Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32337 Publications
Untersuchungen zur Partialoxidation von Isobutan in einem Mikroreaktor unter überkritischen Bedingungen.
Huiras, J.;
Die partielle Oxidation von Isobutan durch Sauerstoff in einem Mikroreaktor wurde im überkritischem Zustand zwischen 135 °C und 145 °C unter Verwendung von di-t-butyl peroxide (DTBP) als Initiator untersucht. Dabei wurden das Verhältnis zwischen Isobutan und Sauerstoff, die Verweilzeit, der Druck, die Initiatorkonzentration und die Temperatur variiert. Ziel war es, die Effizienz des Prozesses durch eine Erhöhung der Selektivität des Produkts t-Butyl hydroperoxide (TBHP) und des Umsatzes zu verbessern. Es war insbesondere zu überprüfen, ob sich der Prozess unter diesen Bedingungen durch die Aufhebung von Stofftransportwiderständen gegenüber dem Zweiphasenprozess bei niedrigeren Temperaturen optimieren lässt. Die Reaktionsprodukte TBHP, Azeton, t-butanol und DTBP wurden mittels GC\MS analysiert. Im Rahmen der Arbeit gelang es die höchsten bisher mit einem Mikroreaktor erzielten Umsätze für die Isobutanoxidation zu erzielen. Jedoch gingen die Umsätze nicht wesentlich über die Umsätze hinaus, die aufgrund des zu erwartenden Temperatureffekts bei der Nutzung von überkritischen Bedingungen zu erwarten waren. Auch war die Umsatzerhöhung nur auf Kosten der Selektivität des TBHP zu erzielen. Die Arbeit bietet jedoch aufgrund Ihrer Ergebnisse eine wichtige Grundlage für weitere Untersuchungen.
Keywords: Isobutanoxidation, überkritischer Prozess, Effizienzoptimierung, t-Butylhydroperoxid, Mikroreaktor
  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    63 Seiten

Publ.-Id: 24852 - Permalink


Time-Resolved Studies of the Light-Induced Insulator-Metal Transition in NbO2 and VO2 Thin Films
Beebe, M.; Klopf, J. M.; Wang, Y.; Kittiwatanakul, S.; Lu, J.; Wolf, S. A.; Lukaszew, R. A.;
While vanadium dioxide (VO2) is one of the most extensively studied highly correlated materials, there are intriguing similarities and differences worth exploring in another highly correlated oxide, niobium dioxide (NbO2). Both materials exhibit a thermally-induced first-order insulator-metal transition at a material-dependent critical temperature, which is considerably higher in NbO2 than in VO2 – approximately 1080 K and 340 K in bulk, respectively. This transition, evidenced by up to 6 orders of magnitude change in DC and optical conductivities, can also be induced in VO2 via photo-doping on a sub-picosecond timescale. Here, we present the first ultrafast pump-probe studies on the optically-induced transition of NbO2 thin films and the comparison with similar VO2 films. It is observed that NbO2 films transition faster and exhibit significantly faster recovery time than VO2 films of similar thickness and microstructure, showcasing that NbO2 is a promising material for next generation high-speed optoelectronic devices.
Keywords: (240.0310) Thin films; (310.6860) Thin films, optical properties; (310.6845) Thin film devices and applications; (320.7100) Ultrafast measurements; (320.7130) Ultrafast processes in condensed matter, including semiconductors.

Publ.-Id: 24851 - Permalink


The double role of Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates
Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.;
We have investigated the in-situ surface modification of a SiOx/Si(111) substrate by Ga droplets and its effect on the subsequent self-catalyzed growth of GaAs nanowires. Using a procedure of Ga droplet formation and subsequent re-evaporation prior to the nanowire growth, we found that the number density of nanowires at a given growth temperature can be varied deliberately within four orders of magnitude without affecting the nanowire diameter. A detailed study of the Ga droplet formation in a wide range of substrate temperatures revealed the physical processes that control the number density and size of the droplets.
Keywords: Nanowire, Ga droplets, oxide etching, nanoholes, GaAs, Si substrate
  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy, 04.09.2016, Montpellier, France

Publ.-Id: 24850 - Permalink


Optimierung und Validierung der GC/MS-Methode zur Bestimmung der Reaktionsprodukte der Partialoxidation von Isobutan mit Sauerstoff im Mikroreaktor.
Liu, W.;
Die partielle Oxidation von Isobutan, t-Butyl Hydroperoxid (TBHP) wurde zum ersten Mal als ein Zwei-Phasen-Prozess in einer Kapillare als Mikro Reaktor durchgeführt und analytisch untersucht. Um detaillierte Informationen über Produkte, Ausbeute, Selektivität und Reaktion Wege zu erhalten, mussten die Produkte mittels GC-MS analysiert werden. Zur Trennung der flüssigen Produkte wurde eine GC-MS Methode erstellt, optimiert und validiert, die eine Rxi-5ms-Säule und einen PTV-Injek-tors verwendet. Im Rahmen der Validierung wurden der Konzentrationsfehler wie auch der Mess¬fehler des MS-Signals aus sämtlichen Kalibrierschritten ermittelt sowie die entsprechenden analytischen Normen (z.B. DIN 38402) für die Kalibrierung berücksichtigt. Außerdem wurden statistische Tests auf Trends (nach Neumann), Ausreißer (nach Dixon), Normalverteilung (nach David) etc. durchgeführt. Die flüssigen Produkte wurden mittels MS identifiziert: Als Hauptprodukte traten TBHP, di-t-Butyl-Peroxid (DTBP), t-Butanol (TBA) und Propanone auf. Für die Zielprodukte TBHP und DTBP wurden Korrelationkoeffiuienten von r2 > 0,999, für TBA und Azeton r2 > 0,995 erzielt. Daneben traten Nebenprodukte wie z.B. Methanal, Methanol, Isopropanol, Isobutanol und Isobutanal auf, von denn alle bis auf Methanol und Methanal ebenfalls kalibriert wurden.
Keywords: TBHP, DTBP, Vslidierung, isobutanoxidation
  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas Willms
    68 Seiten

Publ.-Id: 24849 - Permalink


“Reverse Epitaxy” on semiconductor surfaces by low energy ion irradiation
Engler, M.; Ou, X.; Facsko, S.;
Ion beam irradiation can produce different patterns on semiconductor surface. While the surface is amorphized at low temperatures, the surface remains crystalline above the dynamic recrystallization temperature. Reverse Epitaxy leads to pattern formation, which is driven by diffusion of vacancies and adatoms on the surface, above this temperature. The mechanisms of Reverse Epitaxy epitaxy are quite similar to mound formation in homoepitaxial growth. The surface is destabilized in both cases by an effective uphill diffusion current driven by Ehrlich-Schwoebel barriers. The patterns formed depend of step formation energies, diffusion on terraces, and Ehrlich-Schwoebel barriers, which all are anisotropic. Their anisotropy is determined by the surface symmetry. By changing the surface symmetry the resulting patterns are be changed.
  • Invited lecture (Conferences)
    XI-th International Conference on Ion Implantation and other Applications of Ions and Electrons - ION 2016, 13.06.2016, Kazimierz Dolny, Polska

Publ.-Id: 24848 - Permalink


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

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

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

For multiple samples we can extend the idea of ANOVA of measuring the variability of the group means. The variability is measured in terms of the variation matrix. For each entry of the variatin matrix we quantify its quantile in the bootstrap population. We take then the maximum of the quantiles and bootstrap this maximum. In this way we again get a subcompositionally test for equal mean in all samples. Weighted modifications might improve power of the test in case of unequal sample sizes.
  • Lecture (Conference)
    CoDaWork 2017, 06.-9.6.2017, Abbadia San Salvatore, Italia

Publ.-Id: 24847 - Permalink


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

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

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


With regard to testing, there are some philosophical difficulties in a classical ``zero slope hypothesis''. A strict test for dependence could be very misleading when used for model selection in a non-parametric setting. As an alternative we propose to check, whether the prediction by the non-parametric model outperforms the prediction by parametric (constant) one. We propose to compare the jacknifed residuals of the two models. This construction allows to construct all meaningful tests of compositional dependence, namely: global lack of dependence, lack of dependence within a subcomposition, as well as restricted dependence within a subcomposition.
  • Lecture (Conference)
    CoDaWork 2017, 06.-09.06.2017, Abbadia San Salvatore, Italia

Publ.-Id: 24846 - Permalink


Fluid dynamics in novel sandwich packings for absorption and distillation
Sohr, J.; Schubert, M.; Hampel, U.;
Poster zum EMR-Meeting am 21.09.2016 am HZDR
  • Poster
    EMR-Meeting, 21.09.2016, Dresden, Deutschland

Publ.-Id: 24845 - Permalink


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

Publ.-Id: 24844 - Permalink


Metalle schürfen aus Elektronikschrott
Ell, R.; Scharf, C.; (Editors)
Metallurgen entwickeln neue Strategien, um Rohstoffe aus alten Handys zurückzugewinnen.
  • VDI-Nachrichten 44(2016), 23-23

Publ.-Id: 24843 - Permalink


Kritische Rohstoffe aus zweiter Hand
Scharf, C.;
Seit drei Jahren lehre und forsche ich als Professorin für Metallurgie und Recycling der Hochtechnologiemetalle in Freiberg. Mein Team und ich setzen uns für einen nachhaltigen Umgang mit kritischen Metallen und anderen Industriemineralen ein. Wir erforschen neue Verfahren, um beispielsweise Produktionsabfälle zu reduzieren und die Wiederverwertung von Rohstoffen aus Altgeräten zu verbessern. Schlacken, Schlämme, Stäube, Späne oder Abwässer — in der Mineralrohstoff und Metallindustrie gibt es, technisch bedingt, viele Rückstände und damit auch eine große Menge bisher nicht genutzter Wertstoffe. Gemeinsam mit den wiederverwertbaren Stoffen, die in alten Elektrogeräten und sonstigen ausgedienten Produkten stecken, gelten sie inzwischen
als wichtiger Hebel für das Erreichen einer maximalen Ressourceneffizienz in der Kreislaufwirtschaft. Um solche „Rohstoffe aus zweiter Hand“, auch sekundäre Ressourcen genannt, dreht sich die Arbeit meines Forscherteams.
  • Contribution to external collection
    Prof. Roewer: ACAMONTA - Zeitschrift für Freunde und Förderer der Technischen Universität Bergakademie Freiberg, Marienberg: Erzdruck GmbH, 2016, ISSN 2193-309X, 27-28

Publ.-Id: 24842 - Permalink


Synthese neuer Imidazol-Derivate für die Entwicklung eines 18F-PET-Radioliganden zur Bildgebung des Cannabinoid Rezeptors 2 im Gehirn
Hausmann, K.;
Es ist kein Abstract vorhanden.
  • Master thesis
    Universität Leipzig, 2016
    Mentor: Dr. R.-P. Moldovan
    71 Seiten

Publ.-Id: 24841 - Permalink


Entwicklung eines 18F-markierten Radioliganden zur Bildgebung der Phosphodiesterase 10A im Gehirn durch Positronen-Emissions-Tomographie
Wagner, S.;
Es ist kein Abstract vorhanden.
  • Doctoral thesis
    Universität Leipzig, 2016
    Mentor: Dr. Matthias Scheunemann
    166 Seiten

Publ.-Id: 24840 - Permalink


Preliminary Studies on the Partial Oxidation of Isobutane with Oxygen in Multiphase Flows.
Lu, X.;
Oxidation of hydrocarbon is an industrially important reaction. Many valuable chemicals are synthesized by the oxidation of relatively cheap raw materials derived from petroleum. The oxidation of isobutane is one of the most important oxidation oxidation processes. For example, isobutane oxidation can be conducted as the preoxidation in oxirane process to produce propylene oxide and tert.-butanol, in which propylene oxide and TBA are important industrial raw materials and widely used in the syntheses of pharmaceuticals, agrochemicals and other fine chemicals (Qi et al., 2014).
In more recent times, there is more and more interest of researchers in the application of microreactors in chemical engineering because of the opportunities of microreactors in chemical process development and intensification, such as excellent heat and mass transfer (Kashid et al., 2014). In this thesis, the oxidation of isobutane in two-phase flow is investigated in a microreactor (100 m long, 1mm ID). The experiments were carried out under different conditions. The start-up behavior of the oxidation of isobutane has been investigated and discussed. In addition, the effect of temperature, pressure, residence time, oxygen-isobutene ratio, the nitrogen dilution and initiator concentration on the performance of isobutane has also been preliminary investigated and discussed. Furthermore, the rate constant of isobutene oxidation has been calculated for 130 °C.
Keywords: microreactor, isobutane oxidation, two phase flow
  • Diploma thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    89 Seiten

Publ.-Id: 24839 - Permalink


Partikelentstehung und -transport im Reaktorwasser von DWR nach Kühlmittelverluststörfällen (KMV) - Untersuchungen im Labormaßstab
Harm, U.; Kryk, H.; Hampel, U.; Seliger, A.; Renger, S.; Kästner, W.;
Im Rahmen der nuklearen Sicherheitsforschung des Bundesministeriums für Wirtschaft und Energie (BMWi) erfolgten an der Hochschule Zittau/Görlitz (HSZG) in Kooperation mit der Technischen Universität Dresden (TUD) und dem Helmholtz-Zentrum Dresden-Rossendorf (HZDR) experimentelle und methodische Untersuchungen für die systematische Klärung physiko-chemischer Mechanismen im Kühlmittel und deren Auswirkungen auf thermo-fluiddynamische Prozesse im Reaktorkern, welche während des Sumpfumwälzbetriebes als Langzeitnachkühlung nach Kühlmittelverluststörfällen (KMV) in Druckwasserreaktoren (DWR) auftreten können. Durch Korrosionsprozesse an feuerverzinkten Installationen im Sicherheitsbehälter (SHB) von DWR wird Zink in ionischer Form im borierten Kühlwasser gelöst. Die freigesetzten Zink-Ionen werden aus dem Reservoir des Nachkühlmittels im SHB über die Not- und Nachkühlsysteme bis in den Reaktorkern gefördert. Im Reaktor wird das eingespeiste Kühlmittel (KM) aufgeheizt.
Im Fokus generischer Experimente standen Untersuchungen zum Verhalten derart zusam-mengesetzter Fluide unter Berücksichtigung von Temperaturunterschieden zwischen dem Kühlmittelreservoir im SHB und dem Reaktorwasser an den Brennstäben im Reaktorkern. Diese generischen Untersuchungen erfolgten an elektrisch beheizten Stabkonfigurationen, welche die durch Nachzerfallsleistung beheizten Brennstäbe im Kern von DWR nachbildeten. Bei der Aufheizung des zinkhaltigen KM innerhalb solcher Konfigurationen wurden Trübungen durch Kolloidbildung beobachtet, gefolgt von Ausscheidungen partikelförmiger, fester Korrosionsprodukte in Form von Zinkboraten. Diese erschienen in Abhängigkeit von der umgebenden KM- bzw. Staboberflächentemperatur als leicht mobilisierbare, flockenartige Dispersphase oder wiesen schichtenbildenden Charakter auf.
Die temperaturabhängigen Umwandlungen von gelösten Zink-Ionen in feststoffartige Zinkborate bewirkten sowohl Ablagerungen an den Heizstäben als auch an den Abstandshaltern (AH) und führten zu erhöhtem Differenzdruckaufbau über die AH sowie Strömungsumverteilungen in der Stabkonfiguration. In Folge dieser Ablagerungen wurden Änderungen des Wärmetransports vom beheizten Stab ans Fluid nachgewiesen, die eine Aufheizung der Heizstäbe bewirkten und damit sicherheitsrelevanten Charakter hinsichtlich der Nachwärmeabfuhr tragen. Aktuell wird dieses generisch ermittelte Verhalten des Reaktorwassers hinsichtlich der Übertragbarkeit auf sicherheitsrelevante Fragestellungen realer DWR mit Bezug auf anzunehmende Leckgrößen und Nachkühlbedingungen und den daraus resultierenden thermohydraulischen Randbedingungen im Sicherheitsbehälter und im Reaktorkern untersucht. Hierfür werden durch Störfallanalysen die Zustände und Bedingungen abgrenzend ermittelt, bei denen eine Gefährdung der Kernkühlung aus Sicht vorhandener Erkenntnisse zu den physiko-chemischen Effekten eintreten könnte. Wesentliche Untersuchungsschwerpunkte bilden die im SHB von DWR auftretenden chemischen und thermodynamischen Einflüsse auf die Zinkfreisetzung und das Ausfällungs- und Ablagerungsverhalten der Korrosionsprodukte an Heißstellen im Reaktorkern.
Die Untersuchungsergebnisse finden u.a. für die Parametrierung von Simulationscodes sowie in alternativen Modellansätzen Verwendung und dienen der sicherheitstechnischen Einschätzung des DWR-Reaktorverhaltens für verschiedene KMV-Störfallszenarien. Die quantitative Analyse der experimentellen Daten zum zeitlichen Ablauf des Quelle-Senke-Mechanismus der Zinkkorrosion und der Umwandlung des gelösten Zinks in feste Produkte unter realen Störfallbedingungen stellt auf Grund der Komplexität und der gegebenen Rückwirkungen eine Herausforderung dar.
Die Vorhaben werden mit Mitteln des Bundesministeriums für Wirtschaft und Energie (BMWi) unter den Förderkennzeichen 150 1491 und 150 1496 gefördert und fachlich von einer Monitoring Group begleitet, welche sich aus Repräsentanten der Forschungsbetreuung des Projektträgers, Gutachtern, Herstellern und Anlagenbetreibern zusammensetzt.
Keywords: Nuclear energy; Loss of coolant accident; corrosion; zinc release; experiments
  • Contribution to proceedings
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 22.-23.09.2016, Zittau, Deutschland
    Proceedings des Zittauer Kraftwerkschemischen Kolloquiums
  • Lecture (Conference)
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 23.09.2016, Zittau, Deutschland

