Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
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
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-01-16
    DOI: 10.14278/rodare.75

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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

Downloads:

Publ.-Id: 28662 - 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


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


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

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  • Secondary publication expected from 11.04.2020

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


Small samples, nearly no chemistry and a big accelerator: Beryllium‑7 measurements as low as 1 mBq
Merchel, S.ORC; Bemmerer, D.ORC; Querfeld, R.; Steinhauser, G.; Rugel, G.; Scharf, A.; Tiessen, C.
Introduction
Beryllium-7 (T1/2 = 53.22 d), mainly measured via gamma-spectrometry, is used as a (natural) radiotracer for educational and scientific purposes. For samples with lower activities (<0.1 Bq) and especially for natural samples containing both ⁷Be and the longer-lived ¹⁰Be (T1/2 = 1.387 Ma), accelerator mass spectrometry (AMS) is the method-of-choice. Here, we demonstrate that ⁷Be- and ¹⁰Be-AMS can be performed at the Dresden AMS facility (DREAMS) [1,2] on the same chemically prepared BeO from rain water samples collected in Germany.

Results
Detection limits for ⁷Be are as low as 0.6 mBq, which is one-to-two orders of magnitude better than “standard/ordinary” and “sophisticated” decay counting (e.g. in an underground laboratory). Validation measurements by gamma-counting of two larger rainwater samples were in excellent agreement with our AMS results. Uncertainties are usually 6-7% for small samples.
Sample sizes as small as tens of milliliters of rain water can be chemically processed to BeO within a few hours without the need for more expensive, time-consuming and labor-intense methods like ion exchange. Basic steps are: Acidification (of utmost importance), filtration, ⁹Be carrier addition, hydroxide precipitation, washing, drying, ignition, and mixing with Nb. Isobar (⁷Li) suppression by chemistry and AMS is sufficient.

Conclusion and outlook
Both the detection limit and uncertainty can be improved by more precise decay counting measurements of the calibration material (high ⁷Be activities from p-activated Li), the removal of so-called “dummy” steps currently required by the AMS machine software, and better tuning conditions. Our study qualifies AMS at DREAMS for being an ultrasensitive, cheap, and fast detection method for ⁷Be allowing high sample throughput.
Our ⁷Be and ¹⁰Be data clearly showed the very first rain (<5 min) collected being enriched in particulate matter (Fig. 1). Hence, AMS analyzing small samples can be used for time evolution studies of rain. The low detection limit and the high sample throughput will also enable future studies of small timescale phenomena where high-precision measurements of small sample volumes are needed. Further information is given by Tiessen et al. [3].

Figure 1: ⁷Be concentrations of rainwater water samples from Dresden (Drs) and Hannover (Hann). Drs 05_05, Drs 05_06, Drs 2, and Drs 3 were collected at the start of rainfall containing a larger amount of dust. Drs 5 was also from the start of rainfall but after long rain the night before, likely depleting the air of particulate matter. *Both Hannover samples are depleted in ⁷Be due to long collection times and partially missing acidification (Hann only).

Acknowledgements
Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. We appreciate support of Dominik Güttler, René Ziegenrücker and the DREAMS operator team during AMS-measurements, of Gyürky György (Hungarian Academy of Sciences) for providing ⁷Be for the calibration material, and of BMBF (05K16MG1) and DAAD-RISE Professional (HZDRPH-456) for funding. It was a pleasure to discuss ⁷Be-AMS with Andrew Smith (ANSTO).

References
[1] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 (2013) 5-10.
[2] G. Rugel et al., Nucl. Instr. Meth. B 370 (2016) 94-100.
[3] C. Tiessen et al., Accelerator mass spectrometry (AMS) for beryllium-7 measurements in smallest rainwater samples, JRNCh, 2018, doi: 10.1007/s10967-018-6371-6.
Keywords: AMS, rain
  • Poster
    27th Seminar on Activation Analysis and Gamma Spectrometry (SAAGAS 27), 24.-27.02.2019, München, Deutschland

Publ.-Id: 28616 - Permalink


Graphene Oxide Functional Nanohybrids with Magnetic Nanoparticles for Improved Vectorization of Doxorubicin to Neuroblastoma Cells
Lerra, L.; Farfalla, A.; Sanz, B.; Cirillo, G.; Vittorio, O.; Voli, F.; Le Grand, M.; Curcio, M.; Pasquale Nicoletta, F.; Dubrovska, A.; Hampel, S.; Iemma, F.; Goya, G.;
With the aim to obtain a site-specific doxorubicin (DOX) delivery in neuroblastoma SH-SY5Y cells, we designed an hybrid nanocarrier combining graphene oxide (GO) and magnetic iron oxide nanoparticles (MNPs), acting as core elements, and a curcumin–human serum albumin conjugate as functional coating. The nanohybrid, synthesized by redox reaction between the MNPs@GO system and albumin bioconjugate, consisted of MNPs@GO nanosheets homogeneously coated by the bioconjugate as verified by SEM investigations. Drug release experiments showed a pH-responsive behavior with higher release amounts in acidic (45% at pH 5.0) vs. neutral (28% at pH 7.4) environments. Cell internalization studies proved the presence of nanohybrid inside SH-SY5Y cytoplasm. The improved efficacy obtained in viability assays is given by the synergy of functional coating and MNPs constituting the nanohybrids: while curcumin moieties were able to keep low DOX cytotoxicity levels (at concentrations of 0.44–0.88 µM), the presence of MNPs allowed remote actuation on the nanohybrid by a magnetic field, increasing the dose delivered at the target site.
Keywords: graphene oxide; iron oxide nanoparticles; magnetic targeting; nanohybrids; synergism

Publ.-Id: 28613 - Permalink


Subspace Multinomial Logistic Regression Ensemble for Classification of Hyperspectral Images
Khodadadzadeh, M.; Ghamisi, P.; Contreras, C.; Gloaguen, R.;
Exploiting multiple complementary classifiers in an ensemble framework has shown to be effective for improving hyperspectral image classification results, especially when the training samples are limited. With a different principle and based on this assumption that hyperspectal feature vectors effectively lie in a low-dimensional subspace, the subspace-based techniques have shown great classification performance. In this work, we propose a new ensemble method for accurate classification of hyperspectral images, which exploits the concept of subspace projection. For this purpose, we extend the subspace multinomial logistic regression classifier (MLRsub) to learn from multiple random subspaces for each class. More specifically, we impose diversity in constructing MLRsub by randomly selecting bootstrap samples from the training set and subsets of the original hyperspectral feature space, which leads to generate different class subspace features. Experimental results, conducted on two real hyperspectral data sets, indicate that the proposed method provides significant classification results in comparison with other state-of-the-art approaches.
Keywords: Hyperspectral images, classification, ensemble-based approaches, subspace multinomial logistic regression, remote sensing
  • Contribution to proceedings
    IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 22.-27.07.2018, Valencia, Spain

Publ.-Id: 28612 - Permalink


Tuning of electrocatalytic properties of MoS2 by chalcogenide ion implantation
Luxa, J.; Mazánek, V.; Mackova, A.; Malinsky, P.; Akhmadaliev, S.; Sofer, Z.;
MoS2 is one of the most explored and promising material for electrocatalytic water splitting by hydrogen evolution reaction (HER). However, in its bulk form, MoS2 possesses only poor activity towards HER. Therefore, appropriate treatment has to be employed to tune its catalytic properties. In this study, we report the influence of ion bombardment (S, Se and Te ions) with medium ion energy (400 keV) and various ion fluences (1 × 1014–1 × 1016 ions/cm2) on the electrocatalytic properties of bulk MoS2 crystals. Our results showed that upon irradiation, sulfur vacancies were created. Upon exposure to ambient atmosphere, sulfur vacancies were partially replaced by oxygen, which led to surface oxidation. Nevertheless, samples irradiated using the higher range of ion fluences have generally showed enhanced catalytic HER performance in comparison with untreated MoS2 crystals. Furthermore, we have also demonstrated that ion irradiation/implantation can serve as a tool for doping of MoS2 crystals with Se and Te which can also influence the HER performance. The reported results demonstrate that ion beam irradiation can be used for doping as well as creation of sulfur vacancies in bulk MoS2 crystals which is fundamental for the HER performance.
Keywords: Electrocatalysis, Hydrogen evolution reaction, Ion implantation, MoS2

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  • Secondary publication expected from 29.12.2019

Publ.-Id: 28611 - Permalink


Subspace clustering algorithms for mineral mapping
Khodadadzadeh, M.; Contreras, C.; Tusa, L.; Gloaguen, R.;
The application of drill core hyperspectral data in exploration campaigns is receiving great interest to obtain a general overview of a mineral deposit. However, the main approach to the investigation of such data is by visual interpretation, which is subjective and time-consuming. To address this issue, recently, the use of machine learning techniques is proposed for the analysis of this data. For drill core samples that for which only very little prior knowledge is often available, applying classification algorithms which are supervised learning methods is very challenging. In this paper, we suggest to use clustering (unsupervised) methods for mineral mapping, which are similar to classification but no predefined class labels are needed. To handle mapping of the very highly mixed pixels in drill core hyperspectral data, we propose to use advanced subspace clustering methods, in which pixels are assumed to lie in a union of low-dimensional subspaces. We conduct a comparative study and evaluate the performance of two well-known subspace clustering methods, i.e., sparse subspace clustering (SSC) and low-rank representation (LRR). For the experiments, we acquired VNIR-SWIR hyperspectral data and applied scanning electron microscopy based Mineral Liberation Analysis (MLA) for two drill core samples. MLA is a high-resolution imaging technique that allows detailed mineral characterization. We use the high-resolution MLA image as a reference to analyze the clustering results. Qualitative analysis of the obtained clustering maps indicates that the subspace clustering methods can accurately map the available minerals in the drill core hyperspectral data, especially in comparison to the traditional k-means clustering method.
Keywords: Mineral mapping, drill core, hyperspectral data, subspace clustering, remote sensing
  • Contribution to proceedings
    SPIE Image and Signal Processing for Remote Sensing XXIV, 10.-13.09.2018, Berlin, Germany

Publ.-Id: 28609 - Permalink


Multidimensional fluid mixing capabilities of ATHLET 3.1A during an overcooling transient in a generic PWR KONVOI
Diaz Pescador, E.;
In the presented work, a simulation of a 10% main steam line break (MSLB) in steam generator (SG) 1 in a generic German PWR KONVOI model is carried out and investigated by means of the system code ATHLET 3.1A. The accident analysis is focused first, on a thermal-hydraulic transient characterization, in order to subsequently study the multidimensional fluid mixing in the reactor pressure vessel (RPV), and further verification against suitable experimental data. With this aim, in the ATHLET simulation, the nominal plant operational parameters of the generic KONVOI reactor are transposed with the boundary conditions from the test PKL G3.1. The obtained results show an increase in the heat removal through the U-tubes of SG 1during boil-off, giving rise to an asymmetric overcooling in the reactor coolant system. At the arrival of the overcooled water to the RPV, the cold water stream mixes with the ambient coolant in the downcomer and eventually spreads across the whole region. In the core region, the overcooled water propagates from the periphery towards the core centre. The obtained behavior is in good agreement with the experimental results from the ROCOM and PKL test facilities.
  • Poster
    Workshop of Doctoral Candidates (PhD student seminar), 13.12.2018, Zittau, Germany

