Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35818 Publications

Top-down fabrication and characterization of reconfigurable silicon nanowire-based field effect transistors with Schottky contacts

Deb, D.; Khan, M. B.; Georgiev, Y. M.; Löffler, M.; Weber, W.; Helm, M.; Erbe, A.

In the last 60 years the size of a transistor has been reduced from few centimeters to few nanometers. Smarter, faster and cheaper: these are the three factors that motivated the miniaturization crusade in the silicon chip industry. Now we reach the end of physical scaling and it is expected that future development will be based on new ideas1: (i) new materials (high-mobility channel materials accompanied by metal gates with high-k gate dielectrics), (ii) new architectures (e.g. 3D integration), (iii) new functionality (e.g. reconfigurability), (iv) new computation principles (e.g. spintronics, quantum computing), etc.
In this work we deal with this problem by introducing reconfigurability in transistors. We report on characterization of reconfigurable, undoped silicon nanowire field effect transistors (FETs) with Schottky junctions fabricated on silicon on insulator (SOI) substrates by an industry compatible top-down process. Reconfigurable transistors employ an axial nanowire heterostructure (metal/intrinsic-silicon/metal) with independent gating of the two Schottky junctions and can be reversely configured as p-FET or n-FET simply by the application of an electric signal2.
The fabrication scheme is based on electron beam lithography (EBL) using hydrogen silsesquioxane (HSQ), a negative-tone electron beam resist, followed by inductively-coupled plasma (ICP) etching. The etch recipe was optimized with respect to selectivity, sidewall roughness and anisotropy by selecting an appropriate gas chemistry (SF6/C4F8) and controlling the ICP hardware parameters such as gas flow, mixed gas ratio, plasma power and chamber pressure. We produced silicon nanowires of 20 nm width and nanowire arrays with a pitch of ≈ 200 nm.
A nickel (Ni) layer of 50 nm thickness was sputtered on the Si nanowires at lithographically defined areas followed by lift-off and thermal annealing to create nickel-silicide Schottky junctions inside the nanowires. In this way, the source and drain regions were formed creating silicide-silicon-silicide contacts. Diffusion of Ni in Si nanowires was precisely controlled by the radial crystal orientation of the nanowires, which was checked by transmission electron microscopy (TEM). The Schottky junctions were electrostatically modulated by a back gate potential. Transport properties of these nanowires could be switched from p-type to n-type and vice-versa by changing the polarity of the back gate.

References
1. L. Risch, Solid-State Electronics. 50, 527 (2006).
2. A. Heinzig, T. Mikolajick, J. Trommer, D. Grimm and W. M. Weber, Nano Letters. 13, 4176 (2013).

Keywords: Nanowires; FETs; Schotky Junctions; Silicides

  • Lecture (Conference)
    ICSNN 2016 - 19th International Conference on Superlattices, Nanostructures and Nanodevices, 25.-29.07.2016, Hong Kong, China

Permalink: https://www.hzdr.de/publications/Publ-25029
Publ.-Id: 25029


Characterisation of top-down fabricated NixSiy-Si hetrostructure undoped nanowires

Deb, D.; Loffler, M.; Khan, M. B.; Georgiev, Y. M.; Erbe, A.

Semiconductor industry reaches the end of physical scaling soon and it is expected that future development will be based on new concepts: (i) new materials (high-mobility channel materials accompanied by metal gates with high-k gate dielectrics), (ii) new architectures (e.g. 3D integration), (iii) new functionality (e.g. reconfigurability), (iv) new computation principles (e.g. spintronics, quantum computing), etc [1]. In our work we focus on new functionality, specifically reconfigurable logic. The most promising industry compatible hardware for this logic is silicon nanowire based Schottky junction FET [2]. However, NiSi2-Si Schottky junctions in axial heterostructures (metal/intrinsic silicon/metal) are still complex and detailed studies of these structures are essential.
We report on heterostructure (NixSiy-Si) characterisation of reconfigurable, undoped silicon nanowire Schottky junction FETs. The nanowires are fabricated on silicon on insulator (SOI) substrates by electron beam lithography (EBL) using hydrogen silsesquioxane (HSQ), a negative-tone electron beam resist, followed by inductively-coupled plasma (ICP) etching. We produced silicon nanowires of 20 nm width and arrays of them with a pitch of ≈ 200 nm. Nickel was sputtered on the Si nanowires at lithographically defined areas followed by thermal annealing to create nickel-silicide Schottky junctions inside the nanowires, which also act as source-drain contacts. Silicidation was done on single nanowires and nanowire arrays with varying cross-sections and also for different annealing times.
We investigated the corresponding devices using SEM and TEM concerning their morphology and silicidation and determined the necessary parameters to allow for a reproducible scaling of these structures.
Furthermore, some cross-sections of nanowire samples were prepared by the standard FIB technique followed by low voltage FIB cleaning to preserve the crystal structure. We observed that the interface between the Ni silicide and the intrinsic silicon forms {111} facets. In contrast to common expectations, also features such as grain boundaries, nanotwins and multiple silicide phases between the Ni source and the Si part of the nanowire have been observed. Those features pose a technological challenge towards large-scale integration in future reconfigurable semiconductor devices and need to be properly studied and taken into account.
[1] L. Risch, Solid-State Electronics. 50 (2006) 527-535.
[2] A. Heinzig, T. Mikolajick, J. Trommer, D. Grimm and W. M. Weber, Nano Lett. 13 (2013) 4176-4181.

Keywords: Nanowires; TEM; silicon on insulator; Schottky junction; FETs; Silicidation

  • Poster
    42nd Micro and Nano Engineering international conference (MNE 2016), 19.-23.09.2016, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-25028
Publ.-Id: 25028


Open volume defects in annealed and ion irradiated SrTiO3 systems

Liedke, M. O.; Potzger, K.; Srinivasan, N.; Wagner, A.

The formation of vacancies in SrTiO3 due to annealing in vacuum [1] or low-energy ion irradiation [2] also leads to the modification of electronic properties that could be exploited in applications like resistivity switching. Here, we employ both these modification methods combined with in-situ defects evolution analysis by means of Doppler Broadening Positron Annihilation Spectroscopy (DB-PAS). Two reference SrTiO3 single crystals, undoped and Nb-doped have been investigated. Vacuum annealing of undoped SrTiO3 increases the defect concentration which can be attributed to the creation of oxygen and strontium vacancies close to the sample surface and deeper inside the substrate, respectively. Variable energy DB-PAS reveals the depth-dependent open volume defects concentration. Second, in-situ room and low temperature (about 165K) Ar+ irradiation has been utilized as a preliminary attempt to understand a vacancy migration process beneath the kinetical ion penetration depth. For that purpose, a frozen vacancy state is required, which could be achieved by lowering the system temperature below the vacancy activation energy. Although, that part of the experiment has been not entirely successful due to not low enough temperature realized during ion irradiation, however, a strong conclusion has been drawn about necessity of performing such type of experiments in-situ. A clear indication of oxygen deficiency at the sample surface due to ion irradiation, as found from DB-PAS is diminished after repeated ex-situ measurements.

Keywords: strontium titanate; annealing; PAS; Doppler broadening; AIDA

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

Permalink: https://www.hzdr.de/publications/Publ-25027
Publ.-Id: 25027


Positron annihilation spectroscopy of ion and laser irradiation driven spin reorientation transitions in Pt/Co/Pt systems

Liedke, M. O.; Sveklo, I.; Jakubowski, M.; Anwand, W.; Yuan, Y.; Zhou, S.; Kurant, Z.; Wawro, A.; Maziewski, A.; Wagner, A.

Multilayer ultrathin-films with perpendicular magnetic anisotropy (PMA) show a perspective as candidates for spintronic devices. The effective magnetic anisotropy strongly depends on the magnetic layer thickness – spin reorientation transition (SRT) at a critical thickness takes place from the inplane to out-of-plane magnetization direction. Moreover, SRT can be shifted to higher thicknesses by means of ion [1] and fs-laser irradiation [2]. Here, we employ variable energy positron annihilation spectroscopy (PAS) that is sensitive to open volume defects and their atomic surrounding to compare these two methods of the SRT inducement. Molecular beam epitaxy deposited films with different bottom Pt layer thicknesses and growth temperatures have been investigated. In case of Ar+ ion irradiated trilayers magnetization can be driven to the out-of-plane state twice as a function of ion fluence [1], whereas our preliminary studies of UV laser irradiation suggest only one SRT.
PAS analysis (Fig. 1) of the as-grown samples reveal slight differences in crystal quality and defect concentration that is likely due to a thicker bottom Pt layer used for the ion irradiation experiment.
Films utilized for the laser irradiation exhibit larger initial positron diffusion length, L+ that is close to L+ of the substrate (~60nm). In case of lower ion and laser fluences only minor and no interface intermixing has been found, respectively. The sample irradiated with lower ion fluence shows a slight increase of S (for E~1.5keV) being likely due to Co-vacancy increase, which could be responsible for first SRT. The sample irradiated with lower laser fluence shows no difference compare to the asgrown stacks, where only increase of magnetic anisotropy was found. The larger ion and laser fluences reorients magnetization to the out-of-plane state that is evidenced by both magneto-optical and PAS studies – S(E) curves nicely overlap. Moreover, large intermixing is expected, thus creation of the CoPt alloy with PMA. To elucidate stoichiometry and atomic surrounding of open volume defect coincidence Doppler broadening investigations will be presented.
*Corresponding author. E-mail address: m.liedke@hzdr.de
[1] A. Maziewski et al., Phys. Rev. B. 85, 054427 (2012)
[2] J. Kisielewski et al., J. Appl. Phys. 115, 053906 (2014)

Keywords: perpendicular magnetic anisotropy; positron annihilation spectroscopy; Doppler broadening; ion irradiation; UV ns-laser irradiation

  • Poster
    Joint European Magnetic Symposia (JEMS), 21.-26.08.2016, Glasgow, United Kligdom

Permalink: https://www.hzdr.de/publications/Publ-25026
Publ.-Id: 25026


Positron annihilation lifetime spectroscopy study of self-assembled porous low-k films

Kraatz, M.; Clausner, A.; Gall, M.; Zschech, E.; Liedke, M. O.; Anwand, W.; Wagner, A.; Krause-Rehberg, R.; Pakbaz, K.

We investigated advanced, self-assembled, porous organosilicate glasses with varying porogen level, resulting in varying dielectric constants (k-values ranging from 1.8 to 2.7, including a non-porous reference sample with 3.0). We used positron annihilation lifetime spectroscopy (PALS) to determine the pore size. The pores are fabricated by self-assembly into the OSG by a sol-gel process. The pore size is a critical parameter to characterize the quality of the OSG thin film. Other critical parameters, which were not investigated in this study are connectedness of pores and pore size distribution. Porous OSG is used in the microelectronic industry as insulating material for the wiring of microchips. Since pores not only lower the k-value, but also degrade mechanical stability of film stacks in microchips, knowledge of pore characteristics is crucial. Low-k materials are a necessity to lower microchip power consumption, maintain signal speed and reduce coupling in the relentless icroelectronics miniaturization process.

Keywords: positron annihilation spectroscopy; low-k; dielectrics; porous materials; positron lifetime

  • Poster
    14th International Conference Reliability and Stress-Related Phenomena in Nanoelectronics – Experiment and Simulation, 30.05.-01.06.2016, Bad Schandau, Germany

Permalink: https://www.hzdr.de/publications/Publ-25025
Publ.-Id: 25025


P1608 - Ionenmikroskopievorrichtung

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

Die Erfindung betrifft eine Ionenmikroskopievorrichtung mit einer Ionenquelle zum Erzeugen eines Ionenstrahls, einem Detektor, einer Spannungsquelle und einem Photonenpuls-Generator, wobei die Ionenmikroskopievorrichtung zum Bestrahlen eines Objekts mit dem Ionenstrahl unter Erzeugung von Wechselwirkungsteilchen ausgebildet ist, wobei die Ionenquelle eine Gasionisationskammer, eine in derselben angeordnete spitzenförmige Elektrode und eine Gegenelektrode aufweist, der Detektor zum Erfassen der Wechselwirkungsteilchen dient, die Spannungsquelle zum Anlegen einer elektrischen Spannung zwischen die Elektrode und die Gegenelektrode dient, und der Photonenpuls-Generator zum Erzeugen von in die Ionisationskammer gerichteten Photonenpulsen dient.

  • Patent
    DE102016112328 - Erteilung: 05.01.2017

Permalink: https://www.hzdr.de/publications/Publ-25024
Publ.-Id: 25024


Single Molecule Level Measurements

Kilibarda, F.; Ahmed, O.; Öktem, G.; Kiriy, A.; Cuniberti, G.; Erbe, A.

In the quest for miniaturizing the transistor nodes, the technology does not look so promising and alternates have to be done in order to sustain the ‘Beyond CMOS’ trend. One of the promising technology can be the use of ‘Molecular Electronics’. In recent years, microelectronics industry is reaching its limits with transistor miniaturization. One of the possibilities is to abandon standard silicon technologies and start using single molecules and atoms as building blocks. By taking this route, it is first important to characterize and choose the right molecular candidates for future implementation. Till recent years this area was very slow in development, but as the techniques of electronic lithography, nanoscale manufacture and chemical synthesis continue to improve, it is accelerating in progress. In our research we are working with Mechanically Controlled Break Junctions (MCBJ) as a method of characterizing electrical properties of molecules and apply Landauer theoretical approach to model the behavior of the junctions. In parallel to that, we are examining possibilities to gate the molecules while they are being characterized. Our experiments show successful coupling to the molecules and accompanying change in conductance. In regard to gating we show possibility of manufacturing sub-20nm gaps for side gating of the molecular system.The developed techniques presented here may prove to be important in future many-level measurements and transistor implementation.

Keywords: Molecular electronics; MCBJ; electronic lithography; gating; nanogaps

  • Poster
    NanoNet International Workshop 2016, 30.08.-02.09.2016, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-25023
Publ.-Id: 25023


P1511 - Thermisches Anemometer

Schleicher, E.; Berger, R.; Arlit, M.

Die Erfindung betrifft ein thermisches Anemometer zum Charakterisieren einer Fluidströmung, wobei das Anemometer ein Sensorelement zum Einbringen in die Fluidströmung aufweist, das mittels einer Spannung elektrisch beheizbar ist; wobei das Anemometer zum abwechselnden Betreiben des Sensorelements mit einer kleineren ersten und einer größeren zweiten Spannung ausgebildet ist, sodass ein abwechselndes Erwärmen und Abkühlen des Sensorelements erfolgt; wobei beim Betreiben des Sensorelements mit der ersten Spannung beim Erreichen eines unteren Temperatur-Schwellenwertes ein Umschalten zu der zweiten Spannung erfolgt, beim Betreiben des Sensorelements mit der zweiten Spannung beim Erreichen eines oberen Temperatur-Schwellenwertes ein Umschalten zu der ersten Spannung erfolgt, und das Anemometer zum Charakterisieren der Fluidströmung basierend auf den Zeitabständen zwischen den Umschalt-Zeitpunkten, an denen ein Umschalten der Spannung erfolgt, ausgebildet ist.

  • Patent
    DE102015114139 - Erteilung: 08.12.2016

Permalink: https://www.hzdr.de/publications/Publ-25022
Publ.-Id: 25022


The influence of local ion implantation on magnetic domains, magnetoresistance and spin wave propagation

Osten, J.; Hula, T.; Wagner, K.; Henschke, A.; Lenz, K.; Schultheiss, H.; Lindner, J.; Fassbender, J.

The influence of ion induced magnetic patterning on the anisotropic magnetoresistance (AMR) is investigated in the first part. The AMR directly depends on the angle between the applied current and the magnetization of the material. To investigate this relationship a Kerr microscope for visualizing the magnetic domains is combined with magneto-transport measurements. The investigated samples are magnetic hybrid structures from irradiated and non-irradiated permalloy.

In the second part ion implantation is used to create spin wave channels. Fe60Al40films in the B2 phase is paramagnetic. Starting from a FeAl film in the paramagnetic state the incident ions randomize the site occupancies and, thereby, transform it to the chemically disordered, ferromagnetic A2 phase. Spin waves, the eigen-excitations of ferromagnets, are promising candidates for spin transport in lateral devices. The aim is to investigate spin wave propagation in this ferromagnetic material in free standing structure as well as in structure within a paramagnetic matrix.

  • Lecture (others)
    Hard Condensed Matter Theory Seminar, 24.01.2017, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25021
Publ.-Id: 25021


P1413 - Verfahren zur Metallisierung von Kunststoffteilen sowie Lösung

Hofinger, J.; Roos, S.; Günther, T.; Maffert, A.

Die Erfindung umfasst ein Verfahren zur Metallisierung von Kunststoffteilen mit den Schritten Vorbehandlung der Kunststoffoberfläche, chemische Metallisierung, wobei zur Vorbehandlung, die Oberfläche des Kunststoffteiles mit mindestens einer niedrig siedenden organischen Flüssigkeit angelöst und/oder angequollen wird, sodass anschließend die angelöste und/oder angequollene Kunststoffoberfläche durch Verdampfen der mindestens einen niedrig siedenden organischen Flüssigkeit strukturiert wird und sodass die so strukturierte Oberfläche ohne Chromsäure-Schwefelsäure-Lösung hydrophiliert wird.

  • Patent
    DE102015201562 - Offenlegung: 04.08.2016, Nachanmeldungen: WO

Permalink: https://www.hzdr.de/publications/Publ-25020
Publ.-Id: 25020


German Resource Research Institute (GERRI): Concept and Aims of a Raw Materials Network

Köpf, H.; Rasenack, K.

The German Resource Research Institute “GERRI” was founded as a virtual institute and a national network in 2015 by five leading German research institutions of the raw materials sector. The founding partners of GERRI - TU Bergakademie Freiberg, RWTH Aachen University, Clausthal University of Technology, Fraunhofer project group materials recycling and resource strategies IWKS at the Fraunhofer Institute ISC and the Helmholtz-Institute Freiberg for Resource Technolo-gy (HIF) at the HZDR – offer broad knowledge and experience in the following fields of expertise: exploration & mining, processing, hydrometallurgy, pyrometallurgy, materials, waste management, machinery, modeling and special analytics. The main goal of GERRI is to strengthen transdiscipli-nary research along the entire value chain of mineral metalliferous and raw materials. Furthermore, GERRI is intended to become a central nucleus for innovation between politics, industry and aca-demic research.
GERRI´s unique feature of GERRI is competence mapping, which bundles the available knowledge and experience within all competence fields of this network. There methods and processes of tech-nical infrastructure are directly linked to relevant elements of periodic table and material flows.
GERRI is embedded in the "Research for Sustainable Development (FONA)" program of the Ger-man Federal Ministry of Education and Research (BMBF), which is part of the funding program "r4 - Innovative Technologies for Resource Efficiency - Research on the Provision of Economic Strate-gic Raw Materials". After the expiry of the five-year funding period, GERRI is envisioned to persist independently as a network and will be financed, amongst others, by industrial and research funds.

Keywords: Competence mapping; infrastructure sharing; interdisciplinary research; network; synergies

  • Contribution to proceedings
    European Metallurgical Conference (EMC) 2017, 25.-28.06.2017, Leipzig, Deutschland
    German Resource Research Institute (GERRI): Concept and Aims of a Raw Materials Network
  • Lecture (Conference)
    European Metallurgical Conference 2017, 25.-28.06.2017, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25019
Publ.-Id: 25019


Das virtuelle Rohstoffforschungsinstitut GERRI: Innovationskatalysator für Deutschland

Köpf, H.; Güth, C.; Rasenack, K.; Rombach, E.; Schmid, E.; Friedrich, B.; Goldmann, D.; Reuter, M. A.; Stauber, R.; Stelter, M.

Das German Resource Research Institute GERRI ist ein nationales Netzwerk im Bereich metallischer und mineralischer Rohstoffe. Ziel ist die Bündelung und Koordination der Akteure für eine optimierte gemeinsame Forschung entlang der Rohstoffkette. GERRI hat erstmals eine Methodik entwickelt, über die Kompetenzen strukturiert erfasst, ausgewertet und verfügbar gemacht werden können. Dadurch schafft GERRI Transparenz und legt die Grundlage zur Realisierung von Synergien.

Keywords: Wirtschaftsstrategische Rohstoffe; Rohstoffstrategie; KIC EIT RawMaterials; German Ressource Research Institute (GERRI); strategische Forschungskooperation; Kompetenzmapping

  • Contribution to proceedings
    Berliner Rohstoff- und Recyclingkonferenz, 06.-07.03.2017, Berlin, Deutschland
    Proceedings der Berliner Rohstoff- und Recyclingkonferenz

Permalink: https://www.hzdr.de/publications/Publ-25018
Publ.-Id: 25018


P1412 - Pockelszellen-Treiberschaltung mit Induktivitäten

Bergmann, T.; Siebold, M.; Löser, M.

Die Treiberschaltung enthält eine erste Leitung, welche mit einem ersten Anschluss der Pockelszelle (18; CP) zu verbinden ist, und eine zweite Leitung, welche mit einem zweiten Anschluss der Pockelszelle (18; CP) zu verbinden ist, wobei die erste Leitung und/oder die zweite Leitung eine Induktivität 10 (14, 15; 24, 25) aufweist.

