Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Incorporation of Al in ZnO by reactive pulsed magnetron sputtering: electrical properties and dopant activation
Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.;
Al-doped ZnO (AZO) films which combine maximum carrier mobility (μe), moderate free electron densities (Ne) and high surface roughness are of special interest for application as transparent front electrode in thin film solar cells. They posses high transmission in the near infrared region, close to the bandgap energy of absorber materials like Si (Eg =1.11 eV), and enable a superior light trapping behaviour. A key to tailor AZO film properties is understanding the mechanisms and effects of the Al-dopant incorporation into the ZnO matrix. The present work focuses on investigation of the influence of Al concentration on the electrical properties of AZO and on establishing performance limits with respect to carrier mobility and resistivity (ρ). Polycrystalline and epitaxial AZO films are grown on fused silica and c-axis oriented sapphire substrates, respectively, by reactive pulsed magnetron sputtering using several sets of Zn/Al alloy targets with an Al concentration (cAl) between 0.7 and 8.7 at%. A systematic variation of process parameters such as substrate temperature (Ts) and oxygen partial pressure results in polycrystalline films with μe>45 cm2V-1s-1 and
<2.3x10-4 Ωcm at optimum conditions, whereas μe~55 cm2V-1s-1 could be obtained for epitaxial films. It is observed that cAl has a strong influence on the optimum value of Ts, the maximum μe and Ne values and also on film structure and surface roughness. The observed dependence of carrier mobility Ne in AZO is discussed in the framework of ionized impurity scattering and clustering as well as grain boundary limited transport which predicts a fundamental physical limit of μe.
Rutherford Backscattering (RBS) and elastic recoil detection analysis (ERDA) confirm a considerable Al enrichment in the films when Ts is increased above its optimum value which correlates with the deterioration of their electrical properties. Combining ion beam analysis and Hall-effect measurements allows to estimate the fraction of electrically active Al dopants, which is rarely reported in a quantitative and systematic manner. The influence of intrinsic defects and charge compensation complicate the interpretation of the results. Nevertheless the target Al concentration as well as the substrate temperature are shown to have an impact on the dopant activation.
Keywords: Al-doped ZnO transparent conductive oxide zinc oxide magnetron sputtering doping activation
  • Lecture (Conference)
    MRS Spring Meeting 2011 (Symposium S: Plasma-assisted Materials Processing and Synthesis), 25.-29.04.2011, San Francisco, USA

Publ.-Id: 16506 - Permalink


Determination of the electrically active Al fraction in Al doped ZnO grown by pulsed reactive magnetron sputtering
Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.;
Al-doped ZnO (AZO) films which combine maximum carrier mobility (µe), moderate free electron densities (Ne) and high surface roughness are of special interest for application as transparent front electrode in thin film solar cells. They posses high transmission in the near infrared region, close to the bandgap energy of absorber materials like Si (Eg=1.11 eV), and enable a superior light trapping behaviour.
A key to tailor AZO film properties is understanding the mechanisms and effects of the Al-dopant incorporation into the ZnO matrix. It is well accepted that the mobilities in degenerately doped AZO are limited by ionized impurity scattering. A way to overcome this limitation would be to reduce the density of ionized impurities which either don’t donate electrons themselves or compensate the Al donor. This is equivalent to increasing the fraction of electrically active Al in the ZnO host material. Systematic and quantitative investigations on this topic are rarely reported in literature. Therefore this work focuses on quantification of the Al concentration by ion beam analysis methods in conjuction with Hall-effect measurements for AZO films grown by reactive pulsed magnetron sputtering. The influence of parameters like target composition and substrate temperature on the Al activation will be discussed.
Keywords: Al-doped ZnO transparent conductive oxide magnetron sputtering activation doping
  • Lecture (Conference)
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 16505 - Permalink


Nonlinear terahertz spectroscopy of semiconductor quantum structures
Schneider, H.;
There is no abstract.
Keywords: infrared/terahertz spectroscopy, nonlinear quadratic detection, semiconductor quantum wells, intersubband transsitions
  • Invited lecture (Conferences)
    2. IR-ON Symposium: InfraRed Optical Nanostructures, 10.03.2011, Wien, Österreich

Publ.-Id: 16504 - Permalink


Voigt effect measurements on PLD grown nickel oxide thin films
Scarlat, C.; Mok, K. M.; Zhou, S.; Lorenz, M.; Grundmann, M.; Helm, M.; Schubert, M.; Schmidt, H.;
NiO has great potential applications in spin valves, magnetooptical sensors, optical fibers, solar thermal absorbers, or in non-volatile resistive random memories [1]. In our study NiO, NiMnO, and NiMnLiO thin films have been grown on double-side polished r-plane sapphire substrates by pulsed laser deposition. We measured the complex Voigt angle using the polarized light from a HeCd laser, a Glan Taylor polarizer, a Hinds PEM-100 and two LockIns [2]. The Voigt effect is a second-order magneto-optic effect [3]. The polarization state of light after transmission through a sample consisting of ca. 1 μm thick, weak ferromagnetic and diamagnetic NiO thin films on purely diamagnetic r-plane sapphire substrates has been modelled using the 4x4 matrix formalism [2] in dependence of an external magnetic field applied in-plane, i.e. in Voigt configuration. The modelling results revealed that for the bare diamagnetic substrate the Voigt angle depends parabolically on the external magnetic field and that the weak ferromagnetic and diamagnetic NiO thin films changed the parabolic dependence of the Voigt angle in the range of ±0.3 T to a flat-top shape in agreement with the experimentally determined Voigt angle. Furthermore, due to the NiO thin films the Voigt angle increased ca. (1±i)10-5 deg for an external in-plane field of ±0.3 T.
[1] U. Russo, D. Ielmini, A.L. Lacaita, A. Pirovano, F. Pellizer and R. Bez, IEEE Electron Device Lett. 25 (2004) 507-509.
[2] C. Scarlat, K. M. Mok, S. Zhou, M. Vinnichenko, M. Lorenz, M. Grundmann, M. Helm, M. Schubert, H. Schmidt, Phys. Stat. Sol. (C) 7 (2010) 334-337.
[3] R. Carey and B.W.J. Thomas, J. Phys.: D: Appl. Phys. 7 (1974) 2362-2368.
  • Lecture (Conference)
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 16503 - Permalink


Optical and magnetic properties of Cr-implanted indium oxides thin films
Scarlat, C.; Zhou, S.; Vinnichenko, M.; Kolitsch, A.; Helm, M.; Schmidt, H.;
Dilute magnetic oxides using the electron spin rather than its charge as information carrier are expected to play a key role in the development of spinelectronics. As it has been shown recently, indium oxide (IO), a transparent conducting material, is of potential importance also as a material for spintronics. Polycrystalline and amorphous (ca. 300 nm thick) n-type conductive IO films were grown on SiO2/Si substrates using reactive magnetron sputtering. The films were implanted with Cr+ ions in order to reach Cr concentrations of 1, 2, 3, 4 and 5 at%. The implantation energy was 120 keV. Cr is chosen as a dopant because of its large magnetic moment in the ionic state, and the antiferomagnetic nature of Cr metal segregations. It is non-trivial to form any ferromagnetic secondary phase of Cr oxide. Highly oxygen deficient 2%Cr:IO co-evaporated films revealed ferromagnetism. Here we study the effect of the post-growth treatment on the structural, electrical, magnetic, and optical properties of Cr-implanted IO films. It is shown that only the 2%Cr:IO implanted film is weakly ferromagnetic at 5 K. A reasonable model for the Cr:IO implanted films has been developed to extract optical constants from spectroscopic ellipsometry data below 3 eV in dependence on the Cr concentration.
  • Poster
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 16502 - Permalink


Infrared photodetectors based on quantum wells
Schneider, H.;
There is no abstract.
Keywords: infrared/terahertz detector, semiconductor quantum well, GaAs/AlGaAs, thermal imaging
  • Invited lecture (Conferences)
    Workshop on Infrared Technology, 05.-09.12.2011, Rio de Janeiro, Brasil

Publ.-Id: 16501 - Permalink


Annealed, stress-free, and ferromagnetic Mn-doped indium tin oxide films
Scarlat, C.; Xu, Q.; Zhou, S.; Potzger, K.; Salvan, G.; Helm, M.; Schmidt, H.; Iacomi, F.;
Indium tin oxide (ITO) is a transparent semiconductor and can be highly conductive at room temperature (RT) when doped, making ferromagnetic ITO films attractive candidates for magnetooptical and spintronic devices. Undoped and Mn doped indium tin oxide (ITO) thin films have been grown on SiO2/Si substrates by vacuum thermal evaporation (VTE) technique using targets with the atomic ratio In:Sn:Mn=114:12:13, 109:12:7, 122:12:4 and 122:12:0. In order to have practically stress-free samples [1] all the samples were annealed at 450 oC for 2 hours in air. Magnetotransport measurements revealed negative magnetoresistance and no anomalous Hall effect is observed. The ITO doped films exhibit RT ferromagnetism after annealing. The samples were investigated by magnetooptical Kerr effect (MOKE) spectroscopy measurements.

[1] L Kerkache et al, J. Phys. D: Appl. Phys. 39 184–189, (2006).
  • Poster
    subtherm 2011, 25.-27.10.2011, Dresden, Germany

Publ.-Id: 16500 - Permalink


Magnetic Mn-doped indium tin oxide films prepared by vacuum thermal evaporation
Scarlat, C.; Xu, Q.; Mok, K.; Shalimov, A.; Fronk, M.; Salvan, G.; Zahn, D. R. T.; Helm, M.; Schmidt, H.; Iacomi, F.;
Indium tin oxide (ITO) can be made a highly conductive transparent coating contact in photovoltaics by doping. Undoped and Mn doped indium tin oxide (ITO) thin films were grown on SiO2/Si substrates by vacuum thermal evaporation (VTE) using sources with atomic ratios of In:Sn:Mn=114:12:13, 109:12:7, 122:12:4, and 122:12:0. In order to have practically stress-free ITO films [1], all the samples were annealed at 450 oC for 2 hours in air. Magnetotransport measurements reveal negative magnetoresistance while no anomalous Hall effect is observed. The Mn-doped ITO films exhibit room temperature ferromagnetism after annealing. We analyzed the magnetization data from SQUID measurements using simulations based on the Preisach approach and derived the magnetic parameters of nanoparticles in the Mn-doped ITO films, namely, the magnetization of individual particles and the distributions of coercive and interparticle interaction fields. The samples were also investigated by magneto-optical Kerr effect spectroscopy and Vector Magnetooptical Generalized Ellipsometry measurements to explore possible combined functionalities in photovoltaics and magnetooptics.

[1] L Kerkache et al., J. Phys. D: Appl. Phys. 39 184–189, (2006).
  • Poster
    Next Generation Solar Energy From Fundamentals to Applications, 12.-14.12.2011, Erlangen, Germany

Publ.-Id: 16499 - Permalink


ROssendorf BeamLine II - New experimental possibilities for in-situ diffraction experiments
Baehtz, C.; Shalimov, A.; Grenzer, J.; von Borany, J.;
New experimental possibilities of the upgraded ROBL-beamline will be represented as well as results of the in-situ growth investigation of carbon nano tubes and graphene.
Keywords: Synchrotron radiation, in-situ diffracton, carbon nano tubes
  • Lecture (others)
    7. Wissenschaftliches Seminar des Dresdner Fraunhofer-Clusters Nanoanalytik, 27.01.2012, Dresden, Deutschland

Publ.-Id: 16498 - Permalink


Bildung von Nanolöchern auf KBr-Oberflächen durch Beschuss mit hochgeladenen Ionen
Wilhelm, R. A.;
Hochgeladene Ionen tragen eine große Menge potentieller Energie (bis zu 100 keV), die als Summe der Bindungsenergien der fehlenden Elektronen definiert ist. Mit Hilfe dieser potentiellen Energie können auf Festkörperoberflächen Strukturen im Bereich von einigen Nanometern erzeugt werden, wobei durch geringe kinetische Energien der Ionen (weniger als 100 eV) Schaden im Festkörpervolumen vermieden werden kann. Die Produktion von Nanolöchern auf KBr(001)-Oberflächen durch den Beschuss mit einzelnen hochgeladenen Ionen wurde bereits untersucht. Diese Arbeit befasst sich aufbauend auf bekannten Ergebnissen mit des Einflusses hoher Fluenzen hoch- und niedriggeladener Ionen auf den Lochbildungsprozess. Diese Untersuchungen sind von Bedeutung um den Mechanismus der defektinduzierten Desorption als treibende Kraft für die Bildung von Nanolöchern zu identifizieren. Ergebnisse von Bestrahlungen von KBr(001)-Oberflächen mit hoch- und niedriggeladenen (4 ≤ q ≤ 54) Ionen bei hohen Fluenzen von (10^10..10^15) cm^−2 und verschiedenen Temperaturen werden in dieser Arbeit vorgestellt. Das zugrunde liegende Modell der defektinduzierten Desorption wird anhand der vorliegenden Ergebnisse diskutiert.

Highly charged ions carry a large amount of potential energy (up to 100 keV), which is defined as the sum of the binding energies of all missing electrons. This energy can be used to modify surfaces on the nano-scale, and due to very low kinetic energies (less than 100 eV), significant bulk damage can be avoided. The production of nanometer sized pit-like structures on KBr(001) surfaces by the impact of single highly charged ions was previously studied in detail. Therefore, investigations of high fluence effects of highly and lowly charged ions are important to clearly identify the mechanism of defect mediated desorption as the driving force for the creation of pit-like nanostructures on ionic crystals like KBr. Results of high fluence compared to low fluence irradiations in range of (10^10..10^15) cm^−2 with highly charged ions (4 ≤ q ≤ 54) and the influence of the temperature on the nanostructure production on KBr(001) surfaces are shown. Moreover, the defect mediated desorption model is discussed.
  • Thesis / Students' report
    TU Dresden, 2010
    58 Seiten

Publ.-Id: 16497 - Permalink


In-Situ Analysis of Nanostructures Induced by Slow Highly Charged Ions
Wilhelm, R. A.; Heller, R.; Facsko, S.;
The sum of the binding energies of all missing electrons (potential energy) of highly charged ions can induce surface modifications on the nanometer scale. We present results of a set-up for slow highly charged ion irradiations and scanning probe microscopy studies under in-situ conditions. A Dresden-EBIT is used to provide ions of different species with charge states up to q=40 (e.g. for Xe). An electrostatic deceleration lens system allows to vary the kinetic energies of the ions in the range of 10eV· q up to 5keV· q. Furthermore, we studied surface nanostructures on various substrates by an Omicron ultra high vacuum (UHV) scanning probe microscope, which is directly connected to the ion source. The size and the shape of nanostructures created by the deposition of potential energy and analyzed in-situ under UHV conditions are discussed and compared to those observed by recent studies under ex-situ conditions.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16496 - Permalink


Surface Modification on KBr(001) with Slow Highly Charged Ions in High Fluence and High Potential Energy Regime
Wilhelm, R. A.; Heller, R.; Facsko, S.;
Highly charged ions (HCI) have an unique property, their potential energy, which can induce modifications on surfaces on the nano-scale without a significant bulk damage. The potential energy, defined as the sum of the binding energies of all missing electrons, can exceed 100 keV, e.g. for Xe50+ or Au60+. This amount of energy is mainly released by the emission of electrons with energies of several 10 eV as described by the classical over the barrier model. The release of the HCI’s potential energy as emission of electrons right in front of the surface or in the first nanometers of the solid leads to a strong interaction with the electronic system of the solid. Especially in ionic crystals like KBr many electron-hole pairs are created near the impact site of the HCI. Due to a strong electronphonon coupling in ionic crystals these excitons become self-trapped and can either recombine or decay into so called colour centres. In KBr F and H-centres are created. H-centres are defined as an interstitial molecular halide atom and a F-center is an electron at an anion site. F-centres, which were produced near the surface, can recombine with surface ions (K+) and lead to their neutralisation and desorption. Also a Br-atom desorption occurs when the H-centre recombines with the surface.
Recently nano-pits on KBr surfaces induced by single ion impacts were investigated and a potential as well as a kinetic energy-threshold for their formation was found. The depths of the pits produced by a single ion impact was found to be one atomic monolayer for Xe charge states up to q = 40 and various kinetic energies. Low charge state (q>10) irradiations, in contrast, show pits as well, but only for much higher fluences (several 10^13 cm^-2). We present studies of high fluence irradiations with highly (q>10) and lowly (q<10) charged Xe ions. For high charge states a deepening of the pits (with increasing fluence) was found, while for low charge state irradiations a depletion region close to low coordinated sites like step edges has been observed. For irradiations with highest charges states, i.e. Au54+ ions and low fluences (<10^10 cm^-2) pit structures could be observed with double monolayer depths for single impacts. This indicates a second energy-threshold for the desorption of the second monolayer by a single ion impact. A qualitative model will be discussed to describe and identify the observed potential and kinetic energy effects.
  • Poster
    XXVII International Conference on Photonic, Electronic and Atomic Collisions, 27.07.-02.08.2011, Belfast, United Kingdom

Publ.-Id: 16495 - Permalink


Nanostructures induced by slow highly charged ions on KBr(001) surfaces
Wilhelm, R. A.; Heller, R.; Facsko, S.;
Highly charged ions carry a large amount of potential energy (up to 100 keV) which is defined as the sum of all binding energies of all missing electrons. This energy can be used to modify surfaces on the nano-scale and due to very low kinetic energies (less than 100 eV) significant bulk damage can be avoided. The production of nanometer sized pit-like structures on KBr(001) surfaces by the impact of single highly charged ions was studied in detail previously. The investigation of high fluence effects of highly and lowly charged ions is important to clearly identify the mechanism of defect mediated desorption as the driving force for the creation of pit-like nanostructures on ionic crystals like KBr. Results of high fluence compared to low fluence irradiations will be shown and kinetic and potential energy effects will be discussed.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 17.03.2011, Dresden, Deutschland

Publ.-Id: 16494 - Permalink


Pit formation on poly(methyl methacrylate) due to ablation induced by individual slow highly charged ion impact
Ritter, R.; Wilhelm, R. A.; Ginzel, R.; Kowarik, G.; Heller, R.; El-Said, A. S.; Papaléo, R. M.; Rupp, W.; Crespo López-Urrutia, J. R.; Ullrich, J.; Facsko, S.; Aumayr, F.;
We report the formation of nano-sized pits on poly(methyl methacrylate) after exposure to slow highly charged ion beams. The pits are formed on the polymer surface as a direct result of individual ion impacts. Intermittent contact mode atomic-force microscopy was employed to study the size evolution of the pits in dependence of potential and kinetic energies of the incident ions. A potential energy threshold value of approximately 7 keV was found for pit formation. Above this value an increase in potential energy results in an increasing pit volume, while the pit shape can be tuned by varying the kinetic energy.

