Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34757 Publications

Radiometric Correction and 3D Integration of Long-Range Ground-based Hyperspectral Imagery for Mineral Exploration of Vertical Outcrops

Lorenz, S.; Salehi, S.; Kirsch, M.; Zimmermann, R.; Unger, G.; Sørensen, E. V.; Gloaguen, R.

Recently, ground-based hyperspectral imaging has come to the fore, supporting the arduous task of mapping near-vertical, difficult-to-access geological outcrops. The application of outcrop sensing within a range of one to several hundred meters, including geometric corrections and integration with accurate terrestrial laser scanning models, is already developing rapidly. However, there are only very few studies dealing with ground-based imaging of distant (i.e., in the range of several kilometres) targets such as mountain ridges, cliffs, and pit walls. In particular the extreme influence of atmospheric effects and topography-induced illumination differences have remained an unmet challenge on the spectral data. Those effects cannot be corrected by means of common correction tools for nadir satellite- or airborne data. Thus, this article presents an adapted workflow to overcome the challenges of long-range outcrop sensing, including straightforward atmospheric and topographic corrections. Using two datasets with different characteristics, we demonstrate the application of the workflow and highlight the importance of the presented corrections for a reliable geological interpretation. The achieved spectral mapping products are integrated with 3D photogrammetric data to create large-scale now-called “hyperclouds”, i.e. geometrically correct representations of the hyperspectral datacube. The presented workflow opens up a new range of application possibilities of hyperspectral imagery by significantly enlarging the scale of ground-based measurements.

Keywords: hyperspectral; topographic correction; atmospheric correction; radiometric correction; long-range; long-distance; Structure from Motion (SfM); photogrammetry; mineral mapping; Minimum Wavelength mapping; Maarmorilik; Riotinto

  • Open Access Logo Remote Sensing 10(2018)2, 176
    DOI: 10.3390/rs10020176
  • Lecture (Conference)
    Whispers Conference 9th Workshop on Hyperspectral Image and Signal Processing, 23.-26.09.2018, Amsterdam, Nederland

Publ.-Id: 26688

FLUKA simulations of the neutron flux in the Dresden Felsenkeller

Grieger, M.; Bemmerer, D.; Hensel, T.; Müller, S. E.; Zuber, K.

The Dresden Felsenkeller ist a shallow-underground site featuring a rock overburden of 47 m which hosts a 5 MV Pelletron accelerator in tunnels VIII and IX. Using previous measurements in the lowbackground 𝛾-couting facility in tunnel IV as a benchmark, a FLUKA simulation has been developed to predict the neutron flux in tunnels VIII and IX. The simulation results provide insight into local neutron field inhomogenities caused by the measurement environment itself.

  • Lecture (Conference)
    DPG Frühjahrstagung, 26.02.-02.03.2018, Bochum, Deutschland

Publ.-Id: 26687

Long-Wave Hyperspectral Imaging For Lithological Mapping: A Case Study

Lorenz, S.; Kirsch, M.; Zimmermann, R.; Tusa, L.; Möckel, R.; Chamberland, M.; Gloaguen, R.

Hyperspectral long-wave infrared imaging (LWIR HSI) adds a promising complement to visible, near infrared, and shortwave infrared (VNIR and SWIR) HSI data in the field of mineral mapping. It enables characterization of rock- forming minerals such as silicates and carbonates, which show no detectable or extremely weak features in VNIR and SWIR. In the last decades, there has been a steady increase of publications on satellite, aerial, and laboratory LWIR data. However, the application of LWIR HIS for ground- based, close-range remote sensing of vertical geological outcrops is sparsely researched and will be the focus of the current study. We present a workflow for acquisition, mosaicking, and radiometric correction of LWIR HSI data. We demonstrate the applicability of this workflow using a case study from a gravel quarry in Germany. Library spectra are used for spectral unmixing and mapping of the main lithological units, which are validated using sample X-ray diffraction (XRD) and thin section analysis as well as FTIR point spectrometer data.

Keywords: long wave infrared; thermal infrared; mineral mapping; hyperspectral

  • Contribution to proceedings
    International Geoscience and Remote Sensing Symposium, IGARSS 2018, 23.-27.07.2018, Valencia, España

Publ.-Id: 26686

FLUKA simulations of neutron transport in the Dresden Felsenkeller

Grieger, M.; Bemmerer, D.; Müller, S. E.; Szücs, T.; Zuber, K.

A new underground ion accelerator with 5 MV acceleration potential is currently being readied for installation in the Dresden Felsenkeller. The Felsenkeller site consists of altogether nine mutually connected tunnels. It is shielded from cosmic radiation by a 45 m thick rock overburden, enabling uniquely sensitive experiments. In order to exclude any possible effect by the new accelerator in tunnel VIII on the existing low-background gamma-counting facility in tunnel IV, Monte Carlo simulations of neutron transport are being performed. A realistic neutron source field is developed, and the resulting additional neutron flux at the gamma-counting facility is modeled by FLUKA simulations. – Supported by NAVI (HGF VH-VI-417).

  • Lecture (Conference)
    DPG Frühjahrstagung, 23.-27.03.2015, Heidelberg, Deutschland

Publ.-Id: 26685

Strahlenschutzrechnungen für den Untertage-Ionenbeschleuniger am Standort Felsenkeller

Grieger, M.

Geringe natürliche Hintergrundstrahlung ist für die Untersuchung von Brennprozessen in Sternen von hoher Bedeutung. Für mehrere Szenarien wurden detaillierte FLUKA durchgeführt um die zusätzliche Strahlungserzeugung durch den neuen 5 MV Pelletron Beschleuniger zu studieren - mit dem Ziel die benötigte Abschirmung zu optimieren.

  • Poster
    Lange Nacht der Wissenschaften Dresden, 16.06.2017, Dresden, Deutschland

Publ.-Id: 26684

Flue dust from the copper converter process - Recovery of Cu and In by solvent extraction

Rädecker, P.; Scharf, C.; Zürner, P.; Frisch, G.; Pieplow, G.; Lindner, D.; Koch, J.

Flue dusts from copper metallurgy are resources for base metals such as copper, zinc, tin or lead. However, there is also a potential for the recovery of strategic elements like indium. At the moment flue dusts are recirculated within the copper process, but residues are available from historic produc-tion processes.
Hydrometallurgical processes seem to be a promising method to recover the base and strategic met-als from these fine-grained flue dusts. In preparation for further processing, the secondary material was characterized by mineral liberation analysis (MLA) and electron probe micro analysis (EPMA). An iron- and zinc-rich spinel phase (Zn,Fe,Mn)(Fe,Mn)2O4 was detected as the main phase (76 wt.-%) in the flue dust. The chemical composition of the flue dust was analysed by X-ray fluo-rescence spectroscopy (XRF spectroscopy). Leaching by sulfuric acid leads to precipitation of lead sulphate and calcium sulphate, which remain in the residue. The level of some impurities in the solu-tion can be controlled.
This work focuses on the selective recovery of copper and indium by solvent extraction from the leaching solution. Preliminary synthetic solutions of copper, iron(III), zinc, indium and mixtures of them were used for the investigations. The influence of pH value, concentration of acidic extract-ants, extraction time, and phase ratio on the extraction of copper, iron(III), zinc, and indium were studied. The results of the selective extraction of copper in the presence of iron(III) will be present-ed.

  • Contribution to proceedings
    European Metallurgical Conference EMC2017, 25.-28.06.2017, Leipzig, Deutschland
    Proceedings of the EMC2017, Clausthal-Zellerfeld: GDMB Verlag GmbH, 978-3-940276-74-2, 1121-1132
  • Lecture (Conference)
    European Metallurgical Conference EMC 2017, 25.-28.06.2017, Leipzig, Deustchland

Publ.-Id: 26682

The Natural Neutron Background Underground: Measurement Using Moderated ³He Counters in Felsenkeller

Grieger, M.

A FLUKA simulation has been made to analyse the propagation of neutrons from the future Felsenkeller accelerator throughout the tunnel system of Felsenkeller. A neutron flux measurement with detectors loaned by the BELEN-collaboration has been performed to put the accelerator induced neutron flux into perspective with the natural neutron background. To deduce the neutron flux from the counting rates, FLUKA has been used to simulate the detector responses. The three measured locations in the existing γ-measurement facility in tunnel IV show different traits in their neutron spectra. Their cause has been analysed and the results had an impact on the construction planning of the new Felsenkeller laboratory in tunnels VIII and IX.

  • Poster
    Felsenkeller Workshop, 26.-28.06.2017, Dresden, Deutschland
  • Poster
    NDRA 2016, 29.06.-02.07.2016, Riva del Garda, Italia
  • Lecture (Conference)
    DPG Frühjahrstagung, 14.-18.03.2016, Darmstadt, Deutschland
  • Master thesis
    TU Dresden, 2016
    Mentor: PD Dr. Daniel Bemmerer

Publ.-Id: 26681

Fakultät für Werkstoffwissenschaft und Werkstofftechnologie an der TU Bergakademie Freiberg

Rädecker, P.

Vorstellung der Studiengänge der Fakultät 5 der TU Bergakademie Freiberg.

  • Lecture (others)
    Studieninformationstag am BSZ Konrad Zuse, 14.11.2017, Hoyerswerda, Deutschland

Publ.-Id: 26680

Construction and setup of a KÜHNI column in pilot scale

Rädecker, P.; Scharf, C.; Zürner, P.; Frisch, G.; Pieplow, G.; Lindner, D.; Koch, J.

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. Es wurden die Reaktionsisotherme für Kupfer, die Zeit- und Konzentrationsabhängigkeiten 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.

Keywords: KÜHNI-Kolonne; Solventextraktion; Kupfer; LIX984

  • Poster
    Neue Verfahren und Materialien für Energie- und Umwelttechnik, 09.11.2017, Zwickau, Deutschland

Publ.-Id: 26679

FLUKA Radiation Safety Calculations for the Underground Accelerator Laboratory Felsenkeller/Dresden

Grieger, M.; Bemmerer, D.

The study of stable stellar burning reactions in nuclear astrophysics requires the use of ion accelerators in a low-background setting underground. Currently, there is only one such laboratory, the LUNA 0.4 MV accelerator deep underground in Gran Sasso/Italy. Several higher-energy underground accelerators are under development worldwide, including a 5 MV Pelletron to be placed in the Felsenkeller underground laboratory in Dresden/Germany. The shielding requirements for underground accelerators, where the paramount concern is the background in neighbouring rare-event searches is reviewed. Detailed FLUKA simulations have been carried out to study several different operating scenarios of the new 5 MV Felsenkeller accelerator, with a focus on the side effects on an existing γ-counting facility in the same tunnel system. The results of the simulations and practical implications will be discussed.

  • Poster
    Felsenkeller Workshop, 26.-28.06.2017, Dresden, Deutschland

Publ.-Id: 26678

FLUKA shielding calculations for the underground accelerator laboratory Felsenkeller/Dresden

Grieger, M.

The study of stable stellar burning reactions in nuclear astrophysics requires the use of ion accelerators in a low-background setting underground. Currently, there is only one such laboratory, the LUNA 0.4 MV accelerator deep underground in Gran Sasso/Italy. Several higher-energy underground accelerators are under development worldwide, including a 5 MV Pelletron to be placed in the Felsenkeller underground laboratory in Dresden/Germany. The shielding requirements for underground accelerators, where the paramount concern is the background in neighbouring rare-event searches is reviewed. Detailed FLUKA simulations have been carried out to study several different operating scenarios of the new 5 MV Felsenkeller accelerator, with a focus on the side effects on an existing γ-counting facility in the same tunnel system. The results of the simulations and practical implications will be discussed.

  • Poster
    SATIF-13, 10.-12.10.2016, Dresden, Deutschland

Publ.-Id: 26677

XPS spectra, electronic structure, and magnetic properties of RFe5Al7 intermetallics

Finkelstein, L. D.; Efremov, A. V.; Korotin, M. A.; Andreev, A. V.; Gorbunov, D. I.; Mushnikov, N. V.; Zhidkov, I. S.; Kikharenko, A. I.; Cholakh, S. O.; Kurmaev, E. Z.

The results of X-ray photoelectron spectroscopy measurements (core levels and valence bands) of RFe5Al7 (R = Lu, Tm, Er, Ho, Dy, Tb, Gd) single crystals are presented in comparison with the results of bulk magnetization studies and electronic structure calculations. It is shown that the increase of the Curie temperature in RFe5Al7 from Tm to Gd is associated with an increase of the indirect R 4f - Fe 3d exchange interaction at the expense of the multiplicity 2S + 1 (statistical weight) in the ground state 2S + 1LJ of R3+ ions. The nonmonotonic behavior of the ferrimagnetic compensation temperature, Tcomp, as well as the values of the spontaneous magnetic moment, Ms, and formation energy, Eform, of the 4fn levels in R metals in a series from ErFe5Al7 to GdFe5Al7 are explained by the difference in the quantum numbers L, J and S of the ground state of R3+ ions, leading to a maximum value of Tcomp, Ms and Eform for the Dycontaining compound. The electronic structure of Gd/LuFe5Alsub>7 is calculated using the GGA+U approach, on the basis of which the physical mechanism and relative strength of the interatomic R-Fe and Al-Fe interactions are considered, and also the difference in the magnetic moments of iron atoms in different structural positions is explained.

Publ.-Id: 26676

Process Simulation of Si Dot Fabrication for SETs by Ion Beam Mixing and Phase Separation in Nanopillars

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

The single electron transistor (SET) is considered a promising candidate to continue the revolution of information technology due to its very low energy consumption (~100 times less then common FET). The big challenge is the manufacturability of SETs working at room temperature (RT). This requires the fabrication of much smaller structures (<5nm) than present-day and even future (multi-E-beam or EUV) lithography can provide.

Here we propose an ion-beam-assisted, CMOS compatible fabrication process of SETs. To realize the controlled tunneling of single electrons we propose a nanopillar of a Si/SiO2/Si stack with a single Si quantum dot embedded in SiO2 and connected by tunnel junctions to Si electrodes, which makes the drain and source. For RT operation the quantum dot has to be smaller than 5nm and requires tunnel distances lower than 2nm. The size of this pillar needs to be in the range of 10-20nm.

In this presentation we show the simulation of a CMOS compatible process to fabricate this quantum dot by using ion beam mixing and self-assembly. Earlier projects proved already the reliability of dot formations using ion beam mixing technologies. Starting with a layerstack of Si/SiO2/Si, the ion beam irradiation by high energy Si+ ions causes mixing of the two Si/SiO2 interfaces what transforms the SiO2 layer into metastable SiOx (Figure 1). During subsequent heat treatment the mixed region of SiOx (<10nm2) separates into Si and SiO2, what leads to the formation of one single Si nanodot in the SiO2 layer (Figure 2). The irradiation simulations are done by TRIDYN and TRI3DYN program codes and the annealing by a self-developed Kinetic Monte Carlo program. We will present, how this process can be controlled using the ion beam irradiation values, geometrical sizes and the heat treatment parameters, so that it is yielding suitable conditions for application in hybrid SET-CMOS devices operating at RT.

This part of the work is being funded by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET).

Keywords: SET; CMOS; Phase Separation; Ion Beam Mixing

  • Lecture (Conference)
    Electron, Ion, and Photon Beam Technology and Nanofabrication, 30.05.-02.06.2017, Orlando, USA

Publ.-Id: 26675

Determining antiferromagnetic domain patterns electrically

Kosub, T.; Hübner, R.; Appel, P.; Shields, B.; Maletinsky, P.; Kopte, M.; Schmidt, O. G.; Faßbender, J.; Makarov, D.

Extrinsic effects on Cr2O3 thin films are shown. Also a statistical method to evaluate AF domain pattern in an electric way is demonstrated.

  • Poster
    AF Spintronics Workshop, 25.10.2017, Grenoble, France

Publ.-Id: 26672

Purely Antiferromagnetic Magnetoelectric RAM

Kosub, T.; Kopte, M.; Appel, P.; Shields, B.; Maletinsky, P.; Hübner, R.; Fassbender, J.; Schmidt, O. G.; Makarov, D.

MERAM based on Cr2O3/Pt is presented

  • Lecture (Conference)
    DPG-Frühjahrstagung, 19.03.2017, Dresden, Germany
  • Invited lecture (Conferences)
    CIMTEC Ceramics Congress, 18.-22.06.2018, Perugia, Italien
  • Invited lecture (Conferences)
    MMM Pittsburgh, 13.-17.11.2017, Pittsburgh, USA
  • Invited lecture (Conferences)
    EMN Meeting, 16.-20.07.2018, Berlin, Deutschland

Publ.-Id: 26671

Purely Antiferromagnetic MERAM

Kosub, T.; Kopte, M.; Appel, P.; Shields, B.; Maletinsky, P.; Hübner, R.; Schmidt, O. G.; Faßbender, J.; Makarov, D.

Magnetoelectric and purely antiferromagnetic RAM is shown based on Cr2O3/Pt

  • Lecture (Conference)
    IEEE Dublin, 24.04.2017, Dublin, Ireland

Publ.-Id: 26669

Unconventional spin dynamics in the honeycomb-lattice material α-RuCl3: High-field electron spin resonance studies

Ponomaryov, A. N.; Schulze, E.; Wosnitza, J.; Lampen-Kelley, P.; Banerjee, A.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Kolezhuk, A. K.; Zvyagin, S. A.

We present high-field electron spin resonance (ESR) studies of the honeycomb-lattice material α-RuCl3, a prime candidate to exhibit Kitaev physics. Two modes of antiferromagnetic resonance were detected in the zigzag ordered phase, with magnetic field applied in the ab plane. A very rich excitation spectrum was observed in the field-induced quantum paramagnetic phase. The obtained data are compared with the results of recent numerical calculations, strongly suggesting a very unconventional multiparticle character of the spin dynamics in α-RuCl3. The frequency-field diagram of the lowest-energy ESR mode is found consistent with the behavior of the field-induced energy gap, revealed by thermodynamic measurements.

Publ.-Id: 26668

Optimized Synthesis of the Bismuth Subiodides BimI4 (m = 4, 14, 16, 18) and the Electronic Properties of Bi14I4 and Bi18I4

Weiz, A.; Le Anh, M.; Kaiser, M.; Rasche, B.; Herrmannsdörfer, T.; Doert, T.; Ruck, M.