  • Patent
    EP3023832 - Offenlegung: 25.05.2016, Nachanmeldungen: US

Permalink: https://www.hzdr.de/publications/Publ-25017
Publ.-Id: 25017


Micro reactor experiments on the partial isobutane oxidation as a multiphase process.

Willms, T.; Kryk, H.; Hampel, U.

Tertiary butyl hydroperoxide (TBHP), as an intermediate for the production of propylene oxide according to the Oxirane process, is currently produced at industrial scale by the partial oxidation of liquid isobutane using bubble columns or bubble tray reactors. In this process, liquid isobutane reacts with oxygen at temperatures of 120 to 140 °C and pressures of 25 to 37 bar at high residence times of up to 12 hours. The conversion is limited to 35 to 50 % in order to obtain a TBHP selectivity of 50 to 60 % minimizing the formation of by-products, which are caused by the decomposition of the TBHP due to the complex reaction mechanism. Besides safety aspects, the high reaction enthalpy of the oxidation as well as heat and mass transport problems are further issues of this process. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“, this reaction is investigated for the first time as a Taylor-Flow process in a broad range of flow rates, temperatures and pressures in a micro reactor with the aim to enhance the space-time yield of the process. The advantage of micro reactors are the high surface – volume ratio for an efficient heat transfer, the related, improved – nearly inherent – safety and the resulting possibility to investigate yet unexplored process windows for instance within the explosive region of a reaction mixture. A number of levers for the process intensification have been identified. In addition to the parameter ranges studied so far, higher pressures of up to 100 bar and uninvestigated initiator types, especially e.g hydrogen peroxide and high oxidation concentrations (50 to 100%) are applied, which have not been studied yet. Also, the influence of process parameters on the start-up time is investigated. Finally, the reaction medium characteristics of the isobutane – oxidant flow is modified by adding additives to the liquid phase or inert gases to the gas phase. For all parameters, the selecti¬vity and conversion of the reaction is studied. Therefore, the reaction course is followed by sampling and analyzing the reaction by GC/MS and GC–TCD where analytical methods have been developed to detect a maximum of by-products and intermediates. In the frame of the presentation, the results of preliminary investigations and the first multiphase flow oxidation experiments are given and discussed with respect to the reaction characteristics.

Keywords: isobutane oxidation; microreactor; t-butyl hydroperoxide; two phase process

  • Poster
    10th European Congress of Chemical Engineering, 3rd European Congress of Applied Biotechnology, 5th European Process Intensification Conference ECCE10+ECAB3+EPIC5, 27.09.-01.10.2015, Nice, France
  • Contribution to proceedings
    10th European Congress of Chemical Engineering, 3rd European Congress of Applied Biotechnology, 5th European Process Intensification Conference ECCE10+ECAB3+EPIC5, 27.09.-01.10.2015, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-25016
Publ.-Id: 25016


Fabrication of sub-50 nm silicon nanowires using inductively coupled plasma etching

Khan, M. B.; Deb, D.; Georgiev, Y. M.; Erbe, A.

Development of an etching process for fabrication of ultrathin silicon nanowires (SiNWs) with inductively coupled plasma (ICP) source and C4F8/SF6 mixed gas recipe at 18 oC is reported. Etch selectivity of silicon (SOI) to hydrogen silsesquioxane (HSQ), a negative tone electron beam resist and selectivity of silicon (SOI) to SiO2 are investigated to identify suitable process window. Effects of ICP power, RF power, chamber pressure, flow rates and ratio of C4F8/SF6 on etch rate, selectivity and surface roughness are examined. Atomic force microscopy (AFM) is used for identifying surface roughness of the plain silicon (SOI) substrates after etching. Thereafter etching of HSQ patterned substrates is performed. Scanning electron microscopy is performed to observe the etch profile. Parameters such as flow rates of C4F8/SF6 are optimized to attain sub-50 nm SiNWs with smooth and vertical sidewalls.

  • Poster
    DPG Regensburg, 06.-11.03.2016, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-25015
Publ.-Id: 25015


Ge-doped GaSb thin films with zero mass density change upon crystallization for applications in phase change memories

Putero, M.; Coulet, M. V.; Muller, C.; Baehtz, C.; Raoux, S.; Cheng, H. Y.

In order to optimize materials for phase change random access memories (PCRAM), the effect of Ge doping on Ga-Sb alloy crystallization was studied using combined in situ synchrotron x-ray techniques, electrical measurements, and static laser testing. The present data emphasize that the crystallization temperature can be increased up to 390C with subsequent higher thermal stability of the amorphous phase; phase segregation is evidenced with GaSb, Sb, and Ge phases that crystallize in a two-step crystallization process. The Ge-doped GaSb films exhibit a larger electrical contrast as compared to undoped GaSb alloy (up to 100). The optical contrast measured by laser testing is shown to follow the mass density change variations upon crystallization, with a negative contrast (higher value in amorphous state) whatever Ge-doping levels. In situ x-ray reflectivity measurements show that zero mass density change can be achieved by low Ge-doping. Ge-doped GaSb alloys look promising since a phase change material with zero mass density change and higher crystallization temperature satisfactorily fulfills the specifications for reliable PCRAM cells in terms of endurance and data retention.

Keywords: phase change memories; thin films

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Permalink: https://www.hzdr.de/publications/Publ-25014
Publ.-Id: 25014


In Situ Observations of Phase Transitions in Metastable Nickel (Carbide)/Carbon Nanocomposites

Bayer, B. C.; Bosworth, D. A.; Michaelis, F. B.; Blume, R.; Habler, G.; Abart, R.; Weatherup, R. S.; Kidambi, P. R.; Baumberg, J. J.; Knop-Gericke, A.; Schloegl, R.; Baehtz, C.; Barber, Z. H.; Meyer, J. C.; Hofmann, S.

Nanocomposite thin films comprised of metastable metal carbides in a carbon matrix have a wide variety of applications ranging from hard coatings to magnetics and energy storage and conversion. While their deposition using nonequilibrium techniques is established, the understanding of the dynamic evolution of such metastable nanocomposites under thermal equilibrium conditions at elevated temperatures during processing and during device operation remains limited. Here, we investigate sputterdeposited nanocomposites of metastable nickel carbide (Ni3C) nanocrystals in an amorphous carbon (a-C) matrix during thermal postdeposition processing via complementary in situ X-ray diffractometry, in situ Raman spectroscopy, and in situ Xray photoelectron spectroscopy. At low annealing temperatures (300 °C) we observe isothermal Ni3C decomposition into face-centered-cubic Ni and amorphous carbon, however, without changes to the initial finely structured nanocomposite morphology. Only for higher temperatures (400−800 °C) Ni-catalyzed isothermal graphitization of the amorphous carbon matrix sets in, which we link to bulk-diffusion-mediated phase separation of the nanocomposite into coarser Ni and graphite grains. Upon natural cooling, only minimal precipitation of additional carbon from the Ni is observed, showing that even for highly carbon saturated systems precipitation upon cooling can be kinetically quenched. Our findings demonstrate that phase transformations of the filler and morphology modifications of the nanocomposite can be decoupled, which is advantageous from a manufacturing perspective. Our in situ study also identifies the high carbon content of the Ni filler crystallites at all stages of processing as the key hallmark feature of such metal−carbon nanocomposites that governs their entire thermal evolution. In a wider context, we also discuss our findings with regard to the much debated potential role of metastable Ni3C as a catalyst phase in graphene and carbon nanotube growth.

Keywords: nickel carbide, carbon nano tubes; in-situ xray diffraction

Permalink: https://www.hzdr.de/publications/Publ-25013
Publ.-Id: 25013


Controlling Catalyst Bulk Reservoir Effects for Monolayer Hexagonal Boron Nitride CVD

Caneva, S.; Weatherup, R. S.; Bayer, B. C.; Blume, R.; Cabrero-Vilatela, A.; Braeuninger-Weimer, P.; Martin, M. B.; Wang, R.; Baehtz, C.; Schloegl, R.; Meyer, J. C.; Hofmann, S.

Highly controlled Fe-catalyzed growth of monolayer hexagonal boron nitride (h-BN) films is demonstrated by the dissolution of nitrogen into the catalyst bulk via NH3 exposure prior to the actual growth step. This “pre-filling” of the catalyst bulk reservoir allows us to control and limit the uptake of B and N species during borazine exposure and thereby to control the incubation time and h-BN growth kinetics while also limiting the contribution of uncontrolled precipitation-driven h-BN growth during cooling. Using in situ X-ray diffraction and in situ X-ray photoelectron spectroscopy combined with systematic growth calibrations, we develop an understanding and framework for engineering the catalyst bulk reservoir to optimize the growth process, which is also relevant to other 2D materials and their heterostructures.

Keywords: hexagonal boron nitride (h-BN); chemical vapor deposition (CVD); borazine (HBNH)3

Permalink: https://www.hzdr.de/publications/Publ-25012
Publ.-Id: 25012


Micro structure and strain relaxation in thin nanocrystalline platinumfilms produced via different sputtering techniques

Gruber, W.; Baehtz, C.; Horisberger, M.; Ratschinski, I.; Schmidt, H.

In this study we investigated the correlation between microstructure and residual strain relaxation innanocrystalline Pt films with a thickness of about 20 nm produced by different deposition techniques:magnetron sputtering and ion beam sputtering. X-ray diffractometry was carried out using synchrotronradiation. The out-of-plane interplanar distance was measured during isothermal in situ annealing attemperatures between 130◦C und 210◦C. The thermoelastic expansion coefficient is equal for both types of nanocrystalline Pt films and slightly lower than for coarse grained Pt. The relaxation of residual out-of-plain strain depends on temperature and is significantly stronger in the case of the magnetron sputteredfilms than for the ion beam sputtered films. Different relaxation of compressive stress is ascribed tothe different microstructures which evolve during deposition via the corresponding deposition tech-nique. Thickness fringes around the (1 1 1) Bragg peak deposited via magnetron sputtering reveal thatthese films are essentially composed of columnar (1 1 1) oriented grains which cover the whole filmthickness. In contrast, no thickness fringes are observed around the (1 1 1) Bragg peak of films preparedby ion beam sputtering indicating a significantly different microstructure. This is confirmed by ElectronBackscatter Diffraction which reveals a (1 1 1) texture for both types of films. The (1 1 1) texture, however,is significantly stronger in the case of the magnetron sputtered films. Grain growth at low homologoustemperatures is considered to be an important contribution to relaxation of residual stress.

Keywords: microstructure; sputtering; diffraction

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Permalink: https://www.hzdr.de/publications/Publ-25011
Publ.-Id: 25011


Measurements of the diameter of rising gas bubbles by means of the ultrasound transit time technique

Richter, T.; Keplinger, O.; Strumpf, E.; Wondrak, T.; Eckert, K.; Eckert, S.; Odenbach, S.

This study presents ultrasound transit time technique (UTTT) measurements of single Ar bubbles rising in Galinstan under an applied magnetic field. Two setups were used to analyze the bubble rise, which led to differently oriented zig-zag trajectories. UTTT is able to visualize the bubble trajectory and to measure the variations of the apparent bubble diameters associated with the zig-zag trajectory. Due to the straightening of the bubble trajectories with increasing magnetic field, an increase of the apparent bubble diameter was detected.

Keywords: ultrasound transit time technique; single bubble; bubble diameter; Galinstan

  • Open Access Logo Magnetohydrodynamics 53(2017)2, 383-392

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Permalink: https://www.hzdr.de/publications/Publ-25010
Publ.-Id: 25010


Microstructure of multilayer heterosystems containing molecules of Ge quantum dots in Si on the stages of nucleation and growth as revealed by EXAFS spectroscopy

Erenburg, S. B.; Trubina, S. V.; Zvereva, V. V.; Zinov’Ev, V. A.; Dvurechenskiy, A. V.; Kuchinskaya, P. A.; Kvashnina, K. O.

GeK edge EXAFS (Extended X-Ray Absorption Fine Structure) spectra have been measured for multilayer semiconducting heterosystems containing interacted groups of quantum dots (“molecules from quantum dots”) ordered in rings on different stages of their growth depending on topologic parameters and growth conditions. In accordance with our results obtained previously for the quantum dots of SiGe, for the molecules of quantum dots it was found that deformation at the interface leads to decrease in the interatomic distance of Ge–Ge by ~0.03 Å. Effect of heterosystem topology and temperature at different stages of their growth on interlayer diffusion was investigated. It was found that at the first growth stage (growth of “seeded islands” serving as a basis for obtaining the molecules) at 700°C a concentration of Ge atoms in the system is ~38%. With further growth of the vertically-matched quantum dots groups the concentration of Ge increases up to ~43-47% depending on the growth conditions. Comparable analysis of different modes of EXAFS measurements was performed to determine precisely structural parameters of heterosystem SiGe with different thickness grown on Si(100) surface.

Keywords: microstructure; semiconductor heterosystem; molecules of quantum dots GeSi; EXAFS spectra

Permalink: https://www.hzdr.de/publications/Publ-25009
Publ.-Id: 25009


P1410 - Elektromagnet zur Führung von Teilchenstrahlen zur Strahlentherapie

Schürer, M.; Karsch, L.; Pawelke, J.; Zschetzsche, J.; Kroll, F.

Die Erfindung betrifft Elektromagnete zur Führung von Teilchenstrahlen zur Strahlentherapie mit einer Spule in Verbindung mit einer elektrischen Energiequelle zur Ausbildung eines magnetischen Feldes. Die Elektromagnete zeichnen sich insbesondere dadurch aus, dass die Führung der Teilchenstrahlen mit einem gepulsten Magnetfeld erfolgt. Dazu besteht die Spule aus mindestens einem aus einem elektrisch nichtleitenden Material bestehenden Grundkörper mit wenigstens einem elektrischen und flexiblen Leiter mit mindestens einer Biegung. Weiterhin ist die Spule mit einer eine gepulste Energie liefernden Energiequelle verbunden. Die Spule besteht damit im Wesentlichen aus dem elektrischen Leiter und dem Grundkörper, wobei der Grundkörper ausschließlich als Träger fungiert. Der Grundkörper besitzt damit keine elektrischen Eigenschaften.

  • Patent
    DE102015200213 - Offenlegung: 14.07.2016

Permalink: https://www.hzdr.de/publications/Publ-25008
Publ.-Id: 25008


Electrical characterization of two-dimensional materials and their heterostructures

Arora, H.; Seifert, G.; Cuniberti, G.; Helm, M.; Erbe, A.

Two-dimensional (2D) materials have gained enormous attention in recent years owing to their excellent transport properties and mechanical flexibility. Several 2D materials like graphene, MoS2, h-BN are under intense study in the areas of electronics, optics and sensing. Apart from these materials, 2D polymers are also rapidly gaining attention due to easy tuning of their properties by altering their synthesis parameters. Polymers and inorganics together, allow us to develop 2D nanostructures whose electrical properties can be controlled. Thus, in this project, we aim to investigate novel 2D materials followed by their structural and electrical characterizations w.r.t transistor properties. Another focus will be to fabricate vertical heterostructures by stacking different 2D materials together and investigate resulting functionalities of the stack.

Keywords: Two-dimensional (2D) materials; 2D polymers; nanostructures; heterostructures

  • Open Access Logo Contribution to proceedings
    2016 Radio and Antenna Days of the Indian Ocean (RADIO), 10.-13.10.2016, Reunion Island, France
    IEEE Xplore Digital Library: IEEE, 978-1-5090-2580-0
    DOI: 10.1109/RADIO.2016.7772014
  • Lecture (Conference)
    2016 Radio and Antenna Days of the Indian Ocean (RADIO), 10.-13.10.2016, Reunion Island, France
  • Poster
    Tailor-made 2D-materials and functional devices, 27.06.-01.07.2016, Bremen, Germany
  • Poster
    IHRS NanoNet International Workshop 2016, 30.08.-02.09.2016, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-25007
Publ.-Id: 25007


Retention of uranium(VI) by Ca-bentonite at high ionic strength and high pH studied by batch sorption tests and TRLFS

Philipp, T.; Schmeide, K.; Stumpf, T.

The retention behavior of U(VI) by Ca-bentonite was studied in saline and alkaline solution via batch sorption experiments and TRLFS. At pH 8.5-9.5 sorption is lower in the presence of CO2 due to the formation of weakly sorbing uranyl carbonate species, which have been observed to dominate speciation up to pH 10 by TRLFS. In the pH range10-12 the U(VI) retention is almost complete both in the absence as well as in the presence of CO2 (carbonate concentrations between 1∙10-4 and 1∙10-3 M). This retention appears to be a combination of adsorption of uranyl hydroxo complexes and precipitation of uranium due to an altered solubility of U(VI) induced by ions leached out of the bentonite. At pH > 12 the U(VI) retention decreases again, pre-sumably due to the formation of the strongly negatively charged 1:4 uranyl hydroxo complex.

  • Poster
    7th International Conference on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, 24.-27.09.2017, Davos, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-25006
Publ.-Id: 25006


Electrical characterization of atomically thin InSe layers

Arora, H.; Schönherr, T.; Erbe, A.

Two-dimensional (2D) materials have gained enormous attention in recent years owing to their huge potential in future electronics and optics. On the one hand, conventional 2D materials like graphene, MoS2, h-BN are being intensively studied, on the other hand, search for novel 2D materials is at a rapid pace. In this study, we have investigated electrical properties of 2D nanosheets of ultrathin Indium Selenide (InSe), a member of the family of III-VI chalcogenides. The InSe layers were prepared via micromechanical cleavage of its bulk crystal and were integrated into a field-effect transistor (FET) device as the transport channel. On characterizing the InSe-based FET, InSe showed n-type conductance with the mobility of 2.1x10-4 cm2V-1s-1.

Keywords: Two-dimensional (2D) materials; Indium Selenide; Field-effect transistors; micromechanical cleavage

  • Open Access Logo Contribution to proceedings
    IEEE Radio and Antenna Days of the Indian Ocean 2016, 10.-13.10.2016, Reunion Island, France
    IoP Conference Series: Materials Science and Engineering.: IEEE
    DOI: 10.1088/1757-899X/198/1/012002
  • Poster
    MRS Spring Meet 2017, 17.-21.04.2017, Phoenix, USA

Permalink: https://www.hzdr.de/publications/Publ-25005
Publ.-Id: 25005


Towards an Electronic Model for Reconfigurable Transistors

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

In contrast to conventional CMOS transistors, reconfigurable field effect transistors (RFETs) can be switched between n- and p-type behavior, which allows more compact and flexible circuit designs [1, 2]. Symmetry between n- and p-current is required and this can be achieved by strain engineering as experimentally demonstrated in Ref. [2]. However, a detailed understanding of the electron transport across the strained interface is not yet available and requires electronic models to capture all relevant transport mechanism.
We investigate the relation between strain and electron transport properties of planar interfaces between metallic NiSi 2 and semiconducting Si in <110> crystal orientation. We apply the non-equilibrium Green’s functions formalism together with density functional theory as implemented in Atomistix ToolKit [3] to calculate the transmission spectra. Using a modified version of the Landauer formula, we than obtain an expression for the current through the RFET and hence, the transfer characteristic can be investigated. A comparison between the calculated transfer characteristic using this model and experimental reference data [2] are performed. A very good agreement can be seen which verifies our model. However, in the experiment, the RFET was compressed during the oxidation process. Because the structure in the simulation was supposed to be unstrained, some pre-strain might be present in the simulation. We also study how strain, either applied perpendicular or parallel to the transport direction, alters the current. It can be seen that a small amount of strain is sufficient to change the ratio between n- and p-current and that symmetry can be achieved. Considering the above-mentioned pre-strain in the simulation, the general trend is also in agreement with experimental studies [1, 2].

[1] A. Heinzig et al., Reconfigurable Silicon Nanowire Transistors. Nano Letters 12, 119 (2012)
[2] A. Heinzig et al., Dually Active Silicon Nanowire Transistors and Circuits with Equal Electron and Hole Transport. Nano Letters 13, 4176 (2013)
[3] Atomistix ToolKit 15, QuantumWise A/S (www.quantumwise.com)

Keywords: reconfigurable transistor; silicon; density functional theory; non-equilibrium Green's function formalism; strain

  • Poster
    NanoNet International Workshop 2016, 30.08.-02.09.2016, Praha, Česká republika

Permalink: https://www.hzdr.de/publications/Publ-25004
Publ.-Id: 25004


Businesskontept für die Wirtschaftlichkeitsprüfung einer Haldensanierung der Tiefenbachhalde in Altenberg

Scholz, A.

Die vorliegende Masterarbeit beschäftigt sich mit dem Thema eines "Businesskonzepts für die Wirtschaftlichkeitsprüfung einer Haldensanierung der Tiefenbachhalde in Altenberg".
Es geht um die Frage, ob ein Re-mining, sprich eine Haldensanierung der Tiefenbachhalde mit Rohstoffrückgewinnung, wirtschaftlich durchgeführt werden und sich selbst finanzieren kann. Um die Wirtschaftlichkeit des Vorhabens überprüfen zu können, wurden alle schon vorhandenen Daten der möglichen Erlöse und der anfallenden Kosten recherchiert und zusammengetragen. Bei noch fehlenden Daten sollten Möglichkeiten zur Informationsbeschaffung aufgezeigt werden. Im Laufe der Arbeit hat sich gezeigt, dass genügend Daten für eine Wirtschaftlichkeitsbetrachtung vorhanden sind. Somit konnten im Anschluss daran verschiedene Szenarien bearbeitet werden. Das Ergebnis ist eine Gegenüberstellung der Erlöse zu den Kosten, wobei die Kosten um den Faktor 2,29 höher sind als die Erlöse. Auch bei den betrachteten Szenarien sind die Kosten jeweils höher als die Erlöse. Um eine Wirtschaftlichkeit erreichen zu können, müsste der Zinnpreis sehr stark ansteigen. Insgesamt sind die Ergebnisse kritisch zu beurteilen, da Annahmen das Ergebnis beeinflussen und die Aufbereitung auf einem Prozess von 1982 basiert.

