn, M. E. Werner, A. E. Perkins, J. Kolthammer, and J. S. Karp, “Performance of Philips Gemini TF PET/CT scanner with special consideration for its time-of-flight imaging capabilities.” Journal of nuclear medicine : official publication, Society of Nuclear Medicine, vol. 48, no. 3, pp. 471–480, 2007.
[3] A. Lougovski, F. Hofheinz, J. Maus, G. Schramm, E. Will, J. van den Hoff, and J. van den Hoff, “A volume of intersection approach for on-the-fly system matrix calculation in 3D PET image reconstruction,” Physics in Medicine and Biology, vol. 59, no. 3, pp. 561–577, feb 2014.
[4] C. C. Watson, “Extension of Single Scatter Simulation to Scatter Correction of Time-of-Flight PET,” IEEE Transations on Nuclear Science, vol. 54, no. 5, pp. 1679–1686, 2007.
Keywords: PET, PET/MR, TOF, time resolution, calibration
  • Poster
    PSMR 2018 - 7th Conference on PET-MRI and SPECT-MRI, 21.-23.05.2018, Isola d'Elba, Italy

Publ.-Id: 28678 - Permalink


Sorption of Eu(III) on Eibenstock granite studied by µTRLFS: A novel spatially-resolved luminescence-spectroscopic technique
Molodtsov, K.; Schymura, S.; Rothe, J.; Dardenne, K.; Schmidt, M.;
Granite is one of the possible host rocks for a high-level radioactive waste repository, as such it is important to understand its interactions with relevant radionuclides like Cm(III) and Am(III). Because granite is a highly heterogeneous mixture of quartz, feldspar, and mica, as well as minor components, it is difficult to study sorption mechanisms on the molecular level with conventional techniques. Consequently, most studies use isolated constituents rather than the whole system. In this study a novel technique, micro-focus time-resolved laser-induced luminescence spectroscopy (µTRLFS) is presented to overcome the problem of spatial heterogeneity. µTRLFS is a spatially-resolved upgrade of conventional TRLFS, which separates the many-phase problem of granite into many single-phase problems by reducing the beam size of the analytic laser beam to below the size of mineral grains within the natural material. This allows a point-by-point mapping of sorption capacity as well as speciation of a luminescent probe, here Eu3+. A thin-section of granitic rock from Eibenstock, Saxony, Germany was analyzed regarding its mineralogy with microprobe X-ray fluorescence (µXRF) and electron probe microanalysis (EPMA). Afterwards, it was reacted with 5.0 × 10-5 mol/L Eu3+ at pH 8.0 and uptake was quantified by autoradiography. Finally, the speciation of adsorbed Eu3+ and its uptake were studied by µTRLFS. Despite the extremely low concentration of Eu3+ on the sample, results from µTRLFS clearly show that the materials interact differently with Eu3+, and often even on one mineral grain different speciations can be found. Alkali-feldspar shows very high uptake, with an inhomogeneous distribution, and intermediate sorption strength. On quartz uptake is almost 10-fold lower, while the complexation strength is higher than on feldspar. This may be indicative of adsorption only at surface defect sites, in accordance with long lifetimes and low hydration of the observed species.
Keywords: TRLFS, granite, µTRLFS, Europium, sorption

Publ.-Id: 28677 - Permalink


Coherent control of spin qubit modes associated with defects in silicon carbide
Astakhov, G. V.;
Quantum bit or qubit is a two-level system, which builds the foundation for quantum computation, simulation, communication and sensing. Quantum states of higher dimension, i.e., qutrits (D = 3) and especially qudits (D = 4 or higher), offer significant advantages. Particularly, they can provide noise-resistant quantum cryptography, simplify quantum logic and improve quantum metrology. Flying and solid-state qudits have been implemented on the basis of photonic chips and superconducting circuits, respectively. However, there is still a lack of room-temperature qudits with long coherence time and high spectral resolution. The silicon vacancy centers in silicon carbide (SiC) with spin S = 3/2 are quite promising in this respect. Here, Dr. Astakhov reports a two-frequency protocol to excite and image multiple qudit modes in a SiC spin ensemble under ambient conditions. Strikingly, their spectral width is about one order of magnitude narrower than the inhomogeneous broadening of the corresponding spin resonance. By applying Ramsey interferometry to these spin qudits, a spectral selectivity of 600 kHz and a spectral resolution of 30 kHz are achieved. As a practical consequence, we demonstrate absolute DC magnetometry insensitive to thermal noise and strain fluctuations.
Keywords: Spin defects, quantum applications, coherent control, silicon carbide
  • Invited lecture (Conferences)
    Theo Murphy international scientific meeting. SiC quantum spintronics: towards quantum devices in a technological material, The Royal Society at Chicherley Hall, 05.-06.11.2018, Buckinghamshire, United Kingdom

Publ.-Id: 28676 - Permalink


Millisecond Flash Lamp Annealing and Application for SiGe-HBT
Scheit, A.; Lenke, T.; Schumann, T.; Rebohle, L.; Skorupa, W.; Häberlein, S.;
A 200 mm millisecond flash lamp annealing (FLA) prototype was developed beside the EU project DOTSEVEN, named after the target for the maximum oscillation frequency (fmax) of 0.7 THz of a SiGe-HBT (Hetero Bipolar Transistor) [1]. The substitution of the final spike annealing (SPA) by FLA reduces the thermal budget despite higher peak temperatures. The development of the FLA process has to focus on the best dopant activation of the implants for high fmax and low deactivation of the intrinsic HBT base for high transit frequency (fT). For FLA the wafers are heated by halogen lamps to an intermediate temperature between 650°C and 850°C. The following Xenon flash lamp pulse increases the front surface temperature with an energy density between 10 J/cm² and 25 J/cm² within 1,0 ms (105 K/s). The pulse energy is limited by the occurrence of wafer breakage.
Among different experiments n-type Si (100) wafers (8-12 Ωcm) were pre amorphized with Germanium (5*1014/cm²; 15 keV) followed by Boron (B) (2*1015/cm²; 1 keV) [2]. FLA (780°C, 5s & 16 J/cm²) results in a suppressed B diffusion (Fig.1a) with concurrent higher activation (Rs = 202 Ω/sq) compared to spike annealing (SPA) at 1020°C with 250 K/s (Rs = 348 Ω/sq). The dopant loss trough the surface is about 30% for both annealings. A higher ratio of flash energy versus pre heat temperature (730°C, 5s & 23 J/cm²) enables a higher activation (Rs = 164 Ω/sq) with a steeper profile (5 nm/dec) and a negligible dopant loss. The slope can be adjusted from 5 nm/dec to 10 nm/dec. The second experiment is based on a model SiGe-HBT with a B base of 8 nm width at a concentration of 1018/cm³ to investigate the influence of the thermal treatment on the shape of the profile. SPA at 1020°C with 250 K/s results in a 40 nm broad profile. The reduction of this broadening down to 20 nm was defined as an internal project goal. FLA (780°C, 30s & 14 J/cm²) reduces the profile broadening by 10 nm. A stronger flash pulse with a colder pre heat (730°C, 5s & 21 J/cm²) achieve our requirements. Based on this FLA process an experimental SiGe HBT technology featuring fT / fmax / BVCEO = 505 GHz / 720 GHz / 1.6 V was developed.
Keywords: flash lamp annealing, heterojunction bipolar transistor, spike annealing, Germanium
  • Lecture (Conference)
    22nd International Conference on Ion Implantation Technology 2018, 16.-21.09.2018, Würzburg, Deutschland

Publ.-Id: 28675 - Permalink


Engineering of highly coherent spin centers in silicon carbide
Astakhov, G. V.;
Building quantum devices based on silicon carbide (SiC) is highly desirable, facilitated by established SiC CMOS technology. Optoelectronic SiC devices have already been demonstrated, however, the signal- mediating quantum defects are usually introduced in a semi-random manner, by bulk electron or neutron irradiation. We present the controlled generation of quantum centers in silicon carbide (SiC) by focused proton beam in a noncomplex manner without need for pre- or postirradiation treatment. The generation depth and resolution can be predicted by matching the proton energy to the material’s stopping power, and the amount of quantum centers at one specific sample volume is tunable from ensembles of millions to discernible single photon emitters. We identify the generated centers as silicon vacancies through their characteristic magnetic resonance signatures and demonstrate that they possess highy coherent spin properties even at room temperature.
Keywords: Spin defects, quantum applications, silicon carbide
  • Invited lecture (Conferences)
    3rd International Conference on Metamaterials and Nanophotonics METANANO 2018, 16.-21.09.2018, Sochi, Russian