Publ.-Id: 24838 - Permalink


Helmholtz-Zentrum Dresden-Rossendorf Helmholtz Institute Freiberg for Resource Technology Introduction CHROMIC
Scharf, C.; Kelly, N.; Helbig, T.;
Helmholtz-Zentrum Dresden-Rossendorf
Helmholtz Institute Freiberg for Resource Technology
Introduction
CHROMIC
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730471
This presentation reflects only the author’s views and neither Agency nor the Commission are responsible for any use that may be made of the information contained therein.
  • Invited lecture (Conferences)
    CHROMIC, Kick-Off-Meeting, 07.-08.12.2016, Mol, Belgien

Publ.-Id: 24837 - Permalink


CHROMIC WP4 Presentation
Scharf, C.; Kelly, N.; Helbig, T.;
CHROMIC
WP4 Presentation
Prof. Dr.-Ing. Christiane Scharf (HZDR, HIF)
This project has received funding from the European Union’s Horizon 2020 research and
innovation programme under grant agreement No 730471
This presentation reflects only the author’s views and neither Agency nor the Commission are responsible for any use that may be made of the information contained therein.
  • Invited lecture (Conferences)
    CHROMIC, Kick-Off-Meeting, 07.-08.12.2016, Mol, Belgien

Publ.-Id: 24836 - Permalink


Koordinierungsgespräch HIF – Technikum
Scharf, C.;
Koordinierungsgespräch
HIF – Technikum
Christiane Scharf
29.4.2016, Helmholtz-Zentrum Dresden-Rossendorf
  • Lecture (others)
    Koordinierungsgespräch, SMWK, SAB, SIB, HZDR, 29.04.2016, Dresden-Rossendorf, Deutschland

Publ.-Id: 24835 - Permalink


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

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

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

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

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

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

Was war dabei Ihr Erfolgsrezept?
Ich würde sagen, eine Strategie der kleinen Schritte. Wenn ich mir schon beim Abitur denke, in 20 Jahren musst du auf dieser Position sitzen, dann ist das eine riesige Hürde. Es kann dann schnell passieren, dass man bei den ersten Niederlagen, die mit großer Wahrscheinlichkeit kommen werden, zu verzweifeln beginnt. Es geht eher darum, immer am Ball zu bleiben. Der rote Faden muss erkennbar bleiben, ohne krampfhaft auf ein einziges Ziel hinzuarbeiten. Jeder erfolgreiche Schritt, auch wenn er klein sein mag, bringt dann neue positive Energie.
Das Interview führte Simon Schmitt.
  • Communication & Media Relations
    Interview 11.03.2016
    1 Seiten

Publ.-Id: 24834 - Permalink


Frauen in der Wissenschaft - Karrierewege
Scharf, C.;
Frauen in der Wissenschaft - Karrierewege
Christiane Scharf
Helmholtz-Zentrum Dresden-Rossendorf, 4.3.2016
  • Lecture (others)
    Einladung HZDR-Veranstaltung, Gleichstellungsbüro, 10.03.2016, Dresden-Rossendorf, Deutschland

Publ.-Id: 24833 - Permalink


KIC – Network of Infrastructure for Metal-based Lightweight Materials Metallurgy and Recycling Department
Scharf, C.; Balinski, A.;
KIC – Network of Infrastructure for Metal-based Lightweight Materials
Metallurgy and Recycling Department
Christiane Scharf
Freiberg, 29th November 2016
  • Invited lecture (Conferences)
    KIC – Network of Infrastructure for Metal-based Lightweight Materials Kick-Off-Meeting, 29.11.2016, Freiberg, Deutschland

Publ.-Id: 24832 - Permalink


High Magnetic Moment in Ferrimagnetic NiCo2O4 films via He Ion Irradiation
Pandey, P.; Bitla, Y.; Zschornak, M.; Wang, M.; Xu, C.; Grenzer, J.; Gemming, S.; Helm, M.; Chu, Y.-H.; Zhou, S.;
The spinel NiCo2O4 (NCO) exhibits unique combination of electrical conductivity, infrared transparency, electro catalytic activity, and ferrimagnetic order, which makes it an attractive material for spintronic applications.1 The NCO thin-films electrical and magnetic properties can be manipulated from high temperature ferrimagnetic and metallic to low temperature ferromagnetic and insulating by changing the growth temperature.2 The high quality epitaxial NCO films were grown on MgAl2O4 (100) substrate at ~ 400°C exhibits metallic behavior accompanied by ferrimagnetic order with moment ~ 2 μB/fu.1,2 Here, we report the impact of He-ion irradiation with fluence ranging from 5×1015/cm2 – 3×1016/cm2 on these metallic NCO films. The use of He-ion irradiation results in the coherent control of out-of-plane lattice parameter of these films without changing its in-plane lattice parameter (Figure 1). The comprehensive study of magnetization data reveals the magnetic moment increases drastically to ~ 4 μB/fu (Figure 1). The X-ray absorption spectroscopic study also suggests the possible charge redistribution within the octahedral sites of the NCO films which corroborates well with the increase in the magnetic moment.
  • Poster
    MEMRIOX International Workshop 2016, 25.-27.09.2016, Berghotel Bastei, Germany

Publ.-Id: 24831 - Permalink


SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch Calixarene
Scharf, C.; Balinski, A.;
Ausgangssituation und Zielsetzung
Die Gewinnung von Seltenen Erden (SE) ist aufgrund ihrer Eigenschaften sehr komplex, aufwendig und dadurch kostspielig. Die größten Herausforderungen liegen in der Separation der einzelnen SE-Elemente sowie in der notwendigen Abtrennung von Uran und Thorium. Ziel des Projektes SE-FLECX ist die Entwicklung neuer Extraktionsmittel zur effizienten Trennung der Actinoide (Typ A) und der SE-Elemente (Typ B) und die Auslegung ihres Herstellungsprozesses im industriellen Maßstab.
  • Poster
    r4-Konferenz, Statusveranstaltung, 20.-21.10.2016, Hannover, Deutschland

Publ.-Id: 24830 - Permalink


SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch präorganisierte Calixarene
Scharf, C.; BASF; CMI UVK; TU BAF; Universität Leipzig; Balinski, A.;
SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch präorganisierte Calixarene
Koordinator: Prof. Dr. Christiane Scharf
Förderkennzeichen: 033R132A
r4-Konferenz 2016 | Hannover | 20. und 21. Oktober 2016
Verbundpartner
BASF SE, Ludwigshafen
Helmholtz-Zentrum Dresden-Rossendorf,
Helmholz-Institut Freiberg für Ressourcentechnologie, Freiberg
Und Institut für Ressourcenökologie, Leipzig
CMI UVK GmbH, Montabaur
Technische Universität Bergakademie Freiberg, Freiberg
Universität Leipzig, Leipzig
  • Invited lecture (Conferences)
    r4-Konferenz, Innovative Technologien für Ressourceneffizienz, Statusveranstaltung, 20.-21.10.2016, Hannover, Deutschland

Publ.-Id: 24829 - Permalink


Turn on/off the high-temperature ferromagnetism in Si1-xMnx thin films through Mn-ion implantation
Pandey, P.; Rylkov, V. V.; Yuan, Y.; Semisalova, A. S.; Mikhalevskiy, V. A.; Novodvorskii, O. A.; Tugushev, V. V.; Helm, M.; Zhou, S.;
Silicon based alloys with Mn-ions are a potential candidate for the spintronics applications, as they exhibit complex electric and magnetic phenomena which can be effectively utilized as the integrated-circuit elements in the contemporary microelectronic technology. Though, The Si1-xMnx alloys shows high-temperature ferromagnetism at low Mn concentration x ~ 0.05 – 0.1, but the small solubility of Mn-ions in Si leads to the formation of MnSi1.7 nanoparticles,1 which drives the system in an inhomogeneous phase and makes it irrelevant for the technological applications. However, a high Mn concentration in the Si1-xMnx alloys screens the precipitation of different inhomogeneous magnetic phases with high Curie temperature (TC).2 In this context, a set of thin films of Si1-xMnx (x = 0.44 – 0.57) alloy were prepared by the pulsed laser deposition technique on Al2O3 (0001) substrate. We have found room temperature ferromagnetism and a large magnetic moment for the Si0.43Mn0.57 film as compared to the rest of samples. But, surprisingly, the TC (as well as the moment) of Si0.43Mn0.57 film drastically decreases from 300 K to ~ 40 K as the Mn-ion concentration was increased in the film through the ion implantation process. In contrast, the stoichiometric film Si0.5Mn0.5 exhibits a huge increase in the magnetic moment by one-order in magnitude after ~ 2% Mn-ion implantation. The TC of the stoichiometric film also increases from 50 K to 300 K with the increase in the Mn-ion concentration.
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft e.V, 06.-11.03.2016, Regensburg, Germany

Publ.-Id: 24828 - Permalink


Hydrodynamic characterization of a novel external loop airlift inverse semi-fluidized bed reactor packed with loofa particles
Hegeholz, G.; Mohammed, I. H. M.; Schubert, M.;
In biochemical processes, column reactors replaced the stirred tank reactors for their advantages, like mild agitation. Among different configurations of column reactors airlift reactors constitute attractive systems for bio-catalyzed reactions due to the simple de-sign, low investment and operation costs. The advantages of combined external loop airlift and fluidized bed reactor in the downcomer over three-phase fluidized bed reactor and other configuration of airlift reactors are the unique hydrodynamic properties as it requires lower liquid flow rate for complete suspension of solid and good contact among the phases, easy removal of particles, rapid mixing, and easier scale up. This enables inverse fluidizing of low-density particles in the downcomer zone, characterized by low shear rates.
Keywords: fluidized airlift reactor, riser, downcomer, low-density particles, wire mesh sensor
  • Diploma thesis
    TU Dresden, 2016
    Mentor: Hampel Uwe

Publ.-Id: 24827 - Permalink


Metallurgy and Recycling Division
Scharf, C.;
Metallurgy and Recycling Division
Christiane Scharf
Freiberg, 10th March 2016
  • Lecture (others)
    Metallurgy and Recycling Division, Visit of the company Outotec, 10.03.2016, HIF, Deutschland

Publ.-Id: 24826 - Permalink


Recycling of metals by vacuum distillation and solvent extraction
Scharf, C.;
  • Invited lecture (Conferences)
    METYK Metallialan ympäristö- ja kiertotalous, METYK Seminar, 14.06.2016, Pori, Finnland

Publ.-Id: 24825 - Permalink


Metallurgy and Recycling Department
Scharf, C.;
Metallurgy and Recycling Department
Visit of Prof. Mari Lundström
Christiane Scharf
Freiberg, 15th Dezember 2016
  • Lecture (others)
    Metallurgy and Recycling Department Visit of Prof. Mari Lundström (Aalto University), 15.12.2016, HIF, Deutschland

Publ.-Id: 24824 - Permalink


Direct numerical simulations of particle attachment to solids and deformable surfaces
Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.;
The present talk deals with the transport and the deposition of micron particles to solid wall surfaces and fluid-fluid interfaces. Various particle-interface models are presented and tested with direct numerical flow simulations. The various micro processes observed during the particle attachment and particle detachment are well captured. The results compare well with those experimentally obtained on-site.
  • Lecture (others)
    Institute seminar, 14.12.2016, Karlsruhe, Germany

Publ.-Id: 24823 - Permalink


Metallurgy and Recycling Department
Scharf, C.;
Metallurgy and Recycling Department
Visit of Prof. Peter Tasker
Christiane Scharf
Freiberg, 13th Dezember 2016
  • Lecture (others)
    Metallurgy and Recycling Department Visit of Prof. Peter Tasker (University Edinburgh), 13.12.2016, HIF, Deutschland

Publ.-Id: 24822 - Permalink


Optical components in harsh space environment
Pelizzo, M. G.; Corso, A. J.; Tessarolo, E.; Zuppella, P.; Böttger, R.; Hübner, R.; Della Corte, V.; Palumbo, P.; Taglioni, G.; Preti, G.; Foggetta, L.; Valente, P.; Rancoita, P.; Martucci, A.; Napolitani, E.;
Space exploration is linked to the development of increasingly innovative instrumentation, able to withstand the operation environment, rich in ion particles and characterized by high temperatures. Future space missions such as JUICE and SOLAR ORBITER will operate in a very harsh and extreme environment-. Electrons and ions are considered among the causes of potential damage of the optical instrumentation and components. Development of hard coatings capable to preserve their optical properties is pivotal. Different coating materials have been exposed to ion irradiation in particle accelerators. Change in optical performances has been observed in the extreme ultraviolet and visible spectral region and structural properties have been analyzed by different techniques. The knowledge of the damage mechanisms and thresholds allows the selection of more promising candidate materials to realize the optical components for the new frontiers space missions. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Keywords: Optical components ; Optical properties ; Particle accelerators ; Particles ; Coating ; Electrons ; Extreme ultraviolet ; Hard coatings ; Ions

Publ.-Id: 24821 - Permalink


Metallurgy and Recycling Division
Scharf, C.;
Metallurgy and Recycling Division
Christiane Scharf
Freiberg, 8th September 2016
  • Lecture (others)
    Metallurgy and Recycling Division, Einladung Herr Wilson (Aalto University), 08.09.2016, HIF, Deutschland

Publ.-Id: 24820 - Permalink


Recycling of Strategic Elements by Extractive Metallurgy
Scharf, C.;
Summer School 2016
Recycling of Strategic Elements by Extractive Metallurgy
Christiane Scharf
5th October 2016, TU Dresden
  • Invited lecture (Conferences)
    Summer School 2016, 05.10.2016, Dresden, Deutschland