Feasibility study to remediate the Tiefenbachhalde in Altenberg The Tiefenbachhalde Altenberg is a tailing of a former tin mine in the Erzgebirge. An extensive exploration conducted by researchers from HIF and TUBAF showed that the dump still contains about 8000 tons of valuable tin. However there are also about 4000 tons of arsenic, which could be an environmental hazard, if the tailing is treated improperly.
The idea is to remediate the dump and cover the costs by Re-mining of the tin. In this master thesis the economic feasibility of this concept is evaluated by a feasibility calculation.

Keywords: Wirtschaftlichkeitsprüfung; Haldensanierung; Re-mining; feasibility calculation; dump remediation; re-mining

  • Master thesis
    TU Bergakademie Freiberg, 2016
    Mentor: Prof. Dr. Michael Höck, Prof. Dr. Karl Gerald van den Boogaart
    0105 Seiten

Permalink: https://www.hzdr.de/publications/Publ-25003
Publ.-Id: 25003


3D-geologische Modellierung der Nb-Ta-P-(LREE-) Lagerstätte Epembe, Namibia

Unger, G.

Das aus den vorhandenen Daten erstellte Modell der Nb-Ta-P-(LREE)-Lagerstätte Epembe in Nordwest-Namibia, beinhaltet die Störungssysteme, sowie flexible 3D-Stratigraphische Grids (SGrids) der Sektoren B und K. Das Modell lässt Aussagen über die räumlichen Beziehungen zwischen Anreicherungszonen und Störungen im Untergrund zu. Die im Untersuchungsgebiet vorkommenden Lithologien wurden in Lithoeinheiten zusammengefasst und mit den geochemischen Daten verglichen. Dabei stellte sich heraus, dass die Anreicherungszonen der Elemente nicht mit den anstehenden Lithoeinheiten korrelieren. Des Weiteren ergaben sich lineare Zusammenhänge der Elemente U-Ta, U-Nb, Ta-Nb, HREE-LREE aus den geochemischen Daten der Bohrungen. Dies unterstreicht eine Intrusion von Magmen, die mit inkompatiblen Elementen angereichert waren. Die linearen Zusammenhänge der Elemente, spiegeln sich in den gleichen Anreicherungszonen der SGrids wieder. Die Korrelationen mit Uran werden im Modell nicht bestätigt, aufgrund der aufsummierten Darstellung der Gehalte von Uran, Thorium und Kalium. Eine weitere Ausnahme bilden die Anreicherungszonen von HREE-LREE im Sektor B. Da die Gehalte der schweren Seltenen Erden in den Anreicherungszonen der leichten Erden sehr gering sind. Diese Zonen wurden wahrscheinlich hydrothermal überprägt und es kam zur Auslaugung der HREE. Mit dem Modell konnte eine störungsgebundene Anreicherung von inkompatiblen Elementen (HFSE) nachgewiesen werden.
Mithilfe des Modells können Thesen der Genese der Lagerstätte aufgestellt werden:
1) Bei der Intrusion (vor 1215 MA) von gabbroiden, syenitischen Magmen in den Epupa Komplex, bildete sich der Karbonatit Dyke aus. Die Magmen waren vermutlich mit inkompatiblen Elementen angereichert.
2) Infolge der tektonischer Überprägung des Epembe Karbonatit Syenit Komplexes wurden diese Elemente wahrscheinlich durch hydrothermale Prozesse aus dem Umgebungsgestein gelaugt und kristallisierten dann entlang von Störungen aus. Dabei bildeten sich die modellierten Anreicherungszonen der Lagerstätte.
3) Die Auslaugung bildete Anreicherungszonen von Elementen, aber auch Zonen mit extrem geringen Elementgehalten (HREE). Da einige Elemente mobiler sind als andere.
4) Tektonische Strukturen spielten bei der Genese der Lagerstätte eine zentrale Rolle für Aufstiegs- und Platznahmemöglichkeiten von alkalischen oder karbonatischen Magmen und assoziierten REE-reichen Fluiden.
Die vorliegende Arbeit unterstreicht den Fakt, dass Seltene Erden Lagerstätten nicht ausschließlich durch magmatische Prozesse entstehen, sondern auch in Kombination mit hydrothermalen Prozessen. Des Weiteren wurde bewiesen das zur Genese von REE Lagerstätten, tektonische Strukturen eine entscheidende Rolle spielen.

  • Bachelor thesis
    Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institut Freiberg, 2015
    Mentor: Dr. Richard Gloaguen
    46 Seiten

Permalink: https://www.hzdr.de/publications/Publ-25002
Publ.-Id: 25002


Hyperspectral remote sensing for mineral mapping of structural related mineralizations around Mount Isa, Queensland, Australia

Jakob, S.

The present report demonstrates the possibilities and limitations of remote sens- ing, especially hyperspectral data, for mineral mapping purposes, using the example of the Mount Isa Inlier. This geological area is situated in Northern Queensland, Australia, and is known for its considerable ore deposits and consequent mining of predominantly copper, zinc, lead, silver and gold. Beside hyperspectral HyMap data, multispectral Landsat 8 and SRTM digital elevation data were analyzed. A three-week field study supported the investigations by data delivered from rock sampling and field spectral measurements. The observations were concentrated on four study areas and four main objectives: the location of orebodies near Mount Isa mine by mapping their altered outcrops, the targeting of critical elements at the Mary Kathleen U-REE deposit, the investigation of the dependency between the shear and fault-controlled vein-copper deposits of Mount Isa inlier and main deep-crustal faults and the testing of a fixed-wing drone for 3D-photogrammetry of geological features.
Throughout the study, mineral mapping using remote sensing data, especially hyperspectral data, turned out to deliver high qualitative results when it is supported by additional infor- mation. In situ investigation of the observed mineralizations for validation is important and can deliver such data, for instance by the investigation of rock samples or spectral measure- ments. Since mineralizations and alterations are often related to structures, their analysis and consideration can provide crucial hints. Without additional data it is very difficult up to impossible to create and interpret mineral mapping results accurately. The most significant result throughout the study was the determination of a new site of gossanous, silicified ridges south of the Mount Isa mining complex. They coincide with the outcrops of mineralized parts of the Urquhart Shale, which form the mined Pb-Zn-Ag deposits and are probably related to structures. Their occurrence was validated through fieldwork observations including rock sampling and spectral measurements. The gathered information additionally supported the mapping of those ridges using HyMap data, which confirmed the connection between the north-south trending ridges and the Mount Isa mine deposits.

  • Master thesis
    Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institut Freiberg, 2014
    Mentor: Dr. Richard Gloaguen
    75 Seiten

Permalink: https://www.hzdr.de/publications/Publ-25001
Publ.-Id: 25001


Hyperspectral remote sensing of carbonatite hosted REE-deposits in Namibia

Zimmermann, R.

In this thesis, two case-studies for exploration of carbonatite hosted REE-deposits in Namibia using hyperspectral remote sensing data are presented. REEs have enormous economic importance because they are the major constituents of high-tech electronic devices and are non-substitutable.
The two areas of interest in Namibia are Epembe/Kunene region and Lofdal/Bergville Farm close to Khorixas. Namibia is convenient because of less vegetation, a good data coverage, and a good geological knowledge.
Multi- and hyperspectral data of multiple source and scale in combination with tectonic geomorphology were used for data analysis. In a first step, spectral signatures and geomorphic indices were extracted, followed by expert classification made by a Decision Tree approach. The detailed processing chain is shown in figure 1.
Standard procedures for spectral unmixing (e.g. Spectral Feature Fitting, Matched Filtering) are well suited to map the abundances of carbonate minerals. However, calcretes, meta-sedimentary units, and amphibolites have similar spectral signatures in the SWIR range and are difficult to distinguish.
More advantageous approaches, like Self-Organizing maps and Decision Trees, were used to discriminate the carbonatite from surrounding rocks with similar signatures. The carbonatites are associated to specific textural, geomorphic and structural patterns. Incorporating these features into hyperspectral data analysis improve classification results and reduce misclassifications for carbonatite.

  • Master thesis
    Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institut Freiberg, 2014
    Mentor: Dr. Richard Gloaguen
    67 Seiten

Permalink: https://www.hzdr.de/publications/Publ-25000
Publ.-Id: 25000


Exploration mit Drohnen

Gloaguen, R.

Am Helmholtz-Institut Freiberg für Ressourcentechnologie entwickeln wir neue Methoden zur Erkundung mineralischer Rohstoffe mittels Drohnen. Unser Hexacopter transportiert beispielsweise eine hyperspektrale Kamera, die uns die Kartierung von Schlüsselmineralen erlaubt und so mögliche Lagerstätten identifizieren lässt. Einsätze in Namibia, Grönland und Spanien haben diese Erwartungen bestätigt.

  • Invited lecture (Conferences)
    Future Technologies - Innovationen aus den Technikwissenschaften, 26.01.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24999
Publ.-Id: 24999


Sorption of NpO2+ on montmorillonite: influence of ferrous iron

Marques, M. M.; Scheinost, A. C.; Baeyens, B.

The interaction of radionuclides with clay minerals, major constituents of the multi-barrier system of a radioactive waste repository (i.e. host rocks and backfill materials), is a key process in retarding their migration. It is very important to develop a fundamental understanding of the uptake processes of (radio-)contaminants onto clay minerals and to implement sorption models to reliably predict their fate in the near- and far-fields of radioactive waste repositories. 
Redox phenomena play an important role for radionuclide retention in the safety case. In the near-field, the corrosion of steel canisters will release large amounts of ferrous iron (FeII) and produce H2 with a strong influence on the redox potential (Eh). In the undisturbed bentonite it is anticipated that FeII concentrations in the porewater will lie typically between 10-5 and 10-4 M, controlled by the solubility of siderite, and Eh is predicted to be ~-200 mV [1]. The presence of high concentrations of FeII and reducing conditions in the interstitial porewater of bentonite can potentially influence the sorption behaviour of redox-sensitive nuclides. The mobility of elements such as U, Np and Tc highly depends on their oxidation state. In their most oxidized form +V, +VI (as oxocations NpO2+, UO2+2+) and +VII (as oxoanion TcO4-) these radionuclides are highly mobile, whereas their transport is strongly decreased when reduced to the oxidation state +IV.
With respect to reduction reactions of inorganic and organic compounds, FeII bound to oxide/clay minerals (surface mediated reduction) has been observed to be much more reactive than dissolved FeII [2-6]. Not only the kinetics of reaction is faster but also the redox potential of the clay/oxide associated FeII/FeIII redox couple is lower than this of dissolved iron. 

The aim of this study is to investigate the sorption of the long-lived neptunium (237Np, t1/2 = 2.14·106 a) on montmorillonite under reducing conditions mimicking “in situ” geochemical repository conditions. Most of sorption, modelling and spectroscopic studies on clay minerals so far have focused on the uptake of the mobile and very soluble NpO2+ under oxic and anoxic conditions. Sorption data for Np under reducing conditions or in the presence of FeII on clay minerals are sparse. 

The sorption of NpV on montmorillonite (Na-STx) was measured under electrochemically established reducing conditions in a bulk electrolysis cell composed of a three electrode system at a fixed redox potential in the absence and presence of varying ferrous iron concentrations (up to 44 mmol·kg-1). Fig. 1a shows the temporal evolution of the sorption of NpV in the absence and presence of ~44 mmol·kg-1 FeII at pH 7.8 and Eh -291 mV (vs SHE). If no Fe is added the sorption of Np remained nearly constant and no noticeable increase of sorption compared to anoxic conditions could be observed. In the presence of Fe, the sorption of Np steadily increased up to log Rd ~ 3.8 L/kg, suggesting the reduction of NpV at the clay surface. 

Evidence for the oxidation state and type of surface complex formed was obtained from extended X-ray absorption fine structure (EXAFS) spectroscopy (Fig. 1b). The derived structural parameters confirm that under the above mentioned experimental conditions, Np sorbed on montmorillonite is fully reduced to NpIV and is strongly associated to surface bound Fe. 
The results of this study (i.e. influence of different FeII concentrations, nature of surface complex) will be presented at the conference.

Figs. 1: Sorption of NpO2+ on Na-STx under anoxic conditions and under reducing conditions (-291 mV) in the absence and presence of FeII. a) Temporal evolution and b) Fourier Transforms of the Np-LIII edge EXAFS spectra of Np adsorbed to Na-STx.

References:
1. Nagra (2014). Montmorillonite stability under near-field conditions. Nagra Technical Report NTB 14-12, Nagra, Wettingen, Switzerland.
2. Charlet, L., Liger, E. and Gerasimo, P. (1998). Decontamination of TCE- and U-rich waters by granular iron: role of sorbed Fe(II). Journal of Environmental Engineering, 124: 25–30.
3. Charlet, L., Scheinost, A. C., Tournassat, C., Grenèche, J. M., Géhin, A., Fernandez-Martinez, A., Coudert, S., Tisserand, D. and Brendlé, J. (2007). Electron transfer at the mineral/water interface: Selenium reduction by ferrous iron sorbed on clay. Geochimica et Cosmochimica Acta, 71: 5731–5749.
4. Felmy, A. R., Ilton, E. S., Rosso, K. M. and Zachara, J. M. (2011). Interfacial reactivity of radionuclides: emerging paradigms from molecular-level observations. Mineralogical Magazine, 75: 2379–2391.
5. Hofstetter, T. B., Neumann, A and Schwarzenbach, R.P. (2006). Reduction of nitroaromatic compounds by Fe(II) species associated with iron-rich smectites. Environmental Science and Technology, 40: 235–242.
6. Liger, E, Charlet, L. and Van Cappellen, P. (1999). Surface catalysis of uranium(VI) reduction by iron(II). Geochimica Cosmochimica Acta, 63: 2939–2955.

Keywords: clay; montmorillonite; nuclear radioactive waste; EXAFS; Neptunium; Redox

  • Lecture (Conference)
    7th International Conference on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, 24.-27.09.2017, Davos, Switzerland
  • Lecture (Conference)
    Goldschmidt 2017, 13.-18.08.2017, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-24998
Publ.-Id: 24998


Novel Nanoelectronic Devices and Technologies for Their Fabrication

Georgiev, Y.

The traditional scaling of microelectronic devices was over in 2003 (130 nm node). New “performance boosters” are being used since then: (i) strained silicon (Si) since 2004 (90 nm node), (ii) high-k gate dielectrics + metal gates (HKMG) instead of SiO2 + poly-Si gates since 2008 (45 nm node) and (iii) non-planar 3D (tri-gate) transistor architecture since 2012 (22 nm node). Further improvements are expected by the implementation of (i) new device architectures, (ii) high-mobility channel materials such as silicon-germanium (SiGe), Ge, III-Vs, carbon nanotubes (CNTs), graphene and/or other 2D materials, etc., (iii) new (non-digital) functionalities (e.g. sensing), usually referred to as “More than Moore”, and (iv) new computational principals such as spintronics, quantum computing, etc.

In this talk I will present three novel nanoelectronics devices that have been proposed and demonstrated for the first time in the last 5-6 years: (i) junctionless nanowire transistors (JNTs) [1], (ii) 3D vertically stacked nanowire field effect transistors (VSNFETs) [2] and (iii) reconfigurable field effect transistors (RFETs) [3]. These devices embody to some extent the first three of the above-mentioned future “performance boosters”: (i) they have advanced transistor architecture, (ii) JNTs have been fabricated not only in Si but also in Ge as a high-mobility channel material and (iii) JNTs and VSNFETs have been implemented as chemical and biosensors demonstrating excellent sensing performance.
I will briefly discuss the specifics in the functioning of those devices, outlining their advantages and disadvantages. I will then consider the technologies for their fabrication and the challenges that they are facing. Finally, I will present examples of the devices fabricated for some particular applications, showing results of their structural and electrical characterisation. In the case of JNTs and VSNFETs I will focus mostly on their application as chemo/biosensors [4-8]. Additionally, I will also show the first Ge-based JNTs [9]. In the case of RFETs I will present the recent results of top-down fabrication and characterisation of such devices on silicon-on-insulator (SOI) wafers.

[1] J.P. Colinge, C.-W. Lee, A. Afzalian, N.D. Akhavan, R. Yan, I. Ferain, P. Razavi, B. O’Neill, A. Blake, M. White, A.-M. Kelleher, B. McCarthy and R. Murphy, Nanowire transistors without junctions. Nat. Nanotechnol. 5 (2010) 225.
[2] E. Buitrago, M. Fernández-Bolaños, A.M. Ionescu, Vertically stacked Si nano-structures for biosensing applications, Microelectron. Eng. 97 (2012) 345–348.
[3] A. Heinzig, T. Mikolajick, J. Trommer, D. Grimm and W. M. Weber, Nano Lett. 13 (2013) 4176-4181.
[4] Y. M. Georgiev, N. Petkov, B. McCarthy, R. Yu, V. Djara, D. O'Connell, O. Lotty, A. M. Nightingale, N. Thamsumet, J. C. deMello, A. Blake, S. Das, J. D. Holmes. Fully CMOS-compatible top-down fabrication of sub-50 nm silicon nanowire sensing devices. Microelectron. Eng. 118 (2014) pp. 47-53.
[5] Y. M. Georgiev, R. Yu, N. Petkov, O. Lotty, A. M. Nightingale, J. C. deMello, R. Duffy, J. D. Holmes. Silicon and Germanium Junctionless Nanowire Transistors for Sensing and Digital Electronics Applications. In "Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting.", A. Nazarov, F. Balestra, V. Kilchytska, D. Flandre eds. Springer International Publishing AG, Cham, Switzerland, 2014, pp. 367-388.
[6] E. Buitrago, G. Fagas, M. Fernández-Bolanos Badia, Y.M. Georgiev, M. Berthomé, A.M. Ionescu. Junctionless silicon nanowire transistors for the tunable operation of a highly sensitive, low power sensor. Sens. Actuators B 183 (2013) 1– 10.
[7] E. Buitrago, M. Fernández-Bolaños, Y. M. Georgiev, R. Yu, O. Lotty, J. D. Holmes, A. M. Nightingale, H. M. Guerin, A. M. Ionescu. Electrical Characterization of High Performance, Liquid Gated Vertically Stacked SiNW-Based 3D FET for Biosensing Applications. Sens. Actuators B 199 (2014) pp. 291-300.

  • Invited lecture (Conferences)
    IEEE 25th International Scientific Conference Electronics - ET2016, 12.-14.09.2016, Sozopol, Bulgaria

Permalink: https://www.hzdr.de/publications/Publ-24997
Publ.-Id: 24997


High Resolution Nanofabrication

Georgiev, Y.

The aim of nanofabrication is to create structures and devices with minimum dimensions lower than 100 nm. There are two main nanofabrication approaches, bottom-up and top-down. In the former, the structures and devices are created from small to large in an additive fashion, which relies to a great extent on self-organisation processes. In the latter, the fabrication goes from large to small where nanostructures and devices are carved from a larger piece of material in a subtractive fashion. It is much more mature than the bottom-up approach and is based on two long-established processes: (i) nanolithography, where a stencil with the required pattern is created in a sacrificial layer called “resist”, deposited on the main working material, and (ii) pattern transfer through the resist stencil into the base material.

In the present paper we will present results on high-resolution nanofabrication of structures and devices with critical dimensions (CD) below 10 nm on silicon (Si), silicon-on-insulator (SOI), germanium (Ge) and germanium-on-insulator (GeOI) substrates. The fabrication was mainly within the frames of the top-down approach and was based on electron beam lithography (EBL) with positive and negative resists followed by a pattern transfer with both additive (metal deposition and lift-off) and subtractive (dry etching) methods. Moreover, high-end results on combination of bottom-up and top-down approaches will also be presented such as (i) contacting of bottom-up grown and randomly distributed nanostructures and fabrication of devices out of them as well as (ii) pattern density multiplication by directed self assembly (DSA) of block-copolymers (BCP). We believe that these results are showing some of the promising trends for future development of high-resolution nanofabrication.

  • Lecture (Conference)
    12th International Conference "Electron Beam Technologies" (EBT 2016), 13.-18.06.2016, Varna, Bulgaria

Permalink: https://www.hzdr.de/publications/Publ-24996
Publ.-Id: 24996


Top-down fabrication of silicon nanowires

Georgiev, Y.

Results on top-down fabrication of silicon (Si) nanowires (Ws) towards junctionless nanowire transistors, Si NW-based biosensors and reconfigurable field effect transistors have been presented at the SENTECH "Plasma Process Technology” seminar.