Publ.-Id: 28674 - Permalink


Magnetic imaging with high spatial and temporal resolution at the PolLux endstation of the Swiss Light Source
Finizio, S.; Wintz, S.; Witte, K.; Watts, B.; Raabe, J.;
Scanning transmission x-ray microscopy (STXM) is an x-ray microscopy technique that relies on the use of diffractive optics (Fresnel zone plates) to focus a monochromatic x-ray beam onto a spot of an x-ray transparent sample, and record the transmitted x-ray intensity with a suitable detector. By raster scanning the sample with a piezoelectric stage and recording the transmitted intensity at each point of the scan, a STXM image is then formed. STXM imaging combines the elemental sensitivity of monochromatic x-rays with the x-ray magnetic circular dichroism (XMCD) effect, allowing for the imaging of e.g. micro- and nanostructured magnetic materials, and multilayered magnetic systems. Depending on the employed zone plate, spatial resolutions on the order of 10 to 30 nm can be achieved with STXM imaging in the soft x-ray region. Time-resolved STXM imaging in the pump-probe regime is also possible. This is made possible by the use of avalanche photodiodes to detect the x-rays, and allows the achievement of temporal resolutions on the order of 50-100 ps. In this contribution, we present the current status and operation performances of the X07DA PolLux STXM endstation of the Swiss Light Source [1]. In particular, the perfor- mance of the endstation in imaging magnetic systems at high spatial and temporal resolutions will be presented. Furthermore, thanks to its modular design, the PolLux endstation allows for the implementation of specific setups aimed at the imaging of magnetic systems under special configurations. An example of such specific setups, which will be presented in this contribution, is the combination of STXM imaging with electrical transport measurements (e.g. aimed at the measurement of topological contributions of magnetic skyrmions to the anomalous Hall effect [2]).
  • Poster
    International Conference on Magnetism, 15.-20.07.2018, San Francsisco, USA

Publ.-Id: 28673 - Permalink


Evaluation of Nanoparticle Inks on Flexible and Stretchable Substrates for Biocompatible Application
Schubert, M.; Wang, Y.; Vinnichenko, M.; Rebohle, L.; Fritsch, M.; Schumann, T.; Bock, K.;
The flexible and stretchable electronic market is increasing particularly in the field of biomedical electronics. Widely used printed silver conductive tracks today are only eligible for on-skin applications. However, for biomedical applications fully biocompatible, flexible and even stretchable materials for device fabrication are needed. This paper presents an additive printing approach to fabricate flexible and stretchable electronics by using a biocompatible platinum material. Usually, in order to realize electrically conducting Pt-interconnects by inkjet printing, it requires a furnace sintering at prohibitively high temperatures, which are not compatible with thermal sensitive polymeric substrates. This paper describes a high-power diode laser sintering (HPDL) and a flash lamp annealing (FLA) as promising alternative sintering methods. Both processes are eligible whereas laser sintering showed slightly better results. Bending tests and adhesive strength tests of platinum printed inks on polyimide with up to 180 000 cycles, show that printed platinum is a suitable biocompatible material for flexible electronics.
Keywords: flexible, stretchable, biocompatible, photonic sintering, platinum, silver, nanoparticle ink, flash lamp, laser sintering
  • Poster
    7th Electronic System-Integration Technology Conference, 18.-21.09.2018, Dresden, Deutschland
  • Open Access LogoContribution to proceedings
    7th Electronic System-Integration Technology Conference, 18.-21.09.2018, Dresden, Deutschland
    DOI: 10.1109/ESTC.2018.8546494

Publ.-Id: 28672 - Permalink


Time-resolved imaging of the gyration dynamics of nπ states in weak PMA systems
Finizio, S.; Wintz, S.; Gliga, S.; Mruczkiewicz, M.; Kirk, E.; Wessels, T.; Zeissler, K.; Weigand, M.; Raabe, J.;
Despite the numerous predictions from micromagnetic simulations [1], only limited experimental investigations of the dynamical processes of perpendicularly magnetized spin configurations, such as e.g. magnetic skyrmions [2,3] exist. One of the causes behind this is the relatively high Gilbert damping (e.g. for Pt/Co stacks on the order of 0.2 [4]), and to the relatively high density of pinning sites of the typical materials employed for the stabilization of such magnetic states. Such high values of both pinning and Gilbert damping strongly influence the behavior of the perpendicularly magnetized spin configurations both statically [5] and dynamically [3]. In this contribution, we present an alternative solution to the use of multilayer stacks exhibiting perpendicular magnetic anisotropy (PMA) for the time-resolved investigation of the dynamical processes of magnetic skyrmions and the more complex nπ states. This solution relies on the use of a Permalloy-based PMA system exhibiting a weak PMA [6]. By judiciously optimizing the sample design, we were able to stabilize magnetic configurations ranging from magnetic skyrmions to more complex nπ states (see Fig. 1) in nano- structured elements. The nπ states stabilized in the nanostructured elements were excited by RF and pulsed magnetic fields generated through the injection of electrical currents across a tailored antenna fabricated close to the magnetic nanostructures. Thanks to the combination of a low Gilbert damping and a relatively low density of pinning sites of this weakly-PMA system, the gyration dynamics in magnetic states ranging from magnetic skyrmions to the more complex nπ states could be imaged by time-resolved scanning transmission x-ray microscopy, proving the feasibility of this material for the study of the dynamical processes in magnetic skyrmions and in nπ states.
  • Lecture (Conference)
    International Conference on Magnetism, 15.-20.07.2018, San Francisco, USA

Publ.-Id: 28671 - Permalink


Flash lamp annealing of memristive BiFeO3 thin films simulated with COMSOL Multiphysics
Bürger, D.; Baitule, S.; Rebohle, L.; Schulz, S.; Schmidt, H.;
Annealing techniques are key technologies in semiconductor industry. Removing implantation damage, activating dopants, and crystallizing sputtered amorphous layers are only some applications of annealing technologies. Pulsed laser annealing on the nanosecond timescale and longterm annealing in the range of hours are on the short and on the long end of the time scale, respectively. On an intermediate millisecond time scale, flashlamp annealing (FLA) plays an important role as an homogenous annealing technique with a large throughput for industrial applications [1]. Adjustable FLA parameters are energy density and the duration of the pulse. Pulse repetition frequency and shape of the pulse are technical aspects of FLA setups with lower energy density which are commonly used for materials on flexible substrates. So far, less attention has been paid to the geometry of the chamber and to the substrate holder influencing the temperature of the annealed wafer. The former one is influencing the irradiance distribution, the latter one is influencing the heat conduction and the cooling rate of the wafer. The irradiance distribution has a large influence on the temperature close to inhomogeneities on the surface or the edge of the sample [2]. The cooling rate after the FLA pulse determines the effect of thermal treatment on the sample properties due to diffusion processes within the sample. Our studies on BiFeO3 thin films on Si/SiO2/Ti/Pt substrates, which we develop for resistive switching applications, show that highly energetic pulses may lead to a phase separation in BiFeO3 and can cause formation of metallic-like conduction paths whereas multiple flashes with lower energy density keep the insulating and memristive properties of BiFeO3 (BFO).
To understand these aspects in detail, we simulated the FLA of BFO using COMSOL. In a first step, we have constructed the geometry of a typical flashlamp annealing chamber (Fig. 1). Within this geometry, the Raytracing module of COMSOL has been used to study the distribution of the rays within the chamber. As a result after MATLAB-treatment of the raw data, we have obtained an polar information of the irradiance distribution depending on the angle of incidence (Fig. 2). This information can help to understand the incorporated energy on the sample surface/wafer edges in a better way. For example, the intensity of the light at an angle of 30° with respect to the wafer-normal is still 89% of the intensity compared with the intensity directly from the top (0°). At 45° and at 65° the intensity is reduced to 75% and 38%, respectively. This irradiance distribution causes overheating of wafers at positions with non-planar structure.
In a second step, the heat conduction through a wafer has been simulated with different underlying materials of different thermal conductivity. The motivation for these simulation is caused by the fact that BFO thin films on Si/SiO2/Ti/Pt substrates annealed by one highly energetic pulse do not show the expected memristive switching. Instead, BFO thin films on Si/SiO2/Ti/Pt substrates which have been annealed with multiple low energy pulses show memristive switching. In that case the sample lies on a thermally insulating SiO2 wafer which should prevent the flow of the energy in the underlying metallic plate. The strongly reduced cooling rate of the annealed wafer after each FLA pulse allows a step-by-step increase in temperature during multiple FLA pulses. The complete annealing process with 10 3 ms-pulses takes 6.6 seconds, but it is still more effective for BFO than alternative thermal annealing techniques. Fig. 3 presents the simulated surface temperature after 10 ms. Due to the transmission of the light, the surface of the SiO2 wafer remains quite cold. In contrast to that the surface temperature of the BFO thin film on Si/SiO2/Ti/Pt is enhanced. After 100 ms (Fig. 4), the temperature of the surface of the SiO2 wafer is increasing because the hot steel plate transfer a part of the energy to the SiO2 wafer. In general, the temperature of the BFO on Si/SiO2/Ti/Pt is enhanced with respect to the SiO2 wafer. Multiple pulses lead to a step-by-step increase in temperature which might be one reason for the success of the annealing of BFO.
Keywords: flash lamp annealing, BiFeO3, COMSOL Multiphysics
  • Lecture (Conference)
    Materials for Advanced Metallization, 18.-21.03.2018, Milano, Italy