Publ.-Id: 28606 - Permalink


Integration of drone-borne hyperspectral and geomagnetic data. A combined approach in geologic remote sensing. A test from the Siilinjärvi carbonatite, Finland.
Jackisch, R.; Zimmermann, R.; Lorenz, S.; Saartenoja, A.; Pirttijärvi, M.; Heincke, B.; Gloaguen, R.;
The worlds need for critical materials sees a surge since the last two decades. Most of Europe’s larger mineral deposits have been discovered and exploited by now. A rising need to include formerly unattractive or inaccessible prospects is apparent. Here, using drones for detailed prospecting of small areas comes in handy. Drones have the advantage of being cost-efficient, easily deployable and having a short turn-around time for high resolution data.
With this study, we introduce a novelty approach for non-invasive mineral exploration based on the integration of remote sensing applications. In particular, we combine the advantage of light-weight drone technology with a snapshot hyperspectral camera and a magnetometer. The platform delivers specified, integrated measurements of spectrometric high-resolution surface images fused with data of the earth’s magnetic field. This allows us to identify surficial rock exposures and the estimation of the subsurface proportions of the aforesaid target.
The sensor system is attached to an octocopter platform with a flight endurance of around 30 minutes. A fixed-wing drone is used to acquire magnetic data of the same target with a larger area. The combined data is processed through a framework of correction software and projected on digital elevation models (DEMs) from the target area. The DEMs are acquired via Structure-from-Motion Multi-View Stereo photogrammetry. Hyperspectral data is corrected for topographic effects and automatically georeferenced using the MEPHYSTo toolbox. Magnetic data is calibrated for orientation effects and corrected for diurnal and external induced field fluctuations via base station recordings. We validate the measurements with a field-tested assembly of different techniques, e.g., mineralogical and geochemical analysis, in-situ ground spectroscopy and geomagnetic readings.
The results are promising and we demonstrate that drone-based exploration becomes more affordable, intuitive and accessible to the mining sector and the geoscientific community.
Keywords: UAS, UAV, remote sensing, mineral exploration, hyperspectral, geomagnetic, fluxgate

Publ.-Id: 28605 - Permalink


Atomistic Simulations to Design a Room-Temperature Single Electron Transistor
Prüfer, T.; Möller, W.; von Borany, J.; Heinig, K. H.;
For future low power-consumption nanoelectronics, a room-temperature single-electron transistor may be configured by placing a small (few nm diam.) Si nanodot in a thin (<10 nm) SiO2 interlayer in Si. This can be achieved by ion-irradiation induced interface mixing, which turns the oxide layer into metastable SiOx, and subsequent high-temperature thermal decomposition which leaves, for a sufficiently small mixed volume, a single Si nanodot in the SiO2 layer. Corresponding ion mixing simulations have been performed using the binary collision approximation (BCA)[1], followed by kinetic Monte-Carlo (KMC) simulations[2] of the decomposition process, with good qualitative agreement with the structures observed in related experiments. Quantitatively, however, the BCA simulation appears to overestimate the mixing effect. This is attributed to the neglect of the positive entropy of mixing of the Si-SiO2 system, i.e. the immiscibility counteracts the collisional mixing by “up-hill diffusion” [3]. Consequently, intermitting KMC diffusion steps have been introduced into the BCA mixing simulation, resulting in an excellent predictive power for the irradiation step of the production process. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.

• [1] W. Möller et al., NIM B, 322, 23–33
• [2] M. Strobel et al., PRB 64, 245422
• [3] B. Liedke et al., NIM B 316 (2013) 56–61
  • Lecture (Conference)
    E-MRS 2018 Fall Meeting, 17.-21.09.2018, Warschau, Polen

Publ.-Id: 28603 - Permalink


Si Quantum Dots for Single Electron Transistor: Synthesis, Characterization and Theoretical Comparison
Prüfer, T.; Wolf, D.; Engelmann, H.-J.; Hübner, R.; Bischoff, L.; Hlawacek, G.; Heinig, K.-H.; Facsko, S.; Xu, X.; von Borany, J.;
The appearance of quantum effects makes nanoparticles (NPs) more and more important in semiconductor physics and especially in nanoelectronics. One very promising application is the single electron transistor (SET). Common field effect transistors (FET) could be outperformed by SETs in many applications because of their ultra-low power consumption (~100 times). Important for the fabrication of SETs operating at room temperature is the control of position and size of nano dots (<5nm). Our CMOS-compatible approach to manufacture SETs follows a two-step synthesis of NPs: (i) Producing tiny SiOx volumes by ion beam irradiation of ultrathin buried SiO2 layers (<10nm) and (ii) self-organizing single Si nanodots by phase separation during thermal treatment.
Energy-filtered transmission electron microscopy (EFTEM) is an advanced technique for the structural analysis of Si NPs in buried SiO2 layers. Although the NPs in the SiO2 layer superimpose in 2-dimentional projections from cross-sectional TEM samples, we managed to characterize the density and size distribution of the formed nanoclusters using the knowledge of the electron mean free path length to convert the Si-plasmon-loss filtered TEM image into a Si-thickness map. Here we will present the characterization and a comparison with theory to show a significant overestimation of the mixing effect by BCA simulation. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.
  • Lecture (Conference)
    European Materials Research Society Fall Meeting, 17.-21.09.2018, Warschau, Polen

Publ.-Id: 28602 - Permalink


A sizeable change in the electronic properties of GaAs via strain engineering in lattice-mismatched core/shell nanowires
Schneider, H.; Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Shan, S.; Fotev, I.; Pashkin, A.; Ghorbani-Asl, M.; Krasheninnikov, A.; Helm, M.; Dimakis, E.;
III-V compound semiconductors have fueled many breakthroughs in physics and technology owing to their direct band gap and high electron mobility. It has also been very important that these fundamental properties can be tailored in ternary or quaternary alloys by selecting the chemical composition appropriately. Here we explore the great possibilities for strain engineering in core/shell nanowires as an alternative route to tailor the properties of III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/InₓGa₁₋ₓAs or GaAs/InₓAl₁₋ₓAs core/shell nanowires can sustain unusually large misfit strains that would have been impossible in equivalent thin-film heterostructures, and undergoes a significant modification of its electronic properties. Core/shell nanowires were grown in the self-catalyzed mode on SiOₓ/Si(111) substrates by molecular beam epitaxy. Strain analysis was performed using synchrotron X-ray diffraction and Raman scattering spectroscopy, and showed that for a thin enough core, the magnitude and the spatial distribution of the built-in misfit strain can be regulated via the composition and the thickness of the shell. Beyond a critical shell thickness, we obtain a heavily tensile-strained core and an almost strain-free shell. The tensile strain of the core exhibits a predominantly-hydrostatic character and causes the reduction of the GaAs band gap energy in accordance with our theoretical predictions using deformation-potential theory and first-principle calculations. For 7 % of strain (x = 0.54), the band gap energy was reduced to 0.87 eV at 300 K, i.e. a remarkable reduction of 40 %. Signatures of valence-band splitting were also identified in polarization-resolved photoluminescence measurements, as a result of the strain anisotropy in GaAs. Presuming a reduced effective mass of electrons in the tensile-strained core of GaAs/InₓAl₁₋ₓAs nanowires (core diameter = 22 nm, x = 0.39 - 0.49), the corresponding electron mobility was measured by time-domain terahertz spectroscopy to be in the range of 4000 cm²/V·s at 300 K. These values are the highest reported, even in comparison to GaAs/AlₓGa₁₋ₓAs nanowires with double the core thickness. Our results demonstrate that strained GaAs in core/shell nanowires can resemble the electronic properties of InₓGa₁₋ₓAs, surmounting issues with phase separation, surface segregation or alloy disorder that typically exist in ternary alloys and limit the device performance.
Keywords: core/shell III-V semiconductor nanowires, molecular eam epitaxy, MBE, strain, effective mass
  • Poster
    34-th International Conference on the Physics of Semiconductors (ICPS 2018), 29.07.-03.08.2018, Montpellier, Frankreich

Publ.-Id: 28601 - Permalink


Squeezing information about ThO2 nanoparticles’ size and shape from high resolution XANES
Amidani, L.; Rossberg, A.; Romanchuk, A.; Plakhova, T.; Kvashnina, K.;
Extracting information on the size and shape of very small nanoparticles (NPs) is not a trivial task and it is fundamental to push the analysis of the available techniques to extract as much in-formation as possible from the available data. In this perspective we present a detailed modelling of Th L3 edge high resolution XANES collected on ThO2 NPs showing how the size and shape of the NP impacts the spectral shape.
Nanoparticles of ThO2 with average size between 2 and 35 nm were synthesized by chemical precipitation and measured at Th L3 edge with High-Energy Resolution Fluorescence Detected (HERFD) XANES. The HERFD-XANES spectrum of NPs with diameter above 2.5 nm are all very similar, while for NPs below 2.5 nm the first post edge feature is missing. In order to un-derstand what this absence could be correlated to, we performed a series of simulations with the FDMNES code on particles of different shape and with size close to 2 – 2.5 nm. We considered three possible shapes and cut the structures from ThO2 bulk. As a first approximation we did not consider disorder at the surface, but only the effects induced by size and shape. After cutting the NPs from the bulk, the symmetry of the crystal is lowered and different Th atoms have different local environment. We set the cutoff radius of our simulations to 6 Å and identified the groups of equivalent Th atoms by comparing the local environment of each Th up to 6 Å. To fully characterize the XANES of the NP under study, a separate simulation per equivalent Th atom was performed with the FDMNES code.
By comparing the simulations of Th atoms at the surface and inside the NP it clearly emerges that the first post edge feature is particularly sensitive to the number of Th second nearest neigh-bors. The spectrum of a specific shape is given by the weighted average of all the different Th in the NP. Considering that the shape determines how many Th with a specific local environment will be present, each shape results in a different final spectrum. By comparing the data and the simulations we suggest that the ThO2 NP with diameter below 2.5 nm have octahedral shape.
  • Lecture (Conference)
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28600 - Permalink