  • Invited lecture (Conferences)
    SENTECH "Plasma Process Technology” seminar, 07.04.2016, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24995
Publ.-Id: 24995


A new precision measurement of the α-decay half-life of 190Pt

Braun, M.; Georgiev, Y.; Schönherr, T.; Wilsenach, H.; Zuber, K.

A laboratory measurement of the alpha-decay half-life of 190Pt has been performed using a low background Frisch grid ionisation chamber. A total amount of 216.60(17) mg of natural platinum has been measured for 75.9 days. The resulting half-life is (4.97+-0.16)x10e11 years, with a total uncertainty of 3.2%. This number is in good agreements with the half-life obtained using the geological comparison method.

Permalink: https://www.hzdr.de/publications/Publ-24994
Publ.-Id: 24994


Ultrahigh Sensitivity Chemical and Biological Sensors Based on Silicon Junctionless Nanowire Transistors

Georgiev, Y.; Yu, R.; Buitrago, E.; Nightingale, A. M.; Lotty, O.; Petkov, N.; Holmes, J. D.

Junctionless nanowire transistors (JNTs) are very promising as chemo- biosensors due to their simple structure, easy fabrication and potential for ultrahigh sensitivity. Therefore, JNT sensors with various numbers, lengths, and widths (down to 10 nm) of the nanowires were fabricated by a top-down process on positively doped SOI wafers. The nanowires were functionalised either with 3-aminopropyltriethoxysilane (APTES) or with APTES and biotin. Polydimethylsiloxane (PDMS) stamps with microfluidic channels were then attached to the chip surface and buffer solutions containing different analytes were flowed over the sensors by a syringe pump. In this way, series of experiments for sensing ionic strength, pH value, and the protein streptavidin were performed. The JNT sensors demonstrated the highest sensitivity reported to date towards streptavidin, corresponding to a detection of only few protein molecules.

  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensbur, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24993
Publ.-Id: 24993


Setup for tumor growth delay studies in small animals for low energy x-rays and small irradiation fields

Hunger, A.; Burger, K.; Stein, M.; Dierolf, M.; Günther, B.; Porth, A.-K.; Bartzsch, S.; Urban, T.; Achterhold, K.; Gleich, B.; Beyreuther, E.; Pfeiffer, F.; Combs, S.; Wilkens, J. J.; Schmid, T. E.

Introduction: The tumor growth delay assay is a well-accepted technique in experimental animal tumor models for the measurement of the response to treatments. Tumor growth delay assays were mostly performed with subcutaneous xenograft tumors in the hind leg of small animals. However, some radiation qualities with low energy and/or very small irradiation fields cannot use this method.
This study was performed to test a new irradiation setup at the Small Animal Radiation Research Platform (SARRP, Xtrahl Ltd.) which can be especially used to irradiate very small tumors with low energy X-rays.

Methods: This study was performed with a human head and neck cancer cell line (FaDu). 100 000 FaDu cells were suspended in Matrigel® and subcutaneously injected at the right ear of immunocompromised NMRI nu/nu mice. Tumors with a size of 2x2 mm2 were irradiated with 3 Gy and 6 Gy operating the SARRP at 70 kVp X-rays. Tumor growth was determined over a follow-up of 20 days with a caliper. The tumor growth delay was compared between homogeneously and non-irradiated mice. 20 days after irradiation tumor cells were transferred in cell culture.

Results: In this pilot study using 70 kVp X-rays, six tumor-bearing mice were irradiated with either 3 or 6 Gy. Three tumor-bearing mice served as a control. The tumor volume doubling time of unirradiated tumors was 2.75 ± 0.4 days. Out of three, one mouse showed an obvious tumor growth delay at 3 Gy. However, all tumors irradiated with 6 Gy were controlled. The tumor cells which were transferred into cell culture medium showed normal growth characteristics.

Conclusion and Outlook: We successfully implemented a xenograft tumor system in mouse ears and irradiations of 2x2 mm2 tumors at the SARRP. The mouse ear tumor model allows an accurate and simple method to determine the tumor volume. In future, this tumor-bearing mouse ear model will enable irradiations which are limited due to small irradiation fields and/or low X-ray energies. Moreover, it is possible to isolate tumor cells out of the mouse ear for future in-vitro analysis. This new method could be used at the first brilliant and compact synchrotron X-ray source (Munich Compact Light Source) where the dose can be deposited by spatially fractionated X-ray beamlets like microbeam radiation therapy (MRT).

Acknowledgements: This work was supported by the DFG-Cluster of Excellence ‘‘Munich-Centre for Advanced Photonics’’.

  • Abstract in refereed journal
    Strahlentherapie und Onkologie 193(2017), S54
  • Contribution to proceedings
    ERRS & GBS 2017, 17.-21.09.2017, Essen, Germany

Permalink: https://www.hzdr.de/publications/Publ-24992
Publ.-Id: 24992


Sites of recurrent disease and prognostic factors in SCLC patients treated with radiochemotherapy

Bütof, R.; Gumina, C.; Valentini, C.; Sommerer, A.; Appold, S.; Zips, D.; Löck, S.; Baumann, M.; Troost, E. G. C.

Introduction: Concurrent radiochemotherapy (RCHT) is standard treatment in locally advanced small cell lung cancer (SCLC) patients. Due to conflicting results on elective nodal irradiation (ENI) or selective node irradiation (SNI) there is no clear evidence on optimal target volumes. Therefore, the purposes of this study were to assess the sites of recurrent disease in SCLC and to evaluate the feasibility of SNI versus ENI.

Methods: A retrospective single-institution study of 54 consecutive patients treated with RCHT was performed. After state-of-the-art staging, all patients underwent three-dimensional conformal radiotherapy to a total dose of 45 Gy in twice-daily fractions of 1.5 Gy starting concurrently with the first or second chemotherapy cycle. All sites of loco-regional recurrences were correlated to the initial tumor and dose delivered. The impact of potential prognostic variables on outcome was evaluated using the Cox-regression model.

Results: After a median time of 11.1 months, 17 patients (31.5%) relapsed locally or regionally: six within the initial primary tumor volume, five within the initially affected lymph nodes, three metachronously within primary tumor and initially affected lymph nodes, and three both inside and outside of the initial nodal disease. All sites of loco-regional recurrence had received 92%-106% of the prescribed dose. Among all investigated co-factors only total GTV revealed a significant correlation with patient outcome.

Conclusion: In our study most recurrences occurred within the primary tumor or initially affected lymph nodes, or distantly. We did not register any case of isolated nodal failure, supporting the use of selective nodal irradiation, possibly with the addition of supraclavicular irradiation in patients with nodal disease in the upper mediastinum.

Keywords: SCLC; radiochemotherapy; site of relapse

Permalink: https://www.hzdr.de/publications/Publ-24991
Publ.-Id: 24991


Tunneling Magnetoresistance with Zero-moment Half-metallic electrodes

Borisov, K.; Betto, D.; Lau, Y. C.; Fowley, C.; Titova, A.; Thiyagarajah, N.; Atcheson, G.; Lindner, J.; Deac, A. M.; Coey, M.; Stamenov, P.; Rode, K.

In recent years, great attention has been paid to the research of intermetallic Heusler compounds. These materials have widely tuneable properties. They display high spin polarisation , low magnetic moment , low Gilbert damping α and high effective magnetic anisotropy field. All of the above-mentioned characteristics play key role at the choice of materials for integration in spin-transfer-torque oscillators. Here we have successfully integrated a compensated half-metallic ferrimagnet as a fixed layer in magnetic tunnel junctions (MTJ). Theoretically this class of materials was predicted in 1995 by van Leuken and de Groot, but experimentally the zero-moment half-metal was realised only in 2014 for a near-cubic Heusler alloy of Mn, Ru and Ga (MRG). Here, MTJs with different insertion layers between MRG and the tunnel barrier were studied. Sufficient tunnelling magnetoresistance (TMR) ratios were demonstrated for Mn2RuGa / Al 0.6 nm / MgO / CoFeB MTJs. We measured the switching properties of MTJ as a function of applied bias voltage and ex-situ annealing temperature. At low bias (U ≈ 10mV), the as-grown sample shows TMR ratio ≈ 1.6% at room-temperature, annealing at 375°C leads to increasing of TMR to ≈ 7.5%. At higher negative bias (U ≈ - 0.5 V), the TMR varies from -2.9 to -6.3%, for the as-grown sample and the sample annealed at 375°C, respectively. Low temperature measurements on the same device show in excess of 40% TMR close to zero bias. Moreover, we demonstrate non-zero TMR while cooling through the compensation temperature (when the magnetic moment is zero). Finally, by changing the electrode composition from Mn2Ru0.65 Ga through to Mn2Ru1.1Ga we also demonstrate finite TMR at ambient temperature with an electrode designed to be compensated at room temperature.

Keywords: Magnetic Tunnel Junctions; Heusler Alloy; Ferrimagnetism; Half-metal

  • Lecture (Conference)
    61st Annual Conference on Magnetism and Magnetic Materials, 31.10.-04.11.2016, New Orleans, Louisiana, United States of America

Permalink: https://www.hzdr.de/publications/Publ-24990
Publ.-Id: 24990


Highly ordered 3D nanoparticle superlattices investigated by microresonator ferromagnetic resonance

Josten, E.; Narkowicz, R.; Kakay, A.; Meertens, D.; Banholzer, A.; Bergström, L.; Suter, D.; Brückel, T.; Lenz, K.; Fassbender, J.; Lindner, J.

Magnetic nanoparticles and their assembly into highly correlated superstructures are of great interest for future applications, e.g. as material for magnon-spintronic. These systems are not only distinguished by the obvious miniaturization but by their novel physical properties emerging due to their limited size and ordered arrangement. These superstructures are formed from nanometer-sized building blocks ordered like atoms in a crystal, which render them a new class of materials.

Recently, single micrometer-sized three-dimensional magnetic nanoparticle assemblies (so-called mesocrystal) became available, exhibiting a high degree of structural order close to that of an atomic crystal. These systems provide a good basis for the magnetic investigation of nanoparticle superstructures.

Novel Microresonators, provide the necessary sensitivity for the investigation of static and dynamic magnetic properties of nano- and micrometer-sized objects using ferromagnetic resonance (FMR) [1,2]. Due to the much higher filling factor as compared to conventional microwave cavities, they offer several orders of magnitude increased sensitivity gain. A focused ion beam (FIB) was used to isolate an individual 3D mesocrystal from an ensemble [3] and to transfer it into the microresonator loop (see Fig. 1). The FMR study reveals the magnetic anisotropy of the single mesocrystal, which is corroborated by micromagnetic simulations. It was possible for us to functionalize the system and to switch between two anisotropy components.

[1] A. Banholzer, R. Narkowicz, C. Hassel, R. Meckenstock, S. Stienen, O. Posth, D. Suter, M. Farle, and J. Lindner, Nanotechnology 22, 295713 (2011)
[2] C. Schoeppner, K. Wagner, S. Stienen, R. Meckenstock, M. Farle, R. Narkowicz, D. Suter, and J. Lindner J. Appl. Phys. 116, 033913 (2014)
[3] S. Disch, E. Wetterskog, R.P. Hermann, G. Salazar-Alvarez, P. Busch, T. Brückel, L. Bergström and S. Kamali, Nano Lett., 10, 799 (2010)

Keywords: magnetic nanoparticles; self-assembly; mesocrystals; microresonator; FMR

  • Poster
    MML 2016 - 9th International Symposium on Metallic Multilayers, 19.-23.06.2016, Uppsala, Sweden
  • Poster
    MML workshop, 14.-16.12.2016, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24989
Publ.-Id: 24989


Modelling of liquid metal stirring induced by four counter-rotating permanent magnets

Dzelme, V.; Scepanskis, M.; Geza, V.; Jakovics, A.; Sarma, M.

In this work, the stirring of liquid gallium in a rectangular crucible induced by four counter-rotating permanent magnets is investigated numerically. The mean velocity and turbulence kinetic energy for different distances of the magnets from the vessel with liquid metal and the magnet rotation rate are investigated. The flow is modeled using two turbulence models - detached eddy simulation and k-ω shear stress transport - and compared with experimental results obtained using the dynamic neutron radiography method. Numerical results show qualitative agreement with experiment. The simulation results evidence that the applied turbulence models predict the velocity and the turbulence kinetic energy equally well. It is also shown that in this system the characteristic turbulence kinetic energy is proportional to the square of the characteristic velocity magnitude.

  • Open Access Logo Magnetohydrodynamics 52(2016)4, 461-470

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Permalink: https://www.hzdr.de/publications/Publ-24988
Publ.-Id: 24988


Coordination of Tetravalent Actinides (An=Th-IV, U-IV, Np-IV, Pu-IV) with DOTA: From Dimers to Hexamers

Tamain, C.; Dumas, T.; Hennig, C.; Guilbaud, P.

Three tetravalent actinide (An(IV)) hexanuclear clusters with the octahedral core [An6(OH)4O4]12+ and (An(IV) = U(IV), Np(IV), Pu(IV)) were structurally characterized in solid state and in aqueous solution using single crystal X-ray diffraction, X-ray absorption, IR, Raman and UV-Visible spectroscopy. The observed structure, [An6(OH)4O4(H2O)8(HDOTA)4].HNO3.nH2O (An = U (I), Np (II), Pu (III)), consists of a An(IV) hexanuclear pseudo- octahedral cluster stabilized by (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) (DOTA) ligands. The six actinide atoms are connected through alternative µ3-O2- and µ3-OH- groups. EXAFS investigations combined with UV-vis spectroscopy evidence the same local structure in moderate acidic and neutral aqueous solutions. The synthesis mechanism was partially elucidated and the main physical chemical properties (pH range stability, solubility and protonation constant) of the cluster were determined. The results underline the importance (i) to consider such polynuclear species in thermodynamic models and (ii) importance of competing reactions between hydrolysis and complexation. It is interesting to note that the same synthesis route with thorium(IV) leads to the formation of a dimer, Th2(H2O)10(H2DOTA)2.4NO3.xH2O (IV), which in contrast to the structure of the other An(IV) hexamers.

Keywords: Pu(IV); Np(VI); U(IV); DOTA; EXAFS; XRD; UV-Vis

Permalink: https://www.hzdr.de/publications/Publ-24987
Publ.-Id: 24987


New Generation Electron Beam Resists: A Review

Gangnaik, A. S.; Georgiev, Y.; Holmes, J. D.

Semiconductor industry has already entered sub-10 nm region, which has led to the development of cutting-edge fabrication tools. However, there are other factors that hinder the best outcome of these tools, such as the substrate and resist materials, pre- and post-fabrication processes, etc. Amongst the most lithography techniques, electron beam lithography (EBL) is the prime choice when a job requires dimensions lower than 10-20 nm, since it can easily achieve such critical dimensions in reasonable time and effort. When obtaining pattern features in single nanometer regime, the resist material properties play an important role in determining the size.
With this agenda in mind, many resists have been developed over the years suitable for attaining required resolution in lesser EBL writing time. This review article addresses the recent advancements made in EBL resists technology. It first describes the different lithography process briefly and then progresses on to parameters affecting the EBL fabrications processes. EBL resists are then bifurcated into their “family types” depending on their chemical composition. Each family describes one or two examples of the new resists; and their chemical formulation, contrast-sensitivity values and their highest resolution are described. The review finally gives an account of various alternate next-generation lithography techniques, promising dimensions in the nanometer range.

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Permalink: https://www.hzdr.de/publications/Publ-24986
Publ.-Id: 24986


Lift force acting on single bubbles in linear shear flows

Aoyama, S.; Hayashi, K.; Hosokawa, S.; Lucas, D.; Tomiyama, A.

Lift coefficients, CL, of single bubbles in linear shear flows are measured to investigate effects of the bubble shape, the liquid velocity gradient and the fluid property on CL. The range of the Morton number, M, tested are from logM = −6.6 to −3.2. The shapes of bubbles are spherical and ellipsoidal. A correlation of bubble aspect ratio for single bubbles in infinite stagnant liquids proposed in our previous study can give good evaluations for bubbles in the linear shear flows. The CL of spherical bubbles at low bubble Reynolds numbers, Re, depend on the dimensionless shear rate Sr and Re and decrease with increasing Re. These characteristics agree with the Legendre-Magnaudet correlation. The use of a single dimensionless group such as Re, the Eötvös number, the Weber number and the Capillary number cannot correlate CL of non-spherical bubbles. The trend of the critical Re for the reversal of the sign of CL is the same as that for the onset of oscillation of bubble motion, which supports the mechanism proposed by Adoua et al., at least within the range of -6.6 < logM < -3.2. An experimental database of CL is provided for validation of available CL models and CFD.

Keywords: Lift coefficient; Shear rate; Critical Reynolds number; Bubble shape

Permalink: https://www.hzdr.de/publications/Publ-24985
Publ.-Id: 24985


Novel germanium surface modification for sub-10 nm patterning with electron beam lithography and hydrogen silsesquioxane resist

Gangnaik, A.; Georgiev, Y.; Collins, G.; Holmes, J. D.

Germanium is a promising high-mobility channel material for future nanoelectronic devices.
Hydrogen silsesquioxane (HSQ) is a well known high-resolution electron beam lithography (EBL) resist, which is usually developed in aqueous based developers. However, this feature of HSQ causes troubles while patterning Ge surface as it is always shielded with native Ge oxides. GeO2 is a water soluble oxide, and since HSQ resist is developed in aqueous solvents, this oxide interferes with the patterning. After the EBL exposure, GeO2 is washed off during the development, lifting the patterned structures and making the high-resolution patterning impossible. To avoid this issue, it is necessary to either clean and passivate the Ge surface or use buffer layers between the native Ge oxides and the HSQ layer. In this article, a novel technique to clean the Ge surface prior to HSQ deposition, using simple “household” acids like citric acid and acetic acid, is reported. The acids are able to remove the native Ge oxides as well as efficiently passivate the surface. The acid passivation was found to hold the HSQ sturdily to the Ge surface, even during development with the aqueous salty solvent.
Using this process, Ge nanowires having widths down to 5 nm were successfully patterned on germanium-on-insulator substrates. To the best of our knowledge, these are the smallest top-down fabricated Ge nanostructures reported till date.

Keywords: electron beam lithography; sub-10 nm resolution; acid treatment; germanium; HSQ resist

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Permalink: https://www.hzdr.de/publications/Publ-24984
Publ.-Id: 24984


Dispersion of nanoparticles in steel melt by superimposed steady and alternating magnetic fields

Sarma, M.; Miran, S.; Grants, I.; Gerbeth, G.

A strong axial magnetic field is applied during the induction-melting of stainless steel samples with the purpose of dispersing ceramic nano-particles in the melt by acoustic cavitation. The cross product of the axial magnetic field with the high frequency azimuthal induction currents creates an oscillating radial body force that supports an oscillating pressure field (power ultrasound). Acoustic evidence of cavitation onset has been observed. The samples have been inspected by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). It is found that most of the particles have been pushed out of the bulk. Individual inclusions containing intact initial particles are observed. It is assumed that a too high number of large bubbles stemming from excessive porosity of the initial metal-particle mixture have pushed the particles out of the metal.

Keywords: Ultrasound Cavitation; Particle Dispersion; Steel

  • Contribution to proceedings
    International Conference on Heating by Electromagnetic Sources, 24.-27.05.2016, Padova, Italy
    Proceedings of the International Conference on Heating by Electromagnetic Sources

Permalink: https://www.hzdr.de/publications/Publ-24982
Publ.-Id: 24982


Complex patterns and elementary structures of solutal Marangoni convection: experimental and numerical studies

Eckert, K.; Boeck, T.; Koellner, T.; Schwarzenberger, K.

The transfer of a solute between two liquid layers is susceptible to convective instabilities of the time-dependent diffusive concentration profile that may be caused by the Marangoni effect or buoyancy. Marangoni instabilities depend on the change of interfacial tension and Rayleigh instabilities on the change of liquid densities with solute concentration. Such flows develop increasingly complex cellular or wavy patterns with very fine structures in the concentration field due to the low solute diffusivity. They are important in several applications such as extraction or coating processes. A detailed understanding of the patterns is lacking although a general phenomenological classification has been developed based on previous experiments. We use both highly resolved numerical simulations and controlled experiments to examine two exemplary systems. In the first case, a stationary Marangoni instability is counteracted by a stable density stratification producing a chaotic but hierarchical cellular pattern. In the second case, Rayleigh instability is opposed by the Marangoni effect causing solutal plumes and eruptive events with short-lived Marangoni cells on the interface. A good qualitative and acceptable quantitative agreement between the experimental visualizations and measurements and the corresponding numerical results is achieved in simulations with a planar interface, and a simple linear model for the interface properties, i.e. no highly specific properties of the interface are required for the complex patterns.
Simulation results are also used to characterize the mechanisms involved in the pattern formation.

Keywords: Marangoni instability; Rayleigh instability; direct numerical simulation; relaxation oscillations

  • Book chapter
    D. Bothe, A. Reusken: Advances in Mathematical Fluid Mechanics, Berlin: Springer/Birkhäuser, 2017, 445-488
    DOI: 10.1007/978-3-319-56602-3_16

Permalink: https://www.hzdr.de/publications/Publ-24981
Publ.-Id: 24981


Structural and optical properties of vanadium ion-implanted GaN

Macková, A.; Malinský, P.; Jagerová, A.; Sofer, Z.; Klímová, K.; Sedmidubský, D.; Mikulics, M.; Lorinčík, J.; Veselá, D.; Böttger, R.; Akhmadaliev, S.