We optimized the syntheses of α- and β-Bi4I4 and transferred the method to the very bismuth-rich iodides Bi14I4, Bi16I4, and Bi18I. Phase-pure, microcrystalline powders of BimI4 (m = 4, 14, 18) can now by synthesized on a multigram scale. Conditions for the growth of single crystals of Bi16I4 and Bi18I4 were determined. The redetermination of the crystal structure of Bi16I4 hints at a stacking disorder or the presence of 1͚[BimI4] ribbons with m = 14 and 18 among the dominant type along with m = 16. The electronic band structures for m = 14, 16, and 18 were calculated including spin-orbit coupling. They vary markedly with m and show numerous bands crossing the Fermi level, predicting a 3D-metallic behavior. Measurements of the electrical resistivity of a polycrystalline sample of Bi14I4 as well as polycrystalline and single-crystalline samples of Bi18I4 confirmed their metallic nature over the temperature range 300 K to 2 K. For BiI4, a positive and strictly linear magnetoresistance at 2 K in static magnetic fields up to 14 T was observed, which could indicate a topologically nontrivial electronic state.

Publ.-Id: 26667

Flat Bands, Indirect Gaps, and Unconventional Spin-Wave Behavior Induced by a Periodic Dzyaloshinskii-Moriya Interaction

Gallardo, R. A.; Cortés-Ortuno, D.; Schneider, T.; Roldán-Molina, A.; Ma, F.; Lenz, K.; Fangohr, H.; Lindner, J.; Landeros, P.

Periodically patterned metamaterials are known for exhibiting wave properties similar to the ones observed in electronic band structures in crystal lattices. In particular, periodic ferromagnetic (FM) materials, also known as magnonic crystals (MCs), are characterized by the presence of bands and bandgaps (BGs) at tunable frequencies in their spin-wave (SW) spectrum. While those frequencies typically cover the GHz-range, no fundamental reason prevents one from extending this range towards THz-frequencies, a regime of high importance in communication technologies. Recently, the fabrication of magnets hosting Dzyaloshinskii-Moriya interactions (DMIs) has been pursued with high interest since properties such as the stabilization of chiral spin textures and nonreciprocal SW propagation originate from this antisymmetric exchange interaction. In this context, to further engineer the band structure of MCs, we propose the implementation of MCs with periodic DMIs, which can be obtained, for instance, patterning periodic arrays of heavy metals (HMs) on top of an ultrathin FM film. We demonstrate through theoretical calculations and micromagnetic simulations that such systems exhibit a unique evolution of the standing SWs around the BGs in areas of the FM film that are in contact with the HM wires. We also predict the emergence of at SW bands and indirect magnonic gaps, and we show that these effects depend on the strength of the DMI. This study opens further pathways towards engineered metamaterials for SW-based devices.

Keywords: chiral; magnonics; spin waves; DMI; Dzyaloshinskii-Moriya Interaction; magnonic crystals; metamaterials; micromagnetic simulations; ferromagnetic resonance; FMR

  • Open Access Logo Physical Review Letters 122(2019), 067204
    DOI: 10.1103/PhysRevLett.122.067204
  • Poster
    MMM 2019 - Annual Conference on Magnetism and Magnetic Materials, 04.-08.11.2019, Las Vegas, United States of America


Publ.-Id: 26666

Transglutaminase 2 as a target for functional tumour imaging: From substrates to inhibitors to radiotracers

Löser, R.

The talk is covering the efforts of our group in the development of inhibitor-based radiotracers for the imaging of tumour-associated transglutaminase 2. After introducing the biological function of transglutaminase 2, the development of substrates for fluorimetric activity assays will be lined out. Major emphasis will be put on the synthesis, kinetic characterisation and in vitro pharmacokinetic profiling of acrylamide-based irreversible inhibitors. Finally, labelling of these compounds with fluorine-18 and initial results towards their radiopharmacological evaluation will be discussed.

  • Lecture (others)
    Pharmazeutisches Kolloquium, 03.11.2017, Bonn, Deutschland

Publ.-Id: 26665

Metallic Photocathodes for Superconducting RF Photo Guns

Teichert, J.; Xiang, R.

Report on results and status of photocathode development and measurement in the EC project EuCARD2.

Keywords: photocathode; quantum efficiency; magnesium; lead; niobium

  • Lecture (Conference)
    EuCARD2 WP11 Annual Meeting, 14.-15.03.2017, Warsaw/Swierk, Poland

Publ.-Id: 26664

Structural characterization of (Sm,Tb)PO4 solid solutions and pressure-induced phase transitions

Heuser, J. M.; Palomares, R. I.; Bauer, J. D.; Lozano Rodriguez, M. J.; Cooper, J.; Lang, M.; Scheinost, A. C.; Schlenz, H.; Winkler, B.; Bosbach, D.; Neumeier, S.; Deissmann, G.

Sm1-xTbxPO4 solid solutions were synthesized and extensively characterized by powder X-ray diffraction, vibrational spectroscopy, and X-ray absorption spectroscopy. At ambient conditions solid solutions up to x = 0.75 crystallize in the monazite structure, whereas TbPO4 is isostructural to xenotime. For x = 0.8 a mixture of both polymorphs was obtained. Moreover, a phase with anhydrite structure was observed coexisting with xenotime, which was formed due to mechanical stress. Selected solid solutions were investigated at pressures up to 40 GPa using in situ high pressure synchrotron X-ray diffraction and in situ high pressure Raman spectroscopy. SmPO4 and Sm0.5Tb0.5PO4 monazites are (meta)stable up to the highest pressures studied here. TbPO4 xenotime was found to transform into the monazite structure at a pressure of about 10 GPa. The transformation of Sm0.2Tb0.8PO4 xenotime into the monazite polymorph commences already at about 3 GPa. This study describes the reversibility of the pressure-induced (Sm,Tb)PO4 xenotime-monazite transformation.

Keywords: monazite; xenotime; anhydrite; solid solutions; phase transformation


Publ.-Id: 26663

MoS₂ quantum dots as an efficient catalyst material for oxygen evolution reaction

Mohanty, B.; Ghorbani-Asl, M.; Kretschmer, S.; Ghosh, A.; U. Guha, P.; Panda, S. K.; Jena, B.; Krasheninnikov, A. V.; Jena, B. K.

The development of an active, earth-abundant and inexpensive catalyst for oxygen evolution reaction (OER) is highly desirable but remains a great challenge. Here, by combining experiments and first-principles calculations, we demonstrate that MoS₂ quantum dots (MSQDs) are an efficient material for OER. We use a simple route for the synthesis of MSQDs from a single precursor in aqueous medium avoiding the formation of unwanted carbon quantum dots (CQDs). The as-synthesized MSQDs exhibit higher OER activity with the lower Tafel slope as compared to that for the state-of-the-art catalyst IrO₂/C. The potential cycling of the MSQDs activates the surface and improves the OER catalytic properties. The density functional theory calculations reveal that MSQD vertices are reactive and the vacancies at the edges also promote the reaction, which indicates that the small flakes with defects at the edges are efficient for OER. The presence of CQDs affects the adsorption of reaction intermediates and dramatically suppresses the OER performance of the MSQDs. Our theoretical and experimental findings provide important insights into the synthesis process of MSQDs and their catalytic properties and suggest promising routes to tailoring the performance of the catalysts for OER applications.

Keywords: MoS₂; Quantum Dots; Electrocatalysis; Oxygen Evolution Reaction; First-Principles Calculations; Defects


Publ.-Id: 26662

Si amorphization by focused ion beam milling: Point defect model with dynamic BCA simulation and experimental validation

Huang, J.; Loeffler, M.; Muehle, U.; Moeller, W.; Mulders, J. J. L.; Kwakman, L. F. T.; van Dorp, W. F.; Zschech, E.

A Ga focused ion beam (FIB) is often used in transmission electron microscopy (TEM) analysis sample preparation. In case of a crystalline Si sample, an amorphous near-surface layer is formed by the FIB process. In order to optimize the FIB recipe by minimizing the amorphization, it is important to predict the amorphous layer thickness from simulation. Molecular Dynamics (MD) simulation has been used to describe the amorphization, however, it is limited by computational power for a realistic FIB process simulation. On the other hand, Binary Collision Approximation (BCA) simulation is able and has been used to simulate ion-solid interaction process at a realistic scale. In this study, a Point Defect Density approach is introduced to a dynamic BCA simulation, considering dynamic ion-solid interactions. We used this method to predict the c-Si amorphization caused by FIB milling on Si. To validate the method, dedicated TEM studies are performed. It shows that the amorphous layer thickness predicted by the numerical simulation is consistent with the experimental data. In summary, the thickness of the near-surface Si amorphization layer caused by FIB milling can be well predicted using the Point Defect Density approach within the dynamic BCA model.

Keywords: Amorphization; Beam plasma interactions; Computational chemistry; Defect density; Focused ion beams; High resolution transmission electron microscopy; Ion beams; IonsMilling (machining); Molecular dynamics; Point defects; Silicon; Surface defects; Transmission electron microscopy

Publ.-Id: 26661

Addendum: Ion beam irradiation of nanostructures: sputtering, dopant incorporation, and dynamic annealing

Holland-Moritz, H.; Johannes, A.; Möller, W.; Ronning, C.

A previously published formalism to derive nanosphere sputtering yields is corrected and refined.

Keywords: Ion Irradiation; Nanostructures; Sputtering

Publ.-Id: 26660

Relative biological effectiveness in proton beam therapy – current knowledge and future challenges

Lühr, A.; von Neubeck, C.; Krause, M.; Troost, E. G. C.

This review summarizes recent abstracts to international meetings and international peer-reviewed publications on the potential variation of the RBE and its possible side-effects, and compares these with past publication on photon beam irradiation. Moreover, recent literature on how to deal with potential RBE variations and the resulting uncertainty during treatment planning as well as solutions to correlate dose and LET distributions to subsequent (magnetic resonance) imaging changes are presented. Finally, the current status on RBE measured in vitro and in vivo is reviewed and input given on how to bridge the existing gap between lab and clinic.

Keywords: RBE; relative biological effectiveness; clinical side-effects; in vitro and in vivo models; MRI; dose recalculation

Publ.-Id: 26658

Prognostic Value of Head and Neck Tumor Proliferative Sphericity From 3’-Deoxy-3’-[18F] Fluorothymidine Positron Emission Tomography

Majdoub, M.; Hoeben, B.; Troost, E. G. C.; Oyen, W.; Kaanders, J.; Le Rest, C.; Visser, E.; Visvikis, D.; Hatt, M.

Background: Enhanced proliferative activity in head and neck squamous cell carcinoma (HNSCC) adversely affects outcome after (chemo)radiotherapy. 3’-deoxy-3’-[18F] fluorothymidine (18F-FLT) positron emission tomography (PET) can be used for quantifying tumour proliferation and its changes during therapy. In this study, we investigated the complementary prognostic value of sphericity and standard metrics in 18F-FLT PET images before and during (chemo)radiotherapy regarding 4-year disease-free survival (DFS).
Methods: 48 HNSCC patients treated with radiotherapy (n=32) or chemoradiotherapy (n=16) with curative intent, underwent 18F-FLT PET-CT scans before and in the second week of treatment. Patients were followed for a median of 52 months. Primary tumours were delineated using the Fuzzy Locally Adaptive Bayesian algorithm. The proliferative volumes were further characterized by extracting SUV, volume and sphericity. Prognostic value for disease-free survival (DFS) of features was assessed using Kaplan-Meier survival analysis.
Results: In univariate analysis, the per-treatment sphericity (p=0.02, HR=4.2 [1.3– 13.9]) and SUVmean (p=0.03, HR=4.1 [1.2 – 14.2]) were prognostic factors, whereas none of the pre-treatment features were significant. Reduction in SUVmax (p=0.04, HR=4 [1.1 – 15.1]) was also a prognostic factor, but reduction of proliferative tumour volume did not reach statistical significance. The best stratification of patients for DFS was achieved with the combination of the two per-treatment features SUVmean and sphericity (p<0.001, HR=6.7 [1.8 – 25]).
Conclusion: High sphericity combined with low mean 18F-FLT SUV during treatment were associated with better DFS. These results suggest the potential prognostic value of advanced tumour proliferative volume characterization from 18F-FLT PET in HNSCC that may be further explored in larger cohorts.

Publ.-Id: 26657

Strain distribution in GaAs/InxGa1-xAs core/shell nanowires grown by molecular beam epitaxy on Si(111) substrates

Balaghi, L.; Hübner, R.; Bussone, G.; Grifone, R.; Hlawacek, G.; Grenzer, J.; Schneider, H.; Helm, M.; Dimakis, E.

Strain distribution in GaAs/InxGa1-xAs core/shell nanowires grown by molecular beam epitaxy on Si(111) substrates

  • Lecture (Conference)
    Workshop on Surface and Interface Diffraction in Condensed Matter Physics and Chemistry (CMPC), 09.-10.03.2017, DESY, Hamburg, Germany

Publ.-Id: 26656

Strain distribution in highly mismatched GaAs/(In,Ga)As core/shell nanowires

Balaghi, L.; Hübner, R.; Bussone, G.; Grifone, R.; Ghorbani, M.; Krasheninnikov, A.; Hlawacek, G.; Grenzer, J.; Schneider, H.; Helm, M.; Dimakis, E.

The core/shell nanowire (NW) geometry is suitable for the pseudomorphic growth of highly mismatched semiconductor heterostructures, where the shell thickness can exceed significantly the critical thickness in equivalent planar heterostructures. We have investigated the accommodation of misfit strain in self-catalyzed GaAs/(In,Ga)As core/shell NWs grown on Si (111) substrates by molecular beam epitaxy. The NWs have their axis along the [111] crystallographic direction, six {11 ̅0} sidewalls, and their crystal structure is predominantly zinc blende. For strain analysis, we used Raman scattering spectroscopy, transmission electron microscopy, X-ray diffraction and photoluminescence spectroscopy. Within a certain range of core/shell dimensions and shell composition, our findings reveal that the elastic energy in NWs without misfit dislocations can be confined exclusively inside the core, allowing for the shell to be strain-free. The experimental results are also compared with theoretical simulations of the strain (continuum elasticity theory) and phonon energy (density functional theory).

  • Lecture (Conference)
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Germany

Publ.-Id: 26655

Nanoscale surface patterning by non-equilibrium self-assembly of ion-induced vacancies and ad-atoms

Facsko, S.; Ou, X.; Engler, M.; Erb, D.; Skeren, T.; Bradley, R. M.

Various self-organized nanoscale surface patterns can be produced by low- and medium-energy ion beam irradiation [1], depending on the irradiation conditions. Hexagonally ordered dot or pit patterns, checkerboard patterns, as well as periodic ripple patterns oriented perpendicular or parallel to the ion beam direction are formed spontaneously during the continuous surface erosion by ion sputtering. On amorphous surfaces, the formation of these patterns results from an interplay of different roughening mechanisms, e.g. curvature dependent sputtering, ballistic mass redistribution, or altered surface stoichiometry on binary materials, and smoothing mechanisms, e.g. surface diffusion or surface viscous flow.

An additional surface instability arises above the recrystallization temperature of the material. In this case, ion induced bulk defects are dynamically annealed and amorphization is prevented. The diffusion of ion-induced vacancies and ad-atoms on the crystalline surface is now affected by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier to cross terrace steps. Vacancies and ad-atoms are trapped on terraces and can nucleate to form new extended pits or terraces, respectively [2].

For the mathematical description of the pattern formation and evolution in the reverse epitaxy regime, a continuum equation can be used which combines the ballistic effects of ion irradiation and effective diffusion currents due to the ES barrier on the crystalline surface. By comparison with experimental studies of pattern formation on Ge and GaAs surfaces at different angles and temperatures, we will show that the pattern evolution is determined by the surface instability due to the ES barrier, surface diffusion, and ballistic effects of ion irradiation.

[1] A. Keller and S. Facsko, Materials 3, 4811 (2010).
[2] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender, and S. Facsko, Nanoscale 7, 18928 (2015).

Keywords: ion beam irradiation; surface patterning; reverse epitaxy

  • Invited lecture (Conferences)
    20th International Conference on Surface Modification of Materials by Ion Beams, 09.-14.07.2017, Lisbon, Portugal

Publ.-Id: 26654

Constraining the economic potential of by-product recovery by using a geometallurgical approach: the example of rare earth element recovery at Catalão I, Brazil

Pereira, L.; Birtel, S.; Möckel, R.; Michaux, B.; Silva, A. C.; Gutzmer, J.

Located in Goiás state of Brazil, Catalão I is a carbonatite complex that is part of the Alto Paranaíba Igneous Province. A niobium deposit in the complex, named Boa Vista, has been exploited for more than 40 years and is currently the world’s second largest niobium producer. The deposit is owned and operated by Niobrás, part of China Molybdenum Co.. Phosphates are also produced in the Catalão I complex at the Chapadão mine, an operation that is owned and operated by Copebrás, also part of China Molybdenum Co.. The phosphate production tailings are reprocessed at Boa Vista for recovering niobium as a by-product. Rare earth elements, albeit present in significant concentrations, are not recovered as by-products. This study provides quantiative mineralogical and microfabric data on the occurrence of rare earth minerals – and provides constraints for concentration of rare earth elements during current niobium beneficiation routes at the Tailings plant. Nine samples from different stages of the process were taken and characterized by Mineral Liberation Analyzer, X-ray powder diffraction and bulk rock chemistry. The recovery of rare earth elements in each of the tailing streams was quantified by mass balance. The results are used to identify the most suitable approach to recover REE as a by-product – without placing limitations on niobium production.
Monazite, the most common rare earth mineral identified in the feed to the Tailings Plant, occurs as Ce-rich and La-rich varieties that can be easily distinguished by SEM-based image analysis. Quartz, FeTi-oxides and several phosphate minerals are the main gangue minerals. The highest rare earth element content concentrations (1.75 wt.% TREO) and the greatest potential for REE processing are reported for the final flotation tailings stream. To place tentative economic constraints on REE recovery from the tailings material, an analogy to the Brown's Range deposit in Australia is drawn. Its technical flow sheet was used to estimate the cost for a hypothetical REE-production at Boa Vista. Parameters derived from SEM-based image analysis were used to model possible monazite recovery and concentrate grades. This exercise illustrates that a marketable REE concentrate could be obtained at Boa Vista, if the process could recover all particles with at least 60% of monazite on their surface. Applying CAPEX and OPEX values similar to that of Brown’s Range showed that such an operation would be profitable at current REE prices.

