Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31635 Publications
Immune Monitoring of Cancer Patients Prior to and During CTLA-4 or PD-1/PD-L1 Inhibitor Treatment
Tunger, A.; Kießler, M.; Wehner, R.; Temme, A.; Meier, F.; Bachmann, M.; Schmitz, M.;
Targeting the immune checkpoint receptors cytotoxic T lymphocyte antigen 4 (CTLA-4), programmed cell death protein 1 (PD-1), or programmed cell death 1 ligand 1 (PD-L1) represents a very attractive treatment modality for tumor patients. The administration of antibodies against these receptors can promote efficient antitumor effects and can induce objective clinical responses in about 20–40% patients with various tumor types, accompanied by improved survival. Based on their therapeutic efficiency, several antibodies have been approved for the treatment of tumor patients. However, many patients do not respond to checkpoint inhibitor therapy. Therefore, the identification of biomarkers is required to guide patient selection for this treatment modality. Here, we summarize recent studies investigating the PD-L1 expression or mutational load of tumor tissues as well as the frequency and phenotype of immune cells in tumor patients prior to and during CTLA-4 or PD-1/PD-L1 inhibitor treatment.

Publ.-Id: 28710 - Permalink


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

Publ.-Id: 28709 - Permalink


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

Publ.-Id: 28708 - Permalink


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

Publ.-Id: 28707 - Permalink


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

Publ.-Id: 28706 - Permalink


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

Publ.-Id: 28705 - Permalink


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

Publ.-Id: 28704 - Permalink


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

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

Publ.-Id: 28703 - Permalink


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

Publ.-Id: 28702 - Permalink


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

Publ.-Id: 28701 - Permalink


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

Publ.-Id: 28700 - Permalink


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

Publ.-Id: 28699 - Permalink


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

Publ.-Id: 28698 - Permalink


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

Publ.-Id: 28697 - Permalink


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

Publ.-Id: 28696 - Permalink


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

Publ.-Id: 28695 - Permalink


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

Publ.-Id: 28694 - Permalink


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

Publ.-Id: 28693 - Permalink


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

Publ.-Id: 28692 - Permalink


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

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  • Secondary publication expected from 15.12.2019

Publ.-Id: 28691 - Permalink


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

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Publ.-Id: 28690 - Permalink


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

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Publ.-Id: 28687 - Permalink


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

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  • Secondary publication expected from 10.01.2020

Publ.-Id: 28686 - Permalink


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

Publ.-Id: 28684 - Permalink


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

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  • Secondary publication expected from 04.04.2020

Publ.-Id: 28683 - Permalink


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

Publ.-Id: 28682 - Permalink


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

Publ.-Id: 28681 - Permalink


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

Publ.-Id: 28680 - Permalink


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

Publ.-Id: 28679 - Permalink


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

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

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

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

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

Publ.-Id: 28678 - Permalink


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

Publ.-Id: 28677 - Permalink


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

Publ.-Id: 28676 - Permalink


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

Publ.-Id: 28675 - Permalink


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

Publ.-Id: 28674 - Permalink


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

Publ.-Id: 28673 - Permalink


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

Publ.-Id: 28672 - Permalink


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

Publ.-Id: 28671 - Permalink


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

Publ.-Id: 28669 - Permalink


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

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Publ.-Id: 28668 - Permalink


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

Publ.-Id: 28667 - Permalink


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

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

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

Keywords: centrifugal pump; two-phase flow investigations; ultrafast X-ray computed tomography
  • 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

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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

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


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


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