Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34121 Publications

Spin colour centres in SiC as a material platform for sensing and information processing at ambient conditions

Anisimov, A.; Soltamov, V.; Baranov, P.; Astakhov, G.; Dyakonov, V.

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

Keywords: Quantum technology; atom-scale defects; silicon carbide

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Permalink: https://www.hzdr.de/publications/Publ-28668
Publ.-Id: 28668


Evaluation of defects in two-dimensional MoTe2: from point to extended defects

Ghorbani-Asl, Mahdi; Lehnert, T.; Köster, J.; Komsa, H.-P.; Kaiser, U.; Krasheninnikov, A.

Defects frequently govern the characteristics of solids, e.g., mechanical or optical properties. They also provide an efficient way to engineer materials properties, similar to doping in semiconductors. Using first-principles calculations combined with high-resolution transmission electron microscopy experiments, we study the creation, agglomeration, and evolution of vacancies in monolayer MoTe 2 under electron irradiation. Various types of point and extended defects are studied and their atomic structures and formation energies are determined. The stability of flower-like defects and trefoil-like defects are compared with the line vacancies. Our results show that single Te vacancies have a tendency for agglomeration into vacancy lines. The stability of line defects is also found to be dependent on their orientation. We have also studied the effects of uniaxial and biaxial strain on the stability and dynamics of line defects. Our electronic structure calculations show that the defects can change the electronic properties of MoTe2, suggesting new opportunities for defect engineering in these layered materials.

Keywords: 2D materials beyond graphene; TMDCs; defects; MoTe2

  • Lecture (Conference)
    DPG Spring Meeting, 16.03.2018, Berlin, Germany
  • Poster
    Conference on Physics of Defects in Solids: Quantum Mechanics Meets Topology, 09.07.2018, ICTP, Trieste, Italy
  • Poster
    Flatlands beyond Graphene, 03.09.2018, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-28667
Publ.-Id: 28667


Ultrafast X-ray tomography data set for the investigation of gas-liquid two-phase flows in an impeller of a centrifugal pump

Schäfer, T.; Bieberle, A.; Pietruske, H.; Hampel, U.

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

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

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

Related publications

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

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-28666
Publ.-Id: 28666


Simulation of Nanodevices

Wagner, C.; Teichert, F.; Fuchs, F.; Schuster, J.; Schreiber, M.; Gessner, T.

Presentation of TP1 / DFG research unit 1713 “Sensoric micro- and nano systems

  • Lecture (others)
    Abschlussverteidigung DFG Forschergruppe 1713 "Sensorische Mikro- und Nanosysteme", 20.09.2018, Chemnitz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28664
Publ.-Id: 28664


Dressing intersubband transitions at terahertz frequencies

Schmidt, J.; Winnerl, S.; Dimakis, E.; Helm, M.; Schneider, H.

We combine intense, spectrally narrow THz pulses from a free-electron laser with broadband THz probe pulses and electro-optic sampling for highly nonlinear THz spectroscopy. We exploit this approach for dressing intersubband transitions in a wide GaAs quantum well and for investigating the associated coherent phenomena with added spectral resolution.

Keywords: terahertz spectroscopy; intersubband transition; quantum well; free-electron laser

  • Lecture (Conference)
    43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 09.-14.09.2018, Nagoya, Japan
  • Contribution to proceedings
    43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 09.-14.09.2018, Nagoya, Japan
    2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz): IEEE
    DOI: 10.1109/IRMMW-THz.2018.8510160

Permalink: https://www.hzdr.de/publications/Publ-28663
Publ.-Id: 28663


Strain-dependent scaling of excitons in carbon nanotubes

Wagner, C.; Schuster, J.; Schleife, A.

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

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

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

[1] V. Perebeinos et al., Phys. Rev. Lett. 92, 257402 (2004).

  • Lecture (Conference)
    DPG-Frühjahrstagung und EPS-CMD27, 12.-16.03.2018, Berlin, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-28662
Publ.-Id: 28662


Synthesis and preliminary radiopharmacological characterisation of an 11C-labelled azadipeptide nitrile as potential PET tracer for imaging of cysteine cathepsins

Laube, M.; Frizler, M.; Wodtke, R.; Neuber, C.; Belter, B.; Kniess, T.; Bachmann, M.; Gütschow, M.; Pietzsch, J.; Löser, R.

An O-methyltyrosine-containing azadipeptide nitrile was synthesised and investigated for its inhibitory activity towards cathepsins L, S, K and B. Labelling with carbon-11 was accomplished by reaction of the corresponding phenolic precursor with [11C]methyl iodide starting from cyclotron-produced [11C]methane. Radiopharmacological evaluation of the resulting radiotracer in a mouse xenograft model derived from a mammary tumour cell line by small animal PET imaging indicates tumour targeting with complex pharmacokinetics. Radiotracer uptake in the tumour region was considerably lower under treatment with the non-radioactive reference compound and the epoxide-based irreversible cysteine cathepsin inhibitor E64. The in vivo behaviour observed for this radiotracer largely confirms that of the corresponding 18F-fluoroethylated analogue and suggests the limited suitability of azadipeptide nitriles for the imaging of tumour-associated cysteine cathepsins

Keywords: pharmacokinetics; cysteine cathepsins; tumour-associated enzymes; molecular imaging; enzyme inhibitors

  • Open Access Logo Journal of Labelled Compounds and Radiopharmaceuticals 62(2019)8, 448-459
    DOI: 10.1002/jlcr.3729

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Permalink: https://www.hzdr.de/publications/Publ-28661
Publ.-Id: 28661


Interessante Beobachtungen in der FIB - Artefakte oder wissenschaftlich neue Ergebnisse?

Engelmann, H.-J.; Hübner, R.

Interessante Beobachtungen in der FIB - Artefakte oder wissenschaftlich neue Ergebnisse?

  • Lecture (others)
    6. Sächsisches TEM-Präparatorentreffen, 10.04.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28660
Publ.-Id: 28660


Impact of flotation hydrodynamics on the optimization of fine-grained carbonaceous sedimentary apatite ore beneficiation

Hoang, D. H.; Hassanzadeh, A.; Peuker, U. A.; Rudolph, M.

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

Keywords: Carbonaceous sedimentary apatite; Locked cycle flotation; Impeller speed; Pulp density; Rare earth; Design of experiment

Permalink: https://www.hzdr.de/publications/Publ-28659
Publ.-Id: 28659


Fundamentals of Actinide Chemistry by Cutting Edge X-ray Methods and Models

Kvashnina, K.

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

  • Lecture (Conference)
    E-MRS Spring Meeting, 27.-31.05.2019, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-28658
Publ.-Id: 28658


Applying SEM-based automated mineralogy in petrology: a case study on volcanic rocks from the Salina Island, Italy

Gilbricht, S.; Krause, J.; Heinig, T.; Sanchez-Garrido, C. J. M. G.

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

Keywords: Mineral Liberation Analysis; Pumice; Electron Microprobe; MLA; EPMA; Volcanic rocks

  • Contribution to proceedings
    EMAS 2018 - Microbeam Analysis in the Earth Sciences, 04.-08.09.2018, Bristol, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-28657
Publ.-Id: 28657


Non-ferrous metals metallurgy industry

Reuter, M. A.

Recycling forms the heart of the Circular Economy (CE) system. Ultimately all products will have to be recycled at their End-of-Life (EoL). Maximizing the recovery of materials and also especially strategic elements from EoL products requires a deep understanding of the fundamental limits and the dynamics of the evolving system, thus an adaptive processing and metallurgical infrastructure is critical to recover all metals and materials. Paramount is the quantification of the “mineralogy”, the complex and interlinked composition of products, to trace and quantify specifically all the losses of materials, metals, alloys, etc. due to thermodynamic and other non-linear interactions. We named this product centric recycling. The recycling potential and performance must be quantified and demonstrated for products, collection systems, waste separation and recovery technologies, and material supply. Emphasis is also placed on informing the consumer through iRE i.e. informing Resource Efficiency in an easy-to-understand way. System Integrated Metal Processing (SIMP) using big-data, multi-sensors, simulation models, metallurgy, etc. links all stakeholders through Circular Economy Engineering (CEE), an important enabler to maximize Resource Efficiency and thus iRE.

Keywords: Circular Economy (CE); Digitalization; CE system; Design for recycling

  • Lecture (others)
    Non-ferrous metals metallurgy industry / Academic course, 13.12.2018, Madrid, Spanien

Permalink: https://www.hzdr.de/publications/Publ-28656
Publ.-Id: 28656


Quantitative Ranking of Geological Conceptual Models using Multi-Point Geostatistics

Selia, S. R. R.; Tolosana Delgado, R.; van den Boogaart, K. G.; Schaeben, H.

Geological interpretation plays a crucial role in every phase of subsurface characterization from exploration to exploitation, e.g. of an oil reservoir or a mineral deposit. In general, the distribution of physical properties is controlled by the architecture of geological objects. Therefore, defining it becomes the initial step of geological modelling. However, insufficient data and the complexity of the earth processes create an ill-posed problem where many models are plausible. Consequently, several geologists will produce different geological models for the same location. This contribution proposes a way to objectivise the ranking of those conceptual models by comparing them with hard data.

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

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

  • Lecture (Conference)
    EGU General Assembly 2019, 07.-12.04.2019, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-28655
Publ.-Id: 28655


Oxygen in ultrahigh magnetic fields

Nomura, T.

  • Invited lecture (Conferences)
    12th International Conference on Research in High Magnetic Fields (RHMF 2018), 24.-28.06.2018, Santa Fe, USA

Permalink: https://www.hzdr.de/publications/Publ-28654
Publ.-Id: 28654


On the magnetocaloric properties of Heusler compounds

Gottschall, T.

  • Invited lecture (Conferences)
    DPG Frühjahrstagung, 11.-16.03.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28653
Publ.-Id: 28653


Temporal evolution of dissolution kinetics of polycrystalline calcite

Bollermann, T.; Fischer, C.

The variability in crystal surface reactivity under identical chemical conditions is responsible for a significant intrinsic reaction rate variation. Such variability is quantified using rate maps of reacting surfaces and rate spectra as a statistical concept. In this study, we show the existence and the temporal variability of multiple dissolution rate contributors that combine to an overall rate of dissolving polycrystalline calcite. At least three different high rate contributors control the overall dissolution rate and show no steady state behavior over a reaction period of 10 hours. We conclude that the data about spatial and temporal rate evolution combined with information about crystal size, orientation, and grain boundaries provide constraints for the prediction of porosity pattern in polycrystalline materials. We discuss the density and distribution of surface kink sites as the critical parameter controlling the observed rate variability.

Keywords: Crystal dissolution; Interferometry; Rate spectra; Rate contributor; Surface kink sites

Permalink: https://www.hzdr.de/publications/Publ-28652
Publ.-Id: 28652


Welche (globale) Recycling-Infrastruktur braucht eine Circular Economy?

Reuter, M. A.

Recycling forms the heart of the Circular Economy (CE) system. Ultimately all products will have to be recycled at their End-of-Life (EoL). Maximizing the recovery of materials and also especially strategic elements from EoL products requires a deep understanding of the fundamental limits and the dynamics of the evolving system, thus an adaptive processing and metallurgical infrastructure is critical to recover all metals and materials. Paramount is the quantification of the “mineralogy”, the complex and interlinked composition of products, to trace and quantify specifically all the losses of materials, metals, alloys, etc. due to thermodynamic and other non-linear interactions. We named this product centric recycling. The recycling potential and performance must be quantified and demonstrated for products, collection systems, waste separation and recovery technologies, and material supply. Emphasis is also placed on informing the consumer through iRE i.e. informing Resource Efficiency in an easy-to-understand way. System Integrated Metal Processing (SIMP) using big-data, multi-sensors, simulation models, metallurgy, etc. links all stakeholders through Circular Economy Engineering (CEE), an important enabler to maximize Resource Efficiency and thus iRE.

Keywords: Metallurgical Recycling infrastructure; circular economy

  • Invited lecture (Conferences)
    NEXUS - Tagung zur Rohstoffgewinnung und -recycling und dem nötigen Energiebedarf, 07.12.2018, Stuttgart, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28651
Publ.-Id: 28651


Robust optimierte intensitäts-modulierte Protonentherapie mit simultan integriertem Boost reduziert die periphere Dosis im Normalgewebe bei Patienten mit nicht-metastasiertem Pankreaskarzinom

Stefanowicz, S.; Zschaeck, S.; Troost, E. G. C.