Publ.-Id: 24819 - Permalink


Sub-Channel Flow Behavior in Vertical Tube Bundles in Bubble Columns
Möller, F.; Hampel, U.; Schubert, M.;
Bubble columns are simple multiphase reactor and contactor devices, which are widely applied due to their superior heat and mass transfer characteristics. Furthermore, they are relatively simple in construction due to the absence of moving parts. Bubble columns are used for various chemical processes such as methanol and Fischer-Tropsch synthesis. Since most of the processes running in bubble columns are of exothermic nature, a variety of heat exchangers, e.g. internal heat exchanging tube bundles, are installed in order to ensure proper reaction conditions. Such tube bundles cover a significant ratio (up to 60 %) of the entire column cross-section. Accordingly, the column performance is dominated by the hydrodynamics proceeding at smaller characteristic length scale in the sub-channels. However, the evolving sub-channel flow has not been studied yet.
Therefore, this study focusses on the analysis of the multiphase flow in the sub-channels of an internal heat exchanging tube bundle with longitudinal flow of various configurations (square and triangular pattern) and tube diameter sizes (8 mm and 13 mm). The investigations were carried out in a 100 mm (inner diameter) bubble column for an air / deionized water system using a perforated plate type sparger. To ensure comparability, the covered rector’s cross-sectional area was kept similar for all configurations.
The hydrodynamic parameters were studied separately for sub-channels at various radial positions in the bundles as well as for the entire column. Approaches to link experimental data from both scales for a multiscale evaluation are suggested. Furthermore, the results are compared with an advanced horizontal stage-model considering breakup and coalescence mechanisms to calculate the bubble size distribution, breakup and coalescence rates and the overall gas holdup.
  • Lecture (Conference)
    Jahrestreffen Dresden - Jahrestreffen der ProcessNet-Fachgruppen Mehrphasenströmungen, Partikelmesstechnik, Zerkleinern und Klassieren, Computational Fluid Dynamics, Mischvorgänge und dem TAK Aerosoltechnologie, 14.-17.03.2017, Dresden, Deutschland

Publ.-Id: 24817 - Permalink


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

Publ.-Id: 24816 - Permalink


Creating nanoporous graphene with swift heavy ions
Vazquez, H.; Ahlgren, E. H.; Ochedowski, O.; Leino, A. A.; Mirzayev, R.; Kozubek, R.; Lebius, H.; Karlusic, M.; Jaksic, M.; Krasheninnikov, A. V.ORC; Kotakoski, J.; Schleberger, M.; Nordlund, K.; Djurabekova, F.
We examine swift heavy ion-induced defect production in suspended single layer graphene using Raman spectroscopy and a two temperature molecular dynamics model that couples the ionic and electronic subsystems.We show that an increase in the electronic stopping power of the ion results in an increase in the size of the pore-type defects, with a defect formation threshold at 1.22e1.48 keV/layer. We also report calculations of the specific electronic heat capacity of graphene with different chemical potentials and discuss the electronic thermal conductivity of graphene at high electronic temperatures, suggesting a value in the range of 1Wm?1 K?1. These results indicate that swift heavy ions can create nanopores in graphene, and that their size can be tuned between 1 and 4 nmdiameter by choosing a suitable stopping power.
Keywords: Graphene, ion irradiation, two-temperature model, atomistic simulations

Downloads:

  • Secondary publication expected

Publ.-Id: 24815 - Permalink


Vibrational properties of a two-dimensional silica Kagome lattice
Björkman, T.; Skakalova, V.; Kurasch, S.; Kaiser, U.; Meyer, J. C.; Smet, J. H.; Krasheninnikov, A. V.ORC
Kagome lattices are structures possessing fascinating magnetic and vibrational properties, but in spite of a large body of theoretical work, experimental realizations and investigations of their dynamics are scarce. Using a combination of Raman spectroscopy and density functional theory calculations, we study the vibrational properties of two- dimensional silica (2D-SiO2), which has a kagome lattice structure. We identify the signatures of crystalline and amorphous 2D-SiO2 structures in Raman spectra and show that, at finite temperatures, the stability of 2D-SiO2 lattice is strongly influenced by phonon−phonon interaction. Our results not only provide insights into the vibrational properties of 2D-SiO2 and kagome lattices in general but also suggest a quick nondestructive method to detect 2D-SiO2.
Keywords: Raman spectroscopy, first-principles calculations, 2D materials

Publ.-Id: 24814 - Permalink


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

(1) M. Schubert, M. Piechotta, M. Beyer, E. Schleicher, U. Hampel and J. Paschold, ‘An imaging technique for characterization of fluid flow pattern on industrial-scale column sieve trays’, Chemical Engineering Research and Design, vol. 111, pp.138–146, 2016.
Keywords: Distillation Column, Sieve Tray, Tray Efficiency, Flow Non-idealities
  • Poster
    Treffen des Wissenschaftlichen Programmausschusses EMR, 21.-22.09.2016, HZDR, Dresden, Germany

Publ.-Id: 24813 - Permalink


CFD codes benchmark on TOPFLOW-PTS experiment
Mérigoux, N.; Apanasevich, P.; Mehlhoop, J.-P.; Lucas, D.; Raynaud, C.; Badillo, A.;
In the frame of the European Union NURESAFE project a benchmark test between NEPTUNE_CFD, CFX and TransAT CFD codes on a reference TOPFLOW-PTS experiment was conducted. The work is a part of the work package on multi-scale and multi-physics simulation of Pressurized Thermal Shock (PTS). The article includes a short description of the TOPFLOW-PTS facility and the reference steam-water experiment. Furthermore the boundary and initial conditions for the CFD simulations are presented. The computational grids that are used for the benchmark simulations and the models used are introduced. Finally, the results of CFD calculations are compared with the experimental data and differences between simulations and experiment are discussed.
Keywords: Benchmark tests; Boundary and initial conditions; CFD simulations; Computational grids; European union; Multiphysics simulations; Pressurized thermal shock; Work packages

Publ.-Id: 24812 - Permalink


Quantum regime of a free-electron laser: relativistic approach
Kling, P.; Sauerbrey, R.; Preiss, P.; Giese, E.; Endrich, R.; Schleich, W. P.;
In the quantum regime of the free-electron laser, the dynamics of the electrons is not governed by continuous trajectories but by discrete jumps in momentum. In this article, we rederive the two crucial conditions to enter this quantum regime: (1) a large quantum mechanical recoil of the electron caused by the scattering with the laser and the wiggler field and (2) a small energy spread of the electron beam. In contrast to our recent approach based on nonrelativistic quantum mechanics in a co-moving frame of reference, we now pursue a model in the laboratory frame employing relativistic quantum electrodynamics.
Keywords: Electrodynamics; Free electron lasers; Quantum electronics; Quantum theory

Publ.-Id: 24811 - Permalink


Discovering complex groundwater dynamics of a multiple aquifer system on the base of stable and radio-isotope patterns
Wilske, C.; Roediger, T.; Suckow, A.; Geyer, S.; Weise, S.; Merchel, S.; Rugel, G.; Pavetich, S.; Merkel, B.; Siebert, C.;
The water supply in semi-arid Israel and Palestine, predominantly relies on groundwater as freshwater resource, stressed by increasing demand and low recharge rates. Sustainable management of such resources requires a sound understanding of its groundwater migration through space and time, particularly in structurally complex multi-aquifer systems as the Eastern Mountain Aquifer, affected by salting. To differentiate between the flow paths of the different water bodies and their respective residence times, a multi-tracer approach, combining age dating isotopes (36Cl/Cl; 3H) with rock specific isotopes like 87Sr/86Sr and δ34S-SO4 was applied. As a result, the investigated groundwaters from the two Cretaceous aquifers and their respective flow paths are differentiable by e.g. their 87Sr/86Sr signatures, resembling the intensity of the rock-water interaction and hence indirectly residence times. In the discharge areas within the Jordan Valley and along the Dead Sea shore, δ34S-SO4 ratios reveal the different sources of salinity (ascending brines, interstitial brines and dissolved salts). Based on 36Cl and 3H and the atmospheric input functions, very heterogeneous infiltration times and effective flow velocities, respectively, indicate an at least dual porosity system, resulting in distinctly different regimes of matrix and pipe flow.
Keywords: 36Cl/Cl, 3H, groundwater age dating, 87Sr/86Sr, δ34S, aquifer characterization, western Dead Sea Basin
  • Poster
    European Geosciences Union (EGU) General Assembly, 23.-28.04.2017, Wien, Österreich

Publ.-Id: 24810 - Permalink


Self-assembly of single Si quantum dots in SiO2
Heinig, K.-H.; Stegemann, K.-H.; von Borany, J.; Facsko, S.; Hlawacek, G.; Hübner, R.; Bischoff, L.; Möller, W.; Prüfer, T.; Xu, X.;
However, such structures are not small enough to operate at room temperature (RT) quantum devices with switching mechanisms different from CMOS. E.g., the extremely low-power device Single Electron Transistor (SET) works at RT only if the size of the quantum dot is below 5 nm, and if the tunnel distances through SiO2 are a few nm only.
Here we present a directed self-assembly process of a 2-3 nm small single Si dot located in the middle of a SiO2 layer with distances of ~2 nm to the upper and lower Si. The self-assembly occurs by phase separation of metastable SiOx during a heat treatment. The self-assembly becomes directed by constraining and shaping the SiOx volume in such a manner that a single Si quantum dot in the requested position forms. The SiOx is fabricated by collisional mixing of Si atoms from above and below in the SiO2 layer. Two methods to form a local, constrained volume of SiOx are presented: (i) A large-area Si/SiO2/Si layer stack is irradiated with a 2 nm narrow energetic Ne+ beam in a Helium Ion Microscope (HIM), which results in a ~10 nm disk of SiOx in the buried SiO2 layer. (ii) Si pillars (<20 nm) with an embedded SiO2 layer are irradiated with a broad beam of energetic Si+ ions. Method (ii) will be used to fabricate SETs in a CMOS technology.
This work has been funded by the European Union's Horizon 2020 research and under grant agreement No 688072 innovation program.
Keywords: quantum dots, nano-electronics, ion irradiation, ion beam mixing, phase separation
  • Lecture (Conference)
    E-MRS 2016 Fall Meeting, 19.-22.09.2016, Warszawa, Poland

Publ.-Id: 24808 - Permalink


A multivariate discrimination scheme of detrital garnet chemistry for use in sedimentary provenance analysis
Tolosana-Delgado, R.; von Eynatten, H.; Krippner, A.; Meinhold, G.;
Garnet chemistry provides a well-established tool in the discrimination and interpretation of sediment provenance. Current discrimination approaches, however, (i) suffer from using less variables than available, (ii) subjective determination of discrimination fields with strict boundaries suggesting clear separations where in fact probabilities are converging, and (iii) significant overlap of compositional fields of garnet from different host-rock groups. The new multivariate discrimination scheme is based on a large database, a hierarchical discrimination approach involving three steps, linear discriminant analysis at each step, and the five major host-rock groups to be discriminated: eclogite- (A), amphibolite- (B) and granulite- (C) facies metamorphic rocks as well as ultramafic (D) and igneous rocks (E). The successful application of statistical discrimination approaches requires consideration of the a priori knowledge of the respective geologic setting. This is accounted for by the use of prior probabilities. Three sets of prior probabilities (priors) are introduced and their advantages and disadvantages are discussed. The user is free to choose among these priors, which can be further modified according to the specific geologic problem and the level of a priori knowledge. The discrimination results are provided as integrated probabilities of belonging to the five major host-rock groups. For performing calculations and results a supplementary Excel® spreadsheet is provided. The discrimination scheme has been tested for a large variety of examples of hard rocks covering all of the five major groups and several subgroups from various settings. In most cases, garnets are assigned correctly to the respective group. Exceptions typically reflect the peculiarities of the regional geologic situation. Evaluation of detrital garnets from modern and ancient sedimentary settings of the Western Gneiss Region (Norway), Eastern Alps (Austria) and Albertine Rift (Uganda) demonstrates the power to reflect the respective geologic situations and corroborate previous results. As most garnet is derived from metamorphic rocks and many provenance studies aim at reconstructing the tectonic and geodynamic evolution in the source area, the approach and the examples emphasize discrimination of metamorphic facies (i.e., temperature-pressure conditions) rather than protolith composition.
Keywords: garnet; mineral chemistry; linear discriminant analysis; compositional data; prior probabilities; provenance
  • Contribution to proceedings
    European Geosciences Union General Assembly 2017, 23.-28.04.2017, Wien, Österreich
    Proceedings of the European Geoscience Union General Assembly 2017
  • Open Access LogoSedimentary Geology 375(2018), 14-26
    DOI: 10.1016/j.sedgeo.2017.11.003

Downloads:

Publ.-Id: 24807 - Permalink


Hybride 3D Modellierungen im Gifhorner Trog für die Kombination von Übertage und Untertage-Gravimetrie
Götze, H.-J.; Schmidt, S.; Menzel, P.;
Für die hier dargestellte Studie im Bereich des Gifhorner Trogs wurden neben ca. 500 Messpunkten mit vollständig korrigierten Bougueranomalien ca. 4400 digitalisierte ältere Drehwaagemessungen aus dem beginnenden 20. Jahrhundert verwendet. Mit Hilfe der „alten“ Drehwaagemessungen konnten im Detail dann die Schwerehorizontalgradienten Wxz und Wyz sowie die Krümmungsgrößen der Schwere (WΔ = Wyy – Wxx und 2Wxy) in die 3D-Modellierung integriert werden. Neben den an der Oberfläche gemessenen Anomalien standen auch Untertagemessungen des Schwerefeldes zur Verfügung.
Modelliert wurde mit der hauseigenen Modelliersoftware IGMAS+, die nicht nur die simultane 3D Modellierung von Potentialfeldern (GravMag) ermöglicht, sondern auch deren Gradienten. Ein Vergleich von häufig verwendeten 2D-Modellierungen natürlicher 3D-Strukturen im Untergrund mit 3D-Berechnungen zeigt deutlich, wie groß die Gefahr von Fehlinterpretation eines solchen methodisch fragwürdigen Vorgehens ist. Die Modelldichten können variabel – in Abhängigkeit von den „wahren Geschwindigkeitsverhältnissen“ im Modelliergebiet angegeben werden. Als Beispiel zeigen wir das 3D Dichtemodell der Tiefbohrung KTB zusammen mit der Bohrlochgravimetrie – in Ermangelung anderer, frei zugänglicher Datensätze.
Die vorliegende Modellierung von Detailstrukturen im Gifhorner Trog belegt eindeutig, dass eine hybride 3D Modellierung von Potentialfeldern zusammen mit ihren Gradienten wertvolle Informationen über den Untergrund bis in Tiefen von 5 – 10 km liefert, die gemeinsam mit seismischen Informationen einen erheblichen Mehrwert für die Interpretation darstellen.
Keywords: 3D Potentialfeldmodellierung, Geophysik, Untergrundmodellierung
  • Lecture (Conference)
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
  • Contribution to proceedings
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
    DGMK-Tagungsbericht 2016-1, Hamburgf: DGMK, 978-3-941721-64-7, 91-96

Publ.-Id: 24806 - Permalink


Magnetic Nanostructures Designed For Hard Disk Drive Applications
Hellwig, O.;
Continued progress in hard disk drive areal density for conventional perpendicular magnetic recording (PMR) based on granular media has become increasingly difficult. Although adoption of energy assisted magnetic recording (EAMR), specifically Heat Assisted Magnetic Recording (HAMR) is widely viewed as a promising solution for thermal stability issues, challenges in grain size scaling and managing media noise may limit the rate of progress for EAMR based on granular media. Bit patterned recording (BPR) stands as an attractive alternative to granular media, offering a path to thermally stable recording at high density and significantly reduced media noise by replacing the segregated random grains of PMR media with lithographically defined single domain islands. Figure 1 compares and summarizes basic characteristics of currently used conventional PMR based on granular media and BPR based on pre-defined bits. In my talk I will discuss various choices for BPR magnetic materials, such as Co/Pd and Co/Pt multilayers as well as CoCrPt and FePt L10 alloys. I will highlight advantages and disadvantages of the different magnetic material systems with respect to potential applications in BPR and outline the specific challenges when comparing conventional PMR, BPR and currently emerging HAMR systems.
Keywords: magnetic recording, hard disk drive, perpendicular magnetic recording, bit patterned recording, heat assisted magnetic recording
  • Invited lecture (Conferences)
    International Conference on Solid Films and Surfaces, 28.08.-02.09.2016, Chemnitz, Germany