The Structural and Compositional Changes of Graphene Oxide Induced by Irradiation With 500 keV Helium and Gallium Ions
Malinsky, P.; Macková, A.; Florianová, M.; Cutroneo, M.; Hnatowicz, V.; Bohácová, M.; Szokölová, K.; Böttger, R.; Sofer, Z.;
Structural and compositional modification of 2D materials as graphene or graphene oxide (GO) are topical objects of nowadays due to their many technological applications. Ion irradiation of graphene based materials, as a method for improvement of their surface properties started recently. Ion mass, energy, and fluence are crucial for forming of GO electrical, optical, and mechanical properties. In this work, the GO films are irradiated with 500 keV He and Ga ions to different fluences. The ions with different masses and electronic/nuclear stopping power ratios, are chosen with the aim to examine mechanisms of radiation defect creation. The elemental composition of the GO is investigated using Rutherford back-scattering (RBS) and elastic recoil detection analysis (ERDA) techniques. The structural and chemical changes are characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy and the electrical properties are determined by two-point method. The RBS and ERDA analyses indicate deoxygenation and dehydrogenation of the irradiated GO surface. The thickness and the degree of O and H depletion depend on the ion mass. XPS and Raman spectroscopy show removal of oxygen functionalities and structural modifications leading to a decrease in the surface resistivity.
Keywords: graphene oxide, ion Irradiation, Helium, Gallium, structure, composition

Publ.-Id: 28598 - Permalink


A Time-of-Flight Secondary Ion Mass Spectrometer Add-on for the Helium Ion Microscope
Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Facsko, S.;
In a Helium Ion Microscopes (HIM) a Gas Field Ion Source (GFIS) is used to create a Helium or Neon ion beam with a diameter smaller than 0.5 nm and 1.8 nm, respectively. The method is well known for its high resolution imaging and nano-fabrication capabilities which it is able to provide not only for conducting but also insulating samples without the need for a conductive coating.

However, the existing HIM tools suffered from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. Recently, we designed, implemented and reported on the first time-of-flight secondary ion mass spectrometry (TOF-SIMS) add-on that can be retrofitted to existing microscopes [1,2,3].

After a brief introduction to the HIM, I will focus on the new time-of-flight setup. It is based on fast blanking electronics that chop the primary beam into pulses with a minimal length of 20 ns. In combination with a MCP based stop detector this enables TOF backscattering spectrometry with 54 nm lateral resolution [1,2] - the world record for spatially resolved backscattering spectrometry. In order to extend the TOF setup for SIMS an ion optic has been designed and optimized for high transmission by ion transport simulations and an evolutionary algorithm. The high transmission is crucial to collect enough signal from nanoparticles prior to their complete removal by ion sputtering.

The setup can obtain SIMS data from a region of interest or can be used in imaging mode to obtain elemental line profiles and maps of the surface. For m/q ≤ 80 u a m/∆m > 200 has been achieved. This is sufficient for many life science applications that rely on the isotope identification of light elements (e.g. C, N). The lateral resolution has been evaluated to 8 nm using the knife edge method and a 75%/25%. The results will be compared to the theoretical achievable lateral resolution and the limiting experimental and physical constraints of this approach will be reviewed.


References

[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Notte, J. A.; Huang, J. and Facsko, S. (2016). Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry, Ultramicroscopy 162 : 91-97.
[2] Heller, R.; Klingner, N.; Hlawacek, G. (2016). Backscattering Spectrometry in the Helium Ion Microscope: Imaging Elemental Compositions on the nm Scale. In: Hlawacek, G. & Gölzhäuser, A. (Ed.), Helium Ion Microsc., Springer International.
[3] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von Borany, J.; (2018) Time-of-flight secondary ion mass spectrometry in the helium ion microscope, submitted.
  • Lecture (Conference)
    SIMS Europe 2018, 16.-18.09.2018, Münster, Germany

Publ.-Id: 28592 - Permalink


Compositional analysis and in-situ experiments in the HIM
Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Serralta, E.; Facsko, S.;
The HIM is well known for its imaging with spot sizes below 0.5 nm, its nano-fabrication capabilities, the small energy spread of less than 1 eV and the extremely high brightness. However, it still suffers from the lack of instruments for in-situ studies as well as capabilities for a well integrated material analysis. In the first part a plug and socket system for sample holders will be shown with up to six freely customizable high-voltage electrical connections Additionally time-of flight spectrometry has been implemented for compositional analysis [1]. New results, drawbacks and derive conclusions for the practical use of time-of-flight SIMS will be presented [2]. Our setup delivers a mass resolution delta m < 0.3 u (for m/q < 80 u) and a lateral resolution of 8 nm.

[1] N. Klingner, R. Heller, G. Hlawacek, J. von Borany, J.A. Notte, J. Huang, S. Facsko. Ultramicroscopy 162 (2016), pp 91-97
[2] N. Klingner, R. Heller, G. Hlawacek, S. Facsko, J. von Borany (2018), submitted
  • Lecture (Conference)
    2nd international HeFIB conference on Helium and emerging Focused Ion Beams, 11.-13.06.2018, Dresden, Germany

Publ.-Id: 28591 - Permalink


High Resolution in 3 dimensions – TOF-SIMS in the Helium Ion Microscope
Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S.; von Borany, J.;
Ongoing miniaturization in semiconductor industry, nanotechnology and life science requirement further improvements for high-resolution imaging, fabrication and analysis of the produced nanostructures. Continuously shrinking object dimensions lead to an enhanced demand on spatial resolution and surface sensitivity of modern analysis techniques. Secondary ion mass spectrometry (SIMS), as one of the most powerful techniques for surface analysis, performed on the nanometer scale may comply with this demands. The direct determination of the sputtered ions mass provides elemental and molecular information and even allows to measure isotope concentrations.

During the last decades, primary ion species used in SIMS have been optimized in terms of best ionization probabilities and less molecular fragmentation. Thereby, highest mass-resolution has been one of the biggest design goals in the development of new SIMS spectrometers. In contrast to former developments, our approach aims for ultimate lateral resolution.

In recent years helium ion microscopy has been developed as a valuable tool for nanofabrication and high-resolution imaging. Helium ion microscopy (HIM) utilizes a gas field ion source to form a helium or neon ion beam with a diameter of less than 0.5 nm and 1.8 nm, respectively. This is not only possible for conducting but also for insulating samples without the need for a conductive coating. However, the existing tools suffer from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. While the technology is relatively young several efforts have been made to add such an analytic capability. Past and ongoing activities of various labs for in situ analysis will be summarized.

Recently, we implemented time-of-flight (TOF) spectrometry to measure the energy of backscattered particles, the mass of sputtered ions [1, 2]. In future activities we intent to determine the energy loss of transmitted particles as well. Based on the findings obtained with this first approachof integrating a TOF SIMS setup, a dedicated extraction optics for secondary ions has been designed and tested (see figure 1).

The focus of this presentation will be on the technical realization of the significantly improved setup. The setup can be operated in spot mode to obtain local mass spectra or in imaging mode to obtain element maps of the specimen surface (see figure 2).

New results, drawbacks and derived conclusions for the practical use of this promising technique will be presented [4]. Similarities and differences to the also recently developed system using a sophisticated magnetic sector field analyzer will be shown [5]. We will reveal that SIMS can be performed with unprecedented lateral resolutions.

First experiments revealed a very high relative transmission which is crucial to collect enough signal from nanoparticles prior to their complete removal by ion sputtering. For m / q <= 80 u a mass resolution of delta m <= 0.3 u has been achieved. This is sufficient for many life science applications that rely on the isotope identification of light elements (e.g.: C, N). The lateral resolution of 8 nm has been evaluated using the knife edge method and a 75 % / 25 % criterion and represents a world record for spatially resolved secondary ion mass spectrometry.

The results will be compared to the theoretical limit of achievable lateral and depth resolution and the experimental and physical constraints of this approach will be reviewed.
  • Invited lecture (Conferences)
    HRDP 9 - 9th International Workshop on High-Resolution Depth Profiling, 25.-29.06.2018, Uppsala, Sweden

Publ.-Id: 28590 - Permalink


Application of a new model for bubble-induced turbulence to bubbly flows in containers and vertical pipes
Liao, Y.; Ma, T.; Krepper, E.; Lucas, D.; Fröhlich, J.;
The present paper extends the baseline model for the CFD-simulation of turbulent poly-disperse bubbly flows in the Euler-Euler framework by improving the modelling of bubble-induced turbulence. The closure terms in the transport equations of the k-ω SST model are revisited and replaced with a new model recently proposed by Ma et al. (Ma et al., Physical Review Fluids 2, 034301, 2017) which is based on an analysis of the turbulent kinetic energy budget obtained from direct numerical simulation data. Detailed validation results for various flow configurations with a wide range of gas and liquid volumetric fluxes are presented. In case of vertical pipe flow significant improvements in the predicted gas volume fraction and velocity profiles are obtained, especially in high gas volume fraction cases where bubble-induced turbulence is dominant. Simulations of other configurations, such as uniform and non-uniform bubble columns, show that the new model results in an also for these cases overall improvement. Therefore, the baseline model is now updated to include the new model for bubble-induced turbulence.
Keywords: Bubbly flow; Bubble-induced turbulence; Euler-Euler modelling; Baseline model

Downloads:

  • Secondary publication expected from 07.03.2020

Publ.-Id: 28589 - Permalink


Verification of ATHLET against TRACE on Superphenix start-up tests
Di Nora, V. A.; Fridman, E.; Mikityuk, K.;
The thermal-hydraulics (TH) code ATHLET has been upgraded to be capable of sodium flow modeling. Its new extension is under verification and validation phase. The presented study aimed to demonstrate ATHLET capability in Sodium-cooled Fast Reactor (SFR) transient predictions, through the comparison against TRACE TH code, this last being more established and tested for SFR applications. Calculations were performed on a set of start-up tests on Superphénix (SPX) SFR, and compared with TRACE results, which were used as a reference. It has been shown that given a specific set of reactivity coefficients, ATHLET and TRACE give consistent and close results.
Keywords: Superphénix start-up tests; Benchmarking ATHLET against TRACE; ATHLET for SFRs
  • Lecture (others)
    Workshop of Doctoral Candidates (PhD student seminar), 13.12.2018, Zittau, Deutschland

Publ.-Id: 28588 - Permalink


Time-lapse imaging of particle invasion and deposition in porous media using in situ X-ray radiography
Godinho, J. R. A.; Chellappah, K.; Collins, I.; Ng, P.; Smith, M.; Withers, P. J.;
This paper introduces time-lapse radiography as an in situ technique to image and quantify changes in the internal structure of a porous medium with sub-second temporal resolution. To demonstrate the technique’s potential, an experiment was performed using a model system involving flow of a suspension containing ground marble particles through a porous bed of compacted glass beads housed within a pressurized flow rig. During the experiment, particle deposition occurred both within the internal porous structure and on its surface (forming a filter cake). The volume of particles deposited was derived from changes in the grey scale of the radiographs. At the initial stages of the experiment, the volume of particles deposited internally was seen to increase linearly with time. The subsequent growth and compaction of an external filter cake decreased the rate of internal particle deposition. The filter cake’s structure was observed to fail owing to increasing stress at higher pressures. The demonstrative experiment illustrates the potential of time-lapse radiography as a new tool to elucidate mechanisms underpinning formation damage, and to optimize drilling fluids and enhanced oil recovery (EOR). A critical assessment of the technique’s advantages and limitations to characterise particulate behaviour within porous media is included.
Keywords: Permeability; formation damage; fines migration; filter cake; EOR; computed tomography

