Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41709 Publications

Integrated drone-borne and ground-based hyperspectral imaging for exploration targeting

Herrmann, E.; Zimmermann, R.; Gloaguen, R.

Abstract

The Iberian Pyrite Belt (IPB) in Southwest Spain and South Portugal is best known for its numerous massive sulphide deposits. With their 4000 years history of mining, the mines of Rio Tinto are of important economic importance in the IPB. Orebodies and related alteration zones were mined for copper, gold, silver and many other pre- cious metals. We selected this site as a case study for the exploration of massive sulphide deposits due to its excellent data basis, economic importance and excellent outcrops. Ground-based and drone-borne hyperspectral data were acquired during 3 field campaigns in 2017 and 2017. Drone-borne hyperspectral images are acquired by a RIKOLA Hyperspectral Imager in the wavelength range from 500 to 900 nm. Not only spectral information can be gathered that way, overlapping images can also be used to calculate 3D surface models using Structure-from-Motion photogrammetry. Resulting point cloud can be basis for 3D data integration and correlation of spatial orientation of surfaces to spectral characteristics. Ground-based data are acquired with a Specim AisaFenix hyperspectral camera with a wavelength range from 400 to 2500 nm.
A complex geological history lead to the appearance of numerous regional geochem- ical and structural characteristics correlated to the orebodies that comprise different types of syn- and post-mineralisation alteration zones. These features are hardly re- cognisable using classical geological fieldwork techniques. Until now, time consum- ing and expensive geological interpretations rely almost exclusively on geochemical data. Instead, we argue that by using in hyperspectral data, those alteration zones can easily be determined, due to characteristic features in the VNIR and SWIR range. This provides a powerful tool for a fast, low-cost and spatially precise altera- tion mapping to guide the exploration process. The result of this data integration is comparable to an early stage geological surface model. It can provide a very precise tool for exploration and mining at all stages.
We chose the Corta Atalaya in Riotinto/Spain, one of the most profitable mines in the Spanish part of the Iberian pyrite belt, to demonstrate this approach of modern, re- mote sensing based geological exploration methods. Methods include traditional al- gorithms like Spectral Feature Fitting and Mapping absorption wavelength, but also non-linear unsupervised classification algorithms. Different kind of alteration zones are discriminated and interpreted in terms of their spectral-spatial distribution.

  • Poster
    10th EARSeL SIG Imaging Spectroscopy Workshop, 19.-21.04.2017, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-24906


Hyperspectral imaging for structural geology: An example for more interdisciplinary data analysis in mineral exploration

Zimmermann, R.; Herrmann, E.; Rosa, D.; Kirsch, M.; Gloaguen, R.

Abstract

Since the applications of hyperspectral imaging found their way into geological investigations, mineral mapping has reached a completely new level of spatial and spectral resolution. Thanks to increasing technological developments in hyperspectral imaging, system resolutions steadily became better at lower prices. Although these methods are already frequently applied in the field of economic geology and petrology, so far, these techniques have rarely been used for structural mapping and interpretation. The actual tool of choice, photogeology, makes just the use of true-color RGB images. However, detailed mineral and lithological maps from hyperspectral imaging can bring a new dimension. Hyperspectral imaging can highlight small mineralogical differences in rocks that cannot be picked-up in traditional RGB images and thus allow lithological contacts to be easily identified. Potential applications include, e.g., mapping dykes of different spectral signatures and their genetic relations or folds in (inaccessible) homogeneous rocks like marbles or quartzites. Furthermore, different types of alteration, associated with structural information can allow the detection of pathways for mineralising fluids and their structural control, one of the most important application of applied structural geology in mineral exploration. Potential methods include mapping absorption wavelength, spectral unmixing and non-linear classifications. All hyperspectral results are integrated into 3D point-clouds for interpretation. We exemplify the interdisciplinary analysis of hyperspectral data, independent of scale and source and their use for structural geology.
In the first case the barely accessible, 1000 m high marble cliffs of Maarmorilik/Greenland were scanned with a ground-based hyperspectral imaging (HSI) system. In certain structural positions a Pb-/Zn-mineralisation is hosted. A preliminary analysis with focus on carbonate mineralogy using absorption wavelengths identified fold structures of calcite-rich and dolomite-rich marbles, which are not visible in standard RGB images. Furthermore, some marble horizons are rich in evaporite minerals (e.g., anhydrite). The distribution of those horizons is mapped using spectral unmixing techniques and can be used to elucidate the structural relationship between deformation, mineralising fluids and ore emplacement.
At the inaccessible mine-pit of Peña de Hierro/Spain hyperspectral imaging is used to enhance the understanding of ore emplacement in relation with faults. Various mineral mapping methods, e.g., Spectral Feature Fitting, and non-linear unsupervised clustering, e.g., Self-Organising Maps, are applied. Faults and folds can easily recognised in RGB images here. However, in hyperspectral data we observe a degradation of hydrothermal activity around faults and orebodies that lead to a better understanding of the interaction between faulting and ore emplacement. Small scale structures in overlying meta- sedimentary rocks are highlighted in hyperspectral images too. They give indication of post-mineralisation deformation and, thus, pathways for secondary alteration and ore replacement.

  • Poster
    10th EARSeL SIG Imaging Spectroscopy Workshop, 19.-21.04.2017, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-24905


Modeling patterns of anatomical deformations in prostate patients undergoing radiation therapy with an endorectal balloon

Brion, E.; Richter, C.; Macq, B.; Stützer, K.; Exner, F.; Troost, E.; Hölscher, T.; Bondar, L.

Abstract

External beam radiation therapy (EBRT) treats cancer by delivering daily fractions of radiation to a target volume. For prostate cancer, the target undergoes day-to-day variations in position, volume, and shape. For stereotactic photon and for proton EBRT, endorectal balloons (ERBs) can be used to limit variations. To date, patterns of non-rigid variations for patients with ERB have not been modeled. We extracted and modeled the patient-specific patterns of variations, using regularly acquired CT-images, non-rigid point cloud registration, and principal component analysis (PCA). For each patient, a non-rigid point-set registration method, called Coherent Point Drift, (CPD) was used to automatically generate landmark correspondences between all target shapes. To ensure accurate registrations, we tested and validated CPD by identifying parameter values leading to the smallest registration errors (surface matching error 0.13+-0.09 mm). PCA demonstrated that 88+-3.2% of the target motion could be explained using only 4 principal modes. The most dominant component of target motion is a squeezing and stretching in the anterior-posterior and superior-inferior directions. A PCA model of daily landmark displacements, generated using 6 to 10 CT-scans, could explain well the target motion for the CT-scans not included in the model (modeling error decreased from 1.83+-0.8 mm for 6 CT-scans to 1.6+-0.7 mm for 10 CT-scans). PCA modeling error was smaller than the naive approximation by the mean shape (approximation error 2.66+-0.59 mm). Future work will investigate the use of the PCA-model to improve the accuracy of EBRT techniques that are highly susceptible to anatomical variations such as, proton therapy.

Keywords: External beam radiation therapy; nonrigid registration; principal component analysis; mathematical modeling; motion management in radiotherapy; prostate cancer

  • Contribution to proceedings
    SPIE Medical Imaging 2017, 11.-16.02.2017, Orlando, USA
    Proc. SPIE 10135, Medical Imaging 2017: Image-Guided Procedures, Robotic Interventions, and Modeling: SPIE digital library, 1013506-1-1013506-9
    DOI: 10.1117/12.2251933
    Cited 1 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-24904


Understanding actinide reactivity at the water-mineral interface

Stumpf, T.

Abstract

The behaviour of radionuclides in the environment is determined by interfacial reactions such as adsorption, ion exchange and incorporation processes. In literature such processes are often described by operational solid-liquid distribution ratios (Rd values). Distribution ratios are defined as the ratio of the quantity of a radionuclide sorbed per solid mass and the equilibrium concentration of the radionuclide. They are macroscopic parameters which are strictly valid only for the mineral and solute combination in the experimental system. For reliable and trustworthy long-term predictions of radionuclide transport behaviour, interaction mechanisms and processes occurring at the solid-water interface, they need to be understood at the molecular level. This can only be achieved by the application of spectroscopic methods.
In the talk a multi-spectroscopic approach will be presented. We used a combination of microscopy, laser and X-ray based techniques to gain process understanding on a molecular level of the interaction of actinides with mineral surfaces. The derived data are used to improve surface complexation modelling. Therefore, the advanced spectroscopic techniques used in Dresden-Rossendorf are an important contribution to the long-term performance assessment of a nuclear waste disposal.

Keywords: radionuclides; nuclear waste disposal

  • Invited lecture (Conferences)
    les Journées Nationales de Radiochimie et de Chimie Nucléaire (JNR) 2016, 08.-09.09.2016, Nice, Frankreich
  • Lecture (Conference)
    Frontiers in Environmental Radioactivity 2016, 06.-07.01.2016, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-24902


Electron effective mass enhancement in Ga(AsBi) alloys probed by cyclotron resonance spectroscopy

Pettinari, G.; Drachenko, O.; Lewis, R. B.; Tiedje, T.

Abstract

The effect of Bi incorporation on the conduction band structure of Ga(AsBi) alloys is revealed by a direct estimation of the electron effective mass via cyclotron resonance absorption spectroscopy at THz frequencies in pulsed magnetic fields up to 65 T. A strong enhancement in the electron effective mass with increasing Bi content is reported, with a value of mass ∼40% higher than that in GaAs for ∼1.7% of Bi. This experimental evidence unambiguously indicates a Bi-induced perturbation of the host conduction band states and calls for a deep revision of the theoretical models describing dilute bismides currently proposed in the literature, the majority of which neglect or exclude that the incorporation of a small percentage of Bi may affect the conduction band states of the host material.

Permalink: https://www.hzdr.de/publications/Publ-24901


Organic synthesis, radiofluorination and in vitro evaluation of two novel fluorenones targeting the alpha 7 nicotinic acetylcholine receptor (α7 nAChR)

Scheunemann, M.; Teodoro, R.; Wenzel, B.; Deuther-Conrad, W.; Steinbach, J.; Brust, P.

Abstract

Objectives: Derivatives of the antiviral drug tilorone have recently been discovered as novel α7 nAChR ligands. Based on a tricyclic heteroaromatic unit linked to one or two conformationally rigidified cyclic amines, highly affine compounds were obtained [1]. [18F]DBT10 [2] and [18F]ASEM [3] (Fig.) were developed as promising α7 nAChR PET tracers. This study investigates bioisosteric sulfur-free analogues of DBT10 and its ortho-isomer obtained by replacement of the functional group SO2 by CO.
Methods: The p-fluoro and o-fluoro derivatives 1 and 2 and the corresponding nitro precursors were prepared in three and five steps from the appropriate nitro-fluoren-9-ones. Affinities towards human α7, α4β2, and α3β4 nAChRs were determined. Radiosynthesis of [18F]1 and [18F]2 via nucleophilic aromatic radiofluorination was optimised and finally performed using an automated module. In vitro autoradiography of [18F]1 on pig brain slices was performed.
Results: The fluorenones 1 and 2 were prepared in 25% yield. Both bind with high affinity and selectivity towards nAChRs (1: Ki = 1.18 nM, 1500 nM, and 46.0 nM; 2: Ki = 1.12 nM, 1796 nM, and 33.2 nM for α7, α4β2, and α3β4 nAChR, respectively). Highest labeling efficiencies (≈ 80%) were obtained in DMF under microwave assisted heating, yielding [18F]1 and [18F]2 with radiochemical purities of ≥ 97% and molar activities of 30 ± 6 GBq/μmol and 44 ± 3 GBq/μmol, respectively. Binding of [18F]1 on pig brain slices was markedly reduced by α7 nAChR-specific ligands.
Conclusions: New highly affine α7 nAChR ligands were synthesized based on the tilorone scaffold by replacement of the SO2 by a CO group. The high nitro-to-[18F]fluoro conversion obtained for the fluorenones suggests a comparable electron withdrawing effect of the two functionalities. Further studies will investigate the potential of [18F]1 and [18F]2 as PET imaging agents.
References [1] M. R. Schrimpf, K. B. Sippy, C. A. Briggs, et al. Bioorg. Med. Chem. Lett. 2012, 22, 1633-1638. [2] R. Teodoro, M. Scheunemann, W. Deuther-Conrad, et al. Molecules 2015, 20, 18387-18421. [3] A. G. Horti, Y. Gao, H. Kuwabara, et al. J. Nucl. Med. 2014, 55, 672-677.

Keywords: α7 nAChR ligands; fluorenones; radiofluorination

  • Poster
    22nd International Symposium On Radiopharmaceutical Sciences (ISRS 2017), 14.-19.05.2017, Dresden, Deutschland
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)1, 585
    DOI: 10.1002/jlcr.3508
    ISSN: 1099-1344
    Cited 3 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-24900


Emission spectroscopy for the identification of rare earth elements using laser-induced photoluminescence

Fuchs, M. C.; Gloaguen, R.; Beyer, J.; Jakob, S.; Heitmann, J.

Abstract

We present rare earth element (REE) emission spectra stimulated by lasers with wavelength of 325 nm, 442 nm and 532 nm. Measured spectra represent REE standards in phosphates and fluorides, one set embedded in epoxy resin and one set in form of free-standing single grains. The comparison of emission features from the different specimen allows to evaluate, which emission peaks are robust and unequivocal for REE identification. Results showed that photoluminescence spectroscopy allows successful identification of characteristic emission peaks for Dy3+, Er3+, Eu3+, Gd3+, Nd3+, Sc3+, Sm3+, Tb3+, and Yb3+, when using laser stimulation at 325 nm. However, strong matrix emissions such as from epoxy resin may mask weaker luminescence emissions. In such cases, the adequate choice of longer stimulation wavelength is crucial to suppress the strong matrix emission without loosing the REE luminescence. Using laser stimulation at 442 nm and 532 nm shows promising results, but the optimal laser wavelength seems to be REE-specific and consequently, requires comprehensive analyses.

Keywords: emission spectroscopy; photoluminescence; rare earth elements; exploration; raw materials

  • Lecture (Conference)
    WHISPERS - 8th workshop on hyperspectral image and signal processing, 21.-24.08.2016, Los Angeles, USA

Permalink: https://www.hzdr.de/publications/Publ-24898


Preclinical Applications of Brain PET/MRI

Deuther-Conrad, W.

Abstract

The two imaging techniques positron emission tomography (PET) and magnetic resonance imaging (MRI) enable advanced in vivo imaging in different fields of biomedical research. The combination of these two imaging modalities into a single device merges functional and morphologic information. High-resolution MRI of morphology with good soft-tissue contrast and spectroscopic detection of endogenous metabolite distributions is completed by means of high-sensitive PET by functional parameters such as glucose metabolism, amino acid transport, proliferation, receptor density, or drug concentration.
In preclinical research, the acquisition of PET and MR images of the same animal has been realized using different strategies in recent years. While initially most studies have been performed on separate devices with subsequent co-registration of the images, new and more integrated systems are available. Accordingly, fused images are obtained by the use of (i) separate instruments, (ii) in-line/sequential PET/MRI, or (iii) fully integrated PET/MRI scanners. Preclinical PET/MRI benefits in particular brain imaging in various small-animal models of diseases, including genetically-engineered animals. By providing a powerful tool for identification as well as functional characterization of new drug targets or disease biomarkers, the obtained information supports e.g. the development and follow-up of the efficacy of accordingly targeting drugs significantly.
Our research group at the Helmholtz-Zentrum Dresden-Rossendorf has been focused on the development of radiopharmaceuticals for brain PET imaging for almost two decades. Four newly developed radioligands for imaging of depression and dementia have been translated into human application within the last eight years. Related to the programme-oriented research within the Helmholtz Association the main emphasis of the group has recently moved into cancer research trying to visualize and characterize molecular switches which are involved in brain tumor development and progression by means of preclinical PET/MRI.

  • Invited lecture (Conferences)
    BRAIN & BRAIN PET 2017, 01.-04.04.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24897


3D Mapping of electric potentials and magnetic fields at the nanoscale using Electron Holographic Tomography

Wolf, D.; Lubk, A.; Lichte, H.

Abstract

Off-axis electron holography (EH) is a TEM technique that records the phase information of an electron wave transmitted through a thin specimen in an electron hologram. By reconstructing this phase information, it enables electrostatic and magnetic potentials to be mapped quantitatively with high spatial resolution and, when combined with tomography to electron holographic tomography (EHT), in three dimensions (3D) [1,2]. Tomograms obtained by EHT provide the 3D mean inner potential (MIP) distribution of nanoscale materials from which the 3D morphology and the chemical composition can be inferred [3]. Moreover, functional potentials, e.g., introduced by doping of impurities in semiconductors, have been successfully revealed in 3D [4]. Recently, we succeeded in the 3D reconstruction of the axial component of the B-field prevailing in magnetic nanowires [5,6].

EHT as applied on magnetic samples proceeds as follows (see Fig. 1): (1) an electron hologram tilt series (ideally covering a range of 360°) is acquired, (2) the phase image tilt series is reconstructed from the holograms, (3) electric and magnetic phase shifts are separated by computing half of the sum/difference between opposite (180° tilted) projections, and (4) both the electric potential and the B-field component parallel to the tilt axis are reconstructed with tomographic techniques. Here, we report EHT studies achieved by means of tomography-dedicated TEM sample holders, in combination with advanced in-house developed software packages for acquisition, alignment and tomographic reconstruction.

Fig. 2 shows the 3D electric potential reconstruction of a GaAs/AlGaAs core-multishell nanowire (NW) grown by metalorganic vapour phase epitaxy (MOVPE) using an Au nanoparticle (NP) as catalyst. Such NWs may serve as novel coherent nanoscale light sources (lasers), because they provide an effective gain medium, low-loss optical waveguiding, and strong optical confinement for axially guided optical modes. The difference in the MIP allows discriminating between GaAs and AlGaAs within the NW. Longitudinal (Fig. 2b) and cross-sectional (Fig. 2e) 2D slices averaged over a well-defined thickness reveal not only the GaAs core and the AlGaAs shell, but also a 5nm thin GaAs shell within the AlGaAs, which acts as a quantum well.