Publ.-Id: 28669 - Permalink


Spin colour centres in SiC as a material platform for sensing and information processing at ambient conditions
Anisimov, A.; Soltamov, V.; Baranov, P.; Astakhov, G.ORC; Dyakonov, V.
Atomic-scale colour centres in bulk and nanocrystalline SiC are promising systems for quantum photonics compatible with fiber optics, quantum information processing and sensing at ambient conditions. Colour centres which acts as stable single photon sources in SiC can be key elements for quantum photonics and communications. It has been shown that there are at least two families of colour centres in SiC with S = 1 and S = 3/2, which have the property of optical alignment of the spin levels even at room temperature and above. The spin state can be initialized, manipulated and readout by means of optically detected magnetic resonance (ODMR), level anticrossing and cross-relaxation. Recently, we observed the effects of “hole burning” in the ODMR spectra, which made it possible to narrow the ODMR line by approximately an order of magnitude, which substantially increases the possibilities of technological applications of spin centres.
Keywords: Quantum technology, atom-scale defects, silicon carbide

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Publ.-Id: 28668 - Permalink


Evaluation of defects in two-dimensional MoTe2: from point to extended defects
Ghorbani-Asl, MahdiORC; Lehnert, T.; Köster, J.; Komsa, H.-P.; Kaiser, U.; Krasheninnikov, A.
Defects frequently govern the characteristics of solids, e.g., mechanical or optical properties. They also provide an efficient way to engineer materials properties, similar to doping in semiconductors. Using first-principles calculations combined with high-resolution transmission electron microscopy experiments, we study the creation, agglomeration, and evolution of vacancies in monolayer MoTe 2 under electron irradiation. Various types of point and extended defects are studied and their atomic structures and formation energies are determined. The stability of flower-like defects and trefoil-like defects are compared with the line vacancies. Our results show that single Te vacancies have a tendency for agglomeration into vacancy lines. The stability of line defects is also found to be dependent on their orientation. We have also studied the effects of uniaxial and biaxial strain on the stability and dynamics of line defects. Our electronic structure calculations show that the defects can change the electronic properties of MoTe2, suggesting new opportunities for defect engineering in these layered materials.
Keywords: 2D materials beyond graphene, TMDCs, defects, MoTe2
  • Lecture (Conference)
    DPG Spring Meeting, 16.03.2018, Berlin, Germany
  • Poster
    Conference on Physics of Defects in Solids: Quantum Mechanics Meets Topology, 09.07.2018, ICTP, Trieste, Italy
  • Poster
    Flatlands beyond Graphene, 03.09.2018, Leipzig, Germany

Publ.-Id: 28667 - Permalink


Ultrafast X-ray tomography data set for the investigation of gas-liquid two-phase flows in an impeller of a centrifugal pump
Schäfer, T.; Bieberle, A.ORC; Pietruske, H.; Hampel, U.ORC

In this study the behaviour of gas-liquid two-phase flow inside a centrifugal pump impeller is investigated using

  • ultrafast X-ray computed tomography
  • different rotational speed (1300 rpm, 1480 rpm, 1600 rpm)
  • different inlet gas/liquid fractions
  • different inlet gas-liquid flow regimes (disperse, swirling) 

Keywords: centrifugal pump; two-phase flow investigations; ultrafast X-ray computed tomography
Related publications
Ultrafast X-ray CT imaging for hydrodynamic investigations … (Id 29455) is supplemented by this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-01-16
    DOI: 10.14278/rodare.75

Downloads:

Publ.-Id: 28666 - Permalink


Simulation of Nanodevices
Wagner, C.; Teichert, F.ORC; Fuchs, F.; Schuster, J.ORC; Schreiber, M.ORC; Gessner, T.
Presentation of TP1 / DFG research unit 1713 “Sensoric micro- and nano systems
  • Lecture (others)
    Abschlussverteidigung DFG Forschergruppe 1713 "Sensorische Mikro- und Nanosysteme", 20.09.2018, Chemnitz, Deutschland

Publ.-Id: 28664 - Permalink


Dressing intersubband transitions at terahertz frequencies
Schmidt, J.; Winnerl, S.; Dimakis, E.; Helm, M.; Schneider, H.;
We combine intense, spectrally narrow THz pulses from a free-electron laser with broadband THz probe pulses and electro-optic sampling for highly nonlinear THz spectroscopy. We exploit this approach for dressing intersubband transitions in a wide GaAs quantum well and for investigating the associated coherent phenomena with added spectral resolution.
Keywords: terahertz spectroscopy, intersubband transition, quantum well, free-electron laser
  • Lecture (Conference)
    43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 09.-14.09.2018, Nagoya, Japan
  • Contribution to proceedings
    43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 09.-14.09.2018, Nagoya, Japan
    2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz): IEEE
    DOI: 10.1109/IRMMW-THz.2018.8510160

Publ.-Id: 28663 - Permalink


Strain-dependent scaling of excitons in carbon nanotubes
Wagner, C.ORC; Schuster, J.ORC; Schleife, A.ORC
Optical transitions in carbon nanotubes (CNTs) show a strong strain sensitivity, which makes them suitable for optical strain sensing at the nano-scale and for strain-tunable emitters. The origin of this effect is the dependence of the CNT band-gap on strain and chirality, which is well explored. However, there is no quantitative model for the strain dependence of optical transitions — which are subject to strong excitonic effects due to the quasi one-dimensional structure of CNTs.

One approach towards such a model is a parametrized description of the quasiparticle gap as well as the scaling relation of the exciton binding energy in CNTs given by Perebeinos et al [1]. However, the description of screening in the scaling relation is insufficient, since for CNTs, a one-dimensional wave-vector dependent dielectric function є(q) is required instead of an effective-medium dielectric constant є0.

We improve the approach by Perebeinos et al [1] by relating the screening physics in CNTs to the electronic transitions. The resulting model is fitted to electronic-structure calculations within many-body perturbation theory. This enables us to quantitatively predict the strain dependence of optical transitions for any CNT.

[1] V. Perebeinos et al., Phys. Rev. Lett. 92, 257402 (2004).
  • Lecture (Conference)
    DPG-Frühjahrstagung und EPS-CMD27, 12.-16.03.2018, Berlin, Deutschland

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Publ.-Id: 28662 - Permalink


Synthesis and preliminary radiopharmacological characterisation of an 11C-labelled azadipeptide nitrile as potential PET tracer for imaging of cysteine cathepsins
Laube, M.; Frizler, M.; Wodtke, R.; Neuber, C.; Belter, B.; Kniess, T.; Bachmann, M.; Gütschow, M.; Pietzsch, J.; Löser, R.;
An O-methyltyrosine-containing azadipeptide nitrile was synthesised and investigated for its inhibitory activity towards cathepsins L, S, K and B. Labelling with carbon-11 was accomplished by reaction of the corresponding phenolic precursor with [11C]methyl iodide starting from cyclotron-produced [11C]methane. Radiopharmacological evaluation of the resulting radiotracer in a mouse xenograft model derived from a mammary tumour cell line by small animal PET imaging indicates tumour targeting with complex pharmacokinetics. Radiotracer uptake in the tumour region was considerably lower under treatment with the non-radioactive reference compound and the epoxide-based irreversible cysteine cathepsin inhibitor E64. The in vivo behaviour observed for this radiotracer largely confirms that of the corresponding 18F-fluoroethylated analogue and suggests the limited suitability of azadipeptide nitriles for the imaging of tumour-associated cysteine cathepsins
Keywords: pharmacokinetics, cysteine cathepsins, tumour-associated enzymes, molecular imaging, enzyme inhibitors
  • Journal of Labelled Compounds and Radiopharmaceuticals 62(2019)8, 448-459
    DOI: 10.1002/jlcr.3729