Publ.-Id: 28586 - Permalink


Bubble Generation by Micro-Orifices with Application on Activated Sludge Wastewater Treatment
Mohseni, E.ORC; Herrmann-Heber, R.; Reinecke, S. F.; Hampel, U.
We studied the initial gas dispersion performance of diffuser concepts based on micro-orifices and needles with very fine orifice diameters in the range from 30 µm to 200 µm, as such diffusers are currently in discussion for energy-efficient wastewater treatment plants. To evaluate the performance of these micro-orifices, we compared them with industrial rubber membrane diffusers with respect to Sauter mean bubble diameter, pressure drop, frequency of bubble formation, oxygen transfer rate, and power demand for air compression. Our study revealed that, in comparison with rubber membrane diffusers bubbles generated from the micro-orifices transfer up to 82% more oxygen content into the continuous phase at up to 75% less power demand. Moreover, these micro-orifices are able to produce bubble sizes in the same range as the needle diffusers at 60% less pressure drop and 60% higher bubble generation frequency. Therefore, we also expect an improvement in the oxygen transfer coefficient KLa and standard oxygen transfer efficiency SOTE compared to commercial rubber membrane diffusers.
Keywords: Bubble Generation, Micro-orifices, Aeration, Biological Wastewater Treatment, Rubber Membrane Diffusers, Oxygen Transfer
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Publ.-Id: 28585 - Permalink


Ion-induced surface patterning and its application in nanofabrication via templated growth
Erb, D.; Malsch, G.; de Schultz, R.; Facsko, S.;
Low-energy ion irradiation of surfaces can lead to nanoscale pattern formation with a wide variety of morphologies, resulting from a number of interacting ballistic and diffusive mechanisms which govern the mass redistribution under ion irradiation. The choice of process parameters such as sample temperature or ion incidence angle determines the relative influence of these mechanisms and thereby the pattern morphology.
After briefly outlining the patterning mechanisms and discussing the resulting morphologies on semiconductor surfaces, we present our approaches at templated nanostructure growth based on these ion-induced surface patterns. They include epitaxial nanowires via geometric shading, long-range chemical ordering in diblock-copolymer thin films, and engineering of magnetic anisotropy in topographically modulated thin films.
The required technologies of low-energy ion irradiation, polymer chemistry, and physical vapor deposition are well-established and can readily be implemented at industrially relevant scales. Thus, nanostructured materials fabricated in such bottom-up manner have the potential to make substantial contributions to solving our society’s present challenges: They can increase the sensitivity of diagnostical tools in medicine, lead to novel information technology, or enhance the efficiency of energy harvesting from renewable sources.
  • Poster
    SNI2018 - Conference for Research with Synchrotron Radiation, Neutrons and Ion Beams at Large Facilities, 17.-19.09.2018, Garching, Deutschland

Publ.-Id: 28584 - Permalink


Nanostructure arrays via templated growth
Erb, D.; Schlage, K.; Röhlsberger, R.; Facsko, S.;
Nanostructured materials have the potential to make substantial contributions to solving our society’s present challenges, e.g. in the fields of medicine, information technology, or energy harvesting from renewable sources. The possibility to fabricate them at industrially relevant scales will maximize the impact of such materials.
We present bottom-up nanopatterning approaches which promise easy implementation and scale-up by combining well-established techniques and effects:
(a) spontaneous nanopatterning of crystalline surfaces upon heating,
(b) suface nanopatterning induced by low-energy ion irradiation,
(c) diblock copolymer self-assembly
(d) physical vapor deposition with selective wetting,
(e) physical vapor deposition with geometrical sha-ding.
Combinations of these techniques and effects can result in highly regular nanostructure arrays of various morphologies and are applicable to a wide range of materials. The versatility of these approaches enables creative research and may lead to beneficial applications in diverse fields, ranging from optics and magnetism to catalysis.
  • Invited lecture (Conferences)
    NAP2018 - 8th International Conference on Nanomaterials: Applications & Properties, 09.-14.09.2018, Zatoka, Ukrajina

Publ.-Id: 28583 - Permalink


Surface nanopatterning induced by low-energy ion irradiation: Experimental investigations of non-equilibrium pattern formation
Erb, D.; de Schultz, R.; Malsch, G.; Facsko, S.;
Irradiating a surface with low-energy ions of about 100 to 1000 eV activates a number of different processes: the surface is eroded by sputtering; the ion impacts create vacancies and ad-atoms; mass redistribution of the mobile species proceeds via both diffusive and ballistic effects; anisotropies in mass redistribution can be induced both by the ion beam and the structure of the surface on the atomic scale. Some mechanisms destabilize the surface height while others lead to surface smoothing. The simultaneous presence of such counteracting effects can result in the formation of periodic nanoscale surface patterns. Depending on factors such as temperature, ion energy, or the incidence orientation of the ion beam, the individual surface processes are enhanced or suppressed, yielding different pattern morphologies. The fact that the patterning can be influenced by various readily accessible external parameters offers a way toward deeper understanding of the underlying processes and their interactions. Furthermore, it enables large-scale production of novel templates for bottom-up fabrication of nanostructures or nanostructured materials for future applications in diverse fields, ranging from optics and magnetism to catalysis.
We discuss our experimental studies of ion-induced pattern formation on different semiconductor surfaces in dependence of external process parameters and with regard to temporal evolution, pattern symmetry and morphology, and patterning defects. Further, we present our approaches to employing these patterned surfaces for nanostructure fabrication, especially by means of physical vapor deposition.
  • Lecture (Conference)
    CAARI 2018 - 25th Conference on Application of Accelerators in Research and Industry, 12.-17.08.2018, Grapevine, USA

Publ.-Id: 28582 - Permalink


Morphology, density, and temporal evolution of topological defects in reverse epitaxy
Erb, D.; Malsch, G.; Facsko, S.;
Low-energy ion-irradiation of semiconductors above their recrystallization temperature has been shown to induce regular nanoscale patterning of the crystalline surface. The mechanism is called reverse epitaxy in analogy to epitaxy in growth: ion-induced mobile vacancies and ad-atoms on the crystalline surface encounter the Ehrlich-Schwoebel energy barrier for crossing terrace steps and exhibit preferential diffusion along specific in-plane directions. This can lead to the formation of well-defined faceted surface structures with morphologies strongly dependent on crystalline structure and surface orientation. For instance, GaAs(001) and InAs(001) develop periodic ripple structures with a saw tooth profile.
We have studied the topological defects in ion-induced patterns on GaAs(001) and InAs(001), i.e. ripple junctions, and present results from both experiments and simulations on the following aspects:
- defect morphology and the influence of polar and azimuthal ion incidence angles thereon
- dependence of the defect density on sample temperature and ion energy
- temporal evolution of the defect density
- defect motion and annihilation processes
We find strong dependencies on the easily controllable external process parameters, which is crucial information when preparing ion-induced surface patterns for specific applications.
  • Poster
    Ion Beam Workshop 2018 - MAT Science Week, 24.04.2018, Darmstadt, Deutschland

Publ.-Id: 28581 - Permalink


A route to epitaxial growth of periodic metal nanostructure arrays
Erb, D.; Malsch, G.; Hübner, R.; Lenz, K.; Lindner, J.; Facsko, S.; Helm, M.; Fassbender, J.;
Epitaxial thin film growth on planar substrate surfaces is well-established for many materials. We present a novel bottom-up approach showing that it can also be feasible to grow nanostructures in an oriented manner on nanopatterned crystalline surfaces. Produced by a scalable procedure on large surface areas, such nanostructure arrays may find diverse applications in research and technology, e.g. in the fields of magnetism or catalysis.
On semiconductor substrates, nanoscale surface patterns with well-defined lateral periodicity form under low-energy ion irradiation via non-equilibrium self-assembly of vacancies and ad-atoms [1]. For appropriate process temperatures, the crystallinity of the substrate is retained during ion irradiation. When a material is then deposited onto the substrate by PVD under non-normal incidence, shadowing effects give rise to the formation of separated nanostructures [2], while a suitable lattice matching can induce epitaxial growth.
In this contribution, we outline the patterning and growth procedure. As an example, we will present periodic Fe/Au nanostructure arrays and discuss their strongly anisotropic optical and magnetic properties.

[1] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender,
S. Facsko, Nanoscale 7, 18928 (2015)
[2] Q. Jia, X. Ou, M. Langer, B. Schreiber, J. Grenzer, P. F. Siles, R. D. Rodriguez,
K. Huang, Y. Yuan, A. Heidarian, R. Hübner, T. You, W. Yu, K. Lenz, J. Lindner,
X. Wang, and S. Facsko, Nano Research 15, 1 (2017)
  • Poster
    DPG Frühjahrstagung 2018 - Sektion Kondensierte Materie, 11.03.2018, Berlin, Deutschland

Publ.-Id: 28580 - Permalink


Ion-induced nanopatterning of crystalline surfaces for applications in bottom-up nanostructure fabrication
Erb, D.; Hübner, R.; Malsch, G.; de Schultz, R.; Grenzer, J.; Lenz, K.; Lindner, J.; Facsko, S.;
Nanostructured materials will be key components in future technological solutions of our society’s present challenges: They can enhance the efficiency of energy harvesting from renewable sources, increase the sensitivity of diagnostical tools in medicine, or enable novel information technology. For making substantial contributions to these fields by applying nanostructured materials, we must be able to fabricate them easily and reproducibly on industrially relevant scales. This can be achieved by the bottom-up approach of templated growth on substrates nanopatterned by ion irradiation: The required technologies of low-energy ion irradiation, polymer chemistry, and physical vapor deposition are well-established.
In this contribution, we outline the mechanism of self-assembly of vacancies and adatoms on crystalline semiconductor surfaces induced by low-energy ion irradiation [1,2]: At temperatures above the material’s recrystallization temperature, the substrate crystallinity is retained. Thus, diffusion of vacancies and adatoms on the surface is highly anisotropic, which leads to the formation of surface nanopatterns reflecting the crystal symmetry of the substrate material. The various resulting pattern morphologies and the influence of external process parameters will be presented. We hope to initiate discussion and collaboration by highlighting potential applications based on these ion-induced nanopatterns, such as growing epitaxial nanowire arrays by shadowing effects at oblique incidence deposition, or inducing long-range order in copolymer thin films to fabricate chemically nanopatterned templates for nanostructure growth [3].