Fragestellung
Für Patienten mit einem grenzwertig resektablen oder irresektablen, lokal fortgeschrittenen, nicht metastasierten Pankreaskarzinom (LAPC) sind die neoadjuvante oder primäre Radiochemotherapie neben der neoadjuvanten/primären Chemotherapie Behandlungsoptionen. Aufgrund der angrenzenden, strahlensensitiven Risikoorgane (OAR) und der dadurch limitierten Dosisverschreibung ist die durch die Strahlentherapie erzielte lokale Kontrolle derzeit unzureichend. Eine simultane Bestrahlung des elektiven Volumens mit der aktuellen Standarddosis und eines simultan integrierten, dosisintensivierten Boosts (SIB) auf das Tumorvolumen (GTV) könnte den Therapieerfolg zukünftig verbessern. In dieser in-silico Bestrahlungsplanungsstudie wurde unter Anwendung eines dosiseskalierten SIBs die robust optimierte intensitäts-modulierte Protonentherapie (IMPT) mit der photonen-basierten, volumenmodulierte Strahlentherapie (VMAT) dosimetrisch verglichen.

Methodik
Für fünf Patienten mit einem LAPC wurden je ein robust multi-field optimierter IMPT und ein VMAT Bestrahlungsplan auf frei-geatmeten Bestrahlungsplanungs-CTs in der Bestrahlungsplanungssoftware RayStation generiert. Für die VMAT Pläne wurde eine Dosisabdeckung von mindestens 95% des GTVs (Boost) bzw. des elektiven Planungszielvolumens (PTV=CTV+5mm) mit im Minimum 95% der verschriebene Dosis von 66Gy bzw. 51Gy vorgesehen (D95%≥95%). Eine Dosis von 107% in 2% des Volumens sollte nicht überschritten werden (D2%≤107%). Aufgrund der robusten Optimierung mit Unsicherheitsparametern von 5mm (Positionierung) und 3.5% (Reichweite) wurden bei der IMPT die entsprechenden Dosen (RBE) auf das GTV bzw. CTV verschrieben. Die Dosisgrenzwerte der OARs richteten sich nach lokalen und QUANTEC Vorgaben. Jeder Bestrahlungsplan wurde dosimetrisch ausgewertet, und die Ergebnisse miteinander verglichen.

Ergebnis
Alle Bestrahlungspläne erreichten die verschriebenen Dosen. Aufgrund der an das Zielvolumen angrenzenden oder überlappende OARs Leber, Darm und Magen wurde bei diesen Organen in allen Bestrahlungsplänen mindestens ein Dosisgrenzwert überschritten. Während die VMAT-Technik das Magen-Volumen, welches eine Dosis von 50Gy erlangte (V50Gy), reduzierte (Median V50Gy: VMAT 1.2cm3 vs. IMPT 4.5cm3), zeigte die IMPT eine geringere Dosis in den übrigen Organen, z.B. Leber (Median V30Gy: VMAT 93.6cm3 vs. IMPT 39.2cm3). Darüber hinaus wurde durch die IMPT die periphere Dosis außerhalb des CTVs (V20Gy) im umliegenden Normalgewebe erheblich verringert (Median V20Gy: VMAT 1483.4cm3 vs. IMPT 756.2cm3).

Schlussfolgerung
Unter Vernachlässigung der inter- und intrafraktionellen Organbewegung ist die Dosiseskalation mit SIB sowohl für robust optimierte IMPT- als auch VMAT-Technik anwendbar. Im Vergleich zur VMAT reduziert die IMPT die Dosis in den umliegenden Geweben. Bedingt durch die robuste Optimierung, erhöht die IMPT allerdings die V50Gy für mit dem Zielvolumen überlappende OARs. Weitere Patienten werden in die Studie eingeschlossen.

  • Lecture (Conference)
    25. Jahrestagung der DEGRO, 13.-16.06.2019, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28650
Publ.-Id: 28650


Tarnkappen-Technologie für leuchtende Nanopartikeln

Stephan, H.; Zarschler, K.

Aufgrund ihrer außergewöhnlichen Eigenschaften gewinnen Nanomaterialien zunehmend an Bedeutung für medizinische Anwendungen. Insbesondere sehr kleine Nanomaterialien mit einer Größe < 10 nm können als ideale Transportvehikel betrachtet werden, weil sie über den Blutkreislauf im Körper überall hin gelangen können. Eine spezifische Tumoranreicherung kann durch eine entsprechende Oberflächengestaltung der Nanoteilchen erreicht werden und ihre intrinsischen Eigenschaften ermöglichen deren Einsatz für die nichtinvasive Bildgebung. In diesem Zusammenhang gewinnen sogenannte Upconverting Nanoparticles (UCNPs) - „aufwärtskonvertierende“ Nanoteilchen - an Bedeutung, weil sie u.a. eine intensive Fluoreszenz aufweisen und damit sehr gut in biologischen Systemen detektierbar sind. Bisher ist allerdings nur wenig über das Verhalten von derartigen anorganischen Nanoteilchen in einer komplexen biologischen Umgebung bekannt. Ein erfolgreicher Einsatz in der Medizin scheitert gegenwärtig u.a. an einer unzureichenden In-Vitro- und In-Vivo-Stabilität sowie einer geringen Spezifität der eingesetzten Materialien.

  • Open Access Logo GIT Labor-Fachzeitschrift (2019)8, 55-57

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Permalink: https://www.hzdr.de/publications/Publ-28649
Publ.-Id: 28649


Helmholtz-Institut Freiberg für Ressourcentechnologie: Vorstellung des HIF, Forschung und neues Technikum

Kelly, N.; Recksiek, V.; Scharf, C.

Helmholtz-Institut Freiberg für Ressourcentechnologie: Vorstellung des HIF, Forschung und neues Technikum

  • Lecture (Conference)
    34. Arbeitskreis Magnesiumrecycling, 19.04.2018, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28648
Publ.-Id: 28648


Überführung der Kupfer-Eisen-Trennung vom Becherglas- in den Pilotmaßstab

Rädecker, P.; Scharf, C.

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

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Extraktion & Rohstoffe, 12.03.2018, Frankfurt/Main, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28647
Publ.-Id: 28647


Zur selektiven Flüssig-Flüssig-Extraktion von Oxoanionen aus alkalischen Lösungen

Kelly, N.; Mansel, A.; O'Toole, N.; Scharf, C.

Europa steht vor der Herausforderung, eine gesicherte Versorgung von Metallen wie Chrom, Vanadium, Niob oder Molybdän zu gewährleisten, welche eine wichtige Rolle hinsichtlich der Wettbewerbsfähigkeit im Fertigungssektor und bei den Innovationen im Hochtechnologiebereich spielen. Gleichzeitig sind solche Metalle in großen Mengen in Sekundärressourcen gebunden, wo ihr eigentlicher Wert nicht voll ausgenutzt werden kann. Das Verfahren der Solventextraktion stellt dabei eine vielversprechende Methode da, um diese Metalle aus zuvor erhaltenen Laugungslösungen selektiv zurückzugewinnen.
Der vorliegende Beitrag beschäftigt sich mit der Untersuchung der Extraktionseigenschaften von kommerziell erhältlichen Extraktionsmitteln wie Aliquat 336 gegenüber den gebildeten Oxoanionen von Chrom, Vanadium, Molybdän und Niob. Detaillierte Studien zum Einfluss der Parameter pH-Wert (Abb.1), Kontaktzeit und Volumenverhältnis der beiden Phasen sowie die Rolle der eingesetzten Modifier bzw. zusätzlicher Extraktionsmittel oder anwesender Anionen (Abb. 2) werden näher diskutiert.

  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppe Extraktion & Rohstoffe, 12.03.2018, Frankfurt/Main, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28646
Publ.-Id: 28646


Heteropolynuclear Cu(II)/Ln(III) complexes of hexadentate Schiff bases: Syntheses, structures and solution studies

Kelly, N.; Doert, T.; Gloe, K.; Weigand, J. J.; Gloe, K.

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

  • Invited lecture (Conferences)
    The 10th International Symposium on Nano & Supramolecular Chemistry, 12.07.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28645
Publ.-Id: 28645


Tuning Ferromagnetic Resonance via Disorder/Order Interfaces

Schneider, T.; Lenz, K.; Semisalova, A.; Gollwitzer, J.; Heitler-Klevans, J.; Potzger, K.; Fassbender, J.; Lindner, J.; Bali, R.

Ferromagnetic resonance of a thin film alloy has been tuned by inducing lateral interfaces between layers differing in their lattice ordering and magnetic properties. We show that the resonance lines at 10 GHz are shifted by 284 mT and 35 mT, for fields applied perpendicular-to-plane and in-plane, respectively. The resonance line-shift occurs over a broad frequency range, and is driven by strain relaxation due to the increasing magnetic layer thickness. A finer anomalous line shift occurs as the A2/B2 interface approaches the film/substrate interface prior to being removed from the film. The A2 structure can be re-annealed to B2 order, implying that disorder/order interface modification can provide a path for reversibly encoding resonant properties in alloy thin films.

Keywords: Interface effects; Ferromagnetic resonance; Disorder/Order interfaces

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-28644
Publ.-Id: 28644


Heterodinuclear Metal Complexes of Multifunctional Diimine and Diamine Ligands in Synergistic Extraction

Kelly, N.; Gloe, K.

Heterodinuclear Metal Complexes of Multifunctional Diimine and Diamine Ligands in Synergistic Extraction

  • Invited lecture (Conferences)
    5th International Conference on Methods and Materials for Separation Processes "Separation Science - Theory and Practice", 27.08.2018, Kudowa-Zdroj, Polen

Permalink: https://www.hzdr.de/publications/Publ-28643
Publ.-Id: 28643


Antimonite complexation with thiol and carboxyl/phenol groups of particulate organic matter

Besold, J.; Kumar, N.; Scheinost, A. C.; Lezama Pacheco, J.; Fendorf, S.; Planer-Friedrich, B.

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

Keywords: antimonite; peat; thiol; carboxylate; EXAFS; XANES

Permalink: https://www.hzdr.de/publications/Publ-28642
Publ.-Id: 28642


Combining hyperspectral and geomagnetic drone- borne data for non-invasive mineral exploration.

Jackisch, R.; Madriz, Y.; Zimmermann, R.; Saartenoja, A.; Pirttijarvi, M.; Salmirinne, H.; Jylaenki, J.; Heincke, B.; Gloaguen, R.

Combining hyperspectral and geomagnetic and drone- borne data for non-invasive mineral exploration.

Keywords: UAS; hyperspectral; multispectral; mineral exploration; geomagnetic field; fluxgate; magnetometer

  • Invited lecture (Conferences)
    4. ArcHub meeting, 19.-20.11.2018, Copenhagen, Denmark

Permalink: https://www.hzdr.de/publications/Publ-28641
Publ.-Id: 28641


A machine learning technique for drill core hyperspectral data

Contreras, C.; Khodadadzadeh, M.; Tusa, L.; Ghamisi, P.; Gloaguen, R.

  • Invited lecture (Conferences)
    Innovative Technologies in Exploration and Mineral Detection. Practical Workshop, 2nd edition., 12.-13.12.2018, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-28640
Publ.-Id: 28640


Mineral exploration, based on ground and airborne hyperspectral imaging

Gloaguen, R.; Kirsch, M.; Zimmermann, R.; Lorenz, S.; Booysen, R.; Tusa, L.; Brazzo, N.; Unger, G.; Herrmann, E.

Mineral exploration, based on ground and airborne hyperspectral imaging

Keywords: UAS; drone; hyperspectral; magnetic; drill core; outcrop sensing

  • Invited lecture (Conferences)
    Practical workshop on Innovative technologies in exploration and mineral detection, 12.-14.12.2017, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-28639
Publ.-Id: 28639


A novel approach combining geomagnetic and hyperspectral drone-borne data. Advances in remote sensing based mineral exploration and environmental monitoring.

Jackisch, R.; Zimmermann, R.; Lorenz, S.; Saartenoja, A.; Pirttijärvi, M.; Gloaguen, R.

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

Keywords: UAS; hyperspectral; remote sensing; drone; magnetic; fluxgate

  • Lecture (Conference)
    Resources for Future Generations - RFG, 16.-21.06.2018, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-28638
Publ.-Id: 28638


Seltene Erden – Woher sie kommen und wie wir sie gewinnen

Möckel, R.

Wie und wo kommen die Seltenen Erden vor und wie werden sie gewonnen? Die Seltenen Erden sind gar nicht so selten, wie ihr Name vielleicht vermuten lässt. Trotzdem sind die Gewinnung und die damit verbundenen Risiken nicht zu unterschätzen. Der Vortrag gibt einen Einblick in die Geologie der Seltenen Erden, moderne Konzepte und Entwicklungen für eine künftig sichere Versorgung mit den begehrten Metallen sowie diesbezüglich aktuelle Projekte am Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF), das zum Helmholtz-Zentrum Dresden-Rossendorf gehört.