Publ.-Id: 16493 - Permalink


Ferromagnetic Ge:Mn prepared by ion implantation and pulsed laser annealing
Zhou, S.; Bürger, D.; Li, L.; Skorupa, W.; Helm, M.; Oesterlin, P.; Schmidt, H.;
We report the fabrication of Ge:Mn ferromagnetic semiconductors by Mn-ion implantation into Ge followed by
pulsed laser annealing. The implanted Ge layer was recrystallized during annealing. We observed that the longitudinal and
Hall resistances exhibit the same hysteresis as the magnetization, which is usually considered as a sign of carrier-mediated
ferromagnetism.
Keywords: Magnetic semiconductors, Spin polarized transport in semiconductors, Elemental semiconductors, Magnetotransport phenomena; materials for magnetotransport

Publ.-Id: 16492 - Permalink


Microbial synthesis of core/shell gold/palladium nanoparticles for applications in green chemistry
Deplanche, K.; Merroun, M. L.; Casadesus, M.; Tran, D. T.; Mikheenko, I. P.; Bennett, J. A.; Wood, J.; Jones, I. P.; Attard, G. A.; Selenska-Pobell, S.; Macaskie, L. E.;
We report a novel biochemical method based on the sacrificial hydrogen strategy to synthesise bimetallic Au/Pd nanoparticles (NPs) with a core/shell configuration. The ability of E. coli cells supplied with H2 as electron donor to rapidly precipitate Pd(II) ions from solution is used to promote the reduction of soluble Au(III). Pre-coating cells with Pd(0) (bioPd) dramatically accelerated Au(III) reduction, with the Au(III) reduction rate being dependent upon the initial Pd loading by mass on the cells. Following Au(III) addition, the bioPd/Au(III) mixture rapidly turned purple indicating the formation of colloidal gold. Mapping of bio-NPs by energy dispersive X-ray microanalysis (EDX) suggested Au-dense core regions and peripheral Pd but only Au was detected by X-ray diffraction analysis. However surface analysis of cleaned NPs by cyclic voltammetry (CV) revealed largely Pd surface sites, suggesting, since XRD shows no crystalline Pd component, that layers of Pd atoms surround Au NPs. Characterisation of the bimetallic particles using X-ray absorption spectroscopy (XANES and EXAFS) confirmed the existence of Au-rich core and Pd-rich shell type bimetallic biogenic NPs. These showed comparable catalytic activity to chemical counterparts with respect to the oxidation of benzyl alcohol, in air, and at a low temperature (90 oC).
Keywords: bioreduction, bimetallic catalysts, catalysis, core/shell, Escherichia coli, gold, palladium

Publ.-Id: 16491 - Permalink


Biomineralization of Uranium in Natural Environments
Selenska-Pobell, S.; Reitz, T.; Geissler, A.; Merroun, M.;
Prokaryotic microorganisms (bacteria and archaea) are the most ubiquitous organisms in terrestrial and aquatic environments. They play a major role in deposition and weathering of a large variety of minerals enriched with or consisting mainly of different metals, such as iron, manganese, copper, gold, and even radionuclides (e.g. uranium). The structure of biologically synthesized minerals is strongly influenced by the metabolic properties of the bacterial or archaeal strains involved in their production and also by the different metal binding potential of their cell wall components.
The talk will focus on cell wall dependent accumulation and biomineralization of uranium by particular Gram-positive and Gram-negative bacteria recovered from uranium mining wastes. By using TEM, EXAFS and TRLF we were able to demonstrate that the Gram-negative and most of the Gram-positive bacteria inhabiting the oligotrophic uranium mining waste pile environments immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. Particular Gram-positive bacterial isolates, possessing highly ordered proteinaceous surface layers (S-layers), are immobilizing U(VI) by both phosphate groups of their thick peptidoglycan and of their phosphorylated S-layer and also by the carboxylic groups of the aspartate and glutamate stretches of their S-layers.
In contrast to bacteria, archaeal diversity is not very high in uranium polluted environments. In addition, these prokaryotic organisms interact with uranium in a significantly different way then bacteria. We were able to demonstrate that some archaeal organisms, indigenous for the uranium mining wastes, are not able to accumulate high amounts of uranium and that the mechanisms of uranium binding differ significantly from those of all studied bacteria. The latter is related to the unusual cell wall structure of the studied archaeal cells.
  • Lecture (Conference)
    Uranium biogeochemistry: transformations and applications, 11.-16.03.2012, Monte Verita, Ascona, Switzerland

Publ.-Id: 16488 - Permalink


In-situ characterization of the carbon nanotube growth process by X-ray diffraction
Baehtz, C.; Wirth, T. C.; Bayer, B. C.; Hofmann, S.; von Borany, J.;
In the last few years carbon nanotubes (CNT) attract more and more attention due to their interesting physical properties especially in the field of micro electronics. Synthesis of CNTs with tailored properties is still a critical point, especially for their applications as interconnects. The growth of CNT by chemical vapor deposition (CVD) is an established synthesis route and it was used in this study.
In-situ X-ray diffraction experiments during growth conditions are performed at the beamline BM20 at the ESRF operated by the Helmholtz-Zentrum Dresden-Rossendorf using a high temperature annealing chamber suitable for reactive gases. Acetylene was used as carbon precursor for the CVD of CNT. Different catalyst systems were studied. For iron nano-particles acting as CNT catalyst, there is still a debate which species can be catalytically active: metallic iron and/or iron carbide. The formation of the metal nano-particles by dewetting and respective crystallisation of the initial thin film was followed by X-Ray reflectivity (XRR) and diffraction (XRD) measurements. We proved that CNT growth can occur without the presence of Fe3C. In general two reaction pathways denoted by a high and low (or zero) iron carbide concentration were observed. Which route the growth follows depends in a statistical way on the ratio of different iron phases (α- and γ-Fe) present in the nano-particles. This can be influenced also by the reaction conditions like temperature and kind of the buffer layer supporting the catalyst film. One challenge is to grow CNT on a conducting support without scarifying the CNT yield and structural quality of the grown CNTs.
Using a Co-buffer layer in-between Si-support and Fe-catalyst leads to the formation of conductive CoSi2 via CoSi by subsequent silicidation during the growth process. Herby a high yield of CNT was obtained.
CoSi2 support is more promising than Ta support, but we used Ta as model system to explain all possible interactions, all occurring phases during processing by side reactions were recorded. Notable CNT yield triggered by high catalytic activity of iron at low temperatures ~550C was observed.
This study shows that in-situ diffraction experiments are a powerful tool to investigate catalytic reactions. The understandings of these processes are the basis of tailoring future materials.
Keywords: Carbon nano tubes, synchrotron radiation, in-situ diffraction
  • Lecture (Conference)
    IUCr2011 - XXII Congress and General Assembly, 22.-30.08.2011, Madrid, Spain

Publ.-Id: 16487 - Permalink


Nanostrukturierte Verschleißschutzschichten für den Automobilbau - von der Konzeption zur Anwendung
Fassbender, J.ORC; Möller, W.; Beyer, E.; Seifert, G.; Zellbeck, H.; Abrasonis, G.; Gemming, S.; Hübner, M.; Joswig, J.-O.; Krause, M.; Kunze, T.; Leson, A.; Makowski, S.; Posselt, M.; Weihnacht, V.
Optimierte, leichte, aber widerstandsfähige Werkstoffe eröffnen dem Fahrzeugbau die Möglichkeit, Energieeffizienz- und Klimaschutzziele mit einer Verbesserung der funktionalen Fähigkeiten des Fahrzeugs zu verbinden. Ziel des Projekts ist die Herstellung und Optimierung der dafür erforderlichen neuartigen, nanoskalig strukturierten, harten und selbstschmierenden Schichten für verschleißbelastete Motorenteile. Konventionelle dünne Funktionsschichten auf Kohlenstoffbasis werden in der Regel durch Niederdruck-Beschichtungsverfahren hergestellt. In den letzten Jahren sind neue Ansätze zur Weiterentwicklung dieser Materialklasse entstanden, die besonders auf nanoskalig strukturierte Systeme fokussieren, und die in Teilprojekt D1 ‘NanoCarbCoat’ für den automobilen Leichtbau erschlossen werden sollen. Dazu verbindet das betont interdisziplinär ausgerichtete Teilprojekt die Expertise von Partnern aus Natur- und Ingenieurwissenschaften zur Abscheidung und physikalischen Charakterisierung kohlenstoffbasierter Schichten, zur Modellierung der tribologischen Vorgänge an Schichten im Kontakt miteinander und mit einem Schmierstoff und zum Test der Beschichtung unter realistischen Bedingungen im Verbrennungsmotor.
Keywords: tribology, wear-resistant coatings, nanotribology, multiscale modeling, motor
  • Contribution to external collection
    W.A. Hufenbach: ECEMP – European Centre for Emerging Materials and Processes, Hightech – Made in Germany – Created in Saxony, Auerbach: Verlag Wissenschaftliche Skripten, 2011, 3000221093, 179-190

Publ.-Id: 16486 - Permalink


Phase Separation and Size Controlled Nanocrystal Formation in GeO
Sahle, C. J.; Sternemann, C.; Nyrow, A.; Schwamberger, A.; Wieland, F.; Zschintzsch, M.; von Borany, J.; Hohl, A.; Tolan, M.;
Semiconducting group IV nanocrystals (NC), such as Ge- and Si-NC, have drawn a lot of attention in recent years because of their potential use in new generations of light emitting diodes, fast and stable non-volatile flash memories or highly efficient solar cells. Although intensive research has been conducted regarding the photoluminescence and charge storage properties of readily produced oxide embedded NCs little is known about the phase separation and NC formation process. Here, we present in and ex situ X-ray absorption near edge structure (XANES) spectroscopy data of the temperature induced disproportionation, i.e phase separation of GeOx (x ≈ 1) into Ge and GeO2, which leads to the formation of Ge NCs embedded in a Ge oxide matrix. The formation of size controlled Ge NCs is achieved using a GeOx–SiO2 superlattice approach. The influence of reducing hydrogen in the annealing ambient on the phase separation process and resulting NC density is discussed.
  • Lecture (Conference)
    DPG Spring Meeting, Dresden, Germany Symposium: Condensed Matter: Semiconductor Physics, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 16485 - Permalink


Charge carrier depth profiling at ultra-shallow pn-junctions
Schmidt, B.; Philipp, P.; Zier, M.;
According to the continuously shrinking of semiconductor device dimensions the fabrication of ultra-shallow pn-junctions is the essential requirement for modern CMOS technology. Therefore the importance of measurement techniques for dopant depth profiles is rising and the demands in resolution and accuracy are continuously increasing. The established methods like SIMS and spreading resistance profiling become less suitable for these applications because of their disadvantages at measurements close to the silicon surface. The Stepwise Oxidation Profiling (SWOP) is a new measurement technique for ultra shallow boron doped layers with pn-junction depths less than 20 nm. SWOP is based on the continuous anodic oxidation technique (CAOT) proposed by S. Prusin [1] and was applied to boron doped layers formed by ion implantation with rapid thermal annealing and by a new doping technique called flash lamp diffusion (FLD).
[1] S. Prussin, AIP Conference Proceedings 931, 275 (2007).
Keywords: ultra-shallow doping profiles, charge carrier depth profiling
  • Invited lecture (Conferences)
    Workshop "Moderne Methoden der Oberflächen- und Dünnschichtanalytik", 30.11.2011, Dresden, Deutschland

Publ.-Id: 16484 - Permalink


Nitrogen Implanted GaAs as a Promising Photovoltaic Material
Gao, K.; Prucnal, S.; Skorupa, W.; Helm, M.; Yastrubchak, O.; Gluba, L.; Zhou, S.;
As a III-V photovoltaic material, gallium arsenide has promising prospects in aerospace applications and concentrator cells in virtue of its high efficiency, outstanding thermal stability, as well as the resistance to radiation damage.
In order to further increase the efficiency of GaAs based solar cells, one reasonable method is to modify its bandgap thereby the absorption range. A cell with a GaAs base can have several layers of slightly different compositions that allow a cell designer to precisely control the generation and collection of electrons and holes. Alloying is one method to tailor the properties of semiconductor materials for specific applications. The introduction of nitrogen into the GaAs matrix allows to vary the band gap energy in a broad energy range from ~3.4 eV (GaN) to ~0.8 eV (GaN0.15As0.85)1.
Here we present the synthesis of GaNxAs1-x layers using ion implantation and millisecond flash lamp annealing (FLA) techniques. After nitrogen implantation the GaAs wafer is amorphous within the implantation range and N atoms are located mainly in the interstitial position. Post-implantation thermal annealing restores the initial properties of the matrix and leads to the GaNxAs1-x layers formation. The optical properties of the GaNxAs1-x layers were investigated by -Raman spectroscopy, temperature dependence photoluminescence and photoreflectance spectroscopy. It is shown that during milliseconds range FLA nitrogen can be efficiently incorporated into the GaAs matrix. The band gap of nitrogen reach GaAs layer can be easily tuned from 1.34 down to 1 eV by varying the nitrogen fluence and annealing parameters.
Keywords: GaN(x)As(1-x), Ion Implantation, Flash Lamp Annealing
  • Poster
    Next Generation Solar Energy, 12.-14.12.2011, Erlangen, Germany

Publ.-Id: 16483 - Permalink


Extremely large-scale simulation of a Kardar-Parisi-Zhang model using graphics cards
Kelling, J.; Ódor, G.;
The octahedron model introduced recently has been implemented onto graphics cards, which permits extremely large-scale simulations via binary lattice gases and bit-coded algorithms. We confirm scaling behavior belonging to the two-dimensional Kardar-Parisi-Zhang universality class and find a surface growth exponent: β=0.2415(15) on 217×217 systems, ruling out β=1/4 suggested by field theory. The maximum speedup with respect to a single CPU is 240. The steady state has been analyzed by finite-size scaling and a growth exponent α=0.393(4) is found. Correction-to-scaling-exponent are computed and the power-spectrum density of the steady state is determined. We calculate the universal scaling functions and cumulants and show that the limit distribution can be obtained by the sizes considered. We provide numerical fitting for the small and large tail behavior of the steady-state scaling function of the interface width.
Keywords: 05.70.Ln, 05.70.Np, 82.20.Wt

Publ.-Id: 16482 - Permalink


Imaging of spin-torque induced magnetization dynamics in lateral spin injector configuration
Buhl, M.; Bernert, K.; Wintz, S.; Henschel, T.; Mattheis, R.; Raabe, J.; Grebing, J.; Potzger, K.; Erbe, A.; Fassbender, J.ORC
Electrical transport characteristics of structures consisting of normal metals and ferromagnetic materials depend strongly on the magneti- zation direction of the ferromagnets. Thus, different spin polarizations can lead to different resistance values of such structures. The absorp- tion of spin polarized electrons in a ferromagnetic material (spin transfer torque) by domain/domain walls leads to magnetization switching or domain wall movement. This can be achieved by driving a current perpendicular to the plane of the ferromagnet (CPP) or in the plane (CIP). In this experiment we investigate the magnetization behavior of ferromagnetic nanopillars located between two lateral spin injectors in the CIP configuration. Using Scanning Transmission X-ray Mircoscopy (STXM) these studies will give more insights in the switching behav- ior and dynamics. Technological applications can mostly be found in memory structures, where the magnetization can be stored and read out.
Keywords: current in plane, CIP, spin transfer torque, STT, scanning transmission x-ray microscopy, STXM, spin polarization, lateral spin injection, ferromagnetism, Cobalt, Co
  • Poster
    DPG Spring Meeting Dresden 2011, 14.-18.03.2011, Dresden, Germany

Publ.-Id: 16481 - Permalink


Estimation of carbon ion induced activity distributions with the yield approach
Priegnitz, M.; Enghardt, W.; Laube, K.; Fiedler, F.;
Phantom irradiation with pencil-like beams of carbon ions have been performed at GSI Darmstadt. The induced β+-activity has been monitored by means of the dedicated in-beam PET scanner mounted at the irradiation site. On the basis of the yield approach ion beam induced positron emitter distributions have been predicted for these irradiation and activity distributions have been estimated. The comparison of predicted and measured activity profiles provides promising results.
  • Contribution to external collection
    in: GSI Scientific Report 2011, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung, 2012, 533