Publ.-Id: 24805 - Permalink


Karrat Zinc 2016 - Personal field report
Zimmermann, R.ORC
Results of the 2016 Karrat fieldwork, 11.08.2016 – 24.08.2016
  • Other report
    Kopenhagen: Geological Survey of Denmark and Greenland, 2016
    224 Seiten

Publ.-Id: 24804 - Permalink


Experimental Investigation of Bubble Column Reactors with Longitudinal Flow Heat Exchanging Internals Using Ultrafast X-Ray Tomography
Seiler, T.;
Bubble column reactors are multiphase devices which are commonly applied in the chemical process industry due to their advantageous heat and mass transfer properties as well as the abstinence of moving parts. Since most of the reactions operated in these devices are of exothermic nature, the developed heat has to be sufficiently removed off the system in order the guarantee optimal reaction conditions. One, among others, of those heat exchanging devices can be internally inserted tube bundles, which have the advantage to remove the heat directly at its source. On the downside, a large portion of the reactor's cross-sectional area has to be covered by the tube bundle, whereas typical values range between 20 and 30%. Hence, the influence of the internals is not negligible and has a strong effect on the global and local hydrodynamics. Therefore, the influence of various tube bundle layouts (square and triangular pitch) with two tube sizes (8 and 13 mm) having the same coverage of the reactor's cross-sectional area (~25%) have been investigated using the ultrafast X-ray CT to get insight into the local and global hydrodynamics. A cylindrical column with 10 cm ID and a height of 2m was used. Furthermore, to cover all hydrodynamic flow regimes, the superficial gas velocity was varied between 2 – 20 cm/s. It has been found out that the tube configuration has strong impact on the radial holdup profile, which governs the liquid mixing and gas velocity profile. Furthermore, square configurations showed better hydrodynamic performance regarding holdup, holdup profiles and bubble size distribution.
  • Study thesis
    TU Dresden, 2016
    Mentor: Felix Möller, Uwe Hampel

Publ.-Id: 24803 - Permalink


Dynamical universality classes of simple growth and lattice gas models
Kelling, J.; Odor, G.; Gemming, S.;
Large scale, dynamical simulations have been performed for the two dimensional octahedron model, describing Kardar-Parisi-Zhang (KPZ) for nonlinear, or Edwards-Wilkinson (EW) for linear surface growth. The autocorrelation functions of the heights and the dimer lattice gas variables are determined with high precision. Parallel random-sequential (RS) and two-sub-lattice stochastic dynamics (SCA) have been compared. The latter causes a constant correlation in the long time limit, but after subtracting it one can find the same height functions as in case of RS. On the other hand the ordered update alters the dynamics of the lattice gas variables, by increasing (decreasing) the memory effects for nonlinear (linear) models with respect to RS. Additionally, we support the KPZ ansatz in 2+1 dimensions and provide a precise growth exponent value β = 0.2414(2).. We show the emergence of finite size corrections, which occur much earlier than the height saturation.
Keywords: Non-Equilibrium Thermodynamics, Surface Growth, GPU, Kardar-Parisi-Zhang
Related publications
Efficient Parallel Monte-Carlo Simulations for Large-Scale … (Id 27533) has used this publication of HZDR-primary research data

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Publ.-Id: 24802 - Permalink


The spatial coefficient of variation in arterial spin labeling cerebral blood flow images
Mutsaerts, H. J.; Petr, J.; Václavů, L.; van Dalen, J. W.; Robertson, A. D.; Caan, M. W.; Masellis, M.; Nederveen, A. J.; Richard, E.; Macintosh, B. J.;
Macro-vascular artifacts are a common arterial spin labeling (ASL) finding in populations with prolonged arterial transit time (ATT) and result in vascular regions with spuriously increased cerebral blood flow (CBF) and tissue regions with spuriously decreased CBF. This study investigates whether there is an association between the spatial signal distribution of a single post-label delay ASL CBF image and ATT. In 186 elderly with hypertension (46% male, 77.4+-2.5 years), we evaluated associations between the spatial coefficient of variation (CoV) of a CBF image and ATT. The spatial CoV and ATT metrics were subsequently evaluated with respect to their associations with age and sex – two demographics known to influence perfusion. Bland–Altman plots showed that spatial CoV predicted ATT with a maximum relative error of 7.6%. Spatial CoV was associated with age (b=0.163, p=0.028) and sex (b=-0.204, p=0.004). The spatial distribution of the ASL signal on a standard CBF image can be used to infer between-participant ATT differences. In the absence of ATT mapping, the spatial CoV may be useful for the clinical interpretation of ASL in patients with cerebrovascular pathology that leads to prolonged transit of the ASL signal to tissue.
Keywords: Arterial spin labeling, ASL, cerebral blood flow, cerebral hemodynamics, perfusion weighted MRI

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Publ.-Id: 24801 - Permalink


Kooperative Entwicklung ressourceneffizienter Verfahren in der Produktion
Rädecker, P.; Scharf, C.; Zeidler, O.;
Kooperative Entwicklung ressourceneffizienter Verfahren in der Produktion
Philipp Rädecker, Oliver Zeidler & Prof. Christiane Scharf
Freiberg, 24. November 2016
  • Invited lecture (Conferences)
    Ressourceneffizienz vor Ort Wettbewerbsplus Ressourceneffizienz Angebote für KMU in Sachsen, 24.11.2016, Freiberg, Deutschland

Publ.-Id: 24800 - Permalink


Influence of realignment-induced interpolation errors on the estimation of cerebral blood flow using arterial spin labeling fMRI
Petr, J.ORC; Mutsaerts, H.ORC; de Vita, E.ORC; Shirzadi, Z.; Cohen, S.; Blokhuis, C.; Pajkrt, D.ORC; Hofheinz, F.; van den Hoff, J.; Asllani, I.
Purpose/Introduction: The realignment transformation needed for motion correction in fMRI has been shown to have the adverse effect of smoothing the realigned images1. This effect is independent of the accuracy of the estimated motion parameters (it can occur even for accurately estimated motion parameters) and can, in ASL, cause gray-matter (GM) cerebral-blood-flow (CBF) underestimation compared to an acquisition without motion. Here, we investigated the smoothing of the realignment transformation in ASL by creating simulated CBF maps based on T1-weighted (T1w) images and motion parameters obtained from ASL images acquired on patients2.
Methods: ASL data from 66 children (age: 8-18y, median: 12.8y, 34 males) were obtained from the NOVICE study2. This dataset is characterized by a relatively high head motion often associated with scanning children. Images were acquired on Philips 3T Ingenia (pCASL: voxel-size 3x3x6.6mm3, 30 controls/label pairs; T1w: voxel-size 1x1x1mm3).
To simulate ASL time-series that reflect motion from real acquisition, the following processing steps were implemented: (1) T1w-image was co-registered to the first ASL volume and segmented into gray and white-matter posterior probability maps (pGM/pWM) using SPM12. (2) ASL images were realigned with respect to the first volume3 (average motion >1mm or >1° was considered 'high'). (3) The motion-parameters from step 2 were applied to pGM/pWM maps, and the maps were down-sampled to the ASL resolution. This resulted in 60 pGM/pWM volumes mimicking a real ASL acquisition (Fig. 1b). (4) The pGM/pWM maps were realigned to their first respective volume (Fig. 1d) and averaged (Fig. 2d).
Two sets of simulated CBF maps were created: (1) from the pGM/pWM corresponding to the first ASL volume (CBF-static), (2) from the realigned pGMs/pWMs described above (CBF-motion), assuming GM-CBF of 80 mL/min/100g and GM/WM CBF ratio of 3. Local and global GM-CBF values of CBF-motion were compared against the idealized CBF-static case.
Results: Figures 1d and 2d show ‘blurring’ of the realigned pGM in high movement cases. The local GM-CBF in CBF-motion was up to 10% lower than in CBF-static (Fig. 2e); negligible differences (<1%) were seen in relatively low movement cases (Fig. 2f). In all 'high-motion' participants, 4-7% lower global GM-CBF was observed (Fig. 3).
Discussion/Conclusion: Relatively high motion during ASL acquisitions appears to result in a GM-CBF underestimation of 4-7% globally and up to 10% locally. This finding can have important implications in studying patients who tend to move more than their healthy counterparts, which may lead to a GM-CBF underestimation in patients relative to controls.
Keywords: cerebral blood flow, perfusion, arterial spin labeling, motion correction
  • Contribution to proceedings
    ESMRMB 2016, 33rd Annual Scientific Meeting, 29.09.2016, Vienna, Austria
    Magnetic Resonance Materials in Physics, Biology and Medicine: Springer, 0968-5243
    DOI: 10.1007/s10334-016-0568-x
  • Lecture (Conference)
    ESMRMB 2016, 33rd Annual Scientific Meeting, 29.09.2016, Vienna, Austria

Publ.-Id: 24799 - Permalink


Retargeting of T lymphocytes to PSCA- or PSMA positive prostate cancer cells using the novel modular chimeric antigen receptor platform technology “UniCAR”
Feldmann, A.; Arndt, C.; Bergmann, R.; Loff, S.; Cartellieri, M.; Bachmann, D.; Aliperta, R.; Hetzenecker, M.; Ludwig, F.; Albert, S.; Ziller-Walter, P.; Kegler, A.; Koristka, S.; Gärtner, S.; Schmitz, M.; Ehninger, A.; Ehninger, G.; Pietzsch, J.; Steinbach, J.; Bachmann, M.;
New treatment options especially of solid tumors including for metastasized prostate cancer (PCa) are urgently needed. Recent treatments of leukemias with chimeric antigen receptors (CARs) underline their impressive therapeutic potential. However CARs currently applied in the clinics cannot be repeatedly turned on and off potentially leading to severe life threatening side effects. To overcome these problems, we recently described a modular CAR technology termed UniCAR: UniCAR T cells are inert but can be turned on by application of one or multiple target modules (TMs). Here we present preclinical data summarizing the retargeting of UniCAR T cells to PCa cells using TMs directed to prostate stem cell-(PSCA) or/and prostate membrane antigen (PSMA). In the presence of the respective TM(s), we see a highly efficient target-specific and target-dependent activation of UniCAR T cells, secretion of proinflammatory cytokines, and PCa cell lysis both in vitro and experimental mice.

Publ.-Id: 24798 - Permalink


Crystal structure and magnetism of UOsAl
Andreev, A. V.; Danis, S.; Sebek, J.; Henriques, M. S.; Vejpravova, J.; Gorbunov, D. I.; Havela, L.;
Crystal structure, magnetization, and specific heat were studied on single crystal of uranium intermetallic compound UOsAl. It is a hexagonal Laves phase of MgZn2 type, space group P63/mmc, with lattice parameters a = 536.4 pm, c = 845.3 pm. Shortest inter-uranium distance 313 pm (along the c-axis) is considerably smaller than the Hill limit (340 pm). The compound is a weakly temperature-dependent paramagnet with magnetic susceptibility of ≈1.5*10−8 m3 mol (at T=2 K), which is slightly higher with magnetic field along the a-axis compared to the c-axis. The Sommerfeld coefficient of electronic specific heat has moderate value of γ = 36 mJ mol−1 K−2.

Publ.-Id: 24797 - Permalink


Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-Point fluctuations, and possible two-dimensional universal behavior
Brambleby, J.; Goddard, P. A.; Singleton, J.; Jaime, M.; Lancaster, T.; Huang, L.; Wosnitza, J.; Topping, C. V.; Carreiro, K. E.; Tran, H. E.; Manson, Z. E.; Manson, J. L.;
We present the magnetic and thermal properties of the bosonic-superfluid phase in a spin-dimer network using both quasistatic and rapidly changing pulsed magnetic fields. The entropy derived from a heat-capacity study reveals that the pulsed-field measurements are strongly adiabatic in nature and are responsible for the onset of a significant magnetocaloric effect (MCE). In contrast to previous predictions we show that the MCE is not just confined to the critical regions, but occurs for all fields greater than zero at sufficiently low temperatures. We explain the MCE using a model of the thermal occupation of exchange-coupled dimer spin states and highlight that failure to take this effect into account inevitably leads to incorrect interpretations of experimental results. In addition, the heat capacity in our material is suggestive of an extraordinary contribution from zero-point fluctuations and appears to indicate universal behavior with different critical exponents at the two field-induced critical points. The data at the upper critical point, combined with the layered structure of the system, are consistent with a two-dimensional nature of spin excitations in the system.

Publ.-Id: 24796 - Permalink


The cancer cell adhesion resistome: mechanisms, targeting and translational approaches
Dickreuter, E.; Cordes, N.;
Cell adhesion-mediated resistance limits the success of cancer therapies and is a great obstacle to overcome in the clinic. Since the 1990s, where it became clear that adhesion of tumor cells to the extracellular matrix is an important mediator of therapy resistance, a lot of work has been conducted to understand the fundamental underlying mechanisms and two paradigms were deduced: cell adhesion-mediated radioresistance (CAM-RR) and cell adhesion-mediated drug resistance (CAM-DR). Preclinical work has evidently demonstrated that targeting of integrins, adapter proteins and associated kinases comprising the cell adhesion resistome is a promising strategy to sensitize cancer cells to both radiotherapy and chemotherapy. Moreover, the cell adhesion resistome fundamentally contributes to adaptation mechanisms induced by radiochemotherapy as well as molecular drugs to secure a balanced homeostasis of cancer cells for survival and growth. Intriguingly, this phenomenon provides a basis for synthetic lethal targeted therapies simultaneously administered to standard radiochemotherapy. In this review, we summarize current knowledge about the cell adhesion resistome and highlight targeting strategies to override CAM-RR and CAM-DR.
Keywords: adhesion; CAM-DR; CAM-RR; EGFR; integrin; resistome

Publ.-Id: 24795 - Permalink


Insights into the sonochemical synthesis and properties of salt-free intrinsic plutonium colloids
Dalodière, E.; Virot, M.; Morosini, V.; Chave, T.; Dumas, T.; Hennig, C.; Wiss, T.; Blanco, O. D.; Shuh, D. K.; Tyliszcak, T.; Venault, L.; Moisy, P.; Nikitenko, S. I.;
For the first time, stable intrinsic plutonium colloid was prepared by ultrasonic treatment of PuO2 suspensions in pure water at room temperature. The yield of Pu colloid was found to increase with PuO2 specific surface area and by using reducing carrier gas mixture. Kinetic data evidenced that both chemical and mechanical effects of ultrasound strongly contribute to the mechanism of Pu colloid formation. At first, the fragmentation of initial PuO2 particles accelerates the overall process providing larger surface of contact between cavitation bubbles and solids. Furthermore, hydrogen formed during sonochemical water splitting enables reduction of Pu(IV) to more soluble Pu(III), which then reoxidizes yielding Pu(IV) colloid. Sonochemical colloid was compared with hydrolytic one using HRTEM, Pu LIII XAS, and STXM/NEXAFS (O K-edge) techniques. Both colloids are composed of quasi-spherical nanocrystalline particles of PuO2 (fcc, Fm¯3 m space group) measuring about 7 nm and 3 nm, respectively. Moreover, HRTEM revealed nanostructured morphology for initial PuO2. The EXAFS spectra of colloidal PuO2 nanoparticles were fitted using triple oxygen shell model for the first coordination sphere of Pu(IV). HRTEM and EXAFS studies revealed the correlation between the number of Pu-O and Pu-Pu contacts and atomic surface-to-volume ratio of studied PuO2 nanoparticles. The STXM/NEXAFS study indicated that the oxygen state of hydrolytic Pu colloid is influenced by hydrolyzed Pu(IV) species in much more extent than PuO2 nanoparticles of sonochemical colloid. In general, hydrolytic and sonochemical colloids can be described as core-shell nanoparticles composed of quasi stoichiometric PuO2 core and hydrolyzed Pu(IV) moieties at the surface shell.
Keywords: sonochemistry, Pu(IV) colloids