Acknowledgement
We thank K. Potzger and A. Henschke (HZDR) for their support in MBE for templated nanowire growth.

References
[1] X. Ou et al., Nanoscale 7, 18928 (2015)
[2] Q. Jia et al., Nano Research 15, 1 (2017)
[3] D. Erb et al., Science Advances 1, e1500751 (2015)
  • Lecture (Conference)
    SHIM-ICACS 2018 - 10th InternationaL Symposium on Swift Heavy Ions in Matter & 28th International Conference on Atomic Collisions in Solids, 01.-06.07.2018, Caen, France

Publ.-Id: 28579 - Permalink


Ex situ n+ doping of GeSn alloys via non-equilibrium processing
Prucnal, S.; Berencén, Y.; Wang, M.; Rebohle, L.; Böttger, R.; Fischer, I. A.; Augel, L.; Oehme, M.; Schulze, J.; Voelskow, M.; Helm, M.; Skorupa, W.; Zhou, S.;
Full integration of Ge-based alloys like GeSn with complementary-metal-oxide-semiconductor technology would require the fabrication of p- and n-type doped regions for both planar and tri-dimensional device architectures which is challenging using in situ doping techniques. In this work, we report on the influence of ex situ doping on the structural, electrical and optical properties of GeSn alloys. n-type doping is realized by P implantation into GeSn alloy layers grown by molecular beam epitaxy (MBE) followed by flash lamp annealing. We show that effective carrier concentration of up to 1 × 10^19 cm−3 can be achieved without affecting the Sn distribution. Sn segregation at the surface accompanied with an Sn diffusion towards the crystalline/amorphous GeSn interface is found at P fluences higher than 3 × 10^15 cm−2 and electron concentration of about 4 × 10^19 cm−3. The optical and structural properties of ion-implanted GeSn layers are comparable with the in situ doped MBE grown layers.
Keywords: Ge, GeSn, MBE, n-type doping, flash lamp annealing, ion implantation

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Publ.-Id: 28578 - Permalink


Structural and electrical properties of Se-hyperdoped Si via ion implantation and flash lamp annealing
Liu, F.; Prucnal, S.; Yuan, Y.; Heller, R.; Berencén, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.;
We report on the hyperdoping of silicon with selenium obtained by ion implantation followed by flash lamp annealing. It is shown that the degree of crystalline lattice recovery of the implanted layers and the Se substitutional fraction depend on the pulse duration and energy density of the flash. While the annealing at low energy densities leads to an incomplete recrystallization, annealing at high energy densities results in a decrease of the substitutional fraction of impurities. The electrical properties of the implanted layers are well-correlated with the structural properties resulting from different annealing processing.
Keywords: Silicon, hyperdoping, Se, flash lamp annealing, ion implantation

Publ.-Id: 28577 - Permalink


Prophylactic cranial irradiation in stage IV small cell lung cancer: 5 Selection of patients amongst European IASLC and ESTRO experts
Putora, P. M.; Glatzer, M.; Belderbos, J.; Besse, B.; Blackhall, F.; Califano, R.; Cappuzzo, F.; de Marinis, F.; Dziadziuszko, R.; Felip, E.; Faivre-Finn, C.; Früh, M.; Garrido, P.; Le Pechoux, C.; Mcdonald, F.; Nestle, U.; Novello, S.; O‘Brien, M.; Paz Ares, L.; Peeters, S.; Pöttgen, C.; Ramella, S.; Reck, M.; Slotman, B.; Troost, E. G. C.; Houtte, P. V.; Westeel, V.; Widder, J.; Mornex, F.; de Ruysscher, D.;
Background: Due to conflicting results between major trials the role of prophylactic cranial irradiation (PCI) in stage IV small cell lung cancer (SCLC) is controversial. Methods: We obtained a list of 13 European experts from both the European Society for Therapeutic Radiation Oncology (ESTRO) and the International Association for the Study of Lung Cancer (IASLC). The strategies in decision making for PCI in stage IV SCLC were collected. Decision trees were created representing these strategies. Analysis of consensus was performed with the objective consensus methodol-ogy.
Results: The factors associated with the recommendation for the use of PCI included the fitness of the patient, young age and good response to chemotherapy. PCI was recommended by the majority of experts for non-elderly fit patients who had at least a partial response (PR) to chemotherapy (for complete remission (CR): 85% of radiation oncologists and 69% of medical oncologists, for partial remission: 85% of radiation oncol- ogists and 54% of medical oncologists). For patients with stable disease after chemotherapy, PCI was rec- ommended by 6 out of 13 (46%) radiation oncologists and only 3 out of 13 medical oncologists (23%). For elderly fit patients with CR, a majority recommended PCI (62%) and no consensus was reached for patients with PR. Conclusion: European radiation and medical oncologists specializing in lung cancer recommend PCI in selected patients and restrict its use primarily to fit, non-elderly patients who responded to chemotherapy.
Keywords: Small cell lung cancer, PCI, Stage IV, Expert opinion, ESTRO, IASLC

Publ.-Id: 28576 - Permalink


Oxygen Exchange Kinetics of SrTiO3 Single Crystals: A Non-Destructive, Quantitative Method
Stoeber, M.; Cherkouk, C.; Leisegang, T.; Schelter, M.; Zosel, J.; Walter, J.; Hanzig, J.; Zschornak, M.; Prucnal, S.; Boettger, R.; Meyer, D. C.;
The time-resolved oxygen exchange rate of strontium titanate (SrTiO3) single crystals is studied by means of oxygen solid electrolyte coulometry (OSEC) and compared to model calculations. Experiments are performed on pure, ion implanted (Ni, Ag, O and N ions) and partially covered crystals with silver layer. In this work, a theoretical model is used, which is based on defect chemistry under equilibrium conditions. It is applied as a fit in order to determine the effective rate constants and activation energy of the oxygen exchange reaction on the crystal surface. OSEC is used for the first time to characterize kinetic parameters of oxygen exchange on single crystalline surfaces. Transmission electron microscopy and sputter X-ray photoelectron spectroscopy are performed to determine structural and chemical changes after ion implantation.
Keywords: strontium titanate, ion implantation, oxygen exchange reaction, X-ray photoelectron spectroscopy

Publ.-Id: 28575 - Permalink


Ion Beam Modification of ZnO Epilayers: Sequential Processing
Turos, A.; Ratajczak, R.; Mieszczynski, C.; Jozwik, P.; Stonert, A.; Prucnal, S.; Heller, R.; Skorupa, W.; von Borany, J.; Guziewicz, E.;
Defect agglomeration in ion-implanted compound semiconductors produces lattice stress eventually causing plastic deformation at sufficiently high fluence. Consequently, a dislocations tangle is formed which can hardly be completely removed by thermal annealing. To solve this problem, a new method of sequential processing has been developed consisting of low fluence ion implantation followed by subsequent annealing. The procedure can be then repeated until the required impurity concentration has been reached without producing excessive damage. Epitaxial ZnO layers are grown using the atomic layer deposition (ALD) technique. Structural changes in ZnO epilayers due to Yb-ion implantation and subsequent annealing are analyzed by Rutherford backscattering/channeling (RBS/c) and photoluminescence (PL). Correlation between defect transformations and PL efficiency is determined. Increased Yb-atom optical activation upon sequential processing as compared to the standard single-step annealing is observed.
Keywords: ZnO, ALD, Defects, ion implantation, RBS

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Publ.-Id: 28574 - Permalink


Interplay between localization and magnetism in (Ga,Mn)As and (In,Mn)As
Yuan, Y.; Xu, C.; Hübner, R.; Jakiela, R.; Böttger, R.; Helm, M.; Sawicki, M.; Dietl, T.; Zhou, S.;
Ion implantation of Mn combined with pulsed laser melting is employed to obtain two representative compounds of dilute ferromagnetic semiconductors (DFSs): Ga1−xMnxAs and In1−xMnxAs. In contrast to films deposited by the widely used molecular beam epitaxy, neither Mn interstitials nor As antisites are present in samples prepared by the method employed here. Under these conditions the influence of localization on the hole-mediated ferromagnetism is examined in two DFSs with a differing strength of p-d coupling. On the insulating side of the transition, ferromagnetic signatures persist to higher temperatures in In1−xMnxAs compared to Ga1−xMnxAs with the same Mn concentration x. This substantiates theoretical suggestions that stronger p-d coupling results in an enhanced contribution to localization, which reduces hole-mediated ferromagnetism. Furthermore, the findings support strongly the heterogeneous model of electronic states at the localization boundary and point to the crucial role of weakly localized holes in mediating efficient spin-spin interactions even on the insulator side of the metal-insulator transition.
Keywords: electronic-structure; magnetotransport properties; curie-temperature; coulomb gap; (ga,mn)as; ga1-xmnxas; semiconductors; ferromagnetism
  • Poster
    DPG-Jahrestagung und DPG-Frühjahrstagung, 13.03.2018, Berlin, Deutschland

Publ.-Id: 28572 - Permalink


Luminescence in the Visible Region from Annealed Thin ALD-ZnO Films Implanted with Different Rare Earth Ions
Ratajczak, R.; Guziewicz, E.; Prucnal, S.; Łuka, G.; Böttger, R.; Heller, R.; Mieszczynski, C.; Wozniak, W.; Turos, A.;
Epitaxial ZnO thin films grown by atomic layer deposition on GaN/Al2O3 substrates are implanted with Yb, Dy, and Pr ions to a fluence of 5e14 atcm-2 and subsequently anneals at 800 C using a rapid thermal annealing (RTA) system. Structural properties of implanted and annealed ZnO films and the optical response are evaluated by channeling Rutherford backscattering (RBS/c) and photoluminescence spectroscopy (PL), respectively. RTA leads to a partial removal of the post-implantation defects with simultaneous native defects transformation and optical activation of RE ions. It is found that two groups of defects: defects formed during implantation process and native defects, play an important role in the luminescence in the visible region. The room temperature PL spectra obtained from annealed ZnO:RE films do not show sharp PL lines from transitions within the RE 4f shell, but show near band gap emission and defect related emission, which energy emission is controlled by the RE atoms. It suggests a presence of RE-related complexes that are formed during hightemperature annealing in oxygen atmosphere. The excitonic and defect emission modified by RE ions create an optical response of the system resulting in a specific color of the emitted light.
Keywords: ZnO, flash lamp annealing, PL, ion implantation, rare earth