Keywords: seltene Erden; rare earth elements; Seltenerdelemente

  • Lecture (others)
    Dresdner Seniorenakademie Wissenschaft und Kunst, 10.01.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28637
Publ.-Id: 28637


Chiral Skyrmion and Skyrmionium States Engineered by the Gradient of Curvature

Pylypovskyi, O. V.; Makarov, D.; Kravchuk, V. P.; Gaididei, Y.; Saxena, A.; Sheka, D. D.

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

Permalink: https://www.hzdr.de/publications/Publ-28636
Publ.-Id: 28636


Predictive Geometallurgy: The Role of SEM Based Automated Mineralogy and Statistical Assesment for Mineral Processing

Birtel, S.; Büttner, P.; Bachmann, K.; Kern, M.; Gutzmer, J.

SEM-based image analyses is widely used as major analytical tool to improve the recovery of those constituents (ore minerals) that contain the major products (metals) of existing or planned mining operations and processing plants. Here three very different case studies are presented where SEM based automated mineralogical and microstructural data is combined with complementary analytical data and statistically assessed in order to predict the material behaviour during mineral processing. This approach is applied (1) on the recovery of Sn from a historic flotation tailings storage facility; (2) on by-product recovery from a chromite ore deposit; and (3) on simulated sensor based sorting. The studies were performed by interdisciplinary teams in resource characterization, minerals processing and statistical modelling.

Keywords: SEM-based image analysis; MLA; statistical assesment; geometallury

  • Invited lecture (Conferences)
    Conference in Minerals Engineering 2019, 05.-06.02.2019, Luleå, Sweden
  • Contribution to proceedings
    Conference in Minerals Engineering 2019, 05.-06.02.2019, Luleå, Sweden
    Conference in Minerals Engineering, Luleå: LTU

Permalink: https://www.hzdr.de/publications/Publ-28635
Publ.-Id: 28635


Improved accuracy of prompt-gamma-based range verification system enabling validation of CT-based stopping-power prediction

Berthold, J.; Khamfongkhruea, C.; Petzoldt, J.; Thiele, J.; Hölscher, T.; Wohlfahrt, P.; Pausch, G.; Janssens, G.; Smeets, J.; Richter, C.

Objective:
To improve the accuracy of range verification with prompt-gamma-ray imaging (PGI), enabling the validation of CT-based stopping-power prediction in patients.
Material & Methods:
A PGI-slit-camera system was modified to enhance its positioning accuracy, now using a floor-based docking station. The camera position is calibrated with orthogonal X-rays and its reproducibility was validated with X-ray measurements at two different days with ten repositioning iterations each. To determine the PGI simulation accuracy, the camera position derived with the X-Ray system and PGI-based range shift determination in a PMMA phantom (measured vs. simulated PGI profiles) was correlated.
Subsequently, the PGI system was clinically applied to monitor absolute proton ranges for a 1.5Gy field during eight fractions of a hypo-fractionated prostate-cancer treatment using pencil beam scanning (Fig.1). For all monitored fractions, in-room control CT scans were acquired in treatment position, enabling PGI-based range analysis for the actual patient anatomy.
Results:
The reproducibility of the camera position in beam direction was ±0.55mm (1σ) over different days. A 1.1mm offset in absolute range determination was found. It can be directly identified as simulation accuracy and is corrected in subsequent clinical application. The overall PGI range measurement uncertainty of about 2mm (averaging over multiple spots for global-shift determination) is well below the range prediction uncertainty (3.5%∙Range+2mm). Evaluation of the clinical slit-camera application and the verification of the applied stopping-power prediction using dual-energy CT is ongoing.
Conclusion:
The accuracy of PGI-based range verification was improved to enable the verification of CT-based stopping-power prediction in patients, potentially allowing for a future reduction of currently used range uncertainties.

  • Lecture (Conference)
    PTCOG58 - 58th Annual Conference of the Particle Therapy Co-operative Group, 10.-15.06.2019, Manchester, Großbritannien

Permalink: https://www.hzdr.de/publications/Publ-28634
Publ.-Id: 28634


Dual-energy computed tomography improves delineation in primary brain-tumor patients

Wohlfahrt, P.; Agolli, L.; Krause, M.; Pilz, K.; Richter, C.; Troost, E.

Purpose/Objective:
Dual-energy CT (DECT) improves the accuracy in proton therapy compared to single-energy CT (SECT). Since delineation of tumors and organs-at-risk (OARs) is gaining importance, we assessed whether DECT reduces the intra- and inter-observer delineation variability.
Material/Methods:
Two cohorts of 10 primary brain-tumor patients (adjuvant radio(chemo)therapy) each, receiving either 120kVp SECT or 80/140kVp DECT with identical dose, were evaluated. Four different pseudo-monoenergetic CT (MonoCT) datasets, representing several contrasts, were derived from DECT. Three radiation oncologists delineated the postoperative tumor bed volume (TBV) and several OARs. Delineations on SECT datasets were repeated once to assess intra-observer variability. Finally, delineations were performed on T1/T2-weighted MR scans as clinical reference.
The contour conformity was quantified by Jaccard index (JI) and Hausdorff distance (HD) between the contour intersection and union (Fig.1).
Results:
The median inter-observer TBV conformity (Fig.2A) was almost independent from CT acquisition (HD=6-9mm/JI=61-66%) and comparable to MR (HD=6-7mm/JI = 66-67%). The consistency of brainstem contours (Fig.2B) was best at the lowest energy (median HD=2.8mm/JI=81%). The conformity of parotid glands (Fig.2C) gained slightly from higher energies (0.6mm median HD reduction, 1% JI increase) and led to better results as MR. Smaller inter-observer variations were mostly achieved using the most suitable MonoCT instead of SECT.
The intra-observer TBV variability did not depend on clinical experience. However, less-experienced clinicians are more affected by different tissue contrasts (Fig.2D).
Conclusion:
For primary brain-tumor patients, DECT-derived MonoCT datasets improve intra- and inter-observer delineation conformity compared to SECT. Moreover, they in part led to similar or better results as the gold standard MR.

  • Lecture (Conference)
    PTCOG58 - 58th Annual Conference of the Particle Therapy Co-operative Group, 10.-15.06.2019, Manchester, Großbritannien

Permalink: https://www.hzdr.de/publications/Publ-28633
Publ.-Id: 28633


Chemistry first, Accelerator Mass Spectrometry (AMS) second

Merchel, S.; Rugel, G.; Dreams-Users; Dreams-Friends

Accelerator mass spectrometry (AMS) is the most sensitive analytical method to measure long-lived radionuclides. The detection limits are generally several orders of magnitude better, i.e. as low as 10-16 (radionuclide/stable nuclide), than any other mass spectrometry or decay counting method. AMS needs smaller sample sizes and measurements are finished within a few minutes to hours; though after performing chemical separation of the radionuclide from the sample matrix (ice, snow, rain, ground water, marine sediments, soil, meteorites, deep-sea nodules, lava, rocks). Hence, AMS is right from the start, from sample taking over chemistry and measurements to data interpretation, true interdisciplinary research. Users at the DREAMS (DREsden AMS) facility (www.dresden-ams.de) apply AMS to most diverse projects from astrophysics to Earthquake studies.

Keywords: AMS; radionuclide

  • Invited lecture (Conferences)
    52nd annual conference of the German Society for Mass Spectrometry (DGMS), 10.-13.03.2019, Rostock, Deutschland

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-28632
Publ.-Id: 28632


Drastic Fermi-surface reconstruction in Nd-doped CeCoIn5

Green, E.

  • Invited lecture (Conferences)
    12th International Conference on Research in High Magnetic Fields, 24.-28.06.2018, Santa Fe, USA

Permalink: https://www.hzdr.de/publications/Publ-28631
Publ.-Id: 28631


A novel multicaloric cooling cycle that exploits thermal hysteresis

Gottschall, T.

  • Invited lecture (Conferences)
    9th JEMS Conference 2018 (Joint European Magnetic Symposia), 03.-07.09.2018, Mainz, Germany
  • Invited lecture (Conferences)
    Thermag VIII, 16.-20.09.2018, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-28630
Publ.-Id: 28630


Glacial evolution of the Pamir mountains: insights from geomorphology and cosmogenic radionuclide dating

Stübner, K.; Bookhagen, B.; Merchel, S.; Rugel, G.; Aminov, J.

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

Keywords: ANS; TCN; dating; CRN; glacier

  • Poster
    European Geosciences Union (EGU) General Assembly 2019, 07.-12.04.2019, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-28629
Publ.-Id: 28629


Solid oxygon in ultrahigh magnetic fields

Nomura, T.

  • Invited lecture (Conferences)
    CC2018 - 12th International Conference on Cryocrystals and Quantum Crystals, 26.-31.08.2018, Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-28628
Publ.-Id: 28628


Body size-dependent energy storage causes Kleiber’s law scaling of the metabolic rate in planarians

Thommen, A.; Werner, S.; Frank, O.; Philipp, J.; Knittelfelder, O.; Quek, Y.; Fahmy, K.; Shevchenko, A.; Friedrich, B. M.; Jülicher, F.; Rink, J. C.

Kleiber’s law, or the 3/4 -power law scaling of the metabolic rate with body mass, is considered one of the few quantitative laws in biology, yet its physiological basis remains unknown. Here, we report Kleiber’s law scaling in the planarian Schmidtea mediterranea. Its reversible and life history-independent changes in adult body mass over 3 orders of magnitude reveal that Kleiber’s law does not emerge from the size-dependent decrease in cellular metabolic rate, but from a size-dependent increase in mass per cell. Through a combination of experiment and theoretical analysis of the organismal energy balance, we further show that the mass allometry is caused by body size dependent energy storage. Our results reveal the physiological origins of Kleiber’s law in planarians and have general implications for understanding a fundamental scaling law in biology.

Keywords: calorimetry; metabolism; growth

Permalink: https://www.hzdr.de/publications/Publ-28627
Publ.-Id: 28627


Surface Exposure Dating on Waterfalls to Reconstruct the Landscape Evolution of South Central Africa

Olivotos, S.; Niedermann, S.; Mouslopoulou, V.; Merchel, S.; Cotterill, F.; Flugel, T.; Gärtner, A.; Rugel, G.; Scharf, A.; Bookhagen, B.

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

Keywords: AMS; DNA; geomorphology; TCN; noble gas; dating

  • Poster
    PhD Seminar Geosciences University Potsdam, 25.01.2019, Golm, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28626
Publ.-Id: 28626


Static and dynamic properties of modulated phases in Co/Pt multilayers and their dependence on the total magnetic thickness

Fallarino, L.; Oelschlägel, A.; Arregi, J. A.; Bashkatov, A.; Stienen, S.; Lindner, J.; Gallardo, R.; Landeros, P.; Schneider, T.; Chesnel, K.; Lenz, K.; Hellwig, O.

Ferromagnetic (FM) / non-magnetic multilayers with perpendicular magnetic anisotropy provide an efficient route for controlling magnetism, with highly tunable magnetic properties by changing the individual layer thicknesses or the number of repetitions [1]. During the past years, an extensive work effort has led to an apparently complete understanding of those structures. The majority of these studies, though, utilized very thin FM layers since an in-plane reorientation of the magnetization is expected for larger individual thicknesses. However, for sufficiently thick individual FM layers, the system undergoes a second transition back to out-of-plane orientation [2]. Consequently, we present a study of magnetic properties of [Co(t )/Pt(0.7nm)] multilayers as a function of t thicknesses and Co/Pt bilayer repetitions N. Studying in more detail the influence of the magnetic history on the remanent domain pattern, we determine the range of material properties and magnetic fields where, instead of the typical maze-like domains, a lattice of bubbles is stabilized with extraordinary high density, as depicted in Fig. 1 [3]. The dynamic response of such modulations of the ferromagnetic order parameter is further investigated by ferromagnetic resonance spectroscopy (FMR). We find that the observed FMR modes have a direct correlation to the magnetic phase of the samples and its evolution under the application of a magnetic field, as depicted in Fig.2. Using both micromagnetic modeling and analytical calculations, we are able to quantitatively reproduce our experimental observations, which suggest the existence of localized spin-wave and FMR modes that are dependent on the modulation period as well as on the type of modulation itself [4]. Lastly, we show that such modulations resemble magnonic crystals, where tuning of the band-gap is enabled by the specific magnetic field history.
References: [1] M. T. Johnson et al. Rep. Prog. Phys. 59, 1409 (1996).
[2] L. Fallarino et al. Phys. Rev. B 94, 064408 (2016).
[3] K. Chesnel et al. Phys. Rev. B 98, 224404 (2018).
[4] L. Fallarino et al., accepted in Phys. Rev. B (03/01/2019).