Fig. 3 comprises two recent EHT studies revealing the B-field within a Co nanowire (NW) [5] and a Co2FeGa Heusler alloy NW [6] both with spatial resolution higher than 10 nm. The reconstructions of the dominant axial component of the magnetic induction exhibit a small inversion domain at the apex of the Co NW, whereas at the Co2FeGa NW, a magnetic dead layer of 10 nm width could be revealed.

The powerful approach presented here is widely applicable to a broad range of 3D electric and magnetic nanostructures and may trigger the progress of novel nanodevices.

[1] P A Midgley and R E Dunin-Borkowski, Nat. Mater. 8 (2009) p. 271.

[2] D Wolf, A Lubk, F Röder and H Lichte, Curr. Opin. Solid State and Mater. Sci. 17 (2013) p. 126.

[3] A Lubk, D Wolf, P Prete, N Lovergine, T Niermann, S Sturm and H Lichte, Phys. Rev. B 90 (2014) p. 125404.

[4] D Wolf, A Lubk, A Lenk, S Sturm and H Lichte, Appl. Phys. Lett. 103 (2013) p. 264104.

[5] D Wolf et al., Chem. Mater. 27 (2015) p. 6771.

[6] P Simon, D Wolf, C Wang, A A Levin, A Lubk, S Sturm, H Lichte, G H Fecher and C Felser, Nano letters 16 (2016) p. 114.

[7] We thank N Lovergine of University of Salento, Lecce for provision of the GaAs/AlGaAs core-multishell nanowire samples.

[8] This work was supported by the European Union under the Seventh Framework Program under a contract for an Integrated Infrastructure Initiative Reference 312483-ESTEEM2.

Keywords: 3D reconstruction; magnetic induction; mean inner potential; nanowires

  • Invited lecture (Conferences)
    The 16th European Microscopy Congress, Lyon, France, 28.08.-02.09.2016, Lyon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-24896


Optimization of the Aeration System in Municipal Wastewater Treatment Plant

Mohseni, E.; Herrmann-Heber, R.; Reinecke, S.; Hampel, U.

Abstract

In Germany wastewater is treated in 10000 plants which use 4.400 GWh of energy per year. From this big figure, up to 70% is consumed in the biological treatment and the portion of only aeration of waste water in activated sludge tank is about 50% of the whole figure. Aeration is the essential part of the process since the microorganisms need to be provided by sufficient amount of oxygen to degrade ammonia. Aerators with flexible membranes located at the bottom of the aeration tank are currently state of the art for this process. However the process suffers from some limitations such as high pressure drop, insufficient mixing and underutilization of oxygen. These are mainly due to scarce knowledge about gas dispersion inside the tank.
Initial bubble size in gas dispersion is of a great importance since it determines the ascent and coalescence rate, macro mixing by turbulence, and oxygen transfer from the bubble to the fluid phase. The initial bubble size is drastically influenced by the type of aerator which is being used in the tank. The typical bubble size generated by flexible membrane aerators has been determined to be between 2-4 mm by Hasanen et al. (Hasanen, 2006). However, this is considerably higher than the optimal bubble size calculated by Motarjemi and Jameson (Motarjemi, 1978) who reported the range of 0.7-1.0 mm for the optimal value for the 95% oxygen transfer to water in 3-6 m tank depth.
A novel approach uses solid perforated stainless steel aerators with fine pores in micro scale for gas dispersion. In this work bubble formation of stainless steel aerators has been experimentally investigated with a high resolution optical measurement technique by means of videometry and the results are compared with membrane aerators. Preliminary results of the stainless steel membrane sparger showed a significant reduction in the bubble size up to 47 % and consequently an increase in bubble residence time in comparison with flexible membranes.
A comprehensive set of experiments have been conducted in which the bubble formation with respect to pore size, pore density, plate thickness, flow rate, membrane surface roughness, and bubble generation frequency have been investigated. Thanks to the state of the art manufacturing technique, very fine pores starting at 30 µm up to 200 µm have been processed which resulted in formation of bubbles in the range down to 1.4 mm diameter.
Current poster, presents the motivation of the project and the purposed approaches toward a solution and the initial results of the preliminary experiments done by means of videometry technique.

Keywords: Bubble Generation; Activated Sludge; Aeration; Biological Wastewater Treatment; Multiphase Flow

  • Poster
    11th HZDR PhD Seminar, 17.-19.10.2016, Oberwiesenthal, Germany

Permalink: https://www.hzdr.de/publications/Publ-24895


Development of concepts for high quality image reconstruction based on adaptive grid sizes

Pfahl, A.; Wagner, M.; Bieberle, A.; Buzug, T. M.

Abstract

In this work an alternative data processing concept is investigated for the correct reconstruction of slice images acquired by an ultrafast electron beam X-ray tomography scanner mainly used for analyzing multiphase flows. Currently, image reconstruction is performed on regular pixel grids by filtered back projection to achieve rapid data processing performances but leading to non-optimal image qualities. To accomplish an improved image quality the usage of irregular reconstruction grids and iterative reconstruction methods is analyzed considering the geometric arrangement and, thus, the real spatial resolution of the ultrafast CT scanner. Finally, a two-stage reconstruction approach is proposed reducing the required amount of computer memory as well as the computational time and inserting prior knowledge about the object of interest. First simulations of different irregular grids provide a promising basis for further successful implementation of the proposed two-stage reconstruction concept.

Keywords: computed tomography; irregular grids

Involved research facilities

  • TOPFLOW Facility
  • Contribution to proceedings
    Studierendentagung Lübeck, 07.-09.03.2017, Lübeck, Deutschland
    Student Conference Proceedings 2017
  • Poster
    Studierendentagung Lübeck, 07.-09.03.2017, Lübeck, Deutschland
  • Lecture (Conference)
    Studierendentagung Lübeck, 07.-09.03.2017, Lübeck, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24894


Experimentelle Untersuchung zur Hydrodynamik der Partialoxidation von Isobutan in einem Mikroreaktor

Reichelt, C.

Abstract

Die hydrodynamischen Eigenschaften eines zweiphasigen Gemisches aus Isobutan und Stickstoff wurden in einem Mikroreaktor experimentell untersucht. Dazu wurden eine Hochgeschwindigkeitskamera und eine spezielle Bildanalysesoftware verwendet, mit der Isobutan Gas Strömungen in einer Glaskapillare analysiert und ausgewertet werden konnten. Anhand der erhaltenen Ergebnisse konnten Rückschlüsse auf die Bedingungen der Isobutanoxidation in jenem Reaktor gezogen werden. Ziel war es, den Einfluss der betrachteten Parameter (Eduktströme und Betriebsdruck) auf die Zwei-Phasen-Strömung zu analysieren und zu verstehen. Spezielle Strömungsregime können dabei entscheidende Auswirkungen auf den Stofftransport und somit auf reaktionstechnische Kenngrößen wie Umsatz, Selektivität oder Ausbeute haben. Regelmäßige Taylor-Strömungen zeichnen sich in Mikrokanälen durch besonders gute Stoff- und Wärmetransporteigenschaften aus. Aus diesem Grund wurden die Parameter so gewählt, dass sich dieses Strömungsregime ausbildet. Durch diese Arbeit konnten die Strömungsregime der meisten der bisher durchgeführten Oxidationsexperimente als unregelmäßige Taylor-Strömungen charakterisiert werden. Darüber hinaus konnten die Einflüsse der jeweiligen Versuchsbedingungen auf die charakteristischen Kennzahlen der Taylor-Strömung ermittelt werden. Die Arbeit bietet aufgrund ihrer Ergebnisse eine wichtige Grundlage für die Durchführung der partiellen Oxidation von Isobutan im Mikroreaktor.

Keywords: Isobutan; Zweiphasenprozess; Taylor Flow; Charakteristik

  • Study thesis
    Hochschule für Technik und Wirtschaft Dresden, 2016
    Mentor: Thomas WIllms
    34 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24893


In-situ spectroscopic identification of actinide(V/VI) sorption complexes at the mineral oxide water interface

Müller, K.

Abstract

For the long-term safety assessment of nuclear waste repositories, neptunium and uranium are two of the most environmentally relevant components of nuclear waste to be considered. Hence, great attention is attracted to their geochemistry and migration behavior. Among the various geochemical processes, the migration of radioactive contaminants in the environment is strongly affected by molecular reactions in aqueous solution and at the solid-water interface, e.g. complexation with organic/inorganic ligands, sorption onto mineral phases, surface precipitation, and colloid formation. A detailed description of these interactions on a molecular level is required for a reliable modeling of the contaminants dissemination in the environment.
In the past decade, vibrational spectroscopy has been developed to a powerful tool for the study of dissolved complexes of heavy metal ions with a variety of inorganic and organic ligands and surface complexes on solid phases. In particular, a combined approach of in situ vibrational, time-resolved laser fluorescence and X-ray absorption spectroscopy potentially provides comprehensive molecular information. A survey of very recent spectroscopic results obtained from geochemical reactions of radionuclides, namely Np(V) and U(VI), is given.

Keywords: actinides; vibrational spectroscopy

Involved research facilities

Related publications

  • Lecture (others)
    Institutskolloquium, 29.11.2016, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-24892


Ferromagnetic resonance study of equiatomic FeRh thin films

Semisalova, A.; Stienen, S.; Barton, C. W.; Boettger, R.; Bali, R.; Thomson, T.; Farle, M.; Fassbender, J.; Potzger, K.; Lindner, J.

Abstract

Chemically ordered FeRh alloy with nearly equiatomic composition is antiferromagnetic at room temperature and exhibits a first-order phase transition to the ferromagnetic (FM) state at 370 K. Here, we present the study of FM resonance (FMR) in non-capped and Pt-capped magnetron sputtered 40 nm FeRh films on a MgO(100) substrate and analyse the influence of ion irradiation and chemical disordering on their magnetic properties. The temperature dependent FMR study between 200-500 K allowed us to observe the hysteretic temperature behavior, accompanied by a clear transformation of the FMR line, and explore the complex magnetic structure of films. We distinguished and characterized the contribution of anomalous FM interfacial layers induced by atomic intermixing and lattice strain. Finally, we have revealed the formation of a magnetic phase with an out-of-plane easy axis of magnetization caused by low-fluence irradiation with Ne+ ions.

Involved research facilities

Related publications

  • Lecture (Conference)
    80th Annual Conference of the DPG and DPG Spring Meeting, 06.-11.03.2016, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-24891


Ferromagnetic resonance in Ferh thin films near the antiferromagnetic-ferromagnetic phase transition

Semisalova, A.; Stienen, S.; Barton, C. W.; Boettger, R.; Bali, R.; Thomson, T.; Farle, M.; Fassbender, J.; Potzger, K.; Lindner, J.

Abstract

High-temperature FMR on FeRh thin films

Keywords: FeRh; phase transition; ferromagnetic resonance; ion irradiation

Involved research facilities

Related publications

  • Lecture (Conference)
    Euro-Asian Symposium “Trends in Magnetism” (EASTMAG-2016), 15.-19.08.2016, Krasnoyarsk, Russia
  • Invited lecture (Conferences)
    AMP 2017, Interdisciplinary workshop “Acousto-magneto-plasmonics meets quantum optics”, 28.-30.06.2017, Versailles, France
  • Invited lecture (Conferences)
    International School-Conference Spinus 2018, 01.-06.04.2018, Saint Petersburg, Russia

Permalink: https://www.hzdr.de/publications/Publ-24890


Observation of Negative Magnetic Hysteresis Loop in ZnO Thin Films

Haseman, M.; Winarksi, D.; Saadatkia, P.; Hernandez, A.; Kusz, M.; Anwand, W.; Wagner, A.; Thapa, S.; Colosimo, A. M.; Selim, F. A.

Abstract

We report on the observation of an unusual negative magnetic hysteresis loop in ZnO thin film co-doped with cobalt and aluminum (Co-Al:ZnO), while other transition-metal doped ZnO films such as Cu-doped ZnO and Mn-doped ZnO, exhibit normal hysteresis loops. The unusual magnetic behavior is ascribed to the presence of double magnetic layers with different magnetic moments due to the change of structural defects across the film layers. Positron annihilation measurements confirmed the presence of unique microstructural changes in the Co-Al:ZnO film. This study shows that defects in diluted magnetic semiconductors may induce not only ferromagnetism but also novel magnetic behaviors.

Keywords: magnetism ZnO hysteresis

Involved research facilities

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Permalink: https://www.hzdr.de/publications/Publ-24889


Colloidal particle at a fluidic interface: a direct numerical simulation

Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.

Abstract

Froth flotation is a separation process in which hydrophobic particles attach to the surface of rising air bubbles while the undesired hydrophilic particles settle down the bottom of the cell to eventually be discharged. Current numerical models developed for the simulation of the particle attachment process are still at an early stage of development. The “Smooth Profile Method”, a numerical method originally developed at the University of Kyoto for the direct numerical simulation of colloidal particles in monophasic fluids, was here combined with a newly-defined binary fluid model. The change in the trajectory as the particle approaches the fluid–fluid interface, the collision process, and the sliding down the bubble surface were all reproduced and compared remarkably well with on-site microscale experiments.

  • Lecture (Conference)
    NetFlot: Network of Infrastructure (NOI) - Modelling the Flotation Process, 19.-21.10.2016, Krakau, Gliwice, Polkowice, and Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-24888


Beschleunigermassenspektrometrie in Dresden

Rugel, G.; Scharf, A.; Ziegenrücker, R.; Merchel, S.

Abstract

Beschleunigermassenspektrometrie (AMS, accelerator mass spectrometry) ist eine höchstsensitive Methode um langlebige Radionuklide mit einer Halbwertszeit von einigen Jahren und länger zu messen. Seit Herbst 2011 werden an der AMS-Anlage DREAMS (DREsden AMS, siehe Abbildung), routinemäßig Radionuklide gemessen. Aus der zu analysierenden – bereits chemisch aufbereiteten – Probe werden in einer Cäsium-Sputterionenquelle negative Ionen (Moleküle oder Atome) extrahiert. Diese einfach negativ geladenen Ionen werden in einem Niederenergie-Massenspektrometer nach Energie und Impuls analysiert und gelangen nachfolgend in den Tandembeschleuniger, wo sie durch eine positive Hochspannung (bis zu 6 MV) beschleunigt werden. Beim Durchgang durch ein Argon-Stripper-Gas werden Elektronen abgestreift, dadurch Moleküle zerstört, und die nun positiven Ionen ein zweites Mal beschleunigt. Im Hochenergie-Massenspektrometer werden die Radionuklide dann mit einem geeigneten Detektionssystem (u. a. einer Ionisationskammer) identifiziert. Mit diesem Aufbau lassen sich Isobare sehr effizient, sowie molekularer Untergrund vollständig unterdrücken.
Momentan werden an DREAMS Routinemessungen der Nuklide 10Be, 26Al, 36Cl, 41Ca und 129I – meist in Kooperation mit externen Partnern - durchgeführt [1,2]. Die Nachweisgrenze liegt im Bereich von 10-15 – 10-16 Radionuklid zu stabilem Nuklid.
Um DREAMS weiterzuentwickeln wurde erfolgreich eine Ionenquelle für volatile Ionen - wie Chlor und Iod - entwickelt, die ein geringes Übersprechen (kurz- sowie langfristig) zeigt [3]. Eine Ionenquelle, die effizienter die wertvollen Proben ionisieren soll und damit neue Forschungsbereiche ermöglichen wird, ist gerade in Entwicklung [4].

Ref.: [1] S. Akhmadaliev et al., NIMB 294 (2013) 5. [2] G. Rugel et al., NIMB 370 (2016) 94. [3] S. Pavetich et al., NIMB 329 (2014) 22.
[4] BMBF-Verbundprojektforschung 05K16MG1 (H. Hofsäß, U Göttingen) & 05K16KTB (J. Feige, TU Berlin).

Keywords: AMS; accelerator mass spectrometry

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  • Lecture (Conference)
    Ionentreffen, 13.-15.02.2017, Göttingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24887


Upgrade of the nuclear microprobe at the Ion Beam Center at HZDR

Munnik, F.; Hanf., D.; Heller, R.

Abstract

The nuclear microprobe that was installed in 1994 at the Ion Beam Center of the Helmholtz-Zentrum Dresden-Rossendorf [1], has been in operation up to 2014 with only minor changes. After 20 years it became necessary to make an upgrade to replace old components and bring the setup up to current standards of technology and good working practice.
The major drawback of the old system was the optical microscope, especially the poor resolution and low contrast and brightness. However, a good optical image is essential to localise the areas of interest on, for example, large geological samples. Since the focused beam of MeV ions and the corresponding detectors is the principal investigative tool, any other equipment such as an optical microscope has to be designed around this device. A new microscope has been installed for which the first light-collecting lens is mounted directly into the chamber at only a few centimetres from the sample. The light is then guided over large mirrors and focussed on a CCD camera outside the sample chamber. The illuminating light is fed in through the lenses instead of using an external light source as in the old system. In addition, there is also a light source opposite to the microscope, allowing transmission illumination including through a polarising filter making polarised imaging possible.
Other improvements concern the control of the scanning system as well as the control and monitoring of all relevant experimental parameters. The control of the scan magnets is done by custom-designed hardware to guarantee real-time execution of the scanning without the need for a computer running a real-time operating system. Controlling and monitoring of the experiment are implemented to facilitate easy and secure operation of the microprobe by the user with special emphasis on operation by un-experienced users, since the device is part of the user facility IBC. All standard IBA techniques like PIXE, PIGE, RBS, NRA, ERDA and STIM are available and, in addition, a Channeltron detector has been installed to detect secondary electrons that allow quick imaging of the measurement area.
Technical details and first test measurements with the new system are presented.