Publ.-Id: 16480 - Permalink


Manipulation of Ge quantum dot ordering in alumina matrix by deposition conditions
Buljan, M.; Baehtz, C.; Holý, V.; Radić, N.; Roshchupkina, O.; Prucnal, S.; Mücklich, A.; Valeš, V.; Bernstorff, S.; Grenzer, J.;
We present an investigation of ordering and PL properties of Ge QDs in an alumina matrix formed by magnetron-sputtering deposition of (Ge+Al2O3)/Al2O3 multilayers. The self-assembly process occurs during the deposition and results with the formation of three-dimensional quantum dots lattices. We investigate the dependencies of the size and ordering properties on the deposition temperature, rotation of the substrate holder and direction of the incoming flux of Ge during the deposition process. The results of the investigation show that tuning the deposition temperature enables manipulation with QD sizes and their mutual distances. We show that the ordering of QDs obtained by deposition on fixed substrate holder leads to the formation of a quantum dot crystal, while the rotation of substrate holder leads to randomly rotated domains with regular ordering. The observed phenomenon is explained by a combination of the surface morphology effect on the nucleation positions of Ge quantum dots with a lateral inhomogeneity of the ad-atom flux. In addition, we show that the resulting quantum-dot lattices have size-dependent PL properties.
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16479 - Permalink


In-situ observation of the Self-assembled growth of ordered Ge nanocrystals embedded within a dielectrical matrix
Grenzer, J.; Buljan, M.; Roshchupkina, O.; Baehtz, C.; Holý, V.;
We report on an in-situ X-ray investigation of a self-assembled growth of Ge nanocrystals embedded in a dielectrical matrix forming a BCC-like super structure. Such a material could be a key element for the development of a new generation of solar cells extending the spectral range for energy conversion. Using small angle scattering techniques and X-ray diffraction the formation of crystalline Ge nanoparticles during growth and annealing was studied in-situ at the BM20 beam line at that ESRF using a process chamber for magnetron sputter deposition and annealing that can be inserted into the goniometer. A single some 100nm thick Ge+Al2 O3 layer using magnetron sputtering was deposited at an elevated substrate temperature. The self-assembly during growth or subsequent annealing results in the formation of a well ordered three-dimensional BCC-like quantum dot lattice within the whole deposited volume. The formed nanocrystals are very small in size (< 4.0𝑛𝑚 with a very narrow size distribution and a large spatial density. The parameters of the formed super structure can be directly influenced by changing the deposition parameters. The self-ordering of the quantum dots is explained by diffusion mediated nucleation and surface morphology effects.
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16478 - Permalink


The 25Mg(p,γ)26Al reaction at low astrophysical energies
Strieder, F.; Limata, B.; Formicola, A.; Imbriani, G.; Junker, M.; Bemmerer, D.; Best, A.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Dileva, A.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Lemut, A.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Terrasi, F.; Trautvetter, H. P.;
In the present work we report on a new measurement of resonance strengths in the reaction 25Mg(p,gamma)26Al at E_cm= 92 and 189 keV. This study was performed at the LUNA facility in the Gran Sasso underground laboratory using a 4pi BGO summing crystal. For the first time the 92 keV resonance was directly observed and a resonance strength omega-gamma=(2.9+/-0.6)x10E-10 eV was determined. Additionally, the gamma-ray branchings and strength of the 189 keV resonance were studied with a high resolution HPGe detector yielding an omega-gamma value in agreement with the BGO measurement, but 20% larger compared to previous works.

Publ.-Id: 16477 - Permalink


Phase sensitive monitoring of electron bunch form and arrival time in superconducting linear accelerators
Kaya, C.; Schneider, C.; Al Shemmary, A.; Seidel, W.; Kuntzsch, M.; Bhattacharyya, J.; Mittendorff, M.; Evtushenko, P.; Winnerl, S.; Staats, G.; Helm, M.; Stojanovic, N.; Michel, P.; Gensch, M.;
In this letter we present a simple approach for monitoring electron bunch form and arrival time combining electro-optic sampling and phase and frequency sensitive signal de-tection. The sensitivity of the technique allows on line diagnostic to be performed down to bunch charges in the femtocoulomb regime. The concept has high impact for the develop-ments of the next generation of 4th Generation X-ray light sources working with long pulse trains or continuous wave mode of operation.
Keywords: electro-optic sampling, arrival time monitor, srf, accelerator, electron bunch diagnostic

Publ.-Id: 16476 - Permalink


Ungeduldige Forscher träumen mit DREAMS Bestimmung langlebiger Radionuklide mit Beschleunigermassenspektrometrie
Merchel, S.; Akhmadaliev, S.; Pavetich, S.; Rugel, G.;
Das Helmholtz-Zentrum Dresden-Rossendorf hat sein Spektrum ionenanalytischer Verfahren um eine weitere hochsensitive Methode erweitert: die Beschleunigermassenspektrometrie (accelerator mass spectrometry = AMS). Die AMS ist prädestiniert zur Bestimmung langlebiger Radionuklide (Halbwertszeit ≥ 100 Jahre). Diese werden nicht, wie allgemein üblich, mittels Zerfallszählung detektiert. Vielmehr bestimmen die „ungeduldigen Forscher“ die noch nicht zerfallenen Nuklide wesentlich effizienter massenspektrometrisch.
Keywords: AMS, Radionuklide
  • GIT Labor-Fachzeitschrift 56(2012)Februar, 88-90

Publ.-Id: 16475 - Permalink


Status von AMS–Messungen an DREAMS
Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.;
Am Helmholtz–Zentrum Dresden–Rossendorf wurde im Jahr 2010 die Dresdner Accelerator Mass Spectrometry (DREAMS) Anlage mit einem 6 MV Beschleuniger installiert. Für die Routinemessungen mit 10Be und 26Al wurden Vergleichsmessungen mit anderen Laboren vorgenommen.
Ausserdem wurden die verwendeten in–house–Standards an sogenannte Primärstandards ankalibriert. Von Testmessungen an volatilen Elementen wie Chlor (36Cl) berichtet S. Pavetich [1]. AMS–Messungen von 41Ca/Ca–Verhältnissen wurden an Proben aus dem Rückbau nuklearer Anlagen und an Meteoritenproben (siehe [2]) vorgenommen. In Kooperation mit externen Partnern wurden bisher zahlreiche terrestrische Proben auf 10Be und 26Al untersucht.
Danksagung: Wir danken dem Verein für Kernverfahrenstechnik und Analytik Rossendorf e. V. für die Bereitstellung von Probenmaterial.
Ref.: [1] S. Pavetich et al., diese Tagung. [2] S. Merchel et al., diese Tagung.
Keywords: accelarator mass spectrometry, radionuclide, AMS
  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 12.-16.03.2012, Stuttgart, Deutschland

Publ.-Id: 16474 - Permalink


Cosmogenic nuclides in meteorites
Merchel, S.; Akhmadaliev, S.; Rugel, G.; Cartwright, J. A.; Ott, U.; Faestermann, T.; Fimiani, L.; Korschinek, G.; Ludwig, P.;
After successful installation of the Dresden Accelerator Mass Spectrometry (DREAMS) facility [1], determinations of the lighter radionuclides 10Be, 26Al, and 41Ca are now easily attainable in Germany. Accompanied by data for the heavier radionuclides (i.e. 53Mn and 60Fe) that can be measured at the 14 MV tandem at Munich and stable nuclides such as 21,22Ne and 38Ar from noble gas mass spectrometry at MPI Mainz, complete and unique exposure histories of extraterrestrial material can be reconstructed.
For example, recent analyses of the 100th Martian meteorite Ksar Ghilane 002 [2] and four samples from the nickel-rich ataxite Gebel Kamil [3] show interesting features revealing amazing stories.
Ackn.: A. Bischoff and L. Folco are thanked for providing meteorite material and data for bulk chemical data.
Ref.: [1] G. Rugel et al., this meeting. [2] J. Llorca et al., submitted to Meteorit. Planet. Sci.. [3] L. Folco et al., Science 329 (2010) 804.
Keywords: accelerator mass spectrometry, meteorite, radionuclides, noble gases
  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 12.-16.03.2012, Stuttgart, Deutschland

Publ.-Id: 16473 - Permalink


The 100th Martian meteorite Ksar Ghilane 002 (KG 002): Noble gases and radionuclides point to a strong relationship with Los Angeles
Cartwright, J. A.; Merchel, S.; Rugel, G.; Fimiani, L.; Ludwig, P.; Llorca, J.; Ott, U.;
Ksar Ghilane 002 (KG 002) is the 100th Martian meteorite to be catalogued by the Meteoritical Bulletin, and the first to be recovered from Tunisia (January, 2010). The single stone, weighing 538 g, is a coarse-grained basaltic shergottite that shows remarkable petrological and compositional similarities with evolved shergottite Los Angeles [1,2].
By performing noble gas and radionuclide analysis on KG 002, we aim to contribute further in determining the extent of its similarity with Los Angeles. In particular, we investigate the potential for a launch-pairing of these two meteorites by comparison of cos-mic ray exposure (CRE) ages, where preferred CRE ages for Los Angeles of 3.10 ± 0.70 and 3.35 ± 0.30 Ma have been previously suggested [3,4].
References: [1] Llorca J. et al. (subm.) MAPS. [2] Roszjar J. et al. (2011) LPSC XLIII, this conf. [3] Terribilini, D. et al. (2000) MAPS, 35:A155-A156. [4] Eugster, O. et al. (2002) MAPS, 37:1345-1360.
Keywords: accelerator mass spectrometry, meteorite, noble gases, radionuclides
  • Poster
    43rd Lunar and Planetary Science Conference, 19.-23.03.2012, The Woodlands, Texas, United States

Publ.-Id: 16472 - Permalink


Shock wave synthesis of γ-Si3[O,N]4 in the new Freiberg blasting facility under different conditions
Renno, A. D.; Schlothauer, T.; Schwarz, M. R.; Heide, G.; Kroke, E.;
The new subterranean blasting facility at the TU Bergakademie Freiberg allows experiments at elevated capacities of 20 kg C4-equivalent. The new installation permits the investigation of phase transitions of γ Si3N4 under dynamic loading.
We studied the influence of plate thickness (shock duration) and different precursor-pressure powder (Cu, NaCl) mixtures at charge masses between 2000 and 20.000 g C4.
Systematic studies showed that the Mach-reflection (so called “upstreaming jetting phenomena”) is of vital importance for the synthesis success, due to the fact that the T-p ratio will increase dramatically [Milyavskii et al., 2006].
We synthesized pure γ-Si3[O,N]4 from H-bearing precursors at pressures > 25 GPa [Schlothauer et al., 2011].
The phase transition Si2N2NH into γ-Si3[O,N]4 is completely reconstructive and requires a high temperature-pressure-ratio of 176 K/GPa at pressures up to 35 GPa. Despite the high energy density during the shock wave synthesis process it will be inevitable to prepare the samples under an inert nitrogen atmosphere.
Keywords: Shock wave experiments, Mineral Physics
  • Poster
    AGU Fall Meeting 2011, 05.-09.12.2011, San Francisco, USA

Publ.-Id: 16471 - Permalink


Magnetic model for A2CuP2O7 (A = Na, Li): One-dimensional versus two-dimensional behavior
Lebernegg, S.; Tsirlin, A. A.; Janson, O.; Nath, R.; Sichelschmidt, J.; Skourski, Y.; Amthauer, G.; Rosner, H.;
We report magnetization measurements, full-potential band-structure calculations, and microscopic modeling for the spin-1/2 Heisenberg magnets A2CuP2O7 (A = Na, Li) involving complex Cu-O-O-Cu superexchange pathways. Based on a quantitative evaluation of the leading exchange integrals and the subsequent quantum Monte Carlo simulations, we propose a quasi-one-dimensional magnetic model for both compounds, in contrast to earlier studies that conjectured on a two-dimensional scenario. The one-dimensional nature of A2CuP2O7 is unambiguously verified by magnetization isotherms measured in fields up to 50 T. The saturation fields of about 40 T for both Li and Na compounds are in excellent agreement with the intrachain exchange J1 is about 27 K extracted from the magnetic susceptibility data. The proposed magnetic structure entails spin chains with the dominating antiferromagnetic nearest-neighbor interaction J1 and two inequivalent, nonfrustrated antiferromagnetic interchain couplings of about 0.01J1 each. A possible long-range magnetic ordering is discussed in comparison with the available experimental information

Publ.-Id: 16470 - Permalink


Singlet–Triplet Excitations and High-Field Magnetization in CuTe2O5
Wang, Z.; Schmidt, M.; Goncharov, Y.; Skourski, Y.; Wosnitza, J.; Berger, H.; Krug Von Nidda, H.-A.; Loidl, A.; Deisenhofer, J.;
By measuring the THz electron spin resonance (ESR) transmission spectra and high-field magnetization on the spingapped system CuTe2O5, we identified the singlet–triplet excitations in the dimerized non-magnetic ground state. The determined spin-gap value of hnu0 = 4.94 meV at the Gamma point (Q = 0) is significantly smaller than the strongest antiferromagnetic exchange interaction between the Cu ions predicted by theoretical investigations. We also observed the critical field Ha*c1 = 37.6 T for H perp bc-plane and Hbcc1 = 40.6 T for H parallel bc-plane at the onset of non-zero magnetization, consistent with the gap value and corresponding anisotropic g-factors determined previously. The observed singlet–triplet excitations in Faraday and Voigt configurations suggest a mixing of the singlet state with the Sz = 0 triplet state and the Sz = plus/minus 1 triplet states, respectively, due to the Dzyaloshinskii–Moriya (DM) interaction with a DM vector perpendicular to the crystalline bc-plane.

Publ.-Id: 16469 - Permalink


Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors
Weickert, F.; Nicklas, M.; Schnelle, W.; Wosnitza, J.; Leithe-Jasper, A.; Rosner, H.;
We present the first study of codoped iron-arsenide superconductors of the 122 family (Sr/Ba)1-xKxFe2-yCoyAs2 with the purpose to increase the upper critical field Hc2 compared to single doped Sr/BaFe2As2 materials. Hc2 was investigated by measuring the magnetoresistance in high pulsed magnetic fields up to 64 T. We find, that Hc2 extrapolated to T = 0 is indeed enhanced significantly to approx 90 T for polycrystalline samples of Ba0:55K0:45Fe1:95Co0:05As2 compared to approx 75 T for Ba0.55K0.45Fe2As2 and BaFe1.8Co0.2As2 single crystals. Codoping thus is a promising way for the systematic optimization of iron-arsenic based superconductors for magnetic-field and high-current applications.

Publ.-Id: 16468 - Permalink


Research at Hihgh Magnetic Fields - Activities at the Dresden High Magnetic Field Laboratory
Wosnitza, J.;
  • Invited lecture (Conferences)
    Science Vision for the European Spallation Source, 10.-12.10.2011, Bad Reichenhall, Deutschland

Publ.-Id: 16467 - Permalink


The impact of the Äspö ground water bacterium Pseudomonas fluorescens on the speciation of plutonium
Moll, H.; Lütke, L.; Sachs, S.; Schmeide, K.; Bernhard, G.;
Bacteria are widely distributed in nature and they can strongly influence the behaviour of actinides in the environment. This presentation focuses on the unknown interaction between plutonium (Pu(VI) and Pu(IV)-polymers) and cells of the ground water bacterium Pseudomonas fluorescens isolated from the Äspö site, Sweden. Accumulation experiments were performed in order to obtain information about the amount of Pu bound by the cells in dependence on the contact time and the initial plutonium concentration. We used solvent extraction and UV-vis-NIR absorption spectroscopy to determine the speciation of Pu oxidation states. The Pu oxidation state distributions will be discussed in detail and a model which describes the ongoing processes in the system Pu–P. fluorescens will be presented.
Keywords: Plutonium, Bacteria, Speciation
  • Contribution to proceedings
    Plutonium Futures - The Science 2012, 15.-20.07.2012, Cambridge, UK
  • Lecture (Conference)
    Plutonium Futures - The Science 2012, 15.-20.07.2012, Cambridge, UK

Publ.-Id: 16466 - Permalink


Strain Relaxation and Vacancy Creation in Thin Platinum Films
Gruber, W.; Chakravarty, S.; Baehtz, C.; Leitenberger, W.; Bruns, M.; Kobler, A.; Kübel, C.; Schmidt, H.;
Synchrotron based combined in situ x-ray diffractometry and reflectometry is used to investigate the role of vacancies for the relaxation of residual stress in thin metallic Pt films. From the experimentally determined relative changes of the lattice parameter a and of the film thickness L the modification of vacancy concentration and residual strain was derived as a function of annealing time at 130 °C. The results indicate that relaxation of strain resulting from compressive stress is accompanied by the creation of vacancies at the free film surface. This proves experimentally the postulated dominant role of vacancies for stress relaxation in thin metal films close to room temperature.
Keywords: Synchrotron radiation, Pt thin films, reflectometry

Publ.-Id: 16465 - Permalink


Imaging measurement techniques for the LIMMCAST continuous casting model
Franke, S.; Wondrak, T.; Räbiger, D.; Timmel, K.; Büttner, L.; Czarske, J.; Eckert, S.; Gerbeth, G.;
The properties of the mould flow are significant for the casting quality at the continuous casting of steel. To investigate the flow behaviour model experiments were performed using liquid metal melts with a low melting temperature. Thereto adequate imaging measuring techniques for liquid metal flows are required. We will present three methods: the Ultrasound Doppler Velocimetry (UDV) and the Contactless Inductive Flow Tomography (CIFT) to measure two-dimensional velocity fields in the mould and the Mutual Inductance Tomography (MIT) to measure the two-phase flow distribution in the SEN. The UDV method by means of ultrasonic array transducers provides spatial- and time-resolved measurements at a measuring area of 24 × 24 voxel with frame rates up to 30 fps. A method based on the application of ultrasonic wave guides is presented to extend the limited temperature range of conventional ultrasonic transducers (up to 200°C) to temperatures up to about 700°C. CIFT facilitate measurements of the global flow structure with frame rates of 1 fps. Due to its feature as a contactless measuring method it can be applied at facilities operating at room temperature as well as much higher temperatures. The MIT as well a contactless measuring principle may resolve the two-phase flow distribution in the SEN with up to 20 fps. All three methods were successfully applied at a small-scale continuous casting model based on the metal alloy GaInSn liquid at room temperature and are currently adapted to a large-scale casting model applying the alloy BiSn in a temperature range of 200°C to 350°C.
Keywords: Ultrasound Doppler Velocimetry, Contactless Inductive Flow Tomography, Mutual Inductance Tomography, continuous casting, liquid metal model, mould flow, flow measurements, two-phase flow
  • Lecture (Conference)
    Symposium on Simulation and Modeling of Metallurgical Processes "SymSim", 07.-10.12.2011, Planner Alm, Österreich