Downloads:

  • Secondary publication expected from 26.03.2020

Publ.-Id: 28661 - Permalink


Interessante Beobachtungen in der FIB - Artefakte oder wissenschaftlich neue Ergebnisse?
Engelmann, H.-J.; Hübner, R.;
Interessante Beobachtungen in der FIB - Artefakte oder wissenschaftlich neue Ergebnisse?
  • Lecture (others)
    6. Sächsisches TEM-Präparatorentreffen, 10.04.2018, Dresden, Deutschland

Publ.-Id: 28660 - Permalink


Impact of flotation hydrodynamics on the optimization of fine-grained carbonaceous sedimentary apatite ore beneficiation
Hoang, D. H.; Hassanzadeh, A.; Peuker, U. A.; Rudolph, M.;
The flotation beneficiation of phosphate ore is increasingly facing challenges, especially for finely disseminated sedimentary ores rich in carbonates. This study aims to optimize and assess the impact of key hydrodynamic parameters including pulp density, air flowrate and impeller speed on flotation and metallurgical responses (i.e. grade, recovery, flotation rate constant and selectivity index (SI)). We carried out locked cycle flotation tests using the best conditions from the rougher flotation test to generate an experimental simulation of a continuous circuit. The mineralogical and chemical properties were characterized by mineral liberation analysis (MLA) and inductively coupled plasma optical emission spectroscopy (ICP-OES) techniques, respectively. A modified-McGill bubble size viewer was used for measuring bubble sizes and evaluating the interaction between hydrodynamic factors and bubble diameters. Finally, the design of experiment (DOE) method was applied to determine the relative intensity of the studied factors. It was found that under optimal conditions with the targets of high recovery and maximum SI, the final apatite concentrate achieved a recovery of 86.3 % at a grade of 35.5 %, while the MgO content was 1.2 % and 84.3 % of dolomite was removed from a feed ore containing about 25 % P2O5, 4.6 % MgO, and 41 % CaO. Furthermore, another locked cycle flotation test showed that a 0.82 % MgO content in the final apatite concentrate can be achieved with an apatite recovery of 75.6 % at a P2O5 grade of 36.76 %, and a ratio CaO/P2O5 = 1.33. The obtained concentrate in this investigation under the optimum conditions is the highest in both apatite recovery and grade with low MgO content reported in the literature.
Keywords: Carbonaceous sedimentary apatite; Locked cycle flotation; Impeller speed; Pulp density; Rare earth; Design of experiment

Publ.-Id: 28659 - Permalink


Fundamentals of Actinide Chemistry by Cutting Edge X-ray Methods and Models
Kvashnina, K.;
Understanding the mechanisms of different chemical reactions with actinides at the atomic level is a key step towards safe disposal of nuclear wastes and towards the identification of physical-chemical processes of radionuclides in the environment. This contribution will provide an overview of the recently performed studies on Uranium, Thorium, Plutonium and Cerium contained materials at the Rossendorf Beamline (ROBL) of the European Synchrotron (ESRF) in Grenoble (France). This innovative, recently upgraded, world-wide unique experimental station, funded and operated by HZDR in Dresden (Germany) was used to study actinide systems by several experimental methods: X-ray absorption spectroscopy in high energy resolution fluorescence detection (HERFD) mode, Resonant inelastic X-ray scattering (RIXS) at the An L3 and M4,5 edge and X-ray diffraction (XRD). We will show how the detail information about local and electronic structure of actinide materials can be obtained, including information on the electron-electron interactions, hybridization between molecular orbitals, the occupation and the degree of the f-electron localization. The experimental spectral features have been analysed using a number of theoretical methods based on density functional theory and atomic multiplet theory. It might be of interest for fundamental research in chemistry and physics of actinide systems as well as for the applied science.
  • Lecture (Conference)
    E-MRS Spring Meeting, 27.-31.05.2019, Nice, France

Publ.-Id: 28658 - Permalink


Applying SEM-based automated mineralogy in petrology: a case study on volcanic rocks from the Salina Island, Italy
Gilbricht, S.; Krause, J.; Heinig, T.; Sanchez-Garrido, C. J. M. G.;
Modern SEM-EDS-based automated mineralogy such as Mineral Liberation Analysis (MLA) is a method in which BSE-image analysis and EDS analysis are combined.
Mineral Liberation Analysis is used for a rapid, spatially resolved, automatic, petrographic analysis of solid samples, often in applied mineralogy and metallurgical processing. Amongst other applications, this system can help to determine the chemical composition, mineral mode and micro textures in various sample types. Despite its fast acquisition time (6-12h for scanning of a full 4.5x2.5 cm sample) and the high-resolution nature of BSE imaging combined with the mineral identification capabilities of SEM-based automated mineralogy, it has rarely been applied to volcanic samples [1,2,3,4].
We present here work demonstrating the advantages of using MLA in volcanological studies, especially for fine-grained samples. We applied MLA technique to volcanic samples from Salina Island (Italy). The Salina Island, located in the centre of the Aeolian archipelago, had a rich eruptive history during the past ca. 245 ka that is divided in six eruptive Epochs [5]. Our research focuses on the last eruptive epoch, especially on the eruptive products of the Pollara tuff ring, namely the Punta Fontanelle Formation (Lower Pollara) and the Vallone del Pozzo Formation (Upper Pollara). The pyroclastic eruption from the Upper Pollara formation produced stratified deposits with dark basalt to andesite scoriae in the lower part and light coloured andesite to rhyolite in the upper part. The presence, in the Upper Pollara pyroclastic deposit, of white and grey-banded pumices of sub-alkaline basalt to rhyolite composition are the evidence of mingling/mixing processes between basaltic andesite and rhyolitic magma batches. Analysis of the pumice with SEM-EDS-based MLA (Fig. 1) provides significant information: discrimination of melts with different chemical compositions (rhyolitic in orange, andesitic in red and basaltic in blue in Fig. 1b), proportion of each melt, micro and macro textures between the different melts, mineral mode, mineral association, grain and vesicle geometry, mineral orientation, internal zonation in phenocrysts, reaction rims, etc.
These valuable data, combined with microprobe analyses of the volcanic glass and minerals provide clues on the mixing/mingling processes and the eruption dynamics. In conclusion, the application of SEM-based automated mineralogy e.g. MLA can add important information contributing to the understanding of the pretrogenetic and formation processes of volcanic rocks (and their micro textures).
References:
[ 1] Potter-McIntyre S L et al. 2014 J. Sediment Res. 84 875-892
[ 2] Rukhlov A S et al. 2013 Chem. Geol. 353 280-302
[ 3] Neave D A et al. 2014 J. Pet. 55 2311-2346
[ 4] Ayling B et al. 2011 GRC Transactions 35 301-305
[ 5] Lucchi F et al. 2014 Geol. Soc. London Memoirs 37 155-21
Keywords: Mineral Liberation Analysis, Pumice, Electron Microprobe, MLA, EPMA, Volcanic rocks
  • Contribution to proceedings
    EMAS 2018 - Microbeam Analysis in the Earth Sciences, 04.-08.09.2018, Bristol, Great Britain

Publ.-Id: 28657 - Permalink


Non-ferrous metals metallurgy industry
Reuter, M. A.;
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: Circular Economy (CE), Digitalization, CE system, Design for recycling
  • Lecture (others)
    Non-ferrous metals metallurgy industry / Academic course, 13.12.2018, Madrid, Spanien

Publ.-Id: 28656 - Permalink


Quantitative Ranking of Geological Conceptual Models using Multi-Point Geostatistics
Selia, S. R. R.; Tolosana Delgado, R.; van den Boogaart, K. G.; Schaeben, H.;
Geological interpretation plays a crucial role in every phase of subsurface characterization from exploration to exploitation, e.g. of an oil reservoir or a mineral deposit. In general, the distribution of physical properties is controlled by the architecture of geological objects. Therefore, defining it becomes the initial step of geological modelling. However, insufficient data and the complexity of the earth processes create an ill-posed problem where many models are plausible. Consequently, several geologists will produce different geological models for the same location. This contribution proposes a way to objectivise the ranking of those conceptual models by comparing them with hard data.