The field of advanced electronic and optical devices searches for a new generation of transistors and lasers. The practical development of these novel devices depends on the availability of materials with the appropriate magnetic and optical properties, which is strongly connected to the internal morphology and the structural properties of the prepared doped structures. In this contribution, we present the characterisation of V ion-doped GaN epitaxial layers. GaN layers, oriented along the (0 0 0 1) crystallographic direction, grown by low-pressure metal-organic vapour-phase epitaxy (MOVPE) on c-plane sapphire substrates were implanted with 400 keV V+ ions at fluences of 5 × 1015 and 5 × 1016 cm−2. Elemental depth profiling was accomplished by Rutherford Backscattering Spectrometry (RBS) and Secondary Ion Mass Spectrometry (SIMS) to obtain precise information about the dopant distribution. Structural investigations are needed to understand the influence of defect distribution on the crystal-matrix recovery and the desired structural and optical properties. The structural properties of the ion-implanted layers were characterised by RBS-channelling and Raman spectroscopy to get a comprehensive insight into the structural modification of implanted GaN and to study the influence of subsequent annealing on the crystalline matrix reconstruction. Photoluminescence measurement was carried out to check the optical properties of the prepared structures.

Keywords: GaN implantation; RBS-channelling; Optical properties of metal-implanted GaN

Permalink: https://www.hzdr.de/publications/Publ-24979
Publ.-Id: 24979


Distribution and kinetics of the Kv1.3-blocking peptide HsTX1[R14A] in experimental rats

Bergmann, R.; Kubeil, M.; Zarschler, K.; Chhabra, S.; Tajhya, R. B.; Beeton, C.; Pennington, M. W.; Bachmann, M.; Norton, R. S.; Stephan, H.

The peptide HsTX1[R14A] is a potent and selective blocker of the voltage-gated potassium channel Kv1.3, which is a highly promising target for the treatment of autoimmune diseases and other conditions. In order to assess the biodistribution of this peptide it was conjugated with NOTA and radiolabelled with copper-64. [64Cu]Cu-NOTA-HsTX1[R14A] was synthesised in high radiochemical purity and yield. The radiotracer was evaluated in vitro and in vivo. The biodistribution and PET studies after intravenous and subcutaneous injections showed similar patterns and kinetics. The hydrophilic peptide was rapidly distributed, showed low accumulation in most of the organs and tissues, and demonstrated high molecular stability in vitro and in vivo. The most prominent accumulation occurred in the epiphyseal plates of trabecular bones. The high stability and bioavailability, low normal-tissue uptake of [64Cu]Cu-NOTA-HsTX1[R14A], and accumulation in regions of up-regulated Kv channels both in vitro and in vivo demonstrate that HsTX1[R14A] represents a valuable lead for conditions treatable by blockade of the voltage-gated potassium channel Kv1.3. The pharmacokinetics show that both intravenous and subcutaneous applications are viable routes for the delivery of this potent peptide.

Keywords: scorpion toxin; peptide; positron emission tomography; labelling; distribution; lifetime; autoimmune disease; potassium channel; small animal

Permalink: https://www.hzdr.de/publications/Publ-24977
Publ.-Id: 24977


Assessment of Electromagnetic Stirrer Agitated Liquid Metal Flows by Dynamic Neutron Radiography

Scepanskis, M.; Sarma, M.; Vontobel, P.; Trtik, P.; Thomsen, K.; Jakovics, A.; Beinerts, T.

This paper presents qualitative and quantitative characterization of two-phase liquid metal flows agitated by the stirrer on rotating permanent magnets. The stirrer was designed to fulfill various eddy flows, which may have different rates of solid particle entrapment from the liquid surface and their homogenization. The flow was characterized by visualization of the tailored tracer particles by means of dynamic neutron radiography, an experimental method well suited for liquid metal flows due to low opacity of some metals for neutrons. The rather high temporal resolution of the image acquisition (32 Hz image acquisition rate) allows for the quantitative investigation of the flows up to 30 cm/s using neutron particle image velocimetry. In situ visualization of the two-phase liquid metal flow is also demonstrated.

Keywords: Neutron imaging; Dynamic Neutron Radiography; Liquid Metal Flows

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Permalink: https://www.hzdr.de/publications/Publ-24976
Publ.-Id: 24976


Micro reactor experiments on the partial isobutane oxidation at supercritical conditions.

Willms, T.; Kryk, H.; Hampel, U.

Tertiary butyl hydroperoxide (TBHP), as an intermediate for the production of propylene oxide according to the Oxirane process, is currently produced at industrial scale by the partial oxidation of liquid isobutane using bubble columns or bubble tray reactors. In this process, liquid isobutane reacts with oxygen under two phase conditions at temperatures of 120 to 140 °C and pressures of 25 to 37 bars at high residence times of up to 12 hours. The conversion is limited to 35 to 50 % in order to obtain a TBHP selectivity of 50 to 60 % minimizing the formation of by-products, which are caused by the decomposition of the TBHP due to the complex reaction mechanism. Besides safety aspects, the high reaction enthalpy of the oxidation as well as heat and mass transport problems are further issues of this process. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“, this reaction is investigated for the first time at supercritical conditions in a broad range of flow rates, temperatures and pressures in a micro reactor with the aim to enhance the space-time yield of the process. The advantage of micro reactors are the high surface – volume ratio for an efficient heat transfer, the related, improved – nearly inherent – safety and the resulting possibility to investigate yet unexplored process windows for instance within the explosive region of a reaction mixture. A number of levers for the process intensification have been identified (e.g. initiator type, oxygen concentration, additives and high pressures). Supercritical conditions i.e. pressures above 40 bars and temperatures above 140°C are especially interesting because of the higher reaction rate and lacking mass transfer limitations. In addition to the parameter ranges studied in the past, e.g. oxygen concen¬trations (50 to 100%) and high pressures of up to 100 bars have been applied. Furthermore, the influence of process parameters on the start-up time is investigated. For all experiments, the selectivity and conversion of the reaction have been studied. Therefor, the reaction course is followed by sampling and analyzing the reaction by GC/MS and GC–TCD where analytical methods have been developed to detect a maximum of by-products and intermediates. The results of the first supercri-tical experiments are given and discussed with respect to the reaction characteristics.

Keywords: isobutane Oxidation; tertiary butyl hydroperoxide; supercritical conditions; microreactor

  • Poster
    Jahrestreffen Reaktionstechnik zusammen mit der Fachgruppe Mischungsvorgänge., 02.-04.05.2016, Würzburg, Deutschland
  • Contribution to proceedings
    Jahrestreffen Reaktionstechnik zusammen mit der Fachgruppe Mischungsvorgänge., 02.-04.05.2016, Würzburg, Deutschland
    Proceedings des Jahrestreffens Reaktionstechnik zusammen mit der Fachgruppe Mischungsvorgänge

Permalink: https://www.hzdr.de/publications/Publ-24975
Publ.-Id: 24975


The occurrences of Ca2UO2(CO3)3 in Fe(II) containing deep groundwater at Forsmark, eastern Sweden.

Tullborg, E.-L.; Suksi, J.; Geipel, G.; Krall, L.; Auqué, L.; Gimeno, M.; Puigdomenech, I.

Elevated U concentrations, most evident in a section ~500 mbsl, have been measured in deep Fe(II)-containing groundwater at Forsmark, eastern Sweden and have prompted detailed geochemical and isotopic investigations. The highest U contents (up to 175µg/L) are associated with HCO3- of 120-135 mg/L and Ca2+ of 900-1050 mg/L. Geochemical modelling shows that elevated dissolved U can be stabilized by Ca-uranyl-carbonate complexes. Indeed, time resolved luminescence spectrometry confirmed the Ca2UO2(CO3)3^0 complex, which is identified in deep reducing groundwater for the first time. U isotopes have been monitored in several sections with high U, and show stable but fracture specific activity ratios (ARs) around 1.5 to 2, although the U concentration varies. This is explained by mobilization of a solid phase with the same AR present in the fracture system close to the sampled sections. The AR >1 in this solid phase indicates a Quaternary age.

Keywords: Ca-uranyl-carbonate complexes; groundwater; uranium, luminescence spectrometry, 234U/238U AR; reducing condtions

Permalink: https://www.hzdr.de/publications/Publ-24974
Publ.-Id: 24974


In vivo examination of an injectable hydrogel system crosslinked by peptide-oligosaccharide interaction in immunocompetent nude mice

Tondera, C.; Wieduwild, R.; Röder, E.; Werner, C.; Zhang, Y.; Pietzsch, J.

Hydrogels can serve as matrices to mimic natural tissue function and be used for wide-ranging applications such as tissue regeneration and drug delivery. Injectable hydrogels are particularly favorable because their uses are minimally invasive. However, to create mouldable substance for injection often results in compromised function and stability. Here we report an injectable hydrogel system crosslinked by peptide-oligosaccharide non-covalent interaction. The dynamic network showed fast self-healing, a property essential for injectability. Injected hydrogels in immunocompetent mice and release of encapsulated compound were monitored up to 9 months by magnetic resonance imaging (MRI) and optical imaging. This surprisingly stable hydrogel did not cause adverse inflammatory response, as analyzed by measuring cytokine levels, immunohistochemistry, and MRI. Hydrogel degradation is associated with invasion of macrophages and vascular formation. The facile synthesis, high biocompatibility and stability of this injectable hydrogel could lead to various experimental and clinical applications in regenerative medicine and drug delivery.

Keywords: biomaterials; injectable hydrogels; magnetic resonance imaging; fluorescence imaging; immunohistochemistry

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Permalink: https://www.hzdr.de/publications/Publ-24973
Publ.-Id: 24973


Implementing fluid dynamics obtained from GeoPET in reactive transport models

Lippmann-Pipke, J.; Eichelbaum, S.; Kulenkampff, J.

Flow and transport simulations in geomaterials are commonly conducted on high-resolution tomograms (µCT) of the pore structure or stochastic models that are calibrated with measured integral quantities, like break through curves (BTC). Yet, there existed virtually no method for experimental verification of the simulated velocity distribution results.
Positron emission tomography (PET) has unrivaled sensitivity and robustness for non-destructive, quantitative, spatio-temporal measurement of tracer concentrations in body tissue. In the past decade, we empowered PET for its applicability in opaque/geological media – GeoPET (Kulenkampff et al.; Kulenkampff et al., 2008; Zakhnini et al., 2013) and have developed detailed correction schemes to bring the images into sharp focus. Thereby it is the appropriate method for experimental verification and calibration of computer simulations of pore-scale transport by means of the observed propagation of a tracer pulse, c P ET (x, y, z, t).
In parallel, we aimed at deriving velocity and porosity distributions directly from our concentration time series of fluid flow processes in geomaterials. This would allow us to directly benefit from lab scale observations and to parameterize respective numerical transport models. For this we have developed a robust spatiotemporal (3D+t) parameter extraction algorithm. Here, we will present its functionality, and demonstrate the use of obtained velocity distributions in finite element simulations of reactive transport processes on drill core scale.

Kulenkampff, J., Gruendig, M., Zakhnini, A., Gerasch, R., and Lippmann-Pipke, J.: Process tomography of diffusion with PET for evaluating anisotropy and heterogeneity, Clay Minerals, in press.
Kulenkampff, J., Gründig, M., Richter, M., and Enzmann, F.: Evaluation of positron emission tomography for visualisation of migration processes in geomaterials, Physics and Chemistry of the Earth, 33, 937-942, 2008.
Zakhnini, A., Kulenkampff, J., Sauerzapf, S., Pietrzyk, U., and Lippmann-Pipke, J.: Monte Carlo simulations of GeoPET experiments: 3D images of tracer distributions (18-F, 124-I and 58-Co) in Opalinus Clay, anhydrite and quartz, Computers and Geosciences, 57 183-196, 2013.

Keywords: positron emission tomography; segmentation; geochemical transport modelling; transport experiments

  • Poster
    EGU General Assembly 2016, 18.-22.04.2016, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-24972
Publ.-Id: 24972


Nonnormality of shear flows, transient growth, and its effects on helical and azimuthal magnetorotational instabilities

Mamatsashvili, G.

Magnetized shear flows are ubiquitous in nature and laboratory. The combined action of the magnetic field and velocity shear triggers various important instabilities and dynamical phenomena, ultimately determining transition to turbulence and global evolution of the flows. Here we focus on magnetorotational instability (MRI), and its non-ideal/resistive variants – helical and azimuthal magnetorotational instabilities (HMRI, AMRI) that arise as a result of combined action of magnetic field and differential rotation. It is one of the main instability responsible for turbulence and outward transport of angular momentum in magnetized astrophysical discs, which represent special case of shear flows. The discs are in Keplerian rotation with decreasing angular velocity and increasing angular momentum, which are Rayleigh-stable. However, it is well know that such spectrally stable hydrodynamical shear flows are non-normal or non-self-adjoint and as a consequence perturbations can undergo substantial transient, or non-modal (non-exponential) amplification in there. Since one of the main factors driving MRI in the magnetized case is also shear, the effects of non-normality inevitably influence the dynamics of MRI (i.e., the main linear equations describing MRI contain shear and are therefore non-normal) and should be taken into account. We investigate in detail the shear/non-normality-induced, or non-modal dynamics (growth) of HMRI/AMRI, which dominates at intermediate (dynamical/orbital) times, versus its modal growth that dominates at large times. We show that the non-modal growth of MRI can exceed its modal growth in a range of parameters. This can have implications for nonlinear transition. Interesting connection between the modal growth of HMRI and purely hydrodynamical non-modal growth was identified.

Keywords: Nonnormality of shear flows; transient growth; magnetorotational instability; transition to turbulence

  • Invited lecture (Conferences)
    Seminar at ZARM, University of Bremen, 05.-06.09.2016, Bremen, Germany

Permalink: https://www.hzdr.de/publications/Publ-24971
Publ.-Id: 24971


MHD turbulence in shear flows: self-sustenance via interplay of nonmodal growth and nonlinear transverse cascade

Mamatsashvili, G.

We find and investigate via numerical simulations self-sustained two-dimensional turbulence in a magnetohydrodynamic flow with a maximally simple configuration: plane, noninflectional (with a constant shear of velocity) and threaded by a parallel uniform background magnetic field. This flow is spectrally stable, so the turbulence is subcritical by nature and hence it can be energetically supported just by transient growth mechanism due to shear flow nonnormality. This mechanism appears to be essentially anisotropic in spectral (wavenumber) plane and operates mainly for spatial Fourier harmonics with streamwise wavenumbers less than a ratio of flow shear to the Alfv\'{e}n speed, k_y < S/u_A (i.e., the Alfv\'{e}n frequency is lower than the shear rate). We focused on the analysis of the character of nonlinear processes and underlying self-sustaining scheme of the turbulence, i.e., on the interplay between linear transient growth and nonlinear processes, in spectral plane. Our study, being concerned with a new type of the energy-injecting process for turbulence -- the transient growth, represents an alternative to the main trends of MHD turbulence research. We find similarity of the nonlinear dynamics to the related dynamics in hydrodynamic flows -- to the \emph{bypass} concept of subcritical turbulence. The essence of the analyzed nonlinear MHD processes appears to be a transverse redistribution of kinetic and magnetic spectral energies in wavenumber plane [as occurs in the related hydrodynamic flow, see Horton et al., Phys. Rev. E {\bf 81}, 066304 (2010)] and differs fundamentally from the existing concepts of (anisotropic direct and inverse) cascade processes in MHD shear flows.

Keywords: Nonmodal growth; MHD turbulence; shear flow nonnormality

  • Lecture (Conference)
    Max Planck Princeton Center (MPPC) workshop in Plasma Physics, 12.-15.01.2016, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-24970
Publ.-Id: 24970


Nonmodal dynamics of helical magnetorotational instability

Mamatsashvili, G.; Stefani, F.

The helical magnetorotational instability is known to work for resistive rotational flows with comparably steep negative or extremely steep positive shear. The corresponding lower and upper Liu limits of the shear are continuously connected when some axial electrical current is allowed to flow through the rotating fluid. Using a local approximation we demonstrate that the magnetohydrodynamic behavior of this dissipation-induced instability is intimately connected with the nonmodal growth of the underlying purely hydrodynamic problem. We also present preliminary results on the nonlinear development (saturation) of helical magnetorotational instability and characterize the saturation amplitude as a function of flow Reynolds number.

Keywords: helical magnetorotational instability; nonmodal growth; shear flow nonnormality

  • Lecture (Conference)
    17th MHD days, 30.11.-02.12.2016, Goettingen, Germany

Permalink: https://www.hzdr.de/publications/Publ-24969
Publ.-Id: 24969


The influence of interface curvature on solutal Marangoni convection in the Hele-Shaw cell

Mokbel, M.; Schwarzenberger, K.; Aland, S.; Eckert, K.

We study numerically the impact of interfacial curvature onto the Marangoni convection in a two-layer system of immiscible liquids with mass transfer of an alcohol. Assuming a parabolic velocity profile and constant solute concentration across the gap, the simulations solve Navier-Stokes equations coupled to advection-diffusion equations in both phases. Interfacial curvature imposes concentration gradients along the interface as soon as the mass transfer starts. This leads to an immediate interfacial convection which is superimposed later by the onset of the actual Marangoni roll cells. Prominent impact of interfacial curvature onto the Marangoni cells is the occurrence of a locking effect, i.e., the Marangoni roll cells adapt to the shape of the interface. Whereas mass transfer is enhanced by interfacial curvature compared to the planar interface in the beginning, locking drastically reduces the mass transfer rate. Even for small interface curvature significant differences to the planar case are found, which might explain the accelerated growth of cells in experiments compared to that in numerical simulation recently observed in Koellner et al. [EJP ST 224 (2015), 261-276].

Keywords: Hele-Shaw Cell; Marangoni Convection; Finite Element Method; Interface Curvature

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Permalink: https://www.hzdr.de/publications/Publ-24968
Publ.-Id: 24968


Perspektiven des neuen Dialyse-Membranverfahrens Aus dem Labor zu einer technischen Pilotanlage FCM GmbH: Galliumarsenid-Hersteller Dialyseverfahren für das Gallium-Recycling

Stelter, M.; Zeidler, O.; Scharf, C.; Eichler, S.

Entwicklung einer effizienten und wirtschaftlichen Trennungstechnologie von Ga aus GaAs-führenden Abwässern aus der Wafer-Herstellung

Der Verbrauch des Seltenen Metalls Gallium steigt seit Jahren exponentiell. Ein Großteil wird in der Produktion von Galliumarsenid eingesetzt, das als Halbleiterwerkstoff in der drahtlosen Kommunikation unverzichtbar ist.
Das Helmholtz-Institut Freiberg hat zusammen mit der TUBAF ein innovatives Recyclingver-fahren entwickelt, das die Recyclingquote des strategisch wertvollen Elementes in der Halb-leitererzeugung um 20% erhöhen kann. Beim Projektpartner Freiberger Compound Materials, einem Global Player für GaAs-Wafer, entspricht dies bereits 2-3 Tonnen Gallium pro Jahr mit ca. 0,5 Mio € Marktwert. Dafür wurde vom Bundesministerium für Wirtschaft und Energie (BMWi) der „Deutsche Rohstoffeffizienz-Preis 2014“ verliehen.
Das entwickelte Membranverfahren reinigt verbrauchte Ätzlösungen und Suspensionen, die bei der Fertigung von Wafern und ihrer Weiterverarbeitung von Mikrochips anfallen. Dies ermöglicht eine direkte Gewinnung aus der Lösung, welche bisher nicht ökonomisch war. Bei der Verfahrensentwicklung wurde von Anfang an auf die Ökonomie des entwickelten Pro-zesses geachtet. Da Störstoffe wie Arsensäure mit gewöhnlichem Wasser von der Gallium-lösung getrennt und wie gewohnt neutralisiert werden, entsteht kein zusätzlicher Energie- oder Chemikalienverbrauch. Dafür kommen spezielle Membranen zum Einsatz, die eine effiziente und selektive Trennung erzielen und chemisch hochresistent sind.
Eine Prefeasibility-Study ergab, dass mit Investitionskosten unter 100T Euro und geringen Membrankosten in einem Bereich von 5T € pro Jahr geringe Amortisationsdauern erzielbar sind. Das Projekt befindet sich momentan in der Pilotierungsphase und wird weiter technolo-gisch optimiert. Nach der Einführung in den technischen Maßstab könnte das Verfahren auch für das Recycling anderer Elemente weiterentwickelt werden.

  • Poster
    Woche der Umwelt 2016, 07.-8.6.2016, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24967
Publ.-Id: 24967


Application of Helium Ion Microscopy to study radiation damage

Hlawacek, G.; Veligura, V.; Bali, R.