[1] F. Herrmann, D. Grambole, Nucl. Instr. Meth. B 104 (1995) 26.

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  • Poster
    Ionentreffen (Teil der Serie Workshop Ionenstrahlphysik), 13.-15.02.2017, Göttingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24886


GMR films with crossed anisotropies for perpendicular field measurements

Ganss, F.; Raberg, W.; Luber, S.; Arekapudi, S. S. P. K.; Hellwig, O.; Albrecht, M.

Abstract

As 3-dimensional field sensors require one part being susceptible to perpendicular fields, thin film GMR stacks with a linear and reversible response to such fields are of interest for the development of monolithic sensor devices. Stacks with such a behavior can be achieved by combining a pinning layer with perpendicular easy axis and a free layer with perpendicular hard axis. Furthermore, the stray field of the pinning layer can be minimized and its coercivity enhanced if a ferrimagnet (or antiferromagnet) is used. For the present study, TbxCo100−x alloys have been chosen as the pinning layer material and Ni81Fe19 for the free layer. The single layers have been characterized by SQUID-VSM measurements, the complete layer stack by magneto-resistance measurements. Initial films confirm the expected behavior and exhibit a change in resistivity of 5% in a field range of 10 kOe. Further films will be optimized regarding their magnetic and electric properties. They shall be micro-structured then and equipped with bottom contacts through the substrate.

  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24885


Magnetic properties of nanostructured Tb-Fe alloy thin films

Arekapudi, S. S. P. K.; Hellwig, O.; Albrecht, M.

Abstract

Nanostructured ferrimagnetic Tb-Fe alloy thin films were prepared on pre-patterned substrates as underlying template, consisting of nanodot arrays with a dot diameter of 30 nm and a period of 60 nm. Two distinct magnetic configuration are possible, one where the magnetic material on the nanodot and in the trenches is decoupled from each other for film thicknesses below the nanodot height, and the other where full exchange coupling between magnetic material on the dots and in the trenches is effective for magnetic films thicker than the nanodot height. Regardless, of the magnetic configuration the reversal of the magnetic material on top of the nanodots is found to be nucleation dominated, while the magnetic material in the trenches reverses via domain wall propagation, as confirmed by in-field magnetic force microscopy. The distinct behavior in this system is attributed to the reduced exchange stiffness followed by relatively narrow domain walls (approx. 3-4 nm) present in these rare earth - transition metal alloys. A systematic study of magnetic properties on nanostructured Tb-Fe alloy films as a function of composition and film thickness will be presented.

  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24884


A Comparative Study on Electrical Characteristics of Crystalline AlN Thin Films Deposited by ICP and HCPA-Sourced Atomic Layer Deposition

Altuntas, H.; Bayrak, T.

Abstract

In this work, we aimed to investigate the effects of two different plasma sources on the electrical properties of low-temperature plasma-assisted atomic layer deposited (PA-ALD) AlN thin films. To compare the electrical properties, 50 nm thick AlN films were grown on p-type Si substrates at 200 °C by using an inductively coupled RF-plasma (ICP) and a stainless steel hollow cathode plasma-assisted (HCPA) ALD systems. Al/AlN/p-Si metal-insulatorsemiconductor (MIS) capacitor devices were fabricated and capacitance versus voltage (C-V) and current-voltage (I-V) measurements performed to assess the basic important electrical parameters such as dielectric constant, effective charge density, flat-band voltage, breakdown field, and threshold voltage. In addition, structural properties of the films were presented and compared. The results show that although HCPA-ALD deposited AlN thin films has structurally better and has a lower effective charge density (Neff) value than ICP-ALD deposited AlN films, those films have large leakage current, low dielectric constant, and low breakdown field. This situation was attributed to the involvement of Si atoms into the AlN layers during the HCPA-ALD processing leads to additional current path at AlN/Si interface and might impair the electrical properties.

Keywords: aluminum nitride; effective charge density; atomic layer deposition (ALD); hollow-cathode plasma; inductively coupled RF-plasma; dielectric

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Permalink: https://www.hzdr.de/publications/Publ-24883


Magnetic Reversal and Microstructure Phases in Antiferromagnetically Coupled Multilayer Systems with Perpendicular Anisotropy

Hellwig, O.

Abstract

Strong perpendicular anisotropy systems consisting of Co/Pt or Co/Pd multilayer stacks that are antiferromagnetically coupled via thin Ru or Ir layers have been used as model systems to study the competition between interlayer exchange, perpendicular anisotropy and long-range dipolar interactions [1,2]. The typical layer structure for such systems is illustrated in Fig.1 for a [(Co/Pt)Co/Ru] multilayer system.
Magnetometry and Magnetic Force Microscopy (MFM) studies of such systems reveal complex magnetic phases with a mix of tilted versus non-tilted and antiferromagnetic (AF) versus ferromagnetic (FM) phases depending on the dominance of the various energy contributions. For thin Co/Pt multilayer blocks AF-exchange is dominating and the magnetic structure remains laterally uniform at any stage of the reversal process and is for even number of AF-coupled blocks characterized by bulk and surface spin-flop transitions as shown on the left in Fig. 2. For thicker Co/Pt multilayer blocks the perpendicular anisotropy term takes the lead and prevents any tilting of the spins away from the easy axis normal to the film plane. In this case the reversal into the AF-coupled remanent state occurs via FM/AFM domain formation as shown in the middle part of Fig. 2. For even thicker Co/Pt multilayer blocks the AF-exchange is also overcome by the demagnetization energy and the uniform AF remanent state is replaced by a laterally heterogeneous FM stripe domain state, as illustrated in Fig. 2 on the right.
Ion beam irradiation may be able to control the rich variety of phases in this system on a nanoscopic length scale, thus allowing for a lateral co-existance of all these phases within one and the same sample. This could allow fabricating an infrastructure for controlled spin-wave propagation, such as motivated by recent studies for domain walls and perpendicular anisotropy systems [3,4]. Examples of such initial studies will be discussed.

  • Lecture (Conference)
    Intermag 2017, 24.-28.04.2017, Dublin, Ireland

Permalink: https://www.hzdr.de/publications/Publ-24882


Far-Infrared Nonlinear Optics in Multilayer Epitaxial Graphene

Suess, R. J.; Winnerl, S.; Schneider, H.; Helm, M.; Berger, C.; de Heer, W. A.; Murphy, T. E.; Mittendorff, M.

Abstract

We report terahertz pump-probe experiments on multilayer graphene that measure both reflected and transmitted radiation. The data reveal complex reflection and transmission dynamics which calculations attribute to a transition from interband to intraband processes.

Keywords: graphene; pump-probe spectroscopy; refelection; transmission

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  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-10.06.2016, San Jose, USA

Permalink: https://www.hzdr.de/publications/Publ-24881


Nonlinear Plasmonic THz Absorption in Graphene Ribbons

Mittendorff, M.; Jadidi, M. M.; König-Otto, J. C.; Winnerl, S.; Sushkov, A. B.; Drew, H. D.; Murphy, T. E.

Abstract

We investigate the nonlinear plasmonic absorption in graphene ribbons by THz pump-probe spectroscopy. The optical nonlinearity is increased by more than one order of magnitude, which is in excellent agreement with theoretical calculations.

Keywords: graphene ribbons; plasmonics; nonlinear optics

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  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-10.06.2016, San Jose, USA

Permalink: https://www.hzdr.de/publications/Publ-24880


Three-dimensional Induction Mapping of Magnetic Nanoscale Materials by Electron Holographic Tomography

Wolf, D.; Lubk, A.; Lichte, H.

Abstract

Off-axis electron holography (EH) is a powerful TEM technique that provides access to the 2D projections of both the electric potential, i.e., mainly the mean inner potential (MIP) contribution, and the components of the magnetic induction (B-field) that lie perpendicular to the electron beam path.
Currently, 2D magnetic induction maps may be obtained with a spatial resolution of a few nanometer [1,2] and a sensitivity of a few millitesla [2]. Frequently, however, nanomagnetic applications, such as spin valves or magnetic nanowires require a characterization of the 3D magnetic induction distribution.
In the following, we therefore elaborate on how electron holography is combined with electron tomography to electron holographic tomography (EHT) [1,3] in order to retrieve the 3D distribution of the magnetic induction.
As shown in Fig. 1, the tomographic reconstruction of one B-field component starts with acquiring a tilt series of electron holograms that is subsequently reconstructed to obtain a tilt series of phase images. In order to collect data for the crucial separation of electric and magnetic phase shifts, either a tilt series over 360° (Fig. 1), or two tilt series, one before and one after reversing the direction of magnetization in the specimen (e.g., using the TEM objective lens or flipping the sample up-side down in the holder), have to be acquired. Before separation of electric/magnetic phase shifts by computing half of the sum/difference of corresponding image pairs, relative displacements, rotations, and direction dependent magnification changes between the two phase images are corrected. Also, the alignment of the whole tilt series, i.e., an accurate tilt axis determination and subpixel displacements correction, is of crucial importance. Finally, from the aligned tilt series, tomograms of both the electric potential and the B-field component parallel to the tilt axis are reconstructed with tomographic reconstruction algorithms.
Fig. 2 shows two recent EHT studies revealing the B-field within a Co nanowire (NW) [4] and a Co2FeGa Heusler alloy NW [5] both with spatial resolution higher than 10 nm. The reconstructions of the dominant axial component of the magnetic induction exhibit two interesting features for each case: At the Co NW, a small inversion domain at the apex was observed, whereas at the Co2FeGa NW, a magnetic dead layer of 10 nm width was found. These results were achieved by means of dedicated TEM sample holders for acquisition, in combination with advanced in-house developed software packages for acquisition, alignment and tomographic reconstruction. The powerful approach presented here is widely applicable to a broad range of 3D magnetic nanostructures and may trigger the progress of novel spintronic nonplanar nanodevices. In a next step the reconstruction of all B-field components is envisaged.
References:
[1] P A Midgley and R E Dunin-Borkowski, Nat. Mater. 8 (2009) p. 271.
[2] M Körner, F Röder, K Lenz, M Fritzsche, J Lindner, H Lichte and J Fassbender, Small 10 (2014) p. 5161.
[3] D Wolf, A Lubk, F Röder and H Lichte, Current Opinion in Solid State and Materials Science 17(2013) p. 126.
[4] D Wolf et al., Chem. Mater. 27 (2015) p. 6771.

Keywords: magnetic induction; 3D reconstruction; nanostructure; electron holography; electron tomography

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Unusual Coulomb scattering processes in graphene

Winnerl, S.

Abstract

Graphene, the two-dimensional allotrope of carbon, is characterized by a gapless linear band structure. This unique band structure is directly related to some unusual phenomena regarding the ultrafast Coulomb dynamics in the material. The understanding of this dynamics is of vital interest, both from a fundamental as well as from an application oriented point of view. The elastic Coulomb scattering is the main mechanism for thermalization of a non-equilibrium carrier distribution.
We investigate the carrier dynamics in a regime, where scattering via optical phonons is strongly suppressed. To this end, time resolved spectroscopy was performed with radiation of photon energies around 75 meV, which is smaller than the optical phonon energy (~200 meV). In polarization resolved experiments using co- and cross-polarized linearly polarized pump and probe beams, respectively, the Coulomb scattering dynamics is investigated. We find a two-fold nature of this process, namely very fast (fs timescale) collinear Coulomb scattering but surprisingly slow (ps-timescale) non-collinear scattering [1].
In the presence of a magnetic field, the linear band structure of graphene splits up into a series of non-equidistant Landau levels. Studying the transitions between the lowest Landau levels in pump-probe and four-wave mixing experiments, we find evidence for strong Auger scattering [2, 3].

[1] J. C. König-Otto, M. Mittendorff, T. Winzer, F. Kadi, E. Malic, A. Knorr, C. Berger, W. A. de Heer, A. Pashkin, H. Schneider, M. Helm, and S. Winnerl, Phys. Rev. Lett. 117, 087401 (2016).

[2] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, Nature Phys. 11, 75 (2015).

[3] J. C. König-Otto, Y. Wang, A. Belyanin, C. Berger, W. A. de Heer, M. Orlita, A. Pashkin, H. Schneider, M. Helm, and S. Winnerl (submitted).

Keywords: graphene; carrier dynamics; Coulomb scattering; Auger scattering; ultrafast spectroscopy

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  • Lecture (others)
    MML Workshop at DESY 2016, 14.-16.12.2016, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24878


Plasmonic superlens based on doped GaAs

Winnerl, S.; Fehrenbacher, M.; Kuschewski, F.; von Ribbeck, H.-G.; Döring, J.; Kehr, S.; Eng, L. M.; Schneider, H.; Helm, M.

Abstract

Infrared and THz free-electron lasers are interesting sources for near-field investigations as they are tunable in a range where suitable tabletop sources exist only at particular frequencies. The free-electron laser FELBE at Dresden covers the frequency range from 1.3–75 THz with narrowband (~ 1 % spectral width) radiation. We briefly show for the low-frequency region of FELBE (1.3–75 THz) that scattering near-field microscopy can be performed with a constant spatial resolution of 50 nm, which is determined by the diameter of the scattering tip. For the longest wavelength, this corresponds to /4600 [1]. Mainly, we present results on a superlens, which consists of a doped GaAs layer sandwiched between two intrinsic GaAs layers. Superlensing is expected when the condition 〖Re(ε〗_GaAs^doped)=〖-Re(ε〗_GaAs^intrinsic) is met in the spectral vicinity of the plasmonic resonance. Here, the Drude response in the doped layer induces resonant enhancement of evanescent waves accompanied by a significantly improved spatial resolution at radiation wavelengths around 15 THz (see Fig. 1) [2]. The resonance frequency is adjustable by changing the doping concentration. Compared to superlenses based on phononic resonances the plasmonic superlance features a somewhat broader range of the resonant response. Such a tunable superlense consisting of a single semiconductor material is
a versatile device to enhance signal and spatial resolution in near-field imaging of buried structures.

Keywords: near-field microscopy; superlens; plasmonics; free-electron laser

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  • Invited lecture (Conferences)
    Samller and Faster: Infrared and Terahertz Spectral-Imaging at the Nanoscale with Synchrotron and Free Electron Laser Sources (SAFE), 01.-02.12.2016, Trieste, Italy

Permalink: https://www.hzdr.de/publications/Publ-24877


Carrier dynamics in Graphene

Winnerl, S.

Abstract

We review our results ion the carrier dynamics in graphene and present an applacitation example, namely a high-speed ultra-broadband detector.

Keywords: graphene; carrier dynamics; detector

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  • Lecture (others)
    4. Workshop of SPP 1459 "Graphene", 25.-29.09.2016, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-24876


Population and polarization dynamics in Landau-quantized graphene - evidence for strong Auger scattering

Winnerl, S.; Mittendorff, M.; König-Otto, J. C.; Wendler, F.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.

Abstract

The linear band structure of graphene results in a non-equidistant spectrum of Landau levels (LLs). While transport phenomena have been widely explored after the discovery of graphene in 2004, the ultrafast optical properties of Landau-quantized graphene have been investigated only recently. Predictions of very strong nonlinearities [1], carrier multiplication [2] and Landau-level gain [3] make the system very interesting both from a fundamental and an application-oriented point of view.
Here we present experiments complemented by microscopic theory on the population and polarization dynamics in the subsystem of Landau levels -1, 0 and 1. To this end, multilayer epitaxial graphene in a magnetic field of ~4 T is excited resonantly by ps-pulses of mid-infrared radiation (photon energy 75 meV). Applying circularly polarized radiation allows one to pump and probe the energetically degenerate LL-1 → LL0 and LL0 → LL1 transitions selectively. In pump-probe experiments using all four combinations of pumping and probing with right and left circularly polarized radiation, a surprising change in sign of the measured signal (i.e. induced transmission instead of induced absorption) is observed in one of these configurations. Our analysis shows that this can be associated with a depletion of the LL0 level, even though this level is optically pumped at the same time. Very efficient Auger scattering is responsible for this depletion [4].
Furthermore, we show a very recent study of the polarization dynamics in Landau quantized graphene by means of degenerate four-wave mixing (FWM) spectroscopy. It is carried out on the same subsystem of Landau levels and utilizes similar values of magnetic field and photon energy as in the pump-probe experiments. However, the two incoming beams are linearly polarized in the FWM experiment. A rapid dephasing of the microscopic polarization on a timescale shorter than the pulse duration (4 ps) is observed and attributed to Auger scattering. The FWM signals show the expected dependences on the power of two incoming beams and on the magnetic field.
The results, both for the population as well as the polarization dynamics, depend crucially on the doping level of the sample. The graphene used in the experiments is almost intrinsic, corresponding to a full LL-1 and empty LL1. The occupation of LL0 of about 0.64 is slightly larger than the half-filling corresponding to intrinsic graphene. We will evaluate the implications of this symmetry breaking on Auger scattering and on the FWM signals. Finally, the implications of our results on the feasibility of a graphene based Landau-level laser, which is tunable by the magnetic field, will be discussed.
The sample was grown by C. Berger and W.A. de Heer. We acknowledge valuable discussions with M. Orlita, M. Potemski, Y. Wang, and A. Belyanin. We are grateful to P. Michel and the FELBE team for their dedicated support.
References
[1] X. Yao and A. Belyanin, Phys. Rev. Lett. 108, 255503 (2012).
[2] F. Wendler, A. Knorr, and E. Malic, Nature Commun. 5, 3703 (2014).
[3] F. Wendler and E. Malic, Sci. Rep. 5, 12646 (2015).
[4] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C.