Keywords: REE production; by product; geometallurgy; economic assement


  • Secondary publication expected

Publ.-Id: 26653

Ion-induced patterning of Ge surfaces above the recrystallization temperature

Facsko, S.; Ou, X.; Engler, M.; Erb, D.; Skeren, T.; Bradley, R. M.

Low- and medium-energy ion beam irradiation can lead to various self-organized nanoscale surface patterns depending on the irradiation conditions [1]. If the sample temperature is below the material recrystallization temperature, the ion bombardment results in amorphization of the surface. On such amorphous surfaces, the formation of nanoscale patterns is driven by the interplay of different ion beam induced roughening and smoothing mechanisms: curvature dependent sputtering, ballistic mass redistribution or altered surface stoichiometry (on binary materials) are roughening the surface, while surface diffusion or surface viscous flow are smoothing it.

An additional surface instability arises above the recrystallization temperature of the material, when the surface remains crystalline during ion irradiation. In this case, the diffusion of ion-induced vacancies and ad-atoms on the crystalline surface is affected by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier to cross terrace steps. Vacancies and ad-atoms are thereby trapped on terraces and nucleate to form new extended pits or islands, respectively [2]. In molecular beam epitaxy mounds with different facets are formed due to the ES barrier. In ion-induced reverse epitaxy the additionally diffusing vacancies lead to different morphologies, like inverse pyramid and checkerboard patterns.

However, on Ge (001) surfaces irradiated at incidence angles greater than 50° mound patterns are formed and for angles greater than 75° the pattern turns into ripples. This transition from checkerboard over mound to ripple patterns in the reverse epitaxy regime can be described by a continuum equation which combines the ballistic effects of ion irradiation and the effective diffusion currents due to the ES barrier on the crystalline surface.

[1] A. Keller and S. Facsko, Materials 3, 4811 (2010).
[2] X. Ou, A. Keller, M. Helm, J. Fassbender, and S. Facsko, Phys. Rev. Lett. 111, 016101 (2013).

Keywords: ion beam irradiation; surface patterning; reverse epitaxy

  • Lecture (Conference)
    Nanopatterning 2017, 26.-28.06.2017, Helsinki, Finland

Publ.-Id: 26652

REE by-product potential at Catalão I: a geometallurgical assessment

Birtel, S.; Pereira, L.; Silva, A. C.; Gutzmer, J.

A geometallurgical study of the rare earth mineralogy and microfabric relations was undertaken at the Catalão I deposit, Chapadão mine, Goiás/Brazil. At Catalão I a carbonatite and its lateritic cap have been exploited for more than 40 years; being the world’s second largest niobium deposit and producer. The study was undertaken to assess the technical possibility and feasibility to recover rare earth minerals as a by-product of niobium production. For this purpose, nine samples were collected from different stages of the beneficiation process in the so-called Tailings Plant. Mineral Liberation Analyzer (MLA), X-ray powder diffraction and bulk rock chemistry were used to characterize these samples for their processing properties. The recovery of REE in each of the tailing streams was quantified by mass balance. The results were used to identify the most suitable approach to recover REE as a by-product – without placing constraints on niobium production.

Monazite is the dominant REE mineral in the feed to the Tailings Plant; this feed heralds from the exploitation of lateritic weathering residues. Quartz, FeTi-oxides and phosphate minerals are the main gangue minerals. The highest REE contents are reported in the final flotation tailings stream (1.75 wt.% TREO), with monazite-bearing particles in a size range suitable for further processing (10-120 µm size range). Yet, liberation of monazite in this particle size fraction is rather poor. By seeking an analogy to the Brown's Range deposit in Australia, a tentative economic assessment is attempted for REE production at Chapadão. For this purpose, parameters derived from MLA were used to model possible monazite recovery and concentrate grades. This assessment illustrates that a marketable REE concentrate may be obtained as a by-product at Chapadão even at current REE prices.

Keywords: REE production; by product; geometallurgy

  • Contribution to proceedings
    Resources for Future Generations PREMIER CONFERENCE ON ENERGY • MINERALS • WATER • THE EARTH, 16.-21.06.2018, Vancouver, Kanada
  • Lecture (Conference)
    Resources for Future Generations PREMIER CONFERENCE ON ENERGY • MINERALS • WATER • THE EARTH, 16.-21.06.2018, Vancouver, Canada

Publ.-Id: 26651

Extremely lattice mismatched GaAs/InxGa1-xAs core/shell nanowires: coherent growth and strain distribution

Balaghi, L.; Hübner, R.; Bussone, G.; Grifone, R.; Grenzer, J.; Ghorbani Asl, M.; Krasheninnikov, A.; Hlawacek, G.; Schneider, H.; Helm, M.; Dimakis, E.

Compound semiconductors are versatile materials due to the possibility to tailor their (opto)electronic properties by selecting their composition appropriately. When grown heteroepitaxially, though, this possibility is constrained by the lattice mismatch with the substrate. InxGa1-xAs is a good example because it can have, depending on x, a suitable direct optical band gap for optoelectronic applications in the infrared (e.g. telecommunication wavelengths) or high electron mobility for high-speed transistors. However, the practical choices of x are limited by the available substrates, typically GaAs for low x or InP for x≈0.53.
Nanowires are a promising alternative for the realization of epitaxial heterostructures with high lattice mismatch due to their unique geometry and high surface-to-volume ratio. In addition, the possibility of monolithic integration in Si-CMOS platforms adds to their technological significance. In this work, we have investigated the growth of free-standing GaAs/InxGa1-xAs core/shell nanowires on Si(111) substrates by molecular beam epitaxy and the accommodation of lattice mismatch therein. Specifically, we have concentrated on highly lattice mismatched heterostructures (x=0.20-0.80) and very thin cores (diameter < 25 nm).
Self-catalyzed growth of very thin GaAs core nanowires with a sufficiently low number density (to avoid beam shadowing during the shell growth) was possible on native-oxide/Si(111) substrates, after an in situ treatment of the latter with Ga droplets. This resulted in zinc blende nanowires with their axis along the [111] crystallographic direction and six {1-10} sidewalls. Subsequently, conformal overgrowth of the InxGa1-xAs shell was obtained only under kinetically limited growth conditions that suppressed mismatch-induced bending phenomena. The strain in the core and the shell was studied systematically as a function of the shell composition and thickness. To that end, we used Raman scattering spectroscopy, transmission electron microscopy and (synchrotron/lab source) X-ray diffraction, and compared the results with theoretical predictions based on continuum elasticity and density functional theories. All findings point to the existence of anisotropic tensile strain in the core that increases (as quantified by Raman measurements) with increasing the shell thickness, whereas the corresponding compressive strain in the shell decreases to zero. Our work demonstrates the opportunity to grow not only relaxed InxGa1-xAs shells with high structural quality (as adopted from the GaAs core) in a wide, if not the whole, compositional range, but also highly strained (tensile) GaAs cores with (opto)electronic properties that remain to be explored.

Keywords: core/shell nanowire; strained core; relaxed shell

  • Poster
    Nanowire Week 2017, 29.05.-02.06.2017, Lund, Sweden

Publ.-Id: 26650

Nanoscale surface patterning of crystalline semiconductor surfaces by broad ion beam irradiation

Facsko, S.; Ou, X.; Engler, M.; Erb, D.; Skeren, T.; Bradley, R. M.

arious self-organized nanoscale surface patterns can be produced by low- and medium-energy ion beam irradiation [1], depending on the irradiation conditions. Hexagonally ordered dot or pit patterns, checkerboard patterns, as well as periodic ripple patterns oriented perpendicular or parallel to the ion beam direction are formed spontaneously during the continuous surface erosion by ion sputtering. On amorphous surfaces, the formation of these patterns results from an interplay of different roughening mechanisms, e.g. curvature dependent sputtering, ballistic mass redistribution, or altered surface stoichiometry on binary materials, and smoothing mechanisms, e.g. surface diffusion or surface viscous flow.
An additional surface instability arises above the recrystallization temperature of the material. In this case, ion induced bulk defects are dynamically annealed and amorphization is prevented. The diffusion of ion-induced vacancies and ad-atoms on the crystalline surface is now affected by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier to cross terrace steps. Vacancies and ad-atoms are trapped on terraces and can nucleate to form new extended pits or terraces, respectively [2].
For the description of the pattern formation and evolution in the reverse epitaxy regime, a continuum equation can be used which combines the ballistic effects of ion irradiation and effective diffusion currents due to the ES barrier on the crystalline surface. By comparison with experimental studies of pattern formation on Ge and GaAs surfaces at different angles and temperatures, we will show that the pattern evolution is determined by the combined action of surface instability due to the ES barrier, surface diffusion, and ballistic effects of ion irradiation.
[1] A. Keller and S. Facsko, Materials 3, 4811 (2010).
[2] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender, and S. Facsko, Nanoscale 7, 18928 (2015).

Keywords: ion irradiation; surface patterning; reverse epitaxy

  • Invited lecture (Conferences)
    MRS Fall Meeting, 26.11.-1.12.2017, Boston, USA

Publ.-Id: 26648

Positronium probing of pores in zirconia nanopowders

Prochazka, I.; Cizek, J.; Lukac, F.; Melikhova, O.; Hruska, P.; Anwand, W.; Liedke, M. O.; Konstantinova, T. E.; Danilenko, I. A.

Zirconium di-oxide (ZrO2 , zirconia) receives nowadays a big attention because of a variety of advantageous properties which make zirconia-based materials useful in numerous fields of practice, in particular, in ceramic industry and other high-temperature applications. To make high-temperature phases of zirconia stabilised down to room temperature, doping of the host lattice by proper metal cations has to be usually performed. Nanopowders are currently focused on as starting substances for manufacturing ZrO2-based ceramics by sintering, because well-homogenised materials of a low porosity can be produced more easily. Nanometer-sized defects associated to grain boundaries (GBs) become then to play an enhanced role in nanopowders due to enlarged volume fraction of GBs. Positrons and positronium (Ps) atoms can serve as efficient probes of different structures encountered in particular stages of manufacturing ZrO2-based functional materials. In the present contribution, conventional positron and Ps lifetime measurements were carried out on a variety of zirconia-based nanopowders and ceramics obtained by sintering these nanopowders. Nanopowders studied were doped with various metal cations (Y3+, Cr3+, Ce4+, Mg2+) and differed also in thermal treatment prior sintering. Lifetime experiments were conducted in air or in vacuum and combined with Doppler broadening measurements using slow-positron beam and supplemented with X-ray diffraction (XRD) and mass-density (MD) measurements. In Figure, variability of the lifetime spectra observed is illustrated. In a range of lifetimes from a few ns to ≈ 70 ns, up to three individual lifetime components could be identified, see Figure, (a) and (b). Such observations unambiguously testified Ps formation with subsequent ortho-Ps annihilation. On the other hand, an absence of the ortho-Ps components was found in certain nanopowders giving thus an evidence of a strong Ps inhibition, see Figure, (c). Pore sizes were estimated using current models of correlation between observed ortho-Ps lifetime and pore size. Origins of pores will be discussed on the basis of the ortho-Ps data in combination with the results of slowpositron beam, XRD and MD measurements.

Keywords: zirconia nanopowders; Positronium; grain boundaries; PAS; PALS

  • Poster
    12th International Workshop on Positron and Positronium Chemistry, 28.08.-01.09.2017, Lublin, Poland

Publ.-Id: 26647

Positronium formation in nanostructured metals

Čížek, J.; Melikhova, O.; Hruška, P.; Vlček, M.; Anwand, W.; Liedke, M. O.; Novotný, M.; Bulíř, J.; Cheng, Y.

Nanostructured metals containing nano- and micro-cavities can be prepared by various methods. Morphology of cavities can be controlled by varying the parameters of preparation. This enables fabrication of nanostructured metals with properties tailored for particular applications, e.g. nanostructured metals containing fractal-like cavities with a wide size distribution are used as omnidirectional absorbers of light from the visible into the infrared spectral region. Positronium (Ps) is a non-destructive probe of nanoscopic cavities capable of precise determination of their size distribution. In conventional metals Ps does not form since any bound state of positron and electron is quickly destroyed by the screening of conduction electrons. However, a thermalized positron escaping from a metal through inner surface into a cavity may form Ps by picking an electron on the surface. This process was examined in the present work on nanostructured metals prepared three various methods: (i) thin films of black metals (Au and Al) evaporated in N2 atmosphere; (ii) nano-porous bulk Pd prepared by electrochemical etching of PdCo alloy; (iii) nanostructured Gd prepared by selective evaporation of Mg from MgGd alloy. Our investigations confirmed that Ps was formed in nanostructured metals. The the size distribution of nano-pores in the samples has been determined. The mechanism of Ps formation in these samples is discussed in the paper.

Keywords: Positronium; Nanostructured metals; pores; black Au; Al; Pd; Gd

  • Lecture (Conference)
    12th International Workshop on Positron and Positronium Chemistry, 28.08.-01.09.2017, Lublin, Poland

Publ.-Id: 26646

Nanomembranes Modified by Highly Charged Ions

Facsko, S.; Wilhelm, R. A.; Gruber, E.; Heller, R.; Gölzhäuser, A.; Beyer, A.; Turchanin, A.; Aumayr, F.

Smart membranes play a key role in different sensor applications, e.g. for drug and explosive detection. By tailoring the structure and properties of these membranes physical-chemical functionality can be added to the sensor. One way of modifying membranes is by particle irradiation with electrons or ions. Specifically, highly charged ions (HCI) carry a large amount of potential energy (the stored ionization energy) which is released when interacting with the membrane creating nanopores by a single HCI impact. In order to be able to control the ion induced modification, e.g. defining the pore size, the energy deposition in the membranes has to be determined.
For the interaction of HCI with thin membranes this is particularly interesting because the HCIs are still in a pre-equilibrium interaction regime for thicknesses below a few nm. Within 1 nm thick carbon nano membranes (CNMs) for instance, holes are produced by the passage of highly charged Xeq+ ions only above a threshold in the potential energy of the HCI which depends on the kinetic energy [1]. In order to study the stopping force of the HCIs in the membrane we examined the charge state and the energy loss of the Xeq+ ions after their passage through the CNM. Surprisingly, two distinct exit charge distributions were observed [2]. While some of the ions pass the membrane with almost no charge loss, other ions lose most of their charge. Apparently, the observed charge distribution reflects two different impact parameter regimes. The different impact parameter regimes are also connected to different energy losses: ions with large impact parameters are not stopped, whereas ions in close collisions exhibit high stopping force which is strongly dependent on the incident charge state.
[1] R.A. Wilhelm, E. Gruber, R. Ritter, R. Heller, A. Beyer, A. Turchanin, N. Klingner, R. Hübner, M. Stöger-Pollach, H. Vieker, G. Hlawacek, A. Gölzhäuser, S. Facsko, and F. Aumayr, 2D Mater. 2, 1 (2015).
[2] R.A. Wilhelm, E. Gruber, R. Ritter, R. Heller, S. Facsko, F. Aumayr, Phys. Rev. Lett. 112, 153201 (2014).

Keywords: highly charged ions; nanomembranes

  • Invited lecture (Conferences)
    Towards Reality in Nanoscale Materials IX, 13.-16.02.2017, Levi, Finland

Publ.-Id: 26645

Porosimetry of ultra-low K materials and transformed porous glass-thin layers by Monenergetic Positron Source at ELBE facility

Attallah, A. G.; Koehler, N.; Dornberg, G.; Butterling, M.; Liedke, M. O.; Wagner, A.; Schulz, S. E.; Badawi, E.; Enke, D.; Krause-Rehberg, R.

The pore size of spin-on coated ultra-low K (ULK) materials cured at 4500C for different times was studied by the pulsed slow positron beam (MePS) at ELBE/HZDR. To investigate the pore formation in cured porous spin-on dielectrics, the pore size as a function of positron implantation energy was obtained for samples with different curing times. Such a study is performed to understand the dielectric damage behaviour of ULK dielectrics for the integration in Back-End of Line (BEOL). MePS results revealed that the films contain open and closed pores with ~ 3 nm in diameter which was confirmed by capping the samples. The highest pore concentration is located beneath the surface in the 0.2 - 0.5 m range (We plan to carry out ellipsometric porosimetry and FTIR during this summer). Pseudomorphic transformation of porous glass-thin layers, with pores of 40 - 50 nm diameter and a relatively small surface area, to MCM-41 with ~4 nm pores, with a higher surface area, was studied by MePS. The small pore size of MCM-41 was successfully detected with an intensity growth with transformation degree but the large pores were not detected at all. To understand the disability of detecting the large pores by positron annihilation lifetime, we plan to perform SEM measurements in the same depth as that of the implanted positrons (0.005-2.4 m).
Additionally, the increase in the intensity of positronium lifetime, which correlates the small pores, as a function of positron implantation energy could reflect inner pore isolation or poor interconnectivity.

Keywords: ultra-low K materials; Porosimetry; MePS; ELBE; Positronium

  • Lecture (Conference)
    12th International Workshop on Positron and Positronium Chemistry, 28.08.-01.09.2017, Lublin, Poland

Publ.-Id: 26644

In-situ investigations of the curing process in ultra low-k materials

Liedke, M. O.; Koehler, N.; Butterling, M.; Attallah, A. G.; Krause-Rehberg, R.; Hirschmann, E.; Schulz, S. E.; Wagner, A.