Helium Ion Microscopy (HIM) is well known for its exceptional imaging and nanofabrication capabilities [1]⁠. After a brief introduction of this relatively young technique, I will focus on the localized creation of defects in metals and insulators.
Point defects created by the impinging He beam can be exploited to create sub–micron sized luminescent areas in appropriate materials (NaCl) [2]⁠. This combination of the nano sized beam of the HIM with ionoluminescence also allows to study fundamental processes of the defect formation and interaction [3]⁠. A technological relevant application of low fluence irradiation in the HIM is the formation of arbitrary shaped nano scale ferromagnetic areas in an otherwise para-magnetic matrix. In the particular case Fe60Al40 has been irradiated with fluences of only 6×1014cm-2 to create spin valve structures with a critical spacer length of only 20 nm [4]⁠.
Going beyond normally used ion doses allows to investigate defect agglomeration, blister formation and the subsequent surface restructuring [5]⁠. We present examples of materials modification at doses starting from 1×1017 cm−2 up to 1×1020 cm−2. Examples of surface structures formed under extreme ion fluencies at different temperatures will be presented for a wide range of materials including technological relevant materials for nuclear applications (Gold, Tungsten, Iron).

References:
[1] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema, J. Vac. Sci. Technol. B Microelectron. Nanom. Struct. 32, 020801 (2014).
[2] V. Veligura, G. Hlawacek, U. Jahn, R. van Gastel, H. J. W. Zandvliet, and B. Poelsema, J. Appl. Phys. 115, 183502 (2014).
[3] V. Veligura, G. Hlawacek, R. van Gastel, H. J. W. Zandvliet, and B. Poelsema, J. Phys. Condens. Matter 26, 165401 (2014).
[4] F. Röder, G. Hlawacek, S. Wintz, R. Hübner, L. Bischoff, H. Lichte, K. Potzger, J. Lindner, J. Fassbender, and R. Bali, Sci. Rep. 5, 16786 (2015).
[5] V. Veligura, G. Hlawacek, R. P. Berkelaar, R. van Gastel, H. J. W. Zandvliet, and B. Poelsema, Beilstein J. Nanotechnol. 4, 453 (2013).

  • Invited lecture (Conferences)
    CAARI - The Conference on Application of Accelerators in Research and Industry, 01.11.2016, Fort Worth, USA

Permalink: https://www.hzdr.de/publications/Publ-24966
Publ.-Id: 24966


Revealing crystal orientation and defects in the Helium Ion Microscope using channeling

Hlawacek, G.; Veligura, V.; Jankowski, M.

Helium Ion Microscopy (HIM) is well known for its exceptional imaging and nanofabrication capabilities [1]⁠. HIM has an unprecedented surface sensitivity, and channeling can be utilized to maximize the signal to noise ratio, obtain information on the crystal structure and reveal defects such as dislocation networks.
Using a poly crystalline gold sample we show how channeling can be used to obtain crystallographic information in the HIM [2]⁠.
We demonstrate the resolving power of this technique using a thin (2 ML) silver layer on Pt(111). This is is representative example of a surface confined alloy widely studied in the field surface science. The obtained HIM results are compared to results obtained by low energy electron microscopy, spot profile analysis low energy electron diffraction (SPA-LEED), and atomic force microscopy phase contrast. In HIM single atom layer high steps can be visualized as a result of a work function change—across the otherwise atomically flat terraces—of only 20 meV. By utilizing the dechanneling contrast [3]⁠ mechanism also the surface reconstruction of this thin surface layer can be revealed. We find a threefold periodic structure of channeling (fcc stacking) and dechanneling (hcp stacking) areas. The periodicity of this structure—measured along the <11-2> surface directions—is 6.65 nm [4]⁠. This is in excellent agreement with values obtained by SPA-LEED.

  • Lecture (Conference)
    CAARI - The Conference on Application of Accelerators in Research and Industry, 03.10.2016, Fort Worth, USA

Permalink: https://www.hzdr.de/publications/Publ-24965
Publ.-Id: 24965


Spatially controlled ripple formation in the HIM using Low Voltages and High Temperatures

Hlawacek, G.; Sottili, L.; Engler, M.; Nanda, G.; van Alkemade, P.; Facsko, D.

Ripple formation is a well known phenomenon that is observed for many materials under low energy ion bombardment. Often broad beam noble gas ion irradiation using energies of a few keV is employed to create these self-organized patterns on various metal, semiconductor and insulator surfaces. In addition to the fundamental interest in the formation and evolution of these structures they can be utilized in a number of new applications.
Creating nano scale periodic roughness can be of interest for various microfluidic applications or to control friction in new MEMS and NEMS devices. However, these applications are not realized at their full potential today as the required sub micron patterning which can not easily be realized using broad beams.
Here, we present for the first time ripple patterns that have been created on the GaAs(001) surface using 5 keV Ne ions and elevated temperatures of up to 600 K in a Helium Ion Microscope (HIM). We will present the home built sample heater that can be loaded through the load lock of the Carl Zeiss Orion NanoFab and describe the influence on the device performance, as well as HIM operation at 5 keV.
The evolution of the ripple wavelength changes from 30 nm at low 1e17 Ne/cm² to 80 nm at 1e18 Ne/cm². The orientation of the ripples with respect to the shape can be changed by rotating the pattern on the surface and the influence of the geometrical constrains of the irradiated area on the ripple pattern is studied.

  • Lecture (Conference)
    AVS - International Symposium and Exhibition, 10.11.2016, Nashville, USA

Permalink: https://www.hzdr.de/publications/Publ-24964
Publ.-Id: 24964


Helium-ion microscopy, helium-ion irradiation and post-irradiation nanoindentation of the 9%Cr steel Eurofer97 and oxide dispersion strengthened (ODS) Eurofer

Bergner, F.; Hlawacek, G.; Heintze, C.

Helium embrittlement poses a major challenge for the application of ferritic/martensitic steels in future nuclear devices. The strategy for an effective suppression of helium embrittlement is to reduce the mean free diffusion path of helium by way of introducing nanoparticles into the steel. The study is aimed at clarifying the role of oxide nanoparticles on the formation of helium bubbles and related hardening for the case of He-ion irradiations performed in the He-ion microscope (HIM).

  • Poster
    E-MRS 2016 Fall Meeting, 19.-22.09.2016, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-24963
Publ.-Id: 24963


Charge Collection Efficiency in Segmented Semiconductor Detector Interstrip Region

Alarcon-Diez, V.; Vickridge, I.; Jakšić, M.; Grilj, V.; Schmidt, B.

Charged particle semiconductor detectors have been used in Ion Beam Analysis (IBA) for over four decades without great changes in either design or fabrication. However one area where improvement is desirable would be to increase the detector solid angle so as to improve spectrum statistics for a given incident beam fluence. This would allow use of very low fluences opening the way for example to increased time resolution in real-time RBS or analysis of materials that are highly sensitive to beam damage. In order to achieve this goal without incurring the costs of degraded resolution due to kinematic broadening or large detector capacitance, a single-chip segmented detector (SEGDET) was designed and built within the SPIRIT EU infrastructure project. In this work we present the Charge Collection Efficiency (CCE) in the vicinity between two adjacent segments focusing on the interstrip zone. Microbeam Ion Beam Induced Charge (IBIC) was used to perform X-Y mapping of CCE with different ion masses and energies, as a function of detector operating conditions (bias voltage changes, detector housing possibilities and guard ring configuration). We show the CCE in the active area edge region and have also mapped the charge from the interstrip region, shared between adjacent segments. The results indicate that the electrical extent of the interstrip region is very close to the physical extent of the interstrip and guard ring structure with interstrip impacts contributing less than 8% to the complete spectrum. The interstrip contributions to the spectra can be substantially reduced by an offline anticoincidence criterion through the list mode data analysis, which should also be easy to implement directly in the data acquisition software.

Keywords: silicon detectors; ion beam analysis; segmented detectors

  • Lecture (Conference)
    12th European Conference on Accelerators in Applied Research and Technology (ECAART12), 03.-08.07.2016, Jyväskylä, Finland
  • Poster
    12th European Conference on Accelerators in Applied Research and Technology (ECAART12), 03.-08.07.2016, Jyväskylä, Finland

Permalink: https://www.hzdr.de/publications/Publ-24962
Publ.-Id: 24962


Nanometer Scale Time of Flight Back Scattering Spectrometry in the Helium Ion Microscope

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

TOF-BS and TOF-SIMS

  • Poster
    EMC2016 – The 16th European Microscopy Congress, 28.08.-03.09.2016, Lyon, Frankreich
  • Poster
    Microscopy & Microanalysis 2016 Meeting (M&M2016), 24.-28.07.2016, Columbus, USA

Permalink: https://www.hzdr.de/publications/Publ-24961
Publ.-Id: 24961


Effects of baffles on bubble rising behaviour – extending bubble residence time and mass transfer

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

Up to 80 % of the total energy budget of wastewater treatment plants is consumed by the activated sludge process. To improve the energy efficiency the specific standard oxygen transfer rate (SSOTE) must be increased. This can be achieved by increasing the overall oxygen mass transfer inside the aeration tank. Oxygen mass transfer happens from the gaseous phase of the bubble to the liquid phase of the activated sludge. The amount of transferred oxygen depends on various parameters like interfacial area, surface active substances, concentration gradients, turbulences and bubble residence time. However, parameters such as the interfacial area cannot be changed without additional energy usage.

Our approach is to increase the length of the bubble rising path and to decelerate the bubbles by inserting baffles in the activated sludge tank. The overall oxygen mass transfer is then extended due to the longer bubble residence time in the aeration tank. Furthermore, the bubbles can be guided in their rise inside the aeration tank. By directing bubbles into less oxygenated sludge higher concentration differences occur which lead to higher local oxygen mass transfer.

Hydrophobic and hydrophilic materials were selected for the laboratory experiments to investigate their effects on the bubble rising behaviour. The target parameters were bubble size distribution, equivalent Sauter mean diameter of the bubbles, bubble rise velocity, bubble residence time, local and global mass transfer coefficient under the variation of wetting behaviour of the material (hydrophilic, hydrophobic), roughness profile of the material, inclination angle and length of plate. The wetting characteristics of these plates were also tested within activated sludge to analyse the influence of a developed biofilm to the surface characteristics of the plates. A variety of materials with different surface properties where investigated: glass, PVC, PTFE, stainless steel and various coated and treated stainless steel plates.

Keywords: waste water treatment; bubble rise; bubble residence time; baffles

  • Poster
    The 9th Eastern European Young Water Professionals Conference, 24.-27.05.2017, Budapest, Ungarn
  • Contribution to proceedings
    The 9th Eastern European Young Water Professionals Conference, 24.-27.05.2017, Budapest, Ungarn
    9th Eastern European Young Water Professionals Conference - CONFERENCE PROCEEDINGS Uniting Europe for Clean Water: Cross-Border Cooperation of Old, New and Candidate Countries of EU for identifying problems, finding causes and solutions, Budapest, 433-440

Permalink: https://www.hzdr.de/publications/Publ-24960
Publ.-Id: 24960


Tailoring magnetic nanostructures with neon in the ion microscope

Hlawacek, G.; Bali, R.; Röder, F.; Aleksandrov, Y.; Semisalova, A.; Wintz, S.; Wagner, K.; Schultheiss, H.; Fassbender, J.

In the HIM high fluences of Neon are often used to create structures on the nanoscale. This is not always necessary and certain properties of specific materials systems can be changed using much smaller fluences. The magnetic properties of specific materials as well as the properties connected to the shape of magnets can be influenced.

  • Poster
    1st International Conference on Helium Ion Microscopy and Emerging Focused Ion Beam Technologies (HEFIB 2016), 08.-10.06.2016, Luxemburg, Luxembourg
  • Lecture (Conference)
    Microscopy & Microanalysis 2016 Meeting (M&M2016), 27.07.2016, Columbus, USA

Permalink: https://www.hzdr.de/publications/Publ-24959
Publ.-Id: 24959


Helmholtz-Zentrum Dresden-Rossendorf Ion Beam Center

Hlawacek, G.; Heinig, K.-H.

Introduction IBC

  • Poster
    ECSEL Forum, 03.05.2016, Brüssel, Belgien

Permalink: https://www.hzdr.de/publications/Publ-24958
Publ.-Id: 24958


Writing nanoscale magnets with neon using a gas field ion source microscope

Hlawacek, G.; Röder, F.; Semisalova, A.; Bali, R.; Wintz, S.; Hübner, R.; Bischoff, L.; Lichte, H.; Potzger, K.; Lindner, J.; Fassbender, J.

Writing nanoscale magnets with neon using a gas field ion source microscope

  • Lecture (Conference)
    DPG-Frühjahrstagung 2016, 09.03.2016, Regensburg, Deutschland
  • Lecture (Conference)
    11th DACH FIB Workshop, 27.06.2016, Brünn, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-24957
Publ.-Id: 24957


Gas Dispersion in Biological Wastewater Treatment – Smaller Bubbles for More Efficiency

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

In Germany wastewater is treated in 10000 plants which use 4.400 GWh of energy per year. Up to 80% of the whole energy in these plants is consumed for the aeration of microorganisms in the so called activated sludge tank. Aeration is the essential part of the process since the microorganisms need sufficient amount of oxygen to degrade ammonia. Aerators with flexible membranes located at the bottom of the aeration tank are currently state of the art for this process. However the process suffers from some limitation such as pressure drop, insufficient mixing and underutilization of oxygen. These are mainly due to scarce knowledge about gas dispersion inside the tank. The type of aerator defines the initial size of bubbles dispersed into the tank. The typical bubble size generated by flexible membrane aerators has been determined to be between 2-4 mm by Hasanen et. al. However, this is considerably higher than the optimal bubble size. Motarjemi and Jameson have calculated the optimal value for the 95% oxygen transfer to water in 3-6 m tank depth to be in the range 0.7…1.0 mm.
A novel approach uses solid perforated stainless steel aerators for gas dispersion. In this work bubble formation of stainless steel aerators has been experimentally studied for comparison to membrane aerators. Preliminary results of the stainless steel membrane sparger showed a significant reduction in the bubble size by 47 % and consequently an increase in bubble residence time compared to flexible membranes. Moreover, uniform bubble size has been generated across the sparger which is not the case for membrane aerators. The pressure drop of these novel aerators is compared with flexible membranes. Mass transfer measurements were done in a large scale bubble column setup under realistic process conditions.

Keywords: waste water treatment; gas dispersion; mass transfer; bubble rise; bubble size

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppen Mehrphasenströmungen, Partikelmesstechnik, Zerkleinern und Klassieren, Computational Fluid Dynamics, Mischvorgänge und dem TAK Aerosoltechnologie, 14.-17.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24956
Publ.-Id: 24956


Towards an analytic ion microscope

Hlawacek, G.

Review of the various analytical possibilities in the HIM

  • Lecture (others)
    HZB Seminar, 09.02.2016, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24955
Publ.-Id: 24955


Microbial diversity extreme saline environments

Franze, M.; Cherkouk, A.

Backgrounds: Rock salt formations are considered as potential host rock systems for the long-term storage of highly radioactive waste in a deep geological repository. To date, little is known about the habitat rock salt and the way of life of the microorganisms occurring there. Next to bacteria and fungi, extreme halophilic archaea are dominating this habitat. It is of interest to know what kind of microorganisms are living there, how active they are under repository relevant conditions and how these microorganisms can influence the safe storage of the waste. Objectives: A combination of culture-dependent and -independent methods was used to investigate the microbial diversity in rock salt from potential host rock for nuclear waste disposal as well as saline soil samples from Arava Desert, Israel. Methods: Culture-dependent: A specific portion of the two kinds of samples were incubated in three different sodium chloride concentrations of modified R2A resuscitation buffer and were spread on corresponding agar plates (37°C) to get isolates which were further characterized. Culture-independent: From two samples DNA was extracted, purified for PCR amplification of 16S rRNA genes and sequenced with Illumina MiSeq (RTL Genomics). Conclusions: Halophilic microorganisms could be isolated from both kinds of samples. The soil sample isolates can be assigned to different archaeal genera Natrinema, Halorubrum, and Halobacterium. Bacterial isolates could be related to Bacilli such as Halobacillus and Aquibacillus. From rock salt samples could be isolated different Halobacetrium species. The obtained isolates could be further used for investigations, regarding there activity under repository relevant conditions.

  • Poster
    FEMS 2017 7th congress of european microbiologists, 09.-13.07.2017, Valencia, Spanien

Permalink: https://www.hzdr.de/publications/Publ-24954
Publ.-Id: 24954


Development of highly affine and selective fluorinated cannabinoid receptor type 2 ligands

Moldovan, R.-P.; Hausmann, K.; Deuther-Conrad, W.; Brust, P.

CB2 receptors are involved in various pathological processes and the visualization of the expression level alteration with a non-invasive technique like PET is of high interest. In this work we focused on the introduction of the fluorine atom by modifying at various positions the structure of the highly affine and selective CB2 ligand N-(adamantan-1-yl)-5-ethyl-2-methyl-1-phenyl-1H-imidazole-4-carboxamide (5, Ki(CB2) = 1 nM, Ki(CB1) >10,000 nM). The highest CB2 binding affinity was obtained by derivatization of the imidazole 2-position. This study allowed the identification of compound 15 as one of the most potent (Ki(CB2) = 0.29 nM) and selective (CB1/CB2 > xx), CB2 ligand discovered so far, eligible for the development of an [18F]-PET radiotracer.

Keywords: Cannabinoid receptor type 2; Imidazole; Binding affinity; Fluorine; Positron emission tomography

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-24953
Publ.-Id: 24953


Development of Fluorinated Non-Peptidic Ghrelin Receptor Ligands for Potential Use in Molecular Imaging

Moldovan, R.-P.; Els-Heindl, S.; Worm, D. J.; Kniess, T.; Kluge, M.; Beck-Sickinger, A. G.; Deuther-Conrad, W.; Krügel, U.; Brust, P.

The ghrelin receptor (GhrR) is a widely investigated target in several diseases. However, the current knowledge of its role and distribution in the brain is limited. Recently, the small and non-peptidic compound (S)-6-(4-bromo-2-fluorophenoxy)-3-((1-isopropylpiperidin-3-yl)methyl)-2-methylpyrido[3,2-d]pyrimidin-4(3H)-one ((S)-9) has been described as a GhrR ligand with high binding affinity. Here, we describe the synthesis of fluorinated derivatives, the in vitro evaluation of their potency as partial agonists and selectivity at GhrRs, and their physicochemical properties. These results identified compounds (S)-9, (R)-9, and (S)-16 as suitable parent molecules for 18F-labeled positron emission tomography (PET) radiotracers to enable future investigation of GhrR in the brain.

Keywords: brain, ghrelin receptor; fluorine, positron emission tomography

  • Open Access Logo International Journal of Molecular Sciences 18(2017)4, 768
    Online First (2017) DOI: 10.3390/ijms18040768

Permalink: https://www.hzdr.de/publications/Publ-24952
Publ.-Id: 24952


Development of foam-based layered targets for laser-driven ion beam production

Prencipe, I.; Sgattoni, A.; Dellasega, D.; Fedeli, L.; Cialfi, L.; Choi, I. W.; Kim, I. J.; Janulewicz, K. A.; Kakolee, K. F.; Lee, H. W.; Sung, J. H.; Lee, S. K.; Nam, C. H.; Passoni, M.

We report on the development of foam-based double-layer targets (DLTs) for laser-driven ion acceleration. Foam layers with a density of a few mg cm−3 and controlled thickness in the 8–36 μm range were grown on μm-thick Al foils by pulsed laser deposition (PLD). The DLTs were experimentally investigated by varying the pulse intensity, laser polarisation and target properties. Comparing DLTs with simple Al foils, we observed a systematic enhancement of the maximum and average energies and number of accelerated ions. Maximum energies up to 30 MeV for protons and 130 MeV for C6+ ions were detected. Dedicated three-dimensional particle-in-cell (3D-PIC) simulations were performed considering both uniform and cluster-assembled foams to interpret the effect of the foam nanostructure on the acceleration process.

Keywords: ion acceleration; pulsed laser deposition; carbon foam; laser–plasma interaction; particle-in-cell

Permalink: https://www.hzdr.de/publications/Publ-24951
Publ.-Id: 24951


Inelastic scattering of fast neutrons from 56Fe

Beyer, R.; Birgersson, E.; Dietz, M.; Hannaske, R.; Junghans, A. R.; Kögler, T.; Massarczyk, R.; Matic, A.; Schwengner, R.; Wagner, A.

The inelastic scattering of fast neutrons on Fe-56 was investigated in different manners at the neutron time-of-flight facility nELBE.
The scattering cross section was determined via the measurement of the gamma-ray production and by means of a kinematically complete double time-of-flight method.
In a further measurement the gamma-ray angular distribution was determined to correct the measured cross sections for anisotropy.
The resulting inelastic scattering cross section determined from the photo production cross sections is in very good agreement with evaluations and previous measurements.
In contrast, the result of the double time-of-flight measurement is about 10 % lower than these data, giving a hint to neutron-gamma-ray angular correlations in the process of inelastic neutron scattering.

Keywords: nELBE; fast neutrons; neutron time-of-flight; inelastic scattering; iron

  • Invited lecture (Conferences)
    International Conference on Nuclear Data for Science and Technology - ND2016, 11.-16.09.2016, Bruges, Belgium
  • Open Access Logo European Physical Journal Web of Conferences 146(2017), 02017
    Online First (2017) DOI: 10.1051/epjconf/201714602017

Permalink: https://www.hzdr.de/publications/Publ-24950
Publ.-Id: 24950


Electrical Characterization of DNA Origami Nanostructure

Bayrak, T.