Keywords: Carrier; dynamics; graphene; Landau quantization; Auger scattering; polarization dynamics; four-wave mixing

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  • Invited lecture (Conferences)
    22nd International Conference on High Magnetic Fields in Semiconductor Physics (HMF-22), 24.-29.07.2016, Sapporo, Japan

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Zero-Offset Hall: A new concept for Antiferromagnetic Spintronics

Kosub, T.; Kopte, M.; Radu, F.; Schmidt, O. G.; Makarov, D.

Abstract

Antiferromagnets have the potential to revolutionize spintronics due to their inherently magnetic-field stable magnetic order. The tiny uncompensated magnetic moment of the locally uncompensated antiferromagnetic lattice determines not only the physics of the materials, e.g. topology of antiferromagnetic domain walls [1], but also their application potential for novel magnetoelectric random access memory (MERAM) devices [2] or
antiferromagnetic analogues to racetrack devices. The rich physics of thin film antiferromagnets can be harnessed for prospective spintronic devices given that all-electric assessment of the tiny uncompensated magnetic moment is achieved.

We put forth a new method providing all-electric access to the field-invariant magnetization of antiferromagnetic thin films [3]. This technique – zero-offset Hall – is based on the combination of Anomalous Hall effect magnetometry with dynamic spinning-current offset compensation. We show that this technique opens the scope for magnetic phenomena that can go amiss in conventional Hall measurements with stationary current direction. The adoption of this technique will therefore substantially improve the reach of lab-based transport investigations in the thriving field of antiferromagnetic spintronics and
lead to new application concepts.

On the examples or metallic IrMn and insulating Cr 2 O 3 antiferromagnetic thin films, we demonstrate, that zero-offset Hall can probe thin film magnetism at unprecedented sensitivity, which allows us to reveal previously unknown peculiarities of the physical behavior. The access to insulating magnetic films is enabled by the magnetic proximity effect of certain conductors such as Pt.

The method is not exclusive to anomalous Hall measurements. Instead, all phenomena that alter the transversal resistance, such as the topological Hall effect and the quantum Hall effects, can be studied in greatly improved detail. At the same time, the measurements are technically easy and can be realized in most laboratories making it fast to adopt. Therefore, we believe that zero-offset Hall is of strong relevance for the community of topological and spin phenomena in nanostructures.

[1] M. Bode et al., Nature Materials 5, 477 (2006)
[2] X. He et al., Nature Materials 9, 579 (2010)
[3] T. Kosub et al., Phys. Rev. Lett. 115, 097201 (2015)

Keywords: Zero-Offset Hall; Antiferromagnetic Spintronics

  • Lecture (Conference)
    TOPSPIN 2, 18.-20.05.2016, Groningen, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-24874


Long-lived Anisotropy of Photoexcited Graphene Electrons

Winnerl, S.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.

Abstract

In polarization resolved pump-probe experiments complemented by microscopic modeling we show that an anisotropic carrier distribution persists on ps timescales. In particular, we evaluate the role of non-collinear Coulomb scattering.

Keywords: Carrier dynamics; graphene; ultrafast spectroscopy; Coulomb scattering

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    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-11.06.2016, San Jose, USA

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All-electric measurement of the field-invariant magnetization of antiferromagnets

Kosub, T.; Kopte, M.; Schmidt, O. G.; Makarov, D.

Abstract

Antiferromagnetic materials combine magnetic properties in peculiar combination that is not found in their ferromagnetic counterparts. They are more robust against magnetic disturbances and show great promises in e.g. magnetoelectric applications [1,2]. Despite these fascinating fundamental properties, both the understanding of antiferromagnets and their commercial establishment have progressed slower than for ferromagnets. The tiny uncompensated magnetic moment of the locally uncompensated antiferromagnetic lattice is often the linking element to intrinsic processes that experimenters can exploit or devices can rely on.
One of the most sensitive techniques for thin film magnetometry, the anomalous Hall effect (AHE) [3], is routinely employed to study magnetization eversal in ferromagnets [4] by monitoring the magnetization-proportional anomalous Hall resistance.
However, this typically suffers from a sizable parasitic signal offset due to imperfect device geometry. But, the offset also contains real AHE signals generated by field-invariant magnetization components which are inaccessible in conventional Hall measurements.
We demonstrate, that AHE magnetometry using the spinning-current technique can measure such field-invariant magnetization on an absolute scale by dynamically compensating the parasitic resistance contribution (Fig.) [5]. Thus, we acquire previously unattainable figures about antiferromagnetic materials and refine existing measurements due to the great precision and time-efficiency of AHE magnetometry.
We establish that this technique is suitable to probe a wide range of materials by applying it to polycrystalline IrMn thin films as well insulating Cr 2 O 3 films. Moreover, our all-electric measurements also prove that it is feasible to entirely omit ferromagnets in antiferromagnet-based applications. Doing so paves the way to all-antiferromagnet spintronics with improved performance or improved reliability [6].

[1] X. He, Y. Wang, N. Wu, A. N. Caruso, E. Vescovo, K. D. Belashchenko, P. A. Dowben, and C. Binek, Nature Materials 9, 579 (2010).
[2] J. Heron, J. Bosse, Q. He, Y. Gao, M. Trassin, L. Ye, J. Clarkson, C. Wang, J. Liu, S. Salahuddin, and others, Nature 516, 370 (2014).
[3] N. Nagaosa, J. Sinova, S. Onoda, A. MacDonald, and N. Ong, Rev. Mod. Phys. 82, 1539 (2010).
[4] D. Bhowmik, L. You, and S. Salahuddin, Nature Nanotechnology 9, 59 (2014).
[5] T. Kosub, M. Kopte, F. Radu, O. G. Schmidt, and D. Makarov, Phys. Rev. Lett. 1, 1 (2015).
[6] T. Kosub, O. G. Schmidt, and M. Denys, Patent Applied For (n.d.).

Keywords: Zero-Offset-Hall; antiferromagnetic spintronics

  • Lecture (Conference)
    Joint MMM/Intermag San Diego, 11.-15.01.2016, San Diego, USA
  • Lecture (Conference)
    DPG Regensburg, 14.-18.03.2016, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24872


Analytical Electron Microscopy Study to Resolve the Phase Morphology of Organic Solar Cell Blends

Sedighi, M.; Löffler, M.; Röder, F.; Zschech, E.

Abstract

To increase the efficiency of bulk heterojunctions for organic photovoltaic devices, the complicated photon-to-electron conversion process has to be understood in detail. To this aim, one challenge is to resolve the correlation between processing parameters of organic solar cells (OSC), the resulting nanoscale morphology of the absorber layer, and efficiency of the completed device. Here, we present the effect of substrate heating on the morphology of the OSC where the active layer is a blend of two small molecules; ZnPc (ZnC32H18N8) as donor and C60 as acceptor.

Obtaining insights into the morphology of the active layer requires the spatial resolution and a contrast mechanism to discriminate two phases with similar average atomic number. To tackle this challenge, we combine electron microscopy imaging with different analytical techniques; energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) in TEM, as well as Energy selective Backscattered (EsB) imaging in SEM.

We imaged different phases of the donor and acceptor, forming ordered and non-ordered regions, depending on the way the heterojunction is fabricated. To this aim, we fabricated samples at substrate temperatures of 110°C and 150°C, each in two different configurations:

1) Focused ion beam prepared ultrathin lamella of a complete solar cell stack with glass substrate, Indium tine oxide (ITO) electrode, ZnPc:C60 blend of the active layer between electron and hole transport layers and aluminum top electrode.
2) Plane view sample as ZnPc:C60 blend deposited on a TEM grid coated with ITO layer.

It was shown that at a substrate temperature of 110°C, the solar cell device has high efficiency [1]., so we consider this as the optimum substrate temperature.

Since identification of the composition of each phase in the plane view sample is more straight forward, we use the plane view sample to attribute each structure to one component of the blend. SEM images recorded by using secondary electron detector show that, the high temperature sample consists of rod-like features and cube-shaped material in between the rods. By combination of analytical microscopy techniques, we can attribute the rod-like structures to ZnPc.

An energy-selective backscatter (EsB) electron detector in a SEM is used to obtain backscattered contrast of the plane view sample. Due to the atomic number difference between the donor phase and the acceptor phase, (the average atomic number of 8.6 for ZnPc and 6 for the C60) sufficient contrast can be achieved [2].

A clear confirmation for the attribution of the ZnPc phase to the rod-like features and the attribution of C60 to the granular structure in between can be drawn from the investigation of the sample in SEM using EDX and with even higher precision in TEM using an improved EDX system. The chemical mapping of zinc and carbon, proves the correct phase assignment, in both plane view and ultrathin samples, prepared at high temperature. For the sample produced at optimum temperature, a much smaller roughness was observed because of the absence of large ordered regions. Even in the plane view sample, the imaging contrast is low due to less separated phases and smaller domains.

To conclude, we clearly resolved the phase morphology of the interpenetrating network of ZnPc:C60 blends for high and optimum temperature samples in plane view and furthermore we were even able to reveal the morphology from TEM images of cross-section lamellas of the real solar cell stacks.

Since the ideal active layer should have domain sizes at the range of the exciton diffusion length (10-20nm), the sample produced at high temperature does not show the desired microstructure. Due to the domain sizes of ~100 nm there is no closed path for exciton dissociation. In addition to that, the sample shows a quite high roughness.

Acknowledgement:

Authors thank A. G. Cid for SEM images. This work was supported by the German Science Council Center of Advancing Electronics Dresden (cfaed). TEM-EDX results were achieved by funding (support code 03SF0451) through the Helmholtz Energy Materials Characterization Platform (HEMCP) initiated by the Helmholtz Association and the German Federal Ministry of Education and Research (BMBF).

References:

[1] S. Pfuetzner, C. Mickel, J. Jankowski, M. Hein, J. Meiss, C. Schuenemann, C. Elschner, A.A. Levin, B. Rellinghaus, K. Leo and M. Riede, “The influence of substrate heating on morphology and layer growth in C60:ZnPc bulk heterojunction solar cells” Org. Electron., 12 (2010), pp. 435–441
[2] A. G. Cid, M. Sedighi, M. Löffler, W. F. van Dorp and E. Zschech, “Energy-Filtered Backscattered Imaging Using Low-Voltage Scanning Electron Microscopy: Characterizing Blends of C60:ZnPc for Organic Solar Cells”. (DOI: 10.1002/adem.201600063)

  • Poster
    EMRS Fall Meeting 2016, 19.-22.09.2016, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-24871


Surprising Coulomb-scattering effects in graphene revealed by polarization-resolved THz spectroscopy

Winnerl, S.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Schneider, H.; Helm, M.; Winzer, T.; Wendler, F.; Malic, E.; Knorr, A.

Abstract

We present experiments complemented by microscopic theory that highlight surprising Coulomb scattering effects. In particular, we find that non-collinear Coulomb scattering is compa-rably slow, namely on a scale of few ps. For the case of Landau-quantized graphene we find evidence for strong Auger scattering that can deplete a Landau level that is optically pumped at the same time. Both Coulomb effects are relevant for graphene based THz devices.

Keywords: graphene; carrier dynamcis; Coulomb scattering; Auger scattering; Landau quantization

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  • Invited lecture (Conferences)
    5th EOS Topical Meeting on Terahertz Science & Technology, 08.-11.05.2016, Pecs, Hungary

Permalink: https://www.hzdr.de/publications/Publ-24870


Fast graphene-based hot-electron bolometer covering the spectral range from terahertz to visible

Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. J.; Murphy, T. E.; Chatterjee, S.; Kolata, K.; Ohser, J.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.

Abstract

By using broadband absorber materials, bolometric detectors can typically cover an extremely large spectral range. However, since their response relies on the lattice temperature of the employed material, they exhibit slow response times. Hot electron bolometers (HEBs), on the other hand, can be extremely fast, because they exploit a change in device resistance caused by a varying electron temperature. A major drawback of HEBs based on superconductors is the required cooling to very low temperatures. We have developed a detector for room temperature operation, where the broadband absorption of the gapless material graphene is utilized. To this end, a graphene flake grown by chemical vapor deposition (CVD) is transferred to a SiC substrate and coupled to a logarithmic periodic antenna. Fast detection with a rise time of 40 ps is demonstrated for frequencies ranging from 0.6 THz to 390 THz [1]. Interestingly, the detector properties do not deteriorate for wavelength within the Reststrahlen band of SiC (25 – 50 THz). With a noise-equivalent power of 20 µW/Hz½ (800 µW/Hz½) in the near infrared (mid- and far infrared) the detector is capable of recording pulses with energies of the order of 10 pJ (1 nJ). We show that the detector is a versatile device for timing measurements in multi-color ultrafast spectroscopy studies.
[1] M. Mittendorff et al., Opt. Express 23, 28728 (2015).

Keywords: high-speed detector; broadband detector; graphene

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  • Lecture (Conference)
    7th internationale Workshop Terahertz Technology and Applications, 15.-16.03.2016, Kaiserslautern, Germany

Permalink: https://www.hzdr.de/publications/Publ-24869


Radio-U(H)PLC - the search on the optimal flow cell for the gamma-detector

Kniess, T.; Meister, S.; Fischer, S.; Steinbach, J.

Involved research facilities

  • PET-Center
  • Poster
    18th European Symposium on Radiopharmacy and Radiopharmaceuticals, 07.-10.04.2016, Salzburg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-24868


HgCdTe-based heterostructures for Terahertz photonics

Ruffenach, S.; Kadykov, A.; Rumyantsev, V. V.; Torres, J.; Coquillat, D.; But, D.; Krishtopenko, S. S.; Consejo, C.; Knap, W.; Winnerl, S.; Helm, M.; Fadeev, M. A.; Mikhailov, N. N.; Dvoretskii, S. A.; Gavrilenko, V. I.; Morozov, S. V.; Teppe, F.

Abstract

Due to their specific physical properties, HgCdTe-based heterostructures are expected to play an important role in terahertz photonic systems. Here, focusing on gated devices presenting inverted band ordering, we evidence an enhancement of the terahertz photoconductive response close to the charge neutrality point and at the magnetic field driven topological phase transition. We also show the ability of these heterostructures to be used as terahertz imagers. Regarding terahertz emitters, we present results on stimulated emission of HgCdTe heterostructures in their conventional semiconductor state above 30THz, discussing the physical mechanisms involved and promising routes towards the 5–15 THz frequency domain.

Keywords: narrow-gap semiconductors; HgCdTe (MCT); THz detectors; THz sources

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Permalink: https://www.hzdr.de/publications/Publ-24867


A fluorine-18 radiolabelled celecoxib-based PET probe for Cyclooxygenase-2 monitoring - COX-2 affinity, radiosynthesis and in vitro studies

Kniess, T.; Bechmann, N.; Steinbach, J.; Pietzsch, J.

Involved research facilities

  • PET-Center
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 43(2016)S1, EP844
  • Poster
    Annual Congress of the European Association of Nuclear Medicine, EANM, 15.-19.10.2016, Barcelona, Spanien

Permalink: https://www.hzdr.de/publications/Publ-24866


Dynamics of non-equilibrium charge carriers in p-germanium doped by gallium

Deßmann, N.; Pavlov, S. G.; Tsyplenkov, V. V.; Orlova, E. E.; Pohl, A.; Shastin, V. N.; Zhukavin, R. K.; Winnerl, S.; Mittendorff, M.; Klopf, J. M.; Abrosimov, N. V.; Schneider, H.; Hübers, H.-W.

Abstract

The low-temperature relaxation processes of non-equilibrium holes into gallium centers in moderately doped p-germanium (NA ≈ 2×10^15 cm-3) has been investigated by a degenerate pump-probe experiment using the free electron laser FELBE. The capture time decreases with increasing average photon flux density of the excitation pulse from about 10.9 ns (at ~1.2×10^24 cm-2 s-1) to ~1.2 ns (~2×10^26 cm-2 s-1). Relaxation inside the valence band is almost independent on pump light intensity and its characteristic time is about 200 ps. In Addition, the intracenter relaxation times of the lowest excited Ga states were measured. The lifetimes scale with the phonon density of states controlling a bound hole – acoustic phonon interaction. The lifetime of the lowest excited state, 1Γ_8^-, was measured to be ~275 ps; while the lifetimes of the higher excited states, 2Γ_8^-and 3Γ_8^-, were found to be ~157 ps and 162 ps, respectively.

Keywords: extrinsic semiconducturs; impurity transitions; carrier dynamics

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Permalink: https://www.hzdr.de/publications/Publ-24865


Improving the quantification accuracy of a PET/CT-scanner with pixelated large area detector

Nemer, U.; Maus, J.; Schramm, G.; Meyer, P. T.; Hennig, J.; Mix, M.

Abstract

One of the main benefits of PET/CT imaging is its ability for absolute quantification. Calibration according to the manufacturer‘s procedure specifies an accuracy of about 10%, whereas especially in dynamic clinical studies a higher quantification accuracy is desired. Therefore a more accurate calibration is needed. At the Gemini TF, a scanner with pixelated large-area LYSO detectors, there are differences in the measurement set-up between calibration and clinical acquisition. This study intends to evaluate the influence of those differences on the calibration with the aim to increase the accuracy of quantification. The major difference herein is the acquisition format, as calibration is performed in histogram-mode (HM-Cal) and clinical acquisition in list-mode format. Using the list-mode format for the calibration (LM-Cal), increases the activity recovery coefficient for the histogram-based acquisition from 0.93±0.08 up to 1.00±0.03. This is however only valid for the calibration set-up but not for clinical situations. Considering more realistic situations like lesions outside the centre of the field of view (FOV) or additional random events coming from highly accumulating regions outside the FOV (like bladder or brain), a different calibration can be found (ALL-Cal). In the evaluation of clinical oncological datasets with low count rates, a significant improvement of the reconstructed mean activity concentration in the bladder (compared to measured urine samples) up to 4% (LM-Cal) was achieved. For very high count rates the normalization of the scanner has to be adapted to improve the quantification accuracy as well.