Our proposal is based on Multi-point geostatistics (MPS) methods, which are capable to reproduce complex structures common in geology, such as meandering channels, erosional surfaces and salt bodies. MPS is typically used to produce simulations or scenarios of subsurface geology. In addition to spatial data, the methods need a training image, that might come from an expert opinion, a numerical physical simulation, or even from a modern analogue. Several competing models can be considered as alternative training images and the MPS method can be modified to be able to simultaneously sample from all of them. In this way it is possible to produce a complex arrangement of geological architecture, combining several conceptual models. By tracking the frequency with which every training image is visited we can rank the likelihood of each geological model. This can be done locally, for each voxel of the model, or integrated over a region. In this way, we can assess how likely that region patterns come from one particular training image, that is, from one particular conceptual model.

We demonstrate this method in a synthetic fluvial depositional environment where meandering channels transform into braided streams. A limited amount of hard data is extracted from the synthetic reference and three geological concepts are being imposed in the form of training images. These training images are of distinct patterns either braided, meandering or high sinuosity meandering with an oxbow lake structure. Both hard data and all training images become the input to the proposed MPS method and several realizations are being generated. The results indicate that the new method could be a useful tool in defining which geological concept dominates at a particular region and what are the corresponding frequencies for each training image on that region. In addition to that, the method also gives reasonable realizations that resemble the true setting.
  • Lecture (Conference)
    EGU General Assembly 2019, 07.-12.04.2019, Vienna, Austria

Publ.-Id: 28655 - Permalink


Oxygen in ultrahigh magnetic fields
Nomura, T.;
  • Invited lecture (Conferences)
    12th International Conference on Research in High Magnetic Fields (RHMF 2018), 24.-28.06.2018, Santa Fe, USA

Publ.-Id: 28654 - Permalink


On the magnetocaloric properties of Heusler compounds
Gottschall, T.;
  • Invited lecture (Conferences)
    DPG Frühjahrstagung, 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28653 - Permalink


Welche (globale) Recycling-Infrastruktur braucht eine Circular Economy?
Reuter, M. A.;
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: Metallurgical Recycling infrastructure, circular economy
  • Invited lecture (Conferences)
    NEXUS - Tagung zur Rohstoffgewinnung und -recycling und dem nötigen Energiebedarf, 07.12.2018, Stuttgart, Deutschland

Publ.-Id: 28651 - Permalink


Helmholtz-Institut Freiberg für Ressourcentechnologie: Vorstellung des HIF, Forschung und neues Technikum
Kelly, N.; Recksiek, V.; Scharf, C.;
Helmholtz-Institut Freiberg für Ressourcentechnologie: Vorstellung des HIF, Forschung und neues Technikum
  • Lecture (Conference)
    34. Arbeitskreis Magnesiumrecycling, 19.04.2018, Freiberg, Deutschland

Publ.-Id: 28648 - Permalink


Überführung der Kupfer-Eisen-Trennung vom Becherglas- in den Pilotmaßstab
Rädecker, P.; Scharf, C.;
Die Trennung von Kupfer und Eisen durch Solventextraktion ist in der Metallurgie, speziell bei der Verarbeitung von Lösungen aus dem Laugungsprozess oxidischer Kupfererze, ein vielfältig untersuchtes Verfahren. Im Rahmen der durchgeführten Untersuchungen wurde als Ausgangsmaterial ein Flugstaub aus der historischen Kupfererzeugung verwendet.
Ausgangspunkt für die Untersuchungen bildeten Versuche im Becherglasmaßstab (200 ml) unter Verwendung des Extraktionssystem LIX984 gelöst in Kerosin. Es wurden die Reaktionsisotherme für Kupfer, die Zeit- und Konzentrationsabhängig-keiten sowie die Trennung von Kupfer und Eisen bestimmt. Die ermittelten optimalen Parameter werden angewendet, um den Prozess auf eine gerührte 32-mm KÜHNI-Extraktionskolonne (bereitgestellt durch SULZER Chemtech AG) zu übertragen. Die Einbauten sind aus korrosionsfestem Kunststoff und die wässrige Phase wird als disperse Phase gefahren. Das Ziel ist die selektive Extraktion von Kupfer aus synthetischen Lösungen sowie realen Laugungslösungen mit einem möglichst großen Durchsatz. Dafür werden für die Extraktionskolonne, der Flutpunkt und der Holdup sowie die theoretischen Trennstufen der Kolonne bestimmt.
  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Extraktion & Rohstoffe, 12.03.2018, Frankfurt/Main, Deutschland

Publ.-Id: 28647 - Permalink


Zur selektiven Flüssig-Flüssig-Extraktion von Oxoanionen aus alkalischen Lösungen
Kelly, N.; Mansel, A.; O'Toole, N.; Scharf, C.;
Europa steht vor der Herausforderung, eine gesicherte Versorgung von Metallen wie Chrom, Vanadium, Niob oder Molybdän zu gewährleisten, welche eine wichtige Rolle hinsichtlich der Wettbewerbsfähigkeit im Fertigungssektor und bei den Innovationen im Hochtechnologiebereich spielen. Gleichzeitig sind solche Metalle in großen Mengen in Sekundärressourcen gebunden, wo ihr eigentlicher Wert nicht voll ausgenutzt werden kann. Das Verfahren der Solventextraktion stellt dabei eine vielversprechende Methode da, um diese Metalle aus zuvor erhaltenen Laugungslösungen selektiv zurückzugewinnen.
Der vorliegende Beitrag beschäftigt sich mit der Untersuchung der Extraktionseigenschaften von kommerziell erhältlichen Extraktionsmitteln wie Aliquat 336 gegenüber den gebildeten Oxoanionen von Chrom, Vanadium, Molybdän und Niob. Detaillierte Studien zum Einfluss der Parameter pH-Wert (Abb.1), Kontaktzeit und Volumenverhältnis der beiden Phasen sowie die Rolle der eingesetzten Modifier bzw. zusätzlicher Extraktionsmittel oder anwesender Anionen (Abb. 2) werden näher diskutiert.
  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppe Extraktion & Rohstoffe, 12.03.2018, Frankfurt/Main, Deutschland

Publ.-Id: 28646 - Permalink


Heteropolynuclear Cu(II)/Ln(III) complexes of hexadentate Schiff bases: Syntheses, structures and solution studies
Kelly, N.; Doert, T.; Gloe, K.; Weigand, J. J.; Gloe, K.;
The coordination chemistry of heteropolynuclear 3d/4f metal complexes with multifunctional Schiff base ligands has received increasing attention due to their magnetic and catalytic properties but also for their biological activities and the role in separation processes. The underlying self-assembly processes are controlled by the nature of metal ions, ligands, counter anions or solvents and the experimental conditions. It remains a great challenge to understand the influence of all these factors on the assembly process in order to synthesize materials with defined properties.
In this work we report the synthesis of complexes of 2-hydroxy-3-methoxyphenyl and 3-ethoxy-2-hydroxyphenyl diimines having different linking elements. According to similar ligands in the literature these Schiff bases lead to heteropolynuclear complexes with d- and f-block elements, like Cu(II) and Ln(III), using the N₂O₂ and O₄ donor sets whereby the formation of the bi-, tri and tetranuclear complexes depends on the type of the lanthanide ion and the structure of the organic ligand. The different isolated structures will be compared and discussed in detail as well as results of studies in solution (UV/vis, ESI-MS, solvent extraction).
  • Invited lecture (Conferences)
    The 10th International Symposium on Nano & Supramolecular Chemistry, 12.07.2018, Dresden, Deutschland

Publ.-Id: 28645 - Permalink


Tuning Ferromagnetic Resonance via Disorder/Order Interfaces
Schneider, T.; Lenz, K.; Semisalova, A.; Gollwitzer, J.; Heitler-Klevans, J.; Potzger, K.; Fassbender, J.; Lindner, J.; Bali, R.;
Ferromagnetic resonance of a thin film alloy has been tuned by inducing lateral interfaces between layers differing in their lattice ordering and magnetic properties. We show that the resonance lines at 10 GHz are shifted by 284 mT and 35 mT, for fields applied perpendicular-to-plane and in-plane, respectively. The resonance line-shift occurs over a broad frequency range, and is driven by strain relaxation due to the increasing magnetic layer thickness. A finer anomalous line shift occurs as the A2/B2 interface approaches the film/substrate interface prior to being removed from the film. The A2 structure can be re-annealed to B2 order, implying that disorder/order interface modification can provide a path for reversibly encoding resonant properties in alloy thin films.
Keywords: Interface effects, Ferromagnetic resonance, Disorder/Order interfaces