Porous spin-on glasses belong to ultra low-k (ULK) dielectrics and are promising candidates for integration in the semiconductor device fabrication technology. Their microstructure consists usually of interconnected pore networks distributed across the film rather than separated voids. The pore size and distribution are controllable to a large extent, however, the pore formation process itself is still not well understood. A dielectric damage during integration and material degradation of films with large porosity are still problematic issues. The first results on in-situ investigations of the pore formation during a curing process – a porogen removal by vacuum annealing will be presented. The main motivation is to obtain the insight into early stages of the pore formation and up to its full development. The in-situ annealing and Doppler Broadening – Positron Annihilation Spectroscopy (DB-PAS) measurements have been done on our Apparatus for In-situ Defect Analysis (AIDA) system [1], which is the end-station of the slow positrons beamline at HZDR. The comparison between preliminary ex-situ studies by means of DB-PAS [see Fig. 1], Positron Annihilation Lifetime Spectroscopy (PALS), and Fourier Transform Infrared Spectroscopy (FTIS) will be given.
In Fig. 1(a) it is shown that o-Ps emission increases with t, thus can be a probe of films porosity as long as they are capped. The curing time of 5-30min. is sufficient to fully develop the pore network [Fig. 1(b)]. Porosity development and distribution will be discussed for annealing temperatures in the 100-400°C range and varied annealing time.
[1] M.O. Liedke et al., Journal of Applied Physics 117, 163908 (2015).

Keywords: low-k materials; curing process; Porous spin-on glasses; PAS; AIDA; Positron Annihilation Spectroscopy

  • Lecture (Conference)
    12th International Workshop on Positron and Positronium Chemistry, 28.08.-01.09.2017, Lublin, Poland

Publ.-Id: 26643

Ion Beam-Enabled CMOS-Compatible Manufacturing of SETs Operating at Room Temperature

Facsko, S.; Heinig, K. H.; Stegemann, K. H.; Pruefer, T.; Xu, X.; Hlawacek, G.; Huebner, R.; Wolf, D.; Bischoff, L.; Moeller, W.; von Borany, J.

Electronics has been dominated by silicon since half a century. Si will dominate electronics another decade, however its functionality might change from classical field-controlled currents through channels (the Field Effect Transistor FET) to quantum mechanical effects like field-controlled hopping of single electrons from a source to a drain via a quantum dot (the Single Electron Transistor SET). Due to single electron hopping, the SET is the champion of low-power consumption. This is very attractive for the expanding Internet of Things (IoT): more and more devices need batteries and plugs. Therefore, together with improved batteries, advanced computation and communication must be delivered at extremely low-power consumption. At very low temperatures, the perfect functionality of SETs has been proven for tiny metal dots [1] and larger Si islands [2]. However, large-scale use of SETs requires Room Temperature (RT) operation, which can be achieved with tiny Si dots (<4 nm) in SiO2, exactly located between source and drain with distances of ~1…2 nm allowing quantum mechanical tunneling. Manufacturability of such nanostructures is the roadblock for large-scale use of SETs. Lithography cannot deliver the feature sizes of 1…3 nm required for RT operation. Therefore, there are currently intense studies to fulfill these requirements by self-organization processes. Convincing proof of concepts have been reported [see, e.g., 3] on room temperature operation of silicon based SETs. However, the self-organization processes developed so far are not reliable enough for large-scale integration.
The ion beam technique is a well-established technology in microelectronics used for doping and amorphization of semiconductors and even for ion beam synthesis of buried layers. The parameters of ion beam processing like ion flux, fluence and energy as well as the temperature and time of the subsequent thermal treatment are very well controllable. Therefore we searched for a self-organization process based on ion irradiation which overcomes the bottleneck of manufacturability of SETs working at room temperature.
Thus, in the framework of an international project funded by the European Commission [4], we develop an ion-assisted, CMOS-compatible process [4] which will provide both (i) self-assembly of a single Si dot and (ii) its self-alignment with source and drain.
Based on our knowledge of ion implantation [5,6] and irradiation [7] induced phase separation and Ostwald ripening processes as well as ion-assisted fabrication of non-volatile nanocluster memories [8], we concluded by computer simulations that phase separation of tiny, metastable SiOx volumes (<103 nm3) will transiently lead to a single Si nanodot in SiO2 (see Fig.2).
The tiny, metastable SiOx volume is formed by ion beam mixing of a bulk Si/SiO2/a-Si layer stack. In order to get the very small SiOx volume necessary for single dot formation, two approaches are used: (i) point-like Ne+ irradiation for fundamental studies, and (ii) broad beam Si+ irradiation of nanopillars for the device fabrication (see Fig. 3).
For both approaches, the predictive computer simulations use for the dynamical 3D ion beam mixing the recently developed program TRI3DYN [9]. TRI3DYN provides the initial conditions for phase separation and coarsening processes simulated (see, e.g. Fig. 2) with the 3D kinetic Monte Carlo program 3DkMC [6].
First results of our studies with the Helium Ion Microscope are shown in Figs. 4 and 5. The ion beam mixing of the SiO2 layer as imaged by EFTEM agrees nicely with that predicted by TRI3DYN simulations. Using this mixing profile as input for 3DkMC simulations, a single Si nanocluster is formed (Fig. 4). Although it appears to be extremely difficult to image a single Si nanodot of 2…3 nm diameter embedded in SiO2 in a ~50 nm thick TEM lamella, Fig 5 proves that after annealing such a single cluster can be formed. The next activities will be focused on the single Si nanodot fabrication in Si nanopillars and the optimization of this process for RT-SET fabrication.

This work has been funded by the European Union’s Horizon 2020 research and innovation program under grant agreement No 688072.

1. K. Maeda et al., ACS Nano (2012) 2798.
2. S. Ihara et al., Appl. Phys. Lett. 107 (2015) 13102. SET in SOI
3. V. Deshpande et al., Proc. of the IEDM12-Conf. (2012) 195.
4. Research Project IONS4SET funded by the European Commission
5. M. Strobel et al., NIM B147 (1999) 343.
6. M. Strobel, K.-H. Heinig, W. Möller, Phys. Rev. B64 (2001) 245422.
7. K.H. Heinig, T. Müller, B. Schmidt, M. Strobel, W. Möller, Appl. Phys. A77 (2003) 17.
8. T. Mueller et al., Appl .Phys. Lett. 81 (2002) 3049; ibid 85 (2004) 2373.
9. W. Möller, NIM B322 (2014) 23.

Keywords: ion irradiation; self-assembly; Si nanocrystals; single electron transistor

  • Invited lecture (Conferences)
    Ion-Surface Interactions 2017, 21.-25.08.2017, Moskow, Russia

Publ.-Id: 26642

Hydrogen-induced defects in Ti and their thermal stability

Melikhova, O.; Čížek, J.; Hruška, P.; Lukac, F.; Knapp, J.; Havela, L.; Mašková, S.; Anwand, W.; Liedke, M. O.

Titanium readily absorbs hydrogen and undergoes phase transition into the hydride phase (TiH2). In the hydride phase Ti is able to absorb the hydrogen concentration as high as 1.4 wt.%. These properties make Ti and Ti-based alloys attractive for hydrogen storage applications. Hydrogen absorption in titanium matrix may introduce open volume defects since the volume of TiH2 phase exceeds that of titanium matrix. Absorbed hydrogen may segregate at these defects forming defect-hydrogen complexes.
In the present work positron annihilation spectroscopy was employed for characterization of hydrogen-induced defects in titanium. Defects created by hydrogen loading from the gas phase were compared with those introduced by electrochemical hydrogen charging. In general hydrogen loading introduces a high density of dislocations and vacancy clusters created by agglomeration of hydrogen-induced vacancies. The mean size of vacancy clusters depends on the hydrogen absorption temperature.
Thermal stability of hydrogen absorbed in titanium and recovery of hydrogen-induced defects were studied by positron lifetime spectroscopy combined with in-situ X-ray diffraction and thermal desorption spectroscopy. Fig. 1 shows the temperature dependence of positron lifetimes and relative intensities of individual components for hydrogen gas loaded titanium. The decomposition of TiH2 phase is accompanied with introduction of additional vacancies agglomerating into vacancy clusters. Further annealing of the sample above 500 °C leads to recovery of dislocations.

Keywords: Ti; hydrogen; hydride phase; open volume defects; positron annihilation spectroscopy; positron lifetime

  • Poster
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Publ.-Id: 26641

Defects in high entropy alloy HfNbTaTiZr prepared by spark plasma sintering

Lukac, F.; Dudr, M.; Cinert, J.; Vilemova, M.; Cizek, J.; Harcuba, P.; Vlasak, T.; Zyka, J.; Malek, J.; Liedke, M. O.

High entropy alloys exhibit various combinations of interesting physical properties due to the formation of solid solution stabilized by high configurational entropy. High entropy alloy HfNbTaTiZr exhibits single phase solid solution with BCC structure when prepared by arc melting [1]. Grain refinement achieved in cold rolled samples after recrystallization remarkably enhanced ductility of this alloy [2]. Mechanical alloying by milling and subsequent sintering is a frequent production way of preparing fine grained alloys from chemical elements with high melting temperature. In addition, spark plasma sintering (SPS) method with applied pressure serves as a unique tool of powder metallurgy thanks to fast heating rates and low time of exposition to elevated temperatures. Therefore, the deformation energy introduced during mechanical alloying may be effectively consumed during short sintering process and presents the additional parameter for grain refinement. The present work presents characterization of HfNbTaTiZr alloy prepared by SPS.
Microstructure of samples prepared by SPS was compared with as cast ingots. The samples were characterized by X-ray diffraction and scanning electron microscopy. Positron annihilation spectroscopy was employed for characterization of defects introduced by SPS and their thermal stability.
[1] O.N. Senkov, J.M. Scott, S.V. Senkova. D.B. Miracle, C.F. Woodward: Journal of Alloys and Compounds 509, 6043-6048 (2011).
[2] O.N. Senkov, S.L. Semiatin; Journal of Alloys and Compounds 649, 1110-1123 (2015).

Keywords: High entropy alloys; HfNbTaTiZr; spark plasma sintering; Positron annihilation spectroscopy; X-ray diffraction; scanning electron microscopy

  • Poster
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Publ.-Id: 26640

Slow positron beam spectroscopy study of PMMA nanocomposite films with ion-synthesized silver nanoparticles

Kavetskyy, T. S.; Iida, K.; Nagashima, Y.; Elsayed, M.; Liedke, M. O.; Srinivasan, N.; Wagner, A.; Krause-Rehberg, R.; Šauša, O.; Telbiz, G.; Stepanov, A. L.

Understanding how the size, shape, and the aggregation state of the silver nanoparticles (NPs) are changed after integration into a target matrix is critical to enhance their performance, including molecular diagnostics, photonic and biomedical devices, which take advantage of the novel optical properties of these nanomaterials. In particular, the nanocomposites containing noble metal NPs dispersed in the polymer matrix by high-dose (> 1016 ions/cm2) implantation at low-energy ions (< 100 keV) can be used for the construction of plasmonic waveguides [1] and diffraction gratings [2]. Typically, form and size of Ag NPs in optically transparent matrices are connected with an appearance in visible absorption spectra of composite a surface plasmon resonance band. However, synthesis of Ag NPs by ion implantation in transparent polymer matrix such as polymethylmethacrylate (PMMA) has been found [1] to be quite difficult and unusual.
This problem can be solved with a powerful technique for the characterization of thin films – positron annihilation spectroscopy (PAS) using a variable-energy positron beam (VEPAS), – allowing depth-profiles from tens of nanometers up to several micrometers. This technique has been emerged as a key experimental tool for the understanding high-dose 40 keV boron-ion-implanted polymethylmethacrylate (B:PMMA) [3] with carbon nanostructures and Ag NPs loaded polymer brushes [4]. Also, the first attempt to find difference between the effects of carbonization and formation of Ag NPs in high-dose B:PMMA and Ag:PMMA nanocomposites has been done in the work [5] by using the Doppler broadening slow positron beam spectroscopy (DB-SPBS).
In the present work, the DB-SPBS technique was applied to characterize further the 30 keV Ag:PMMA nanocomposites fabricated by low-energy high-dose Ag-ion implantation. The results of depth profile of the S(Ep) parameter in the near-surface region of irradiated polymer were used to clarify indirectly a formation of Ag NPs in PMMA in dependence on ion dose. By comparative analysis with the S(Ep) parameter trend in polymer brushes with loaded Ag NPs [4], it is found that the density or mass of Ag NPs (‘Ag filling’) in Ag:PMMA increases as ion dose grows. The results obtained are discussed in terms of the positronium formation fraction in the irradiated part of polymer matrix and the model of carbon-shell Ag-core nanoparticles.
[1] A.L. Stepanov, Tech. Phys. 49, 143 (2004).
[2] M.F. Galyautdinov et al., Tech. Phys. Lett. 42, 182 (2016).
[3] T. Kavetskyy et al., J. Phys. Chem. B 118, 4194 (2014).
[4] G. Panzarasa et al., Nanotechnology 27, 02LT03 (2016).
[5] T. Kavetskyy et al., J. Phys.: Conf. Ser. 791, 012028 (2017).

Keywords: positron annihilation spectroscopy (PAS); variable-energy positron beam (VEPAS); PMMA nanocomposite films; Ag

  • Lecture (Conference)
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Publ.-Id: 26639

Defects and porosity in zirconia-based nanomaterials: a study by slow-positron beam technique

Prochazka, I.; Cizek, J.; Melikhova, O.; Lukac, F.; Hruska, P.; Anwand, W.; Liedke, M. O.; Brauer, G.; Konstantinova, T. E.; Danilenko, I. A.

A variety of advantageous thermal, electrical and mechanical properties of zirconium di-oxide (ZrO2, zirconia) make zirconia-based materials widely used in many industrial areas, in particular, in ceramic industry and other high-temperature applications. Doping of the ZrO2 host lattice by proper metal cations is a prerequisite of stabilisation of the high- temperature cubic and tetragonal phases down to room temperature as well as improvement of other functional properties. The use of nanopowders as initial substances in manufacturing ZrO2-based nanoceramics by sintering leads to well-homogenised materials of a low porosity. Due to an appreciable volume fraction of grain boundaries (GBs), pores and nanometer-sized open-volume defects associated to GBs become significant in nanopowders. Obviously, positron as well as positronium (Ps) atom becomes efficient
probes of microstructure evolution during production of ZrO2-based functional nanomaterials by sintering.
In the present contribution, investigation of several zirconia-based nanopowders as well as ceramics, obtained by sintering these nanopowders, will be reported. Nanopowders under study were doped with metal cations of various valency (Mg2+, Y3+, Cr3+, Ce4+) and differed also in thermal treatment. Doppler broadening (DB) measurements using slow-positron beam were conducted in the positron energy E ranging from 0.03 eV to 35 keV and the ordinary S and W shape parameters as well as the relative 3γ fractions were evaluated as functions of E. In Figure, an example of measured S(E) curves is given illustrating the sintering induced disappearance of open volume defects and para-Ps formation as well as grain growth could be observed. The VEPFIT models were fitted to the measured S(E), W(E) curves. The DB experiments were supplemented with the conventional positron lifetime, X-ray diffraction (XRD) and mass-density (MD) measurements. Nature and depth distributions of open-volume defects will be discussed on the basis of the slowpositron beam results correlated with the data on positron lifetimes, XRD and MD.

Keywords: positron annihilation spectroscopy; zirconia; nanomaterials; nanopowders

  • Lecture (Conference)
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Publ.-Id: 26638

Slow positron annihilation studies of Pd-Mg multilayers

Hruška, P.; Čížek, J.; Bulíř, J.; Lukáč, F.; Anwand, W.; Liedke, M. O.; Fekete, L.; Melikhova, O.; Lančok, J.

Palladium is well known for its excellent hydrogen absorption kinetics. The gravimetric hydrogen absorption capacity of Pd is however only 0.93 wt. %. Magnesium exhibits a high hydrogen absorption capacity up to 7.6 wt. %, however the hydrogen absorption kinetics is slow. The aim of this work was to create thin Pd-Mg multilayered films combining positive hydrogen absorption properties of both elements. Pd-Mg multilayers were deposited by RF magnetron sputtering on fused silica substrates coated with 100 nm thick Pd wetting layer. The multilayers consist of alternating Pd and Mg layers (3, 12 and 60) of the same thickness. Three types of Pd-Mg multilayers were compared: (i) as deposited samples, (ii) hydrogen gas loaded samples at room temperature and H2 pressure of 4000 Pa for 2 h, (iii) samples annealed up to 450°C under Ar atmosphere. Defect structure of Pd-Mg multilayers was characterized using variable energy positron annihilation spectroscopy. Doppler broadening of the annihilation photopeak was analyzed using the S and W line-shape parameters and the measured S(E) curves were fitted using the VEPFIT code. The development of the structure during the annealing of the films was monitored by in-situ X-ray diffraction. Atomic force microscopy was employed for the study of the surface morphology. All films were characterized by nanocrystalline structure with a high density of grain boundaries with open-volume defects capable of positron trapping. The density of grain boundaries is determined by the mean grain size which increases with increasing thickness of a single phase layer. Hydrogen loading led to buckling of the film and introduced additional defects into the film. Annealing of the multilayers leads to diffusion of Mg atoms into the Pd layers and precipitates of Mg-Pd phase are formed.

Keywords: PAS; slow positron beam; positron annihilation spectroscopy; Pd; Mg; multilayers

  • Lecture (Conference)
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Publ.-Id: 26637

Magnetic phase transitions in ns-laser irradiated FeAl systems: the role of open volume defects

Liedke, M. O.; Bali, R.; Hübner, R.; Gradauskaite, E.; Ehrler, J.; Wang, M.; Potzger, K.; Zhou, S.; Wagner, A.