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Publ.-Id: 28571 - Permalink


Strain and Band-Gap Engineering in Ge-Sn Alloys via P Doping
Prucnal, S.; Berencén, Y.; Wang, M.; Grenzer, J.; Voelskow, M.; Hübner, R.; Yamamoto, Y.; Scheit, A.; Bärwolf, F.; Zviagin, V.; Schmidt-Grund, R.; Grundmann, M.; Żuk, J.; Turek, M.; Droździel, A.; Pyszniak, K.; Kudrawiec, R.; Polak, M. P.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.;
Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn, or ultrahigh n-type doping. In this work, we use all three approaches together to fabricate direct-band-gap Ge−Sn alloys. The heavily doped n-type Ge−Sn is realized with CMOS-compatible nonequilibrium material processing. P is used to form highly doped n-type Ge−Sn layers and to modify the lattice parameter of P-doped Ge−Sn alloys. The strain engineering in heavily-P-doped Ge−Sn films is confirmed by x-ray diffraction and micro Raman spectroscopy. The change of the band gap in P-doped Ge−Sn alloy as a function of P concentration is theoretically predicted by density functional theory and experimentally verified by near-infrared spectroscopic ellipsometry. According to the shift of the absorption edge, it is shown that for an electron concentration greater than 1 × 10^20 cm the band-gap renormalization is partially compensated by the Burstein-Moss effect. These results indicate that Ge-based materials have high potential for use in near-infrared optoelectronic devices, fully compatible with CMOS technology.
Keywords: Ge, GeSn, n-type doping, ion implantation, x-ray diffraction, Raman spectroscopy, strain

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Publ.-Id: 28570 - Permalink


Advanced doping of Ge and GeSn
Prucnal, S.; Berencén, Y.; Hübner, R.; Böttger, R.; Rebohle, L.; Skorupa, W.; Wang, M.; Helm, M.; Zhou, S.;
One of the main obstacles towards wide application of Ge in nanoelectronics is the indirect band gap of Ge and the lack of an efficient doping method with well controlled junction depth. Heavily n-type doped Ge becomes a quasi-direct bandgap semiconductor [1] which makes it very attractive for modern optoelectronics but n-type Ge doped above 5×10^19 cm-3 is metastable and thus difficult to be achieved [2]. In contrast to Ge, the GeSn alloy with direct band gap is the most promising semiconductor material for light emitters integrated with CMOS technology [3]. Here an overview of different doping techniques of Ge and fabrication methods to form GeSn will be presented. Special attention will be focused on the use of ion implantation followed by flash-lamp (FLA) annealing for the fabrication of heavily doped n-type Ge and GeSn with direct band gap [4]. In contrast to conventional annealing procedures, rear-side FLA leads to full recrystallization of Ge and GeSn, and simultaneously the Sn segregation and diffusion of n-type dopants are supressed. The maximum electron concentration is well above 10^20 cm-3 both in Ge and in GeSn with Sn concentration up to 6%. Due to the ultra-high n-type doping, Ge becomes a quasi-direct band gap semiconductor showing room-temperature photoluminescence from G-HH transitions [4]. The recrystallization mechanism and the dopant distribution in Ge and GeSn alloy synthesized by ion implantation during rear-side FLA are discussed in detail.
Moreover, we report on the strong mid-IR plasmon absorption in heavily n-type doped Ge and GeSn thin films in the wavelength range from 3000 nm to 10 000 nm.

[1] R. E. Camacho-Aguilera et al., Optics Express 20, 11316-11320 (2012)
[2] S. Prucnal et al., Sci. Rep. 6, 27643 (2016).
[3] S. Wirths et al., Nat. Photon., 9, 88–92 (2015)
[4] S. Prucnal et al., Semicond. Sci. Technol. 32, 115006 (2017).
Keywords: Ge, GeSn, ion implantation, flash lamp annealing, n-type doping
  • Lecture (Conference)
    34th International Conference on the Physics of Semiconductors, 29.07.-03.08.2018, Montpellier, France

Publ.-Id: 28569 - Permalink


Abnormal lattice location and electrical activation in chalcogen-hyperdoped Si
Wang, M.; Prucnal, S.; Debernardi, A.; Heller, R.; Yuan, Y.; Xu, C.; Berencén, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.;
Hyperdoping has emerged as a promising method for designing semiconductors with unique physical properties. In general, these properties are primarily determined by the lattice location of the impurity atoms in the host material. In this contribution, the lattice location of implanted chalcogens in Si was experimentally determined by means of Rutherford backscattering/channeling (RBS/C). The implication on the electrical activation of chalcogens in Si will be discussed with respect to the Hall effect results. The obtained carrier concentration and the RBS angular scans across the <100> and <110> axis reveal that the electrically active/inactive concentration of Te correlates with the concentration of substitutional/interstitial site Te atoms. Surprisingly, contrary to the general belief, we find that the interstitial fraction decreases with increasing impurity concentration. This abnormal dependence of lattice location and electrical activation on impurity concentration suggests that the formation energy for the substitutional Te or Te-Te dimers in Si is lower than for the interstitial Te. This assumption is theoretically verified by the first-principles calculations.
  • Lecture (Conference)
    IBMM-2018 - The 23rd International Conference on Ion Beam Analysis, 28.06.2018, San Antonio, USA

Publ.-Id: 28567 - Permalink


Extended infrared photoresponse in room-temperature Si hyperdoped with Te
Wang, M.; Berencén, Y.; Prucnal, S.; García-Hemme, E.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Schneider, H.; Skorupa, W.; Helm, M.; Zhou, S.;
Presently, room-temperature infrared sub-band-gap photoresponse in Si is of great interest for the development of on-chip complementary-metal-oxide-semiconductor (CMOS)-compatible photonic platforms [1]. One of the most promising approaches to further extend the photoresponse of Si to the mid- and far-infrared (MIR/FIR) ranges consists of introducing deep-level dopants into the Si band gap at concentrations in excess of the solid solubility limit [2]. In this work, we demonstrate strong room-temperature sub-band-gap photoresponse of photodiodes based on Si hyperdoped with tellurium [3]. A CMOS-compatible approach of combining ion implantation with pulsed laser melting was applied to synthesize single-crystalline and epitaxial Te-hyperdoped Si layers with a Te concentration five orders of magnitude above the solid solubility limit. Driven by increasing Te concentration, both the insulator-to-metal transition and a band-gap renormalization are observed. The sub-band optical absorptance in the resulting Te-hyperdoped Si layers is found to increase monotonically with increasing Te concentration and extends well into the MIR/FIR ranges (1.4 to 25 μm). Importantly, the MIR/FIR optoelectronic response from Te-hyperdoped Si photodiodes is demonstrated to be related with known Te deep-energy levels into the Si band-gap. This work contributes to pave the way towards establishing a Si-based broadband infrared photonic system operating at room temperature.
  • Lecture (Conference)
    ION 2018 - XII-th International Conference on Ion Implantation and other Applications of Ions and Electrons, 19.06.2018, Kazimierz Dolny, Poland
  • Poster
    IBMM-2018 - The 23rd International Conference on Ion Beam Analysis, 25.06.2018, San Antonio, USA
  • Poster
    ICPS-2018 - 34th International Conference on the Physics of Semiconductors, 30.07.2018, Montpellier, France

Publ.-Id: 28566 - Permalink


Towards room-temperature extended infrared Si-based photoresponse: A case study of Te-hyperdoped Si
Wang, M.; Berencén, Y.; García Hemme, E.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Schneider, H.; Skorupa, W.; Helm, M.; Zhou, S.;
Presently,room-temperature broadband Si-based photodetectors are required for Si photonic systems.Here,we demonstrate roomtemperature sub-band gap photoresponse of photodiodes based on Si hyperdoped with Te.The epitaxially recrystallized Te-hyperdoped Si layers are developed by ion implantation combined with pulsed laser melting and incorporate Te concentrations beyond the solid solubility limit.An insulator-to-metal transition driven by increasing Te concentration accompanied with a band gap renormalization is observed.The optical absorptance is found to increase monotonically with increasing Te concentration and extends well into the mid- and far- infrared regions.This work contributes to establish room temperature Si-based broadband infrared photonic system.
  • Lecture (Conference)
    DPG-Frühjahrstagung 2018, 12.03.2018, Berlin, Germany

Publ.-Id: 28565 - Permalink


Mid- to far-infrared localized surface plasmon resonance in chalcogen-hyperdoped Si
Wang, M.; Prucnal, S.; Berencén, Y.; Rebohle, L.; Schönherr, T.; Yuan, Y.; Xu, C.; Khan, M. B.; Böttger, R.; Skorupa, W.; Helm, M.; Zhou, S.;
Mid-infrared plasmonic sensing allows the direct targeting of molecules relevance in the so-called “vibrational fingerprint region”. Presently, heavily doped semiconductors exhibiting the potential to replace and outperform metals in the mid- infrared frequency range to revolutionize plasmonic devices. In this work, we demonstrate the occurrence of localized surface plasmon resonances (LSPR) in Te heavily-doped Si layers developed by ion implantation combined with flash lamp annealing. We fabricate micrometer-sized antennas out of the Te-hyperdoped Si layers by electron-beam lithography and reactive ion etching processes. The optical response characterized by Fourier-transform infrared (FTIR) spectroscopy demonstrates the enhancement of localized plasmon resonances in antennas, from mid- to far- infrared frequency range. Our results set a new path toward integration of plasmonic sensors with the one-chip CMOS platform.
  • Poster
    DPG-Frühjahrstagung 2018, 14.03.2018, Berlin, Germany

Publ.-Id: 28564 - Permalink


Towards a Vertical Nanopillar-Based Single Electron Transistor – A High-Temperature Ion Beam Irradiation Approach
Xu, X.ORC; Heinig, K.; Möller, W.; Gharbi, A.; Tiron, R.; Engelmann, H.; Bischoff, L.; Prüfer, T.; Hübner, R.; Facsko, S.; Hlawacek, G.; von Borany, J.
We propose an ion irradiation based method to fabricate a single Si nanocrystal embedded in a Si(001)/SiO2/Si nanopillar layer stack as a prerequisite for manufacturing a CMOS-compatible, room-temperature Si single electron transistor. After either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) irradiation of the nanopillars (with diameter of 35 nm and height of 70 nm) 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 program TRI3DYN. We assume that it is the result from the ion beam induced amophisation of Si accompanied by the ion hammering effect. The amorphous nano-structure behaves viscously and the surface capillary force dictates the final shape. To confirm such a theory, ion irradiation at elevated temperatures (up to 672 K) has been performed and no plastic deformation was observed under these conditions. Bright-field transmission electron microscopy micrographs confirmed the crystallinity of the substrate and nanopillars after HT-irradiation.
When a semiconductor material such as silicon is heated above its amorphisation critical temperature during ion irradiation, it stays crystalline due to an interplay between ion damage and dynamic annealing process. Viscous flow does not occur for the crystalline nano-structures and the shape remains intact. 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)
    2018 MRS Fall Meeting & Exhibit, 25.11.2018, Boston, USA