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  • Secondary publication expected from 21.05.2020

Publ.-Id: 28644 - Permalink


Heterodinuclear Metal Complexes of Multifunctional Diimine and Diamine Ligands in Synergistic Extraction
Kelly, N.; Gloe, K.;
Heterodinuclear Metal Complexes of Multifunctional Diimine and Diamine Ligands in Synergistic Extraction
  • Invited lecture (Conferences)
    5th International Conference on Methods and Materials for Separation Processes "Separation Science - Theory and Practice", 27.08.2018, Kudowa-Zdroj, Polen

Publ.-Id: 28643 - Permalink


Antimonite complexation with thiol and carboxyl/phenol groups of particulate organic matter
Besold, J.; Kumar, N.; Scheinost, A. C.; Lezama Pacheco, J.; Fendorf, S.; Planer-Friedrich, B.;
Peatlands and other wetlands with abundant particulate natural organic matter (NOM) are recognized as important sinks for potentially toxic antimony (Sb). While formation of Sb(III) sulfide phases or Sb(III) binding to NOM was shown to reduce Sb mobility, the exact binding mechanisms remain elusive. Here, we reacted increasing sulfide concentrations with purified model peat at pH 6, forming reduced organic sulfur species, and subsequently equilibrated the reaction products with 50 µM of antimonite under anoxic conditions. Sulfur solid-phase speciation and the local binding environment of antimony were analyzed with Sb K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. We found that 85% of antimonite was sorbed by untreated peat, while sulfide reaction with peat increased sorption up to 98%. EXAFS shell-fitting of the spectra of untreated peat revealed that Sb coordinates to oxygen, and Sb-carbon distances of ~2.90 Å are in line with binding to carboxylic groups. With increasing content of reduced organic sulfur, Sb is progressively coordinated to S atoms at distances of ~2.45 Å and Sb-carbon distances of ~3.33 Å, suggesting increasing Sb-thiol binding. The existence of reduced inorganic Sb-sulfur phases, which would have similar Sb-sulfur distances, could be excluded with iterative target factor analysis of the full set of EXAFS spectra. In conclusion, particulate NOM is able to sequester Sb in anoxic, sulfur-enriched environments without need for high free sulfide concentrations.
Keywords: antimonite peat thiol carboxylate EXAFS XANES

Publ.-Id: 28642 - Permalink


Combining hyperspectral and geomagnetic drone- borne data for non-invasive mineral exploration.
Jackisch, R.; Madriz, Y.; Zimmermann, R.; Saartenoja, A.; Pirttijarvi, M.; Salmirinne, H.; Jylaenki, J.; Heincke, B.; Gloaguen, R.;
Combining hyperspectral and geomagnetic and drone- borne data for non-invasive mineral exploration.
Keywords: UAS, hyperspectral, multispectral, mineral exploration, geomagnetic field, fluxgate, magnetometer
  • Invited lecture (Conferences)
    4. ArcHub meeting, 19.-20.11.2018, Copenhagen, Denmark

Publ.-Id: 28641 - Permalink


A machine learning technique for drill core hyperspectral data
Contreras, C.; Khodadadzadeh, M.; Tusa, L.; Ghamisi, P.; Gloaguen, R.;
  • Invited lecture (Conferences)
    Innovative Technologies in Exploration and Mineral Detection. Practical Workshop, 2nd edition., 12.-13.12.2018, Barcelona, Spain

Publ.-Id: 28640 - Permalink


Mineral exploration, based on ground and airborne hyperspectral imaging
Gloaguen, R.; Kirsch, M.; Zimmermann, R.; Lorenz, S.; Booysen, R.; Tusa, L.; Brazzo, N.; Unger, G.; Herrmann, E.;
Mineral exploration, based on ground and airborne hyperspectral imaging
Keywords: UAS, drone, hyperspectral, magnetic, drill core, outcrop sensing
  • Invited lecture (Conferences)
    Practical workshop on Innovative technologies in exploration and mineral detection, 12.-14.12.2017, Barcelona, Spain

Publ.-Id: 28639 - Permalink


A novel approach combining geomagnetic and hyperspectral drone-borne data. Advances in remote sensing based mineral exploration and environmental monitoring.
Jackisch, R.; Zimmermann, R.; Lorenz, S.; Saartenoja, A.; Pirttijärvi, M.; Gloaguen, R.;
The demand for raw materials is constantly growing for more than twenty years in our modern societies. Therefore, there is an acute necessity for the exploration of new deposits to sustain the need for high-technology metals. Remote or formerly non-lucrative mineral deposits suddenly become attractive to the industry. Thus, non-invasive and efficient tools for a sustainable exploration are required to fit our present societal requirements.
We identified light-weight drone technology as one of the disruptive technologies in that respect. Further, making use of these unmanned aerial systems (UAS) with multiple sensors will boost non-invasive exploration.
We present a novel approach for non-invasive mineral exploration based on the integration of remote sensing techniques. Advantages of UAS in this context are that they are fast, easily deployable and deliver high resolution data with short turn-around times. We combine light-weight UAS technology with a hyperspectral sensor and a fluxgate magnetometer. Both datasets of high-resolution hyperspectral surface data and subsurface data using the Earth’s magnetic field are merged. This allows us to identify surficial rock exposures and estimates the subsurface proportions of the aforesaid targets. We also measure the extent of the impact of exploration and mining operations on the environment (e.g., Acid rock drainage) using precise hyperspectral mapping.
An octocopter platform carrying the hyperspectral sensor system maps the area of interest and a fixed-wing UAS acquires magnetic data. Hyperspectral data is corrected for topographic effects and automatically georeferenced. Magnetic data is calibrated for orientation effects of the UAS. External and diurnal induced field fluctuations are rectified with base station data. Validation of the measurements is achieved with traditional field methods and in situ sampling. Ground spectroscopy, X-ray diffraction and fluorescence are used to validate the results. We tested this approach in Namibia, Greenland, Finland and Germany.
The results are promising and demonstrate that drone-based exploration becomes more attractive and feasible to the mining industry and the geoscientific community.
Keywords: UAS, hyperspectral, remote sensing, drone, magnetic, fluxgate
  • Lecture (Conference)
    Resources for Future Generations - RFG, 16.-21.06.2018, Vancouver, Canada

Publ.-Id: 28638 - Permalink


Seltene Erden – Woher sie kommen und wie wir sie gewinnen
Möckel, R.;
Wie und wo kommen die Seltenen Erden vor und wie werden sie gewonnen? Die Seltenen Erden sind gar nicht so selten, wie ihr Name vielleicht vermuten lässt. Trotzdem sind die Gewinnung und die damit verbundenen Risiken nicht zu unterschätzen. Der Vortrag gibt einen Einblick in die Geologie der Seltenen Erden, moderne Konzepte und Entwicklungen für eine künftig sichere Versorgung mit den begehrten Metallen sowie diesbezüglich aktuelle Projekte am Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF), das zum Helmholtz-Zentrum Dresden-Rossendorf gehört.
Keywords: seltene Erden, rare earth elements, Seltenerdelemente
  • Lecture (others)
    Dresdner Seniorenakademie Wissenschaft und Kunst, 10.01.2019, Dresden, Deutschland

Publ.-Id: 28637 - Permalink


Chiral Skyrmion and Skyrmionium States Engineered by the Gradient of Curvature
Pylypovskyi, O. V.; Makarov, D.; Kravchuk, V. P.; Gaididei, Y.; Saxena, A.; Sheka, D. D.;
Curvilinear nanomagnets can support magnetic skyrmions stabilized at a local curvature without any intrinsic chiral interactions. Here, we propose an alternative mechanism to stabilize chiral Neel skyrmion states relying on the gradient of curvature. We illustrate our approach with an example of a magnetic thin film with perpendicular magnetic anisotropy shaped as a circular indentation. We show that in addition to the topologically trivial ground state, there are two skyrmion states with winding numbers +/- 1 and a skyrmionium state with a winding number 0. These chiral states are formed due to the pinning of a chiral magnetic domain wall at a bend of the nanoindentation due to spatial inhomogeneity of the curvature-induced Dzyaloshinskii-Moriya interaction. The latter emerges due to the gradient of the local curvature at the bend. While the chirality of the skyrmion is determined by the sign of the local curvature, its radius can be varied in a broad range by engineering the position of the bend with respect to the center of the nanoindentation. We propose a general method, which enables us to reduce the magnetic problem for any surface of revolution to the common planar problem by means of proper modification of constants of anisotropy and Dzyaloshinskii-Moriya interaction.