Keywords: Calibration; Image reconstruction; Phantoms; Table lookup; Positron emission tomography; Bladder; Detectors

Involved research facilities

  • PET-Center
  • Contribution to proceedings
    2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 31.10.-07.11.2015, San Diego, USA
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2015 IEEE, USA: IEEE, 978-1-4673-9862-6
    DOI: 10.1109/NSSMIC.2015.7582097

Permalink: https://www.hzdr.de/publications/Publ-24864


Unconventional double-bended saturation of optical transmission in graphene due to many-particle interactions

Winzer, T.; Mittendorff, M.; Winnerl, S.; Mittenzwey, H.; Jago, R.; Helm, M.; Malic, E.; Knorr, A.

Abstract

We present a joint theory-experiment study on the transmission/absorption saturation after ultrafast pulse excitation in graphene. We reveal an unconventional double-bended saturation behavior: Both bendings separately follow the standard saturation model exhibiting two saturation fluences, however, the corresponding fluences differ by three orders of magnitude and have different physical origin. Our results reveal that this new and unexpected behavior can be ascribed to an interplay between fluence- and time-dependent many-particle scattering processes and phase-space filling effects.

Keywords: graphene; nonlinear optics; saturation; carrier dynamics

Permalink: https://www.hzdr.de/publications/Publ-24863


Radiosynthesis of O-3-(2-[18F]fluoroethyl)-L-DOPA ([18F]OFED) – a new fluorine-18 labeled phenylalanine derivative.

Kniess, T.; Schröder, S.; Hoepping, A.; Zessin, J.; Fuechtner, F.; Bergmann, R.; Steinbach, J.

Involved research facilities

  • PET-Center
  • Abstract in refereed journal
    Journal of Nuclear Medicine 57(2016)S2, 1039
  • Poster
    Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging, SNMMI, 11.-15.06.2016, San Diego, USA

Permalink: https://www.hzdr.de/publications/Publ-24862


Symmetry-Breaking Supercollisions in Landau-Quantized Graphene

Wendler, F.; Mittendorff, M.; König-Otto, J. C.; Brem, S.; Berger, C.; de Heer, W. A.; Böttger, R.; Schneider, H.; Helm, M.; Winnerl, S.; Malic, E.

Abstract

Recent pump-probe experiments performed on graphene in a perpendicular magnetic field have revealed carrier relaxation times ranging from picoseconds to nanoseconds depending on the quality of the sample. To explain this surprising behavior, we propose a novel symmetry-breaking defect-assisted relaxation channel. This enables scattering of electrons with single out-of-plane phonons, which drastically accelerate the carrier scattering time in low-quality samples. The gained insights provide a strategy for tuning the carrier relaxation time in graphene and related materials by orders of magnitude.

Keywords: Carrier dynamics; graphene; Landau quantization; supercollisions

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Permalink: https://www.hzdr.de/publications/Publ-24861


Automatisierte Radiosynthese von O-2[18F]Fluorethyl-L-DOPA ([18F]OFED) – eine neue 18F-markierte Aminosäure für die Tumor-Diagnostik

Kniess, T.; Schröder, S.; Hoepping, A.; Füchtner, F.; Zessin, J.; Bergmann, R.; Steinbach, J.

Involved research facilities

  • PET-Center
  • Poster
    Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin 2016, 20.-23.04.2016, Dresden, Deutschland
  • Open Access Logo Abstract in refereed journal
    Nuklearmedizin 55(2016)2, P51

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Permalink: https://www.hzdr.de/publications/Publ-24860


Ultrafast processes in graphene: from fundamental manybody interactions to device applications

Winnerl, S.; Mittendorff, M.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winzer, T.; Knorr, A.; Malic, E.

Abstract

A joint experiment-theory investigation of the carrier dynamics in graphene, in particular in the energetic vicinity of the Dirac point, is reviewed. Radiation of low photon energy is employed in order to match the intrinsic energy scales of the material, i.e. the optical phonon frequency (~200 meV) and the Fermi energy (10-20 meV), respectively. Significant slower carrier cooling is predicted and observed for photon energies below the optical phonon frequency. Furthermore, a strongly anisotropic distribution of electrons in k-space upon excitation with linearly polarized radiation is discussed. Depending on photon energy, the anisotropic distribution decays either rapidly via optical phonon emission, or slowly via non-collinear Coulomb scattering. Finally, a room temperature operated ultra-broadband hot-electron bolometer is demonstrated. It covers the spectral range from the THz to visible region with a single detector element featuring a response time of 40 ps.

Keywords: graphene; carrier dynamics; detectors

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Permalink: https://www.hzdr.de/publications/Publ-24859


Eddy current flowrate and local ultrasonic velocity measurements in liquid sodium

Krauter, N.; Franke, S.; Gerbeth, G.; Eckert, S.; Stefani, F.; Gastaldi, O.; Girard, M.

Abstract

For the safe operation of sodium cooling systems a monitoring of the flow field is often desirable. We report first on the development of a new eddy current flowmeter (ECFM) and related tests in sodium. The objective of this sensor is its positioning above the fuel subassemblies and the detection of possible blockages of the sodium flow through the multitude of subassemblies. The sensor consists of a number of coils a part of which is fed by an excitation AC current. The assembly of coils is placed in a thimble and the measured flowrate is proportional to the integral flow around this thimble. In the second part we report on local ultrasonic velocity measurements. Here, the objective is to study the flow field resulting from a large electromagnetic pump installed at the PEMDYN facility of CEA. Both measuring techniques were tested at the sodium facility NATAN of HZDR.

Keywords: Eddy Current Flow Meter; Ultrasound Doppler Method; Liquid metal flow

  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 26.-29.06.2017, Yekaterinburg, Russland
  • Lecture (Conference)
    International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 28.06.2017, Yekaterinburg, Russland

Permalink: https://www.hzdr.de/publications/Publ-24858


Design, synthesis, radiosynthesis, and biological evaluation of radiofluorinated quinoline derivatives for PET imaging of PDE5A in brain

Liu, J.; Wenzel, B.; Dukic-Stefanovic, S.; Teodoro, R.; Ludwig, F.-A.; Deuther-Conrad, W.; Schröder, S.; Chezal, J.-M.; Moreau, E.; Brust, P.; Maisonial-Besset, A.

  • Poster
    EFMC – International Symposium on Medicinal Chemistry 2016, 28.08.2016, Manchester, UK

Permalink: https://www.hzdr.de/publications/Publ-24857


The IAEA Coordinated Research Project on Sodium Properties and Safe Operation of Experimental Facilities in Support of the Development and Deployment of Sodium-cooled Fast Reactors (NAPRO)

Azpitarte, O.; Japas, M.; Chocrón, M.; Vázquez, E.; Villanueva, A.; Long, B.; Xu, C.; Xie, C.; Latgé, C.; Gerschenfeld, A.; Anderhuber, M.; Chacon, L.; Matteo, L.; Cavaro, M.; Féron, D.; Trabuc, P.; Bubelis, E.; Perez-Martin, S.; Stieglitz, R.; Eckert, S.; Krauter, N.; Selvaraj, P.; Raghvachary, S.; Athmalingam, S.; Chellapandi, P.; Ohira, H.; Lee, J.; Park, S.; Lee, Y.; Hong, J.; Jayaraju, S.; Roelofs, F.; Marinenko, E.; Zagorulko, Y.; Passerini, S.; Gerardi, C.; Grandy, C.; Monti, S.; Kriventsev, V.

Abstract

The International Atomic Energy Agency (IAEA) recently established a Coordinated Research Project (CRP) on “Sodium Properties and Safe Operation of Experimental Facilities in Support of the Development and Deployment of Sodium-cooled Fast Reactors - NAPRO”, to be carried out in the period 2013 – 2017. Eleven institutions from ten Member States participate in this CRP. The complete scope of this CRP is covered by three work packages. A specific work package (WP1), under the coordination of ANL (USA), is focused on the compilation and expert assessment of data sets of Na physical and chemical properties, as well as correlations for pressure drops and heat transfer in Na facilities. A second work package (WP2), under the coordination of IPPE (Russian Federation), addresses the compilation, evaluation and development of best practices and guidelines for the design, operation and maintenance of Na facilities. Finally, Work Package 3 (WP3), coordinated by CEA (France), concentrates on the compilation and development of guidelines and rules for the safe operation of Na facilities, including the prevention, detection and mitigation of Na leaks and fires. Finally, this work presents some examples of the principal results obtained so far by WP 1.

Keywords: sodium properties; sodium facilities design; sodium safety

  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 26.-29.06.2017, Yekaterinburg, Russland

Permalink: https://www.hzdr.de/publications/Publ-24856


Local etching of a SiOx layer on Si(111) by Ga droplets and its influence on GaAs nanowire growth

Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.

Abstract

GaAs nanowires (NWs) can be grown epitaxially on Si(111) substrates in the vapour-liquid-solid mode. Typically, Au is used as catalyst, but affects the NW and substrate properties due to contamination. Thus, the self-catalyzed mode appears to be advantageous. The NW growth is initialized by the formation of Ga droplets on the substrate surface, which is normally covered by a thin SiOx layer. The yield of vertical NWs depends on the thickness and the nature of the SiOx, pointing out the complex interaction of the liquid Ga with the SiOx. This work investigates the local etching of a native SiOx on Si(111) by liquid Ga droplets, a mechanism, which is thought to precede the NW nucleation. The droplet formation, the etching process, and their effect on the NW growth were studied as a function of the substrate temperature and the etching time using molecular beam epitaxy. In contrast to previous studies, the oxide etching is distinguished from the subsequent NW nucleation by inserting a thermal annealing step, during which the Ga droplets are evaporated completely from the surface. Finally, the yield of vertical NWs and the NW number density can be controlled just by choosing the appropriate conditions for the oxide etching, independent of those used for the subsequent NW growth.

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  • Poster
    DPG Spring Meeting, 06.03.2016, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-24855


Erstellung einer Benutzeroberfläche in LabVIEW zur Steuerung der Mikroreaktoranlage zur Partialoxidation von Isobutan in flüssiger Phase.

Lu, X.

Abstract

Im Rahmen des Belegs wurde eine graphische Oberfläche unter Labview entwickelt, die zur Durchführung von Steuerungs-, Regelungs- und Messaufgaben für einen im Rahmen des Projektes Helmholtz-Energieallianz entworfenen und aufgebauten Reaktor benötigt wurde.

Keywords: Labview; GUI; MSR software; Mikroreaktor

  • Study thesis
    TU-Dresden, 2014
    Mentor: Thomas Willms
    31 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24854


The effect of deposition processing on structural and luminescent properties of a-SiOC: H thin films fabricated by RF-magnetron sputtering

Vasin, A. V.; Rusavsky, A. V.; Kysil, D. V.; Prucnal, S.; Piryatinsky, Y.; Starik, S. P.; Nasieka, I.; Strelchuk, V. V.; Lysenko, V. S.; Nazarov, A. N.

Abstract

Amorphous silicon oxicarbide thin films (a-SiOC(:H)) were deposited by RF-magnetron sputtering using Si or SiC target in Ar/CH4/O2 flow. Interatomic bonding and light emission properties were analyzed by FTIR in transmission and attenuation total reflection (ATR) mode, Raman scattering and photoluminescence spectroscopy. Comparison of the results obtained by FTIR and ATR allows us to suggest that structural properties of the near-surface region and the bulk of the films are significantly different. The surface layer contains a significant fraction of polymer-like SiOC structural components in the form of Si-O-Si/Si-O-C chains and cages, while bulk of the film is represented by inorganic amorphous SiOx network with amorphous carbon precipitates. Samples with the high fraction of carbon precipitates exhibit white luminescence at room temperature. The origin of strong photoluminescence is discussed.

Keywords: Amorphous silicon oxicarbide thin films; ATR; FTIR; Photoluminescence

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Permalink: https://www.hzdr.de/publications/Publ-24853


Untersuchungen zur Partialoxidation von Isobutan in einem Mikroreaktor unter überkritischen Bedingungen.

Huiras, J.

Abstract

Die partielle Oxidation von Isobutan durch Sauerstoff in einem Mikroreaktor wurde im überkritischem Zustand zwischen 135 °C und 145 °C unter Verwendung von di-t-butyl peroxide (DTBP) als Initiator untersucht. Dabei wurden das Verhältnis zwischen Isobutan und Sauerstoff, die Verweilzeit, der Druck, die Initiatorkonzentration und die Temperatur variiert. Ziel war es, die Effizienz des Prozesses durch eine Erhöhung der Selektivität des Produkts t-Butyl hydroperoxide (TBHP) und des Umsatzes zu verbessern. Es war insbesondere zu überprüfen, ob sich der Prozess unter diesen Bedingungen durch die Aufhebung von Stofftransportwiderständen gegenüber dem Zweiphasenprozess bei niedrigeren Temperaturen optimieren lässt. Die Reaktionsprodukte TBHP, Azeton, t-butanol und DTBP wurden mittels GC\MS analysiert. Im Rahmen der Arbeit gelang es die höchsten bisher mit einem Mikroreaktor erzielten Umsätze für die Isobutanoxidation zu erzielen. Jedoch gingen die Umsätze nicht wesentlich über die Umsätze hinaus, die aufgrund des zu erwartenden Temperatureffekts bei der Nutzung von überkritischen Bedingungen zu erwarten waren. Auch war die Umsatzerhöhung nur auf Kosten der Selektivität des TBHP zu erzielen. Die Arbeit bietet jedoch aufgrund Ihrer Ergebnisse eine wichtige Grundlage für weitere Untersuchungen.

Keywords: Isobutanoxidation; überkritischer Prozess; Effizienzoptimierung; t-Butylhydroperoxid; Mikroreaktor

  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    63 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24852


Time-Resolved Studies of the Light-Induced Insulator-Metal Transition in NbO2 and VO2 Thin Films

Beebe, M.; Klopf, J. M.; Wang, Y.; Kittiwatanakul, S.; Lu, J.; Wolf, S. A.; Lukaszew, R. A.

Abstract

While vanadium dioxide (VO2) is one of the most extensively studied highly correlated materials, there are intriguing similarities and differences worth exploring in another highly correlated oxide, niobium dioxide (NbO2). Both materials exhibit a thermally-induced first-order insulator-metal transition at a material-dependent critical temperature, which is considerably higher in NbO2 than in VO2 – approximately 1080 K and 340 K in bulk, respectively. This transition, evidenced by up to 6 orders of magnitude change in DC and optical conductivities, can also be induced in VO2 via photo-doping on a sub-picosecond timescale. Here, we present the first ultrafast pump-probe studies on the optically-induced transition of NbO2 thin films and the comparison with similar VO2 films. It is observed that NbO2 films transition faster and exhibit significantly faster recovery time than VO2 films of similar thickness and microstructure, showcasing that NbO2 is a promising material for next generation high-speed optoelectronic devices.

Keywords: (240.0310) Thin films; (310.6860) Thin films; (310.6845) Thin film devices and applications; (320.7100) Ultrafast measurements; (320.7130) Ultrafast processes in condensed matter; optical properties

Permalink: https://www.hzdr.de/publications/Publ-24851


The double role of Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates

Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.

Abstract

We have investigated the in-situ surface modification of a SiOx/Si(111) substrate by Ga droplets and its effect on the subsequent self-catalyzed growth of GaAs nanowires. Using a procedure of Ga droplet formation and subsequent re-evaporation prior to the nanowire growth, we found that the number density of nanowires at a given growth temperature can be varied deliberately within four orders of magnitude without affecting the nanowire diameter. A detailed study of the Ga droplet formation in a wide range of substrate temperatures revealed the physical processes that control the number density and size of the droplets.

Keywords: Nanowire; Ga droplets; oxide etching; nanoholes; GaAs; Si substrate

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  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy, 04.09.2016, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-24850


Optimierung und Validierung der GC/MS-Methode zur Bestimmung der Reaktionsprodukte der Partialoxidation von Isobutan mit Sauerstoff im Mikroreaktor.

Liu, W.

Abstract

Die partielle Oxidation von Isobutan, t-Butyl Hydroperoxid (TBHP) wurde zum ersten Mal als ein Zwei-Phasen-Prozess in einer Kapillare als Mikro Reaktor durchgeführt und analytisch untersucht. Um detaillierte Informationen über Produkte, Ausbeute, Selektivität und Reaktion Wege zu erhalten, mussten die Produkte mittels GC-MS analysiert werden. Zur Trennung der flüssigen Produkte wurde eine GC-MS Methode erstellt, optimiert und validiert, die eine Rxi-5ms-Säule und einen PTV-Injek-tors verwendet. Im Rahmen der Validierung wurden der Konzentrationsfehler wie auch der Mess¬fehler des MS-Signals aus sämtlichen Kalibrierschritten ermittelt sowie die entsprechenden analytischen Normen (z. B. DIN 38402) für die Kalibrierung berücksichtigt. Außerdem wurden statistische Tests auf Trends (nach Neumann), Ausreißer (nach Dixon), Normalverteilung (nach David) etc. durchgeführt. Die flüssigen Produkte wurden mittels MS identifiziert: Als Hauptprodukte traten TBHP, di-t-Butyl-Peroxid (DTBP), t-Butanol (TBA) und Propanone auf. Für die Zielprodukte TBHP und DTBP wurden Korrelationkoeffiuienten von r2 > 0,999, für TBA und Azeton r2 > 0,995 erzielt. Daneben traten Nebenprodukte wie z. B. Methanal, Methanol, Isopropanol, Isobutanol und Isobutanal auf, von denn alle bis auf Methanol und Methanal ebenfalls kalibriert wurden.

Keywords: TBHP; DTBP; Vslidierung; isobutanoxidation

  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas Willms
    68 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24849


“Reverse Epitaxy” on semiconductor surfaces by low energy ion irradiation

Engler, M.; Ou, X.; Facsko, S.