Publ.-Id: 16464 - Permalink


Classification of bubbles in vertical gas–liquid flow: Part 1 – An analysis of experimental data
Qi, F. S.; Yeoh, G. H.; Cheung, S. C. P.; Tu, J. Y.; Krepper, E.; Lucas, D.;
In consideration of the practical importance regarding the application of gas–liquid flow in a vertical pipe and the quest towards the development of more robust physical models to accurately predict the essential interfacial parameters of the two-phase flow, comprehensive analysis of the characteristics and phase distribution patterns of such a flow have been performed on both experimental measurements and theoretical predictions. In this first part, analysis of experimental data in a large diameter pipe with an inner diameter of 195.3 mm via the wire-mesh senor measuring technique was presented. The experiments were performed at the TOPFLOW facility of Helmholtz-Zentrum Dresden-Rossendorf. In the present paper, measurements of local interfacial parameters which included the void fraction, volume equivalent bubble diameter, bubble size distribution and interfacial velocities were discussed. Test points covering flow regimes from bubbly to cap to slug to churn-turbulent flow were selected to investigate the flow of different bubble shapes and sizes and the significant bubble coalescence and break-up mechanism throughout the large vertical pipe. The radial and axial evolutions of the local flow structure were interpreted in terms of the classifications of different groups of bubbles (Group-1 and Group-2). In addition, the phase distribution patterns were analyzed through the concept of skewness, which essentially identified two fundamental patterns, namely, wall peak and core peak. In general, Group-1 bubbles being smaller spherical bubbles have shown to exhibit a wall peaking distribution while Group-2 bubbles being larger non-spherical bubbles corresponded to a core peaking distribution. The classification of bubbles that have been performed in this present study can be employed for the development of bubble coalescence and break-up mechanistic kernels and other interfacial force closure models for a two bubble group approach in the context of computational fluid dynamics.
Keywords: Gas–liquid flow, Large diameter pipe, Phase distribution patterns, Skewness

Publ.-Id: 16463 - Permalink


Joint Project: Interaction and transport of actinides in natural clay rock with consideration of humic substances and clay organics - Investigations of temperature dependence of complexation and sorption of trivalent actinides (Am(III)) in the system actinide-NOM-natural clay rock-aquifer (Final Report BMWi Project No.: 02 E 10417)
Acker, M.; Barkleit, A.; Müller, M.; Schott, J.; Bernhard, G.;
The main objective of this project was to study the interaction processes between An(III)/Ln(III), (representated by Am(III) and Eu(III), respectively), organic model ligands, and Opalinus Clay at elevated temperature (until 80°C). The thermodynamic data (log, ΔG, ΔH and ΔS) for the complexation and sorption processes have been derived and led to an enhancement of the thermodynamic database by data at elevated temperatures.

The complexation of Am(III)/Eu(III) with small organic ligands (pyromellitic, salicylic, lactic, acetic, citric, and tartaric acid) that serve as model ligands for natural organic material, like humic substances or clay organic was investigated by temperature dependent UV-Vis and time-resolved laser-induced fluorescence spectroscopy (TRLFS).
For the first time, the UV-Vis absorption spectroscopy utilizing a Long Path Flow Cell (LPFC) has been established for speciation analysis of Am(III) at trace concentrations. A detection limit of 5*10-9 mol/l-1 Am(III) was determined with an 2 m LPFC.
Several Am(III)/Eu(III)-organic ligand complexes were spectroscopically and thermodynamically characterized. General, all studied complexation reactions are endothermic and driven by entropy.
Furthermore, the interaction of Eu(III) with pyromellitc acid (1,2,4,5-benzene-tetracarboxylic acid) had been studied in detail with additional methods like isothermal titration calorimetry (ITC) and Fourier-transform infrared spectroscopy in combination with density function theory (DFT) calculations. At elevated temperature and higher concentration (> 5 mM Eu(III) and pyromellitic acid) a temperature-dependent polymerization was observed. It had been shown that predominantly chelating coordination with two carboxylic groups in the monomeric complex and monodentate binding of a single carboxylic group in the polymeric complex of the polycarboxylate with Eu(III) occurs.

The sorption of Eu(III) on Opalinus Clay was investigated in absence and presence of the small organic ligands citric and tartaric acid at different temperatures and under synthetic pore water conditions (I = 0.4 M, pH = 7.6) by batch experiments. Time-resolved laser-induced fluorescence spectroscopy was used for analysis of the Eu(III) speciation in the binary system Eu(III)-Opalinus Clay and ternary system Eu(III)-Opalinus Clay-small organic ligand under pore water conditions.
The Eu(III) sorption was found to increase generally with temperature in a considerably endothermic reactions with enthalpies of about 50 kJ/mol 1. In presence of tartrate or citrate the Eu(III) sorption decreases with increasing ligand concentration due to a complex formation of Eu(III) in solution. This complex formation was verified by TRLFS investigations. The detected Eu(III) surface species on Opalinus Clay with a luminescence lifetime of (201  9) µs is no influenced by the presence of the studied organic ligands.
Keywords: Americium, Europium, Opalinus clay, organic model ligands, complexation, sorption, elevated temperature, thermodynamics
  • Other report
    Dresden: TU Dresden, 2011
    49 Seiten

Publ.-Id: 16462 - Permalink


In-situ X-ray Scattering: A Tool for Investigation of Nanostructure Formation
Grenzer, J.;
Nowadays, the development of new materials is often associated with specific properties of functionalized nanostructures. X-ray investigations are a very important tool to find the link between the functional (magnetism, luminescence) and the corresponding structural properties (size, orientation etc.) that are generating this function and to explain the underlying physical processes. This knowledge makes it possible to design new materials with specific properties. We report on (in-situ) X-ray studies that are focused on ion-beam sputtering techniques (IBS) creating nanostructures either by ion beam erosion or by sputter deposition processes.
With IBS the roughness of solid surfaces can be modified on lateral scales of a few nanometers to micrometers or even further. In a defined parameter set IBS leads to a surface smoothing, whereas at other parameters the roughness is increased, leading eventually to periodic patterns, i.e. ripple and hexagonal dot patterns. In-situ measurements of the surface roughness during IBS of GaSb surfaces give insight into the detailed mechanisms; especially, if the early time regime is addressed. Modern synchrotron sources give us the possibility to study the nanostructure growth during deposition. A sputtering chamber mounted on a six-circle goniometer allows an insight into the growth of nanostructures using different scattering and diffraction methods. We have investigated the growth of FePt islands incorporated into an Ag matrix. The high brilliance of the synchrotron source had made it possible to obtain a reliable GISAXS signal and to control the cluster morphology during growth even at the initial stage. By depositing 6 nm Ag layer directly on the SiO2 substrate, we obtained well defined FePt clusters. FePt nanoislands have been achieved without degradation of the magnetic properties. We obtained a magnetic asymmetry with magnetic moments preferentially oriented parallel to the layer surface.
  • Invited lecture (Conferences)
    8th Autumn School on X-ray Scattering from Surfaces and Thin Layers, 04.-07.10.2011, Smolenice Castle, Slovakia

Publ.-Id: 16459 - Permalink


Silicon ripple structures produced by Xe+ irradiation at medium energies
Grenzer, J.; Hanisch, A.; Facsko, S.; Mücklich, A.; Biermanns, A.; Pietsch, U.;
We report on the evolution of wave-like nanopatterns induced by Xe+ ion irradiation at high fluences in an energy range between 5 keV and 70 keV. By means of atomic force microscopy a statistical analysis of the ripple amplitude and wavelength was carried out showing that the periodicity and the amplitude of the rippled structures follow a linear dependence on the energy.
However, the evolution of the rippled patterns clearly differs for the lower and higher ion energies. For energies below 25 keV we observed almost no fluence dependence of the wavelength and amplitude in the investigated range of 1...8·1017 cm-2. But for energies above 25 keV and fluences above 1·1017 cm-2 coarsening was found. At energies larger than 50 keV Xe the ripple structures display a saturation regime for fluences higher than 5·1017 cm-2.
Investigations with cross-sectional high resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed the appearance of Xe filled inclusions at ion energies above 25 keV. This result correlates with an almost stable ratio of the ripple wavelength to the ripple amplitude of about 30 occurring above a threshold fluence of 2·1017 cm-2 and above 25 keV.
These results indicate that there is a certain threshold energy and fluence above which a stable form of the investigated wave-like structure is build up. This is possibly caused by the formation of noble gas inclusions at higher ion energies.
  • Poster
    International Workshop on "NANOSCALE PATTERN FORMATION AT SURFACES", 18.-22.09.2011, El Escorial, Spain

Publ.-Id: 16458 - Permalink


Structural investigations of ion beam doped silicon nanowires
Grenzer, J.; Roshchupkina, O.; Kögler, R.; Das Kanungo, P.; Werner, P.;
For the development of nano-optical devices nano wires (NW) are of emerging interest. One of the most important steps in the fabrication of Si devices is doping using ion beam implantation. However, this may lead to a distortion of the NW’s crystalline structure or even to an amorphization. A subsequent annealing procedure is necessary to recover the crystalline structure. The advantage of implanted Si NW’s is that the electrical conductivities are significantly higher than MBE-grown in-situ doped ones [1]. NW’s of about 100nm in diameter and 100..400 nm in length, nominally undoped, were MBE grown on Si(111) using Au as a growth-initiator. We followed the structural changes of the NW’s caused by implantation and annealing. We used rapid thermal annealing up to a temperature of 1100∘ C of about 30 seconds to remove a possible damage induced by implantation. Diffraction experiments were carried out at the ID01 ESRF beamline using a microfocused X-ray beam in combination with a 2D detector to obtain 3D diffraction patterns. Our experiments have shown that defect structure and form of the investigated NW’s change after implantation and annealing.
  • Lecture (Conference)
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 16457 - Permalink


Serpent Monte Carlo code: new methods for few-group cross section generation
Fridman, E.; Leppänen, J.;
The Serpent Monte Carlo (MC) code has been developed since 2004, and publicly distributed since 2009. One of the main applications for the code is the production of homogenized multi-group constants, which can still be considered a relatively unexplored field for the MC method. The calculation techniques required for this task have been implemented and refined during the seven years of Serpent development, with valuable feedback, contribution and new ideas from the user community. This paper presented two such topics: homogenization in leakage-corrected criticality spectrum and group constant generation in reflector regions. The implemented methods were verified and demonstrated by numerical examples. It is concluded that the new methodology improves the results of the deterministic calculation, and paves the way for Monte Carlo based group constant generation.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2012, 22.-24.05.2012, Stuttgart, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2012, 22.-24.05.2012, Stuttgart, Germany

Publ.-Id: 16456 - Permalink


Chemical fingerprinting of Hungarian and Slovakian obsidian using three complementary analytical techniques
Eder, F. M.; Neelmeijer, C.; Pearce, N. J. G.; Sterba, J. H.; Bichler, M.; Merchel, S.;
The natural volcanic glass obsidian is one of the classical objects of archaeometrical analyses. Reliable provenancing by means of its highly specific chemical composition, the “chemical fingerprint”, can provide information about economy, policy and the social system of ancient societies.

Although Mediterranean obsidian have mainly been the focus of characterization since the pioneer work of Cann and Renfrew (1964), provenancing of Central and Eastern Europe obsidian sources attracts increasing attention in the past decades. Fingerprinting of Hungarian and Slovakian obsidian sources is of great interest especially for Central European sites where obsidian has been widely used (Williams-Thorpe et al., 1984, Kasztovszky et al., 2008, Biró, 2009).

The application of three complementary analytical techniques on the same set of raw material samples allows both, a more complete characterization of obsidian sources and a comparison of analytical results. The aim of this multi-methodical approach is to apply three different analytical methods, in particular:

• Instrumental Neutron Activation Analysis (INAA),
• Ion Beam Analysis (IBA) comprising of Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE)
• Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)

to detect a maximum element spectrum and to compare element concentrations determined with at least two analytical techniques. This way a check of self-consistency of analytical results is possible. Furthermore, it allows the identification of a maximum of compositional differences between Hungarian and Slovakian sources by revealing the most characteristic “chemical fingerprint” composed of more than 40 elements.

For this study, NAA, IBA and LA-ICP-MS measurements are scheduled to be applied to 25 raw material samples from sources from Hungary and Slovakia in cooperation with the Natural History Museum Vienna (Hammer, V. and Seemann, R., Department of Mineralogy and Petrography) and the Vienna Lithothek (Trnka, G., Department of Prehistoric and Protohistoric Archaeology).

Up to now, IBA studies have already been carried out using the external 4 MeV proton beam of the 6 MV Tandem accelerator of the Ion Beam Centre of Helmholtz-Zentrum Dresden-Rossendorf. Further NAA investigations will be performed at the TRIGA Mark II 250 kW research reactor of the Atominstitut in Vienna. LA-ICP-MS measurements will be conducted using the Thermo Element 2 ICP-MS coupled to an ArF gas Excimer laser system at the Aberystwyth University.

CANN, J.R. AND RENFREW, C, 1964. The characterization of obsidian and its application to the Mediterranean Region. Proceedings of the Prehistoric Society 30, 111-131.

WILLIAMS-THORPE, O., WARREN, S.E. and NANDRIS, J.G., 1984. The distribution and provenance of archaeological obsidian in central and eastern Europe. Journal of Archaeological Science 11, 183-212.

KASZTOVSZKY, Z., BIRÓ, K., MARKÓ, A. and DOBOSI, V., 2008. Prompt gamma activation analysis for non-destructive characterization of chipped stone tools and raw materials. Journal of Radioanalytical and Nuclear Chemistry 278, 293-298.

BIRÓ, K.T., 2009. Sourcing Raw Materials for Chipped Stone Artifacts: The State-of-the-Art in Hungary and the Carpathian Basin. In: Adams, B. and Blades, B.S. (Eds.) Lithic Materials and Paleolithic Societies (eds B. Adams and B. S. Blades), Wiley & Blackwell, 47-53.
Keywords: ceramics, glazes, glass and vitreous materials, ion beam analysis, neutron activation analyis, ICP-MS
  • Poster
    39th International Symposium on Archaeometry: “50 years of ISA”, 28.05.-01.06.2012, Leuven, Belgium

Publ.-Id: 16455 - Permalink


Entwicklung von Feldbusknoten für den wissenschaftlichen Gerätebau
Kaever, P.;
Mit der Entwicklung spezialisierter Feldbusknoten lässt sich eine für den wissenschaftlichen Gerätebau in vielen Fällen sinnvolle Aufteilung zwischen selbst entwickelten und kommerziell verfügbaren Komponenten unter konsequenter Nutzung vorhandener Automatisierungssysteme erreichen. Im Folgenden wird vorgestellt, welche Schritte dabei erforderlich sind und welche Möglichkeiten sich mit diesem Ansatz ergeben.
Keywords: Automatisierung, Feldbus, Feldbusgeräte, wissenschaftlicher Gerätebau
  • Open Access LogoContribution to proceedings
    102. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2011, 21.-23.03.2011, Darmstadt, Deutschland
    Peter Göttlicher (DESY): 102. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2011, Hamburg: Deutsches Elektronen-Synchrotron, 978-3-935702-58-4, 213-223

Publ.-Id: 16454 - Permalink


Segregation-induced hardening by dislocation loops in bcc FeCr alloys
Terentyev, D.; Bergner, F.; Bonny, G.; Zhurkin, E. E.; Malerba, L.;
Enrichment of Cr on both <100> and ½<111> dislocation loops has been reported under ion, electron and neutron irradiation in Fe-xCr with x=9-15 at.%. Cr enrichment in Fe-9,12Cr around edge of loops is predicted by atomistic Monte Carlo simulations. MC simulations indicate that Cr clustering on loops disappears above equilibrium solubility limit (ΔT~100-150K). MD simulations indicate that Cr enrichment at loops enhances their strength in a range of specific loading conditions.
  • Lecture (Conference)
    16th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-16), 04.-09.12.2011, Santa Barbara, USA
  • Contribution to proceedings
    IGRDM-16, 04.-09.12.2011, Santa Barbara, USA
    Proceedings of IGRDM-16

Publ.-Id: 16453 - Permalink


Small-angle neutron scattering in neutronirradiated Fe-Cr alloys
Bergner, F.; Heintze, C.; Ulbricht, A.; Kuksenko, S.; Pareige, C.; Pareige, P.;
The objectives are to report data for Fe2.5Cr, Fe5Cr, Fe9Cr, Fe12Cr irradiated up to 0.06, 0.6, 1.5 dpa; to calculate nuclear scattering from features reported by Kuksenko et al. based on APT; and to compare with measured nuclear SANS. We have found that the NiSi-enriched clusters observed by APT are not responsible for the observed SANS intensities. Possible sources of the apparent discrepancy between SANS and APT for Fe12Cr are discussed. The dominant source is the overestimation of the Fe fraction in the Cr-rich clusters by APT.
  • Lecture (Conference)
    16th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-16), 04.-09.12.2011, Santa Barbara, USA
  • Contribution to proceedings
    IGRDM-16, 04.-09.12.2011, Santa Barbara, USA
    Proceedings of the IGRDM-16