Keywords: Ferromagnetic multilayers; PMA; FMR; VSM; magnetic domains; not collinear spin textures

  • Lecture (Conference)
    2019 Joint MMM-Intermag, 14.-18.01.2019, Washington D.C., United states of America

Permalink: https://www.hzdr.de/publications/Publ-28625
Publ.-Id: 28625


Controlled coexcitation of direct and indirect ultrafast demagnetization in Co/Pd multilayers with large perpendicular magnetic anisotropy

Pan, S.; Hellwig, O.; Barman, A.

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

Keywords: ultrafast demagnetization; Co/Pd multilayers

Permalink: https://www.hzdr.de/publications/Publ-28624
Publ.-Id: 28624


Rohstoffe für die Energiewende: Systemische Effekte

van den Boogaart, K. G.; Weigelt, A.

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

Keywords: Energiewende; Rohstoffwirtschaft

  • Lecture (others)
    Arbeitsgruppentreffen Topic 4, Energiesysteme 2050, 16.-17.01.2019, Frankfurt, Deutschlad

Permalink: https://www.hzdr.de/publications/Publ-28623
Publ.-Id: 28623


Ion-trap analog of particle creation in cosmology

Fey, C.; Schätz, T.; Schützhold, R.

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

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Permalink: https://www.hzdr.de/publications/Publ-28622
Publ.-Id: 28622


Nanoscale Imaging of Antiferromagnetic Order using Single-spin Magnetometry

Shields, B.; Appel, P.; Kosub, T.; Hedrich, N.; Fassbender, J.; Huebner, R.; Makarov, D.; Maletinsky, P.

Nitrogen vacancy microscopy is used to detect tiny magnetic stray fields from antiferromagnetic Cr2O3 thin films. Domains and domain dynamics are reported.

  • Poster
    International Conference on Magnetism, 15.-20.7.2018, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-28621
Publ.-Id: 28621


Granularity Effects in Antiferromagnetic Spintronics Devices

Kosub, T.; Appel, P.; Shields, B.; Maletinsky, P.; Hübner, R.; Lindner, J.; Fassbender, J.; Makarov, D.

thin films of antiferromagnets are notably different than bulk crystals.

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 11.-16.03.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28620
Publ.-Id: 28620


Discrete worldline instantons

Schneider, C.; Torgrimsson, G.; Schützhold, R.

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

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Permalink: https://www.hzdr.de/publications/Publ-28619
Publ.-Id: 28619


Interaction of a Bose-Einstein condensate with a gravitational wave

Schützhold, R.

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

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Permalink: https://www.hzdr.de/publications/Publ-28618
Publ.-Id: 28618


The CD98 heavy chain is a marker and regulator of head and neck squamous cell carcinoma radiosensitivity

Digomann, D.; Kurth, I.; Tyutyunnykova, A.; Chen, O.; Löck, S.; Gorodetska, I.; Peitzsch, C.; Skvortsova, I.; Negro, G.; Aschenbrenner, B.; Eisenhofer, G.; Richter, S.; Heiden, S.; Porrmann, J.; Klink, B.; Schwager, C.; Dowle, A.; Hein, L.; Kunz-Schughart, L.; Abdollahi, A.; Lohaus, F.; Krause, M.; Baumann, M.; Linge, A.; Dubrovska, A.

Purpose: The heavy chain of the CD98 protein (CD98hc) is encoded by the SLC3A2 gene. Together with the light subunit LAT1, CD98hc constitutes a heterodimeric transmembrane amino acid transporter. High SLC3A2 mRNA expression levels are associated with poor prognosis in patients with head and neck squamous cell carcinoma (HNSCC) treated with radiochemotherapy. Little is known regarding the CD98hc protein mediated molecular mechanisms of tumor radioresistance.
Experimental Design: CD98hc protein expression levels were correlated with corresponding tumor control dose 50 (TCD50) in HNSCC xenograft models. Expression levels of CD98hc and LAT1 in HNSCC cells were modulated by siRNA or CRISPR/Cas9 gene editing. HNSCC cell phenotypes were characterized by transcription profiling, plasma membrane proteomics, metabolic analysis and signaling pathway activation.
Expression levels of CD98hc and LAT1 proteins were examined by immunohistochemical analysis of tumor tissues from patients with locally advanced HNSCC treated with primary radiochemotherapy (RCTx). Primary endpoint was locoregional tumor control (LRC).
Results: High expression levels of CD98hc resulted in an increase in mTOR pathway activation, amino acid metabolism and DNA repair as well as downregulation of oxidative stress and autophagy. High expression levels of CD98hc and LAT1 proteins were significantly correlated and associated with an increase in radioresistance in HNSCC in vitro and in vivo models. High expression of both proteins identified poor prognosis subgroup in patients with locally advanced HNSCC after RCTx.

Keywords: radiotherapy; radiosensitivity; CD98; SLC3A2; LAT1; head and neck squamous cell carcinoma; HNSCC

Permalink: https://www.hzdr.de/publications/Publ-28617
Publ.-Id: 28617


Small samples, nearly no chemistry and a big accelerator: Beryllium‑7 measurements as low as 1 mBq

Merchel, S.; Bemmerer, D.; Querfeld, R.; Steinhauser, G.; Rugel, G.; Scharf, A.; Tiessen, C.

Introduction
Beryllium-7 (T1/2 = 53.22 d), mainly measured via gamma-spectrometry, is used as a (natural) radiotracer for educational and scientific purposes. For samples with lower activities (<0.1 Bq) and especially for natural samples containing both ⁷Be and the longer-lived ¹⁰Be (T1/2 = 1.387 Ma), accelerator mass spectrometry (AMS) is the method-of-choice. Here, we demonstrate that ⁷Be- and ¹⁰Be-AMS can be performed at the Dresden AMS facility (DREAMS) [1,2] on the same chemically prepared BeO from rain water samples collected in Germany.

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

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

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

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

References
[1] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 (2013) 5-10.
[2] G. Rugel et al., Nucl. Instr. Meth. B 370 (2016) 94-100.
[3] C. Tiessen et al., Accelerator mass spectrometry (AMS) for beryllium-7 measurements in smallest rainwater samples, JRNCh, 2018, doi: 10.1007/s10967-018-6371-6.

Keywords: AMS; rain

  • Poster
    27th Seminar on Activation Analysis and Gamma Spectrometry (SAAGAS 27), 24.-27.02.2019, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28616
Publ.-Id: 28616


BRCA1 and EZH2 cooperate in regulation of prostate cancer stem cell phenotype

Gorodetska, I.; Lukiyanchuk, V.; Peitzsch, C.; Kozeretska, I.; Dubrovska, A.

Prostate cancer is the second most common malignancy and the sixth leading cause of cancer-related death among men worldwide. Prostate carcinogenesis is driven by the accumulation of genetic and epigenetic aberrations, which regulate cancer cell Transition between a stem- and non-stem-cell state and accelerate tumor evolution. Elevated expression of enhancer of zeste homolog 2 (EZH2) histone methyltransferase, a core member of the Polycomb Repressive Complex 2 (PRC2), results in cancer progression through histone methylation-driven tumor cells de-differentiation. Previous studies demonstrated that Tumor suppressor BRCA1 (breast cancer 1) is a negative regulator of PRC2-dependent H3K27 methylation and that loss of BRCA1 induces population of breast cancer stem cells (CSCs) and enhances aggressiveness of breast tumors. Our recent studies revealed that inhibition of EZH2-mediated histone methylation radiosensitizes prostate CSC population. However, the link between BRCA1 and EZH2 in regulation of prostate CSCs remains elusive. Present study demonstrated that BRCA1 and EZH2 are co-regulated in patients’ tumors and prostate cancer cell lines and cooperate in regulation of CSC phenotype and properties. Knockdown of BRCA1 expression significantly increases the number and the size of tumor spheres. Inhibition of BRCA1 and EZH2 expression leads to enrichment of ALDH (aldehyde dehydrogenase) positive cell population that is, at least partially, attributed to the upregulation of ALDH1A3 protein, whereas treatment with a global histone methylation regulator DZNeP (3-Deazaneplanocin A) abrogates this regulation. We found that EZH2/BRCA1 signaling mechanisms play an important role in the maintenance of prostate CSC properties and may be a promising target for tumor treatment.

Keywords: BRCA1; EZH2; cancer stem cells; prostate cancer; DZNeP

Permalink: https://www.hzdr.de/publications/Publ-28615
Publ.-Id: 28615


BRCA genes: the role in genome stability, cancer stemness and therapy resistance

Gorodetska, I.; Kozeretska, I.; Dubrovska, A.

Carcinogenesis is a multistep process, and tumors frequently harbor multiple mutations regulating genome integrity, cell division and death. The integrity of cellular genome is closely controlled by the mechanisms of DNA damage signaling and DNA repair. The association of breast cancer susceptibility genes BRCA1 and BRCA2 with breast and ovarian cancer development was first demonstrated over 20 years ago. Since then the germline mutations within these genes were associated with genomic instability and increased risk of many other cancer types. Genomic instability is an engine of the oncogenic transformation of non-tumorigenic cells into tumor-initiating cells and further tumor evolution. In this review we discuss the biological functions of BRCA1 and BRCA2 genes and the role of BRCA mutations in tumor initiation, regulation of cancer stemness, therapy resistance and tumor progression.

Keywords: BRCA1; BRCA2; genomic instability; cancer stem cells; cancer treatment

Permalink: https://www.hzdr.de/publications/Publ-28614
Publ.-Id: 28614


Graphene Oxide Functional Nanohybrids with Magnetic Nanoparticles for Improved Vectorization of Doxorubicin to Neuroblastoma Cells

Lerra, L.; Farfalla, A.; Sanz, B.; Cirillo, G.; Vittorio, O.; Voli, F.; Le Grand, M.; Curcio, M.; Pasquale Nicoletta, F.; Dubrovska, A.; Hampel, S.; Iemma, F.; Goya, G.

With the aim to obtain a site-specific doxorubicin (DOX) delivery in neuroblastoma SH-SY5Y cells, we designed an hybrid nanocarrier combining graphene oxide (GO) and magnetic iron oxide nanoparticles (MNPs), acting as core elements, and a curcumin–human serum albumin conjugate as functional coating. The nanohybrid, synthesized by redox reaction between the MNPs@GO system and albumin bioconjugate, consisted of MNPs@GO nanosheets homogeneously coated by the bioconjugate as verified by SEM investigations. Drug release experiments showed a pH-responsive behavior with higher release amounts in acidic (45% at pH 5.0) vs. neutral (28% at pH 7.4) environments. Cell internalization studies proved the presence of nanohybrid inside SH-SY5Y cytoplasm. The improved efficacy obtained in viability assays is given by the synergy of functional coating and MNPs constituting the nanohybrids: while curcumin moieties were able to keep low DOX cytotoxicity levels (at concentrations of 0.44–0.88 µM), the presence of MNPs allowed remote actuation on the nanohybrid by a magnetic field, increasing the dose delivered at the target site.

Keywords: graphene oxide; iron oxide nanoparticles; magnetic targeting; nanohybrids; synergism

Permalink: https://www.hzdr.de/publications/Publ-28613
Publ.-Id: 28613


Subspace Multinomial Logistic Regression Ensemble for Classification of Hyperspectral Images

Khodadadzadeh, M.; Ghamisi, P.; Contreras, C.; Gloaguen, R.

Exploiting multiple complementary classifiers in an ensemble framework has shown to be effective for improving hyperspectral image classification results, especially when the training samples are limited. With a different principle and based on this assumption that hyperspectal feature vectors effectively lie in a low-dimensional subspace, the subspace-based techniques have shown great classification performance. In this work, we propose a new ensemble method for accurate classification of hyperspectral images, which exploits the concept of subspace projection. For this purpose, we extend the subspace multinomial logistic regression classifier (MLRsub) to learn from multiple random subspaces for each class. More specifically, we impose diversity in constructing MLRsub by randomly selecting bootstrap samples from the training set and subsets of the original hyperspectral feature space, which leads to generate different class subspace features. Experimental results, conducted on two real hyperspectral data sets, indicate that the proposed method provides significant classification results in comparison with other state-of-the-art approaches.

Keywords: Hyperspectral images; classification; ensemble-based approaches; subspace multinomial logistic regression; remote sensing

  • Contribution to proceedings
    IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 22.-27.07.2018, Valencia, Spain

Permalink: https://www.hzdr.de/publications/Publ-28612
Publ.-Id: 28612


Tuning of electrocatalytic properties of MoS2 by chalcogenide ion implantation

Luxa, J.; Mazánek, V.; Mackova, A.; Malinsky, P.; Akhmadaliev, S.; Sofer, Z.

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

Keywords: Electrocatalysis; Hydrogen evolution reaction; Ion implantation; MoS2

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-28611
Publ.-Id: 28611


Probing plutonium dioxide nanoparticles with various synchrotron methods

Gerber, E.; Romanchuk, A.; Pidchenko, I.; Hennig, C.; Trigub, A.; Weiss, S.; Scheinost, A.; Rossberg, A.; Kalmykov, S.; Kvashnina, K.