Fe60Al40 alloys exhibit disorder dependent magnetic phase transitions (MPT), e.g., a ferromagnetic disordered A2-phase turns into a paramagnetic ordered B2-phase [1]. The ordered B2-phase, formed due to annealing up to 500°C in vacuum can be reversed to the disordered A2-phase via ion-irradiation [2]. It has been shown that the physical origin of MPT is related to the so-called anti-site disorder (ASD), i.e., variations in the number of Fe-Fe nearest neighbors due to disordering of the system [3]. However, variations of the lattice parameter, secondary phases, and changes in the concentration and size of open volume defects may play an important role as well. Here, an excimer UV ns-laser has been utilized to induced defects and examine the role of ASD and defects onto magnetic properties of Fe60Al40. Samples of 40 nm thick Fe60Al40 films with different initial order levels were exposed to a range of laser fluences: (i) Ne+ irradiated fully-disordered (A2- Fe60Al40), and (ii) vacuum annealed ordered alloys (B2- Fe60Al40) and (iii) as-grown semi-disordered (A2/B2- Fe60Al40). It is seen that for laser pulses of fluences below 100 mJ·cm^-2 cause subtle changes to the magnetization depending on the Fe60Al40 initial state, whereas for fluences above 150 mJ·cm-2, strong increase in ferromagnetism is observed for all Fe60Al40 initial states. The laser irradiated samples were probed with the Positron Annihilation Spectroscopy (PAS) to analyze for the existence of vacancies and/or phase separation. Although the low fluence region shows nearly no variation in vacancy defect concentration, a slight increase in the number of Al atoms around defect sites is found. For the high fluence regime, it is seen that a large variation in vacancy defects occurs, followed by pronounced phase separation. Structural analysis of the phase separated films shows strong migration of Al atoms leaving behind Fe-enriched regions, consistent with the PAS spectra.
[1] M. O. Liedke et al., J. Appl. Phys. 117, 163908 (2015)
[2] J. Fassbender, et. al., Phys. Rev. B 77, 174430 (2008)
[3] R. Bali, et al., Nano Lett. 14, 435 (2014)

Keywords: positron; positron annihilation spectroscopy; MOKE; ns-laser; magnetic phase transition; order; disorder

  • Invited lecture (Conferences)
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Publ.-Id: 26636

Reversible Tuning of Ferromagnetism and Resistive Switching in ZnO/Cu Thin Films

Younas, M.; Xu, C.; Arshad, M.; Ho, L.; Zhou, S.; Azad, F.; Akhtar, M.; Su, S.; Azeem, W.; Ling, F.

Systematic magnetic, electronic, and electrical studies on the Cu0.04Zn0.96O/Ga0.01Zn0.99O cell structure grown on (001) sapphire by the pulsed laser deposition technique show that the Cu multivalent (CuM+) ions modulate magnetic and resistive states of the cells. The magnetic moment is found to be reduced by ∼30% during the high resistance state (HRS) to low resistance state (LRS) switching. X-ray photoelectron spectroscopy results reveals an increase of the Cu+/Cu2+ oxidation state ratio (which has been determined by the relative positions of the Fermi level and the Cu acceptor level) during the HRS to LRS transition. This decreases the effective spin-polarized Cu2+−Vö−Cu+ channels and thus the magnetic moment. A conduction mechanism involving the formation of conductive filaments from the coupling of the CuM+ ions and Vö has been suggested.

Publ.-Id: 26635

Symmetries and localization properties of defect modes in metamaterial magnonic superlattices

Gallardo, R. A.; Schneider, T.; Roldán-Molina, A.; Langer, M.; Núñez, A. S.; Lenz, K.; Lindner, J.; Landeros, P.

Symmetries and localization properties of defect modes of a one-dimensionsional bi-component magnonic superlattice are theoretically studied. The magnonic superlattice can be seen as a periodic array of nanostripes, where stripes with different width, termed as defect stripes, are periodically introduced. By controlling the geometry of the defect stripes, a transition from dispersive to practically

at spin-wave defect modes can be observed inside the magnonic band gaps. It is shown that the spin-wave profile of the defect modes can be either symmetric or asymmetric by depending on the geometry of the defect. Due to the localization peculiarities of the defect modes, a particular magnonic superlattice is proposed, wherein the excitation of either symmetric or antisymmetric at modes is enabled at the same time. Also, it is demonstrated that the relative frequency position of the asymmetric mode inside the band gap does not significantly change with the application of an external field, while the symmetric modes move to the edges of the frequency band gaps. The results are complemented by numerical simulations, where an excellent agreement is observed between both methods. The proposed theory allows exploring different ways to control the dynamic properties of the defect modes in metamaterial magnonic superlattices, which can be useful for applications on multifunctional microwave devices operating over a broad frequency range.

Keywords: ferromagnetic resonance; spin waves; magnetization dynamics; magnonic crystals; plane wave method; dispersion; superlattices; daemon-eshbach


Publ.-Id: 26634

Towards Substitutionally-Inert Ru(II) Complexes as Photoactivatable Anticancer Agents

Joshi, T.; Pierroz, V.; Ferrari, S.; Spiccia, L.; Gasser, G.

The severe side effects encountered with platinum-based anticancer agents has driven the pursuit of new metal-based chemotherapeutics. The best examples of these are ruthenium compounds which have shown a promising potential to circumvent these side effects on account of their broad antiproliferative profile and novel mechanistic of action against cancer cells. Our work aims at the development of substitutionally inert Ru(II)-tris(diimine) complexes as new anticancer agents. Here we present the anticancer action and cytotoxicity mechanism of a [Ru(dppz)2(CppH)](PF6)2 (1) (CppH = 2-(2′-pyridyl)pyrimidine-4-carboxylic acid; dppz = dipyrido[3,2-a:2′,3′-c]phenazine), a substitutionally-inert polypyridyl Ru(II) complex. Complex 1 induces inhibitory effects comparable to that of cisplatin, targets mitochondria and impairing the mitochondrial membrane potential eventually leads to cell death by apoptosis [1]. Structure-activity correlation studies identify the key functional role of the carboxylate group on the CppH ligand and of the bis(dppz) framework in the cytotoxic activity of 1, with any lipophilicity, charge, and size-based structural and functional modifications resulting in its decreased activity [2]. Complementing these findings, we recently illustrated the first example of a substitutionally-inert metal complex-based prodrug candidate which can efficiently respond to activation by UV-A light (2.58 J cm-2) to display cytotoxicity "on demand" against cervical (HeLa) and bone cancer (U2OS) cells [3]. The reported findings represent a major advancement towards achieving a site-directed spatially and temporally controlled anti-cancer activity from such metallo cytotoxics.

[1] V. Pierroz, T. Joshi, A. Leonidova, C. Mari, J. Schur, I. Ott, L. Spiccia, S. Ferrari, G. Gasser J. Am. Chem. Soc. 134 (2012) 20376−20387.
[2] T. Joshi, V. Pierroz, S. Ferrari, G. Gasser ChemMedChem 9 (2014) 1419–1427.
[3] T. Joshi, V. Pierroz, C. Mari, L. Gemperle, S. Ferrari, G. Gasser Angew. Chem. Int. Ed. 53 (2014) 2960–2963.

  • Invited lecture (Conferences)
    II International Caparica Congress on Translational Chemistry, 04.-07.12.2017, Caparica, Lisbon, Portugal

Publ.-Id: 26633

Neomycin B–cyclen conjugates and their Zn(II) complexes as RNA-binding agents

Joshi, T.; Kong, B.; Tor, Y.; Graham, B.; Spiccia, L.

Aminoglycosides are one of the most well-studied classes of naturally occurring antibacterial agents [1]. Their antibiotic activity derives from their selective binding to the bacterial ribosomal RNA A-site, which ultimately leads to disruption of protein synthesis. Unfortunately, despite exhibiting a promising antibacterial profile, the widespread use of aminoglycosides as antibiotics has been hampered by their adverse side effects and the emergence of bacterial resistance. Herein, we present the synthesis of a series of new neomycin B conjugates featuring a polyazamacrocycle, 1,4,7,10-tetraazacyclododecane (cyclen), appended to the D-ribose ring, together with an examination of their A-site binding properties, as well as those of the corresponding Zn(II) complexes (C1–C3 and Zn(II)-C1–Zn(II)-C3). Since the high affinity of aminoglycosides for RNA is associated with the formation of complementary electrostatic interactions between protonated amine groups on the aminoglycosides and the RNA, the tethered cyclen macrocycle, enhances affinity for the A-site RNA motif due to the introduction of additional ionisable amino groups [2,3]. Furthermore, in agreement with previous findings that Zn(II)-cyclen complexes form reasonably strong interactions with phosphate groups as well as the deprotonated imide groups of the nucleobases, uracil and thymine, complexation of Zn(II) by cyclen in the neomycin B conjugates serves to enhance the affinity further still by allowing the conjugates to form coordination bonds with the RNA target [2,3]. The conjugates are worthy of further investigation as potential new antibiotic agents.

References: [1] Y. Tor, ChemBioChem 2003, 4, 998. [2] B. Kong, T. Joshi, et al., J. Inorg. Biochem. 2016, 162, 334. [3] T. Joshi, et. al., Acc. Chem. Res. 2015, 48, 2366.

  • Invited lecture (Conferences)
    6th Asian Conference on Coordination Chemistry, 24.-28.07.2017, Melbourne, Australia

Publ.-Id: 26632

Spectroscopic Studies on Photoinduced Reactions of the Anticancer Prodrug, trans,trans,trans-[Pt(N3)2(OH)2(py)2]

Vernooij, R. R.; Joshi, T.; Horbury, M. D.; Graham, B.; Izgorodina, E. I.; Stavros, V. G.; Sadler, P. J.; Spiccia, L.; Wood, B. R.

The photodecomposition mechanism of trans,trans,trans-[Pt(N3)2(OH)2(py)2] (1, py = pyridine), an anticancer prodrug candidate, was probed using complementary Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), transient electronic absorption and UV-Vis spectroscopy. Data fitting using Principal Component Analysis (PCA) and multi-curve resolution alternating least squares, suggests the formation of a trans-[Pt(N3)(py)2(OH/H2O)] intermediate and trans [Pt(py)2(OH/H2O)2] as the final product upon 420 nm irradiation of 1 in water. Rapid disappearance of the hydroxido ligand stretching vibration upon irradiation is correlated with a -10 cm-1 shift to the anti-symmetric azido vibration, suggesting a possible second intermediate. Experimental proof of subsequent dissociation of azido ligands from platinum is presented, where at least one hydroxyl radical is formed in the reduction of Pt(IV) to Pt(II). Additionally, the photoinduced reaction of 1 with the nucleotide 5’-guanosine monophosphate (5’-GMP) was comprehensively studied, and the identity of key photoproducts was assigned with the help of ATR FTIR spectroscopy, mass spectrometry and density functional theory calculations. The identification of marker bands for some of these photoproducts (e.g., trans-[Pt(N3)(py)2(5’-GMP)] and trans-[Pt(py)2(5’-GMP)2] will aid elucidation of the chemical and biological mechanism of anticancer action of 1. In general, these studies demonstrate the potential of vibrational spectroscopic techniques as promising tools for studying such metal complexes.

Keywords: vibrational spectroscopy; Attenuated Total Reflection (ATR); Pt(IV) prodrugs; mechanism of action; anticancer

Publ.-Id: 26631

A new data processing approach to study particle motion using ultrafast X-ray tomography scanner: case study of gravitational mass flow

Waktola, S.; Bieberle, A.; Barthel, F.; Bieberle, M.; Hampel, U.; Grudzień, K.; Babout, L.

In most industrial products, granular materials are often required to flow under gravity in various kinds of silo shapes and usually through an outlet in the bottom. There are several interrelated parameters which affect the flow, such as internal friction, bulk and packing density, hopper geometry, and material type. Due to the low spatial resolution of electrical capacitance tomography or scanning speed limitation of standard X-ray CT systems, it is extremely challenging to measure the flow velocity and possible centrifugal effects of granular materials flow effectively. However, the ultrafast electron beam X-ray CT scanner (ROFEX) opens new avenues of granular flow investigation due to its very high temporal resolution. This paper aims to track particles movements and evaluate the local grain velocity during silo discharging process in the case of mass flow. The study has considered the use of the Seramis material, which can also serve as a type of tracer particles after impregnation, due to its porous nature. The presented image processing and analysis approach allows satisfyingly measuring individual particle velocities but also tracking their movements.

Keywords: mass flow; ultrafast X-ray CT; particle tracking; matrix of inertia

Publ.-Id: 26630

Production of 51Cr by proton irradiation of natV and purification by precipitation and ion exchange chromatography

Mansel, A.; Franke, K.

European demand for chromium has grown dramatically, leading to the need for a detailed understanding of recycling of steel sludges and separation methods. To simulate these processes, we will use the radiotracer technique. 51Cr (T1/2 = 27.7 d) was choosen as a radionuclide. The isotope can be produced by the nuclear reaction natV(p,n)51Cr at a cyclotron. We used our recently installed cyclotron Cyclone® 18/9 (IBA) for the irradiation of natV (99.75% 51V). The vanadium foil was put in an aluminium holder with a diameter of 10 mm and a depth of 100 µm. The target was covered by a 100 µm thick aluminium foil. The irradiation was done at a beam of 16 MeV protons and a current of 10 µA for 4 hours. For the separation of 51Cr we established a multistage treatment. After cooling for 20 hours, the vanadium foil was dissolved with 2 ml conc. nitric acid. After addition of 20 mg iron(III) chloride, the hydroxide was subjected to a threefold cycle of precipitation with ammonia and dissolution with nitric acid. Vanadium(V) is soluble under these conditions. The separation of the radionuclide 51Cr and iron(III) was performed by ion exchange chromatography with AG 1-X8 (BIORAD) in conc. HCl. The 51Cr solution was eluted on the resin and the resin was washed six times with 2 ml conc. hydrochloric acid to remove the iron(III). The combined 51Cr solutions were evaporated to dryness and the residue was dissolved in 0.01 M sulfuric acid. The detection of 51Cr was done by gamma-counting (320 keV; 9.91%). The radiochemical yield was 66% at a production rate of 0.575 MBq/µAh.

Keywords: Radiochromium; Vanadium target; Cyclotron; Proton induced nuclear reaction; Radiochemical separation

  • Lecture (Conference)
    18th Radiochemical Conference (RadChem2018), 13.-18.05.2018, Marianske Lazne (Marienbad), Czech Republic

Publ.-Id: 26629

Melanoma brain metastases: Local therapies, targeted therapies, immune checkpoint inhibitors and their combinations- chances and challenges

Kuske, M.; Rauschenberg, R.; Garzarolli, M.; Meredyth-Stewart, M.; Beissert, S.; Troost, E.; Glitza, I.; Meier, F.

Recent phase 2 trials have shown that BRAF/MEK inhibitors and immune checkpoint inhibitors are active in patients with melanoma brain metastases (MBM), reporting intracranial disease control rates of 50-75%. Furthermore, retrospective analyses suggest that combining stereotactic radiosurgery with immune checkpoint inhibitors or BRAF/MEK inhibitors prolongs overall survival. These data stress the need for interand multidisciplinary cooperation that takes into account the individual prognostic factors in order to establish the best treatment for each patient. Although the management of MBM has dramatically improved, a substantial number of patients still progress and die from brain metastases. Therefore, there is an urgent need for prospective studies in patients with MBM that focus on treatment combinations and sequences, new treatment strategies, and biomarkers of treatment response.
Moreover, further research is needed to decipher brain-specific mechanisms of therapy resistance.

Publ.-Id: 26628

Der Beitrag geowissenschaftlicher Forschung zur Erkundung von mineralischen Rohstoffen in Deutschland

Gutzmer, J.; Markl, G.

Invited keynote presentation for the 3rd BGR-Rohstoffkonferenz in Hannover.

  • Lecture (others)
    3. BGR-Rohstoffkonferenz, 29.-30.11.2017, Hannover, Deutschland

Publ.-Id: 26627

HIM-Time-of-Flight-SIMS at HZDR

Klingner, N.; Heller, R.; Hlawacek, G.; Möller, W.; Facsko, S.


  • Lecture (Conference)
    PicoFIB Meeting, 31.01.2018, Dresden, Deutschland

Publ.-Id: 26626

Clinical application of dual-energy computed tomography improves stopping-power prediction

Wohlfahrt, P.; Möhler, C.; Greilich, S.; Richter, C.

Assessment of accuracy and robustness of treatment planning on dual-energy CT (DECT) in a multi-step validation and clinical implementation scheme (Fig.1,2).

To ensure reliable translation of DECT into routine clinical application, scan settings and stopping-power prediction methods were optimized and validated using 13 different animal tissues and an anthropomorphic ground-truth phantom. The clinical relevance of DECT-based stopping-power prediction was evaluated on dual-spiral DECT scans of 102 brain-, 25 prostate- and 3 lung-tumor patients treated with protons. DECT-derived voxelwise correlations of CT number and stopping-power ratio (SPR) were used for adapting the clinically applied CT-number-to-SPR conversion (HLUT) and quantifying intra- and inter-patient variability.

The accuracy of DECT-based stopping-power prediction was within 0.3% stopping-power and 1mm range uncertainty of validation measurements. Clinically relevant mean range shifts (±1SD) of 1.2(±0.7)% for brain-, 1.7(±0.5)% for prostate- and 2.2(±1.2)% for lung-tumor patients were obtained between dose calculations using HLUT or DECT-derived SPR. These deviations were significantly reduced (p<<0.001, two-sample t-test) below 0.3% by HLUT refinement based on patient-specific DECT information. Still, the remaining large intra-patient soft tissue diversity of approx. 6% (95% CI) and age-dependent inter-patient bone variability of 5% cannot be considered by any HLUT-based range prediction.

Additional tissue information provided by DECT allows for accurate stopping-power prediction and incorporation of patients’ tissue diversity in treatment planning. These advantages can contribute to reduce CT-related range uncertainty and have been gradually translated in our clinical routine: (1) DECT-derived pseudo-monoenergetic CT dataset with generic HLUT, (2) DECT-based HLUT adaptation and soon (3) patient-specific DECT-basted stopping-power prediction.

Keywords: proton therapy; range uncertainty; dual-energy CT

  • Lecture (Conference)
    57th Annual Particle Therapy Co-Operative Group (PTCOG) Meeting, 24.-26.05.2018, Cincinnati, Ohio, USA

Publ.-Id: 26625

Improved performance of laser wakefield acceleration by tailored self-truncated ionization injection

Irman, A.; Couperus, J. P.; Debus, A.; Köhler, A.; Krämer, J. M.; Pausch, R.; Zarini, O.; Schramm, U.

We report on tailoring ionization-induced injection in laser wakefield acceleration so that the electron injection process is self-truncating following the evolution of the plasma bubble. Robust generation of high-quality electron beams with shot-to-shot fluctuations of the beam parameters better than 10% is presented in detail. As a novelty, the scheme was found to enable well-controlled yet simple tuning of the injected charge while preserving acceleration conditions and beam quality. Quasimonoenergetic electron beams at several 100MeV energy and 15% relative energy spread were routinely demonstrated with a total charge of the monoenergetic feature reaching 0.5 nC. Finally these unique beam parameters, suggesting unprecedented peak currents of several 10 kA, are systematically related to published data on alternative injection schemes.