Publ.-Id: 24794 - Permalink


Luminescence spectroscopy of An/Ln in environmental systems
Steudtner, R.; Drobot, B.; Haubitz, T.; Schernikau, M.; Lehmann, S.; Bader, M.; Vogel, M.;
Luminescence spectroscopy is a powerful tool to study the chemistry of f-elements (actinides – An, lanthanides – Ln) in trace concentration. Manifold operating mode, e.g. steady-state, time-resolved, laser-induced, site-selective, cryogenic, etc. were used to investigate the environmental behavior of An/Ln in various geological and biological systems.
  • Invited lecture (Conferences)
    ATAS 2016 - International Workshop on Advanced Techniques in Actinide Spectroscopy, 07.-10.11.2016, Richland, USA

Publ.-Id: 24793 - Permalink


Structural and electrical characterization of ALD grown HfO2 thin films
Blaschke, D.; Munnik, F.; Zviagin, V.; Schmidt-Grund, R.; Grundmann, M.; Bogusz, A.; Hübner, R.; Scholz, A.; Schmidt, H.; Zahn, P.; Gemming, S.;
HfO2 films were grown on 4-inch native SiO2/Si wafers by Atomic Layer Deposition (ALD) from tetrakis(dimethylamido)hafnium and deionized water in a Savannah S100 system. The temperature was varied from 100°C to 350°C in steps of 50 K. All other ALD process parameters were fixed. The resulting HfO2 layers were characterized in terms of thickness homogeneity, growth rate per cycle, surface roughness, crystal structure, stoichiometry, mass density, optical bandgap and index of refraction. Based on the obtained growth rate of HfO2 on SiO2/Si, 25 nm thick HfO2 layers were grown on Pt/Ti/SiO2/Si substrates for electrical characterization. Furthermore, the most important structural properties were compared for the growth of HfO2 on Pt/Ti/SiO2/Si and SiO2/Si substrates.
HfO2 breakdown voltages show a clear decrease with increasing growth temperature, which was correlated to the crystallinity of the films due to the preferred breakdown along grain boundaries. For resistive switching, an amorphous HfO2 layer grown at 150°C was compared to a crystalline one grown at 300°C. Furthermore, resistive switching characteristics were tuned by the use of two different top electrode materials, namely an inert Pt or a reactive Ti/Pt electrode. The contact diameter was 50 μm. In the majority of cases, the resistive switching mode was found to be unipolar. Only the combination of a crystalline HfO2 layer with an inert Pt bottom and a reactive Ti/Pt top electrode led to a “pseudo-bipolar” switching mode with a convertible SET and RESET polarity.
Keywords: HfO2, thin film deposition, ALD, resistive switching
  • Poster
    MEMRIOX International Workshop 2016, 25.-27.09.2016, Berghotel Bastei, Lohmen, Germany

Publ.-Id: 24792 - Permalink


Doping by flash lamp annealing
Prucnal, S.; Rebohle, L.; Skorupa, W.;
After a short introduction we will highlight processing issues (setup, comparison of annealing methods, relevant requirements for annealing due to doping, diffusion, activation, recrystallization, defect engineering), as well as doping issues for group IV-semiconductors (shallow junctions, hyperdoping, solar cells, superconductivity) and other semiconductors (manganese doping of GaAs for diluted magnetic semiconductors, doping for transparent conductive oxides). Mostly ion implantation serves as a source of dopants, but also diffusion from deposited layers is of growing importance.
Keywords: flash lamp annealing, pulsed light sintering, group IV-semiconductors, doping, diffusion, activation, recrystallization, defect engineering, diluted magnetic semiconductors, transparent conductive oxides

Publ.-Id: 24791 - Permalink


Bergbau und Konfliktminerale in Afrika
Sterbik, N.ORC
Einerseits sind die Rohstofflieferungen Afrikas für die Versorgung der Weltwirtschaft von Bedeutung, andererseits spielen die Exporte aber auch eine wesentliche Rolle für die Wirtschaft dieser Länder. Die steigende Nachfrage (auch in Schwellenmärkten) und der Preisanstieg für einzelne Rohstoffe könnten eine günstige Gelegenheit für die afrikanischen Bergbauländer darstellen.

In großen Teilen des subsaharischen Afrikas wird der Bergbau jedoch noch in sehr kleinem Maßstab und – aufgrund keiner oder nur geringer Mechanisierung – mit hohem Arbeitsaufwand betrieben. Diese Arbeiten werden allgemein als Einzel- und Kleinbergbau (Artisanal and Small-Scale Mining, ASM) kategorisiert. In Zentralafrika steht der ASM zusätzlich auch mit sogenannten „Konfliktmineralien“ in Verbindung (kurz gesagt, „Konfliktressourcen sind natürliche Ressourcen, deren systematische Ausbeutung und Handel im Kontext eines Konfliktes zu schwersten Menschenrechtsverletzungen, Verletzungen des humanitären Völkerrechts oder Verwirklichung völkerstrafrechtlicher Tatbestände führen kann“ (BICC, 1994)).

Diese Präsentation vermittelt einen Überblick über den Bergbau in Afrika, sowohl über industriellen Bergbau als auch Kleinbergbau, und behandelt das Thema der Konfliktmineralien. Es wird ebenfalls die Verbindung zwischen den beteiligten Akteuren und den Initiativen rund um ASM und Konfliktmineralien aufgezeigt.
Keywords: Bergbau, Kleinbergbau, Afrika, Konflikt-Minerale
  • Invited lecture (Conferences)
    145. Freiberger Kolloquium, 14.04.2016, Freiberg, Germany

Publ.-Id: 24790 - Permalink


A lab scale froth flotation study of tungsten bearing tailings of the Barruecopardo mine (Spain) within the EU Horizon 2020 OptimOre Project
Compañero, R. J.;
This study was done under the framework of the “OptimOre” project which is part of EU Horizon 2020. Froth flotation is applied for obtaining a pre-concentrate from tailings material sourced from an old mine in the Barruecopardo district, located in the province of Salamanca in Spain. Representative samples from the as-received material were submitted to several characterization analyses: MLA, particle size measurements, contact angle measurements, and ICP-AES. Information from the preceding tests were used to design flotation experiments where five factors: collector type, frother type, depressant addition, pH level, and collector dosage were investigated.

Milling was performed on the feed material before flotation because the starting size was too coarse. The flotation behavior of the material was examined and different factor level combinations resulted in varying degrees of recovery and concentrate grades --- the highest attained averaging 35% and 0.36% W (Enrichment ratio = 14) respectively. Further improvements on these results were targeted and thus the grinding time was increased. The merits of this step in terms of mass collection, grade, and recovery are discussed. Exploratory ideas on the effect of the factor levels investigated were also presented.
Keywords: froth flotation; scheelite; depressant; Barruecopardo
  • Master thesis
    HIF/HZDR, 2016
    Mentor: Sterbik, N.

Publ.-Id: 24789 - Permalink


Back-calculating froth flotation rates of scheelite by size fractions and liberation classes : first results
Sterbik, N.ORC; Rudolph, M.ORC
This paper is part of an EU funded collaboration under the Horizon 2020 program on the optimization of mineral processing operations of European tungsten and tantalum complex low-grade ores, called OptimOre. There froth flotation is an important process especially for scheelite. It is a versatile mineral processing method, which still lacks of physical and chemical comprehensive, accurate and internationally recognized models. The work package on froth flotation within OptimOre is thus dedicated to developing improved fundamental flotation models with the help of advanced automated mineralogical analyses of the input and output streams of flotation cells.

Reliable flotation models can be potentially used to simplify and shorten lab testing procedures, better understand and predict ore behavior but also establish the potential recovery and grade of the targeted mineral(s).

A first step in fundamental flotation modelling is to obtain the flotation rates of minerals with respect to their size and liberation. This is achieved by back calculation of recovery rates typically under the assumption of a first-order rate process.

In this paper, froth flotation rates of scheelite are back-calculated by size fractions and liberation classes. Flotation parameters such as reagent regime, cell hydrodynamics and pulp and froth properties are systematically varied in properly designed experiments with measured effects on the bubble surface area flux. Finally these flotation rates are then used to critically assess several existing first principle flotation models (Yoon, Pyke and others), which are compared with each other in terms of applicability and limitations.

The scheelite bearing ore used for the experiments is from the Mittersill deposit (Austria). The particle properties (e.g. liberation, mineral composition) are studied with automated mineralogy (Mineral Liberation Analysis) as well as elemental assays by ICP-MS analyses. Froth flotation tests are conducted with a bottom-driven Magotteaux cell equipped with a bubble cam sizer and froth cam.
Keywords: flotation rates, automated mineralogy, scheelite, size-by-liberation, MLA
  • Poster
    XXVIII International Mineral Processing Congress, 11.-15.09.2016, Québec city, Canada

Publ.-Id: 24788 - Permalink


Technical and Modelling Aspects of Subsecond Thermal Processing with Flash Lamps
Schumann, T.; Rebohle, L.; Skorupa, W.;
This poster gives an overview of the complex technical aspects of Flash-lamp-annealing-tools for thermal processing in the millisecond range used at the Helmholtz Research Center Dresden-Rossendorf (HZDR). It outlines that Flash Lamp Annealing (FLA) is established as a high-performance alternative to Rapid Thermal Annealing and Furnace Annealing when it comes to treatment of the most advanced thin layer and coating materials, thus enabling the fabrication of novel electronic structures and materials. It shows the unique variety of parameters the HZDR is able to provide for applications ranging from annealing of implanted Si and Ge, transparent conductive oxides, photovoltaic materials, silver and copper inks on various non-metal substrates to exceptional applications (roof tiles, watchcases). It explains, how crucial parameters, such as emission spectrum, energy density, and preheat temperature are monitored to provide a reliable reproducibility. Modelling aspects regarding temperature distribution and heat transport within the millisecond range will also be addressed. Furthermore, a summary will be given of characteristic features of our tools to convey the diversity of the fields of application and the enormous range of possible research.
Keywords: Flash-lamp-annealing, millisecond range thermal processing, modelling aspects, thin layers, novel electronic structures
  • Poster
    SVC (Society of Vacuum Coaters) 59th Annual Technical Conference (TechCon), 09.-13.05.2016, Indianapolis, IN, USA

Publ.-Id: 24787 - Permalink


A lab scale froth flotation study of tungsten-bearing tailings of the Barruecopardo mine (Spain)
Sterbik, N.ORC; Compañero, R. J.; Rudolph, M.ORC
The “OptimOre” project, as part of the EU Horizon 2020, proposes the research and development of improved modelling and control technologies of tantalum and tungsten ore processing using advanced sensing and artificial intelligence techniques. The Helmholtz Institute Freiberg for Resource Technology is responsible for the Work Package „Froth flotation”.
Within the frame of the OptimOre project, a lab scale froth flotation study was conducted on the tailings of the Barruecopardo mine (Spain) with scheelite as the main tungsten-bearing mineral and a feed grade of 0,025% tungsten. Barruecopardo is part of the world-class tungsten deposits and is being redeveloped for mining.
The reagent system is the main focus of this study, with an emphasis on the influence of depressant combinations aimed at depressing silicates in the gangue. Two collectors at four dosages, two frothers and four depressant combinations were tested at two different pH.
The results show that a higher pH usually stabilizes the froth regardless of the frother and increases the mass pull but does not impact the tungsten recovery. The depressant combination is highly relevant in grade, as expected, but also in recovery. It can hinder it badly or increase it tremendously. Furthermore, the performance of the first collector without depressant is significantly higher than after adding depressant. On the contrary, the second collector that performed poorly in a depressant-less environment yields the best results in presence of depressants. The presence of sodium carbonate (Na2CO3) enhances that effect. Possible interpretations for these observations are given.
Keywords: flotation; scheelite; depressants
  • Poster
    Tagung Aufbereitung und Recycling, 09.-10.11.2016, Freiberg, Germany

Publ.-Id: 24785 - Permalink


Vertebral fractures – An underestimated side-effect in patients treated with radio(chemo)therapy
Pilz, K.; Hoffmann, A. L.; Baumann, M.; Troost, E. G. C.;
There is no abstract available, since this is an Editorial.

Publ.-Id: 24784 - Permalink


Technical feasibility of integrating 7 T anatomical MRI in image‑guided radiotherapy of glioblastoma: a preparatory study
Compter, I.; Peerlings, J.; Eekers, D. B. P.; Postma, A. A.; Ivanov, D.; Wiggins, C. J.; Kubben, P.; Küsters, B.; Wesseling, P.; Ackermans, L.; Schijns, O. E. M. G.; Lambin, P.; Hoffmann, A. L.;
Objectives: The use of 7 Tesla (T) magnetic resonance imaging (MRI) has recently shown great potential for high-resolution soft-tissue neuroimaging and visualization of microvascularization in glioblastoma (GBM). We have designed a clinical trial to explore the value of 7 T MRI in radiation treatment of GBM. For this aim we performed a preparatory study to investigate the technical feasibility of incorporating 7 T MR images into the neurosurgical navigation and radiotherapy treatment planning (RTP) systems via qualitative and quantitative assessment of the image quality.
Materials and methods: The MR images were acquired with a Siemens Magnetom 7 T whole-body scanner and a Nova Medical 32-channel head coil. The 7 T MRI pulse sequences included magnetization-prepared two rapid acquisition gradient echoes (MP2RAGE), T2-SPACE, SPACE-FLAIR and gradient echo sequences (GRE). A pilot study with three healthy volunteers and an anthropomorphic 3D phantom was used to assess image quality and geometrical image accuracy.
Results: The MRI scans were well tolerated by the volunteers. Susceptibility artefacts were observed in both the cortex and subcortical white matter at close proximity to air-tissue interfaces. Regional loss of signal and contrast could be minimized by the use of dielectric pads. Image transfer and processing did not degrade image quality. The system-related spatial uncertainty of geometrical distortion-corrected MP2RAGE pulse sequences was ≤2 mm.
Conclusion: Integration of high-quality and geometrically-reliable 7 T MR images into neurosurgical navigation and RTP software is technically feasible and safe.
Keywords: Ultra-high field MRI, Radiotherapy, Treatment planning, Glioblastoma, Geometrical distortion

Publ.-Id: 24783 - Permalink


Mineral exploration using hyperspectral remote sensing
Laakso, K.;
There is no abstract associated with the talk.
Keywords: Hyperspectral, remote sensing, mineral exploration
  • Invited lecture (Conferences)
    An informal lecture to the students of Mathias Burisch (Tu Bergakademie Freiberg), associate professor., 06.02.2017, Freiberg, Deutschland

Publ.-Id: 24782 - Permalink


Hyperspectral applications of mineral exploration
Laakso, K.;
The talk does not have an abstract.
Keywords: Hyperspectral, mineral exploration, remote sensing, drill core imaging
  • Invited lecture (Conferences)
    University of Lorraine - an informal meeting where scientific collaboration will be discussed, 24.01.2017, Nancy, France

Publ.-Id: 24781 - Permalink


Extended soft wall model with background related to features of QCD thermodynamics
Zöllner, R.; Kämpfer, B.;
The soft wall model is extended to accommodate at the same time (i) approximately linear ρ meson Regge trajectories at zero temperature T, (ii) various options for the thermodynamics with reference to QCD (cross over or second-order transition or first-order transition at Tc), and (iii) the appearance of vector meson states at T≤Tc. While the vector meson masses display some modest model dependence very near to Tc, they stay below Tc to good accuracy independent of the temperature, that is nearly as at T=0, thus being very consistent with the thermo-statistical models widely employed in analyses of the hadron yields in relativistic heavy-ion collisions in a region where baryon densitiy effects can be neglected and the vacuum hadron masses are used.