Plutonium is one of the most complicated element among actinides. It can exist in four different oxidation states (III, IV, V, VI) under environmental conditions. Due to the small value of standard electrode potentials among these linked oxidation states plutonium can change its oxidation state easily. Moreover, plutonium may exist in several oxidation states simultaneously, which makes its chemistry even more complex.
It was previously shown that plutonium migrates in colloidal form in the subsurface environment with the distance of several kilometers. It turned out that so called “colloidal Pu(IV) polymers” are in fact aggregates of PuO2 nanoparticles with diameters ~ 2 nm. However, the certain structure and stoichiometry of these colloids, as well as presence of other oxidation states but Pu(IV) is still debated.

This contribution will show results of plutonium oxide nanoparticle studies at the large-scale facility – The European Synchrotron (ESRF) by complementary methods that used X-rays in different regimes to probe the Pu oxide nanoparticles. Samples were prepared by rapid chemical precipitation using precursors in the different oxidation states (Pu(III), Pu(IV), Pu(V) and Pu(VI)). These precursors were obtained by chemical reduction or oxidation of Pu stock solution. The obtained nanoparticles were characterized at the different beamlines at the ESRF. It gives the opportunity to study our samples with various techniques: X-ray diffraction (XRD), pair distribution function analysis (PDF), and several types of spectroscopies: high energy resolution fluorescence detection (HERFD) at L3 and M5-edges, X-ray emission spectroscopy (XES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The applying multifold synchrotron methods benefits to discover features, which may be unclear or even indistinguishable, these approach is also crucial to confirm results, obtained with individual methods.
It was found that small (2 nm) nanoparticles are formed from the Pu(III), Pu(IV), Pu(V) aqueous solutions, with the crystal structure close to PuO2, without any other Pu-O contributions or oxidation states of Pu except Pu(IV).

  • Lecture (Conference)
    RAD 2019 Conference, 10.-14.06.2019, Herceg Novi, Montenegro

Permalink: https://www.hzdr.de/publications/Publ-28610
Publ.-Id: 28610


Subspace clustering algorithms for mineral mapping

Khodadadzadeh, M.; Contreras, C.; Tusa, L.; Gloaguen, R.

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

Keywords: Mineral mapping; drill core; hyperspectral data; subspace clustering; remote sensing

  • Contribution to proceedings
    SPIE Image and Signal Processing for Remote Sensing XXIV, 10.-13.09.2018, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-28609
Publ.-Id: 28609


High-precision image-guided proton irradiation of mouse brain sub-volumes

Suckert, T.; Müller, J.; Beyreuther, E.; Bütof, R.; Dietrich, A.; Gotz, M.; Haase, R.; Schürer, M.; Tillner, F.; Krause, M.; Lühr, A.; von Neubeck, C.

Purpose:
Proton radiotherapy offers the potential to reduce normal tissue toxicity. However, clinical safety margins, range uncertainties and varying relative biological effectiveness (RBE) may result in a critical dose in tumor-surrounding normal tissue. To assess potential adverse effects in preclinical studies, we established stereotactic proton mouse brain irradiation and a cell-based analysis of radiation damage repair.
Material and methods:
A setup to shape a proton beam with 7 mm range in water and 3 mm in diameter was built and dosimetrically characterized. Cone-beam computed tomography (CBCT) and orthogonal X-ray imaging were used to delineate the right hippocampus (target) and to position the mice, respectively. For two mouse strains (C57BL/6 and C3H), brains were irradiated with 4 Gy or 8 Gy and excised after 30 min or 3 h. Brain sections (3 µm) were cut every 100 µm and DNA double-strand break (DSB) repair kinetics was visualized by staining for cell nuclei and H2AX. Imaged sections were analyzed with an automated and validated processing pipeline to provide a quantitative, spatially-resolved damage indicator.
Results:
Twenty mice underwent the treatment workflow including imaging, target delineation, positioning, and irradiation. The analyzed DNA damage pattern clearly visualized the radiation effect and could be mapped onto the measured dose distribution. For all evaluated C3H mice, the proton beam hit the right hippocampus and stopped in the brain. Damage pattern became spatially more extended and diffuse for 8 Gy and 3 h after irradiation, respectively. C57BL/6 mice showed comparable damage distributions, however, with larger spatial variation of the beam alignment relative to the hippocampus.
Conclusion:
We established and biologically validated stereotactic proton irradiation of mouse brains. The clinically-oriented workflow facilitates (back-) translational studies. Geometric accuracy and cell-based assessment enable a biologically and spatially resolved analysis of radiation response and RBE.

Keywords: Relative biological effectiveness (RBE); H2AX; particle therapy; small animal irradiation; normal tissue toxicity

Permalink: https://www.hzdr.de/publications/Publ-28608
Publ.-Id: 28608


Tonic signaling and its effects on lymphopoiesis of CAR-armed hematopoietic stem and progenitor cells

Albert, S.; Koristka, S.; Gerbaulet, A.; Cartellieri, M.; Arndt, C.; Feldmann, A.; Berndt, N.; Loureiro, L.; von Bonin, M.; Ehninger, G.; Eugster, A.; Bonifacio, E.; Bornhäuser, M.; Bachmann, M.; Ehninger, A.

Long-term survival of adoptively transferred chimeric antigen receptor (CAR) T cells is often limited. Transplantation of hematopoietic stem cells (HSCs) transduced to express CARs could help to overcome this problem as CAR-armed HSCs can continuously deliver CAR+ multi-cell lineages (e.g. T cells, NK cells). In dependence on the CAR construct a variable extent of tonic signaling in CAR T cells was reported, thus, effects of CAR-mediated tonic signaling on the hematopoiesis of CAR-armed HSCs is unclear. To assess effects of tonic signaling two CAR constructs were established and analyzed: (i) A signaling CAR inducing a solid antigen-independent tonic signaling termed CAR-28/, and (ii) a non-stimulating control CAR construct lacking intracellular signaling domains termed CAR-Stop. Bone marrow (BM) cells from immunocompetent mice were isolated, purified for HSC-containing Lin-cKit+ (LK) cells or the LK Sca-1+ subpopulation (Lin Sca 1+cKit+, LSK) and transduced with both CAR constructs. Subsequently, modified BM cells were transferred into irradiated mice where they successfully engrafted and differentiated into hematopoietic progenitors. HSCs expressing the CAR-Stop sustained normal hematopoiesis. In contrast, expression of the CAR-28/ led to elimination of mature CAR+ T and B cells suggesting that the CAR-mediated tonic signaling mimics autorecognition via the newly recombined immune receptors in the developing lymphocytes.

Keywords: Chimeric antigen receptors; tonic signaling; HSC transplantation; hematopoiesis; HSC engraftment; immunotherapy; adaptive immune system

Permalink: https://www.hzdr.de/publications/Publ-28607
Publ.-Id: 28607


Multidimensional fluid mixing capabilities of ATHLET 3.1A during an overcooling transient in a generic PWR KONVOI

Diaz Pescador, E.

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

  • Poster
    Workshop of Doctoral Candidates (PhD student seminar), 13.12.2018, Zittau, Germany

Permalink: https://www.hzdr.de/publications/Publ-28606
Publ.-Id: 28606


Integration of drone-borne hyperspectral and geomagnetic data. A combined approach in geologic remote sensing. A test from the Siilinjärvi carbonatite, Finland.

Jackisch, R.; Zimmermann, R.; Lorenz, S.; Saartenoja, A.; Pirttijärvi, M.; Heincke, B.; Gloaguen, R.

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

Keywords: UAS; UAV; remote sensing; mineral exploration; hyperspectral; geomagnetic; fluxgate

Permalink: https://www.hzdr.de/publications/Publ-28605
Publ.-Id: 28605


Investigations on the thermal-hydraulic behavior of a generic PWR KONVOI during a 1% cold leg small-break loss of coolant accident using the system code ATHLET

Diaz Pescador, E.; Schäfer, F.; Wilhelm, P.; Kliem, S.

In the presented paper, a simulation of a small-break loss of coolant accident (SBLOCA) with a 1% break in the cold leg 1 in a generic German PWR KONVOI model is carried out and investigated by means of the thermal-hydraulic system code ATHLET 3.1A. The accident analysis is focused first on a thermal-hydraulic characterization of the SBLOCA, and a subsequent qualitative comparison with the test PKL H1.1. With this aim, in the simulation with ATHLET 3.1A, the nominal plant operational parameters of the generic KONVOI reactor are transposed with the boundary conditions of the test PKL H1.1.
The test PKL H1.1 reproduces a SBLOCA superposed by additional system failures, such as unavailability of the high-pressure safety injection and the automatic secondary-side cool-down. The test was conducted in the framework of the OECD/PKL3 project in the large-scale test facility PKL (“Primärkreislauf”), operated by Framatome Germany, as a counterpart test of LSTF/ROSA SB-CL-32.
The second part of the paper is devoted to the study of the boron dilution into the steam generators, and the subsequent transport and fluid mixing phenomena in the reactor pressure vessel. The results in the simulation, show how the implementation of a 200 K/h cool-down through the steam generators, initiated at a peak cladding temperature (PCT) of 500°C, is able to eventually achieve a long-term safe stable condition, due to the injection of cold water, first from the hydro-accumulators at a pressure of 26 bar, and then the actuation of the low pressure safety injection at a pressure of 10 bar.
This outcome is also observed in the test H1.1. Nevertheless, unlike the results obtained in the test, the implementation of the 200 K/h cool-down during the SBLOCA in the simulation cannot avoid core damage, fact strongly influenced by the initial pressure differences between the KONVOI model and the PKL test facility, being the latter limited by design constraints to a maximum pressure of 50 bar.

Keywords: KONVOI; small-break loss of coolant accident; cool-down procedure; emergency core cooling systems; ATHLET 3.1A

  • Lecture (Conference)
    ICONE 27. 27th International Conference on Nuclear Engineering, 19.-24.05.2019, Ibaraki, Japan
  • Contribution to proceedings
    ICONE 27. 27th International Conference on Nuclear Engineering, 19.-24.05.2019, Ibaraki, Japan, Mechanical Engineering Journal (JSME): The Japan Society of Mechanical Engineers

Permalink: https://www.hzdr.de/publications/Publ-28604
Publ.-Id: 28604


Atomistic Simulations to Design a Room-Temperature Single Electron Transistor

Prüfer, T.; Möller, W.; von Borany, J.; Heinig, K. H.

For future low power-consumption nanoelectronics, a room-temperature single-electron transistor may be configured by placing a small (few nm diam.) Si nanodot in a thin (<10 nm) SiO2 interlayer in Si. This can be achieved by ion-irradiation induced interface mixing, which turns the oxide layer into metastable SiOx, and subsequent high-temperature thermal decomposition which leaves, for a sufficiently small mixed volume, a single Si nanodot in the SiO2 layer. Corresponding ion mixing simulations have been performed using the binary collision approximation (BCA)[1], followed by kinetic Monte-Carlo (KMC) simulations[2] of the decomposition process, with good qualitative agreement with the structures observed in related experiments. Quantitatively, however, the BCA simulation appears to overestimate the mixing effect. This is attributed to the neglect of the positive entropy of mixing of the Si-SiO2 system, i.e. the immiscibility counteracts the collisional mixing by “up-hill diffusion” [3]. Consequently, intermitting KMC diffusion steps have been introduced into the BCA mixing simulation, resulting in an excellent predictive power for the irradiation step of the production process. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.

• [1] W. Möller et al., NIM B, 322, 23–33
• [2] M. Strobel et al., PRB 64, 245422
• [3] B. Liedke et al., NIM B 316 (2013) 56–61

  • Lecture (Conference)
    E-MRS 2018 Fall Meeting, 17.-21.09.2018, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-28603
Publ.-Id: 28603


Si Quantum Dots for Single Electron Transistor: Synthesis, Characterization and Theoretical Comparison

Prüfer, T.; Wolf, D.; Engelmann, H.-J.; Hübner, R.; Bischoff, L.; Hlawacek, G.; Heinig, K.-H.; Facsko, S.; Xu, X.; von Borany, J.

The appearance of quantum effects makes nanoparticles (NPs) more and more important in semiconductor physics and especially in nanoelectronics. One very promising application is the single electron transistor (SET). Common field effect transistors (FET) could be outperformed by SETs in many applications because of their ultra-low power consumption (~100 times). Important for the fabrication of SETs operating at room temperature is the control of position and size of nano dots (<5nm). Our CMOS-compatible approach to manufacture SETs follows a two-step synthesis of NPs: (i) Producing tiny SiOx volumes by ion beam irradiation of ultrathin buried SiO2 layers (<10nm) and (ii) self-organizing single Si nanodots by phase separation during thermal treatment.
Energy-filtered transmission electron microscopy (EFTEM) is an advanced technique for the structural analysis of Si NPs in buried SiO2 layers. Although the NPs in the SiO2 layer superimpose in 2-dimentional projections from cross-sectional TEM samples, we managed to characterize the density and size distribution of the formed nanoclusters using the knowledge of the electron mean free path length to convert the Si-plasmon-loss filtered TEM image into a Si-thickness map. Here we will present the characterization and a comparison with theory to show a significant overestimation of the mixing effect by BCA simulation. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.