Publ.-Id: 28563 - Permalink


Synthesis and characterization of transition-metal germanides
Xie, Y.; Yuan, Y.; Hübner, R.; Wang, M.; Helm, M.; Zhou, S.; Prucnal, S.;
Si was sufficient to fulfil the requirements of microelectronic industry for more than five decades. Further progress based on the miniaturisation of transistors is challenging. Therefore new materials and concepts are considered for the next generation of nanoelectronics. In this work, we present the formation of transition-metal germanides epitaxially grown on Ge wafer. Those materials have great promise for both the ohmic contacts to n-type Ge with extremely low specific contact resistivity and spintronics. The transition-metal germanides are synthesized by metal sputtering on Ge followed by millisecond range flash lamp annealing which is suitable for larger-area fabrication and compatible with CMOS technology. On one hand, orthorhombic NiGe whose contact resistivity is only around 1.2×10-6 Ω cm2, is beneficial for achieving high-performance Ge-based nano-electronic devices. On the other hand, cubic FeGe with B20 phase is a Skyrmion-carrier material attractive for spintronics. In summary, the epitaxial transition-metal germanides materials can be obtained by a novel epitaxial approach which provides insight to their technological usage.
Keywords: transition-metal germanides, spintronics
  • Poster
    2018 DPG Spring Meeting Berlin, 12.03.2018, Berlin, Germany

Publ.-Id: 28562 - Permalink


Ultra-fast solid phase epitaxy of Mn5Ge3 on (001) Ge substrate
Xie, Y.; Yuan, Y.; Hübner, R.; Wang, M.; Xu, C.; Grenzer, J.; Helm, M.; Zhou, S.; Prucnal, S.;
In the present work, we report on epitaxial growth of ferromagnetic Mn5Ge3 thin films on (001) Ge substrates induced by Mn in-diffusion during non-equilibrium flash lamp annealing for 20 ms. The ferromagnetic Mn5Ge3/Ge samples with very sharp interface between the Mn5Ge3 layer and the Ge substrate can be used to fabricate spintronic devices. Temperature-dependent magnetization reveals a Curie temperature of 282 K which can be tuned much above room temperature by strain engineering and/or co-doping with C. The microstructural properties of the fabricated films were investigated by X-ray diffraction, cross-sectional TEM and Rutherford backscattering spectrometry. Both used material and technology are highly compatible with complementary metal-oxide-semiconductor (CMOS) technology and can be used for spintronics.
Keywords: Epitaxial growth, ferromagnetic,flash lamp annealing
  • Poster
    2018 EMRS Spring Meeting Strasbourg, 18.06.2018, Strasbourg, France

Publ.-Id: 28561 - Permalink


The Geo-metallurgy of the circular economy: Fairphone
Reuter, M. A.;
tools - HSC Sim & GaBi LCA
Particle description of recycling systems inclusive of exergy & energy
Recycling
Analysis of systems: Rock, residue, recyclate to refined metal
Copper production system: Irreversibility analysis of system & Footprint of complete system
Bill-of-Materials & Full Material Declaration linked to metallurgy, alloy and materials production
Keywords: HSC Sim, GaBi LCA, recycling systems, exergy, energy, Recycling
  • Invited lecture (Conferences)
    International Mineral Processing Congress, 17.-21.09.2018, Moskau, Russland

Publ.-Id: 28558 - Permalink


Thermodynamic evaluation using the law of mass action under consideration of the activity coefficients in the system NdCl3-HCl (or NaOH)-H2O-DEHPA-kerosene
Scharf, C.; Ditze, A.;
For the recovery of neodymium, an important rare earth metal, solvent extraction using DEHPA as extractant is a possible process for winning and recycling. A preceding study by the authors has provided extensive experimental data of the system neodymium-chloride-hydrochloric acid (or sodium hydroxide)-water-di-(2-ethylhexyl)phosphoric acid (DEHPA)-kerosene. It was found that the description of the reaction Nd3+ + 3 (DEHPA)2 <=> Nd(DEHP·DEHPA)3 + 3 H+ by an ideal mass action law is only partly satisfactory. This article investigates the contribution of several parameters to non-ideality. On this basis, expressions for activity coefficients of neodymium in the aqueous phase as well as DEHPA and neodymium in the organic phase are derived. The resulting equations are shown to represent the system with considerably better accuracy than previously possible.
Keywords: thermodynamic evaluation, solvent extraction, neodymium, DEHPA

Publ.-Id: 28557 - Permalink


CIRCULAR ECONOMY STRATEGIES - Responsible Business Practices // Process Model Based Footprints Using HSC Chemistry Software
Reuter, M. A.; Roine, A.;
SusCritMat aims to educate people from Master’s student level up, both in industry and academia about important aspects of Sustainable critical raw materials. In a novel concept, it introduces courses on these complex and interdisciplinary topics in a modula structure, adaptable to a variety of different formats and accessible to both students and managers in industry. These courses will develop new skills which will help participants to better understand the impact and role of critical raw materials in the whole value chain; enabling them to identify and mitigate risks. Understanding the bigger picture and the interconnected nature of global business and society is increasingly necessary to and valued by industry. SusCritMat is an EU-funded project that brings together the technical and pedagogical expertise of leading educational institutions and business partners. It uses and creates teaching materials which can be combined into different course formats. Multi-media education materials will be made available to participants of summer and winter schools so that they can work with state-of-the-art techniques and data.
Keywords: Circular Economy, resource efficiency, sustainability, Digitalization, Simulation
  • Lecture (others)
    SusCritMat Autumn School for Professionals 2018, 24.-26.10.2018, Delft, Niederlande

Publ.-Id: 28556 - Permalink


Interface reactions of differently coated carbon-bonded alumina filters with an AZ91 magnesium alloy melt
Schramm, A.; Bock, B.; Schmidt, A.; Zienert, T.; Ditze, A.; Scharf, C.; Aneziris, C. G.;
To investigate possible reactions between differently coated carbon-bonded alumina filters and an AZ91 magnesium alloy melt, immersion tests were carried out. Uncoated as well as MgAl2O4-, Al2O3-, nano- (carbon nano tubes/alumina nano sheets) and MgO-C-coated filters were tested. Thermodynamic calculations showed that only magnesia (MgO) and carbon are stable against molten magnesium; alumina (Al2O3) and spinel (MgAl2O4) will be reduced under the formation of magnesia. Optical and scanning electron microscopy as well as EDX analysis were performed near and at the filter-magnesium alloy-interface of the cooled and sectioned filter samples after their immersion into the AZ91 melt. The results of the thermodynamic calculations were confirmed by the experiments. The MgO-C-coated filter was the only one that did not show an in situ-formed layer on its surface after being in contact with the magnesium alloy melt. The alumina- or spinel-containing filter surfaces displayed platelet-like in situ layers after their contact with the molten AZ91. The results of the EDX analysis of these layers suggest their composition of MgO, since notable respective Mg and O contents were detected, as predicted by the calculations.
Keywords: Ceramic Foam Filter, Interfaces, Al2O3, MgO

Publ.-Id: 28555 - Permalink


Semi-Solid remelting of Magnesium-Chips
Ohmann, S.; Ditze, A.ORC; Scharf, C.
Compact and loose magnesium chips were processed by means of remelting. The remelting was successfully performed using the new method of semi-solid melting, without the addition of flux, at temperatures between 580°C and 600°C. In this temperature range, the exothermic reaction between magnesium and the oxygen present in the surrounding atmosphere is avoided; in addition, the oxygen layer of the chips is stripped off by the particles of the semi-solid melt. Results show that more than 95% of the magnesium chips can be recovered as metal. Experiments were performed on different scales to obtain production parameters for the recycling process. Larger particle sizes of magnesium chips can be remelted faster than smaller ones. The ability to remelt at temperatures in the semi-solid region of alloys demonstrates the possibility of recovering virtually all of the metal from the chips.

Publ.-Id: 28554 - Permalink


System integration, Environmental impact and Business models
Reuter, M. A.;
Determine economic feasibility (OPEX and CAPEX) for industrial scale pretreatment based on different energy sources and their integration with existing industrial production of Mn-alloys for different cases;
Prepare a business plan for implementation of pretreatment technology at the project partners;
Prepare a strategy for future exploitation of the developed technology outside the project consortium and identify how this will reduce CO2 emissions also by including the embodied energy of the system;
Assess environmental impact on manganese alloy production, especially effect on CO2 emission and energy consumption of industrial scale pretreatment in separate unit integrated with existing industrial Mn-alloy production. This will be estimated by linking system simulation with environmental footprint using LCA and Life Cycle Cost analysis tools; and
Maximize the resource efficiency of manganese production by optimising the processing and the infrastructure of the system of technologies. This will be based on applied scales for mass flows and production processes. Both energy and exergy efficiency will be maximized.
Keywords: energy efficiency, exergy efficiency, resource efficiency
  • Lecture (others)
    PreMa Project Meeting, 22.-23.10.2018, Trondheim, Norwegen

Publ.-Id: 28553 - Permalink


Multi-source hyperspectral imaging of carbonatite-hosted REE-Nb-Ta mineralization at Marinkas Quellen, Namibia
Booysen, R.; Zimmermann, R.; Lorenz, S.; Gloaguen, R.; Nex, P. A. M.;
The demand for mineral and metalliferous resources needs to match the continued global rise in population and global economic growth. Rare Earth Elements (REEs), Niobium (Nb) and Tantalum (Ta) are such deposits in high demand. This global rise makes it difficult to meet the growing demand using only the currently available resources, such as recycled REEs and known REE deposits. Although the concept of a purely circular economy is very attractive through the use of recyclable REE-Nb-Ta, this model is not completely sustainable due to the increased energy needed to bolster such a model. Therefore, a renewed focus on the exploration of REE-Nb-Ta deposits is imperative to ensure the future development of this commodity.
Traditional exploration techniques are mainly based on extensive field work supported by geophysical surveying. Restrictions such as field accessibility, financial status, area size and climate can hinder these traditional exploration techniques. Hence, we suggest to increase the use of multi-source and multi-scale hyperspectral remote sensing in order to decrease conventional restrictions in the exploration of minerals through the use of aerial and ground-based methods. The multi-scale, multi-source approach will consist of a downscaling procedure, moving from low spatial resolution to high spatial resolution. Firstly, satellite data (Sentinel-2) will be used to identify the study area, then hyperspectral airborne data (HyMap) will be used to refine the area of interest. Subsequently, a snapshot hyperspectral camera will be attached to a UAV to acquire drone-borne data for the investigation of the deposit in more detail. We further argue that the addition of drone-borne hyperspectral data can also vastly improve the accuracy of field mapping in future mineral exploration. Drone-borne measurements can supplement and direct geological observation immediately in the field and therefore allow better integration with in-situ ground investigations. In particular, in inaccessible and remote areas with little infra-structure, such systems are an excellent reconnaissance tool because it allows a systematic, dense and completely non-invasive surveying, which is often not possible using ground-based techniques. Additionally, spectral and spatial information will be integrated by combining drone-borne hyperspectral and Light Detection And Raging (LiDAR) data to provide more accurate classification results.
Ultimately, the corrected drone-borne data provide information on the spectral signatures of outcropping lithologies to the exploration teams. This is achieved by using end-member modelling and classification techniques such as non-linear machine learning algorithms, e.g., Neural Networks and decision tree based methods. The drone based data are integrated in a comprehensive workflow including in-situ acquisitions and results in an hypercloud. The validation of the resulting digital outcrop is performed via field spectroscopy, portable XRF and representative geochemical whole-rock analysis.
The area of interest for this study is the massive carbonatite intrusion at Marinkas Quellen, Namibia. The location is in a remote environment and characterized by difficult terrains and a complete carbonatite suite (e.g. calsio-, ferro- and magnesio-carbonatites). The first two factors would normally impede or restrict traditional field surveying. Preliminary results indicate that drone-borne surveying has a very high potential to directly detect REE-concentrations and indicator minerals for Nb and Ta, in fundamentally lowering the acquisition costs and increasing the information potential of data captured in the field.
Keywords: REEs; Multis-source; Hyperspectral; Exploration; Marinkas Quellen
  • Poster
    WHISPERS - Hyperspectral Image and Signal Processing Workshop, 23.-26.09.2018, Amsterdam, The Netherlands