Downloads:

Publ.-Id: 24780 - Permalink


Fragment Molecular Orbital Calculations for Studying Lanthanide-Protein Interaction
Tsushima, S.ORC
no abstract for this talk
  • Invited lecture (Conferences)
    Institute Colloquium at Institute of Innovative Research, Tokyo Institute of Technology, 27.01.2017, Tokyo, Japan

Publ.-Id: 24779 - Permalink


Optik einmal anders
Schultheiss, H.;
Erstmals konnten Forscher experimentell das Brechungsgesetz für Spinwellen direkt nachweisen.
Keywords: Magnonik, Spinwellen, Magnetisierungsdynamik
  • Physik Journal 15(2016)10, 16-17

Publ.-Id: 24778 - Permalink


CdZnTe als Strahlungsdetektor in der therapeutischen Medizin
Weinberger, D.; Römer, K.; Lutz, B.; Fiedler, F.; Kormoll, T.;
Alternativ zu Operation und Chemotherapie bei der Behandlung von Tumoren hat die Strahlentherapie einen festen Platz in der medizinischen Behandlung eingenommen. Neben der Therapie mit Röntgenstrahlung werden auch geladene Atome als Teilchenstrahl verwendet. Diese haben eine endliche Reichweite in Materie und deponieren keine schädliche Dosis dahinter. Um diesen Vorteil nutzen zu können muss die Eindringtiefe des Strahls erfasst werden. CdZnTe als Strahlungsdetektor besitzt dieses Potential.
Keywords: Strahlungsdetektor, CdZnTe-Streifendetektor, Driftstrom, Pulsformenanalyse, Tiefenkorrektur
  • Contribution to proceedings
    18. Nachwuchswissenschaftlerkonferenz ost- und mitteldeutscher Fachhochschulen, 31.05.2017, Mittweida, Deutschland
    Proceedings der 18. Nachwuchswissenschaftlerkonferenz ost- und mitteldeutscher Fachhochschulen

Publ.-Id: 24777 - Permalink


Level-Of-Detail Strategie zur Vereinfachung komplexer Untergrundmodelle - Gifhorner Trog
Menzel, P.; Götze, H.-J.; Schmidt, S.;
In dieser Präsentation werden Verfahren gezeigt, um triangulierte 3D-Untergrundmodelle für die Berechnung ihres „full tensor gravity“-Effektes zu optimieren. Es handelt sich dabei um zwei etablierte Algorithmen aus der Computergrafik zur Vereinfachung von triangulierten Flächen, sowie um ein drittes, an die Erfordernisse der Potentialverfahren angepasstes, Verfahren. Alle drei Algorithmen erzeugen eine Vereinfachungshierarchie für die initiale 3D-Geometrie. Diese „Level-of-Detail“-Hierarchien erlauben es, verschiedene Modell-auflösungen sukzessive ineinander zu überführen. Ein explizites Vorhalten der vereinfachten Geometrieversionen ist aus diesem Grund nicht notwendig.
Die drei verwendeten „Mesh-Simplification“-Ansätze werden auf ein synthetisches 3D-Modell und auf das triangulierte Untergrundmodell zweier realer Salzstöcke angewendet. Die erzeugten vereinfachten Geometrieversionen werden für ihre Verwendbarkeit zur Berechnung des Effektes in den Komponenten der Schwere und des Schweregradienten-tensors evaluiert. Es wird gezeigt, dass die Ergebnisse aller drei Methoden grundsätzliche für eine Berechnung des „full tensor gravity“-Effektes verwendet werden können. Die Ergebnisse der beiden etablierten Verfahren sind allerdings nur bis zu einem relativ geringen Vereinfachungsgrad verwendbar, wenn eine gegebene Fehlertoleranz nicht überschritten werden soll. Das dritte, angepasste Verfahren erzeugt Geometriemodelle, deren Effekt auch für Modellversionen mit sehr wenigen Dreiecken mit dem Effekt des initialen Modells annähernd übereinstimmt.
Die präsentierten Ergebnisse basieren auf den Arbeiten im DGMK-Projekt 771 und das gezeigte 3D-Modell zweier Salzstöcke im Gifhorner Trog wurde von unseren Projektpartnern zur Verfügung gestellt.
Keywords: Mesh-Simplification, Potentialfeldmodellierung, geometrische 3D Modellierung
  • Lecture (Conference)
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
  • Contribution to proceedings
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Germany
    DGMK-Tagungsbericht 2016-1, Hamburg: DGMK, 978-3-941721-64-7, 97-104

Publ.-Id: 24776 - Permalink


Nickel-Enhanced Graphitic Ordering of Carbon Ad-Atoms during Physical Vapor Deposition
Wenisch, R.; Hübner, R.; Munnik, F.; Gemming, S.; Abrasonis, G.; Krause, M.;
Compatibility with commonly used substrate materials is of crucial importance for graphene device production. Low-temperature synthesis approaches are needed to cope with this challenge. Therefore it has to be clarified, to which extend physical vapor deposition can be used to produce ordered graphene structures.

In this contribution, the mechanism of graphitic ordering of atomic C on Ni was investigated at temperatures ranging from room temperature to 550 °C. The C/Ni films were prepared by ion beam sputtering. A temperature-induced and a Ni-induced enhancement of graphitic ordering is demonstrated. The Ni-effect is responsible for the formation of a bi-layer structure of the C films at higher deposition temperatures. In the bi-layers, C forms graphenic planes parallel to the Ni surface within a thickness range of 1-2 nm. Further deposited C grows preferentially perpendicular to the surface. The results are discussed on the basis of hyperthermal atom deposition, surface diffusion, metal-induced crystallization and dissolution-precipitation. Our findings point to a dominating role of surface diffusion-assisted crystallization in the carbon ordering process.
Keywords: graphitic carbon, graphene, physical vapour deposition, Raman, TEM
  • Poster
    International Winterschool on Electronic Properties of Novel Materials 2016, 13.-20.02.2016, Kirchberg, Österreich

Publ.-Id: 24775 - Permalink


Helmholtz Institute Freiberg for Resource Technology - Helmholtz-Zentrum Dresden-Rossendorf - Introduction
Kelly, N.;
Helmholtz Institute Freiberg for Resource Technology
Helmholtz-Zentrum Dresden-Rossendorf
Introduction
  • Lecture (others)
    Meeting FWGM und UIT, 06.01.2017, Freiberg, Deutschland

Publ.-Id: 24774 - Permalink


Radiation oncology in the era of precision medicine
Baumann, M.; Krause, M.; Overgaard, J.; Debus, J.; Bentzen, S. M.; Daartz, J.; Richter, C.; Zips, D.; Bortfeld, T.;
Technological advances and clinical research over the past few decades have given radiation oncologists the capability to personalize treatments for accurate delivery of radiation dose based on clinical parameters and anatomical information. Eradication of gross and microscopic tumours with preservation of health-related quality of life can be achieved in many patients. Two major strategies, acting synergistically, will enable further widening of the therapeutic window of radiation oncology in the era of precision medicine: technology-driven improvement of treatment conformity, including advanced image guidance and particle therapy, and novel biological concepts for personalized treatment, including biomarker-guided prescription, combined treatment modalities and adaptation of treatment during its course.

Publ.-Id: 24773 - Permalink


Magnetic anisotropy of III-Mn-V dilute ferromagnetic semiconductors
Xu, C.; Yuan, Y.; Sawicki, M.; Böttger, R.; Helm, M.; Zhou, S.;
As one of the most important physical properties of III-Mn-V dilute ferromagnetic semiconductors (DFS), the magnetic anisotropy could be tailored by Mn/hole concentrations and by the lattice strain [1, 2]. Particularly, the crystal symmetry lowering in-plane uniaxial anisotropy still remains one of the most puzzling properties of the DFS family. Using a perturbation method and ab initio computations, Birowska et al. showed that the preferential distribution of Mn along (Ga,Mn)As [11(_)0] can produce bulk uniaxial in-plane and out-of-plane anisotropies [3]. This preferential Mn distribution is due to the fact that the nearest-neighbor Mn pair on the GaAs (001) surface has a lower energy for the [11(_)0] axis than the [110] case. However, such a preferential Mn distribution probably will not occur when the material is not grown in a layer-by-layer mode but by a liquid-phase-epitaxy-like process with the growth speed of meters per second, as for the case of ion implantation and pulsed laser melting (II-PLM) [4]. In this work, three typical III-Mn-V DFSs [(In,Mn)As, (Ga,Mn)As, and (Ga,Mn)P] are obtained through II-PLM. We find that both (Ga,Mn)P and (Ga,Mn)As samples exhibit the easy behavior in plane (as shown in Fig. 1) while the (In,Mn)As one reveals perpendicular magnetic anisotropy (not shown). The latter is attributed to the lattice strain due to lattice mismatch between the film and the substrate. The in-plane uniaxial anisotropy is much weakened for (Ga,Mn)P and (Ga,Mn)As from the magnetic hysteresis at 5 K. However, as shown in the inset to Fig. 1, the anisotropy changes with temperature increasing. More experimental results including magnetic hysteresis at different temperatures will be discussed during the conference.

Figure 1: Magnetic hysteresis along different crystalline axis for (Ga,Mn)P and (Ga,Mn)As with different Mn concentration measured at 5 K. The inset shows the magnetic remanence along different crystalline axis for the corresponding sample.
[1] M. Sawicki et al., Phys. Rev. B 70, 245325 (2004).
[2] C. Bihler et al., Phys. Rev. B 78, 045203 (2008).
[3] M. Birowska, et al., Phys. Rev. Lett. 108, 237203 (2012).
[4] M. A. Scarpulla et al., Appl. Phys. Lett. 82, 1251-1253 (2003).
Keywords: Magnetic anisotropy, dilute ferromagnetic semiconductors (DFSs), ion implantation, pulsed laser annealing
  • Lecture (Conference)
    61st Annual Conference on Magnetism and Magnetic Materials (2016 MMM), 31.10.-04.11.2016, New Orleans, United States of America

Publ.-Id: 24772 - Permalink


The magnetic anisotropy of III-Mn-V ferromagnetic semiconductors prepared by ion implantation and pulsed laser melting
Xu, C.; Yuan, Y.; Sawicki, M.; Helm, M.; Zhou, S.;
As one of the most important physical properties of dilute ferromagnetic semiconductors (DFS), the magnetic anisotropy exhibits a complicated character and its origin is under continuous discussion [1, 2]. From the point of view of application, different magnetic anisotropies could meet various needs of spintronic devices. Due to different physical parameters (e.g. band gap, lattice constant) in various Mn doped III-V DMSs, various magnetic anisotropies are expected and could be tailored by Mn or hole concentrations [3-5]. To investigate this in greater detail, we prepare three typical III-Mn-V DFSs, InMnAs, GaMnAs, and GaMnP by ion implantation and pulsed laser annealing, which is a complementary approach to low-temperature molecular beam epitaxy. We report a systematic investigation on the magnetic anisotropy with the aim to understand its physical origin.

[1]. T. Dietl et al., Rev. Mod. Phys. 86, 187-251 (2014)
[2]. M. Birowska et al., Phys. Rev. Lett. 108, 237203 (2012)
[3]. U. Welp et al., Phys. Rev. Lett. 90, 167206 (2003)
[4]. M. Sawicki et al., Phys. Rev. B 70, 245325 (2004)
[5]. C. Bihler et al., Phys. Rev. B 78, 045203 (2008)
Keywords: Magnetic anisotropy, dilute ferromagnetic semiconductors (DFSs), ion implantation, pulsed laser annealing
  • Lecture (Conference)
    European Materials Research Society (E-MRS) 2016 Spring Meeting, 02.-06.05.2016, Lille, France

Publ.-Id: 24771 - Permalink


A Combined Spectroscopic/Molecular Dynamic Study for Investigating a Methyl Carboxylated PEI as a Potential Uranium Decorporation Agent
Lahrouch, F.; Chamayou, A. C.; Creff, G.; Duvail, M.; Hennig, C.; Lozano Rodriguez, M. J.; Den Auwer, C.; Di Giorgio, C.;
Natural uranium has a very limited radioactive dose impact but its chemical toxicity due to chronic exposure is still a matter of debate. Once inside the human body, the soluble uranium, under its uranyl form (U(VI)), is quickly removed from the blood system, partially excreted from the body and partially retained in targeted organs, i.e. the kidneys and bone matrix essentially. It is then crucial to remove or prevent the incorporation of uranium in these organs in order to limit the long term chronic exposure. A lot of small chelating agents such as aminocarboxylate (PACA), catecholamide (CAM) and hydroxypyridonate (HOPO) have been developed so far. However they suffer from poor selectivity and targeting abilities.
Macromolecules and polymers are known to present a passive accumulation (size related), i.e. the so-called EPR (Enhanced Permeability and Retention) effect, towards the main organs, which can be used as indirect targeting. Very interestingly, the methyl carboxylated polyethyleneimine (PEI-MC) derivative, has been described as a potent sequestering agents for heavy metals. It would be therefore an interesting candidate to evaluate as a new class of decorporation agents with passive targeting capabilities matching uranium preferential sequestering sites. In the present work, we have explored the ability of a highly functionalized (89% rate) PEI-MC to uptake U(VI) close to physiological pH using a combination of analytical and spectroscopic techniques (ICP-OES, Inductively Coupled Plasma Optical Emission Spectrometry; EXAFS, Extended X-Ray Absorption Fine Structure; and FT-IR, Fourier transformed Infra-Red) together with molecular dynamics (MD) simulation. A maximum loading of 0.47 mg U(VI) per mg of PEI-MC has been determined by ICP-OES measurements. From FT-IR data, a majority of monodentate coordination of the carboxylate functions of the PEI-MC seems to occur. From EXAFS and MD, a mix of mono and bidentate coordination mode has been observed. Note that agreement between the EXAFS metrical parameters and MD radial distribution functions is remarkable. To the best of our knowledge, this is the first comprehensive structural study of a macromolecular PEI based agent considered for uranium decorporation purposes.
Keywords: methyl carboxylated polyethyleneimine, uranium, ICP-OES, EXAFS, FT-IR, molecular dynamics

Publ.-Id: 24770 - Permalink


LWFA and laser-thomson scattering experiments at HZDR
Irman, A.;
I present recent status of laser wakefield acceleration and laser-thomson scattering experiments at HZDR.
  • Lecture (Conference)
    Laboratory for Laser- and beam-driven plasma Acceleration Workshop, 21.-22.06.2016, Wismar, Germany