Abstract

Ion beam irradiation can produce different patterns on semiconductor surface. While the surface is amorphized at low temperatures, the surface remains crystalline above the dynamic recrystallization temperature. Reverse Epitaxy leads to pattern formation, which is driven by diffusion of vacancies and adatoms on the surface, above this temperature. The mechanisms of Reverse Epitaxy epitaxy are quite similar to mound formation in homoepitaxial growth. The surface is destabilized in both cases by an effective uphill diffusion current driven by Ehrlich-Schwoebel barriers. The patterns formed depend of step formation energies, diffusion on terraces, and Ehrlich-Schwoebel barriers, which all are anisotropic. Their anisotropy is determined by the surface symmetry. By changing the surface symmetry the resulting patterns are be changed.

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    XI-th International Conference on Ion Implantation and other Applications of Ions and Electrons - ION 2016, 13.06.2016, Kazimierz Dolny, Polska

Permalink: https://www.hzdr.de/publications/Publ-24848


Compositional Non-parametric Tests

van den Boogaart, K. G.; Tolosana-Delgado, R.

Abstract

Current compositional methods typically rely on some sort of normality hypothesis for testing. Typical well-known non-parametric tests rely on ranks transforms, which are undefined for multivariate problems. The aim of this contribution is thus to investigate the possibilities for truly multivariate non-parametric tests of location and distribution for compositonal data. The challenge is the to ensure subcompositional coherence, which would bring the possibility to attribute deviations to certain subcompositions.

For the case of tests for a known compositional mean, we propose a bootstrap method, measuring how extreme this mean is with respect to a bootstrap sample of the empirical compositional mean. The extremity is checked in each of the pairwise log-ratios. This ensures a subcompositional coherence in the sense that a rejected hypothesis will always be rejected in at least one subcomposition.

For the case of a two sample test comparing two populations, the same principle can be extended. The mean difference is compared with bootstrap samples of mean differences. The same subcompositional coherence applies.

For multiple samples we can extend the idea of ANOVA of measuring the variability of the group means. The variability is measured in terms of the variation matrix. For each entry of the variatin matrix we quantify its quantile in the bootstrap population. We take then the maximum of the quantiles and bootstrap this maximum. In this way we again get a subcompositionally test for equal mean in all samples. Weighted modifications might improve power of the test in case of unequal sample sizes.

  • Lecture (Conference)
    CoDaWork 2017, 06.-9.6.2017, Abbadia San Salvatore, Italia

Permalink: https://www.hzdr.de/publications/Publ-24847


Compositional Non-parametric Regression

Tolosana-Delgado, R.; van den Boogaart, K. G.

Abstract

Compositional regression is concerned with modelling the dependence of a composition on one or more covariables, or vice versa. State of the art methods typically rely on the assumptions of linearity of the dependence and for tests on the additive logistic normal distribution of the errors. Several different solutions for non-linear regression and tests without normality assumption are available for non-compositional data. Based on them, this contribution derives non-parametric regression models and methods valid for compositional data.

With respect to the non-linear dependence, some sort of regularisation assumption is always required. Different classical approaches can be adapted for compositonal data. LOESS smoothing on pairwise log-ratios or logratio transforms would correspond to some sort of smooth (compositional) derivatives. Regression splines and smoothing splines are already defined in a multivariate way and allow to control the degree of continuity and smoothness by explicit parameters. Piecewise regression needs to be applied to log-ratio transforms and allows to model non-continuous dependence. Geostatistical interpolation or, equivalently, reproducing kernel splines, allow a precise control over the level of continuity and complexity through the variogram.

All methods mentioned admit a multivariate extension which, by virtue of the principle of working in coordinates, automatically give rise to compositional versions of those methods. Moreover, all are either affine equivariant, or else very slight restrictions of them are. Thus, the associated compositional versions deliver results which are: invariant with respect to the choice of basis, scaling invariant, and subcompositionally coherent (in the case of regression with compositional response).

With regard to testing, there are some philosophical difficulties in a classical ``zero slope hypothesis''. A strict test for dependence could be very misleading when used for model selection in a non-parametric setting. As an alternative we propose to check, whether the prediction by the non-parametric model outperforms the prediction by parametric (constant) one. We propose to compare the jacknifed residuals of the two models. This construction allows to construct all meaningful tests of compositional dependence, namely: global lack of dependence, lack of dependence within a subcomposition, as well as restricted dependence within a subcomposition.

  • Lecture (Conference)
    CoDaWork 2017, 06.-09.06.2017, Abbadia San Salvatore, Italia

Permalink: https://www.hzdr.de/publications/Publ-24846


Fluid dynamics in novel sandwich packings for absorption and distillation

Sohr, J.; Schubert, M.; Hampel, U.

Abstract

Poster zum EMR-Meeting am 21.09.2016 am HZDR

  • Poster
    EMR-Meeting, 21.09.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24845


X-Ray Photoelectron Study of Ion Implanted Tetrahedral Carbon

Berova, M.; Sandulov, M.; Tsvetkova, T.; Avramova, I.; Boettger, I.; Bischoff, L.

Abstract

Samples of thin film (d~40nm) tetrahedral amorphous carbon (ta-C), deposited by filtered cathodic vacuum arc (FCVA), have been implanted with N+ and Ga+ at ion energy E = 20 keV and ion fluences D = 3.1014÷3.1015 cm-2. This results in optical properties modification, best manifested by a significant shift of the optical absorption edge to lower photon energies, which is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). These effects could be attributed both to additional defect introduction and increased graphitization, as confirmed by X-ray photo-electron spectroscopy (XPS) measurements. The nonimplanted films show the expected variety of carbon-carbon chemical bonds: three- and fourfold coordinated carbon, while the X-ray results show that ion implantation leads to the introduction of additional disorder in the films. The X-ray photoelectron spectra of the implanted films show that, in addition to the already mentioned changes, the ion bombardment results in an increase of the threefold coordinated as compared to the fourfold coordinated carbon bonds, i.e. increased graphitization of the carbon content in the films. These structural modifications, due to the ion implantation, are the reasons for the observed changes in the optical properties of the films, which could be made use of in the area of high-density optical data storage using focused Ga+ ion beams.

Keywords: tetrahedral amorphous carbon; focused ion beams; optical data storage

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-24844


Metalle schürfen aus Elektronikschrott

Ell, R.; Scharf, C.; (Editors)

Abstract

Metallurgen entwickeln neue Strategien, um Rohstoffe aus alten Handys zurückzugewinnen.

  • VDI-Nachrichten 44(2016), 23-23

Permalink: https://www.hzdr.de/publications/Publ-24843


Kritische Rohstoffe aus zweiter Hand

Scharf, C.

Abstract

Seit drei Jahren lehre und forsche ich als Professorin für Metallurgie und Recycling der Hochtechnologiemetalle in Freiberg. Mein Team und ich setzen uns für einen nachhaltigen Umgang mit kritischen Metallen und anderen Industriemineralen ein. Wir erforschen neue Verfahren, um beispielsweise Produktionsabfälle zu reduzieren und die Wiederverwertung von Rohstoffen aus Altgeräten zu verbessern. Schlacken, Schlämme, Stäube, Späne oder Abwässer — in der Mineralrohstoff und Metallindustrie gibt es, technisch bedingt, viele Rückstände und damit auch eine große Menge bisher nicht genutzter Wertstoffe. Gemeinsam mit den wiederverwertbaren Stoffen, die in alten Elektrogeräten und sonstigen ausgedienten Produkten stecken, gelten sie inzwischen
als wichtiger Hebel für das Erreichen einer maximalen Ressourceneffizienz in der Kreislaufwirtschaft. Um solche „Rohstoffe aus zweiter Hand“, auch sekundäre Ressourcen genannt, dreht sich die Arbeit meines Forscherteams.

  • Contribution to external collection
    Prof. Roewer: ACAMONTA - Zeitschrift für Freunde und Förderer der Technischen Universität Bergakademie Freiberg, Marienberg: Erzdruck GmbH, 2016, ISSN 2193-309X, 27-28

Permalink: https://www.hzdr.de/publications/Publ-24842


Synthese neuer Imidazol-Derivate für die Entwicklung eines 18F-PET-Radioliganden zur Bildgebung des Cannabinoid Rezeptors 2 im Gehirn

Hausmann, K.

  • Master thesis
    Universität Leipzig, 2016
    Mentor: Dr. R.-P. Moldovan
    71 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24841


Entwicklung eines 18F-markierten Radioliganden zur Bildgebung der Phosphodiesterase 10A im Gehirn durch Positronen-Emissions-Tomographie

Wagner, S.

  • Doctoral thesis
    Universität Leipzig, 2016
    Mentor: Dr. Matthias Scheunemann
    166 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24840


Preliminary Studies on the Partial Oxidation of Isobutane with Oxygen in Multiphase Flows.

Lu, X.

Abstract

Oxidation of hydrocarbon is an industrially important reaction. Many valuable chemicals are synthesized by the oxidation of relatively cheap raw materials derived from petroleum. The oxidation of isobutane is one of the most important oxidation oxidation processes. For example, isobutane oxidation can be conducted as the preoxidation in oxirane process to produce propylene oxide and tert.-butanol, in which propylene oxide and TBA are important industrial raw materials and widely used in the syntheses of pharmaceuticals, agrochemicals and other fine chemicals (Qi et al., 2014).
In more recent times, there is more and more interest of researchers in the application of microreactors in chemical engineering because of the opportunities of microreactors in chemical process development and intensification, such as excellent heat and mass transfer (Kashid et al., 2014). In this thesis, the oxidation of isobutane in two-phase flow is investigated in a microreactor (100 m long, 1mm ID). The experiments were carried out under different conditions. The start-up behavior of the oxidation of isobutane has been investigated and discussed. In addition, the effect of temperature, pressure, residence time, oxygen-isobutene ratio, the nitrogen dilution and initiator concentration on the performance of isobutane has also been preliminary investigated and discussed. Furthermore, the rate constant of isobutene oxidation has been calculated for 130 °C.

Keywords: microreactor; isobutane oxidation; two phase flow

  • Diploma thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    89 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24839


Partikelentstehung und -transport im Reaktorwasser von DWR nach Kühlmittelverluststörfällen (KMV) - Untersuchungen im Labormaßstab

Harm, U.; Kryk, H.; Hampel, U.; Seliger, A.; Renger, S.; Kästner, W.

Abstract

Im Rahmen der nuklearen Sicherheitsforschung des Bundesministeriums für Wirtschaft und Energie (BMWi) erfolgten an der Hochschule Zittau/Görlitz (HSZG) in Kooperation mit der Technischen Universität Dresden (TUD) und dem Helmholtz-Zentrum Dresden-Rossendorf (HZDR) experimentelle und methodische Untersuchungen für die systematische Klärung physiko-chemischer Mechanismen im Kühlmittel und deren Auswirkungen auf thermo-fluiddynamische Prozesse im Reaktorkern, welche während des Sumpfumwälzbetriebes als Langzeitnachkühlung nach Kühlmittelverluststörfällen (KMV) in Druckwasserreaktoren (DWR) auftreten können. Durch Korrosionsprozesse an feuerverzinkten Installationen im Sicherheitsbehälter (SHB) von DWR wird Zink in ionischer Form im borierten Kühlwasser gelöst. Die freigesetzten Zink-Ionen werden aus dem Reservoir des Nachkühlmittels im SHB über die Not- und Nachkühlsysteme bis in den Reaktorkern gefördert. Im Reaktor wird das eingespeiste Kühlmittel (KM) aufgeheizt.
Im Fokus generischer Experimente standen Untersuchungen zum Verhalten derart zusam-mengesetzter Fluide unter Berücksichtigung von Temperaturunterschieden zwischen dem Kühlmittelreservoir im SHB und dem Reaktorwasser an den Brennstäben im Reaktorkern. Diese generischen Untersuchungen erfolgten an elektrisch beheizten Stabkonfigurationen, welche die durch Nachzerfallsleistung beheizten Brennstäbe im Kern von DWR nachbildeten. Bei der Aufheizung des zinkhaltigen KM innerhalb solcher Konfigurationen wurden Trübungen durch Kolloidbildung beobachtet, gefolgt von Ausscheidungen partikelförmiger, fester Korrosionsprodukte in Form von Zinkboraten. Diese erschienen in Abhängigkeit von der umgebenden KM- bzw. Staboberflächentemperatur als leicht mobilisierbare, flockenartige Dispersphase oder wiesen schichtenbildenden Charakter auf.
Die temperaturabhängigen Umwandlungen von gelösten Zink-Ionen in feststoffartige Zinkborate bewirkten sowohl Ablagerungen an den Heizstäben als auch an den Abstandshaltern (AH) und führten zu erhöhtem Differenzdruckaufbau über die AH sowie Strömungsumverteilungen in der Stabkonfiguration. In Folge dieser Ablagerungen wurden Änderungen des Wärmetransports vom beheizten Stab ans Fluid nachgewiesen, die eine Aufheizung der Heizstäbe bewirkten und damit sicherheitsrelevanten Charakter hinsichtlich der Nachwärmeabfuhr tragen. Aktuell wird dieses generisch ermittelte Verhalten des Reaktorwassers hinsichtlich der Übertragbarkeit auf sicherheitsrelevante Fragestellungen realer DWR mit Bezug auf anzunehmende Leckgrößen und Nachkühlbedingungen und den daraus resultierenden thermohydraulischen Randbedingungen im Sicherheitsbehälter und im Reaktorkern untersucht. Hierfür werden durch Störfallanalysen die Zustände und Bedingungen abgrenzend ermittelt, bei denen eine Gefährdung der Kernkühlung aus Sicht vorhandener Erkenntnisse zu den physiko-chemischen Effekten eintreten könnte. Wesentliche Untersuchungsschwerpunkte bilden die im SHB von DWR auftretenden chemischen und thermodynamischen Einflüsse auf die Zinkfreisetzung und das Ausfällungs- und Ablagerungsverhalten der Korrosionsprodukte an Heißstellen im Reaktorkern.
Die Untersuchungsergebnisse finden u. a. für die Parametrierung von Simulationscodes sowie in alternativen Modellansätzen Verwendung und dienen der sicherheitstechnischen Einschätzung des DWR-Reaktorverhaltens für verschiedene KMV-Störfallszenarien. Die quantitative Analyse der experimentellen Daten zum zeitlichen Ablauf des Quelle-Senke-Mechanismus der Zinkkorrosion und der Umwandlung des gelösten Zinks in feste Produkte unter realen Störfallbedingungen stellt auf Grund der Komplexität und der gegebenen Rückwirkungen eine Herausforderung dar.
Die Vorhaben werden mit Mitteln des Bundesministeriums für Wirtschaft und Energie (BMWi) unter den Förderkennzeichen 150 1491 und 150 1496 gefördert und fachlich von einer Monitoring Group begleitet, welche sich aus Repräsentanten der Forschungsbetreuung des Projektträgers, Gutachtern, Herstellern und Anlagenbetreibern zusammensetzt.

Keywords: Nuclear energy; Loss of coolant accident; corrosion; zinc release; experiments

  • Contribution to proceedings
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 22.-23.09.2016, Zittau, Deutschland
    Proceedings des Zittauer Kraftwerkschemischen Kolloquiums
  • Lecture (Conference)
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 23.09.2016, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24838


Helmholtz-Zentrum Dresden-Rossendorf Helmholtz Institute Freiberg for Resource Technology Introduction CHROMIC

Scharf, C.; Kelly, N.; Helbig, T.

Abstract

Helmholtz-Zentrum Dresden-Rossendorf
Helmholtz Institute Freiberg for Resource Technology
Introduction
CHROMIC
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730471
This presentation reflects only the author’s views and neither Agency nor the Commission are responsible for any use that may be made of the information contained therein.

  • Invited lecture (Conferences)
    CHROMIC, Kick-Off-Meeting, 07.-08.12.2016, Mol, Belgien

Permalink: https://www.hzdr.de/publications/Publ-24837


CHROMIC WP4 Presentation

Scharf, C.; Kelly, N.; Helbig, T.

Abstract

CHROMIC
WP4 Presentation
Prof. Dr.-Ing. Christiane Scharf (HZDR, HIF)
This project has received funding from the European Union’s Horizon 2020 research and
innovation programme under grant agreement No 730471
This presentation reflects only the author’s views and neither Agency nor the Commission are responsible for any use that may be made of the information contained therein.

  • Invited lecture (Conferences)
    CHROMIC, Kick-Off-Meeting, 07.-08.12.2016, Mol, Belgien

Permalink: https://www.hzdr.de/publications/Publ-24836


Koordinierungsgespräch HIF – Technikum

Scharf, C.

Abstract

Koordinierungsgespräch
HIF – Technikum
Christiane Scharf
29.4.2016, Helmholtz-Zentrum Dresden-Rossendorf

  • Lecture (others)
    Koordinierungsgespräch, SMWK, SAB, SIB, HZDR, 29.04.2016, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24835


„Der Weg ist für jeden hürdenreich“ Neue Veranstaltungsreihe beleuchtet Karrierewege für Frauen in der Wissenschaft

Scharf, C.