  • Lecture (Conference)
    European Materials Research Society Fall Meeting, 17.-21.09.2018, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-28602
Publ.-Id: 28602


A sizeable change in the electronic properties of GaAs via strain engineering in lattice-mismatched core/shell nanowires

Schneider, H.; Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Shan, S.; Fotev, I.; Pashkin, A.; Ghorbani-Asl, M.; Krasheninnikov, A.; Helm, M.; Dimakis, E.

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

Keywords: core/shell III-V semiconductor nanowires; molecular eam epitaxy; MBE; strain; effective mass

  • Poster
    34-th International Conference on the Physics of Semiconductors (ICPS 2018), 29.07.-03.08.2018, Montpellier, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-28601
Publ.-Id: 28601


Squeezing information about ThO2 nanoparticles’ size and shape from high resolution XANES

Amidani, L.; Rossberg, A.; Romanchuk, A.; Plakhova, T.; Kvashnina, K.

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

  • Lecture (Conference)
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-28600
Publ.-Id: 28600


Mineral mapping of drill core hyperspectral data with extreme learning machines

Contreras, C.; Khodadadzadeh, M.; Ghamisi, P.; Gloaguen, R.

Hyperspectral scanners are increasingly being used in the mining industry as a non-destructive and non-invasive technique to efficiently map minerals in drill core samples. Hyperspectral data allows the characterization of different mineral assemblages, structural features and alteration patterns based on reflectance spectrum profiles. Traditional methods to analysis drill core hyperspectral data include the use of reference spectral libraries by visual analysis or a well established software. However, although these approaches produce good results, they are time-consuming and prone to errors. Therefore, in this paper, we take advantage of the latest and advanced machine learning techniques proposed in different scientific fields and explore the use of extreme learning machines (ELM) to map minerals in drill core hyperspectral data. This is a supervised technique that provides fast and automatic means to characterize hyperspectral data. To be able to implement this technique, a reference map was generated from the drill core hyperspectral data. The obtained results indicate that ELM can successfully map minerals in drill core hyperspectral data producing better quantitative and qualitative results than a typical RF classifier.

Keywords: Drill cores; hyperspectral data; mineral mapping; extreme learning machine; random forest

  • Open Access Logo Contribution to proceedings
    2019 IEEE International Geoscience and Remote Sensing Symposium., 28.07.-02.08.2019, Yokohama, Japan
    IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-28599
Publ.-Id: 28599


The Structural and Compositional Changes of Graphene Oxide Induced by Irradiation With 500 keV Helium and Gallium Ions

Malinsky, P.; Macková, A.; Florianová, M.; Cutroneo, M.; Hnatowicz, V.; Bohácová, M.; Szokölová, K.; Böttger, R.; Sofer, Z.

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

Keywords: graphene oxide; ion Irradiation; Helium; Gallium; structure; composition

Permalink: https://www.hzdr.de/publications/Publ-28598
Publ.-Id: 28598


A Machine Learning Technique for Drill Core Hyperspectral Data analysis

Contreras, C.; Khodadadzadeh, M.; Tusa, L.; Ghamisi, P.; Gloaguen, R.

Hyperspectral data are increasingly being used to map minerals in drill core samples allowing a non-invasive and non-destructive characterization of the mineral assemblages, and therefore, the mineralogical composition of a system, its variability, and structural features. The analysis of drill core hyperspectral data is traditionally carried out by a visual interpretation of the spectra and a comparison with reference libraries using spectral similarity measures. Although this approach produces good results it is time-consuming and subjective. In this work, we introduce, for the first time, an innovative automatic mineral mapping technique for drill core hyperspectral data by using a machine learning approach. More specifically, we propose to exploit detailed information coming from the Scanning Electron Microscopy (SEM)-based Mineral Liberation Analysis (MLA) to train a supervised classifier. For the extraction of input features, a traditional technique is explored, i.e., Principal Component Analysis (PCA). For the classification step, we suggest to use Random Forest (RF) because of its significant performance when there are few training samples available. Experimental results conducted on a VNIR-SWIR drill core hyperspectral dataset, show accurate classification results.

Keywords: Drill core hyperspectral data; Mineral Liberation Analysis; Random Forest; mineral mapping

  • Open Access Logo Contribution to proceedings
    9th Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing, 23.-26.09.2018, Amsterdam, The Netherlands
    DOI: 10.1109/WHISPERS.2019.8921163

Permalink: https://www.hzdr.de/publications/Publ-28597
Publ.-Id: 28597


Comparison of pancreatic respiratory motion management with three abdominal corsets for particle radiation therapy

Dolde, K.; Schneider, S.; Stefanowicz, S.; Alimusaj, M.; Flügel, B.; Saito, N.; Troost, E. G. C.; Pfaffenberger, A.; Hoffmann, A. L.

Background and Purpose: Abdominal organ motion seriously compromises the targeting accuracy for particle therapy in patients with pancreatic adenocarcinoma. This study compares three different abdominal corsets regarding their ability to reduce pancreatic motion and their potential usability in particle therapy.

Materials and Methods: A patient-individualized polyurethane (PU), a semi-individualized polyethylene (PE), and a patient-individualized 3D-scan based polyethylene (3DPE) corset were manufactured for one healthy volunteer. Time-resolved volumetric magnetic resonance imaging (4D-MRI) and single-slice 2D cine-MRI scans were acquired on two consecutive days to compare free-breathing motion patterns with and without corsets. The corset material properties, such as thickness variance, material homogeneity in Hounsfield units (HU) on CT scans, and manufacturing features were compared. The water equivalent ratio (WER) of corset material samples was measured using a multi-layer ionization chamber for proton energies of 150 MeV and 200 MeV.

Results: All corsets reduced the pancreatic motion on average by 9.6 mm in inferior-superior and by 3.2 mm in anterior-posterior direction. With corset, the breathing frequency was approximately doubled and the day-to-day motion variations were reduced. The WER measurements showed an average value of 0.993 and 0.956 for the PE and 3DPE corset, respectively, and of 0.298 for the PU corset. The PE and 3DPE corsets showed a constant thickness of 2.8 ± 0.2 mm and 3.8 ± 0.2 mm, respectively and a homogeneous material composition with a standard deviation (SD) of 31 HU and 32 HU, respectively. The PU corset showed a variable thickness of 4.2−25.6 mm and a heterogeneous structure with air inclusions with an SD of 113 HU.

Conclusion: Abdominal corsets are effective devices to reduce pancreatic motion. For particle therapy, PE-based corsets are preferred over PU-based corset due to their material homogeneity and constant thickness.

Keywords: Motion management; pancreatic cancer; abdominal corset; image-guided radiotherapy; 4DMRI; particle therapy

Permalink: https://www.hzdr.de/publications/Publ-28596
Publ.-Id: 28596


Non-classical Liquid Metal Ion Sources for advanced FIB nano-patterning

Mazarov, P.; Bischoff, L.; Pilz, W.; Klingner, N.; Nadzeyka, A.; Stodolka, J.; Gierak, J.

Focused Ion Beam (FIB) processing has been developed into a well-established and still promising technique for direct patterning and proto-typing on the nm scale. Exploring the Liquid Metal Alloy Ion Sources (LMAIS) potential represents a promising alternative to expand the global FIB application fields. Especially, Ion Beam Lithography (IBL) as direct, resistless and three-dimensional patterning enables a simultaneous in-situ process control by cross-sectioning and inspection. Thanks to this, nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last forty years. Key features of a LMAIS are long life-time, high brightness and stable ion current. Recent developments could make these sources to an alternative technology feasible for nano-patterning challenges, e.g. to tune electrical, optical, magnetic or mechanical properties.

In this contribution the operation principle, the preparation and testing process as well as prospective domains for modern FIB applications will be presented. As an example we will introduce a Ga35Bi60Li5 LMAIS in detail. It enables high resolution imaging with light Li ions and sample modification with Ga or heavy polyatomic Bi clusters, all coming from one ion source.

L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Appl. Phys. Rev. 3, 021101 (2016).

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-28594
Publ.-Id: 28594


The race against time: TOF-SIMS in the HIM

Klingner, N.; Heller, R.; Hlawacek, G.

The helium ion microscope (HIM), well known for its high-resolution imaging and nanofabrication performance, suffered from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. Recently, a magnetic sector and a time-of-flight secondary ion mass spectrometer (TOF-SIMS) have been developed that can be retrofitted to existing microscopes [1,2]. We report on our time-of-flight setup using a straight secondary ion extraction optics that has been designed and optimized for highest transmission. The high efficiency is the most crucial parameter to collect enough signal from nanoparticles prior to their complete removal by ion sputtering. As a major advantage the time-of-flight approach inherently can measure all masses in parallel and thus provides the complete picture of the sample composition. The TOF-SIMS is a versatile add-on that helps the user to get previously unknown details about his samples and is therefore beneficial for many applications. At the end we will also give an outlook on future developments.

[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Notte, J. A.; Huang, J. and Facsko, S. (2016). Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry, Ultramicroscopy 162 : 91-97.
[2] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von Borany, J.; (2018). Time-of-flight secondary ion mass spectrometry in the helium ion microscope, submitted.

  • Lecture (Conference)
    Advances in Gas-Ion Microscopy - The Second International Meeting of The PicoFIB Network, 13.02.2019, London, Großbritanien

Permalink: https://www.hzdr.de/publications/Publ-28593
Publ.-Id: 28593


A Time-of-Flight Secondary Ion Mass Spectrometer Add-on for the Helium Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Facsko, S.

In a Helium Ion Microscopes (HIM) a Gas Field Ion Source (GFIS) is used to create a Helium or Neon ion beam with a diameter smaller than 0.5 nm and 1.8 nm, respectively. The method is well known for its high resolution imaging and nano-fabrication capabilities which it is able to provide not only for conducting but also insulating samples without the need for a conductive coating.

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

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

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


References

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

  • Lecture (Conference)
    SIMS Europe 2018, 16.-18.09.2018, Münster, Germany

Permalink: https://www.hzdr.de/publications/Publ-28592
Publ.-Id: 28592


Compositional analysis and in-situ experiments in the HIM

Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Serralta, E.; Facsko, S.

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

[1] N. Klingner, R. Heller, G. Hlawacek, J. von Borany, J.A. Notte, J. Huang, S. Facsko. Ultramicroscopy 162 (2016), pp 91-97
[2] N. Klingner, R. Heller, G. Hlawacek, S. Facsko, J. von Borany (2018), submitted

  • Lecture (Conference)
    2nd international HeFIB conference on Helium and emerging Focused Ion Beams, 11.-13.06.2018, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-28591
Publ.-Id: 28591


High Resolution in 3 dimensions – TOF-SIMS in the Helium Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S.; von Borany, J.

Ongoing miniaturization in semiconductor industry, nanotechnology and life science requirement further improvements for high-resolution imaging, fabrication and analysis of the produced nanostructures. Continuously shrinking object dimensions lead to an enhanced demand on spatial resolution and surface sensitivity of modern analysis techniques. Secondary ion mass spectrometry (SIMS), as one of the most powerful techniques for surface analysis, performed on the nanometer scale may comply with this demands. The direct determination of the sputtered ions mass provides elemental and molecular information and even allows to measure isotope concentrations.

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

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

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

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

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

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

The results will be compared to the theoretical limit of achievable lateral and depth resolution and the experimental and physical constraints of this approach will be reviewed.

  • Invited lecture (Conferences)
    HRDP 9 - 9th International Workshop on High-Resolution Depth Profiling, 25.-29.06.2018, Uppsala, Sweden

Permalink: https://www.hzdr.de/publications/Publ-28590
Publ.-Id: 28590


Application of a new model for bubble-induced turbulence to bubbly flows in containers and vertical pipes

Liao, Y.; Ma, T.; Krepper, E.; Lucas, D.; Fröhlich, J.

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

Keywords: Bubbly flow; Bubble-induced turbulence; Euler-Euler modelling; Baseline model

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Permalink: https://www.hzdr.de/publications/Publ-28589
Publ.-Id: 28589


Verification of ATHLET against TRACE on Superphenix start-up tests

Di Nora, V. A.; Fridman, E.; Mikityuk, K.