Publ.-Id: 24769 - Permalink


New insights into a historical mine site: the Sn-W-Li Zinnwald/Cínovec deposit, eastern Erzgebirge, central Europe
Neßler, J.; Seifert, T.; Gutzmer, J.;
The historically significant Sn-W-Li Zinnwald/Cínovec deposit is characterised by greisen-type mineralization hosted within the apical portion of a small granite intrusion. Similar to other granitic stocks with Sn-W mineralization in the Erzgebirge, the Zinnwald granite intruded during the post- collisional stage of the late-Variscan (Permo-Carboniferous) magmatic evolution. These small Li-F granite bodies are characterised by the prominent enrichment of incompatible elements (F, Li, Rb, Cs, Sn, Nb, Ta) and the depletion of Ba, P, Sr, Zr, Ti, and Mg [1].
The Zinnwald granite is located in the eastern part of the Erzgebirge-Fichtelgebirge anticline and consists of highly evolved, weakly peraluminous and variably altered albite-Li mica leucogranite of anorogenic- type affiliation. Laterally extensive pegmatitic veins, which are located in the apical part of the granite cupola, represent the dominant source for the historically exploited Sn-W mineralisation, whereas sheet-like, metasomatic greisen ore bodies serve as a major resource for Li due to the abundance of Li- mica (zinnwaldite). This was demonstrated recently by extensive exploration of the Li mineralisation carried out by SolarWorld Solicium GmbH (SWS) during 2011 and 2014 [2].
This contribution aims to present new insights into the architecture, mineralization and geochemistry of the Zinnwald deposit based mainly on recent and historic drill core samples and their analysis by light microscopy and scanning electron microscopy, EPMA, LA-ICP-MS and whole rock ICP-MS. The results indicate an orientation of greisen ore bodies and veins parallel to the granite contact as well as a decrease of mineralization thickness and abundance with depth. While the host granite itself is highly evolved in its composition, progressive greisenization (Fig. 1) is accompanied by a decrease of fractionation indices (e.g. K/Rb from 20 to 8) and increasing contents of incompatible elements. For instance, mean grades of the most abundant quartz-mica-topaz-greisen include 3,700 ppm Li, 70 ppm Cs and 3.1 wt.% F. Fluid-controlled metasomatic processes are inferred from microscopic textures, trace element behaviour and significant tetrad-effect in normalized REE patterns. The chemical composition of Li-mica is similar for various greisenized lithologies of the endo- and exocontact, and Li concentrations range from 1.1 to 2.2 wt.%. Greisenization, which corresponds to the formation of zinnwaldite, follows an incipient stage of quartz-replacement and is spatially related, but not genetically linked, to disseminated Sn-W mineralization. This is demonstrated by the presence of disseminated Sn-W mineralization hosted either by greisen lithologies or by albite granite, which was only moderately affected by greisenization. This, in turn, may require a critical assessment of current metallogenetic models.
References
[1] Seifert, Th., Kempe, U (1994) Beiheft z. European Journal of Mineralogy, 6 (2): 125-172 [2] Neumann, M. et al. (2014) Unpublished resource report, pp. 204
[3] Grunewald, V. (1978) Unpublished report, Geological Archive LfULG - EB 1391, pp. 190
  • Open Access LogoContribution to proceedings
    International Geological Congress, 27.08.-04.09.2016, Cape Town, South Africa
    Proceedings of the International Geological Congress, Washington: AGI

Publ.-Id: 24768 - Permalink


Redshifting and harmonic radiation in the nonlinear laser-thomson scattering interaction
Irman, A.;
Thomson scattering of intense laser pulses from relativistic electrons not only allows for the generation of bright x-ray pulses but also serves as a laboratory for strong field physics and nonlinear interactions. We present high resolution angle and energy resolved measurements on the laser-Thomson x-ray distribution generated by colliding picosecond electron bunches from the ELBE linear accelerator with counter-propagating laser pulses from the 150 TW DRACO Ti:Sapphire laser system. As we increase the laser intensity, the electrons start to move in more complex trajectories resulting to emission of x-ray photons at higher harmonics which extends beyond 24 keV. Furthermore the overall radiation spectrum shows the broadening and redshift effect as predicted in the theory of intense laser-relativistic electron interaction in the classical picture. The amount of scattered photon also increases one order of magnitude to 106 photons per shot in the full opening emission angle.
Keywords: Laser-Thomson scattering, DRACO laser, ELBE accelerator
  • Lecture (Conference)
    17th Advanced Accelerator Concepts Workshop, 31.07.-05.08.2016, National Harbor, Maryland, USA

Publ.-Id: 24767 - Permalink


Phosphate mineralization in the Vergenoeg fluorite deposit (RSA) and its implication for the origin of REE-bearing fluid alteration
Höfig, T. W.; Krause, J.; Kern, M.; Birtel, S.; Gutzmer, J.;
The Vergenoeg volcanic pipe, located in the central part of the Bushveld Complex (Republic of South Africa), hosts one of the economically most significant fluorite deposits on Earth. Its iron-oxide – fluorite – fayalite assemblage is well known for marked enrichment of rare-earth elements (REE) and phosphate. Previous studies reported the presence of apatite and a number of REE-rich accessory minerals, particularly phosphates [1, 2, 3]. Here we present a systematic study of REE-phosphates (monazite, xenotime) from the hematite-fluorite zone of the Vergenoeg orebody. Links between mineral che mi cal variations, paragenesis, and microstructural aspects are examined. The results are used to elucidate the genesis of REE-phosphate mineralization in the Vergenoeg fluorite deposit.
For this study, both apatite-bearing and apatite-free samples from the hematite-fluorite zone were selected.Scanning electronmicroscopy-based image analysis has been performed in order to identify and spatially map the distribution of rare-earth phosphates as well as rock-forming minerals throughout the samples in polished sections. Subsequently, the mineral chemistry of the phosphates has been determined by means of electron probe microanalysis.
Two major fabric type scan be distinguished:First,fine-grained monazite and xeno time form euhedral pseudomorphs in the presence or absence of apatite. Second, they occur as infill of interstices and microfractures. Mineral associations of monazite with xenotime, iron-oxide, fluorite or their joint assemblage have been identified,applying to every fabric type.The combination of mineral chemistry data and microstructural observations suggests a link between the spatial occurrence of REE-phosphates and their chemical composition. Different mineral associations also have an effect on the chemical composition. In addition, the deportment of certain elements suggests microstructural and mineralogical changes as controlling factors, respectively.
The mineral chemistry of monazite is inline with the monazite-(Ce)of type 2 from Graupner et al. [3]. Xenotime data point to Y-rich compositions, corresponding to the secondary xenotime generation proposed by Graupner et al. [3]. Besides regular monazite, the presence of grains with comparatively low analytical totals between c. 90 wt% and 98 wt% may reflect altered compositions, resulting from hydration under low-temperature conditions giving rise to formation of hydrated monazite (or even rhabdophane) [e.g., 4, 5]. Similarly low analytical totals for xenotime may also represent hydration. Increasing sulfur contents with decreasing analytical totals for both rare-earth phosphates indicate enhanced sulfur activity of the overprinting fluid.
References:

[1]FouriePJ(2000)In:Hydrothermal Iron Oxide Copper Gold & Related Deposits:A Global Perspective: Australian Mineral Foundation, Adelaide, 309–320
[2] Goff BH et al. (2004) Miner Petrol 80: 173–199
[3] Graupner T et al. (2015) Ore Geol Rev 64: 583–601
[4] Krenn E and Finger F (2007) Lithos 95: 130–147 [5] Berger A et al.(2008)Chem Geol 254:238–248
  • Open Access LogoContribution to proceedings
    International Geological Congress, 27.08.-04.09.2016, Cape Town, South African
    Proceedings of the International Geological Congress, Washington: American Geoscience Institute

Publ.-Id: 24766 - Permalink


Self-assembly of periodic nanostructure arrays based on ion-induced spontaneous surface nanopatterning
Erb, D.; Ou, X.; Schlage, K.; Lenz, K.; Röhlsberger, R.; Lindner, J.; Facsko, S.; Helm, M.; Fassbender, J.ORC
Nanopatterning of different materials is a key requirement in research fields as diverse as magnetism, plasmonics, optics or catalysis. Potential technological applications range from photovoltaics augmented by light trapping [1] to high-sensitivity biomolecule detection using plasmonic signal enhancement [2] and high-speed low-energy information encoding, transmission, and processing based on magnonic crystals [3]. Industrial-scale fabrication of such devices for energy harvesting, medical diagnostics, or information technology requires nanopatterning processes which are fast, facile, cost-effective, scalable, and highly reproducible. A versatile bottom-up nanopatterning approach which can meet these demands is based on ion irradiation of semiconductor surfaces and well-established thin film deposition techniques.

On crystalline semiconductor substrates, nanoscale surface patterns with well-defined lateral periodicity form via the mechanism of reverse epitaxy, i.e. the non-equilibrium self-assembly of vacancies and ad-atoms under ion irradiation [4]. The GaAs(001) surface exhibits highly uniform faceting and therefore lends itself to transferring this pattern regularity to other materials. The nanopatterned GaAs surface can for instance be employed as a substrate for molecular beam epitaxy under grazing incidence, producing arrays of nanodots, nanowires, periodically corrugated thin films, or combinations thereof by geometrical shading. It can also be the basis for hierarchical self-assembly: here, the topography of the GaAs surface provides a preferential direction for the chemical microphase separation in a diblock copolymer thin film. This flat film then serves as a highly ordered chemical template for metal nanostructure growth in a variety of pattern morphologies [5]. The large-area periodically nanopatterned sample systems are especially very well suited for x-ray and neutron scattering experiments.

In this contribution, we outline the reverse epitaxy mechanism and present examples of how the resulting surface nanopatterns can be employed in the fabrication of nanostructure arrays. We hope to stimulate discussion of further applications by emphasizing the simplicity and versatility of this bottom-up approach.

[1] H.A. Atwater and A. Polman, Nature Materials 9 (2010)
[2] J. Vogt et al., Phys. Chem. Chem. Phys. 17 (2015)
[3] D. Grundler, Nature Physics 11 (2015)
[4] X. Ou et al., Nanoscale 7 (2015)
[5] D. Erb et al., Science Advances 1 (2015)
  • Poster
    MML workshop, 14.-16.12.2016, Hamburg, Deutschland

Publ.-Id: 24765 - Permalink


Quantifying the resource potential of flotation tailings storage facilities – the role of geometallurgical characterization
Gutzmer, J.; Osbahr, I.; Leißner, T.; Satgé, L.; Unger, G.; Büttner, P.;
Flotation is the most widely applied separation process in today’s raw materials industry. Billions of tons of flotation tailings are produced every year. As fine-grained residues these are usually deposited in large-scale tailings storage facilities (TSLs). With recoveries commonly below 90%, a significant portion of the value contained in the primary ore finds its way into such TSLs. In addition, commodities that were not targeted by the primary exploitation process may later become valued products. There are many well-known examples of historic tailings (or other mining-related residues) becoming economically attractive targets of renewed exploitation. Arguably the most prominent of these examples is the recovery of gold and uranium from slimes and sand storage facilities of the Witwatersrand goldfields, South Africa. TSLs are thus best described as large, low-grade anthropogenic ore bodies; they are also a prime example of an urban mine.

Retreatment of tailings offers some significant advantages. Very large tonnages of readily milled material are available at surface. Volume and average grade are usually well-known, thus reducing exploration expenses and technical risk. Added economic benefit may be the release of land previously covered by TSLs for development. There are also environmental benefits as particular components identified as environmental risk may be removed and remaining residues transferred into TSLs that comply with modern environmental legislation.

There are, however, also some tangible risks associated with retreatment of materials from TSLs. Most importantly, the value components that have escaped previous separation efforts are likely to be difficult to concentrate. Reasons for losses are manifold, but may include poor liberation or very fine grain size of ore minerals or complex deportment of target metals into various minerals. Furthermore, ore minerals may experience surface alteration processes whilst contained in TSLs for extended periods of time. Such processes result in the development of surface coatings or even complete transformation of primary ore mineral assemblages into a complex paragenesis of secondary products. Ultimately, such processes lead to a complex overprint of the inherent primary stratification related to tailings deposition by a secondary stratification that resembles supergene oxidation and cementation zones.

Given the above it appears only reasonable that TSFs should be exposed to careful geometallurgical characterization prior to retreatment [1]. This contribution will present two examples from the Ore Mountains, Germany [2]. Two large TSLs were systematically drilled; the tailings materials were subjected to comprehensive characterization. 3D models were constructed for the TSLs based on novel recoverability indices that take into account not only grade, but also other tangible characteristics of the tailings material, such as liberation and grain size of value components. In this manner, opportunities and limitations of intended retreatment can be constrained – and an optimal retreatment strategy developed.

References:
[1] Louwrens E et al. (2015) in: Tailings and mine waste management for the 21st Century, AUSIMM, 99-106
[2] http://www.r3-innovation.de/de/15499
  • Open Access LogoContribution to proceedings
    International Geological Congress, 27.08.-04.09.2016, Cape Town, South Africa
    Quantifying the resource potential of flotation tailings storage facilities – the role of geometallurgical characterization, Washington: American Geosciences Institute

Publ.-Id: 24764 - Permalink


Disentangling magnetic order on nanostructured surfaces
Erb, D.; Schlage, K.; Bocklage, L.; Hübner, R.; Merkel, D.; Wille, H.-C.; Rüffer, R.; Röhlsberger, R.;
Nanopatterned magnetic materials are of considerable interest for both academic research and industrial application. We present a novel technique, combining Nuclear Resonant Scattering (NRS) [1] and GISAXS [2], which allows disentangling the magnetic properties of distinct structural units in a nanopatterned system. The underlying idea is to exploit the fact that the nuclear resonant signal (carrying the magnetic information) undergoes the same scattering in q-space as the electronic signal (carrying the structural information). Thus, photons scattered resonantly from different structural units of the sample are separated due to the sample morphology and can be detected at different positions in the scattering pattern. To demonstrate this principle, we fabricated a 57Fe thin film sample with alternating thick and thin stripe-like regions, i.e. with heterogeneous structural and magnetic properties, which vary periodically on the nm-scale. We investigated the sample in-situ during growth (beamline ID18, ESRF) and studied its response to external magnetic fields ex-situ (beamline P01, PETRA III). During film growth, we observed the onset of ferromagnetic ordering first in the thicker regions, then in the thinner regions. Upon applying an external magnetic field, the magnetic moments in thick and thin regions are displaced from the easy axis of magnetization to different extents [3, 4]. Our experiments thus show that nuclear resonant GISAXS is a sensitive method for obtaining information about the magnetic state of individual nm-scaled parts of a magnetically heterogeneous sample.

[1] R. Röhlsberger, Springer Tracts in Modern Physics 208 (2004)
[2] G. Renaud, R. Lazzari, and F. Leroy, Surface Science Reports 64 (2009) 255
[3] D. Erb, Ph.D. thesis, University of Hamburg (2015)
[4] manuscript in preparation
  • Poster
    GISAXS2016 workshop, 16.-18.11.2016, Hamburg, Deutschland

Publ.-Id: 24763 - Permalink


Laser wakefield with external bunch injection, status 2016 (work in progress)
Irman, A.;
Recent progress of laser wakefield acceleration with external bunch injection at HZDR is presented
Keywords: laser wakefield, RF linear-accelerator
  • Lecture (Conference)
    3rd EuCard-2 Annual meeting, 26.-28.04.2016, University of Malta, Malta

Publ.-Id: 24762 - Permalink


The EIT Raw Materials
Gutzmer, J.;
Invited lecture - no abstract
  • Lecture (others)
    Annual Graduation Ceremony of Emerald MSc Students, 23.-24.08.2016, Liege, Belgium

Publ.-Id: 24761 - Permalink


A systematic investigation of the magnetic anisotropy of III-Mn-V dilute ferromagnetic semiconductors
Xu, C.; Yuan, Y.; Sawicki, M.; Helm, M.; Zhou, S.;
As one of the most important physical properties of dilute ferromagnetic semiconductors (DFS), the magnetic anisotropy exhibits a complicated character and its origin is under continuous discussion [1, 2]. From the point of view of application, different magnetic anisotropies could meet various needs of spintronic devices. Due to different physical parameters (e.g. band gap, lattice constant) in various Mn doped III-V DMSs, various magnetic anisotropies are expected and could be tailored by Mn or hole concentrations [3-5]. To investigate this in greater detail, we prepare three typical III-Mn-V DFSs, InMnAs, GaMnAs, and GaMnP by ion implantation and pulsed laser annealing, which is a complementary approach to low-temperature molecular beam epitaxy. We report a systematic investigation on the magnetic anisotropy with the aim to understand its physical origin.