Publ.-Id: 28552 - Permalink


Experimental study of the natural convection heat transfer performance for finned oval tubes at different tube tilt angles
Unger, S.; Beyer, M.; Thiele, J.; Hampel, U.;
The natural convection heat transfer of finned oval tubes was studied for different tube tilt angles (0° to 40°), fin spacing (6 mm to 16 mm) and Rayleigh numbers (11000 to 130000). Fin efficiency was determined by temperature measurements along the fin surface and temperature gradient calculations. Nusselt number and volumetric heat flux density were chosen as assessment parameters for the thermal performance. A comparison of the experimental data with correlations from literature was made and good agreement was found. Furthermore, the uncertainty by the measurements was evaluated. In the horizontal tube orientation (0°) the Nusselt number increases with fin spacing, however the fin efficiency and the volumetric heat flux density reduce. The tilt angle of the longitudinal tube axis was found to have an essential impact on the thermal performance, in particular when the fin spacing is high. For the higher fin spacing values the horizontal orientation gives highest Nusselt number and volumetric heat flux density. At tube tilt angle of 40° the thermal performance becomes lowest for all fin spacing values. When the fin spacing is low, the effect of tube tilt angle is minor. From the experimental results correlations between Nusselt number, Rayleigh number, fin spacing and tube tilt angle are proposed to assist the future design of heat exchanger with tilted finned oval tubes.
Keywords: Finned oval tubes, Natural convection, Heat transfer, Tube tilt angle, Heat transfer correlation

Publ.-Id: 28551 - Permalink


Stoffkreislauf der Metalle – von der Gewinnung bis zum Recycling
Reuter, M. A.; Stelter, M.;
In der heutigen Zeit bestimmen Metalle unser tägliches Leben. Im Bereich der Mobilität – sei es beim Auto mit Verbrennungsmotor oder bei Elektrofahrzeugen – sind immer Metalle die wesentlichen Bestandteile, ohne die unsere Welt nicht funktionieren würde. Im Bereich der Kommunikation, der Unterhaltungselektronik, aber auch in der Medizin sind sie ebenfalls unverzichtbar. Ihre herausragenden Eigenschaften – wie Härte, Duktilität, Umformbarkeit, Korrosionsbeständigkeit – machen sie zu idealen Werkstoffen für fast alle Anwendungen. Besonders zeichnet sie aber die Recyclingfähigkeit aus, denn Metalle können prinzipiell zu 100 % nach ihrer Nutzung zurückgewonnen werden.
Dass wir dies bisher nur eingeschränkt tun, hat verschiedene Ursachen. In der Arbeitsgruppe sollen die Aspekte der Kreislaufwirtschaft beleuchtet werden. So werden technologische Möglichkeiten und Grenzen in Beziehung zu den ökonomischen Bezügen gestellt. Gibt es eine optimale Kreislaufführung und, wenn ja, wie sieht sie aus? Welche Faktoren beeinflussen die dafür notwendigen unangewandten Prozesse? Ist es sinnvoll, in jedem Fall zu versuchen, eine Recyclingrate von 100 % zu erreichen? Und ist dies überhaupt möglich?
Eine differenzierte Betrachtung bezüglich unterschiedlicher Stoffgruppen ist dabei erforderlich. Eine weiter in die Details eindringende Betrachtung soll am Beispiel der Metalle den Teilnehmenden der Arbeitsgruppe Chancen und Risiken der Stoffkreislaufführung vermitteln. In Gesprächsrunden und Diskussionen sollen die Vor- und Nachteile von technologischen Prozessen herausgearbeitet und deren Nutzen für die Kreislaufführung der Werkstoffe bewertet werden.
Keywords: Recyclingfähigkeit, Metalle, optimale Kreislaufführung
  • Lecture (others)
    Workshop - Sommerakademie der Studienstiftung, 19.-30.08.2018, St. Johann, Italien

Publ.-Id: 28550 - Permalink


Circular Economy engineering - Recycling 4.0 - Challenges of the circular economy
Reuter, M. A.;
The last hundred years have brought an unprecedented increase in natural resource use. This trend is likely to continue in the coming decades. Global resource use is expected to double by 2030. For Europe, these developments raise major concerns . Europe's economy depends on an uninterrupted flow of natural resources , metals, minerals, energy carriers and other raw materials , with imports providing a substantial proportion of these materials in many cases. Increasingly, this dependence will be a source of vulnerability, as growing global competition for natural resources has contributed to marked increases in price levels and volatility. Uncertain and unstable prices disrupt the industrial sectors that are dependent on these resources. At the same time, rapid increases in extraction and exploitation of natural resources are having a wide range of negative environmental impacts, particularly in Europe. Air, water and soil pollution, acidification of ecosystems, biodiversity loss, climate change and waste generation put economic and social well-being at risk. Creating a circular economy in Europe can help to address many of these challenges, and further improve the efficiency of resource use. It will have obvious economic benefits, reducing costs and risks while enhancing competitiveness. European leadership in the transition to a circular economy also offers opportunities securing first-mover advantages in the global economy.

The conference will address the issues impacting the transition from the linear take-make-consume-dispose economic model that currently dominates to a circular model that represents a fundamental alternative and explore the huge challenges and business opportunities in a circular economy. The conference will include presentations and panel discussions featuring renowned researchers within circular economy and leading Polish businesses presenting relevant projects and views on why and how the circular economy is introduced in their factories. It will bring together industry leaders, authorities and city planners, technology providers, business consultants, researchers and inventors, all with the common goal of driving innovation in new materials and better, more economic products and services and securing first-mover advantages in the global economy.

Recycling 4.0: digitalizing the system
Recycling 4.0: physics of separation
Recycling 4.0: industrial applications
Recycling 4.0 digital platforms
Keywords: Recycling 4.0
  • Invited lecture (Conferences)
    European Technology Forum 2018 / From Waste to Resources, 26.-27.09.2018, Katowice, Polen
  • Invited lecture (Conferences)
    THM-Kolloquim, 08.10.2018, Freiberg, Deutschland

Publ.-Id: 28549 - Permalink


SOCRATES 3nd Network-Wide Event
Reuter, M. A.;
What have we done so far?
Current Status of SOCRATES projects
Communication, Dissemination and Exploitation progress
What are we going to do? Our contribution to SOCRATES
Keywords: SOCRATES, Copper production process, HSC Sim
  • Lecture (others)
    SOCRATES 3nd Network-Wide Event, 13.-16.02.2018, Bonn, Deutschland

Publ.-Id: 28548 - Permalink


Numerical Studies of Normal Conducting Deflecting Cavity Designs for the ELBE Accelerator
Hallilingaiah, T. G.; van Rienen, U.; Arnold, A.; Lehnert, U.; Michel, P.;
Currently, in the electron linac ELBE there is a single beam line. Therefore, at any given time only single user can use the beam. Moreover, as different user experiments require distinct beam intensity settings, not all the experiments fully utilize the 13 MHz CW beam capability of the facility. To utilize the full beam capacity, multiple beam lines can be established by using an array of transverse deflecting structures. For that, an RF cavity was the design choice due to its inherent advantages with respect to repeatability of the kick voltage amplitude and phase, and the possibility of CW operation in the MHz range. Potential design candidates are the CEBAF RF separator, the three proposed crab cavities for the HL-LHC upgrade project, and a novel NC deflecting cavity design. In this comparative study, the figures of merit of the cavities are computed from electromagnetic field simulations for a transverse voltage of 300 kV. This comparative study supported our selection of the deflecting cavity design for ELBE.
Keywords: normal conducting, RF cavity, RF kicker, beam spreader
  • Open Access LogoContribution to proceedings
    9th International Particle Accelerator Conference, 29.04.-04.05.2018, Vancouver, British Columbia,, Canada
    Proceedings of the 9th International Particle Accelerator Conference: JACoW, ISBN 978-3-95450-184-7, 3824-3827
    DOI: 10.18429/JACoW-IPAC2018-THPAL074

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Publ.-Id: 28547 - Permalink


Sub-threshold production of K0s mesons and Λ hyperons in Au(1.23A GeV)+Au
Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, L.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Selyuzhenkov, I.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.; Leifels, Y.;
We present first data on sub-threshold production of K0s mesons and Λ hyperons in Au+Au collisions at √sNN = 2.4 GeV. We observe an universal scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their part> scaling, and the shapes of the rapidity and the pt spectra to state-of-the-art transport model (UrQMD, HSD, IQMD) predictions, we find that none of the latter can simultaneously describe all observables with reasonable χ2 values.

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Publ.-Id: 28546 - Permalink


Mixed-valent neptunium oligomer complexes based on cation-cation interactions
Schöne, S.ORC; März, J.; Stumpf, T.; Ikeda-Ohno, A.ORC
Mixed-valent tri- and tetranuclear complexes of neptunium, [{NpIVCl4}{NpVO2Cl(THF)3}2]·THF and [{NpIVCl3}{NpVO2(μ2-Cl)(THF)2}3{μ3-Cl}] (THF = tetrahydrofuran), were synthesised and characterised. Both the complexes are formed via the cation-cation interactions between the Np(IV) centre and the axial oxygens of the neptunyl(V) unit (i.e. transdioxo NpO2+ cation), demonstrating the potential of cation-cation interactions for further exploring the oligomer/cluster chemistry of actinides.
Keywords: actinides, neptunium, mixed-valence, oligomers, polymers, coordination, structure characterisation, cation-cation interactions

Publ.-Id: 28545 - Permalink


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