Publ.-Id: 16452 - Permalink


SANS applied to RPV weld material from decommissioned NPP Greifswald taking into account atom probe data
Bergner, F.; Ulbricht, A.; Viehrig, H.-W.; Wagner, A.; Nishida, K.; Soneda, N.;
SANS data are presented for as-irradiated, irradiated and annealed, and re-irradiated weld material from units 4, 2, and 1, respectively, of the decommissioned NPP Greifswald. The unirradiated reference condition is represented by a data scatter band obtained for several unirradiated weld materials of the same kind. The effects or irradiation, annealing and re-irradiation are worked out. Comparison of the SANS data with available atom probe data for the same material from unit 4 indicates an apparent discrepancy between both methods. Possible reasons are carefully discussed. The dominant reason is the overestimation of the Fe fraction in the irradiation-induced clusters by APT due to trajectory overlaps.
  • Lecture (Conference)
    16th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-16), 04.-09.12.2011, Santa Barbara, USA
  • Contribution to proceedings
    IGRDM-16, 04.-09.12.2011, Santa Barbara, USA
    Proceedings of IGRDM-16

Publ.-Id: 16451 - Permalink


Solved and unsolved issues in the interpretation of SANS results obtained for neutron-irradiated Fe-Cr alloys
Bergner, F.; Heintze, C.; Ulbricht, A.;
Full set of nuclear and magnetic SANS data for a number of four Cr levels, three dpa levels each, is presented. The results are given in terms of concentration, size and A-ratio as function of Cr and dpa. A consistent understanding is obtained for Fe12Cr in terms of alpha‘ phase formation. For Fe2.5Cr, Fe5Cr and Fe9Cr, the presence of a second kind of scatterers is indicated, to which impurity elements such as Ni, Si, and C must contribute. The nature of scatterers in Fe2.5Cr, Fe5Cr and Fe9Cr is among the unsolved issues. Candidates are Cr-C-enriched clusters and/or Cr-Si-P-Ni-enriched clusters detected by atom probe tomography. There is an inconsistency between composition reported for APT and composition assumed in the SANS analysis with respect to Cr/Fe-fraction.
  • Lecture (Conference)
    19th Workshop on Multiscale Modelling and Basic Experiments of Iron-Chromium Alloys for Nuclear Applications, 08.-09.11.2011, Sala, Schweden

Publ.-Id: 16450 - Permalink


Modification to the central-cell correction of germanium acceptors
Drachenko, O.; Schneider, H.; Helm, M.; Kozlov, D.; Gavrilenko, V.; Wosnitza, J.; Leotin, J.;
In this paper, we report a correction to the model potential of the Ga acceptor in germanium, evidenced by high-magnetic-field photoconductivity measurements. We found that under high magnetic fields the chemical shift of the binding energy of Ga acceptors vanishes, contrary to the results given by the generally accepted theory. To fit our data, we found that the central-cell correction should contain a repulsive part (i.e., it must be bipolar), in contrast to the purely attractive screened point-charge potential widely used in the literature.
Keywords: Germanium, acceptor, chemical shift, central-cell correction, high magnetic field

Publ.-Id: 16449 - Permalink


Die tertiären Vulkanite Sachsens - neue mineralogische und geochemische Daten zu 'Alten Bekannten'
Renno, A. D.; Keywords: petrology, mineralogy, geochemistry, Saxony, Erzgebirge, Lausitz, Tertiary volcanic rocks
  • Lecture (others)
    Dresdner Geowissenschaftliche Kolloquien, 10.01.2012, Dresden, Deutschland

Publ.-Id: 16448 - Permalink


The trigonal nodal SP3 method of the code DYN3D — verification on pin level
Duerigen, S.; Bilodid, Y.; Fridman, E.;
The neutronics model of the nodal reactor dynamics code DYN3D developed for 3D analyses of steady states and transients in Light-Water Reactors has been extended by a simplified P3 (SP3) neutron transport option – to overcome the limitations of the diffusion approach at regions with significant anisotropy effects. To provide a method being applicable to reactors with hexagonal fuel assemblies and to furthermore allow flexible mesh refinement, the nodal SP3 method has been developed on the basis of a flux expansion in trigonal-z geometry. In this paper, a verification of the methodology on quasi-pin level is performed by means of a single-assembly test example. The corresponding pin-wise few-group cross sections were obtained by the deterministic lattice code HELIOS. The power distributions were calculated using both the trigonal DYN3D diffusion and SP3 solver and compared to the HELIOS reference solutions. Close to regions with non-negligible flux anisotropies, e.g., caused by the presence of a strong absorbing material, the power distribution calculated by DYN3D-SP3 shows a significant improvement in comparison to the diffusion method.
Keywords: simplified P3, SP3, nodal method, trigonal, triangular, hexagonal, mesh refinement, pin level
  • Contribution to proceedings
    Jahrestagung Kerntechnik, 22.-24.05.2012, Stuttgart, Deutschland
  • Lecture (Conference)
    Jahrestagung Kerntechnik, 22.-24.05.2012, Stuttgart, Deutschland

Publ.-Id: 16447 - Permalink


Gamma-induced Positron Annihilation Spectroscopy
Butterling, M.; Anwand, W.; Wagner, A.; Krause-Rehberg, R.;
The setup and idea of the Gamma-induced Positron Spectroscopy (GiPS) using the superconducting LINAC ELBE is presented. Features of a setup using bremsstrahlung to create positrons by pair production as well as the advantages of the characteristics of the ELBE beam will be shown and discussed. The measurement of the positron and positronium lifetime of water at various temperatures is an example for investigation and the connection of theory and experiment and will also show the perfect function of the GiPS setup.
Keywords: Positron Annihilation Spectroscopy, Bremsstrahlung, Positronium
  • Lecture (others)
    Seminar talk as part of a DAAD contract (507 556 28) with Charles University Prague, 12.12.2011, Prague, Czech Republic

Publ.-Id: 16445 - Permalink


Differential cross section and analysing power of the quasi-free pn -> {pp}_s pi- reaction at 353 MeV
Dymov, S.; Azaryan, T.; Barsov, S.; Baru, V.; Benati, P.; Bertelli, S.; Chiladze, D.; Dzyuba, A.; Gebel, R.; Goslawski, P.; Guidoboni, G.; Hanhart, C.; Hartmann, M.; Kacharava, A.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Kurbatov, V.; Lenisa, P.; Lensky, V.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Mielke, M.; Mikirtytchiants, S.; Merzliakov, S.; Ohm, H.; Papenbrock, M.; Rathmann, F.; Serdyuk, V.; Shmakova, V.; Stroeher, H.; Tabidze, M.; Tsirkov, D.; Trusov, S.; Uzikov, Y.; Valdau, Y.; Wilkin, C.;
In order to establish links between p-wave pion production in nucleon-nucleon collisions and low energy three-nucleon scattering, an extensive programme of experiments on pion production is currently underway at COSY-ANKE. The final proton pair is measured at very low excitation energy, leading to an S-wave diproton, denoted here as {pp}_s. By using a deuterium target we have obtained data on the differential cross section and analysing power of the quasi-free pol{p}n -> {pp}_s pi- reaction at 353 MeV. The spectator proton p_sp was either measured directly in silicon tracking telescopes or reconstructed using the momentum of a detected pi-. Both observables can be described in terms of s-, p-, and d-wave pion production amplitudes. Taken together with the analogous data on the pol{p}p -> {pp}_s pi0 reaction, full partial wave decompositions of both processes were carried out.

Publ.-Id: 16444 - Permalink


Gamma-induced Positron Lifetime and Age-Momentum Correlation Measurements (AMOC) of water at temperatures between 20° C and 90° C
Butterling, M.; Anwand, W.; Krause-Rehberg, R.; Wagner, A.;
The Gamma-induced Positron Spectroscopy (GiPS) facility at ELBE (Helmholtz-Zentrum Dresden-Rossendorf) is ideally suited to measure extended volume sample materials like liquids with an information depth of several mm in an appropriate time [1]. Moreover, GiPS allows for studying positron lifetimes and positron momentum within the same experiment and thus allows for realizing Age-Momentum Correlation (AMOC) experiments within a fraction of time needed with conventional setups.

There are still questions about the microscopic structure of liquid water and the behavior of water inside membranes and at boundaries is under vivid investigation.
AMOC experiments revealing additional information about the local environment at the instance of pick-off positron annihilation of o-Ps were performed for water at temperatures between 20°C and 90°C to verify recently reported observations of periodic quantum beats in the AMOC spectra, caused by spin conversion of o-Ps [2]. The radiation effect caused by the use of bremsstrahlung for positron production was also investigated.

Different analysing methods for these spectra with high statistic and quality will be presented. Also the application of common theory for positronium formation and chemical reactions in water will be discussed.
Keywords: Positron Annihilation Spectroscopy, Gamma-induced Positron Spectroscopy, Positron Lifetime, Bremsstrahlung, Positronium
  • Lecture (Conference)
    10th International Workshop on Positron and Positronium Chemistry (PPC10), 05.-09.09.2011, Smolenice, Slovakia

Publ.-Id: 16443 - Permalink


Lead sheets for organ pipes - Positron Spectroscopy for cultural heritage
Butterling, M.; Anwand, W.; Wagner, A.; Skorupa, W.; Eule, A.-C.;
Lead sheets are a basic material to build metal pipes for organ pipes. Mostly lead gets alloyed with tin and in this manner its properties have been seen superior over centuries. But, the classical organ construction (16.-18.century) in the northern parts of Europe comprised the use of alloys with very low (2-3%) or no tin content because of cost reasons. In such cases the lead material shows critical properties regarding the mechanical strength and density. Nowadays, the restoration of organ instruments from this period requires the production of new material to replace corroded material or to substitute missing pipes or other organ parts. An important issue is the engineering of such material by mechanical hammering to increase the density. Microscopic cavities inside the casted material get closed in this way and the mechanical strength gets increased. Up to now there exists only an empirical knowledge about the quality changes due to the hammering treatment within a period of several centuries.
We used the Gamma-induced Positron Spectroscopy (GiPS) setup at ELBE at Helmholtz-Zentrum Dresden-Rossendorf to investigate the porosity of hammered and non-hammered material both for historical material from the 17th century and for newly produced sheet material for the first time to get microscopic information about the effect of the hammering practise. The Gamma-induced Positron Spectroscopy setup at ELBE is worldwide the only suitable setup to investigate solids with an information coming from the whole volume. Results obtained from this are compared with conventional depth resolving Doppler Broadening Spectroscopy measurements using a slow positron beam.
Keywords: Positron Annihilation Spectroscopy, Gamma-induced Positron Spectroscopy, Bremsstrahlung
  • Lecture (Conference)
    Positron Studies of Defects (PSD) 11 Delft, 28.08.-02.09.2011, Delft, Netherlands

Publ.-Id: 16442 - Permalink


DRACO upgrade and the diode-pumped PW laser PEnELOPE
Siebold, M.;
The Helmholtz-Centre Dresden-Rossendorf is now planning to build a fully diode-pumped Petawatt laser for laser-particle acceleration research. Within the PEnELOPE project (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) a pulse energy of 150 J, a repetition rate around 1 Hz and a pulse duration of 150 fs after compression are desired. Furthermore, the existing DRACO laser system - a 200TW flash lamped Ti:Sapphire laser is going to be upgraded soon towards the PW-level at short pulse lengths in the range of 25-30fs. Recent laser plasma experiments as well as issues of the laser development are addressed.
Keywords: high intensity lasers at HZDR
  • Lecture (others)
    Networking Actvity on Ultra-High Intensity Ultrashort Lasers (NAUUL), 16.06.2011, Salamanca, Spanien

Publ.-Id: 16441 - Permalink


High intensity lasers in Dresden: DRACO and PEnELOPE
Siebold, M.;
The Helmholtz-Centre Dresden-Rossendorf is now planning to build a fully diode-pumped Petawatt laser for laser-particle acceleration research. Within the PEnELOPE project (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) a pulse energy of 150 J, a repetition rate around 1 Hz and a pulse duration of 150 fs after compression are desired. Furthermore, the existing DRACO laser system - a 200TW flash lamped Ti:Sapphire laser is going to be upgraded soon towards the PW-level at short pulse lengths in the range of 25-30fs.
Keywords: High intensity lasers at HZDR
  • Lecture (others)
    1st HiLASE workshop, 28.-29.11.2011, Prag, Tschechien

Publ.-Id: 16440 - Permalink


PEnELOPE - a high peak-power laser system for laser-particle acceleration experiments.
Siebold, M.; Loeser, M.; Roeser, F.; Schramm, U.;
With the first demonstration of direct diode-pumped TW lasers with pulse energies of 1 J and more a scaling of this approach for use in PW-class laser systems became feasible. The Helmholtz-Centre Dresden-Rossendorf is now planning to build a fully diode-pumped Petawatt laser for laser-particle acceleration research. Within the PEnELOPE project (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) a pulse energy of 150 J, a repetition rate around 1 Hz and a pulse duration of 150 fs after compression are desired. In order to minimize the required pump peak power and therefore the initial costs a broad-band Ytterbium doped laser material with a long fluorescence lifetime (i.e. Yb:glass or Yb:CaF2) is chosen. A total pump peak-power of 1.2 MW is scheduled assuming a pump pulse duration of 2 ms and an envisioned optical-to-optical conversion efficiency of 10% before compression. Pulses as short as 60fs having an energy of 25nJ are generated in a commercial Yb:KGW oscillator at a center wavelength of 1035nm. In order to employ CPA technique the pulses are stretched to 2ns in a grating stretcher having grating constant of 1760 lines per mm. The amplifier-chain consists of a regenerative amplifier and 4 subsequent multipass amplifiers. While the regenerative amplifier produces a gain 40.000 gain narrowing is required to be suppressed by intra-cavity spectral shaping. In free-running mode (unseeded) a bandwidth of 20nm of the regenerative amplifier operating at the mJ level was achieved. A booster amplifier with a gain of 100 and 3 further multipass amplifiers each having a gain of 10-16 are required to achieve the desired pulse energy. Both, multipass amplification to the Joule-level and a small-signal of >40 in a single-disk Yb:CaF2 booster have been demonstrated recently.
For thermal management of the high-energy lasers the active mirror concept is one of the most promising techniques for room temperature operation of Yb-based lasers providing efficient cooling of the laser material and energy extraction. In order to maintain both efficiency and repetition rate and to suppress parasitic lasing while scaling the aperture of disk amplifiers a multiple disk approach also employing pump-recycling was proposed. Time-resolved thermal lens investigations on a diode-pumped Yb:CaF2 disk revealed a one order of magnitude less impact on the wavefront abberations compared to a Yb:YAG disk having a similar geometry.
In this paper we introduce the basic design concepts and first experimental proofs of the fully diode-pumped high peak-power laser PEnELOPE.
Keywords: High peak power diode pumped lasers
  • Lecture (Conference)
    International Conference on Ultra-intense Laser Interaction Science (ULIS), 10.-13.10.2011, Lisboa, Portugal

Publ.-Id: 16439 - Permalink


Active mirror high energy Yb:YAG amplifier
Loeser, M.; Siebold, M.; Kroll, F.; Roeser, F.; Schramm, U.;
Diode-pumped lasers and amplifiers using Yb-doped materials have attracted increasing interest in the past years. This is owed to the high achievable efficiency of high energy amplifiers with high repetition rates and their potential to provide ultrafast laser pulses in the sub 100fs range. These properties allow their use in high intensity physics, laser fusion or pump sources for ultra-short Ti:Sa and OPCPA systems. Yb:YAG is one of the most important material for ns pulse generation and amplification with high efficiency also at room temperature. Here we present a joule-class Yb:YAG active mirror amplifier and the time-resolved analysis of its thermal lens. The active mirror concept is one of the most promising techniques for room temperature operation of Yb-based lasers providing efficient cooling of the laser material and energy extraction. A pulse energy of 730mJ at a repetition rate of 1Hz was obtained at an optical-to-optical conversion efficiency of 16%. Here a relay-imaging multipass cavity with 4 extraction passes and also 4 pump passes was employed. For seeding a Yb:YAG pre-amplifier with a output energy of 65mJ was used. The disk with an Yb-concentration of 5mol% comprises a thickness 2.5mm and diameter of 12.5mm. At pump energies of 4J and above the small-signal gain was drastically reduced by transverse lasing which was observed as a roll-over of the measured gain and efficiency. In order to get rid of parasitic lasing the doping concentration will be reduced while the thickness is increased such that the optical thickness of the disk remains. Furthermore, a multiple active mirror will be used in a redesigned setup allowing reduced thermal load of each single disk. The thermal lens measurements were compared with a rod type (transversally) cooled disk. At a repetition rate of 10Hz the thermal equilibrium of the disk was attained within the first pump shots while in the case of the rod type cooling serveral seconds were required.
Keywords: High energy lasers, diode pumped lasers, ytterbium
  • Lecture (Conference)
    SPIE Optics & Optoelectronics 2011, 18.-21.04.2011, Prag, Tschechien