Publ.-Id: 28636 - Permalink


Chemistry first, Accelerator Mass Spectrometry (AMS) second
Merchel, S.ORC; Rugel, G.; Dreams-Users; Dreams-Friends
Accelerator mass spectrometry (AMS) is the most sensitive analytical method to measure long-lived radionuclides. The detection limits are generally several orders of magnitude better, i.e. as low as 10-16 (radionuclide/stable nuclide), than any other mass spectrometry or decay counting method. AMS needs smaller sample sizes and measurements are finished within a few minutes to hours; though after performing chemical separation of the radionuclide from the sample matrix (ice, snow, rain, ground water, marine sediments, soil, meteorites, deep-sea nodules, lava, rocks). Hence, AMS is right from the start, from sample taking over chemistry and measurements to data interpretation, true interdisciplinary research. Users at the DREAMS (DREsden AMS) facility (www.dresden-ams.de) apply AMS to most diverse projects from astrophysics to Earthquake studies.
Keywords: AMS, radionuclide
  • Invited lecture (Conferences)
    52nd annual conference of the German Society for Mass Spectrometry (DGMS), 10.-13.03.2019, Rostock, Deutschland

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Publ.-Id: 28632 - Permalink


Drastic Fermi-surface reconstruction in Nd-doped CeCoIn5
Green, E.;
  • Invited lecture (Conferences)
    12th International Conference on Research in High Magnetic Fields, 24.-28.06.2018, Santa Fe, USA

Publ.-Id: 28631 - Permalink


A novel multicaloric cooling cycle that exploits thermal hysteresis
Gottschall, T.;
  • Invited lecture (Conferences)
    9th JEMS Conference 2018 (Joint European Magnetic Symposia), 03.-07.09.2018, Mainz, Germany
  • Invited lecture (Conferences)
    Thermag VIII, 16.-20.09.2018, Darmstadt, Germany

Publ.-Id: 28630 - Permalink


Glacial evolution of the Pamir mountains: insights from geomorphology and cosmogenic radionuclide dating
Stübner, K.; Bookhagen, B.; Merchel, S.; Rugel, G.; Aminov, J.;
The Pamir mountains at the western end of the Himalaya-Karakorum-Tibet mountain belt are characterized by landscape extremes: The western Pamir has an extreme local relief of >2000 m. The eastern Pamir plateau is a low-relief orogenic plateau at ~4100 m. In most of the Pamir, modern glaciers are small and often are rock glaciers restricted to the north sides of the crests but significant ice caps occur in the eastern Pamir (Muztagh Ata, Kongur Shan) and in the northwestern Pamir, where the Fedchenko glacier is the longest glacier outside the polar regions. Glaciation of the Pamir contrasts with the strong glaciation of the Karakorum ranges farther south reflecting differences in annual precipitation between the Monsoon-influenced Karakorum and the arid, Westerlies-controlled Pamir.
Glacial and glaciogenic sediments that have been mapped throughout the Pamir suggest much more widespread glaciation during the Pleistocene. Cosmogenic radionuclide (CRN) dates indicate that one or several glacial maxima occurred >100 ka, but the extent of the mid-Pleistocene ice cover is currently not known. While CRN exposure ages of glacially polished bedrock in the west-Pamir valleys suggest that these may have been formed by mid-late Pleistocene Alpine glaciers there is little record of the glacial advances on the east-Pamir plateau. We present new CRN exposure ages that elucidate the glacial and post-glacial history of the Pamir. We also present a geomorphological analysis focusing on the strong east-west difference in topography and on morphological evidence of glaciation in the eastern Pamir. Our analysis sheds light on the landscape evolution and on the competing effects of fluvial and glacial erosion and mass-wasting processes in an arid mountain environment.
Keywords: ANS, TCN, dating, CRN, glacier
  • Poster
    European Geosciences Union (EGU) General Assembly 2019, 07.-12.04.2019, Wien, Österreich

Publ.-Id: 28629 - Permalink


Solid oxygon in ultrahigh magnetic fields
Nomura, T.;
  • Invited lecture (Conferences)
    CC2018 - 12th International Conference on Cryocrystals and Quantum Crystals, 26.-31.08.2018, Wroclaw, Poland

Publ.-Id: 28628 - Permalink


Body size-dependent energy storage causes Kleiber’s law scaling of the metabolic rate in planarians
Thommen, A.; Werner, S.; Frank, O.; Philipp, J.; Knittelfelder, O.; Quek, Y.; Fahmy, K.; Shevchenko, A.; Friedrich, B. M.; Jülicher, F.; Rink, J. C.;
Kleiber’s law, or the 3/4 -power law scaling of the metabolic rate with body mass, is considered one of the few quantitative laws in biology, yet its physiological basis remains unknown. Here, we report Kleiber’s law scaling in the planarian Schmidtea mediterranea. Its reversible and life history-independent changes in adult body mass over 3 orders of magnitude reveal that Kleiber’s law does not emerge from the size-dependent decrease in cellular metabolic rate, but from a size-dependent increase in mass per cell. Through a combination of experiment and theoretical analysis of the organismal energy balance, we further show that the mass allometry is caused by body size dependent energy storage. Our results reveal the physiological origins of Kleiber’s law in planarians and have general implications for understanding a fundamental scaling law in biology.
Keywords: calorimetry metabolism growth

Publ.-Id: 28627 - Permalink


Surface Exposure Dating on Waterfalls to Reconstruct the Landscape Evolution of South Central Africa
Olivotos, S.; Niedermann, S.; Mouslopoulou, V.; Merchel, S.; Cotterill, F.; Flugel, T.; Gärtner, A.; Rugel, G.; Scharf, A.; Bookhagen, B.;
Northern Zambia and south-eastern Katanga Province (D.R. Congo) comprise a tectonically dynamic landscape, which lies within the southwest extension of the East African Rift System. The seismotectonic research in the area has been minimal, despite the fundamental importance of neotectonics, which controls all landscapes southwest of the Tanganyika graben. Two major sets of fault systems (Mweru and Upemba) were revealed by preliminary Google Earth mapping. The recorded seismicity patterns of both systems, during the last 35 years, indicate their current active behavior.
The novelty of our interdisciplinary project is to combine methods, such as DNA sequencing of selected fish groups to define molecular clocks with surface exposure dating of key landforms using cosmogenic nuclides (CNs). Quartz-rich samples were collected from selected waterfalls with the aim of quantifying exposure ages and erosion rates.
Combined analyses of radionuclides ¹⁰Be and ²⁶Al and stable ²¹Ne are necessary, due to the complex exposure scenarios involving surface erosion or retreat of waterfalls. First results from Northern Zambia indicate burial of a large area for an extended period of time. This specific burial may confirm the existence of a significantly deeper Paleo-Lake Mweru before the modern drainage evolved (Dixey, 1943).
²¹Ne and ¹⁰Be-²⁶Al measurements took place at the GFZ Noble Gas Laboratory and at the Accelerator Mass Spectrometry facility of the HZDR, respectively. ¹⁰Be and ²⁶Al targets were prepared at the CN laboratories of University of Potsdam and HZDR. More results from Northern Zambia will be presented.
References
Dixey F. 1943. South African Geographical Journal 25: 20-41.
Keywords: AMS, DNA, geomorphology, TCN, noble gas, dating
  • Poster
    PhD Seminar Geosciences University Potsdam, 25.01.2019, Golm, Deutschland