Abstract

Obwohl sich die Anzahl weiblicher und männlicher Hochschulabsolventen in etwa die Waage hält, sind auf den akademischen Führungspositionen nur selten Frauen zu finden. Über die Gründe wird viel diskutiert. Unter anderem würden den jungen Forscherinnen geeignete Vorbilder fehlen. Die HZDR-Zentralabteilung Verwaltung hat eine Veranstaltungsreihe aufgesetzt, in der Professorinnen des Zentrums ihren Weg in der Wissenschaft vorstellen. Den Anfang machte im März Prof. Christiane Scharf. Sie hält seit Oktober 2013 die Professur für Metallurgie und Recycling von Hochtechnologiemetallen an der TU Bergakademie Freiberg. Außerdem leitet sie die Abteilung Metallurgie und Recycling am Helmholtz-Institut Freiberg für Ressourcentechnologie. insider hat sich mit ihr über die Situation für Frauen in der Wissenschaft unterhalten.

insider: Frau Scharf, Sie sind ein seltener Fall. Nur ein Fünftel aller deutschen Professuren ist weiblich besetzt. Wie kommt das?
Christiane Scharf: Ich persönlich denke, dass das deutsche Familien- und vor allem Frauenbild hier immer noch eine sehr starke Rolle spielt. Der Einfluss des direkten familiären Umfeldes hat enorme Auswirkungen auf die Karriere. Kommt aus dieser Richtung zusätzlicher Widerstand, was wohl leider nicht selten der Fall ist, wird es sehr schwierig, die ohnehin hohen Hürden zu meistern. Wenn man allerdings den Rückhalt spürt, wird Vieles wesentlich leichter. Häufig genügen dafür schon ein oder zwei Personen, auf die man sich verlassen kann.

Gerade bei Frauen kommt es relativ häufig vor, dass sie einen Ruf nicht annehmen. Könnte das in diesen Fällen auch eine Rolle spielen?
Absolut. Industrie und Wissenschaft haben mittlerweile zum großen Teil begriffen, dass viele Frauen alle Qualifikationen mitbringen und neue Ideen beisteuern können. Eine Führungsposition bringt jedoch automatisch neue Pflichten und einen höheren Grad an Verantwortung mit sich. Ob man sich selbst zutraut, dies zu erfüllen, hängt wiederum stark vom persönlichen Umfeld ab. Dabei sollten auch gesellschaftliche Vorstellungen – ich nenne hier zum Beispiel den Begriff der Rabenmutter, selbst wenn das altertümlich klingen mag – nicht unterschätzt werden.

An welcher Stelle könnte man ansetzen, um das zu ändern?
Zu meiner Schulzeit wurde noch stark das Bild vermittelt, dass Frauen in technischen und naturwissenschaftlichen Berufen nichts verloren hätten. Glücklicherweise ändert sich das seit etwa fünfzehn Jahren. Gesellschaftlich hat sich schon viel getan. Am Ende ist es natürlich trotzdem eine Persönlichkeitsfrage: Wie gehe ich zum Beispiel mit Niederlagen um? Nach meinem Chemieingenieursstudium habe ich mehr als 100 Absagen erhalten.

Und wie gingen Sie damit um?
Ich habe als chemische Fachkraft bei einem Privatunternehmen angefangen. Diese Erfahrungen aus der Industrie haben mir später sehr weitergeholfen. In den meisten Fällen ist die größte Hürde, erst einmal in das gewünschte Feld hineinzukommen. Sobald man auf einer sachlichen Ebene diskutiert, sind die Vorurteile sehr schnell entkräftet.

Könnte das auch eine Lösung für ein zurückhaltendes Umfeld sein?
Aus meiner persönlichen Erfahrung würde ich sagen ja. Mit zunehmendem Erfolg wird auch das kritische Umfeld immer ruhiger. Jungen Forscherinnen, und natürlich auch jungen Forschern, kann ich deswegen nur den Mut zusprechen, in sich selbst zu vertrauen, auch wenn die Herausforderungen hoch erscheinen. Man sollte sich immer selbst klar machen, welche Chancen dieser Weg mit sich bringt.

Was war dabei Ihr Erfolgsrezept?
Ich würde sagen, eine Strategie der kleinen Schritte. Wenn ich mir schon beim Abitur denke, in 20 Jahren musst du auf dieser Position sitzen, dann ist das eine riesige Hürde. Es kann dann schnell passieren, dass man bei den ersten Niederlagen, die mit großer Wahrscheinlichkeit kommen werden, zu verzweifeln beginnt. Es geht eher darum, immer am Ball zu bleiben. Der rote Faden muss erkennbar bleiben, ohne krampfhaft auf ein einziges Ziel hinzuarbeiten. Jeder erfolgreiche Schritt, auch wenn er klein sein mag, bringt dann neue positive Energie.
Das Interview führte Simon Schmitt.

  • Communication & Media Relations
    Interview 11.03.2016
    1 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24834


Frauen in der Wissenschaft - Karrierewege

Scharf, C.

Abstract

Frauen in der Wissenschaft - Karrierewege
Christiane Scharf
Helmholtz-Zentrum Dresden-Rossendorf, 4.3.2016

  • Lecture (others)
    Einladung HZDR-Veranstaltung, Gleichstellungsbüro, 10.03.2016, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24833


KIC – Network of Infrastructure for Metal-based Lightweight Materials Metallurgy and Recycling Department

Scharf, C.; Balinski, A.

Abstract

KIC – Network of Infrastructure for Metal-based Lightweight Materials
Metallurgy and Recycling Department
Christiane Scharf
Freiberg, 29th November 2016

  • Invited lecture (Conferences)
    KIC – Network of Infrastructure for Metal-based Lightweight Materials Kick-Off-Meeting, 29.11.2016, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24832


High Magnetic Moment in Ferrimagnetic NiCo2O4 films via He Ion Irradiation

Pandey, P.; Bitla, Y.; Zschornak, M.; Wang, M.; Xu, C.; Grenzer, J.; Gemming, S.; Helm, M.; Chu, Y.-H.; Zhou, S.

Abstract

The spinel NiCo2O4 (NCO) exhibits unique combination of electrical conductivity, infrared transparency, electro catalytic activity, and ferrimagnetic order, which makes it an attractive material for spintronic applications.1 The NCO thin-films electrical and magnetic properties can be manipulated from high temperature ferrimagnetic and metallic to low temperature ferromagnetic and insulating by changing the growth temperature.2 The high quality epitaxial NCO films were grown on MgAl2O4 (100) substrate at ~ 400°C exhibits metallic behavior accompanied by ferrimagnetic order with moment ~ 2 μB/fu.1,2 Here, we report the impact of He-ion irradiation with fluence ranging from 5×1015/cm2 – 3×1016/cm2 on these metallic NCO films. The use of He-ion irradiation results in the coherent control of out-of-plane lattice parameter of these films without changing its in-plane lattice parameter (Figure 1). The comprehensive study of magnetization data reveals the magnetic moment increases drastically to ~ 4 μB/fu (Figure 1). The X-ray absorption spectroscopic study also suggests the possible charge redistribution within the octahedral sites of the NCO films which corroborates well with the increase in the magnetic moment.

Involved research facilities

Related publications

  • Poster
    MEMRIOX International Workshop 2016, 25.-27.09.2016, Berghotel Bastei, Germany

Permalink: https://www.hzdr.de/publications/Publ-24831


SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch Calixarene

Scharf, C.; Balinski, A.

Abstract

Ausgangssituation und Zielsetzung
Die Gewinnung von Seltenen Erden (SE) ist aufgrund ihrer Eigenschaften sehr komplex, aufwendig und dadurch kostspielig. Die größten Herausforderungen liegen in der Separation der einzelnen SE-Elemente sowie in der notwendigen Abtrennung von Uran und Thorium. Ziel des Projektes SE-FLECX ist die Entwicklung neuer Extraktionsmittel zur effizienten Trennung der Actinoide (Typ A) und der SE-Elemente (Typ B) und die Auslegung ihres Herstellungsprozesses im industriellen Maßstab.

Involved research facilities

  • PET-Center
  • Poster
    r4-Konferenz, Statusveranstaltung, 20.-21.10.2016, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24830


SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch präorganisierte Calixarene

Scharf, C.; BASF; CMI UVK; TU BAF; Universität Leipzig; Balinski, A.

Abstract

SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch präorganisierte Calixarene
Koordinator: Prof. Dr. Christiane Scharf
Förderkennzeichen: 033R132A
r4-Konferenz 2016 | Hannover | 20. und 21. Oktober 2016
Verbundpartner
BASF SE, Ludwigshafen
Helmholtz-Zentrum Dresden-Rossendorf,
Helmholz-Institut Freiberg für Ressourcentechnologie, Freiberg
Und Institut für Ressourcenökologie, Leipzig
CMI UVK GmbH, Montabaur
Technische Universität Bergakademie Freiberg, Freiberg
Universität Leipzig, Leipzig

  • Invited lecture (Conferences)
    r4-Konferenz, Innovative Technologien für Ressourceneffizienz, Statusveranstaltung, 20.-21.10.2016, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24829


Turn on/off the high-temperature ferromagnetism in Si1-xMnx thin films through Mn-ion implantation

Pandey, P.; Rylkov, V. V.; Yuan, Y.; Semisalova, A. S.; Mikhalevskiy, V. A.; Novodvorskii, O. A.; Tugushev, V. V.; Helm, M.; Zhou, S.

Abstract

Silicon based alloys with Mn-ions are a potential candidate for the spintronics applications, as they exhibit complex electric and magnetic phenomena which can be effectively utilized as the integrated-circuit elements in the contemporary microelectronic technology. Though, The Si1-xMnx alloys shows high-temperature ferromagnetism at low Mn concentration x ~ 0.05 – 0.1, but the small solubility of Mn-ions in Si leads to the formation of MnSi1.7 nanoparticles,1 which drives the system in an inhomogeneous phase and makes it irrelevant for the technological applications. However, a high Mn concentration in the Si1-xMnx alloys screens the precipitation of different inhomogeneous magnetic phases with high Curie temperature (TC).2 In this context, a set of thin films of Si1-xMnx (x = 0.44 – 0.57) alloy were prepared by the pulsed laser deposition technique on Al2O3 (0001) substrate. We have found room temperature ferromagnetism and a large magnetic moment for the Si0.43Mn0.57 film as compared to the rest of samples. But, surprisingly, the TC (as well as the moment) of Si0.43Mn0.57 film drastically decreases from 300 K to ~ 40 K as the Mn-ion concentration was increased in the film through the ion implantation process. In contrast, the stoichiometric film Si0.5Mn0.5 exhibits a huge increase in the magnetic moment by one-order in magnitude after ~ 2% Mn-ion implantation. The TC of the stoichiometric film also increases from 50 K to 300 K with the increase in the Mn-ion concentration.

Involved research facilities

Related publications

  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft e.V, 06.-11.03.2016, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-24828


Hydrodynamic characterization of a novel external loop airlift inverse semi-fluidized bed reactor packed with loofa particles

Hegeholz, G.; Mohammed, I. H. M.; Schubert, M.

Abstract

In biochemical processes, column reactors replaced the stirred tank reactors for their advantages, like mild agitation. Among different configurations of column reactors airlift reactors constitute attractive systems for bio-catalyzed reactions due to the simple de-sign, low investment and operation costs. The advantages of combined external loop airlift and fluidized bed reactor in the downcomer over three-phase fluidized bed reactor and other configuration of airlift reactors are the unique hydrodynamic properties as it requires lower liquid flow rate for complete suspension of solid and good contact among the phases, easy removal of particles, rapid mixing, and easier scale up. This enables inverse fluidizing of low-density particles in the downcomer zone, characterized by low shear rates.

Keywords: fluidized airlift reactor; riser; downcomer; low-density particles; wire mesh sensor

  • Diploma thesis
    TU Dresden, 2016
    Mentor: Hampel Uwe

Permalink: https://www.hzdr.de/publications/Publ-24827


Metallurgy and Recycling Division

Scharf, C.

Abstract

Metallurgy and Recycling Division
Christiane Scharf
Freiberg, 10th March 2016

  • Lecture (others)
    Metallurgy and Recycling Division, Visit of the company Outotec, 10.03.2016, HIF, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24826


Recycling of metals by vacuum distillation and solvent extraction

Scharf, C.

  • Invited lecture (Conferences)
    METYK Metallialan ympäristö- ja kiertotalous, METYK Seminar, 14.06.2016, Pori, Finnland

Permalink: https://www.hzdr.de/publications/Publ-24825


Metallurgy and Recycling Department

Scharf, C.

Abstract

Metallurgy and Recycling Department
Visit of Prof. Mari Lundström
Christiane Scharf
Freiberg, 15th Dezember 2016

  • Lecture (others)
    Metallurgy and Recycling Department Visit of Prof. Mari Lundström (Aalto University), 15.12.2016, HIF, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24824


Direct numerical simulations of particle attachment to solids and deformable surfaces

Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.

Abstract

The present talk deals with the transport and the deposition of micron particles to solid wall surfaces and fluid-fluid interfaces. Various particle-interface models are presented and tested with direct numerical flow simulations. The various micro processes observed during the particle attachment and particle detachment are well captured. The results compare well with those experimentally obtained on-site.

  • Lecture (others)
    Institute seminar, 14.12.2016, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-24823


Metallurgy and Recycling Department

Scharf, C.

Abstract

Metallurgy and Recycling Department
Visit of Prof. Peter Tasker
Christiane Scharf
Freiberg, 13th Dezember 2016

  • Lecture (others)
    Metallurgy and Recycling Department Visit of Prof. Peter Tasker (University Edinburgh), 13.12.2016, HIF, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24822


Optical components in harsh space environment

Pelizzo, M. G.; Corso, A. J.; Tessarolo, E.; Zuppella, P.; Böttger, R.; Hübner, R.; Della Corte, V.; Palumbo, P.; Taglioni, G.; Preti, G.; Foggetta, L.; Valente, P.; Rancoita, P.; Martucci, A.; Napolitani, E.

Abstract

Space exploration is linked to the development of increasingly innovative instrumentation, able to withstand the operation environment, rich in ion particles and characterized by high temperatures. Future space missions such as JUICE and SOLAR ORBITER will operate in a very harsh and extreme environment-. Electrons and ions are considered among the causes of potential damage of the optical instrumentation and components. Development of hard coatings capable to preserve their optical properties is pivotal. Different coating materials have been exposed to ion irradiation in particle accelerators. Change in optical performances has been observed in the extreme ultraviolet and visible spectral region and structural properties have been analyzed by different techniques. The knowledge of the damage mechanisms and thresholds allows the selection of more promising candidate materials to realize the optical components for the new frontiers space missions. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Keywords: Optical components; Optical properties; Particle accelerators; Particles; Coating; Electrons; Extreme ultraviolet; Hard coatings; Ions

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-24821


Metallurgy and Recycling Division

Scharf, C.

Abstract

Metallurgy and Recycling Division
Christiane Scharf
Freiberg, 8th September 2016

  • Lecture (others)
    Metallurgy and Recycling Division, Einladung Herr Wilson (Aalto University), 08.09.2016, HIF, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24820


Recycling of Strategic Elements by Extractive Metallurgy

Scharf, C.

Abstract

Summer School 2016
Recycling of Strategic Elements by Extractive Metallurgy
Christiane Scharf
5th October 2016, TU Dresden

  • Invited lecture (Conferences)
    Summer School 2016, 05.10.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24819


Sub-Channel Flow Behavior in Vertical Tube Bundles in Bubble Columns

Möller, F.; Hampel, U.; Schubert, M.

Abstract

Bubble columns are simple multiphase reactor and contactor devices, which are widely applied due to their superior heat and mass transfer characteristics. Furthermore, they are relatively simple in construction due to the absence of moving parts. Bubble columns are used for various chemical processes such as methanol and Fischer-Tropsch synthesis. Since most of the processes running in bubble columns are of exothermic nature, a variety of heat exchangers, e.g. internal heat exchanging tube bundles, are installed in order to ensure proper reaction conditions. Such tube bundles cover a significant ratio (up to 60 %) of the entire column cross-section. Accordingly, the column performance is dominated by the hydrodynamics proceeding at smaller characteristic length scale in the sub-channels. However, the evolving sub-channel flow has not been studied yet.
Therefore, this study focusses on the analysis of the multiphase flow in the sub-channels of an internal heat exchanging tube bundle with longitudinal flow of various configurations (square and triangular pattern) and tube diameter sizes (8 mm and 13 mm). The investigations were carried out in a 100 mm (inner diameter) bubble column for an air / deionized water system using a perforated plate type sparger. To ensure comparability, the covered rector’s cross-sectional area was kept similar for all configurations.
The hydrodynamic parameters were studied separately for sub-channels at various radial positions in the bundles as well as for the entire column. Approaches to link experimental data from both scales for a multiscale evaluation are suggested. Furthermore, the results are compared with an advanced horizontal stage-model considering breakup and coalescence mechanisms to calculate the bubble size distribution, breakup and coalescence rates and the overall gas holdup.

Involved research facilities

  • TOPFLOW Facility
  • Lecture (Conference)
    Jahrestreffen Dresden - Jahrestreffen der ProcessNet-Fachgruppen Mehrphasenströmungen, Partikelmesstechnik, Zerkleinern und Klassieren, Computational Fluid Dynamics, Mischvorgänge und dem TAK Aerosoltechnologie, 14.-17.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24817


Mechanical properties and current-carrying capacity of Al reinforced with graphene/BN nanoribbons: a computational study

Kvashnin, D. G.; Ghorbani-Asl, M.; Shtansky, D. V.; Golberg, D.; Krasheninnikov, A. V.; Sorokin, P. B.

Abstract

Record high values of Young’s modulus and tensile strength of graphene and BN nanoribbons as well as their chemically active edges make them promising candidates for serving as fillers in metal-based com- posite materials. Herein, using ab initio and analytical potential calculations we carry out a systematic study of the mechanical properties of nanocomposites constructed by reinforcing an Al matrix with BN and graphene nanoribbons. We consider a simple case of uniform distribution of nanoribbons in an Al matrix under the assumption that such configuration will lead to the maximum enhancement of mechanical characteristics. We estimate the bonding energy and the interfacial critical shear stress at the ribbon/metal interface as functions of ribbon width and show that the introduction of nanoribbons into the metal leads to a substantial increase in the mechanical characteristics of the composite material, as strong covalent bonding between the ribbon edges and Al matrix provides efficient load transfer from the metal to the ribbons. Using the obtained data, we apply the rule of mixtures in order to analytically assess the relationship between the composite strength and concentration of nanoribbons. Finally, we study carbon chains, which can be referred to as the ultimately narrow ribbons, and find that they are not the best fillers due to their weak interaction with the Al matrix. Simulations of the electronic transport properties of the composites with graphene nanoribbons and carbyne chains embedded into Al show that the inclusion of the C phase gives rise to deterioration in the current carrying capacity of the material, but the drop is relatively small, so that the composite material can still transmit current well, if required.