DNA origami method provides programmable bottom up approach for developing of any desired shaped structures from nanoscale components and with the help of the hybridization formation of the functional nanostructures can be controllable by DNA origami nanostructure. One of the goals to design tailored bottom up based nanophotonics, optoelectronics and nanoelectronics devices based on DNA functionalization such as metallization or controlled attachment of nanoparticles to the DNA origami design. However, combination of bottom-up and top-down based methods is required for future nanoelectronic device applications. In this study, gold nanoparticles are decorated on DNA origami accumulated to SiO2 surface utilized for molecular electronics. For this novel approach, we combined bottom-up and top-down based methods, two metallic electrodes contacted on individual gold nanoparticles decorated DNA origami nanotube by electron beam lithography. The charge transport behavior of the molecule between gold nanoparticles occurs in temperature range from room temperature to 4.2 K.

  • Lecture (others)
    NanoNET PhD Seminar, 18.11.2016, IFW,Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-24949
Publ.-Id: 24949


Hydrodynamics of descending gas-liquid flows in solid foams: Liquid holdup, multiphase pressure drop and radial dispersion

Zalucky, J.; Wagner, M.; Schubert, M.; Lange, R.; Hampel, U.

In this contribution we report on spatially resolved analysis of multiphase hydrodynamics in solid foam packed trickle bed reactors. For investigation we used ultrafast X-ray computed tomography and fast response pressure transducers. The SiSiC foams’ pore density, the liquid distribution system as well as gas and liquid flow rates were varied. The transient behavior of the liquid holdup at trickle and pulse flow as well as after drainage were examined and correlations for static and dynamic holdups were derived. The correlations are based on Eötvös, Reynolds and Galileo number, using porosity and specific area for the definition of the hydraulic diameter. The correlations are applicable to a wide range of foam morphologies, pore densities and operation conditions reported in the literature. The axial pressure gradients in the solid foams showed significantly lower pressure drop compared to particle packings of similar specific surface area. The evolution of liquid spreading was analyzed qualitatively and quantitatively with various irrigation patterns. In addition, an approach for the determination of radial liquid dispersion coefficients in solid foams is presented.

Keywords: Solid foams; Liquid holdup; Two-phase Flow; Ultrafast X-ray computed tomography; Radial dispersion; Liquid spreading

Permalink: https://www.hzdr.de/publications/Publ-24948
Publ.-Id: 24948


MHD turbulence in Keplerian disks with net azimuthal magnetic field - bypass concept of self-sustenance via interplay of linear transient growth and nonlinear transverse cascade

Mamatsashvili, G.

We studied the mechanism of the self-sustenance of MHD turbulence in spectrally stable stratified Keplerian disk flows threaded by nonzero net azimuthal magnetic field in the shearing box approximation. For this purpose, we performed direct numerical simulations of (homogeneous, subcritical) turbulence at different aspect ratios of the simulation boxes. Then, we analyzed the turbulence dynamics in Fourier/wavenumber/spectral space based on the simulation data to gain deeper insight into the self-sustaining dynamics of such subcritical MHD turbulence. Specifically, we examined the interplay of linear transient growth of Fourier harmonics and nonlinear processes. In the case of azimuthal field in the shearing box setup, the linear growth of (magnetic) perturbations has a transient nature and is strongly anisotropic in spectral space. This, in turn, leads to anisotropy of nonlinear processes in spectral space and, as a result, the main nonlinear process appears to be not a direct/inverse, but rather a transverse/angular redistribution of harmonics in Fourier space referred to as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by interplay of the linear transient growth and the transverse cascade. The main scheme of this interplay in Keplerian disks was first proposed in Chagelishvili, Zahn, et al. (2003) and then its realization in real flows has been investigated in our recent papers Horton et al. (2010), Mamatsashvili et al. (2014, 2016). This scheme exemplifies the bypass concept of subcritical turbulence in spectrally stable shear flows. Both transient growth and transverse cascade mainly operate at large length scales, comparable to the box size. Consequently, the central, small wavenumber area of Fourier space is crucial in the self-sustenance of the turbulence and is labeled as the vital area. Outside the vital area both transient growth and transverse cascade are of secondary importance - Fourier harmonics are transferred to dissipative scales by the usual nonlinear direct cascade.

Keywords: Nonmodal approach; transient growth; turbulence; accretion disks; transverse cascade

  • Invited lecture (Conferences)
    Seminar at the Paris-Meudon Observatory, 16.-18.11.2016, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-24947
Publ.-Id: 24947


Nonmodal analysis of helical magnetorotational instability

Mamatsashvili, G.; Stefani, F.

The helical and azimuthal magnetorotational instabilities (HMRI), relative of standard MRI, has recently received much attention in connection with liquid metal experiments. Its main advantage is that, being governed by Reynolds and Hartmann numbers, persists at very small magnetic Prandtl numbers (Pm) typical to liquid metals, in contrast to standard MRI. However, its applicability to Keplerian astrophysical discs with similarly small Pm is still not settled and controversial; the main hindering factor is the Liu’s criterion. Aiming to resolve this issue, we carry out nonmodal analysis of HMRI, which allows us to capture its growth at intermediate times due to the non-self-adjointness of shear flows, which can occur even when their modal growth would be absent according to Liu’s criterion.

Keywords: magnetorotationa instability; nonmodal growth; nonnormality; astrophysical Keplerian disks; liquid metals

  • Lecture (Conference)
    GdR dynamo meeting, 27.06.-01.07.2016, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-24946
Publ.-Id: 24946


PET Imaging of α7 Nicotinic Acetylcholine Receptors: A comparative study of [18F]ASEM and [18F]DBT-10 in non-human primates, and further evaluation of [18F]ASEM in humans

Hillmer, A. T.; Li, S.; Zheng, M.-Q.; Scheunemann, M.; Lin, S.-F.; Nabulsi, N.; Holden, D.; Pracitto, R.; Labaree, D.; Ropchan, J.; Teodoro, R.; Deuther-Conrad, W.; Esterlis, I.; Cosgrove, K. P.; Carson, R. E.; Brust, P.; Huang, Y.

The α7 nicotinic acetylcholine receptor (nAChR) is implicated in many neuropsychiatric disorders, making it an important target for positron emission tomography (PET) imaging. The first aim of this work was to compare two PET radioligands specific to α7 nAChRs, [18F]ASEM (3-(1,4-diazabicyclo[3.2.2]nonan-4-yl)-6-([18F]fluorodibenzo[b,d]thiophene 5,5-dioxide) and [18F]DBT-10 (7-(1,4-diazabicyclo[3.2.2]nonan-4-yl)-2-([18F]fluorodibenzo[b,d]thiophene 5,5-dioxide), in nonhuman primates. The second aim was to further assess the quantification and test-retest variability of [18F]ASEM in humans.

Keywords: Nicotine; Nicotinic Acetylcholine Receptor; Alpha7; PET; ASEM

Permalink: https://www.hzdr.de/publications/Publ-24945
Publ.-Id: 24945


Linear stability analysis of magnetized relativistic rotating jets

Bodo, G.; Mamatsashvili, G.; Rossi, P.; Mignone, A.

We perform a linear stability analysis of magnetized rotating cylindrical jet flows in the approximation of zero thermal pressure. We focus our analysis on the effect of rotation on the current driven mode and on the unstable modes introduced by rotation. We find that rotation has a stabilizing effect on the current driven mode only for rotation velocities of the order of the Alfvén velocity. Rotation introduces also a new unstable centrifugal buoyancy mode and the `cold' magnetorotational instability. The first mode is analogous to the Parker instability with the centrifugal force playing the role of effective gravity. The magnetorotational instability can be present, but only in a very limited region of the parameter space and is never dominant. The current driven mode is characterized by large wavelengths and is dominant at small values of the rotational velocity, while the buoyancy mode becomes dominant as rotation is increased and is characterized by small wavelengths.

Keywords: instabilities; MHD; galaxies: jets

  • Open Access Logo Monthly Notices of the Royal Astronomical Society 462(2016), 3031-3052
    Online First (2016) DOI: 10.1093/mnras/stw1650

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-24944
Publ.-Id: 24944


Upgrade of the microprobe at Dresden-Rossendorf

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

The nuclear microprobe that was in operation until 2104 at the Ion Beam Center of the Helmholtz-Zentrum Dresden-Rossendorf was installed in 1994 [1]. It has been in operation since then with only minor changes. This necessitated an upgrade to bring the setup up to current standards of technology and good working practice. This study presents the details of the upgrade and modernization process we have undertaken.
The major drawbacks of the old system were the poor resolution and low contrast and brightness of the optical microscope. However, a good optical image is essential to localise the areas of interest on, for example, large geological samples.
On the other hand, the main investigative tool is the focused beam of high-energy ions and the corresponding detectors. Any other system such as an optical microscope has to be designed around this equipment. A new custom-designed microscope has been installed for which the first light-collecting lens is mounted in the sample chamber at only a few centimetres from the sample. The light is then guided over large mirrors and focussed on a CCD camera outside the sample chamber. Also the illumination is fed in through the lenses instead of using a separate light source as in the old system. The lens system can also serve as a basis for a possible ionoluminescence detector.
Other improvements concern the beam deflection system, the control of the scanning system and the control and monitoring of all relevant parameters for the experiment. The control of the scanning system is done by custom-designed hardware to guarantee the real-time execution of the scanning without the need for a computer with a real-time operating system. This makes it possible to use a standard Windows based computer with commercial software for the data acquisition. A new channeltron has also been installed to detect secondary electrons that can be used to obtain a quick overview of an measurement area.
Technical details and first test measurements with the new system are presented.

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

Keywords: PIXE; nuclear microprobe

  • Poster
    15th International Conference on Particle Induced X-ray Emission, 02.-07.04.2017, Split, Kroatien

Permalink: https://www.hzdr.de/publications/Publ-24943
Publ.-Id: 24943


Single Bubble Dynamics on a Vertical Wall in Sub-cooled Nucleate Boiling

Sarker, D.; Franz, R.; Hampel, U.

Nucleate boiling heat transfer is an efficient way of heat transfer for many engineering applications, like heat exchangers, boilers, electronic cooling systems etc. Therefore, heat transfer enhancement in the nucleate boiling region has received continuous interest for a long time. For the further enhancement of heat transfer performance, fundamental physics of bubble growth and departure process should be revealed clearly. In the current study, high resolution optical instrumentation and highly efficient parallel DNS (Direct Numerical Simulation) solver are used to investigate the single bubble dynamics. Numerical results are validated against experimental results of subcooled nucleate boiling in water at atmospheric pressure, where the heated surface was vertically oriented.

Keywords: subcooled nucleate boiling; single bubble; vertical heater

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Wärme- und Stoffübertragung, 01.-02.03.2016, Kassel, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24942
Publ.-Id: 24942


Nucleate Boiling on Vertical Heater Wall : Role of Heater Surface Properties

Sarker, D.; Franz, R.; Ding, W.; Hampel, U.

Nucleate Boiling is an efficient mode of heat transfer for different engineering applications.In real applications, heat transfer surfaces are always rough in different scale. The effects of surface roughness on single bubble dynamics; namely bubble growth and sliding has not been thoroughly investigated. Surface roughness noticeably affects bubble growth process with the interaction of bubble base or microlayer. In the current study, single bubble growth and sliding for different roughness are investigated and the high resolution imaging techniques are used. Experimental results show that intermediate roughness (Rq=90nm) enhances bubble growth process compare to Rq=4.48 nm and Rq=410 nm. As well as heat transfer to the bubble through microlayer is also noticeably higher for intermediate roughness.

Keywords: vertical heater; high speed video camera; roughness height; microlayer

  • Poster
    Kompetenzzentrum Ost für Kerntechnik, 08.12.2016, HZDR, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24941
Publ.-Id: 24941


Ultrasound measurements in a physical model of Czochralski crystal growth in a horizontal magnetic field

Pal, J.; Grants, I.; Eckert, S.; Gerbeth, G.

A horizontal magnetic field (HMF) may improve conditions in the melt during large silicon single crystal growth by the Czochralski technique. This observation is counter-intuitive as the HMF evidently breaks the rotational symmetry. A previous study has shown that the HMF is not able to significantly delay the Rayleigh-Bénard instability in a rotating cylinder. It has been observed that an oscillating flow sets in soon after the linear onset. Can we expect a stabilizing effect of the HMF in the Czochralski growth? Why the symmetry breaking by the HMF is eventually not so relevant? These are two central questions for our primarily experimental study. Besides, it is also meant as a benchmark for comparison with the numerical codes. To serve the latter purpose the boundary conditions should be preferably well defined. Having this in mind the temperature boundary conditions are defined as follows. An isothermal heating is applied at the bottom of a cylindrical cell filled with GaInSn alloy. The side wall is thermally insulated. An optionally rotating isothermal cooler models the growing crystal. A water-cooled layer of an alkaline solution keeps the rest of the metal surface free from oxides and models the radiation heat loss. The maximum HMF strength is 0.3 T that corresponds to a Hartmann number of about 1200. Velocity profiles are measured by ultrasound Doppler velocimetry.

Keywords: Czochralski crystal growth; Horizontal magnetic field; Ultrasound Doppler velocimetry

  • Lecture (Conference)
    10th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 28.-30.09.2016, Tokyo, Japan
  • Contribution to proceedings
    10th International Conference on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 28.-30.09.2016, Tokyo, Japan
    Proceedings of ISUD10, 9-12

Permalink: https://www.hzdr.de/publications/Publ-24940
Publ.-Id: 24940


Physical model of Czochralski crystal growth in a horizontal magnetic field

Pal, J.; Grants, I.; Eckert, S.; Gerbeth, G.

The horizontal magnetic field (HMF) may improve conditions in the melt during large silicon single crystal growth by the Czochralski technique. This observation is counter-intuitive as the HMF evidently breaks the rotational symmetry. A previous study has shown that the HMF is not able to significantly delay the Rayleigh-Bénard instability in a rotating cylinder [1]. It has been observed [2] that an oscillating flow sets in soon after the linear onset. Can we expect a stabilizing effect of the HMF in the Czochralski growth? Why the symmetry breaking by the HMF is eventually not so relevant? These are two central questions for our primarily experimental study. Besides, it is also meant as a benchmark for comparison with the numerical codes. To serve the latter purpose the boundary conditions should be preferably well defined. Having this in mind the temperature boundary conditions are defined as follows. An isothermal heating is applied at the bottom of a cylindrical cell filled with GaInSn alloy. The side wall is thermally insulated. An optionally rotating isothermal cooler models the growing crystal. A water-cooled layer of an alkaline solution keeps the rest of the metal surface free from oxides and models the radiation heat loss. The maximum HMF strength is 0.3 T that corresponds to a Hartmann number of about 1200. Velocity profiles are measured by ultrasound Doppler velocimetry. Temperatures are monitored in the vicinity of the triple point at the rim of the cooler, at the rim of the cell, inside of the cooler and of the heater. The Nusselt-Grashof number dependency is obtained by controlling the total heat flux injected at the bottom and measuring the temperature difference between the bottom plate and the cooler. The critical cooler rotation rate is determined at which the rotation introduces a significant variation of the velocity field dominated by the HMF-aligned convection rolls.

References
1. I. Grants, G. Gerbeth, J. Cryst. Growth, 358 (2012), 43-50
2. U. Burr, U. Müller, J. Fluid Mech., 453 (2002), 345-370

Keywords: Czochralski crystal growth; horizontal magnetic field

  • Lecture (Conference)
    1st German Czechoslovak Conference on Crystal Growth, 16.-18.03.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24939
Publ.-Id: 24939


The Clinical Target Volume in Lung, Head-and-neck, and Esophageal Cancer: Lessons from Pathological Measurement and Recurrence Analysis

Apolle, R.; Rehm, M.; Bortfeld, T.; Baumann, M.; Troost, E.

Radiotherapy research has achieved remarkable progress in target volume definition. Advances in medical imaging facilitate more precise localization of the gross tumor volume, alongside a more detailed understanding of the geometric uncertainties associated with treatment delivery that has enabled robust safety margins to be customized to the specific treatment scenario at hand. By contrast, the clinical target volume, meant to encompass gross tumor, as well as, adjacent sub-clinical disease, has evolved very little. It is more often defined by clinician experience and institutional convention than on a patient-specific basis. This disparity arises from the inherent invisibility of sub-clinical disease in current medical imaging. Its incidence and expanse can only be ascertained via indirect means. This article reviews two such strategies: histopathological measurements on resection specimen and analyses of locoregional recurrences after radiotherapy.

Keywords: microscopic tumor extension; clinical target volume; adaptive radiotherapy; particle beam irradiation

Permalink: https://www.hzdr.de/publications/Publ-24938
Publ.-Id: 24938


Single Bubble Dynamics during Subcooled Nucleate Boiling on a Vertical Heater Surface: An Experimental Analysis of the Effects of Surface Characteristics

Sarker, D.; Franz, R.; Ding, W.; Hampel, U.

In the present experimental study we investigated the effects of surface characteristics, such as wettability and roughness, on nucleate boiling in de-ionized water at a vertical heater. In the experiments, bubbles were generated from an artificial nucleation site on a stainless steel heater surface. High-resolution optical imaging has been used to capture the bubble life cycle, that is, departure, sliding, and lift-off. We found, that the lower wettability leads to larger departure diameter, longer sliding and larger lift-off diameter of bubbles. Also surface roughness effects have been analyzed and it was found that bubble departure and lift-off diameters are smaller and departure period is longer for a smooth surface. Bubble sliding velocity was found faster for a rough surface compared to a smooth surface. It was also found that the roughness is very influential to bubble growth and departure, which can be explained by considering its interaction with the microlayer underneath the bubble. An “optimal roughness”, which accelerates the bubble growth, was found. The knowledge gained from this study shall be particularly useful to improve nucleate boiling models for numerical simulations.

Keywords: vertical heater; nucleate boiling; bubble dynamics; wettability; optimal roughness

Permalink: https://www.hzdr.de/publications/Publ-24937
Publ.-Id: 24937


A few structural remarks on matrix PTQM and beyond

Günther, U.

In the first part of the talk, the historical and structural origin of PT-symmetric ix3 quantum models is briefly sketched: the Yang-Lee edge singularities for the distribution of the zeros of the partition function of the 2D Ising model in the complex plane, the close relation to criticality in the complex extended Landau-Ginzburg model for 2nd-order phase transitions, Fisher's infra-red (IR) approximation near criticality by a quantum field theory with ix3 coupling. Recent conceptually puzzling results from operator theoretic investigations of related quantum mechanical toy models with PT-symmetric ix3 couplings are reinterpreted in this phase transition context.
In the second part of the talk, the specific structural features of PT-symmetric matrix models are discussed: hidden group theoretical aspects, Lie triple systems following from Cartan decompositions of the corresponding Lie algebras, projectivization embeddings to resolve singularities at PT phase transitions. Starting from these structural findings for finite-dimensional PT-symmetric matrix setups, possible technically feasible extensions toward infinite-dimensional Hilbert-Schmidt Lie groups, Fredholm groups and PT-symmetry related Hilbert-Schmidt Grassmannians are sketched.

Keywords: PT symmetric quantum systems; phase transitions; 2D Ising model; Landau-Ginzburg model; infra-red limit; criticality; operator theory; group theory; Lie triple systems; projectivization embeddings; Hilbert-Schmidt Lie groups; Fredholm groups; Hilbert-Schmidt Grassmannians

  • Invited lecture (Conferences)
    PHHQP16: Progress in Quantum Physics with Non-Hermitian Operators, 08.-12.08.2016, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-24936
Publ.-Id: 24936


From Landau-Ginzburg to PTQM: a few structural remarks

Günther, U.

The historical and structural origin of PT symmetric ix3 quantum models is briefly sketched. Open questions are discussed and related possible lines for future research are suggested.

Starting from the Yang-Lee result on the distribution of complex zeros of the partition function for the 2D Ising model the structure and origin of the so called Yang-Lee edge singularities is discussed. The close structural relation to complex extended criticality in the Landau-Ginzburg model of 2nd-order phase transitions is shown and Fisher's result is recalled on the field theoretical infra-red (IR) limit of the fluctuating fields as an effective quantum field theory (QFT) with ix3 coupling. Based on this specific phase-transition related conceptual background of the ix3 model recent operator-theoretic findings and still open puzzles of the corresponding quantum mechanical toy model approximations are interpreted as having their origin in such still operator-theoretically unexplored phase-transition related model peculiarities. Possible strategies for future research are briefly sketched to fill corresponding mathematical and technical gaps.

Keywords: PT quantum systems; 2D Ising model; Yang-Lee edge singularities; IR-limit; Landau-Ginzburg theory of phase transitions; operator theory

  • Invited lecture (Conferences)
    Analytic and algebraic methods in physics XIII, 06.-09.06.2016, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-24935
Publ.-Id: 24935


Full-field PIXE imaging: Multi-frame super-resolution to overcome optics pattern and imaging-based resolution limitations

Buchriegler, J.; Klingner, N.; Munnik, F.; Nowak, S. H.; von Borany, J.; Ziegenrücker, R.