Publ.-Id: 16438 - Permalink


Joule-level, diode-pumped, room-temperature Yb:CaF2 amplifiers
Loeser, M.; Siebold, M.; Kroll, F.; Roeser, F.; Schramm, U.;
The Research Centre Dresden-Rossendorf is planning to build a fully diode-pumped Petawatt laser based on Ytterbium-doped calcium fluoride. A pulse energy of 200J, a repetition rate of 1Hz and a pulse duration of 200fs after compression are desired. In this project a total pump peak-power of 1.5MW is scheduled assuming a pump pulse duration of 2ms and a targeted optical-to-optical conversion efficiency of 10%. Here we present gain measurements and time-resolved analysis of the thermal lens of different Yb:CaF2 amplifier configurations. The active mirror concept is one of the most promising techniques for room temperature operation of Yb-based lasers providing efficient cooling of the laser material and energy extraction. Therefore, a disk amplifier was compared with a rod laser. A pulse energy of 600mJ at a repetition rate of 1Hz was achieved using a cylindrical rod with a length of 20mm, a diameter of 28mm and an Yb-concentration of 2mol%. For seeding an Yb:YAG pre-amplifier produced pulses with a duration of 6ns. With a 2-disk Yb:CaF2 amplifier comprising of 8 extracting beams and a pump recovery configuration the minimum required pump fluence in order to bleach out re-absorption at the laser wavelength of 1030nm was reduced roughly by a factor of two down to 13J/cm2. Furthermore, the thermal lens power was reduced from 5dpt of the rod down to smaller than 0.05dpt for 3mm thin disks at 10Hz.
Keywords: laser materials, diode pumped lasers, high peak power
  • Lecture (Conference)
    SPIE Optics & Optoelectronics, 18.-21.04.2011, Prag, Tschechien

Publ.-Id: 16437 - Permalink


Broadband, diode-pumped Yb:SiO2 multicomponent glass laser
Loeser, M.; Roeser, F.; Reichelt, A.; Kroll, F.; Siebold, M.; Schramm, U.; Grimm, S.; Litzkendorf, D.; Kirchhof, J.;
Here we present first lasing and tunability results of a diode-pumped Yb:SiO2 multicomponent glass laser. The multicomponent glass consists of 70 mol% SiO2, 20 mol% Al2O3, 9.1 mol% La2O3, and a doping level of 0.875 mol% Yb2O3. Due to the high contingent of SiO2 the spectroscopic properties of the multicomponent glass is similar to Yb-doped fused silica glass. The huge advantage of the here presented multicomponent fused silica glass as gain material is its fabrication technique. It can be produced directly out of a glass melt with large active volume and high optical quality.
The Yb-doped multicomponent glass sample in the experiment had a thickness of 1.5 mm and was polished in laser quality. For pumping a fiber coupled laser diode was used with power of 6W at 975nm. The pump absorption was about 60%. In order to increase the pump absorption the non-absorbed pump was re-imaged back into the Yb:SiO2. The laser cavity was a V-shaped resonator and the folding mirror had a curvature of 200mm. This results in a stable confocal resonator with a beam waist of about 50 µm in the glass and 600 µm on the output coupler. The free running laser wavelength was centered around 1055nm. The slope efficiency results in a value of 32%. The wavelength tunability of the laser cavity was achieved inserting a brewster prism (SF10) in between the folding mirror and the output coupler. At a pump level of 5W the laser had a tuning range from 1010 nm to 1080nm.
Keywords: ytterbium doped laser materials
  • Lecture (Conference)
    SPIE Optics & Optoelectronics, 18.-21.04.2011, Prag, Tschechien

Publ.-Id: 16436 - Permalink


High-Efficiency Cryogenic-Cooled Diode-Pumped Amplifier with Relay Imaging for Nanosecond Pulses
Koerner, J.; Hein, J.; Kahle, M.; Liebetrau, H.; Kaluza, M.; Siebold, M.; Loeser, M.;
We present temperature dependent gain measurements with different Ytterbium doped laser media, such as Yb:YAG, Yb:FP15-glass and Yb:CaF2 in a multi-pass amplifier setup. The temperature of these materials was adjusted arbitrarily between 100K and 300K, while heat removal was realized by transverse cooling. In order to obtain a good beam profile throughout the amplification process, we used an all-mirror based relay imaging setup consisting of a telescope accomplishing a 4f-imaging with a plane mirror in each image plane. The amplification beam is then coupled into the cavity and doing several round trips wandering over the surface of the spherical mirrors. Hence the laser material is placed in one of the image planes, the beam quality of the amplifier was ruled by the intensity profile of the pumping laser diodes consisting of two stacks with 2.5kW peak output power each. Due to the given damage threshold fluence, the output energy of the amplifier was limited to about 1J at a beam diameter of 4.5 mm (FWHM). The seed pulses with a duration of 6 ns were generated in a Yb:FP15-glass cavity dumped oscillator with further amplification up to the 100mJ level by a room temperature Yb:YAG multi pass amplifier. The 1 Hz repetition rate of the system was limited by the repetition rate of the front-end. With Yb:YAG for instance an output energy of 1.1 J with an record high optical to optical efficiency of more than 35% was achieved, which was further increased to 45% for 500 mJ output energy.
Keywords: Diode-pumped laser, ytterbium doped material, cryogenic
  • Contribution to proceedings
    SPIE Optics & Optoelectronics, 18.-21.04.2011, Prag, Tschechien
    Proc. SPIE Vol. 8080, 80800D

Publ.-Id: 16435 - Permalink


Temperature Dependent Measurement of Absorption and Emission Cross Sections for Various Yb3+ Doped Laser Materials
Koerner, J.; Hein, J.; Kahle, M.; Liebetrau, H.; Kaluza, M.; Loeser, M.; Siebold, M.;
For laser performance simulations, optical properties of applied active materials have to be exactly known. Here we report on temperature dependent emission and absorption cross section measurements for Yb:YAG, Yb:CaF2 and Yb:FP15-glass. The temperature of the samples was aligned in steps of 20 K between 100 K and room temperature with a liquid nitrogen driven cryostat. Absorption spectra were obtained with a fiber coupled white light source and fluorescence spectra by excitation with a fiber coupled 10W laser diode at 970 nm. All spectral measurements were performed with a scanning spectrum analyzer, providing a spectral resolution down to 0.05 nm. By applying the McCumber relation in combination with the Fuchtbauer-Ladenburg method, we were able to obtain a valid emission cross section over the whole range of interest from the measured data.
Keywords: ytterbium doped laser materials, diode pumped lasers
  • Contribution to proceedings
    SPIE Optics & Optoelectronics, 18.-21.04.2011, Prag, Tschechien
    Proc. SPIE Vol. 8080, 808 003

Publ.-Id: 16434 - Permalink


Optical properties of CaF2 and Yb3+:CaF2 for laser applications
Staeblein, J.; Poehl, K.; Weisleder, A.; Von-Der-Goenna, G.; Toepfer, T.; Hein, J.; Siebold, M.;
Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.
Keywords: ytterbium doped laser materials
  • Contribution to proceedings
    SPIE Optics Optoelectronics 2011, 18.-21.04.2011, Prag, Tschechien
    SPIE Volume 8080A, 808002

Publ.-Id: 16433 - Permalink


Cryogenic-cooled Yb:YAG amplifier for ns-pulses obtaining high optical efficiencies
Koerner, J.; Liebetrau, H.; Hein, J.; Kahle, M.; Loeser, M.; Siebold, M.;
Since typically low temperatures turn the quasi three level system of Yb:YAG into a four level system much higher efficiencies are expected by cryogenic cooling. Former experiments achieved efficiencies up to 30 % [3], which is below theoretical expectations [1,2]. To increase the efficiency through a better overlap between the pumped area and the seed beam profile, a novel all-reflective relay imaging amplifier has been built. Astigmatism compensation of the setup was achieved by folding the beam pass out of plane. The Yb:YAG crystal was placed in a liqiud nitrogen cooled mount inside a vaccum chamber.
The amplifier design allows to switch between different numbers of passes easily. In a six pass configuration a maximum optical-to-optical efficiency of 46% with a output energy of more than 600 mJ was achieved (s. Figure 1). With a slightly modified setup the output energy was increased to 1.1 J in a eight-pass scheme at a reduced efficiency of 36 %.
Keywords: diode-pumped lasers, ytterbium doped materials
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics (CLEO) Europe, 22.-26.05.2011, München, Deutschland
    Conference on Lasers and Electro-Optics, CA10.3

Publ.-Id: 16432 - Permalink


Temperature resolved measurements of absorption and emission cross sections for various Yb3+-doped gain media from 100K to room temperature
Koerner, J.; Hein, J.; Liebetrau, H.; Kahle, M.; Lenski, M.; Loeser, M.; Siebold, M.;
It has been shown, that cryogenic cooling of Yb3+-doped media is increasing laser performance significantly[1,2]. The reason for this is the thermal depopulation of the lower laser levels turning the quasi three level extraction scheme into a real four level scheme. By now most of these cryogenic cooled amplifiers aim on liquid nitrogen temperature. For future systems it has to be estimated what is an optimum operation temperature as compromise between laser performance and effort for cooling. This is needed as well from an energetic point of view as from an financial point of view. For this it is necessary to know the basic absorption and emission cross sections in dependence of temperature.
We present measurement of such cross sections in an temperature range from 100K to room temperature for various gain material such as Yb:YAG, Yb:CaF2 and Yb:FP15-glass. The absorption cross sections are calculated from the absorption spectra. The emission cross sections are determined from the absorption and emission spectra employing the Füchtbauer-Ladenburgmethod and theMcCumber relation [3,4]. Additional wavelength dependent gain measurements are used to cross check the validity of the measurements.
Keywords: diode-pumped laser, ytterbium-doped materials
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics (CLEO) Europe, 22.-26.05.2011, München, Deutschland
    Conference on Lasers and Electro-Optics, CAP.3

Publ.-Id: 16431 - Permalink


High-energy, diode-pumped Yb:CaF2 disk-laser
Siebold, M.; Loeser, M.; Roeser, F.; Kroll, F.; Koerner, J.; Hein, J.; Schramm, U.;
Previous works on Ytterbium-doped alcaline-earth fluoride have impressively shown that these materials are suitable for high-peak power operation [1,2] due to their broad emission spectrum comparable with rare-earth doped laser glasses. From the scaling point of view Yb:CaF2 is the most promising material since crystal growth at large sizes with diameters up to 100 mm and more with high optical quality have been demonstrated so far. Also the thermo-mechanical and thermo-optical properties such as the negative thermal lens of Yb:CaF2 are superior for high-average power lasers [3]. Moreover, the high saturation fluence (i.e. 80 J/cm2) pushes the potential energy limit of thin disk lasers by about one order of magnitude compared to oxide laser materials such as Yb:YAG. This means that at a given stored energy parasitic lasing is reduced by a low transverse gain [4]. However, the low single-pass gain of Yb:CaF2 lasers must compensated by a large number of amplifier passes. We built a multi-pass Yb:CaF2 disk amplifier pumped with a diode laser module having a peak power of 16.8 kW (provided by Lastronics GmbH, Germany). A maximum pump energy of 40.3 J at a wavelength of 940 nm was obtained at a pump duration of 2.4 ms while the flat-top shaped pump profile (6 × 6 mm2) was homogenized by a doublet of micro-lens arrays inside the module and imaged into the gain medium. The seed pulses with a duration of 6 ns (FWHM) were generated in a Q-switched Yb:YAG oscillator and then pre-amplified from 400 μJ to 100 mJ at a repetition rate of 1 Hz in a booster Yb:YAG amplifier. For comparison a rod type and a disk Yb:CaF2 amplifier were build and analyzed. While the laser rod with a diameter of 28 mm and a length of 20 mm was 2.2 mol% Yb-doped the doping concentration of the disk with a thickness of 2.7 mm and diameter of 20 mm was 4.5 mol% Yb. In case of the rod a two-side anti-reflection (AR) coating and a highly reflective (HR) mirror was used, whereas the disk was HR-coated from the rear side and glued on a plane copper-mirror for thermal contact. A maximum output pulse energy of 1.2 J at a repetition rate of 1 Hz of the multi-pass Yb:CaF2 amplifier with the rod-type material was measured. Above 1.2 J laser induced damage occurred in the rod volume while at 270 mJ surface damage on the AR-side was observed in the case of the disk. This very low damage resistance of ~1 J/cm2 is owed to the surface quality in our specific case and therefore the optical-to-optical conversion efficiency was limited to 1.5%. In the case of the rod type amplifier an efficiency of 4% was obtained. Fig. 1 illustrates the setup and the dynamic of both Yb:CaF2 amplifier configurations. Although the efficiency achieved was limited it becomes obvious that the performance of the disk is improved compared to the rod with regard to the total gain and minimum pump energy in order to bleach out the reabsorption at the laser wavelength of 1030 nm. Future work is now in progress in order to boost the pulse energy and hence the extraction efficiency of the disk Yb:CaF2 amplifier.
Keywords: diode-pumped lasers, ytterbium doped materials
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics (CLEO) Europe, 22.-26.05.2011, München, Deutschland
    Conference on Lasers and Electro-Optics, CA4.4

Publ.-Id: 16430 - Permalink


Innovative Informationstechnik im Dienste der Forschung am Beispiel des Helmholtz-Zentrums Dresden-Rossendorf.
Konrad, U.;
Das Papier beschreibt innovative Anwendungen der Informationstechnologie in der Forschung am Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Dazu werden Beispiele aus den Gebieten High Performance Computing, Visualisierung und Virtual Reality sowie Identity Management erläutert, bei denen das HZDR zusammen mit Partnern fortschrittliche Lösungen entwickelt hat.
Keywords: Information Technology, High Performance Computing, Visualization, Virtual Reality, Identity Management, Research Infrastructure
  • Invited lecture (Conferences)
    Regenerative Energien als Zukunftstechnologien, Internationale Tagung anlässlich des 120-jährigen Jubiläums der Ingenieurausbildung am Standort Köthen, 13.-14.10.2011, Köthen, Deutschland

Publ.-Id: 16429 - Permalink


Joint Project: Interaction and transport of actinides in natural clay rock with consideration of humic substances and clay organics - Characterization and quantification of the influence of clay organics on the interaction and diffusion of uranium and americium in the clay (Final Report BMWi Project No.: 02 E 10156)
Schmeide, K.; Joseph, C.; Sachs, S.; Steudtner, R.; Raditzky, B.; Günther, A.; Bernhard, G.;
The objective of this project was the study of basic interaction processes in the systems actinide - clay organics - aquifer and actinide - natural clay - clay organics - aquifer. Thus, complexation, redox, sorption and diffusion studies were performed.
To evaluate the influence of nitrogen, phosphorus and sulfur containing functional groups of humic acid (HA) on the complexation of actinides in comparison to carboxylic groups, the Am(III) and U(VI) complexation by model ligands was studied by UV-Vis spectroscopy and TRLFS. The results show that Am(III) is mainly coordinated via carboxylic groups, however, probably stabilized by nitrogen groups. The U(VI) complexation is dominated by carboxylic groups, whereas nitrogen and sulfur containing groups play a minor role. Phosphorus containing groups may contribute to the U(VI) complexation by HA, however, due to their low concentration in HA they play only a subordinate role compared to carboxylic groups. Applying synthetic HA with varying sulfur contents (0 to 6.9 wt.%), the role of sulfur functionalities of HA for the U(VI) complexation and Np(V) reduction was studied. The results have shown that sulfur functionalities can be involved in U(VI) humate complexation and act as redox-active sites in HA for the Np(V) reduction. However, due to the low content of sulfur in natural HA, its influence is less pronounced.
In the presence of carbonate, the U(VI) complexation by HA was studied in the alkaline pH range by means of cryo-TRLFS (-120°C) and ATR FT-IR spectroscopy. The formation of the ternary UO2(CO3)2HA(II)4− complex was detected. The complex formation constant was determined with log β0.1 M = 24.57 ± 0.17.
For aqueous U(VI) citrate and oxalate species, luminescence emission properties were determined by cryo-TRLFS and used to determine stability constants. The existing data base could be validated.
The U(VI) complexation by lactate, studied in the temperature range 7 to 65°C, was found to be endothermic and entropy-driven. In contrast, the complex stability constants determined for U(VI) humate complexation at 20 and 40°C are comparable, however, decrease at 60°C.
For aqueous U(IV) citrate, succinate, mandelate and glycolate species stability constants were determined. These ligands, especially citrate, increase solubility and mobility of U(IV) in solution due to complexation.
The U(VI) sorption onto crushed Opalinus Clay (OPA, Mont Terri, Switzerland) was studied in the absence and presence of HA or low molecular weight organic acids, in dependence on temperature and CO2 presence using OPA pore water as background electrolyte. Distribution coefficients (Kd) were determined for the sorption of U(VI) and HA onto OPA with (0.0222 ± 0.0004) m3/kg and (0.129 ± 0.006) m3/kg, respectively. The U(VI) sorption is not influenced by HA (50 mg/L), however, decreased by low molecular weight organic acids (> 1×10-5 M), especially by citrate and tartrate. With increasing temperature, the U(VI) sorption increases both in the absence and in the presence of clay organics.
The U(VI) diffusion in compacted OPA is not influenced by HA at 25 and 60°C. Predictions of the U(VI) diffusion show that an increase of the temperature to 60°C does not accelerate the migration of U(VI). With regard to uranium-containing waste, it is concluded that OPA is suitable as host rock for a future nuclear waste repository since OPA has a good retardation potential for U(VI).
Keywords: Actinides, americium, uranium, neptunium, humic substances, clay organics, model ligands, Opalinus clay, complexation, reduction, sorption, diffusion, migration, repository
  • Other report
    Dresden: Helmholtz-Zentrum Dresden-Rossendorf, 2011
    157 Seiten

Publ.-Id: 16428 - Permalink


Superconducting layers in silicon - Get ready for the quantum interference -
Fiedler, J.; Skrotzki, R.;
Ausgezeichnet mit dem DFCNA-Sonderpreis 2011 vom Dresdner Fraunhofer-Cluster Nanoanalytik im Rahmen der Vergabe der Dresdner Barkhausen-Poster-Preise
  • Poster
    Dresdner Barkhausen-Poster-Preis 2011, 10.02.2012, Dresden, Deutschland