Keywords: Self-Truncation Ionization Injection; beam loading; laser wakefield acceleration

Publ.-Id: 26624

Rhenium recovery from diluted solutions by solvent extraction

Helbig, T.; Scharf, C.

A total of 230.000 tons of the so called “Theisenschlamm”, a waste material of the former copper shale processing in the Mansfeld region, was deposited between the years 1978 and 1990. Besides about 20 wt.-% of zinc and minor amounts of lead, copper and tin, this material also contains valuable strategic elements, like rhenium and germanium. Nowadays rhenium is used as an important alloying element in nickel-base superalloys, or in catalysts.
The r4-project “Theisenschlamm” aims at a recovery of the valuable metal content by bioleaching, followed by element specific separation methods. An effective method for the selective separation and concentration of metals is solvent extraction where an organic phase is used to extract the elements of interest from an aqueous phase. But since the metal concentrations in the bioleaching solution are low, the processing is challenging. However, there are multiple parameters allowing an optimization of the solvent extraction process. The findings for a selective enrichment of rhenium from synthetic (bioleaching) solution will be presented in this talk.

  • Lecture (Conference)
    67. Berg- und Hüttenmännischer Tag, 08.-10.06.2016, Freiberg, Deutschland

Publ.-Id: 26623

Recovery of Rhenium from Low Concentrated Bioleaching Solutions by Solvent Extraction

Helbig, T.; Scharf, C.

The r4-project "Theisenschlamm" focuses on the recovery of elements of strategic economic importance (like Rhenium or Molybdenum). The first step within the research approach is bioleaching of the Theisenschlamm, which is a waste material of the former copper shale processing in the Mansfeld region (Germany). As a next process step the project partners investigate different element selective separation methods to recover the valuable elements from the bioleaching solution. An efficient rhenium recovery from synthetic (bioleaching) solutions is achieved using solvent extraction with teriary amines. It could be shown that rhenium can be enriched in the organic phase and that a good selectivity over zinc, copper, cobalt, germanium and iron(III) is obtained.

  • Poster
    "24 Stunden für Ressourceneffizienz", Ressourceneffizienz-Kongress für Nachwuchsforscherinnen und Nachwuchsforscher, 14.-15.02.2017, Pforzheim, Deutschland

Publ.-Id: 26622

Atomistic study of the hardening of ferritic iron by Ni-Cr decorated dislocation loops

Bonny, G.; Bakaev, A.; Terentyev, D.; Zhurkin, E.; Posselt, M.

The exact nature of the radiation defects causing hardening in reactor structural steels consists of several components that are not yet clearly determined. While generally, the hardening is attributed to dislocation loops, voids and secondary phases (radiation-induced precipitates), recent advanced experimental and computational studies point to the importance of solute-rich clusters (SRCs). Depending on the exact composition of the steel, SRCs may contain Mn, Ni and Cu (e.g. in reactor pressure vessel steels) or Ni, Cr, Si, Mn (e.g. in high-chromium steels for generation IV and fusion applications). One of the hypotheses currently implied to explain their formation is the process of radiation-induced diffusion and segregation of these elements to small dislocation loops (heterogeneous nucleation), so that the distinction between SRCs and loops becomes somewhat blurred. In this work, we perform an atomistic study to investigate the enrichment of loops by Ni and Cr solutes and their interaction with an edge dislocation. The dislocation loops decorated with Ni and Cr solutes are obtained by Monte Carlo simulations, while the effect of solute segregation on the loop's strength and interaction mechanism is then addressed by large scale molecular dynamics simulations. The synergy of the Cr-Ni interaction and their competition to occupy positions in the dislocation loop core are specifically clarified.

Keywords: Iron; Ferritic steel; Precipitation; Dislocation; Molecular dynamics

  • Journal of Nuclear Materials 498(2018), 430-437

Publ.-Id: 26621

Causative treatment of acid aspiration induced acute lung injury – recent trends from animal experiments and critical perspective

Gramatté, J.; Pietzsch, J.; Bergmann, R.; Richter, T.

Aspiration of low-pH gastric fluid leads to an initial pneumonitis, which may become complicated by subsequent pneumonia or acute respiratory distress syndrome. Current treatment is at best supportive, but there is growing experimental evidence on the significant contribution of both neutrophils and platelets in the development of this inflammatory pulmonary reaction, a condition that can be attenuated by several medicinal products. This review aims to summarize novel findings in experimental models on pathomechanisms after an acid-aspiration event. Given the clinical relevance, specific emphasis is put on deduced potential experimental therapeutic approaches, which make use of the characteristic alteration of microcirculation in the injured lung.

Keywords: Acute respiratory distress syndrome; critical care medicine; pneumonitis; pulmonary inflammation; pulmonary blood flow; targeted anti-inflammatory therapies

  • Open Access Logo Clinical Hemorheology and Microcirculation 69(2018), 187-195
    DOI: 10.3233/CH-189113


Publ.-Id: 26620

The Transition from a Thin Film to a Full Magnonic Crystal and the Role of the Demagnetizing Field

Langer, M.; Röder, F.; Gallardo, R. A.; Schneider, T.; Stienen, S.; Gatel, C.; Hübner, R.; Lenz, K.; Lindner, J.; Landeros, P.; Fassbender, J.

The transition from a film to a full magnonic crystal is studied by sequentially ion-milling a 40 nm Ni80Fe20 film. The spin-wave resonances of each stage are detected by ferromagnetic resonance for both in-plain field main axes. Theoretical calculations and micromagnetic simulations yield the individual mode profiles, which are analyzed in order to track changes of the mode character. The latter is strongly linked to the evolution of the internal demagnetizing field. It’s role is further studied by electron holography measurements of a hybrid magnonic crystal with 10 nm deep surface modulation. The complex effects of mode coupling, mode localization and anisotropy-like contributions by the internal field are unraveled. Simple transition rules from the 𝑛th film mode to the 𝑚th mode of the full magnonic crystal are formulated.

Keywords: Ferromagnetic resonance; magnonic crystals; demagnetizing fields; thin films; spin waves

  • Poster
    81. Frühjahrstagung der Sektion Kondensierte Materie der DPG, 19.-24.03.2017, Dresden, Deutschland

Publ.-Id: 26619

The Role of the Demagnetizing Fields in the Transition from Thin Films to Magnonic Crystals

Lenz, K.; Langer, M.; Röder, F.; Gallardo, R. A.; Schneider, T.; Stienen, S.; Gatel, C.; Hübner, R.; Lindner, J.; Landeros, P.; Fassbender, J.

The transition from a film to a full magnonic crystal is studied by sequentially ion-milling a periodic stripe pattern into a 40 nm thick Ni$_{80}$Fe$_{20}$ film. The spin-wave resonances of each milling stage are detected by ferromagnetic resonance for both in-plain main field axes, i.e. parallel and perpendicular to the stripe pattern. Theoretical calculations and micromagnetic simulations yield the individual mode profiles, which are analyzed in order to track changes of the mode character. The latter is strongly linked to the evolution of the internal demagnetizing field. It’s role is further studied and imaged by electron holography measurements on a hybrid magnonic crystal, which is made with a 10 nm deep surface modulation. The complex effects of mode coupling, mode localization, and anisotropy-like contributions by the internal field are unraveled. Simple transition rules from the $𝑛^_\mathrm{th}$ film mode to the $𝑚\mathrm{th}$ mode of the full magnonic crystal are formulated.
This work has been supported by DFG grant KL2443/5-1.

Keywords: Ferromagnetic resonance; magnonic crystals; demagnetizing fields

  • Poster
    Magnonics 2017, 07.-11.08.2017, Oxford, United Kingdom

Publ.-Id: 26618

Maternal immune activation results in complex microglial transcriptome signature in the adult offspring that is reversed by minocycline treatment

Mattei, D.; Ivanov, A.; Ferrai, C.; Jordan, P.; Guneykaya, D.; Buonfiglioli, A.; Schaafsma, W.; Przanowski, P.; Deuther-Conrad, W.; Brust, P.; Hesse, S.; Patt, M.; Sabri, O.; Ross, T. L.; Eggen, B. J. L.; Bodecke, E. W. G. M.; Kaminska, B.; Beule, D.; Pombo, A.; Kettenmann, H.; Wolf, S. A.

Maternal immune activation (MIA) during pregnancy has been linked to an increased risk of developing psychiatric pathologies in later life. This link may be bridged by a defective microglial phenotype in the offspring induced by MIA, as microglia have key roles in the development and maintenance of neuronal signaling in the central nervous system. The beneficial effects of the immunomodulatory treatment with minocycline on schizophrenic patients are consistent with this hypothesis. Using the MIA mouse model, we found an altered microglial transcriptome and phagocytic function in the adult offspring accompanied by behavioral abnormalities. The changes in microglial phagocytosis on a functional and transcriptional level were similar to those observed in a mouse model of Alzheimer’s disease hinting to a related microglial phenotype in neurodegenerative and psychiatric disorders. Minocycline treatment of adult MIA offspring reverted completely the transcriptional, functional and behavioral deficits, highlighting the potential benefits of therapeutic targeting of microglia in psychiatric disorders.


Publ.-Id: 26617

Circular Economy

Reuter, M. A.

Prof Markus Reuter, Director at the Helmholtz Institute for Resource Technology in Freiberg in Germany, was awarded the degree Doctor of Engineering (DEng), honoris causa for his outstanding contributions to the science and technology of the production and recycling of metals, as well as to the integration of academic research and practice. His work on recycling, design for recycling, and resource efficiency has contributed towards the creation of processes and tools to develop a sustainable society.

  • Lecture (others)
    Awarding of Degrees, Diplomas and Certificates (including Doctoral Degrees), 04.-08.12.2017, Stellenbosch, Südafrika

Publ.-Id: 26616

Digitizing the Circular Economy

Reuter, M. A.

Metallurgy is a key enabler of a circular economy (CE), its digitization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated. The true boundaries of sustainability can be determined in addition to the techno-economic evaluation of RE. The integration of metallurgical reactor technology and systems digitally, not only on one site but linking different sites globally via hardware, is the basis for describing CE systems as dynamic feedback control loops, i.e., the m-IoT. It is the linkage of the global carrier metallurgical processing system infrastructure that maximizes the recovery of all minor and technology elements in its associated refining metallurgical infrastructure. This course will illustrate some of these concepts with hands-on training.

Keywords: circular economy; recycling

  • Invited lecture (Conferences)
    Digitizing the Circular Economy / Summer school, 17.-20.07.2017, Leuven, Belgien

Publ.-Id: 26615

Diffuse interface model to simulate the rise of a fluid droplet across a cloud of particles

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

A large variety of industrial and natural systems involve the adsorption of solid particles to the fluidic interface of droplets in motion. A diffuse interface model is here suggested to directly simulate the three-dimensional dynamics of a fluid droplet rising across a cloud of large particles. In this three-phase model the two solid-fluid boundaries and the fluidic boundary are replaced with smoothly spreading interfaces. A significant advantage of the method lies in the fact that the capillary effects, the three-phase flow hydrodynamics, and the inter-particle collisions are all resolved. We first report important numerical limitations associated with the inter-particle collisions in diffuse interface models. In a second stage the effect of the particle concentration on the terminal velocity of a rising fluid droplet is investigated. It is found that, in a quiescent environment, the terminal velocity of the rising the fluid droplet decreases exponentially with the particle concentration. This exponential decay is also confirmed by a simple rheological model.

Keywords: Diffuse interface model; rising droplet; particles at fluidic interface; direct numerical simulation; three phase flows


Publ.-Id: 26614

Attachment of non-spherical particles to the fluidic surface – Experiment and direct numerical simulations

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

The attachment of colloidal particles to the fluidic surface of immersed fluid droplets is central to a wide variety of industrial applications, among which stand out the recovery of minerals by gas bubbles, a process known as flotation. The flotation process involves the attachment of hydrophobised colloidal particles to the surface of rising air bubbles, while the commercially valueless hydrophilic material settles down the cell. Experimental and numerical works dealing with the attachment of non-spherical particles to a fluidic interface are here presented. Using an optical microbubble sensor the various microprocesses associated with the colloidal attachment of elongated fibers are first investigated. In a second stage direct numerical simulations are used to predict the dynamics of such particles at a fluidic interface. Unlike spherical particles, it is found that plate-like particles attach more rapidly to a fluidic interface and are subsequently harder to dislodge when subject to an external force.

Keywords: Flotation Fundamentals: Physics and Chemistry; bubble-particle interactions

  • Poster
    Flotation '17, 13.-16.11.2017, Cape Town, South Africa

Publ.-Id: 26613

Structure variations within certain rare earth-disilicides

Nentwich, M.; Zschornak, M.; Sonntag, M.; Gumeniuk, R.; Gemming, S.; Leisegang, T.; Meyer, D. C.

The dimorphism of the RSi2 and R2TSi3 compounds is a well known phenomenon (R is an alkaline earth metal, rare earth metal or actinoide, T is a transition metal). They crystallize in structures, which derive from hexagonal AlB2 or tetragonal ThSi2 prototypes. Despite their local similarities, both prototypes do not have a common root in the Bärnighausen diagram, which summarizes the symmetry relations between the high symmetrical basic structures and their lower symmetric variations.
We performed an extensive literature research based on more than 400 structure reports of the RSi2 and R2TSi3 compounds. To gain an overview of the various structure reports within these compounds we summarized composition, lattice parameters a and c, ratios c/a, formula units per unit cell, and structure types in an extensive table. We performed DFT calculations on carefully chosen compounds to evaluate the probability of a successful synthesis. Finally, we discuss peculiarities of symmetry distribution among the RSi2 and R2TSi3 compounds and several correlations related to structural parameters.
We found that the thermal treatment has a massive effect to the formation of superstructures. Furthermore, there are two different kinds of hexagonal R2TSi3 compounds being ionic or metallic, depending on the R element. Additionally, the main influence to the variation of the Si-T bonds is the electronic interplay between R element and Si lattice rather than the R radii.

Keywords: rare earth; silicides; density-functional

  • Lecture (Conference)
    IUCR 2017 - 24th Congress of the International Union of Crystallography, 21.-27.08.2017, Hyderabad, Indien

Publ.-Id: 26612

THz-spectroscopic studies on electron dynamics in a GaAs single quantum well and an InAs single quantum dot

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

Intense, spectrally narrow terahertz fields from the free-electron laser (FEL) facility FELBE in Dresden, Germany, provide interesting opportunities for investigating the carrier dynamics in III-V semiconductor nanostructures. This talk will focus on recent FEL studies on dressing intersubband transitions in a wide GaAs single quantum well using terahertz time-domain spectroscopy, and on exciton dynamics in a single InAs/GaAs quantum dot using time-dependent photoluminescence.

Keywords: terahertz free-electron laser; intersubband; exciton; quantum well; quantum dot

  • Invited lecture (Conferences)
    14-th International Conference on Intersubband Transitions in Quantum Wells (ITQW2017), 10.-15.09.2017, Singapore, Singapore

Publ.-Id: 26611

Luminescence of defects in the structural transformation of layered tin dichalcogenides

Sutter, P.; Komsa, H.-P.; Krasheninnikov, A. V.; Huang, Y.; Sutter, E.

Layered tin sulfide semiconductors are both of fundamental interest and attractive for energy conversion applications. Sn sulfides crystallize in several stable bulk phases with different Sn:S ratios (SnS2, Sn2S3, and SnS), which can transform into phases with a lower sulfur concentration by introduction of sulfur vacancies (VS). How this complex behavior affects the optoelectronic properties remains largely unknown but is of key importance for understanding light-matter interactions in this family of layered materials. Here, we use the capability to induce VS and drive a transformation between few-layer SnS2 and SnS by electron beam irradiation, combined with in-situ cathodolumines- cence spectroscopy and ab-initio calculations to probe the role of defects in the luminescence of these materials. In addition to the characteristic band-edge emission of the endpoint structures, our results show emerging luminescence features accompanying the SnS2 to SnS transformation. Comparison with calculations indicates that the most prominent emission in SnS2 with sulfur vacancies is not due to lumi- nescence from a defect level but involves recombination of excitons bound to neutral VS in SnS2. These findings provide insight into the intrinsic and defect-related optoelectronic properties of Sn chal- cogenide semiconductors.

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

Publ.-Id: 26610

Terahertz dephasing of Landau level transitions in graphene

Schneider, H.; König-Otto, J. C.; Pashkin, A.; Helm, M.; Winnerl, S.; Wang, Y.; Belyanin, A.

Using degenerate four-wave mixing (DFWM), we have investigated the coherent polarization between the lowest Landau levels in graphene under resonant excitation with narrowband THz pulses. A pronounced DFWM signal is observed and its dependence on THz field strength and magnetic field detuning is explored and compared with theoretical expectations.

Keywords: terahertz; graphene; four-wave mixing; coherent polarization; free-electron laser

  • Lecture (Conference)
    The 42nd International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2017), 27.08.-01.09.2017, Cancun, Mexico
  • Contribution to proceedings
    The 42nd International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2017), 27.08.-01.09.2017, Cancun, Mexico
    Proceedings of the IRMMW-THz'2017
    DOI: 10.1109/IRMMW-THz.2017.8066873

Publ.-Id: 26609

Protecting Pulsed High-Power Lasers with Real-Time Image Classification

Kelling, J.; Gebhardt, R.; Helbig, U.; Bock, S.; Schramm, U.; Juckeland, G.

Learn how to combine computer vision techniques and deep learning to improve the sensitivity of a real-time, GPU-powered safety system. In Petawatt laser systems, firing at 10Hz, suddenly appearing scatterers can damage components.
Damage(-spreading) can be avoided by suspending operation immediately on occurrence of such an event.

We present our approach for the automatic detection of critical failure states from intensity profiles of the laser beam. By Incorporating quick feature detection and learned heuristics for feature classification, both real-time constraints and limited available training data are accommodated. Localization of triggering feature is crucial for when the problem is located in non-sensitive sections and will not be removed from the beam in production.