The combination of a pnCCD-based detector (264 x 264 pixels) with a polycapillary X-ray optics was installed and examined at HZDR [1]. The set-up is intended for PIXE imaging with protons (2-4 MeV) to survey large, flat/polished geological samples with respect to their (trace) elemental composition. In the standard configuration a 1:1 polycapillary X-ray optics (78 mm length, 20 µm capillary diameter) is used to guide the emitted photons towards the pnCCD-chip divided into nearly 70000 pixels. Their dimensions of 48 x 48 µm² cause a native lateral resolution of about 100 µm. By applying dedicated sub-pixel algorithms to recalculate the footprint of the photon’s electron cloud in the chip [2], this limitation can be bypassed and the lateral resolution is then mainly determined by the capillary’s diameter.
Nevertheless, all images gathered with this kind of set-up from a single measurement are superimposed by the optics pattern. The optics’ capillaries are grouped in hexagonal bundles during the fabrication process and these bundles are grouped together again. This process results in a reduced transparency in the regions where the bundles are joint making the hexagonal pattern visible. This influence can be (largely) removed by combining several short measurements with slightly shifted positions. The optics pattern is averaged out and in addition the lateral information (shift-lengths) can be used to further improve the resolution limit beyond the pixels’/capillaries’ dimensions. The total measurement time can be kept almost similar by dividing the single measurement time by the number of “shots” without losing statistics/sensitivity.
Results from descriptive image-sets of first test-measurements will be shown to demonstrate the potential of this technique for full-field PIXE imaging.

[1] D. Hanf et al., NIM B, Vol. 377, pp. 17-24 (2016).
[2] S.H. Nowak et al., X-ray Spec., Vol. 44 (3), pp. 135-140 (2015).

Keywords: full-field imaging; capillary optics; super resolution

  • Lecture (Conference)
    15th International Conference on Particle Induced X-ray Emission, 02.-07.04.2017, Split, Croatia

Permalink: https://www.hzdr.de/publications/Publ-24934
Publ.-Id: 24934


Unravelling the structure of the ocean-continent transition from high resolution, photo-based 3D reconstructions of onshore dyke complexes

Kirsch, M.; Kaiser, A.; Eltner, A.

The temporal and spatial partitioning of strain between faulting and magmatism during continental breakup has important implications for the development of the crust- and upper mantle structure at rifted margins, but remains poorly understood. Late Neoproterozoic basaltic dyke complexes emplaced into continental basement and sedimentary cover units in the northern Scandinavian Caledonides represent an onshore-analogue of an ocean-continent transition. The dykes and their host-rocks are largely unaffected by Caledonian deformation and metamorphism, and are excellently exposed in three dimensions owing to a combination of glacial dissection and glacial retreat. Many of these outcrops of potentially high scientific value remain unmapped, mainly because they occur along steep, up to 300 m high ridges of glacier cirques in rugged mountain terrain that is largely inaccessible for traditional field mapping. Combined terrestrial and UAV-based Structure-from-Motion (SfM) photogrammetry provides an accurate and quick method of obtaining high resolution 3D information of such outcrops with minimal logistical effort. SfM-derived point clouds can be processed to identify structural discontinuities, such as faults and lithological contacts, and extract parameters such as strike, dip, thickness, density, and relative sequence of emplacement of the dykes. Based this information, the history of progressive intrusion and tilting can be reconstructed, and the amount of tectonic extension vs. magmatic dilation estimated. To demonstrate the effectiveness of this approach, we present a case study from a quarry in Lusatia, Germany. Here, like in northern Scandinavia, several generations of cross-cutting basalt dikes are exposed along a vertical, rocky cliff, but with the benefit of easy accessibility, permitting direct observation and verification of the digital data with field measurements. To improve accuracy, and to allow the extraction of oriented and scaled data as well as draping of independently acquired spectral data, ground control points are established in the scene using total station surveying. Multi-and hyperspectral data will potentially be used as complementary information to accurately distinguish composite dikes lacking intervening screens of host-rock.

Keywords: Structure-from-motion photogrammetry; structural geology; rifting

  • Poster
    2nd Virtual Geoscience Conference, 21.-23.09.2016, Bergen, Norway

Permalink: https://www.hzdr.de/publications/Publ-24933
Publ.-Id: 24933


Differential sorption behavior of U(VI) and Pu(VI) dependent on their redox chemistry

Hellebrandt, S.; Knope, K. E.; Lee, S. S.; Lussier, A. J.; Stubbs, J. E.; Eng, P. J.; Soderholm, L.; Fenter, P.; Schmidt, M.

In a recent paper (Schmidt et al. 2013) our group suggested the surface-catalyzed formation of Pu(IV)-oxo-nanoparticles due to an enhanced concentration of Pu(III) at the surface of muscovite mica in equilibrium with a small amount of Pu(IV). The study took three possible pathways for the reaction into account: (1) Pu(III) adsorbs on the muscovite surface, where the oxidation to Pu(IV) takes place. (2) The oxidation of Pu(III) to Pu(IV) happens in solution, whereupon Pu(IV) adsorbs on the surface. In both cases (1) and (2) the increased Pu(IV) concentration leads to oligomerization and afterwards the formation of Pu(IV)-oxo-nanoparticles. Another pathway (3) is the formation of Pu(IV)-oxo-nanoparticles in solution which subsequently adsorb at the mica surface. This pathway was considered less likely, due to a clear enhancement of the reaction in the presence of the interface, which cannot be explained by this process. Motivation of the current study was to test the viability of these mechanisms, but also to investigate the interfacial reactivity of Pu’s various oxidation states.
The mobility of radionuclides in the environment and thus their hazard potential will be controlled by their reactivity at the water/mineral interface. Thus, it is necessary to understand how Pu behave in contact with mineral surfaces on a molecular level, to make reliable long-term predictions about the safety of a nuclear waste repository. In order to understand these processes analytical methods shall ideally be both surface specific and sensitive. X-ray reflectivity techniques, particularly resonant anomalous X-ray reflectivity (RAXR) and crystal truncation rod (CTR) measurements have proven to be a successful combination to investigate geochemical interfacial regimes (Fenter 2002). Plutonium is one of the most important radionuclides in term of nuclear waste disposal due to its long half-life period and high radiotoxicity. That’s why it has been subject of different studies over the last decades. While these studies could show an enhancement of the mobility of plutonium in the presence of colloidal matter (Kersting et al., 1999 and Novikov et al., 2006), the formation of Pu(IV)-nanoparticles is still content of ongoing research (e.g. Kersting 2013, Walther & Deneke 2013).
In the current study a comparison of the interaction of UO2 2+ and PuO2 2+ ([Pu] = 0.1 mmol L-1, [U] = 1 mM mmol L-1, I(NaCl) = 0.1 mol L-1, pH 3.2 ± 0.2) with muscovite mica and the effect of the actinides’ different redox properties were investigated using a combination of surface X ray diffraction, alpha spectrometry and grazing-incidence X-ray adsorption near-edge structure (GI-XANES) spectroscopy. RAXR data of a Pu(VI) solution in contact with muscovite show a broad Pu distribution, which cannot be explained by simple ionic adsorption of PuO2 2+, indicating the formation of Pu(IV)-oxo-nanoparticles. Alpha spectrometry confirms these findings; the occupancy was determined to be ~ 8.3 Pu/AUC (where AUC = 46.72 Å2 is the unit cell area). This means the mechanism of the redox partner independent formation of Pu(IV)-nanoparticles previously observed for Pu(III) can be confirmed for Pu(VI) as well.
UO2 2+ shows clearly different performance. No RAXR signal was observable, indicating no adsorption of UO2 2+. The persistence of the hexavalent oxidation state of U was confirmed by GI-XANES spectroscopy. Furthermore, Alpha spectrometry and GI-XANES spectroscopy showed very weak signals or no signal at all, in agreement with the RAXR findings. Assuming that the sorption behavior of UO2 2+ and PuO2 2+ is equivalent excluding their redox chemistry, no Pu(VI) should be present at the surface. Therefore, the previously proposed mechanism (1) cannot contribute significantly to the observed formation of Pu(IV)-oxo-nanoparticles from Pu(VI) solution. To distinguish mechanisms (2) and (3) UV/Vis spectroscopy was performed similar to our previous study. No Pu(IV) was detectable, even if measured over a longer periode of time than available for the X-ray reflectivity experiment. Hence mechanism (3) also appears to be implausible. Apparently, the observed formation of Pu(IV)-nanoparticles follows mechanism (2). Because of the redox properties of Pu, an equilibrium of Pu(IV), Pu(V) and Pu(VI) will be present in solution. Thus available Pu(IV) will adsorb on the muscovite (001) basal plane. The tetravalent oxidation state of interfacial Pu was confirmed by GI XANES spectroscopy. Since a threshold is reached polymerization occurs as a consequence of hydrolysis, through an olation (Knope et al., 2015) or oxolation (Knope & Soderholm, 2013) mechanism.

Keywords: Plutonium; Pu; Uranium; U; Redox; Sorption; Muscovite; Nanoparticles

  • Lecture (Conference)
    Plutonium Futures - The Science 2016, 18.-22.09.2016, Baden-Baden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24932
Publ.-Id: 24932


Self-Organized Compound Semiconductor Patterning by Polyatomic Ion Irradiation

Bischoff, L.; Böttger, R.; Pilz, W.; Facsko, S.; Heinig, K.-H.

Irradiation of solids by heavy polyatomic ions (e.g Au2, Bi3) can cause localized melting at the ion impact point due to the enhanced energy density in the collision cascade of a polyatomic ion impact [1]. Former studies demonstrated the formation of high aspect ratio, hexagonal dot patterns on Ge, Si and GaAs after high fluence, normal incidence irradiation choosing a suited combination of energy density deposition (i.e. poly- or monatomic ions) and substrate temperature, which facilitated transient melting of the ion collision cascade volume [2-5].
This study underscores the universality of this ion impact-melting-induced, self-organized pattern formation mechanism probing the compound semiconductors InSb and GaSb under polyatomic Au ion irradiation with various irradiation conditions.
Calculations of the needed melting energies per atom (Emelt) for different materials show, that among others InSb and GaSb are preferring candidates for a successful surface patterning by mon- and polyatomic heavy ions.
HRSEM, AFM and EDX analysis of irradiated surfaces reveal that for compound semiconductors, additional superstructures are evolving on top of the regular semiconductor dot patterns, indicating superposition of a second dominant driving force for pattern self-organization.
[1] C. Anders et al., Phys. Rev. B 87 (2013) 245434.
[2] L. Bischoff et al., Nucl. Instr. Meth. Phys. Res. B 272 (2012) 198.
[3] R. Böttger et al., J. Vac. Sci Technol. B 30 (2012) 06FF12.
[4] R. Böttger et al., Phys. Stat. Sol. RRL 7 (2013) 501.
[5] L. Bischoff et al., Appl. Surf. Sci. 310 (2014) 154.

Keywords: Surface pattern; polyatomic ions; temperature; angle of incidence

  • Lecture (Conference)
    Workshop für Ionenstrahlen und Nanostrukturen, 12.-15.02.2017, Göttingen, Germany

Permalink: https://www.hzdr.de/publications/Publ-24931
Publ.-Id: 24931


Time of Flight Spectrometry in the HIM

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

Time of Flight Spectrometry in the HIM
N. Klingner1,2*, R. Heller1, G. Hlawacek1, J. von Borany1 and S. Facsko1
1 Ion Beam Center (IBC), Institute for Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Bautzner Landstraße 400, 01328 Dresden, Germany
2 Technical University Dresden, School of Science, Helmholtzstraße 10, 01069 Dresden, Germany
*n.klingner@hzdr.de
Helium Ion Microscopy (HIM) is well known for its high-resolution imaging and nano fabrication capabilities. However, in terms of analytic capabilities it lacks behind comparable techniques such scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Although several primary and secondary particles are available, to date none of them has been exploited in a practical way to obtain analytic information.
Here, we present the first successful attempt to use time of flight backscattering spectrometry (TOF-BS) and secondary ion mass spectrometry (TOF-SIMS) in the HIM for materials characterization [1]. The successful use of sputtered particles for analytic purposes has also been demonstrated by adding a sophisticated SIMS spectrometer to the HIM [2].
For the TOF measurements the start pulse is generated by chopping the primary beam of the ion microscope using the build-in blanker and a custom made electronics that allows pulse length of 10 ns to 250 ns. The stop signal is given by the arrival of the backscattered particles at the counting micro channel plate. The setup provides high lateral resolution and a good time resolution. Moreover it is minimal invasive to the microscope and therefore the high-resolution capabilities of the device are not derogated when the TOF setup is not in use.
TOF-BS spectra of thin HfO2 films on Si are presented in fig. 1. The time resolution is limited by the physical length of the microscope blanker to approximately 17 ns or 5.4%. This value can be decreased to 2.7% by using a longer flight path. Thanks to a home built scan electronic to control the beam, TOF data can be recorded also in imaging mode. This allows an efficient post acquisition analysis by applying energy filters to extract the elemental distribution. A lateral resolution of 54 nm has been achieved so far. Although this is significantly worse than the native resolution of the tool, this value is close to the physical limit and can be overcome by using correlative approaches in connection with the high resolution SE data available in the HIM.
Modifying the sample holder slightly one can also perform TOF-SIMS. The sputtered particles are accelerated towards the stop detector of the TOF setup by means of a high voltage applied to the sample and a grounded grid. TOF-SIMS spectra obtained from different samples are presented in fig. 2. TOF-BS and TOF-SIMS performed in-situ complement each other and therefore deliver a maximum of compositional information on the sample.

References
[1] N. Klingner, R. Heller, G. Hlawacek, J. von Borany, J. A. Notte, J. Huang, S. Facsko: “Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry”, Ultramicroscopy 162 (2016), 91-97. DOI:10.1016/j.ultramic.2015.12.005
[2] T. Wirtz, P. Philipp, J.-N. Audinot, D. Dowsett, S. Eswara. “High-resolution high- sensitivity elemental imaging by secondary ion mass spectrometry: from traditional 2D and 3D imaging to correlative microscopy”, Nanotechnology 26 (2015), 434001. DOI:10.1088/0957-4484/26/43/434001

  • Lecture (Conference)
    The 1st International Conference on Helium Ion Microscopy and Emerging Focused Ion Beam Technologies, 06.10.2016, Luxembourg City, Luxembourg
  • Poster
    Joint ICTP-IAEA Advanced Workshop on High Sensitivity 2D & 3D Characterisation and Imaging with Ion Beams, 28.09.2016, Trieste, Italien

Permalink: https://www.hzdr.de/publications/Publ-24930
Publ.-Id: 24930


Structural, Optical and Electrical Characteristics of Low Temperature Grown BaSrTiOx Thin Films

Bayrak, T.; Goldenberg, E.; Biyikli, N.

Among several perovskite oxides BaSrTiOx (BST) thin films have attracted a great interest for their potentials in oxide-based electronics. However, their reliability and efficiency depend strongly on the precise knowledge of microstructure, as well as optical and electrical constants. In the present work, BST films were deposited using radio frequency magnetron sputtering technique on UV fused silica and Si substrates at room temperature. The dependences of film microstructure, surface morphology, absorption edge, refractive index, and dielectric constants on deposition pressure, partial oxygen flow and the post-deposition annealing were examined by grazing-incidence X-ray diffraction, scanning electron microscopy, spectrophotometry, ellipsometry, as well as photoluminescence, capacitance-voltage and current-voltage measurements. Well-adhered, uniform and amorphous films were prepared at room temperature. For all as-deposited films, the average optical transmission was ~85% in the visible and near infrared spectrum. The refractive indices of BST films were in the range of 1.90 to 2.07 (λ = 550 nm) as a function of deposition conditions. Post-deposition annealing at 800 oC for 1 hr produced polycrystalline films, increased refractive indices and dielectric constants but considerably lowered film optical transmission. Frequency dependent dielectric constants were found to be 46-72, and the observed leakage current was very small ~1A. Initial results revealed that low-temperature-grown BST thin films have promising properties for device applications.

  • Poster
    IHRS NanoNET International Workshop, 30.08.-02.09.2016, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-24929
Publ.-Id: 24929


Coulomb breakup of neutron-rich 29,30Na isotopes near the island of inversion

Rahaman, A.; Datta, U.; Aumann, T.; Beceiro-Novo, S.; Boretzky, K.; Caesar, C.; Carlson, B. V.; Catford, W. N.; Chakraborty, S.; Chartier, M.; Cortina-Gil, D.; de Angelis, G.; Diaz-Fernandez, P.; Emling, H.; Ershova, O.; Fraile, L. M.; Geissel, H.; Gonzalez-Diaz, D.; Johansson, H.; Jonson, B.; Kalantar-Nayestanaki, N.; Kröll, T.; Krücken, R.; Kurcewicz, J.; Langer, C.; Le Bleis, T.; Leifels, Y.; Marganiec, J.; Münzenberg, G.; Najafi, M. A.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Plag, R.; Reifarth, R.; Ricciardi, V.; Rigollet, C.; Rossi, D.; Scheidenberger, C.; Scheit, H.; Simon, H.; Taylor, J. T.; Togano, Y.; Typel, S.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Winfield, M.; Yakorev, D.; Zoric, M.; Weigand, J. S.

First results are reported on the ground state configurations of the neutron-rich 29,30Na isotopes, obtained via Coulomb dissociation (CD) measurements.
The invariant mass spectra of these nuclei have been obtained through measurement of the four-momenta of all decay products after Coulomb excitation of those nuclei on a 208Pb target at energies of 400-430 MeV/nucleon using the FRS-ALADIN-LAND setup at GSI, Darmstadt. Integrated inclusive Coulomb-dissociation cross-sections (CD) of 89 (7) mb and 167 (13) mb for one neutron removal from 29Na and 30Na, respectively, have been extracted up to an excitation energy of 10 MeV. The major part of one neutron removal, CD cross-sections of those nuclei populate the core, in its’ ground state. A comparison with the direct breakup model, suggests the predominant occupation of the valence neutron in the ground state of 29Na(3/2+) and 30Na(2+) is the d-orbital with a small contribution from the s-orbital, which are coupled with the ground state of the core. One of the major components of the ground state configurations of these nuclei are 28Nags(1+) ⊗ νs,d and 29Nags(3/2+) ⊗ νs,d,respectively. The ground state spin and parity of these nuclei obtained from this experiment are in agreement with earlier reported values. The spectroscopic factors for the valence neutron occupying the s and d orbitals for these nuclei in the ground state have been extracted and reported for the first time. A comparison of the experimental findings with shell model calculation using the MCSM suggests a lower limit of around 4.3 MeV of the sd − pf shell gap in 30Na.

Keywords: Coulomb-dissociation 29Na 30Na breakup spin parity

Permalink: https://www.hzdr.de/publications/Publ-24927
Publ.-Id: 24927


In-situ synchrotron studies of dendritic growth in solidifying Ga – In alloys

Grenzer, J.; Shevchenko, N.; Roshchupkina, O.; Baehtz, C.; Hoppe, D.; Cantelli, V.; Rack, A.

X-ray absorption contrast techniques are an important diagnostic tool to investigate solidification processes in metallic alloys. This work is devoted to an in situ visualization of the dendritic growth during the bottom-up solidification of a Ga-25wt%In alloy under natural convection. The coupling of X-ray imaging with X-ray diffraction techniques provides additionally information of the crystallographic orientation of the growing dendrites.
A main advantage of X-ray radiography is the possibility to study simultaneously solidification phenomena on different length scales delivering information on both: the dendrite structure and the flow patterns especially in the vicinity of solidification front. Melt flow, mainly the convective transport of the solute, induces various effects on the dendrite and grain morphology [5]. All these phenomena depend sensitively on the local conditions like the dendrite arm spacing and orientation, the detachment of side branches, the local direction and intensity of the flow it self [3-5]. A more detailed analysis of these particular processes requires a much better spatial resolution. Using synchrotron radiation the spatial resolution of the radiography experiment was improved by more than a factor of 10 reaching a value of below 1µm. Moreover, using synchrotron radiation, the time to record a tomogram was considerably reduced making it possible to visualize a stable dendrite structure in a melt flow.
An other not sufficiently investigated phenomenon is the orientation selection in dendrite evolution. It was demonstrated that the primary dendrite growth directions can vary continuously between different crystallographic directions as a function of the composition–dependent anisotropy parameters [6]. Therefore a challenging part of this experiment was the combination of two in situ techniques: X-ray radiography and synchrotron X-ray diffraction. X-ray diffraction measurements can help to reconstruct crystallographic orientations of growing dendrites.
The first radiography / diffraction experiments with solidifying Ga-25wt%In alloy were performed at BM20 and ID19 at a spatial resolution of < 0.5 µm. The radiography/ diffraction experiments performed at the beamline BM20 were carried out at an energy of 28.5keV, where as at ID 19 the radiography and tomographic experiments were performed at energies at about 65keV using a filtered undulator spectrum without any additional monochromator.
An existing solidification setup and the solidification cell were improved for synchrotron experiments guaranteeing a stable(~0.1°C) temperature gradient to control the convection inside the cell. The nominal composition of the Ga–25wt%In alloy was prepared from 99.99% Ga and 99.99% In. The alloy was melted and filled into the Plexiglas hele-shaw cell with an area of ~230 x 230 mm2 and inner cell thickness of 150μm. The tomography experiment was carried out using a capillary with an inner diameter of 400µm cell.

Keywords: In-Ga alloy solidification crystal growth

  • Poster
    XTOP 2016 – 13th Biennial Conference on High-Resolution X-Ray Diffraction and Imaging, 04.-08.09.2016, Brno, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-24926
Publ.-Id: 24926


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