[1]. T. Dietl et al., Rev. Mod. Phys. 86, 187-251 (2014)
[2]. M. Birowska et al., Phys. Rev. Lett. 108, 237203 (2012)
[3]. U. Welp et al., Phys. Rev. Lett. 90, 167206 (2003)
[4]. M. Sawicki et al., Phys. Rev. B 70, 245325 (2004)
[5]. C. Bihler et al., Phys. Rev. B 78, 045203 (2008)
Keywords: Magnetic anisotropy, dilute ferromagnetic semiconductors (DFSs), ion implantation, pulsed laser annealing
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft 2016, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 24760 - Permalink


Das Helmholtz Institut Freiberg für Ressourcentechnologie: Status und Ausblick
Gutzmer, J.;
No abstract - invited lecture
  • Lecture (others)
    Jahrestagung der Praxispartner, Interdisziplinäres Ökologisches Zentrum, 28.04.2016, Freiberg, Germany

Publ.-Id: 24759 - Permalink


Reverse epitaxy: Nanopattern formation by vacancy self-assembly upon low energy ion irradiation of crystalline semiconductor surfaces
Erb, D.; Engler, M.; Ou, X.; Facsko, S.;
Uniform crystalline nanostructures are sought-after in many fields of research and technology, ranging from ranging from catalysis [1] to electronics [2]: crystalline nanostructures have the potential of becoming the building blocks of future information technology or of boosting development in energy conversion and storage.

Crystalline nanostructures are successfully grown in wet-chemical procedures [3] or by molecular beam epitaxy (MBE) [4]. Reverse epitaxy [5,6] is an alternative approach to fabricating highly ordered arrays of crystalline nanostructures on large areas of semiconductor surfaces. In contrast to ion irradiation under non-normal incidence at room temperature, where ripples are formed on the amorphized semiconductor surface [7], reverse epitaxy occurs at substrate temperatures above the recrystallization temperature, which ensures that the semiconductor surface retains its crystallinity.
Based on the kinetically restricted diffusion (Ehrlich-Schwoebel barrier for crossing atomic steps) of vacancies created by low energy ion irradiation, this subtractive process is considered analogous and complementary to the additive homoepitaxial growth via MBE. The resulting nanostructure morphology can be controlled via easily accessible parameters such as substrate material, surface orientation, temperature, ion species and fluence. Possible morphologies include sawtooth facets and square or hexagonal pyramidal pits with feature sizes of a few tens of nanometers.

We discuss the underlying principles and the mechanism of nanostructure formation by reverse epitaxy. The variety of nanopatterned morphologies on different semiconductor surfaces will be highlighted. We hope to stimulate discussion by presenting recent examples of our research and proposing possible applications.

[1] H. G. Yang et al., Nature 453, 638 (2008)
[2] Y. Huang et al., Science 291, 630 (2001)
[3] W. Li et al., Nanotechnology 27, 324002 (2016)
[4] C. Teichert, Phys. Rep. 365, 335 (2002)
[5] X. Ou et al., Phys. Rev. Lett. 111, 016101 (2013)
[6] X. Ou et al., Nanoscale 7, 18928 (2015)
[7] W. L. Chan et al., J. Appl. Phys. 101, 121301 (2007)
  • Invited lecture (Conferences)
    24th International Conference on the Application of Accelerators in Research and Industry, 30.10.-04.11.2016, Fort Worth, USA

Publ.-Id: 24758 - Permalink


Compositional Data Analysis: introduction and applications (and some practice)
Tolosana-Delgado, R.;
This lecture will cover the fundamental aspects of compositional data analysis, from brief theoretical concepts to most widely used statistical analysis tools. Concepts will be illustrated with examples from Sediment Provenance Analysis. These will include estimating modal compositions, building confidence regions and drawing them in ternary diagrams, developing supervised classification methods to infer the origin of a sediment out of its (bulk or varietal grain) composition, and establishing regression models to describe compositional linear processes such as comminution and weathering.
Keywords: alr, centered logratio, principal components, sediment provenance, spurious correlation
  • Invited lecture (Conferences)
    Sedimentary Provenance Analysis (short course), 21.-23.09.2016, Göttingen, Deutschland

Publ.-Id: 24757 - Permalink


Recent progress on laser cooling of relativistic Lithium-like 12C3+ ion beams at heavy ion storage ring CSRe
Wen, W. Q.; Wang, H. B.; Huang, Z. K.; Zhang, D. C.; Hai, B.; Zhu, X. L.; Chuai, X. Y.; Zhao, D. M.; Yang, J.; Li, J.; Li, X. N.; Mao, L. J.; Mao, R. S.; Wu, J. X.; Xia, J. W.; Yang, J. C.; Yuan, Y. J.; Zhao, H. W.; Zhao, T. C.; Eidam, L.; Loeser, M.; Rein, B.; Siebold, M.; Winters, D.; Bussmann, M.ORC; Ma, X. W.
aser cooling of relativistic heavy ion beams at storage rings is one of the most promising techniques to reach high phase-space densities and achieve phase transition, ordered beam even crystalline beam. Compared with the established cooling schemes at storage rings, such as stochastic cooling and electron cooling, laser cooling has many advantages such as fast-cooling, ultra-strong cooling force and providing an ultra-low temperature(m K) ion beams. In addition, the precision laser spectroscopy of the highly charged ions can be performed by using the laser-cooled ion beams during the laser cooling experiments. We introduce the experimental principal and methods of laser cooling of relativistic ion beams at the experimental cooler storage ring of the CSRe at the Institute of Modern Phyics, Chinese Academy of Sciences. The first experimental results from a beam time aiming for laser cooling of 122 Me V/u Li-like 12C3+ at the CSRe with a pulsed laser are presented, and laser cooling and precision laser spectroscopy of relativistic Li-like and Na-like highly charged ions at the future large facility HIAF and FAIR are outlined.
Keywords: laser cooling, relativistic, ion beam

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Publ.-Id: 24756 - Permalink


Hierarchical self-assembly: Three steps to highly ordered arrays of uniform metal nanostructures
Erb, D.; Schlage, K.; Röhlsberger, R.;
Nanopatterning via self-assembly has gained considerable interest as an alternative to lithography-based techniques for nanostructure fabrication. We propose a procedure for producing highly ordered arrays of uniform metallic nanostructures based exclusively on three subsequent self-assembly processes [1]: crystal surface reconstruction, copolymer microphase separation, and metal diffusion on chemically heterogeneous surfaces. The versatile approach allows for preparing nanostructures with scalable sizes and in a variety of shapes and materials. With this high-throughput technique, nanopatterns covering areas of several square centimeters can be fabricated easily.
We present results of in-situ structural and magnetic investigations of Fe nanodot arrays during formation by grazing incidence small angle X-ray scattering [2] and nuclear resonant scattering of synchrotron radiation [3], examining the dependence of the nanodot shape on deposition conditions and observing the evolution of magnetic moment dynamics during nanodot growth [4]. Possible applications of self-assembled nanopatterns could range from high-density magnetic data storage to catalysis or sensing based on surface plasmon resonance.

[1] D. Erb, K. Schlage, R. Röhlsberger, Science Advances 1 (2015) e1500751
[2] G. Renaud, R. Lazzari, and F. Leroy, Surface Science Reports 64 (2009) 255
[3] E. Gerdau and H. de Waard (eds.), Hyperfine Int. 123-124 (1999)
[4] D. Erb, Ph.D. thesis, University of Hamburg (2015)
Keywords: self-assembly diblock copolymers metal nanostructures
  • Lecture (Conference)
    International Conference on Solid Films and Surfaces, 28.08.-02.09.2016, Chemnitz, Deutschland

Publ.-Id: 24755 - Permalink


Comparison of Atomistic Quantum Transport and Numerical Device Simulation for Carbon Nanotube Field-effect Transistors
Fuchs, F.; Zienert, A.; Mothes, S.; Claus, M.; Gemming, S.; Schuster, J.;
Carbon nanotube field-effect transistors (CNTFETs) are studied using atomistic quantum transport simulation and numerical device simulation. The studied CNTFETs consist of n-doped source- and drain-electrodes with an ideal wrap-around gate. Both the off- as well as the on-currents are described in very good agreement by both methods, which verifies the employed simplified approach in the numerical device simulation. The off-current is strongly dependent on interband tunneling in the studied CNTFETs. Thus, the good agreement between the methods verifies the tunneling model in the numerical device simulator, which can therefore be used to describe other tunneling devices, too. On the basis of the two methods we also discuss the effect of different channel lengths and aggressive gate scaling.
Keywords: carbon nanotube, field-effect transistor, numerical device simulation, atomistic quantum transport simulation
  • Contribution to proceedings
    Simulation of Semiconductor Processes and Devices (SISPAD), 06.-08.09.2016, Nürnberg, Deutschland
    Proceedings of SISPAD: IEEE, 978-1-5090-0818-6
    DOI: 10.1109/SISPAD.2016.7605197
  • Poster
    Simulation of Semiconductor Processes and Devices (SISPAD), 06.-08.09.2016, Nürnberg, Deutschland

Publ.-Id: 24754 - Permalink


Investigation of Carbon Nanotube Field-effect Transistors Using Atomistic Quantum Transport and Numerical Device Simulation
Fuchs, F.; Zienert, A.; Schuster, J.; Mothes, S.; Claus, M.; Gemming, S.;
Carbon nanotube based field-effect transistors (CNTFETs) are studied by using atomistic quantum transport simulation and numerical device simulation. Atomistic simulations are based on the non-equilibrium Green’s functions formalism, where self-consistent extended Hückel theory is used [1]. We apply a parameter set previously developed in our group to describe contacts between metals and carbon nanotubes with a density functional theory (DFT)-like accuracy [2]. Numerical device simulations based on the effective-mass Schrödinger equation are done for comparison [3] to highlight the strengths but also the limitations of this widely used method.
The studied CNTFETs consist of n-doped source- and drain-electrodes together with an ideal wrap-around gate. Thus, the transistor exhibits Ohmic contacts and is comparable to the one studied experimentally by Lu et al. [4]. Different CNTs with diameters ranging from 0.5 nm (7,0-CNT) to 1.3 nm (16,0-CNT) are compared. For larger diameters, band-to-band tunneling (BTBT) takes place, leading to ambipolar transfer characteristics. For small diameters, however, states within the channel are strongly localized and the BTBT is subsequently suppressed, resulting in very high on/off ratios of about 107 and ideal unipolar transfer characteristics. We investigate how different device parameters influence the device performance and show that the studied CNTFET shows excellent properties for channel lengths down to 8 nm and for a very small gate electrode of only 0.4 nm length. Finally, a comparison between the atomistic model and numerical device simulation is given. We show that the on- and off-currents are described in very good agreement and discuss the differences with respect to the switching behavior.
[1] Calculations performed using Atomistix ToolKit 12.8 (www.quantumwise.com)
[2] Zienert et al., Nanotechnology 25 (2014)
[3] Claus et al., Journal of Computational Electronics 13 (2014)
[4] Lu et al., Journal of the American Chemical Society 128 (2006)
Keywords: carbon nanotubes, numerical device simulation, atomistic quantum transport simulation, electron transport, field-effect transistors
  • Lecture (Conference)
    11th International Symposium on Computational Challenges and Tools for Nanotubes, 28.08.-02.09.2016, Wien, Österreich

Publ.-Id: 24753 - Permalink


An Atomistic Model for Carbon Nanotube Based Field-effect Transistors: Interband Tunneling and Device Scaling
Fuchs, F.; Zienert, A.; Schuster, J.; Gemming, S.;
We study carbon nanotube based field-effect transistors (CNTFETs) consisting of n-doped source and drain electrodes together with an ideal wrap-around gate. This system is comparable to the one studied experimentally by Lu et al. [1] and is our model for comparing different simulation approaches. In this contribution, we present our results based on a fully atomistic quantum transport model.
Carbon nanotubes (CNTs) with diameters ranging from 0.5 nm to 1.3 nm, which corresponds to the (7,0) CNT and (16,0) CNT, respectively, are studied. We find that in case of thick CNTs, the band-to-band tunneling (BTBT) strongly increases the leakage current in the off-state. This leads to ambipolar transfer characteristics in agreement with experimental results1. Concerning very thin CNTs, the BTBT has not been studied in much detail, yet. We demonstrate that for these kind of CNTs, states within the channel are strongly localized. They do not allow carrier transport and thus suppress the BTBT, which results in ideal unipolar transfer characteristics and on/off ratios of about 107.
We furthermore present a systematic investigation of the relation between device parameters and the resulting transistor characteristics, which can guide future device scaling. Thin CNTs for example allow outstanding device properties even for short channel lengths down to 8 nm. It is crucial to maintain channel control in ultra-scaled transistors. Thus, our studies also elucidate the impact of aggressive gate scaling. Even for a very small gate electrode of only 0.4 nm length, good switching properties can be preserved.
The non-equilibrium Green’s functions formalism together with self-consistent extended Hückel theory is used for the simulations. Thanks to a parameter set previously developed in our group [2], we can describe CNTs with a density functional theory-like accuracy.
[1] Lu et al., Journal of the American Chemical Society 128 (2006)
[2] Zienert et al., Nanotechnology 25 (2014)
Keywords: carbon nanotubes, field-effect transistor, extended Hückel theory, electron transport
  • Poster
    17th International Conference on the Science and Application of Nanotubes and Low-Dimensional Materials (NT16), 28.08.-02.09.2016, Wien, Österreich

Publ.-Id: 24752 - Permalink


Stress Analysis in Semiconductor Devices by Kelvin Probe Force Microscopy
Sheremet, E.; Fuchs, F.; Paul, S. D.; Haas, S.; Vogel, D.; Rodriguez, R. D.; Zienert, A.; Schuster, J.; Reuter, D.; Geßner, T.; Zahn, D. R. T.; Hietschold, M.;
The determination of built-in strain in semiconductor devices with nanometer spatial resolution and high sensitivity is needed for the characterization of nanoscale electronic devices. Kelvin probe force microscopy (KPFM) is an atomic force microscopy-based method that provides the spatially resolved surface potential at the sample surface, fulfilling the requirements on resolution and sensitivity. The contrast observed in KPFM imaging is often attributed to stress, but there are only a few reports on the application of KPFM for quantitative stress analysis [1]. In this contribution we focus on the application of KPFM for analysis of stress in silicon devices, such as copper through silicon vias and silicon membranes. The experimental results are compared with density functional theory calculations of strained silicon. This work provides critical insights into the quantitative determination of stress at the nanoscale that so far has gone largely unnoticed in the scanning probe microscopy community.
[1] W. Li, D.Y. Li, J. Appl. Phys. 99, 073502 (2006).
Keywords: silicon, kelvin probe force microscopy, density functional theory
  • Poster
    DPG Frühjahrstagung Regensburg, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 24751 - Permalink


Electronic Structure and Transport Properties of Thin Silicon Nanowires
Fuchs, F.; Gemming, S.; Schuster, J.;
Silicon nanowires (SiNWs) are promising candidates as building blocks for electronic devices. For the simulation of SiNWs, numerical device simulations, based on the silicon bulk band structure, are often used. When the diameter of the wires is reduced, however, atomistic quantum simulations become mandatory at some point. In the present work, thin hydrogen-passivated SiNWs with diameters between 1 and 6 nm are studied by means of density functional theory. It is shown that the band gap approaches the bulk value in the limit of infinitely thick nanowires and increases for thin wires due to quantum confinement. Using a radially resolved density of states it is demonstrated, that the density of states is highest in the nanowire center, where most of the current transport would occur, and decreases near the surface. Comparing the density of states between SiNWs with different diameters, the transition to bulk silicon can be observed. This justifies the use of bulk band structure approximations for thicker SiNWs, but also highlights the need for atomistic quantum simulations in case of thinner ones.
Keywords: silicon nanowire, density functional theory, quantum confinement
  • Lecture (Conference)
    DPG Frühjahrstagung Regensburg 2016, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 24750 - Permalink


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