Keywords: nanocomposites; atomistic simulation; mechanical properties

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-24816


Creating nanoporous graphene with swift heavy ions

Vazquez, H.; Ahlgren, E. H.; Ochedowski, O.; Leino, A. A.; Mirzayev, R.; Kozubek, R.; Lebius, H.; Karlusic, M.; Jaksic, M.; Krasheninnikov, A. V.; Kotakoski, J.; Schleberger, M.; Nordlund, K.; Djurabekova, F.

Abstract

We examine swift heavy ion-induced defect production in suspended single layer graphene using Raman spectroscopy and a two temperature molecular dynamics model that couples the ionic and electronic subsystems.We show that an increase in the electronic stopping power of the ion results in an increase in the size of the pore-type defects, with a defect formation threshold at 1.22e1.48 keV/layer. We also report calculations of the specific electronic heat capacity of graphene with different chemical potentials and discuss the electronic thermal conductivity of graphene at high electronic temperatures, suggesting a value in the range of 1Wm?1 K?1. These results indicate that swift heavy ions can create nanopores in graphene, and that their size can be tuned between 1 and 4 nmdiameter by choosing a suitable stopping power.

Keywords: Graphene; ion irradiation; two-temperature model; atomistic simulations

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-24815


Vibrational properties of a two-dimensional silica Kagome lattice

Björkman, T.; Skakalova, V.; Kurasch, S.; Kaiser, U.; Meyer, J. C.; Smet, J. H.; Krasheninnikov, A. V.

Abstract

Kagome lattices are structures possessing fascinating magnetic and vibrational properties, but in spite of a large body of theoretical work, experimental realizations and investigations of their dynamics are scarce. Using a combination of Raman spectroscopy and density functional theory calculations, we study the vibrational properties of two- dimensional silica (2D-SiO2), which has a kagome lattice structure. We identify the signatures of crystalline and amorphous 2D-SiO2 structures in Raman spectra and show that, at finite temperatures, the stability of 2D-SiO2 lattice is strongly influenced by phonon−phonon interaction. Our results not only provide insights into the vibrational properties of 2D-SiO2 and kagome lattices in general but also suggest a quick nondestructive method to detect 2D-SiO2.

Keywords: Raman spectroscopy; first-principles calculations; 2D materials

Permalink: https://www.hzdr.de/publications/Publ-24814


Effect of Fluid Dynamics on Separation Efficiency of Sieve Tray

Vishwakarma, V.; Schubert, M.; Hampel, U.

Abstract

Sieve trays are popular among vapour-liquid contacting devices in distillation columns due to their versatility and simple construction. Flow and mixing patterns on the trays have strong influence on their mass-transfer efficiency. Plug flow is considered ‘ideal’ whereas flow non-idealities such as liquid channelling, bypassing, re-circulation and stagnant zones are disadvantageous for the tray efficiency. Flow patterns quantified by Schubert et. al. (2016) using wire-mesh sensor are analysed using existing mathematical models for efficiency predictions. A serious loss in efficiency is predicted for the tray with large stagnant zones.

(1) M. Schubert, M. Piechotta, M. Beyer, E. Schleicher, U. Hampel and J. Paschold, ‘An imaging technique for characterization of fluid flow pattern on industrial-scale column sieve trays’, Chemical Engineering Research and Design, vol. 111, pp.138–146, 2016.

Keywords: Distillation Column; Sieve Tray; Tray Efficiency; Flow Non-idealities

  • Poster
    Treffen des Wissenschaftlichen Programmausschusses EMR, 21.-22.09.2016, HZDR, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-24813


CFD codes benchmark on TOPFLOW-PTS experiment

Mérigoux, N.; Apanasevich, P.; Mehlhoop, J.-P.; Lucas, D.; Raynaud, C.; Badillo, A.

Abstract

In the frame of the European Union NURESAFE project a benchmark test between NEPTUNE_CFD, CFX and TransAT CFD codes on a reference TOPFLOW-PTS experiment was conducted. The work is a part of the work package on multi-scale and multi-physics simulation of Pressurized Thermal Shock (PTS). The article includes a short description of the TOPFLOW-PTS facility and the reference steam-water experiment. Furthermore the boundary and initial conditions for the CFD simulations are presented. The computational grids that are used for the benchmark simulations and the models used are introduced. Finally, the results of CFD calculations are compared with the experimental data and differences between simulations and experiment are discussed.

Keywords: Benchmark tests; Boundary and initial conditions; CFD simulations; Computational grids; European union; Multiphysics simulations; Pressurized thermal shock; Work packages

Involved research facilities

  • TOPFLOW Facility

Permalink: https://www.hzdr.de/publications/Publ-24812


Quantum regime of a free-electron laser: relativistic approach

Kling, P.; Sauerbrey, R.; Preiss, P.; Giese, E.; Endrich, R.; Schleich, W. P.

Abstract

In the quantum regime of the free-electron laser, the dynamics of the electrons is not governed by continuous trajectories but by discrete jumps in momentum. In this article, we rederive the two crucial conditions to enter this quantum regime: (1) a large quantum mechanical recoil of the electron caused by the scattering with the laser and the wiggler field and (2) a small energy spread of the electron beam. In contrast to our recent approach based on nonrelativistic quantum mechanics in a co-moving frame of reference, we now pursue a model in the laboratory frame employing relativistic quantum electrodynamics.

Keywords: Electrodynamics; Free electron lasers; Quantum electronics; Quantum theory

Permalink: https://www.hzdr.de/publications/Publ-24811


Discovering complex groundwater dynamics of a multiple aquifer system on the base of stable and radio-isotope patterns

Wilske, C.; Roediger, T.; Suckow, A.; Geyer, S.; Weise, S.; Merchel, S.; Rugel, G.; Pavetich, S.; Merkel, B.; Siebert, C.

Abstract

The water supply in semi-arid Israel and Palestine, predominantly relies on groundwater as freshwater resource, stressed by increasing demand and low recharge rates. Sustainable management of such resources requires a sound understanding of its groundwater migration through space and time, particularly in structurally complex multi-aquifer systems as the Eastern Mountain Aquifer, affected by salting. To differentiate between the flow paths of the different water bodies and their respective residence times, a multi-tracer approach, combining age dating isotopes (36Cl/Cl; 3H) with rock specific isotopes like 87Sr/86Sr and δ34S-SO4 was applied. As a result, the investigated groundwaters from the two Cretaceous aquifers and their respective flow paths are differentiable by e.g. their 87Sr/86Sr signatures, resembling the intensity of the rock-water interaction and hence indirectly residence times. In the discharge areas within the Jordan Valley and along the Dead Sea shore, δ34S-SO4 ratios reveal the different sources of salinity (ascending brines, interstitial brines and dissolved salts). Based on 36Cl and 3H and the atmospheric input functions, very heterogeneous infiltration times and effective flow velocities, respectively, indicate an at least dual porosity system, resulting in distinctly different regimes of matrix and pipe flow.

Keywords: 36Cl/Cl; 3H; groundwater age dating; 87Sr/86Sr; δ34S; aquifer characterization; western Dead Sea Basin

Involved research facilities

Related publications

  • Poster
    European Geosciences Union (EGU) General Assembly, 23.-28.04.2017, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-24810


Self-assembly of single Si quantum dots in SiO2

Heinig, K.-H.; Stegemann, K.-H.; von Borany, J.; Facsko, S.; Hlawacek, G.; Hübner, R.; Bischoff, L.; Möller, W.; Prüfer, T.; Xu, X.

Abstract

However, such structures are not small enough to operate at room temperature (RT) quantum devices with switching mechanisms different from CMOS. E.g., the extremely low-power device Single Electron Transistor (SET) works at RT only if the size of the quantum dot is below 5 nm, and if the tunnel distances through SiO2 are a few nm only.
Here we present a directed self-assembly process of a 2-3 nm small single Si dot located in the middle of a SiO2 layer with distances of ~2 nm to the upper and lower Si. The self-assembly occurs by phase separation of metastable SiOx during a heat treatment. The self-assembly becomes directed by constraining and shaping the SiOx volume in such a manner that a single Si quantum dot in the requested position forms. The SiOx is fabricated by collisional mixing of Si atoms from above and below in the SiO2 layer. Two methods to form a local, constrained volume of SiOx are presented: (i) A large-area Si/SiO2/Si layer stack is irradiated with a 2 nm narrow energetic Ne+ beam in a Helium Ion Microscope (HIM), which results in a ~10 nm disk of SiOx in the buried SiO2 layer. (ii) Si pillars (<20 nm) with an embedded SiO2 layer are irradiated with a broad beam of energetic Si+ ions. Method (ii) will be used to fabricate SETs in a CMOS technology.
This work has been funded by the European Union's Horizon 2020 research and under grant agreement No 688072 innovation program.

Keywords: quantum dots; nano-electronics; ion irradiation; ion beam mixing; phase separation

Involved research facilities

Related publications

  • Lecture (Conference)
    E-MRS 2016 Fall Meeting, 19.-22.09.2016, Warszawa, Poland

Permalink: https://www.hzdr.de/publications/Publ-24808


A multivariate discrimination scheme of detrital garnet chemistry for use in sedimentary provenance analysis

Tolosana-Delgado, R.; von Eynatten, H.; Krippner, A.; Meinhold, G.

Abstract

Garnet chemistry provides a well-established tool in the discrimination and interpretation of sediment provenance. Current discrimination approaches, however, (i) suffer from using less variables than available, (ii) subjective determination of discrimination fields with strict boundaries suggesting clear separations where in fact probabilities are converging, and (iii) significant overlap of compositional fields of garnet from different host-rock groups. The new multivariate discrimination scheme is based on a large database, a hierarchical discrimination approach involving three steps, linear discriminant analysis at each step, and the five major host-rock groups to be discriminated: eclogite- (A), amphibolite- (B) and granulite- (C) facies metamorphic rocks as well as ultramafic (D) and igneous rocks (E). The successful application of statistical discrimination approaches requires consideration of the a priori knowledge of the respective geologic setting. This is accounted for by the use of prior probabilities. Three sets of prior probabilities (priors) are introduced and their advantages and disadvantages are discussed. The user is free to choose among these priors, which can be further modified according to the specific geologic problem and the level of a priori knowledge. The discrimination results are provided as integrated probabilities of belonging to the five major host-rock groups. For performing calculations and results a supplementary Excel® spreadsheet is provided. The discrimination scheme has been tested for a large variety of examples of hard rocks covering all of the five major groups and several subgroups from various settings. In most cases, garnets are assigned correctly to the respective group. Exceptions typically reflect the peculiarities of the regional geologic situation. Evaluation of detrital garnets from modern and ancient sedimentary settings of the Western Gneiss Region (Norway), Eastern Alps (Austria) and Albertine Rift (Uganda) demonstrates the power to reflect the respective geologic situations and corroborate previous results. As most garnet is derived from metamorphic rocks and many provenance studies aim at reconstructing the tectonic and geodynamic evolution in the source area, the approach and the examples emphasize discrimination of metamorphic facies (i.e., temperature-pressure conditions) rather than protolith composition.

Keywords: garnet; mineral chemistry; linear discriminant analysis; compositional data; prior probabilities; provenance

  • Contribution to proceedings
    European Geosciences Union General Assembly 2017, 23.-28.04.2017, Wien, Österreich
    Proceedings of the European Geoscience Union General Assembly 2017
  • Open Access Logo Sedimentary Geology 375(2018), 14-26
    Online First (2017) DOI: 10.1016/j.sedgeo.2017.11.003
    ISSN: 0037-0738
    Cited 42 times in Scopus

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Permalink: https://www.hzdr.de/publications/Publ-24807


Hybride 3D Modellierungen im Gifhorner Trog für die Kombination von Übertage und Untertage-Gravimetrie

Götze, H.-J.; Schmidt, S.; Menzel, P.

Abstract

Für die hier dargestellte Studie im Bereich des Gifhorner Trogs wurden neben ca. 500 Messpunkten mit vollständig korrigierten Bougueranomalien ca. 4400 digitalisierte ältere Drehwaagemessungen aus dem beginnenden 20. Jahrhundert verwendet. Mit Hilfe der „alten“ Drehwaagemessungen konnten im Detail dann die Schwerehorizontalgradienten Wxz und Wyz sowie die Krümmungsgrößen der Schwere (WΔ = Wyy – Wxx und 2Wxy) in die 3D-Modellierung integriert werden. Neben den an der Oberfläche gemessenen Anomalien standen auch Untertagemessungen des Schwerefeldes zur Verfügung.
Modelliert wurde mit der hauseigenen Modelliersoftware IGMAS+, die nicht nur die simultane 3D Modellierung von Potentialfeldern (GravMag) ermöglicht, sondern auch deren Gradienten. Ein Vergleich von häufig verwendeten 2D-Modellierungen natürlicher 3D-Strukturen im Untergrund mit 3D-Berechnungen zeigt deutlich, wie groß die Gefahr von Fehlinterpretation eines solchen methodisch fragwürdigen Vorgehens ist. Die Modelldichten können variabel – in Abhängigkeit von den „wahren Geschwindigkeitsverhältnissen“ im Modelliergebiet angegeben werden. Als Beispiel zeigen wir das 3D Dichtemodell der Tiefbohrung KTB zusammen mit der Bohrlochgravimetrie – in Ermangelung anderer, frei zugänglicher Datensätze.
Die vorliegende Modellierung von Detailstrukturen im Gifhorner Trog belegt eindeutig, dass eine hybride 3D Modellierung von Potentialfeldern zusammen mit ihren Gradienten wertvolle Informationen über den Untergrund bis in Tiefen von 5 – 10 km liefert, die gemeinsam mit seismischen Informationen einen erheblichen Mehrwert für die Interpretation darstellen.

Keywords: 3D Potentialfeldmodellierung; Geophysik; Untergrundmodellierung

  • Lecture (Conference)
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
  • Contribution to proceedings
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
    DGMK-Tagungsbericht 2016-1, Hamburgf: DGMK, 978-3-941721-64-7, 91-96

Permalink: https://www.hzdr.de/publications/Publ-24806


Magnetic Nanostructures Designed For Hard Disk Drive Applications

Hellwig, O.

Abstract

Continued progress in hard disk drive areal density for conventional perpendicular magnetic recording (PMR) based on granular media has become increasingly difficult. Although adoption of energy assisted magnetic recording (EAMR), specifically Heat Assisted Magnetic Recording (HAMR) is widely viewed as a promising solution for thermal stability issues, challenges in grain size scaling and managing media noise may limit the rate of progress for EAMR based on granular media. Bit patterned recording (BPR) stands as an attractive alternative to granular media, offering a path to thermally stable recording at high density and significantly reduced media noise by replacing the segregated random grains of PMR media with lithographically defined single domain islands. Figure 1 compares and summarizes basic characteristics of currently used conventional PMR based on granular media and BPR based on pre-defined bits. In my talk I will discuss various choices for BPR magnetic materials, such as Co/Pd and Co/Pt multilayers as well as CoCrPt and FePt L10 alloys. I will highlight advantages and disadvantages of the different magnetic material systems with respect to potential applications in BPR and outline the specific challenges when comparing conventional PMR, BPR and currently emerging HAMR systems.

Keywords: magnetic recording; hard disk drive; perpendicular magnetic recording; bit patterned recording; heat assisted magnetic recording

  • Invited lecture (Conferences)
    International Conference on Solid Films and Surfaces, 28.08.-02.09.2016, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-24805


Karrat Zinc 2016 - Personal field report

Zimmermann, R.

Abstract

Results of the 2016 Karrat fieldwork, 11.08.2016 – 24.08.2016

  • Other report
    Kopenhagen: Geological Survey of Denmark and Greenland, 2016
    224 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24804


Experimental Investigation of Bubble Column Reactors with Longitudinal Flow Heat Exchanging Internals Using Ultrafast X-Ray Tomography

Seiler, T.

Abstract

Bubble column reactors are multiphase devices which are commonly applied in the chemical process industry due to their advantageous heat and mass transfer properties as well as the abstinence of moving parts. Since most of the reactions operated in these devices are of exothermic nature, the developed heat has to be sufficiently removed off the system in order the guarantee optimal reaction conditions. One, among others, of those heat exchanging devices can be internally inserted tube bundles, which have the advantage to remove the heat directly at its source. On the downside, a large portion of the reactor's cross-sectional area has to be covered by the tube bundle, whereas typical values range between 20 and 30%. Hence, the influence of the internals is not negligible and has a strong effect on the global and local hydrodynamics. Therefore, the influence of various tube bundle layouts (square and triangular pitch) with two tube sizes (8 and 13 mm) having the same coverage of the reactor's cross-sectional area (~25%) have been investigated using the ultrafast X-ray CT to get insight into the local and global hydrodynamics. A cylindrical column with 10 cm ID and a height of 2m was used. Furthermore, to cover all hydrodynamic flow regimes, the superficial gas velocity was varied between 2 – 20 cm/s. It has been found out that the tube configuration has strong impact on the radial holdup profile, which governs the liquid mixing and gas velocity profile. Furthermore, square configurations showed better hydrodynamic performance regarding holdup, holdup profiles and bubble size distribution.

Involved research facilities

  • TOPFLOW Facility
  • Study thesis
    TU Dresden, 2016
    Mentor: Felix Möller, Uwe Hampel

Permalink: https://www.hzdr.de/publications/Publ-24803


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