  1. extended abstract:
High-power lasers are operated at our research center for investigations of exotic states of matter and medical applications, among others. This project to improve the automatic shutdown/interlock system of two lasers (one in operation, one currently under construction) has the goal of reducing the probability of, potentially expensive, damage-spreading scenarios, while at the same time avoiding false alarms at high sensitivity.
The project to be presented is currently in a proof-of-concept phase, with workable proof existing for a specific failure mode for which data was available (the breaking of a single mirror). Next to the 100ms real-time constraint, the lack sufficient training data, demanded a two-stage approach to solve this problem: Classical feature detection with a low threshold works as a fast anomaly detector, followed by feature-classification using CNNs (mostly GoogLeNet) to identify true positive triggers.
From this, the audience can learn how to design for short response times (to which end we employ Caffe, OpenCV on GPU and use C++ as main programming language). The application also demonstrates how prior domain knowledge and known algorithms can be combine with machine learning to create heuristics to fill in gaps.

Keywords: Image Classification; Caffe; automatik Laser-safety shutdown; GoogLeNet

  • Lecture (Conference)
    GTC 2018 Silicon Valley, 26.-29.03.2018, San Jose, CA, USA
  • Lecture (Conference)
    1st MLC Workshop, 15.05.2018, Dresden, Deutschland

Publ.-Id: 26608

The Exchange bias in oxygen-implanted Co/Au thin film heterostructures

Perzanowski, M.; Gregor-Pawłowski, J.; Zarzycki, A.; Böttger, R.; Hübner, R.; Potzger, K.; Marszałek, M.

Magnetic systems exhibiting exchange bias effect are being considered as functional parts of modern data storage devices. A model system for the investigation of this effect is an antiferromagnetic-ferromagnetic CoO/Co interface. In this paper we present the studies of magnetic properties of Co-CoO/Au multilayers where the cobalt oxide was formed by oxygen ion beam implantation. Special emphasis is given to the role of the oxygen concentration profile in the magnetic properties. By properly designed the implantation conditions (ion beam energy and fluence) it is possible to fabricate a system revealing controlled stepwise magnetization reversal process. This underlines the great potential of this approach to tailor the magnetic properties through modification of implantation profiles.

This work was supported by DAAD Service with contract No. PPP-PL 57214850 „Magnetic anisotropies in cobalt heterostructures induced by oxidation”.

Keywords: Ion Implantation; Magnetic multilayers

  • Poster
    The European Conference Physics of Magnetism 2017, PM’17, 26.-30.06.2017, Poznan, Polen

Publ.-Id: 26607

Metallurgy key enabler of the Circular Economy

Reuter, M. A.

Metallurgy is a key enabler of a circular economy (CE), its digitalization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitalization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated.

Keywords: Circular Economy; Circular Economy Engineering; Fairphone; Recycling

  • Lecture (others)
    Workshop, 30.11.2017, Madrid, Spanien

Publ.-Id: 26606

The Akademii Nauk ice core and solar activity

Fritzsche, D.; von Albedyll, L.; Merchel, S.; Opel, T.; Rugel, G.; Scharf, A.

Ice cores are well-established archives for paleo-environmental studies, but this requires a reliable ice core chronology. The concentration of cosmogenic radionuclides in ice cores reflects the solar activity in the past and, thus, can be used as a dating tool for ice cores. Accelerator mass spectrometry (AMS) allows the determination of nuclides in high resolution. Here, we present results of a 10Be study in an ice core from Akademii Nauk (Severnaya Zemlya, Russian Arctic). AMS analyses of more than 500 samples were carried out using the 6 MV accelerator facility of the Ion Beam Center of the Helmholtz-Zentrum Dresden-Rossendorf. For the time period 400 to 2000 CE the temporal variations of 10Be reflect the centennial variations of solar activity known from similar studies of Greenlandic ice cores and from 14C production reconstructions. The 10Be peak of 775 CE, today understood as result of the strongest known solar particle storm, was found by high-resolution core analysis. This peak is used as a tie point (additionally to volcanic reference horizons) for the development of the depth-age relationship of the Akademii Nauk ice core. Indications of the so called “Carrington Event” of 1859 CE, 20 to 30 times weaker than 775 CE, could also be detected in the core.

Keywords: AMS; climate; ice core

  • Lecture (Conference)
    27th International Polar Conference, 25.-29.03.2018, Rostock, Deutschland

Publ.-Id: 26603

Search for Recent 60Fe Deposition in Antarctic Snow via AMS

Koll, D.; Busser, C.; Faestermann, T.; Fimiani, L.; Gomez-Guzman, J. M.; Kinast, A.; Korschinek, G.; Krieg, D.; Lebert, M.; Merchel, S.; Sterba, J.; Welch, J.; Kipfstuhl, S.

60Fe with a half-life of 2.6 Myr [1] is produced in stellar Environments and ejected into space mainly by core-collapse supernovae. Due to its long half-life, traces of 60Fe were deposited and incorporated on Earth and on the Moon and have been detected there [2,3,4,5].
Here, a new possible reservoir will be presented: Antarctic snow.
This time, in contrast to former investigations, any signal detected would be recent material which might origin from the local interstellar cloud. 500 kg of Antarctic snow were chemically processed and are going to be analyzed by AMS in Munich at the 14 MV tandem. First results for 60Fe measurements will be presented as well as chemical extraction methods applied.
[1] Rugel et. al. ; Phys. Rev. Lett. 103, 072502 (2009)
[2] Knie et. al. ; Phys. Rev. Lett. 93, 171103 (2004)
[3] Ludwig et. al. ; PNAS 113 (33), 9232-9237 (2016)
[4] Wallner et. al. ; Nature 532, 69-72 (2016)
[5] Fimiani et. al. ; Phys. Rev. Lett. 116, 151104 (2016)

Keywords: supernovae; AMS

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 04.-09.03.2018, Erlangen, Deutschland

Publ.-Id: 26602

The Flux of Interplanetary Dust on Earth: Status

Krieg, D.; Busser, C.; Faestermann, T.; Fimiani, L.; Gomez-Guzman, J. M.; Kinast, A.; Koll, D.; Korschinek, G.; Lebert, M.; Merchel, S.; Welch, J.; Kipfstuhl, S.

Earth’s accumulation rate of Interplanetary Dust Particles (IDPs) is a matter of discussion, ranging from 5 (middle atmosphere measurements) up to 300 (space borne dust detection) tons per day. A new approach for a more precise measurement of this accumulation rate is made by extracting manganese from 500 kg of Antarctic snow collected near the Kohnen station, and measuring the concentration of 53Mn with AMS at the MLL in Munich.
This 53Mn (t1/2 = 3.7 Ma) is mostly produced by nuclear reactions of cosmic rays on the iron of the IDPs. Relating the amount of 53Mn to the precipitation rate, a meridional transport and deposition model based on 10Be measurements, and to a chemical model of meteoritic ablation will help to reduce the uncertainty of the IDP input on Earth. The method of our measurement and the status of this study will be discussed.

Keywords: IDP; AMS

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 04.-09.03.2018, Erlangen, Deutschland

Publ.-Id: 26601

Phase Formation and Selectivity on Cr (co-)Doped TiOU+2082 through Interface Engineering and Post-Deposition Flash Lamp Annealing

Gago, R.; Prucnal, S.; Palomares, J.; Jiménez, I.; Hübner, R.

Many applications of TiO2 partially rely on its good performance as solvent for numerous impurities [1]. In particular, metal (cation) dopants have been used to functionalize or enhance TiO2 as catalyst [2], diluted magnetic semiconductor [3] or transparent conductor [4]. One of the most interesting properties of TiO2 relies on its photoactivity, exploited in many applications from catalysis, hydrogen production, pigments or solar cells [2]. However, TiO2 is mostly active in the ultraviolet (UV) region of the solar spectrum (band-gap > 3 eV) and there is a great interest in band-gap narrowing of TiO2 to achieve visible-light (VISL) response [2]. Metal doping do so and increases VISL absorption significantly but, unfortunately, introduces structural distortions in the host matrix that result in carrier recombination centers [5]. Apart from the structural quality, another relevant consideration on the production of doped TiO2 relies on the particular oxide matrix phase (anatase/rutile) [6]. For example, anatase has superior photoactivity than rutile although phase mixtures with high anatase content may present even higher photoactivity [7]. Therefore, special attention should also be devoted to the phase selectivity. Moreover, (heavily) doped TiO2 may display a completely different electronic structure that the pristine oxide material.
The aim of this study is to promote customized phase formation in Cr (co-)doped TiO2 films produced by magnetron co-sputtering. Special attention is paid to the structural arrangements around host and dopant sites from the X-ray absorption near-edge structure. We report the conditions driving to single- or mixed-phase formation with the novelty of exploring film architectures based on interface engineering and/or post-deposition flash-lamp annealing (FLA) [8]. The latter is a non-contact rapid thermal processing extensively used in Microelectronics but yet to be explored in the present context. Hence, FLA can be attractive for many industrial applications dealing with the synthesis of band-gap engineered TiO2-based materials.
[1] Sacerdoti et al., J. Solid State Chem. 177, 1781 (2004); [2] Henderson, Surf. Sci. Rep. 66, 185 (2011); [3] Matsumoto et al. Science 291, 854 (2001); [4] Furubayashi et al., Appl. Phys. Lett. 86, 252101 (2005); [5] Serpone et al., J. Phys. Chem. B 110, 24287 (2006); [6] Yang, et al., Phys. Rev. B 76, 195201 (2007); [7] Scanlon et al., Nat. Mater. 12, 798 (2013); [8] D. Reichel et al., Phys. Status Solidi C 9, 2045 (2012)

  • Invited lecture (Conferences)
    2017 MRS Fall Meeting & Exhibit, 26.11.-01.12.2017, Boston, MA, USA

Publ.-Id: 26600

Energy-filtered TEM studies on silicon nanoparticles acting as quantum dots in single electron transistors

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

The miniaturization of computing devices and the introduction of the internet of things generate an increasing demand for the development of low-power devices. Single electron transistors (SETs) are ideally suited for this demand, because they are promising very low power dissipation devices. For roomtemperature operation of an SET it is necessary to create a single quantum dot (QD) with a diameter below 5 nm exactly positioned between source and drain at a tunnel distance of only a few nanometers. Within the IONS4SET project [1], we aim to achieve this goal by ion irradiation induced Si-SiO2 mixing and subsequent thermally activated self-assembly of single Si nanocrystals surrounded by a thin SiO2 layer. This process is illustrated in Fig. 1 by means of simulations results.
Here, we present energy-filtered (EF)TEM studies in order to monitor the influence of process parameters, such as stack geometry, ion fluence for irradiation, annealing temperature and annealing time, on the self-assembly of Si QDs. Fig. 2 shows representative EFTEM micrographs of a Si-SiO2-Si layer stack imaged using different electron energy-loss (EEL) windows. The Si plasmon-loss filtered images yield thereby the best signal-to-noise for detection of Si nanodots, because the Si plasmon peak is the most intense peak with a relatively small FWHM of 4 eV in the EEL spectrum.
Moreover, since the obtained (raw) EFTEM images provide only qualitative information about the Si concentration in the oxide layer, they cannot give a clear answer if for example the observed contrast corresponds to one or more Si nanodots (NDs) in projection. Therefore, EFTEM images are quantified further by converting them into so-called thickness over mean free path length (MFPL) t/λSi maps, in which λSi is the MFPL corresponding to the chosen energy range. The experimental t/λSi maps are then compared with simulated t/λSi maps of a single Si ND. Fig. 3 depicts that our approach enables us not only to detect single Si nanodots (Fig. 3c,e) but also to count them if they are arranged in projection direction of the electron beam (Fig. 3d,f). For these experiments, the layer stacks were irradiated with Ne+ ions within an Orion NanoFab (Zeiss). This allows controlled line or point irradiation and ensures Si QD formation within a confined region. In a next step, confined regions will be established by fabricated nanopillars that enhances reproducibility as the volume relevant for the self-assembly of the nanocluster will be better defined.
[1] We thank for financial support within the European Union"s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET).

  • Lecture (Conference)
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland
  • Contribution to proceedings
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland, 12-14

Publ.-Id: 26599

Insights into the 3D electric potential structure of III-V semiconductor core-multishell nanowires through combined STEM and holographic tomography

Wolf, D.; Hübner, R.; Sturm, S.; Lubk, A.

Off-axis electron holographic tomography (EHT) has been successfully applied to reveal the 3D structure of III-V semiconductor core-shell nanowires (NWs) [1,2]. The technique probes the phase shift of an electron wave transmitted through such a NW that is proportional to the NWs projected electrostatic potential. Thus, a tilt series of phase images (projected potentials) can be used as input to compute a 3D tomogram of the electrostatic potential by tomographic reconstruction algorithms. Typically, the recovered 3D potential is dominated by the mean inner potential (MIP), which is related to the materials composition. Consequently, space charge potentials determining for example the electric properties, e.g., at interfaces or pn-junctions in semiconductors [2] may be superimposed by MIP variations caused by compositional changes within the heterostructures.
Here, we show on the example of a GaAs/AlGaAs core-multishell NW, how the space charge potentials can be uncovered from materials contrast (MIP) by determining the latter independently: To this end, high-angle annular dark-field (HAADF) STEM tomography was applied in addition to EHT on the same NW. STEM tomograms provide solely materials contrast that depends exponentially on the atomic number. Fig. 1 compares both methods in terms of the relation between reconstructed signal and projected property, exemplary for three different tomogram regions identified as pure Au, GaAs and AlGaAs: In case of EHT between the reconstructed potential and the MIP, and in case of STEM tomography between the reconstructed intensity and the atomic number. The latter relation enables converting the STEM tomogram in units of (mean) atomic numbers.
Tilt series were acquired from -70° to +71° with 3° tilt steps in holography mode, and from -68° to +68° with 2° tilt steps in STEM mode. Since phase images of axially scattered electrons are used for EHT, it suffers much more from diffraction contrast than STEM tomography (high-angle scattering). Consequently, only 39 projections could be used for tomographic reconstruction in the case of EHT compared to 68 in the case of STEM tomography. For this reason, resolution and contrast in the 3D potential are slightly lower than in the STEM tomogram, which can be seen on the cross-section of the NW in Fig. 2. Nevertheless, the core-shell structure, the ca. (5-10) nm thick GaAs shell acting as quantum well tube (QWT), and unintended Al segregations are clearly resolved in both cases. Last but not least, longitudinal slices (Fig.3) exhibit clear differences of both tomograms that strongly suggest additional local space-charge related potentials to be investigated in greater detail in a next step.
[1] A Lubk, D Wolf, P Prete, N Lovergine, T Niermann, S Sturm and H Lichte, Phys. Rev. B 90 (2014) p. 125404.
[2] D Wolf, A Lubk, P Prete, N Lovergine and H Lichte, J. Phys. D: Appl. Phys. 49 (2016) p. 364004
[3] We thank N Lovergine of University of Salento, Lecce for provision of the samples.
[4] We thank the group of Michael Lehmann at TU Berlin for access to the TEM FEI Titan 80-300 Berlin Holography Special.
[5] DW acknowledges financial support within the European Union"s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET). AL has received funding from the European Research Council (ERC) under the European Union"s Horizon 2020 research and innovation programme (grant agreement No 715620).

  • Poster
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland
  • Contribution to proceedings
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland, 753-755

Publ.-Id: 26598

Subsurface Engineering of Silicon for 3D Devices

Tokel, O.; Turnali, A.; Makey, G.; Elahi, P.; Ilday, S.; Colakoglu, T.; Yavuz, O.; Hübner, R.; Zolfaghari, M.; Pavlov, I.; Bek, A.; Turan, R.; Ilday, O.

Recently we have demonstrated a new 3D-laser-fabrication method which enabled, for the first time, creating highly-controlled subsurface structural modifications (structural imperfections, or defects) buried deep inside Silicon (Si) wafers [1]. Characterizing the material properties of these subsurface Si structures are very critical towards enabling new optical and micro-mechanical applications inside chips [2,3]. Here, we present optical, chemical and microscopic analysis of these buried structures. Specifically, Transmission Electron Microscopy (TEM) studies, Optical Birefringence Analysis and Selective Chemical Etching analysis of the modifications will be presented. Infrared Transmission Microscopy will be shown to be applicable for subsurface imaging, providing a diagnostic tool without damaging the samples.

Material properties of the disruptions in the crystal lattice are then exploited for fabricating various micro-devices. For instance, oxidation-reduction chemistry on laser-induced modifications enables the creation of highly-controllable, uniform and large-area micropillar arrays for solar cell applications, embedded microfludic channels for chip cooling and thru-Si vias for electrical interconnects in Si. These elements, which are challenging to form with conventional methods, can find use in various MEMS and electronics applications. The optical properties (refractive index change) of the structures are used to fabricate functional components such as lenses and gratings buried in chips. Further, the birefringence effect induced in Si may lead to holograms and other photonic applications, such as creating wave plates and polarizers. These functional optical and MEMS elements created inside Si, may find use in imaging and sensing in the near- and mid-infrared wavelength range, as well as in micro-devices towards micro-surgical tools, micro-motors, and micro-resonators. Thus, these capabilities are leading to a new fabrication approach in Si, which is fully CMOS compatible, rapid and mechanically robust, and builds on the optical,electrical and chemical properties of the modified volumes in Si.

[1] Tokel et. al.,
[2] Tokel et. al, Direct Laser Writing of Volume Fresnel Zone Plates in Silicon., CLEO/Europe - EQEC, Munich, Germany, 2015.
[3] Tokel et. al., 3D Functional Elements Deep Inside Silicon with Nonlinear Laser Lithography, APS March Meeting, Baltimore, USA, 2016.

  • Poster
    2017 MRS Spring Meeting & Exhibit, 17.-21.04.2017, Phoenix, AZ, USA

Publ.-Id: 26597

Application of Ion Beams to Fabricate and Modify Properties of Dilute Ferromagnetic Semiconductors

Yuan, Y.; Helm, M.; Sawicki, M.; Dietl, T.; Zhou, S.