Publ.-Id: 16427 - Permalink


Substrate effect on the resistive switching in BiFeO3 thin films
Shuai, Y.; Ou, X.; Wu, C.; Zhang, W.; Zhou, S.; Bürger, D.; Reuther, H.; Slesazeck, S.; Mikolajick, T.; Helm, M.; Schmidt, H.;
BiFeO3 thin films have been deposited on Pt/sapphire and Pt/Ti/SiO2/Si substrates with pulsed laser deposition using the same growth conditions. Au was sputtered as the top electrode. The microscopic structure of the thin film varies by changing the underlying substrate. Thin films on Pt/sapphire are not resistively switchable due to the formation of Schottky contacts at both the top and the bottom interfaces. However, thin films on Pt/Ti/SiO2/Si exhibit an obvious resistive switching behavior under forward bias. The conduction mechanisms in BiFeO3 thin films on Pt/sapphire and Pt/Ti/SiO2/Si substrates are discussed to understand the different resistive switching behaviors.
  • Contribution to proceedings
    56th Annual Conference on Magnetism and Magnetic Materials, 30.10.-03.11.2011, Scottsdale, USA
    Journal of Applied Physics
  • Journal of Applied Physics 111(2012), 07D906

Publ.-Id: 16426 - Permalink


Nonvolatile resistive switching in Au/BiFeO3 rectifying junction
Shuai, Y.; Wu, C.; Zhang, W.; Zhou, S.; Bürger, D.; Slesazeck, S.; Mikolajick, T.; Helm, M.; Schmidt, H.;
Resistive switching in oxides has attracted increasing attention due to the potential application for nonvolatile memory devices [1,2]. Resistive switching has been observed usually in a metal-insulator-metal (MIM) capacitor-like structure, which can be set and reset to low resistance state and high resistance state by applying external voltages with opposite polarities. In an asymmetric MIM structure where a Schottky contact and an Ohmic contact are formed at the two interfaces, respectively, it is generally believed that the Schottky interface dominates the bipolar resistive switching behavior.
BiFeO3 thin films have been grown on Pt/Ti/SiO2/Si substrates with pulsed laser deposition. RF sputtered Au has been used for the top electrode. The transport properties of the BiFeO3 thin films have been previously demonstrated to be sensitive to the interface [3]. In the present work, an interface-related resistive switching behavior with large switching ratio of ~300 has been observed in the Au/BiFeO3/Pt structure [4]. The different polarities of the external voltage induce an electron trapping or detrapping process, and consequently change the depletion layer width below the Au Schottky contact, which is revealed by capacitance-voltage measurements and by long-term low/high resistance state capacitance transient measurements at zero bias. The resistive switching shows a long term retention and non-destructive read-out character, which is proved by pulsed voltage measurements. A dynamic equilibrium process involving the extension of the depletion region can be used to explain the good retention in the Au/BiFeO3/Pt structure. The present work can help to further understand the physical origin of bipolar switching in BiFeO3 and in other thin film oxides with electron trapping centers.

[1] K. Terabe et al., Nature 433, 47 (2005).
[2] R. Waser and M. Aono, Nature Mater. 6, 833 (2007).
[3] Y. Shuai et al., J. Appl. Phys., in press.
[4] Y. Shuai et al., Appl. Phys. Lett. 98, 232901 (2011).
Keywords: resistive switching, nonvolatile, Schottky contact
  • Lecture (Conference)
    2011 MRS Fall Meeting & Exhibit, 28.11.2011, Boston, MA, United States of America

Publ.-Id: 16425 - Permalink


Temperature Measurement in Ultra-Short Annealing Processes
Reichel, D.; Skorupa, W.; Schumann, T.;
Industrial demands for short process times at low cost are steadily increasing. Considerable attention is thereby drawn to ultra-short annealing cycles on the order of just a few milliseconds. Flash Lamp Annealing allows for directed thermal treatment of surfaces within just a few milliseconds without or with drastically reduced thermal stress of the bulk material. Due to the selected wavelength range in the visible and near infrared region the lightpulse is absorbed by the near-surface layers and diffusion into the bulk is limited by the ultrashort time span. Thereby temperatures up to 2000°C are achieved dependent on the energy of the lightpulse and the optical properties of the sample. Cooling takes place by heat conduction into the bulk. To control the annealing process a precise temperature measurement is required that can filter the intense background radiation to obtain the true wafer temperature from its thermal radiation. A new method for temperature measurement will be presented which imposes a modulation on the lamp radiation to extract the true wafer signal.
Keywords: Flash Lamp Annealing, Ultra-Short Annealing, Temperature Measurement, Ripple Pyrometry
  • Lecture (Conference)
    Subsecond Thermal Processing of Advanced Materials, 25.-27.10.2011, Dresden, Deutschland

Publ.-Id: 16424 - Permalink


Aus alt mach neu – Ripple Pyrometrie für die Blitzlampenausheilung
Reichel, D.; Skorupa, W.; Schumann, T.;
Dieser Vortrag befasst sich mit der Temperaturmessung in der Kurzzeitausheilung. Dazu werden die besonderen Anforderungen an die Temperaturmessung in Kurzzeitausheilungsprozessen beleuchtet und historische Lösungen vorgestellt, darunter auch die Ripple Pyrometrie. Letztere wird seit Mitte der Neunziger Jahre erfolgreich für Heißprozesse im Sekundenbereich angewandt. Den Autoren ist es gelungen, diese Methode für Prozesse im Millisekundenbereich (Blitzlampenausheilung) umzusetzen. Experimentelle Ergebnisse werden vorgestellt und hinsichtlich ihres Einflusses auf den Gesamtfehler der Messung analysiert.
Keywords: Ultra-Short Annealing, Temperature Measurement, Ripple Pyrometry, Flash Lamps
  • Lecture (Conference)
    Nutzertreffen Heißprozesse, 23.-24.11.2011, Blaubeuren, Deutschland

Publ.-Id: 16423 - Permalink


3d transition metal diffusion in diluted magnetic semiconductors prepared by pulsed laser processing
Bürger, D.; Seeger, M.; Zhou, S.; Skorupa, W.; Schmidt, H.;
High dopant concentrations are often a prerequisite condition for the realization of semiconductors with new functionalities. For example, magnetic dopants can be used to fabricate ferromagnetic semiconductors (FMS) [1] or intermediate band semiconductors for solar cells [2, 3]. The main problem for processing these materials is the very low solubility of magnetic dopants in elementary and III-V semiconductors. Therefore, thermodynamical non-equilibrium conditions have to be applied to overcome these limits. Thereby, the diffusion path during processing has to be as short as possible to reduce clustering processes which would result in a deactivation of dopants.
The diffusion barrier Q of standard shallow donor or acceptor dopants in the solid phase
is generally high which results in very low diffusion coefficients. Therefore, during the fast cooling process after PLA, diffusion or hopping of such shallow dopant atoms in recrystallized Si and GaAs has not been considered in detail and no models were developed which quantify interdiffusion processes of dopants for materials with large bulk diffusion barriers Q. However, 3d transition metal dopants in the most important semiconductors have relatively small bulk diffusion barriers Q that result in higher diffusion rates as compared to standard shallow donors. Therefore, the usual assumption that dopants remain fixed on their initial position during PLA processing has to be verified for each type of magnetic dopant in semiconductor spintronics materials.
In this work, we perform a Monte Carlo Study on a three-dimensional diffusion model to evaluate the kinetics of initial clustering in a simple cubic host:dopant system. In a second step, the temperature quenching process during PLA was calculated for the materials GaAs and Si and conclusions about diffusion and clustering of typical 3d transition metal dopants can be drawn with respect to the PLA parameters. For Mn in GaAs we also consider declustering effects that have to be included for strongly diffusing dopants like Mn in Si.

[1] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287, 1019 (2000).
[2] A. Luque and A. Marti, Phys. Rev. Lett. 78, 5014 (1997).
[3] J. Olea, M. Toledano-Luque, D. Pastor, G. Gonzáles-Díaz, and I. Mártil, J. Appl. Phys. 104, 016105 (2008).
Keywords: nanoscale clustering, diffusion, diluted magnetic semiconductor
  • Poster
    subtherm 2011, 24.-27.10.2011, Dresden, Deutschland

Publ.-Id: 16422 - Permalink


CFD-Simulations of an impinging jet using a polydispersed multi-field model approach
Hänsch, S.; Lucas, D.; Krepper, E.; Danciu, D.-V.;
A new CFD-strategy of a generalized two-phase flow (GENTOP) is presented. The idea of GENTOP combines a multi-field simulation with the recently developed Multiple Size Group (MUSIG) -approach. In the MUSIG-framework, transfers between the different bubble size groups due to bubble coalescence and –breakup are described. By modelling an additional mass transfer between the polydispersed and continuous gas phase, transitions between different gas morphologies can be considered. The continuous gas phase represents the largest gas structures so that for these structures the gas-liquid-interfaces are resolved. This new concept can give a more detailed explanation of complex flow situations, particularly with higher gas fractions, such as the impinging jet being just one application. First results computed by the CFD-code CFX 13.0 are compared to experiments and theoretical data reported in literature.
Keywords: multiphase flow, turbulent impinging jet, free surface, air entrainment, multi-field simulation, MUSIG-model
  • Contribution to proceedings
    6th International Berlin Workshop on Transport Phenomena with Moving Boundaries, 24.-25.11.2011, Berlin, Deutschland
    Proceedings of the 6th International Berlin Workshop on Transport Phenomena with Moving Boundaries
  • Lecture (Conference)
    6th International Berlin Workshop on Transport Phenomena with Moving Boundaries, 24.-25.11.2011, Berlin, Deutschland

Publ.-Id: 16421 - Permalink


Magnetic and optical properties of virgin arc furnace grown MgO crystals
Prucnal, S.; Shalimov, A.; Ozerov, M.; Potzger, K.; Skorupa, W.;
Transition metal ions (Mn2+, Cr3+, Fe2+/3+, V2+) as substitutional impurities in cubic crystals play an important role due to their influence on the magneto-optical properties of the virgin crystals. The optical and magnetic properties of commercial MgO(001) single crystals were investigated. The PL spectra of 3d impurity ions (Cr3+ and V2+) show narrow zero phonon lines with decay times in the range of milliseconds and a broad multiphonon sideband decaying in microseconds. The EPR study exhibits hyperfine components corresponding to Mn atoms and to V atoms located in orthorhombic symmetry. The intensity change of the EPR and PL spectra as well as the variation of the decay time with temperature can be explained by electron-spin lattice relaxation due to the Raman process.
Keywords: MgO, Point defects, Magneto-optic materials, Photoluminescence, Magnetism

Publ.-Id: 16420 - Permalink


Determination of secondary ion mass spectrometry relative sensitivity factors for polar and non-polar ZnO
Laufer, A.; Volbers, N.; Eisermann, S.; Potzger, K.; Geburt, S.; Ronning, C.; Meyer, B.;
Zinc oxide (ZnO) is regarded as a promising material for optoelectronic devices, due to its electronic properties. Solely, the difficulty in obtaining p-type ZnO impedes further progress. In this connection, the identification and quantification of impurities is a major demand. For quantitative information using secondary ion mass spectrometry (SIMS), so-called relative sensitivity factors (RSF) are mandatory. Such conversion factors did not yet exist for ZnO. In this work, we present the determined RSF values for ZnO using primary (ion implanted) as well as secondary (bulk doped) standards. These RSFs have been applied to commercially available ZnO substrates of different surface termination (a-plane, Zn-face, and O-face) to quantify the contained impurities. Although these ZnO substrates originate from the same single-crystal, we observe discrepancies in the impurity concentrations. These results cannot be attributed to surface termination dependent RSF values for ZnO.
Keywords: ZnO, SIMS

Publ.-Id: 16419 - Permalink


Systematics of azimuthal asymmetries in heavy ion collisions in the 1 A GeV regime
Reisdorf, W.; Leifels, Y.; Andronic, A.; Averbeck, R.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasik, P.; Grishkin, Y.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kis, M.; Koczon, P.; Korolija, M.; Kotte, R.; Kress, T.; Lebedev, A.; Lopez, X.; Matulewicz, T.; Merschmeyer, M.; Neubert, W.; Petrovici, M.; Piasecki, K.; Rami, F.; Ryu, M. S.; Schuettauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stockmeier, M.; Stoicea, G.; Tyminski, Z.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z. G.; Xu, H. S.; Yushmanov, I.; Zhilin, A.;
Using the large acceptance apparatus FOPI, we study central and semi-central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni+58Ni (0.15, 0.25, 0.4), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 129Xe+CsI (0.15, 0.25, 0.4), 197Au+197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include directed and elliptic flow. The data are compared to earlier data where possible and to transport model simulations. A stiff nuclear equation of state is found to be incompatible with the data. Evidence for extra-repulsion of neutrons in compressed asymmetric matter is found.

Publ.-Id: 16418 - Permalink


Actinide(IV)-oxyhydroxide colloids vs. actinide(IV)-silica colloids: their relevance for environmental conditions
Zänker, H.; Hennig, C.; Weiss, S.;
Evidence is provided by PCS, ultrafiltration and ultracentrifugation that uranium(IV) can form silicate-containing colloids. The particles are generated in near-neutral to slightly alkaline solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). They remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne U(IV) was observed which is a concentration much higher than the concentrations of truly dissolved or colloidally suspended waterborne An(IV) species hitherto reported for the near-neutral pH range. The prevailing size of the particles is below 20 nm. Laser Doppler velocimetry reveals that the nanoparticles are stabilized in solution by electrostatic repulsion due to a negative zeta potential caused by the silicate. The isoelectric point of the nanoparticles is shifted toward lower pH values by the silicate. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that U-O-Si bonds, which increasingly replace the U-O-U bonds of the amorphous uranium(IV) oxyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids.
Keywords: uranium(IV), silicate, colloids, near-neutral pH
Keywords: uranium(IV), thorium(IV), silicate, colloids, near-neutral pH
  • Lecture (Conference)
    12. Koordinierungsgespräch HZDR – PSI/LES, 08.-09.12.2011, 08.-09.12.2011, Villigen, Schweiz

Publ.-Id: 16417 - Permalink


Singular surfaces associated with multiple eigenvalues and related physical effects
Kirillov, O.;
It is common to consider that generically discrete eigenvalues of an operator are simple. However, in multiparameter operator families multiple eigenvalues are a robust phenomenon. Singular ruled surfaces were studied already by John Wallis, who in 1655 introduced his famous conical wedge known in the modern physical literature under the name of the “double coffee filter”. Later on, due to the efforts of Monge, Catalan, Plücker, Steiner and Cayley, the development of the theory of the ruled surfaces had lead to the formulation of the projective geometry. A first non-trivial physical effect related to the double semi-simple eigenvalue was discovered by Hamilton in 1833, who established that it determines a conical singularity of the dispersion surface – the Hamilton’s diabolical point (DP) – that yields a conical ray surface, which is observable in experiments with birefringent crystals as a conical refraction. In the presence of absorption and optical activity the conical singularities of the dispersion surface can transform into branch points that correspond to double eigenvalues with the Jordan block (exceptional points, EPs). This happens because the matrix determining the dispersion relation becomes a non-Hermitian one, for which an EP has a lower codimension than for a DP. In my presentation I will talk about manifestation of the multiple eigenvalues and the singular surfaces associated with them in modern physical applications such as magnetohydrodynamics dynamo and helical magnetorotational instability where the singularities determine non-trivial scaling laws and help to establish important limits for the critical parameters. I will discuss the role of the singularities in dissipation-induced instabilities on the example of the Brouwer’s problem on a heavy particle in a rotating vessel and show its connection to the modern works on crystal optics, wave propagation and rotor dynamics. Finally, I will touch the issue of the geometric phase in non-Hermitian systems.
Keywords: Instability threshold, parameters, optimization, non-smooth merit functions, multiple eigenvalues, dissipation-induced instabilities
  • Lecture (others)
    Lecture at the seminar of Prof. Roland Ketzmerick, Max-Planck-Institut für Physik komplexer Systeme (MPI-PKS), 21.01.2011, Dresden, Germany

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Publ.-Id: 16416 - Permalink


Singular surfaces and multiple eigenvalues in stability and optimization of non-conservative systems
Kirillov, O.;
it is common to consider that generically discrete eigenvalues of an operator are simple. However, in multiparameter operator families multiple eigenvalues are a robust phenomenon. Singular ruled surfaces were studied already by John Wallis, who in 1655 introduced his famous conical wedge known in the modern physical literature under the name of the “double coffee filter”. Later on, due to the efforts of Monge, Catalan, Plücker, Steiner and Cayley, the development of the theory of the ruled surfaces had lead to the formulation of the projective geometry. In XXth century the singular surfaces reappeared again in the form of a powerful singularity theory. In my presentation I will talk about multiple eigenvalues and associated singular surfaces in stability and optimization problems for non-conservative systems. First, I consider circulatory systems without damping that describe stability of columns under follower loads and torques, friction-induced instabilities in rotor dynamics as well as aeroelastic stability problems. I present an algorithm for classification of generic singularities on the stability boundary of a circulatory system and list all generic singularities up to codimension 10. I plot generic singularities on the stability boundary for one-, two-, and three-parameter families of circulatory systems and show how to approximate the boundary near the singularities studying perturbation of simple and multiple eigenvalues. I illustrate the general theory by the examples from robotics, rotor dynamics and structural optimization. In the latter case structural optimization of the m-link Ziegler pendulum will be considered and derivation of optimality conditions as well as the connection of the optimal solutions to singularities on the stability boundary will be discussed. Then, I will study the effect of small dissipation on the stability of circulatory systems. In 1952 Ziegler found that an infinitesimally small amount of damping leads to a finite change in the stability domain of a two-link pendulum loaded by the follower force. In 1956 Bottema resolved this destabilization paradox by means of the Whitney umbrella singularity that as he established exists on the stability boundary of the damped Ziegler’s pendulum. I will talk about extensions of this result to general finite dimensional and continuous circulatory systems as well as to the gyroscopic systems with small damping and non-conservative positional forces. Examples of similar paradoxal phenomena from rotor dynamics, soil mechanics and magnetohydrodynamics will be considered in detail.
Keywords: Multiparameter stability problems, stability boundary, singularities, parametric optimization, multiple eigenvalues, dissipation-induced instabilities
  • Lecture (others)
    Lecture at the seminar of Prof. Felix Darve, Laboratoire 3S-R: Sols, Solids, Structures, Risques, 24.02.2011, Grenoble, France