The thermal-hydraulics (TH) code ATHLET has been upgraded to be capable of sodium flow modeling. Its new extension is under verification and validation phase. The presented study aimed to demonstrate ATHLET capability in Sodium-cooled Fast Reactor (SFR) transient predictions, through the comparison against TRACE TH code, this last being more established and tested for SFR applications. Calculations were performed on a set of start-up tests on Superphénix (SPX) SFR, and compared with TRACE results, which were used as a reference. It has been shown that given a specific set of reactivity coefficients, ATHLET and TRACE give consistent and close results.

Keywords: Superphénix start-up tests; Benchmarking ATHLET against TRACE; ATHLET for SFRs

  • Lecture (others)
    Workshop of Doctoral Candidates (PhD student seminar), 13.12.2018, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28588
Publ.-Id: 28588


Time-lapse imaging of particle invasion and deposition in porous media using in situ X-ray radiography

Da Assuncao Godinho, J. R.; Chellappah, K.; Collins, I.; Ng, P.; Smith, M.; Withers, P. J.

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

Keywords: Permeability; formation damage; fines migration; filter cake; EOR; computed tomography

Permalink: https://www.hzdr.de/publications/Publ-28586
Publ.-Id: 28586


Bubble Generation by Micro-Orifices with Application on Activated Sludge Wastewater Treatment

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

We studied the initial gas dispersion performance of diffuser concepts based on micro-orifices and needles with very fine orifice diameters in the range from 30 µm to 200 µm, as such diffusers are currently in discussion for energy-efficient wastewater treatment plants. To evaluate the performance of these micro-orifices, we compared them with industrial rubber membrane diffusers with respect to Sauter mean bubble diameter, pressure drop, frequency of bubble formation, oxygen transfer rate, and power demand for air compression. Our study revealed that, in comparison with rubber membrane diffusers bubbles generated from the micro-orifices transfer up to 82% more oxygen content into the continuous phase at up to 75% less power demand. Moreover, these micro-orifices are able to produce bubble sizes in the same range as the needle diffusers at 60% less pressure drop and 60% higher bubble generation frequency. Therefore, we also expect an improvement in the oxygen transfer coefficient KLa and standard oxygen transfer efficiency SOTE compared to commercial rubber membrane diffusers.

Keywords: Bubble Generation; Micro-orifices; Aeration; Biological Wastewater Treatment; Rubber Membrane Diffusers; Oxygen Transfer

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Permalink: https://www.hzdr.de/publications/Publ-28585
Publ.-Id: 28585


Ion-induced surface patterning and its application in nanofabrication via templated growth

Erb, D.; Malsch, G.; de Schultz, R.; Facsko, S.

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

  • Poster
    SNI2018 - Conference for Research with Synchrotron Radiation, Neutrons and Ion Beams at Large Facilities, 17.-19.09.2018, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28584
Publ.-Id: 28584


Nanostructure arrays via templated growth

Erb, D.; Schlage, K.; Röhlsberger, R.; Facsko, S.

Nanostructured materials have the potential to make substantial contributions to solving our society’s present challenges, e.g. in the fields of medicine, information technology, or energy harvesting from renewable sources. The possibility to fabricate them at industrially relevant scales will maximize the impact of such materials.
We present bottom-up nanopatterning approaches which promise easy implementation and scale-up by combining well-established techniques and effects:
(a) spontaneous nanopatterning of crystalline surfaces upon heating,
(b) suface nanopatterning induced by low-energy ion irradiation,
(c) diblock copolymer self-assembly
(d) physical vapor deposition with selective wetting,
(e) physical vapor deposition with geometrical sha-ding.
Combinations of these techniques and effects can result in highly regular nanostructure arrays of various morphologies and are applicable to a wide range of materials. The versatility of these approaches enables creative research and may lead to beneficial applications in diverse fields, ranging from optics and magnetism to catalysis.

  • Invited lecture (Conferences)
    NAP2018 - 8th International Conference on Nanomaterials: Applications & Properties, 09.-14.09.2018, Zatoka, Ukrajina

Permalink: https://www.hzdr.de/publications/Publ-28583
Publ.-Id: 28583


Surface nanopatterning induced by low-energy ion irradiation: Experimental investigations of non-equilibrium pattern formation

Erb, D.; de Schultz, R.; Malsch, G.; Facsko, S.

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

  • Lecture (Conference)
    CAARI 2018 - 25th Conference on Application of Accelerators in Research and Industry, 12.-17.08.2018, Grapevine, USA

Permalink: https://www.hzdr.de/publications/Publ-28582
Publ.-Id: 28582


Morphology, density, and temporal evolution of topological defects in reverse epitaxy

Erb, D.; Malsch, G.; Facsko, S.

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

  • Poster
    Ion Beam Workshop 2018 - MAT Science Week, 24.04.2018, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28581
Publ.-Id: 28581


A route to epitaxial growth of periodic metal nanostructure arrays

Erb, D.; Malsch, G.; Hübner, R.; Lenz, K.; Lindner, J.; Facsko, S.; Helm, M.; Fassbender, J.

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

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

  • Poster
    DPG Frühjahrstagung 2018 - Sektion Kondensierte Materie, 11.03.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28580
Publ.-Id: 28580


Ion-induced nanopatterning of crystalline surfaces for applications in bottom-up nanostructure fabrication

Erb, D.; Hübner, R.; Malsch, G.; de Schultz, R.; Grenzer, J.; Lenz, K.; Lindner, J.; Facsko, S.

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

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

References
[1] X. Ou et al., Nanoscale 7, 18928 (2015)
[2] Q. Jia et al., Nano Research 15, 1 (2017)
[3] D. Erb et al., Science Advances 1, e1500751 (2015)

  • Lecture (Conference)
    SHIM-ICACS 2018 - 10th InternationaL Symposium on Swift Heavy Ions in Matter & 28th International Conference on Atomic Collisions in Solids, 01.-06.07.2018, Caen, France

Permalink: https://www.hzdr.de/publications/Publ-28579
Publ.-Id: 28579


Ex situ n+ doping of GeSn alloys via non-equilibrium processing

Prucnal, S.; Berencén, Y.; Wang, M.; Rebohle, L.; Böttger, R.; Fischer, I. A.; Augel, L.; Oehme, M.; Schulze, J.; Voelskow, M.; Helm, M.; Skorupa, W.; Zhou, S.

Full integration of Ge-based alloys like GeSn with complementary-metal-oxide-semiconductor technology would require the fabrication of p- and n-type doped regions for both planar and tri-dimensional device architectures which is challenging using in situ doping techniques. In this work, we report on the influence of ex situ doping on the structural, electrical and optical properties of GeSn alloys. n-type doping is realized by P implantation into GeSn alloy layers grown by molecular beam epitaxy (MBE) followed by flash lamp annealing. We show that effective carrier concentration of up to 1 × 10^19 cm−3 can be achieved without affecting the Sn distribution. Sn segregation at the surface accompanied with an Sn diffusion towards the crystalline/amorphous GeSn interface is found at P fluences higher than 3 × 10^15 cm−2 and electron concentration of about 4 × 10^19 cm−3. The optical and structural properties of ion-implanted GeSn layers are comparable with the in situ doped MBE grown layers.

Keywords: Ge; GeSn; MBE; n-type doping; flash lamp annealing; ion implantation

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Permalink: https://www.hzdr.de/publications/Publ-28578
Publ.-Id: 28578


Structural and electrical properties of Se-hyperdoped Si via ion implantation and flash lamp annealing

Liu, F.; Prucnal, S.; Yuan, Y.; Heller, R.; Berencén, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

We report on the hyperdoping of silicon with selenium obtained by ion implantation followed by flash lamp annealing. It is shown that the degree of crystalline lattice recovery of the implanted layers and the Se substitutional fraction depend on the pulse duration and energy density of the flash. While the annealing at low energy densities leads to an incomplete recrystallization, annealing at high energy densities results in a decrease of the substitutional fraction of impurities. The electrical properties of the implanted layers are well-correlated with the structural properties resulting from different annealing processing.

Keywords: Silicon; hyperdoping; Se; flash lamp annealing; ion implantation

Permalink: https://www.hzdr.de/publications/Publ-28577
Publ.-Id: 28577


Prophylactic cranial irradiation in stage IV small cell lung cancer: 5 Selection of patients amongst European IASLC and ESTRO experts

Putora, P. M.; Glatzer, M.; Belderbos, J.; Besse, B.; Blackhall, F.; Califano, R.; Cappuzzo, F.; de Marinis, F.; Dziadziuszko, R.; Felip, E.; Faivre-Finn, C.; Früh, M.; Garrido, P.; Le Pechoux, C.; Mcdonald, F.; Nestle, U.; Novello, S.; O‘Brien, M.; Paz Ares, L.; Peeters, S.; Pöttgen, C.; Ramella, S.; Reck, M.; Slotman, B.; Troost, E. G. C.; Houtte, P. V.; Westeel, V.; Widder, J.; Mornex, F.; de Ruysscher, D.

Background: Due to conflicting results between major trials the role of prophylactic cranial irradiation (PCI) in stage IV small cell lung cancer (SCLC) is controversial. Methods: We obtained a list of 13 European experts from both the European Society for Therapeutic Radiation Oncology (ESTRO) and the International Association for the Study of Lung Cancer (IASLC). The strategies in decision making for PCI in stage IV SCLC were collected. Decision trees were created representing these strategies. Analysis of consensus was performed with the objective consensus methodol-ogy.
Results: The factors associated with the recommendation for the use of PCI included the fitness of the patient, young age and good response to chemotherapy. PCI was recommended by the majority of experts for non-elderly fit patients who had at least a partial response (PR) to chemotherapy (for complete remission (CR): 85% of radiation oncologists and 69% of medical oncologists, for partial remission: 85% of radiation oncol- ogists and 54% of medical oncologists). For patients with stable disease after chemotherapy, PCI was rec- ommended by 6 out of 13 (46%) radiation oncologists and only 3 out of 13 medical oncologists (23%). For elderly fit patients with CR, a majority recommended PCI (62%) and no consensus was reached for patients with PR. Conclusion: European radiation and medical oncologists specializing in lung cancer recommend PCI in selected patients and restrict its use primarily to fit, non-elderly patients who responded to chemotherapy.

Keywords: Small cell lung cancer; PCI; Stage IV; Expert opinion; ESTRO; IASLC

Permalink: https://www.hzdr.de/publications/Publ-28576
Publ.-Id: 28576


Oxygen Exchange Kinetics of SrTiO3 Single Crystals: A Non-Destructive, Quantitative Method

Stoeber, M.; Cherkouk, C.; Leisegang, T.; Schelter, M.; Zosel, J.; Walter, J.; Hanzig, J.; Zschornak, M.; Prucnal, S.; Boettger, R.; Meyer, D. C.

The time-resolved oxygen exchange rate of strontium titanate (SrTiO3) single crystals is studied by means of oxygen solid electrolyte coulometry (OSEC) and compared to model calculations. Experiments are performed on pure, ion implanted (Ni, Ag, O and N ions) and partially covered crystals with silver layer. In this work, a theoretical model is used, which is based on defect chemistry under equilibrium conditions. It is applied as a fit in order to determine the effective rate constants and activation energy of the oxygen exchange reaction on the crystal surface. OSEC is used for the first time to characterize kinetic parameters of oxygen exchange on single crystalline surfaces. Transmission electron microscopy and sputter X-ray photoelectron spectroscopy are performed to determine structural and chemical changes after ion implantation.

Keywords: strontium titanate; ion implantation; oxygen exchange reaction; X-ray photoelectron spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-28575
Publ.-Id: 28575


Ion Beam Modification of ZnO Epilayers: Sequential Processing

Turos, A.; Ratajczak, R.; Mieszczynski, C.; Jozwik, P.; Stonert, A.; Prucnal, S.; Heller, R.; Skorupa, W.; von Borany, J.; Guziewicz, E.

Defect agglomeration in ion-implanted compound semiconductors produces lattice stress eventually causing plastic deformation at sufficiently high fluence. Consequently, a dislocations tangle is formed which can hardly be completely removed by thermal annealing. To solve this problem, a new method of sequential processing has been developed consisting of low fluence ion implantation followed by subsequent annealing. The procedure can be then repeated until the required impurity concentration has been reached without producing excessive damage. Epitaxial ZnO layers are grown using the atomic layer deposition (ALD) technique. Structural changes in ZnO epilayers due to Yb-ion implantation and subsequent annealing are analyzed by Rutherford backscattering/channeling (RBS/c) and photoluminescence (PL). Correlation between defect transformations and PL efficiency is determined. Increased Yb-atom optical activation upon sequential processing as compared to the standard single-step annealing is observed.