Dilute ferromagnetic semiconductors (DFS) have been investigated for more than two decades due to their potentials for spintronics. Mn doped III-V semiconductors have been regarded as the prototype of the type. In this contribution, we will show how ion beams can be utilized in fabricating and modifying DFS. First, ion implantation followed by pulsed laser melting (II-PLM) provides an alternative to low-temperature molecular beam epitaxy (LTMBE) to prepare diverse DFS. The prepared DFSs exhibit pronounced magnetic anisotropy, large X-ray magnetic circular dichroism, anomalous Hall effect and magnetoresistance [1-9]. Going beyond LTMBE, II-PLM is successful to bring two new members, GaMnP and InMnP, into the family of III-Mn-V. Both GaMnP and InMnP show clear signatures of ferromagnetism and an insulating behavior. Second, helium ions can be used to precisely compensate the holes while keeping the Mn concentration constant [10-12].
For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a smooth decrease of TC over a wide temperature range with carrier compensation while the conduction is changed from metallic to insulating. We can tune the uniaxial magnetic easy axis of (Ga,Mn)(As,P) from out-of-plane to in-plane with an isotropic-like intermediate state. These materials synthesized or modified by ion beams provide an alternative avenue to understand how carrier-mediated ferromagnetism is influenced by localization.

  • Lecture (Conference)
    20th International Conference on Surface Modification of Materials by Ion Beams, 09.-14.07.2017, Lisbon, Portugal

Publ.-Id: 26596

Modelling of turbulence modulation in bubbly flows with the aid of DNS

Ma, T.; Santarelli, C.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.

Modelling of turbulence modulation in bubbly flows with the aid of DNS data

  • Poster
    15th Multiphase Flow Conference and Short Course, 14.-17.11.2017, Dresden, Deuschland

Publ.-Id: 26595

new model for bubble-induced turbulence based on direct numerical simulation data

Ma, T.; Santarelli, C.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.

Three main issues are addressed in the present study. First, an appropriate time scale is selected with the aid of the energy spectra determined on the basis of the DNS data. Then, links between the unclosed terms in the transport equations of the turbulence quantities and the DNS data for small bubbles are established. Third, a suitably chosen iterative procedure employing the full Reynolds-averaged model provides suitable coefficients for the closure of the terms resulting from BIT while largely removing the influence of others. Here, using DNS data with iterations to obtain term-by-term match (Figure 1b) in the model equations avoids pitfalls of ad hoc models targeting the TKE only. At the same time these results validate the closure, exhibiting very good agreement with the DNS and better performance than the standard closures. Beyond the resulting model itself the study also furnishes a systematic procedure which is of general use. The model is now ready for use and can be employed in practical Euler-Euler simulations.

  • Lecture (Conference)
    The 3rd International Conference on Numerical Methods in Multiphase Flows, 26.-29.06.2017, Tokyo, Japan

Publ.-Id: 26594

DNS-based RANS closure for bubble-induced turbulence

Ma, T.; Santarelli, C.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.

DNS-based RANS closure for bubble-induced turbulence

Keywords: DNS; RANS; bubble-induced turbulence

  • Lecture (Conference)
    ProcessNet Jahrestreffen Dresden, 14.-17.03.2017, Dresden, Deuschland

Publ.-Id: 26593

A contribution to turbulence modelling in bubbly flows

Ma, T.

Modelling turbulence in bubbly flows that arise in the engineering and environment is of great challenges for multiphase Computational Fluid Dynamics. In the present book various turbulence modelling approaches are investigated in bubble columns and bubbly channel flows. The considered approaches contain Scale Resolving Simulations and the traditional Reynolds-averaged Navier-Stokes closure. The focus is set on the representation of the so-called bubble-induced turbulence in the modelling framework. A major chapter addresses a complete route to construct such a model embedded in Euler-Euler approach with the aid of Direct Numerical Simulation data. This procedure is employed to propose an improved model for bubble-induced turbulence.

Keywords: Scale Resolving Simulation; Direct Numerical Simulation data; bubble-induced turbulence

  • Book (Authorship)
    Dresden: TUDpress, 2017

Publ.-Id: 26592

Simulation of Reconfigurable Field-effect Transistors: Impact of the NiSi2-Si Interfaces, Strain, and Crystal Orientation

Fuchs, F.; Schuster, J.; Gemming, S.

Reconfigurable transistors (RFETs) can be switched between electron and hole current by changing the polarity of the gate potential. The device performance of such a transistor is strongly dominated by the contact physics.
In this work, the electron transport across the NiSi2-Si interface is studied using the NEGF formalism and density functional theory. A new model is presented which relates the electron transport through the interface to the transfer characteristic of an RFET. The model is compared to experimental data showing good agreement.
Based on the model, the influence of strain and the choice of the crystal orientation is discussed. It is demonstrated that best symmetry between electron and hole current is achieved for the <110> orientation. Furthermore, this symmetry can be tuned by strain, which is not possible for the <100> and <112> orientations. A discussion of these differences based on band structure analysis will be given, too.

Keywords: Reconfigurable field-effect transistor; silicon; interface

  • Lecture (Conference)
    IHRS NanoNet Annual Workshop 2017, 16.-18.08.2017, Neuklingenberg, Deutschland

Publ.-Id: 26591

Injection locking of constriction based spin Hall nano-oscillators

Hache, T.; Weinhold, T.; Arekapudi, S. S. P. K.; Hellwig, O.; Schultheiss, H.

Spin-Hall nano-oscillators (SHNOs) are modern auto-oscillation devices. Their simple geometry allows for an optical characterization by Brillouin-Light-Scattering microscopy at room temperature. Here we report on the observation of auto-oscillations in constriction based SHNOs under the forcing influence of an added alternating current. We show the possibility of injection locking between the applied external signal and the auto-oscillations driven by a direct current. Within the locking range the frequency of the auto-oscillations is forced to the external stimulus. In addition the intensity of the oscillations is increased strongly and the linewidth decreases. Due to the controllability of the auto-oscillations of the magnetization, injection locking can be used to influence the properties of future communication technologies, i.e. based on synchronized constriction based spin Hall nano-oscillators arrays.

Keywords: spin Hall; spin Hall nano-oscillators; auto-oscillations; injection locking; phase locking; Auto-Oszillationen; Spin-Hall Nanooszillatoren

  • Poster
    2017 European School on Magnetism: Condensed Matter Magnetism : bulk meets nano, 09.-20.10.2017, Cargese, France
  • Poster
    Nano-Magnonics Workshop 2018, 19.-21.02.2018, Diemerstein, Kaiserslautern, Deutschland
  • Poster
    Intermag 2018, 23.-27.04.2018, Marina Bay Sands Convetion Center, Singapore
  • Poster
    IEEE Magnetics Society Summer school, 03.-08.06.2018, Universidas San Francisco de Quito, Equador
  • Poster
    The Joint European Magnetic Symposia 2018, 03.-07.09.2018, Rheingoldhalle, Mainz, Deutschland

Publ.-Id: 26590

Möglichkeiten der Kreislaufwirtschaft

Reuter, M. A.

Knapp 780.000 Tonnen Elektro-Altgeräte wurden laut Umweltbundesamt im Jahr 2010 in Deutschland gesammelt. Das entspricht 8,8 Kilogramm pro Einwohner und Jahr. Viele wertvolle Metalle, Legierungen, funktionale Materialien sowie Kunststoffe sind darin enthalten. Wie kann man die Wertstoffe im Sinne einer Kreislaufwirtschaft (Circular Economy) bestmöglich zurückgewinnen, um neue Güter herzustellen? Was leistet Recycling schon heute? Was müsste getan werden, um es weiter zu verbessern? Und wie energetisch sinnvoll ist es überhaupt?
Prof. Markus Reuter, Direktor am Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) des HZDR, widmet sich diesen Fragen. Der Metallurge und Recyclingexperte beschäftigt sich mit der Wiederverwertbarkeit von Produkten und erforscht innovative, digitale Systeme und Prozesse für optimales Recycling.

Keywords: Kreislaufwirtschaft

  • Lecture (others)
    Möglichkeiten der Kreislaufwirtschaft / Wintersemester der Seniorenakademie, 06.11.2017, Dresden, Deutschland

Publ.-Id: 26589

Auto-oscillations in double constriction spin Hall nano-oscillators

Hache, T.; Wagner, K.; Arekapudi, S. S. P. K.; Hellwig, O.; Lindner, J.; Schultheiss, H.

Spin-Hall nano-oscillators (SHNOs) are modern auto-oscillation devices. Their simple geometry allows for an optical characterization by Brillouin-Light-Scattering microscopy at room temperature. Here we report on the observation of auto-oscillations in constriction based SHNOs. These are devices where the current density is increased locally due to lateral confinement. Hence, the spin current generated by the spin Hall effect can create well defined hot-spots for auto-oscillations.
We present BLS measurements of auto-oscillations in Co60Fe20B20(5 nm)/Pt(7 nm) based samples with two interacting, neighbouring nanoconstrictions.
The precession amplitude in these samples can be driven far from equilibrium, resulting in clear nonlinear signatures in the spinwave spectra. The spatial distributions of the observed modes and current dependencies are shown.

Keywords: spin Hall; spin Hall nano-oscillators; Spin-Hall Nanooszillatoren; spin current; auto-oscillations; Autooszillationen

  • Poster
    DPG-Frühjahrstagung SKM, 19.-24.03.2017, Dresden, Deutschland

Publ.-Id: 26588

Circular Economy within and beyond manufacturing processes

Reuter, M. A.

This workshop will gather around 30 representatives of business support organisations, including established and prospective providers of resource efficiency advisory and consulting services from European countries and regions in the process of setting up resource efficiency services for small and medium-sized enterprises (SMEs).

  • Invited lecture (Conferences)
    Resource Efficiency in the Manufacturing Industry - Workshop, 24.11.2017, Berlin, Deutschland

Publ.-Id: 26586

Dual energy CT: Benefits for proton therapy planning and beyond

Richter, C.; Wohlfahrt, P.; Möhler, C.; Greilich, S.

For about a decade, dual-energy CT (DECT) has been clinically available, mainly for radiology applications. In contrast, in the field of radiotherapy DECT has gained relevant interest over the last few years and here clinical use is still far away from being clinical standard. In this lecture benefits of DECT for radiotherapy applications will be discussed.
The focus will be on application for treatment planning in proton therapy, namely the individual prediction of tissue’s stopping power relative to water (SPR) as an alternative to the standard approach using a generic look-up table (HLUT). The manifold information gathered by two CT scans with different X-ray spectra allow for a patient-specific and direct calculation of relative electron density and SPR [1,2]. This enables the consideration of intra- and inter-patient variabilities in CT-based SPR prediction and ultimately a more accurate range prediction. The talk will cover the validation of the SPR prediction accuracy in realistic ground-truth scenarios [3,4], the investigation of clinical relevant differences between the DECT-based and the standard HLUT-based SPR prediction in clinical patient data [5] as well as the status of its clinical implementation [6].
Furthermore, additional applications in radiotherapy, e.g. for photon treatment planning, delineating and material differentiating will be briefly discussed.

  • Invited lecture (Conferences)
    ESTRO 37, 20.-24.04.2018, Barcelona, España
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S289-S290
    DOI: 10.1016/S0167-8140(18)30854-5

Publ.-Id: 26585

Dual energy CT for range prediction in proton therapy: Validation, clinical benefit & status of implementation

Richter, C.

Overview of DECT project + outlook

  • Invited lecture (Conferences)
    33rd Conference on Clinical and Experimental Research in Radiation Oncology (C.E.R.R.O.), 13.-20.01.2018, Les Menuires, Frankreich

Publ.-Id: 26584

Inter-centre variability of CT-based range prediction in particle therapy: Survey-based evaluation

Taasti, V.; Bäumer, C.; Dahlgren, C.; Deisher, A.; Ellerbrock, M.; Free, J.; Gora, J.; Kozera, A.; Lomax, T.; de Marzi, L.; Molinelli, S.; Teo, K.; Wohlfahrt, P.; Petersen, J.; Muren, L.; Hansen, D.; Richter, C.

Purpose: To assess the inter-center variability of the conversion between CT number and particle stopping power ratio (SPR), a survey-based evaluation was carried out in the framework of the European Particle Therapy Network (EPTN). The CT-to-SPR conversion (Hounsfield look-up table, HLUT) is applied to treatment planning CT scans to finally derive the particle range in patients. Currently, CT scan protocols for treatment planning are not standardized regarding image acquisition and reconstruction parameters. Hence, the HLUT depends on the selected scan settings and must be defined by each center individually. Aiming to access the current inter-center differences, this investigation is a first step towards better standardization of CT-based SPR derivation.
Methods: A questionnaire was sent to particle therapy centers involved in the EPTN and two centers in the United States. The questionnaire asked for details on CT scanners, acquisition and reconstruction parameters, the calibration and definition of the HLUT, as well as body-region specific HLUT selection. It was also assessed whether the influence of beam hardening was investigated and if an experimental validation of the HLUT was performed. Furthermore, different future techniques were rated regarding their potential to improve range prediction accuracy.
Results: Twelve centers completed the survey (ten in Europe, two in the US). Scan parameters, in particular reconstruction kernel and beam hardening correction, as well as the HLUT generation showed a large variation between centers. Eight of twelve centers applied a stoichiometric calibration method, three defined the HLUT entirely based on tissue substitutes while one center used a combination of both. All facilities performed a piecewise linear fit to convert CT numbers into SPRs, yet the number of line segments used varied from two to eleven. Nine centers had investigated the influence of beam hardening, and seven of them had evaluated the object size dependence of their HLUT. All except two centers had validated their HLUT experimentally, but the validation schemes varied widely. Most centers acquired CT scans at 120 kVp, all centers individually customized their HLUT, and dual-energy CT was seen as a promising technique to improve SPR calculation.
Conclusions: In general, a large inter-center variability was found in implementation of CT scans, image reconstruction and especially in specification of the CT-to-SPR conversion. A future standardization would reduce time-intensive institution-specific efforts and variations in treatment quality. Due to the interdependency of multiple parameters, no conclusion can be drawn on the derived SPR accuracy and its inter-center variability. As a next step within the EPTN, an inter-center comparison of CT-based SPR prediction accuracy will be performed with a ground-truth phantom.

Keywords: proton therapy; particle therapy; range prediction; stopping-power ratio; Hounsfield look-up-table; inter-center comparison

Publ.-Id: 26583

Inherited control of crystal surface reactivity

Fischer, C.; Kurganskaya, I.; Lüttge, A.

Material and environmental sciences have a keen interest in the correct prediction of material release as a result of fluid-solid interaction. For crystalline materials, surface reactivity exerts fundamental control on dissolution reactions; however, it is continuously changing during reactions and governs the dynamics of porosity evolution. Thus, surface area and topography data are required as input parameters in reactive transport models that deal with challenges such as corrosion, CO2 sequestration, and extraction of thermal energy. Consequently, the analysis of surface reaction kinetics and material release is a key to understanding the evolution of dissolution-driven surface roughness and topography. Kinetic Monte Carlo (KMC) methods simulate such dynamic systems. Here we apply these techniques to study the evolution of reaction rates and surface topography in crystalline materials. The model system consists of domains with alternating reactivity, implemented by low vs. high defect densities.
Our results indicate complex and dynamic feedbacks between domains of high versus low defect density, with the latter apparently limiting the overall dissolution rate of the former - a limitation that prevails even after their disappearance. We introduce the concept of “inherited” control, consistent with our observation that maximum dissolution rates in high defect density domains are lower than they would be in the absence of low defect density neighboring domains.
The controlling factor is the spatial pattern of surface accessibility of fluids. Thus, the distribution of large etch pits centers is inherited almost independently of spatial contrasts in crystal defect density during ongoing reactions. As a critical consequence, the prediction of both the material flux from the reacting surface and the evolution of topography patterns in crystalline material is constrained by the reaction history. Important applications include the controlled inhibition of reactivity of crystalline materials as well as the quantitative evaluation and prediction of material failure in corrosive environments.

Keywords: Kinetic Monte Carlo simulation; rate spectra; crystal dissolution; surface reactivity; surface topography and roughness patterns


Publ.-Id: 26582

Pulsating dissolution of crystalline matter

Fischer, C.; Lüttge, A.

Fluid-solid reactions result in material flux from or to the solid surface. The prediction of the flux, its variations and changes with time are of interest to a wide array of disciplines, ranging from the material and earth sciences to pharmaceutical sciences. Reaction rate maps that are derived from sequences of topography maps illustrate the spatial distribution of reaction rates across the crystal surface. Here we present highly spatially-resolved rate maps that reveal the existence of rhythmic pulses of the material flux from the crystal surface. This observation leads to a change in our understanding of the way crystalline matter dissolves. Rhythmic fluctuations of the reactive surface site density and potentially concomitant oscillations in the fluid saturation imply spatial and temporal variability in surface reaction rates. Knowledge of such variability could aid attempts to upscale microscopic rates and predict reactive transport through changing porous media.

Keywords: surface reactivity; kinetics; dissolution; fluid-solid interaction; rate spectra

  • Open Access Logo Proceedings of the National Academy of Sciences of the United States of America 115(2018)5, 897-902
    DOI: 10.1073/pnas.1711254115


Publ.-Id: 26581

Vibrational properties of metal phosphorus trichalcogenides from first principles

Hashemi, A.; Komsa, H.-P.; Puska, M.; Krasheninnikov, A. V.

Two-dimensional (2D) sheets of transition metal phosphorus trichalcogenides (TMPTs) offer unique magnetic and optical properties that can complement those found in other 2D materials. Insights into the structure and properties of these materials can be obtained by a juxtaposition of the experimental and calculated Raman spectra, but there is very little theoretical knowledge of the vibrational properties of TMPTs. Using first-principles calculations, we study mechanical and vibrational properties of a large set of monolayer TMPTs. From the phonon dispersion curves, we assess the dynamical stabilities and general trends on the atomic character of the vibrational modes. We determine Raman active modes from group theory, calculate Raman intensities, and analyze them with the help of the corresponding atomic displacements. We evaluate how the mode frequencies shift in response to a biaxial strain. We also determine elastic properties, which show that these systems are softer than many other layered materials. In addition to shedding light on the general features of vibrational properties of these materials, our results should also prove useful for interpreting experimental Raman spectra.

Keywords: 2D materials; transition metal phosphorus trichalcogenides; first-principles calculations; Raman spectra


Publ.-Id: 26580

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