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Publ.-Id: 16415 - Permalink


Re-visiting structural optimization of the Ziegler pendulum: singularities and exact optimal solutions
Kirillov, O.;
Structural optimization of non-conservative systems with respect to stability criteria is a research area with important applications in fluid-structure interactions, friction-induced instabilities, and civil engineering. In contrast to optimization of conservative systems where rigorously proven optimal solutions in buckling problems have been found, for non-conservative optimization problems only numerically optimized designs were reported. The proof of optimality in the non-conservative optimization problems is a mathematical challenge related to multiple eigenvalues, singularities on the stability domain, and non-convexity of the merit functional. We present a study of the optimal mass distribution in a classical Ziegler’s pendulum where local and global extrema can be found explicitly. In particular, for the undamped case, the two maxima of the critical flutter load correspond to a vanishing mass either in a joint or at the free end of the pendulum; in the minimum, the ratio of the masses is equal to the ratio of the stiffness coefficients. The role of the singularities on the stability boundary in the optimization is highlighted and extension to the damped case as well as to the case of higher degrees of freedom is discussed.
Keywords: Non-conservative systems, oscillatory instabilities, stability boundary, singularity, parametric optimization

Publ.-Id: 16414 - Permalink


Singularities on the boundaries of magnetorotational instabilities and scaling laws
Kirillov, O.; Stefani, F.;
In the theory of magnetorotational instability and its modern extensions such as the helical MRI, non-trivial scaling laws between the critical parameters are observed. In case of the standard MRI it is well known that the Reynolds and Hartmann numbers are scaled as Re ∼ Ha2 while for the helical MRI Re ∼ Ha3. What is less known is that the thresholds of SMRI and HMRI plotted as surfaces in the space of parameters, possess singularities that determine the scaling laws. Moreover, the two paradoxes of SMRI and HMRI in the limits of infinite and zero magnetic Prandtl number (Pm), respectively, sharply correspond to the singularities on the instability thresholds. In either case, it is the local Plücker conoid structure that explains the non-uniqueness of the critical Rossby number, and its crucial dependence on the Lundquist number. For HMRI, we have found an extension of the former Liu limit Roc ≃ −0.828 (valid for Lu = 0) to a somewhat higher value Ro ≃ −0.802 at Lu = 0.618 which is, however, still below the Kepler value.
Keywords: Standard Magnetorotational instability, Helical magnetorotational instability, interaction parameter, scaling law

Publ.-Id: 16413 - Permalink


Formation of Soluble Hexanuclear Neptunium(IV) Nano-Clusters in Aqueous Solution: Growth Termination of Actinide(IV) Hydrous Oxides by Carboxylates
Takao, K.; Takao, S.; Scheinost, A.; Bernhard, G.; Hennig, C.;
Complexation of NpIV with several carboxylates (RCOO–; R = H, CH3, CHR’NH2; R’ = H, CH3, CH2SH) in moderately acidic aqueous solutions were studied by using UV-vis-NIR and X-ray
absorption spectroscopy. As pH increased, all investigated carboxylates initiated formation of watersoluble hexanuclear complexes, Np6(μ-RCOO)12(μ3-O)4(μ3-OH)4, where the neighboring Np atoms are connected by RCOO– syn-syn bridges and the triangular faces of the Np6 octahedron are capped with μ3-O2–/μ3-OH–. The structure information of Np6(μ-RCOO)12(μ3-O)4(μ3-OH)4 was extracted from the EXAFS data: Np–O2– = 2.22-2.23 Å (coordination number, N = 1.9-2.2), Np–O(RCOO–) and Np–OH– = 2.42-2.43 Å (N = 5.6-6.7 in total), Np···C(RCOO–) = 3.43 Å (N = 3.3-3.9), Np···Np(neighbor) = 3.80-3.82 Å (N = 3.6-4.0), Np···Np(terminal) = 5.39-5.41 Å (N = 1.0-1.2). For the simpler carboxylates, the gross stability constants of Np6(μ-RCOO)12(μ3-O)4(μ3-OH)4 and related monomers, Np(RCOO)(OH)2 +, were determined from the UV-vis-NIR titration data: R = H, log β6,12,–12 = 42.7 ± 1.2, log β1,1,–2 = 2.51 ± 0.05 at I = 0.62 M and 295 K; R = CH3, log β6,12,–12 = 52.0 ± 0.7, log β1,1,–2 = 3.86 ± 0.03 at I = 0.66 M and 295 K.

Publ.-Id: 16412 - Permalink


Dual beam irradiation of nanostructured FeCrAl oxide dispersion strengthened steel
Chen, C. L.; Richter, A.; Kögler, R.; Talut, G.;
Nanostructured ferritic oxide dispersion strengthened (ODS) alloy is an ideal candidate for fission/fusion power plant materials, particularly in the use of a first-wall and blanket structure of a next generation reactor. These steels usually contain a high density of Y–Ti–O and Y–Al–O nanoparticles, high dislocation densities and fine grains. The material contains nanoparticles with an average diameter of 21 nm and was treated by several cold rolling procedures, which modify the dislocation density. Structural analysis with HRTEM shows that the chemical composition of the initial Y2O3 oxide is modified to perovskite YAlO3 (YAP) and Y2Al5O12 garnet (YAG). Irradiation of these alloys was performed with a dual beam irradiation of 2.5 MeV Fe+/31 dpa and 350 keV He+/18 appm/dpa. Irradiation causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. Extended SRIM calculations for ODS steel indicate a clear spatial separation between the excess vacancy distribution close to the surface and the excess interstitials in deeper layers of the material surface. The helium atoms are supposed to accumulate mainly in the vacancies. Additionally to structural changes, the effect of the irradiation generated defects on the mechanical properties of the ODS is investigated by nanoindentation. A clear hardness increase in the irradiated area is observed, which reaches a maximum at a close surface region. This feature is attributed to synergistic effects between the displacement damage and He implantation resulting in He filled vacancies. Fine He cavities with diameters of a few nanometers were identified in TEM images.
Keywords: Irradiation damage, ion implantation, ODS material, irradiation hardening

Publ.-Id: 16411 - Permalink


Irradiation damage in dual beam irradiated nanostructured FeCrAl oxide dispersion strengthened steel
Richter, A.; Chen, C.-L.; Mücklich, A.; Kögler, R.;
An oxide dispersion strengthened steel is produced which contains Y-Al-Ti-O nanoparticles with an average diameter of 21 nm. HRTEM analysis shows that the chemical composition of the Y2O3 oxide is modified with perovskite YAlO3 (YAP), Y2Al5O12 garnet (YAG) and Y4Al2O9 monoclinic (YAM) particles. Irradiation of these alloys was performed with a dual ion beam system operating simultaneously with 2.5 MeV Fe+ to 31 dpa and 350 keV He+ to 18 appm/dpa. Ion bombardment causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. TRIM calculations for ODS steel indicate a clear spacial separation between vacancies and self-interstitials at which the vacancy distribution is close to the surface and the interstitials are deposited at a deeper position. The helium atoms mainly accumulate in the vacancies. Fine He cavities with diameters of a few nanometers were identified in HRTEM images. Additionally to structural changes, irradiation generated defects also affect the mechanical properties of the ODS steel. These were investigated by nanoindentation, which is a suitable measuring method as the irradiation damage is created within a thin surface layer. A clear hardness increase in the irradiated depth region was observed, which reaches a maximum close to the surface. This indicates the He condensation in the vacancy dominated region as predicted by the simulations.
Keywords: Irradiation damage, ion implantation, ODS material, radiation hardening of materials
  • Materials Research Society Symposium Proceedings 1298(2011), 141-146
    DOI: 10.1557/opl.2011.47

Publ.-Id: 16410 - Permalink


Doping of Si nanowires by ion implantation
Ou, X.; Geyer, N.; Kögler, R.; Schwen, D.; Werner, P.; Skorupa, W.;
Silicon nanowires (Si NWs) have generated enormous scientific interest as building blocks for future nanoelectronics. Due to the quasi-one dimensional structure and a high surface to volume ratio of Si NWs controlled doping to change their electrical properties is challenging. Also, in order to understand the doping mechanism various techniques were used to qualify the spatial distribution and electrical activation of dopant atoms in Si. In our previous work strong surface segregation of implanted phosphorus was found after the rapid thermal annealing (RTA). [1] The studies were carried out for relatively thick Si NWs grown by Molecular Beam Epitaxy (MBE) with a diameter of ~100 nm. However, the preferable size for the future logic application is in the range below 20 nm. This work will also discuss the doping behavior of the thin Si NWs with diameters of sub-20 nanometer fabricated by metal-assisted chemical etching. Electrical characterization of the thin NWs was performed by SSRM of the NW cross section. The issues of the doping of such thin NWs by ion implantation and the diameter dependence of the boron activation in the Si NW are discussed.
[1] Xin Ou et al., Nano Letters, 10 (2010) 171.
Keywords: Nano wires, doping, ion implantation
  • Lecture (Conference)
    Workshop "Ionen- und Positronenstrahlen", 04.07.2011, München, Germany

Publ.-Id: 16409 - Permalink


Laser accelerated protons captured and transported by a pulse power solenoid
Burris-Mog, T.; Harres, K.; Nürnberg, F.; Busold, S.; Bussmann, M.; Deppert, O.; Hoffmeister, G.; Joost, M.; Sobiella, M.; Tauschwitz, A.; Zielbauer, B.; Bagnoud, V.; Herrmannsdoerfer, T.; Roth, M.; Cowan, T. E.;
Using a pulse power solenoid, we demonstrate efficient capture of laser accelerated proton beams and the ability to control their large divergence angles and broad energy range. Simulations using measured data for the input parameters give inference into the phase-space and transport efficiencies of the captured proton beams. We conclude with results from a feasibility study of a pulse power compact achromatic gantry concept. Using a scaled target normal sheath acceleration spectrum, we present simulation results of the available spectrum after transport through the gantry.
Keywords: laser acceleration, laser accelerated protons, pulse power, solenoid focusing, beam transport, proton ion cancer therapy

Publ.-Id: 16408 - Permalink


Fresnoite thin films grown by pulsed laser deposition: photoluminescence and laser crystallization
Müller, A.; Lorenz, M.; Brachwitz, K.; Lenzner, J.; Mittwoch, K.; Skorupa, W.; Grundmann, M.; Höche, T.;
Fresnoite (Ba2TiSi2O8–BTS) thin films were grown on fused quartz, silicon (100), MgO (100), and aplane sapphire by pulsed laser deposition, and crystallized by subsequent thermal or flash lamp annealing. The corresponding texture evolution of the BTS thin films was studied by X-ray diffraction. The preferential (001) texture of the crystallised BTS films was found to be most pronounced on sapphire substrates. The broad photoluminescence band of the BTS thin films depends only weakly on temperature. The intensity of the BTS luminescence can be as high as that of the most efficient oxide scintillator materials. In order to qualify the fresnoite thin films for photonic applications, we demonstrate infrared-laser direct writing in amorphous BTS films which allows a local crystallisation and patterning. A subsequent considerable enhancement of luminescence intensity can be applied for UV-sensitive marking of nearly any object.
Keywords: pulsed laser deposition, photoluminescence, laser crystallization, flash lamp annealing, Fresnoite

Publ.-Id: 16407 - Permalink


Ion beam synthesis of III-V nanocrystals in silicon
Prucnal, S.; Facsko, S.; Baumgart, C.; Schmidt, H.; Liedke, M. O.; Mücklich, A.; Zhou, S.; Skorupa, W.;
Integration of III-V semiconductors with a silicon technology is crucial for the device performance. In this paper we present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs, InP and GaP) formed in silicon. The III-V QDs were obtained by means of sequential ion implantation and flash lamp annealing (FLA). Conventional selective etching was used to form the n-III-V/p-Si heterojunction. In case of InAs/Si heterostructures, the current-voltage measurement confirms the heterojunction diode formation with the ideality factor of 4.6. Kelvin Probe Force Microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.
Keywords: ion implantation, heteroepitaxy, indium arsenide, flash lamp annealing, quantum dots
  • Invited lecture (Conferences)
    46.Deutsches Nutzertreffen Ionenimplantation, 24.11.2011, Blaubeuren, Deutschland

Publ.-Id: 16406 - Permalink


Kelvin probe force microscopy imaging on locally doped silicon nanowires
Baumgart, C.; Habicht, S.; Feste, S.; Helm, M.; Schmidt, H.;
Kelvin probe force microscopy (KPFM) [1] is used for the nanoscale characterization of silicon nanowires (NWs). Horizontal NW arrays have been prepared from a silicon-on-insulator (SOI) starting material. After transferring the NW structures into the Si top layer by means of electron-beam lithography and reactive ion etching, the samples have been locally implanted with B and As. Activation of dopants was carried out by a rapid thermal annealing for 5 s at 1000 °C. Athena simulations showed that for the applied implantation and annealing conditions a box-like dopant distribution with comparable concentration of activated dopants can be assumed [2]. Quantitative dopant profiling by means of KPFM is successfully employed to locate the junctions along the B-doped and As-doped Si NWs. In addition, the influence of local intrinsic electric fields [3] is discussed for the investigated SOI structures.
References
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009). [2] S. F. Feste, J. Knoch, S. Habicht, D. Buca, Q.-T. Zhao, S. Mantl, Solid-State Electronics 53, 1257 (2009). [3] C. Baumgart, A.-D. Müller, F. Müller, and H. Schmidt, Phys. Stat. Sol. A 208, 777 (2011).
  • Poster
    Subtherm 2011, 25.-27.10.2011, Dresden, Deutschland

Publ.-Id: 16405 - Permalink


Gas phase silanization at normal pressure of Si-based integrated light emitters for smart biosensor applications
Germer, S.; Cherkouk, C.; Rebohle, L.; Helm, M.; Skorupa, W.;
A different silanization method for SiO2 surfaces has been raised for Si-based light emitter which are considered as light sources in sensors for the detection of harmful biomolecules. This approach uses a special experimental setup for gas phase silanization (GPS) and is based on the evaporation and deposition in nitrogen atmosphere at normal pressure for 15 minutes with different silane volumes. The light emitter has a SiO2 passivation layer on the top which was hydrolyzed in an in situ hybridization chamber and catalyzed with MES (2-(N-morpholino)ethanaesulfone acid hydrate) buffer solution. Afterward, the substrates were silanized with the GPS method using the organosilane (3-Aminopropyl)trimethoxysilane (APTMS). Infrared spectroscopy, X-ray spectroscopy and Atomic force microscopy were used to control and characterize the structure of the SiO2 surface and the APTMS layer. The results demonstrate a successful covalent binding of the coupling agent and the interaction of the deposited molecules with each other. The roughness of the modified surface was investigated by the Atomic force microscopy. The silanized samples show rough and textured surfaces. At last, the suitability of the developed GPS method was verified on light emitters.
Keywords: Si-based light emitter, biosensor, APTMS, silanization, amines
  • Thesis / Students' report
    Technische Universität Freiberg, 2010
    76 Seiten

Publ.-Id: 16404 - Permalink


Investigation of rare earth implanted SiO2 thin films for Down-conversion applications in Photovoltaic's
Germer, S.; Günz, C.; Lehmann, J.; Rebohle, L.; Helm, M.; Skorupa, W.;
In this report we present our recent investigations of rare earth (Ce, Tb) implanted SiO2 thin films for Down-conversion (DC) as an application for solar cells. Photovoltaic modules (PV) are showing high losses in the ultra violet range of the incident sunlight, because of band gap losses and front layer absorption. DC layers are applied to the front surface of photovoltaic cells to enhance solar cell efficiency
Keywords: down-conversion, photovoltaic, rare earth atoms, solar cells
  • Poster
    Subsecond thermal processing of Advanced Materials 2011, 24.-28.10.2011, Dresden, Deutschland

Publ.-Id: 16403 - Permalink


Liquid phase processing in the millisecond range for III-V heterostructures in silicon
Prucnal, S.; Facsko, S.; Baumgart, C.; Schmidt, H.; Liedke, M. O.; Mücklich, A.; Zhou, S.; Skorupa, W.;
Integration of III-V semiconductors with a silicon technology is crucial for the device performance. In this paper we present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs, InP and GaP) formed in silicon. The III-V QDs were obtained by means of sequential ion implantation and flash lamp annealing (FLA). Conventional selective etching was used to form the n-III-V/p-Si heterojunction. In case of InAs/Si heterostructures, the current-voltage measurement confirms the heterojunction diode formation with the ideality factor of 4.6. Kelvin Probe Force Microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.
Keywords: ion implantation, heteroepitaxy, indium arsenide, flash lamp annealing, quantum dots
  • Invited lecture (Conferences)
    30.Deutsches Nutzertreffen RTP und Heissprozesse, 23.-23.11.2011, Blaubeuren, Deutschland

Publ.-Id: 16402 - Permalink


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