Publ.-Id: 28626 - Permalink


Static and dynamic properties of modulated phases in Co/Pt multilayers and their dependence on the total magnetic thickness
Fallarino, L.; Oelschlägel, A.; Arregi, J. A.; Bashkatov, A.; Stienen, S.; Lindner, J.; Gallardo, R.; Landeros, P.; Schneider, T.; Chesnel, K.; Lenz, K.; Hellwig, O.;
Ferromagnetic (FM) / non-magnetic multilayers with perpendicular magnetic anisotropy provide an efficient route for controlling magnetism, with highly tunable magnetic properties by changing the individual layer thicknesses or the number of repetitions [1]. During the past years, an extensive work effort has led to an apparently complete understanding of those structures. The majority of these studies, though, utilized very thin FM layers since an in-plane reorientation of the magnetization is expected for larger individual thicknesses. However, for sufficiently thick individual FM layers, the system undergoes a second transition back to out-of-plane orientation [2]. Consequently, we present a study of magnetic properties of [Co(t )/Pt(0.7nm)] multilayers as a function of t thicknesses and Co/Pt bilayer repetitions N. Studying in more detail the influence of the magnetic history on the remanent domain pattern, we determine the range of material properties and magnetic fields where, instead of the typical maze-like domains, a lattice of bubbles is stabilized with extraordinary high density, as depicted in Fig. 1 [3]. The dynamic response of such modulations of the ferromagnetic order parameter is further investigated by ferromagnetic resonance spectroscopy (FMR). We find that the observed FMR modes have a direct correlation to the magnetic phase of the samples and its evolution under the application of a magnetic field, as depicted in Fig.2. Using both micromagnetic modeling and analytical calculations, we are able to quantitatively reproduce our experimental observations, which suggest the existence of localized spin-wave and FMR modes that are dependent on the modulation period as well as on the type of modulation itself [4]. Lastly, we show that such modulations resemble magnonic crystals, where tuning of the band-gap is enabled by the specific magnetic field history.
References: [1] M. T. Johnson et al. Rep. Prog. Phys. 59, 1409 (1996).
[2] L. Fallarino et al. Phys. Rev. B 94, 064408 (2016).
[3] K. Chesnel et al. Phys. Rev. B 98, 224404 (2018).
[4] L. Fallarino et al., accepted in Phys. Rev. B (03/01/2019).
Keywords: Ferromagnetic multilayers, PMA, FMR, VSM, magnetic domains, not collinear spin textures.
  • Lecture (Conference)
    2019 Joint MMM-Intermag, 14.-18.01.2019, Washington D.C., United states of America

Publ.-Id: 28625 - Permalink


Controlled coexcitation of direct and indirect ultrafast demagnetization in Co/Pd multilayers with large perpendicular magnetic anisotropy
Pan, S.; Hellwig, O.; Barman, A.;
Ever since its discovery in 1996, ultrafast demagnetization has ignited immense research interest due to its scientific rigor and technological potential. A flurry of recent theoretical and experimental investigations has proposed direct and indirect excitation processes in separate systems. However, it still lacks a unified mechanism and remains highly debatable. Here, we demonstrate that instead of either direct or indirect interaction, simultaneous and controlled excitation of both direct and indirect mechanisms of demagnetization is possible in multilayers composed of repeated Co/Pd bilayers. Moreover, we are able to modulate demagnetization time (from ∼350 to ∼750 fs) by fluence and thickness-dependent indirect excitation due to heat current flowing vertically downward from top layers, which is combined with an altogether different scenario of direct irradiation. Finally, by regulating the pump wavelength, we can effectively control the contribution of indirect process, which gives a confirmation to our understanding of the ultrafast demagnetization process.
Keywords: ultrafast demagnetization, Co/Pd multilayers

Publ.-Id: 28624 - Permalink


Rohstoffe für die Energiewende: Systemische Effekte
van den Boogaart, K. G.; Weigelt, A.;
Ziel des Projektteils am Helmholz Institut Freiberg für Resourchentechnologie war ein grundsätzliches Verständnis zu entwickeln für den Zusammenhang zwischen der Endlichkeit prim"arer Rohstoffquellen und dem erh"ohten Rohstoffbedarf der Erneuerbaren Energien und Energiespeicher. Dazu wurden Modelle verwendet, welche basierend auf Datenstrukturen der Lebenszyklusanalyse eine weitere Zeitdimension hinzufügen und so große transiente Veränderungen, wie beispielsweise die Erschöpfung bestimmter Rohstoffquellen zu erfassen. Als besondere Schwierigkeit hat sich herausgestellt, dass diese Beschreibung nur im globalen Kontext sinnvoll wird und dafür bisher nicht genügend Daten vorliegen. Trotz eines quantitativen Modellansatzes konnten daher bisher nur qualitative Ergebnisse erzielt werden: Aufgrund der begrenzten Lebensdauern der Systeme und der unvollständigen Rückgewinnung der Materialien in Recyclingprozessen sind auch erneuerbare Energien nicht vollständig erneuerbar. Die globale Rohstoffverfügbarkeit kann für Technologien, die auf seltenen Metallen (z.B. Dünnschichtsolarzellen, direct-drive Windturbinen) begrenzend wirken. Nur eine gute Mischung verschiedener Technologien kann sicherstellen, dass nicht einzelne Rohstoffquellen überfordert werden. Durch den erhöhten Bedarf an Rohstoffen und Recycling erzeugt das Energiesystem einen sekundären Bedarf an Energie und Landnutzung, welcher aufgrund eine Rückkopplunseffekts erheblich ansteigen kann, wenn einzelne Rohstoffe sich verknappen. Der primäre Rohstoffbedarf steht durch die Änderung der Energiesysteme und die Einführung der Elektromobilität und das Verzögerte des Rücklaufs aus Recycling vor erheblichen Änderungen und Schwankungen in den nächsten Jahrzehnten. Zusammenfassen kann gesagt werden, dass eine Planung der Energiewende immer global gedacht werden muss und immer auch den Rohstoffbedarf und die dadurch generierten sekundären Auswirkungen mitbedenken muss.
Keywords: Energiewende, Rohstoffwirtschaft
  • Lecture (others)
    Arbeitsgruppentreffen Topic 4, Energiesysteme 2050, 16.-17.01.2019, Frankfurt, Deutschlad

Publ.-Id: 28623 - Permalink


Ion-trap analog of particle creation in cosmology
Fey, C.; Schätz, T.; Schützhold, R.;
We consider the transversal modes of ions in a linear radio-frequency trap where we control the time-dependent axial confinement to show that we can excite quanta of motion via a two-mode squeezing process. This effect is analogous to phenomena predicted to occur in the early universe, in general out of reach for experimental investigation. As a substantial advantage of this proposal in comparison to previous ones we propose to exploit the radial and axial modes simultaneously to permit experimental access of these effects based on state-of-the-art technology. In addition, we propose to create and explore entanglement between the two ions.

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Publ.-Id: 28622 - Permalink


Nanoscale Imaging of Antiferromagnetic Order using Single-spin Magnetometry
Shields, B.; Appel, P.; Kosub, T.; Hedrich, N.; Fassbender, J.; Huebner, R.; Makarov, D.; Maletinsky, P.;
Nitrogen vacancy microscopy is used to detect tiny magnetic stray fields from antiferromagnetic Cr2O3 thin films. Domains and domain dynamics are reported.
  • Poster
    International Conference on Magnetism, 15.-20.7.2018, San Francisco, USA

Publ.-Id: 28621 - Permalink


Granularity Effects in Antiferromagnetic Spintronics Devices
Kosub, T.; Appel, P.; Shields, B.; Maletinsky, P.; Hübner, R.; Lindner, J.; Fassbender, J.; Makarov, D.;
thin films of antiferromagnets are notably different than bulk crystals.
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28620 - Permalink


Discrete worldline instantons
Schneider, C.; Torgrimsson, G.; Schützhold, R.;
The semiclassical approximation of the worldline path integral is a powerful tool to study non-perturbative electron-positron pair creation in spacetime-dependent background fields. Finding solutions of the classical equations of motion, i.e., worldline instantons, is possible analytically only in special cases, and a numerical treatment is nontrivial as well. We introduce a completely general numerical approach based on an approximate evaluation of the discretized path integral that easily and robustly gives the full semiclassical pair production rate in nontrivial multidimensional fields, and apply it to some example cases.

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Publ.-Id: 28619 - Permalink


Interaction of a Bose-Einstein condensate with a gravitational wave
Schützhold, R.;
Partly motivated by recent proposals for the detection of gravitational waves, we study their interaction with Bose-Einstein condensates. For homogeneous condensates at rest, the gravitational wave does not directly create phonons (to lowest order) but merely affects existing phonons or indirectly creates phonon pairs via quantum squeezing-an effect which has already been considered in the literature. For inhomogeneous condensate flows such as a vortex lattice, however, the impact of the gravitational wave can directly create phonons. This more direct interaction can be more efficient and could perhaps help bring such a detection mechanism for gravitational waves a step closer towards experimental realizability-even though there is still a long way to go. Finally, we argue that super-fluid helium might offer some advantages in this respect.

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Publ.-Id: 28618 - Permalink


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