Keywords: ZnO; ALD; Defects; ion implantation; RBS

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Permalink: https://www.hzdr.de/publications/Publ-28574
Publ.-Id: 28574


Fractionwise verification of delivered proton dose to prostate cancer patients based on daily in-room CT imaging

Stützer, K.; Valentini, C.; Agolli, L.; Hölscher, T.; Thiele, J.; Dutz, A.; Löck, S.; Krause, M.; Baumann, M.; Richter, C.

Purpose: Retrospective proton dose calculation based on a unique dataset of daily CT images to confirm our prostate patient positioning and immobilization protocol for counterbalancing interfractional motion.
Material/Methods: For 12 prostate cancer patients treated to 74GyE with double-scattered lateral or anterior oblique proton fields, daily (27-37, median 32) in-room control CTs (cCT) were acquired. Patient preparation includes a drink protocol, water-filled endorectal balloon insertion, bony anatomy alignment by orthogonal X-Ray imaging, and CT-based verification of prostate location via implanted fiducial marker positions. Fraction doses were calculated on all manually delineated cCTs and accumulated on the planning CT by a deformable image registration (DIR) in RayStation 5.99. DVH parameters of iCTVs, bladder, rectum, femoral heads, bladder and rectal wall were analyzed fractionwise prior and after DIR and values from the cumulated and planned dose distributions were compared.
Results: Fig.1 shows the fractionwise assessed DVH parameters for one patient. 275 fraction doses were analyzed in total without finding trends for improving or worsening DVH parameters over treatment time. Intended target coverage, D98%(iCTV)>95%, was missed in 29 cCTs (10.5%) due to suboptimal bladder filling, endorectal balloon position or delineation variation. No overdosage was observed (D2%(iCTV)<105%). DIR led partly to notable changes of DVH parameters (Fig.1). No alarming differences exist between planned and cumulated doses (Fig.2), but significant changes (p<0.05, Wilcoxon signed rank test) were found for D2%(iCTV), V75%(bladder) and V30Gy(bladder wall).
Conclusion: Despite some suspicious fractions, the total delivered doses to prostate cancer patients are accurate with the applied positioning and immobilization protocol.

  • Lecture (Conference)
    58th annual conference of the particle therapy co-operative group, 10.-15.06.2019, Manchester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-28573
Publ.-Id: 28573


Interplay between localization and magnetism in (Ga,Mn)As and (In,Mn)As

Yuan, Y.; Xu, C.; Hübner, R.; Jakiela, R.; Böttger, R.; Helm, M.; Sawicki, M.; Dietl, T.; Zhou, S.

Ion implantation of Mn combined with pulsed laser melting is employed to obtain two representative compounds of dilute ferromagnetic semiconductors (DFSs): Ga1−xMnxAs and In1−xMnxAs. In contrast to films deposited by the widely used molecular beam epitaxy, neither Mn interstitials nor As antisites are present in samples prepared by the method employed here. Under these conditions the influence of localization on the hole-mediated ferromagnetism is examined in two DFSs with a differing strength of p-d coupling. On the insulating side of the transition, ferromagnetic signatures persist to higher temperatures in In1−xMnxAs compared to Ga1−xMnxAs with the same Mn concentration x. This substantiates theoretical suggestions that stronger p-d coupling results in an enhanced contribution to localization, which reduces hole-mediated ferromagnetism. Furthermore, the findings support strongly the heterogeneous model of electronic states at the localization boundary and point to the crucial role of weakly localized holes in mediating efficient spin-spin interactions even on the insulator side of the metal-insulator transition.

Keywords: electronic-structure; magnetotransport properties; curie-temperature; coulomb gap; (ga,mn)as; ga1-xmnxas; semiconductors; ferromagnetism

  • Poster
    DPG-Jahrestagung und DPG-Frühjahrstagung, 13.03.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28572
Publ.-Id: 28572


Luminescence in the Visible Region from Annealed Thin ALD-ZnO Films Implanted with Different Rare Earth Ions

Ratajczak, R.; Guziewicz, E.; Prucnal, S.; Łuka, G.; Böttger, R.; Heller, R.; Mieszczynski, C.; Wozniak, W.; Turos, A.

Epitaxial ZnO thin films grown by atomic layer deposition on GaN/Al2O3 substrates are implanted with Yb, Dy, and Pr ions to a fluence of 5e14 atcm-2 and subsequently anneals at 800 C using a rapid thermal annealing (RTA) system. Structural properties of implanted and annealed ZnO films and the optical response are evaluated by channeling Rutherford backscattering (RBS/c) and photoluminescence spectroscopy (PL), respectively. RTA leads to a partial removal of the post-implantation defects with simultaneous native defects transformation and optical activation of RE ions. It is found that two groups of defects: defects formed during implantation process and native defects, play an important role in the luminescence in the visible region. The room temperature PL spectra obtained from annealed ZnO:RE films do not show sharp PL lines from transitions within the RE 4f shell, but show near band gap emission and defect related emission, which energy emission is controlled by the RE atoms. It suggests a presence of RE-related complexes that are formed during hightemperature annealing in oxygen atmosphere. The excitonic and defect emission modified by RE ions create an optical response of the system resulting in a specific color of the emitted light.

Keywords: ZnO; flash lamp annealing; PL; ion implantation; rare earth

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Permalink: https://www.hzdr.de/publications/Publ-28571
Publ.-Id: 28571


Strain and Band-Gap Engineering in Ge-Sn Alloys via P Doping

Prucnal, S.; Berencén, Y.; Wang, M.; Grenzer, J.; Voelskow, M.; Hübner, R.; Yamamoto, Y.; Scheit, A.; Bärwolf, F.; Zviagin, V.; Schmidt-Grund, R.; Grundmann, M.; Żuk, J.; Turek, M.; Droździel, A.; Pyszniak, K.; Kudrawiec, R.; Polak, M. P.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn, or ultrahigh n-type doping. In this work, we use all three approaches together to fabricate direct-band-gap Ge−Sn alloys. The heavily doped n-type Ge−Sn is realized with CMOS-compatible nonequilibrium material processing. P is used to form highly doped n-type Ge−Sn layers and to modify the lattice parameter of P-doped Ge−Sn alloys. The strain engineering in heavily-P-doped Ge−Sn films is confirmed by x-ray diffraction and micro Raman spectroscopy. The change of the band gap in P-doped Ge−Sn alloy as a function of P concentration is theoretically predicted by density functional theory and experimentally verified by near-infrared spectroscopic ellipsometry. According to the shift of the absorption edge, it is shown that for an electron concentration greater than 1 × 10^20 cm the band-gap renormalization is partially compensated by the Burstein-Moss effect. These results indicate that Ge-based materials have high potential for use in near-infrared optoelectronic devices, fully compatible with CMOS technology.

Keywords: Ge; GeSn; n-type doping; ion implantation; x-ray diffraction; Raman spectroscopy; strain

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Permalink: https://www.hzdr.de/publications/Publ-28570
Publ.-Id: 28570


Advanced doping of Ge and GeSn

Prucnal, S.; Berencén, Y.; Hübner, R.; Böttger, R.; Rebohle, L.; Skorupa, W.; Wang, M.; Helm, M.; Zhou, S.

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

[1] R. E. Camacho-Aguilera et al., Optics Express 20, 11316-11320 (2012)
[2] S. Prucnal et al., Sci. Rep. 6, 27643 (2016).
[3] S. Wirths et al., Nat. Photon., 9, 88–92 (2015)
[4] S. Prucnal et al., Semicond. Sci. Technol. 32, 115006 (2017).

Keywords: Ge; GeSn; ion implantation; flash lamp annealing; n-type doping

  • Lecture (Conference)
    34th International Conference on the Physics of Semiconductors, 29.07.-03.08.2018, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-28569
Publ.-Id: 28569


Robust intensity-modulated proton therapy with dose-escalated simultaneous integrated boost reduces the low-dose to surrounding tissues in pancreatic cancer patients

Stefanowicz, S.; Zschaeck, S.; Troost, E. G. C.

Purpose
This in-silico study on simultaneous integrated boost dose-escalation in non-metastatic pancreatic cancer patients dosimetrically compared robust multi-field optimized intensity-modulated proton therapy (IMPT) with volumetric modulated arc therapy (VMAT).

Material and Methods
For five patients, both treatment plans were optimized on free-breathing CTs using RayStation. For VMAT, at least 95% of the prescribed doses of 66Gy and 51Gy to the boost (GTV) and PTV (CTV+5mm), respectively, were to cover 95% of the targets. For IMPT, robust optimization with a setup uncertainty of 5mm and a density uncertainty of 3.5% was applied to the GTV and CTV, with the aforementioned dose levels (RBE) again covering 95% of the targets. The OAR dose constraints adhered to local guidelines and QUANTEC.

Results
All treatment plans reached the prescribed doses to the targets. Doses to the bowel, stomach and/or liver exceeded at least one constraint in all treatment plans, since those OARs were next to or within the targets. While VMAT reduced the median V50Gy of the stomach, doses to the remaining gastrointestinal organs, e.g. liver and kidneys, were lower for IMPT (Fig. 1). Overall, IMPT deposited less low dose outside the CTV (Fig. 2, median integral V20Gy: 1483.4ccm vs. 756.2ccm).

Conclusion
Disregarding inter- and intra-fractional organ motion, dose escalation with IMPT and VMAT is possible. IMPT reduced the dose to surrounding normal tissues, except for OARs overlapping with the target volume, in which the dose was higher due to the robust optimization approach. Additional patients will be included in this study.

  • Poster
    PTCOG 58, 10.-15.06.2019, Manchaster, UK

Permalink: https://www.hzdr.de/publications/Publ-28568
Publ.-Id: 28568


Abnormal lattice location and electrical activation in chalcogen-hyperdoped Si

Wang, M.; Prucnal, S.; Debernardi, A.; Heller, R.; Yuan, Y.; Xu, C.; Berencén, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

Hyperdoping has emerged as a promising method for designing semiconductors with unique physical properties. In general, these properties are primarily determined by the lattice location of the impurity atoms in the host material. In this contribution, the lattice location of implanted chalcogens in Si was experimentally determined by means of Rutherford backscattering/channeling (RBS/C). The implication on the electrical activation of chalcogens in Si will be discussed with respect to the Hall effect results. The obtained carrier concentration and the RBS angular scans across the <100> and <110> axis reveal that the electrically active/inactive concentration of Te correlates with the concentration of substitutional/interstitial site Te atoms. Surprisingly, contrary to the general belief, we find that the interstitial fraction decreases with increasing impurity concentration. This abnormal dependence of lattice location and electrical activation on impurity concentration suggests that the formation energy for the substitutional Te or Te-Te dimers in Si is lower than for the interstitial Te. This assumption is theoretically verified by the first-principles calculations.

  • Lecture (Conference)
    IBMM-2018 - The 23rd International Conference on Ion Beam Analysis, 28.06.2018, San Antonio, USA

Permalink: https://www.hzdr.de/publications/Publ-28567
Publ.-Id: 28567


Extended infrared photoresponse in room-temperature Si hyperdoped with Te

Wang, M.; Berencén, Y.; Prucnal, S.; García-Hemme, E.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Schneider, H.; Skorupa, W.; Helm, M.; Zhou, S.

Presently, room-temperature infrared sub-band-gap photoresponse in Si is of great interest for the development of on-chip complementary-metal-oxide-semiconductor (CMOS)-compatible photonic platforms [1]. One of the most promising approaches to further extend the photoresponse of Si to the mid- and far-infrared (MIR/FIR) ranges consists of introducing deep-level dopants into the Si band gap at concentrations in excess of the solid solubility limit [2]. In this work, we demonstrate strong room-temperature sub-band-gap photoresponse of photodiodes based on Si hyperdoped with tellurium [3]. A CMOS-compatible approach of combining ion implantation with pulsed laser melting was applied to synthesize single-crystalline and epitaxial Te-hyperdoped Si layers with a Te concentration five orders of magnitude above the solid solubility limit. Driven by increasing Te concentration, both the insulator-to-metal transition and a band-gap renormalization are observed. The sub-band optical absorptance in the resulting Te-hyperdoped Si layers is found to increase monotonically with increasing Te concentration and extends well into the MIR/FIR ranges (1.4 to 25 μm). Importantly, the MIR/FIR optoelectronic response from Te-hyperdoped Si photodiodes is demonstrated to be related with known Te deep-energy levels into the Si band-gap. This work contributes to pave the way towards establishing a Si-based broadband infrared photonic system operating at room temperature.

  • Lecture (Conference)
    ION 2018 - XII-th International Conference on Ion Implantation and other Applications of Ions and Electrons, 19.06.2018, Kazimierz Dolny, Poland
  • Poster
    IBMM-2018 - The 23rd International Conference on Ion Beam Analysis, 25.06.2018, San Antonio, USA
  • Poster
    ICPS-2018 - 34th International Conference on the Physics of Semiconductors, 30.07.2018, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-28566
Publ.-Id: 28566


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