Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33403 Publications

Energy Transfer by Gd to ion Implanted Ce and Er Atoms in Metal-Oxide-Silicon-based Light Emitting Diodes

Prucnal, S.; Sun, J. M.; Reuther, H.; Skorupa, W.
The excitation mechanism of electroluminescence (EL) of cerium and erbium ions co-implanted with gadolinium into the SiO2 layer of MOSLEDs was investigated. Ce and Er ions were implanted into SiO2 with a concentration of 1% and 2%, respectively, subsequently implanted by gadolinium ions with concentrations of 0.5, 1.5 and 3%. Silicon dioxide containing cerium co-implanted with Gd exhibits two different excitation mechanisms: direct Ce3+ ion excitation by hot electrons and transfer of energy from 6PJ energy level of Gd to 5d energy state of Ce leading to an increase of the EL of Ce in the blue region. The EL observed from the sample containing 3% of Gd was 5 times higher in comparison with samples implanted only by Ce. The Er implanted SiO2 exhibits the typical peak at 1540 nm and weak luminescence in the green and blue region. Two green peaks correspond to the transitions from 2H11/2 and 4S3/2 to 4I15/2 and blue peaks to those from 2H9/2 and 4F5/2 to 4I15/2. The additional implantation of Gd leads to an increase of luminescence from Er3+ lines in the visible region caused by the energy relaxation from the Gd excited level 6PJ to the higher energy levels of erbium, whereas it has no influence on the infrared luminescence at 1.54 mm.
Keywords: Gd sensitization, Cer, Erbium, energy transfer, silicon-based light emission, ion implantation, electroluminescence
  • Lecture (Conference)
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-9341
Publ.-Id: 9341


Optical activation and electrical stabilization of the EL from SiO2:Gd gate oxide layers by fluorine and potassium co-implantations

Prucnal, S.; Sun, J. M.; Reuther, H.; Skorupa, W.
When amorphous silica is bombarded with energetic ions, various types of defects are created as consequence of ion-solid interaction (oxygen deficient centres ODC, non-bridging oxygen hole centres NBOHC, E’-centres, etc.). Metal-oxide-silicon (MOS) structure contains gadolinium implanted SiO2 layer exhibit strong ultra violet (UV) electroluminescence (EL) at 316 nm from Gd3+ ions and enhancement of luminescence from defects (465 nm, 520 nm and 650 nm corresponds to ODC, Ed’-centre and NBOHC, respectively). Creation and transformation of point defects in bulk SiO2 contains Gd and F atom during constant current injection was investigated. Elimination of such defects is very important from viewpoint of electrical stability of MOS devices. Additional implantation of fluorine in to SiO2:Gd layer leads to decreasing of number of E’-centres and ODC, improves the stability of EL from Gd3+ at 316 nm and lengths working time of MOS structure.
Keywords: defects, silicon dioxide, ion implantation, silicon-based light emitter, electroluminescence
  • Lecture (Conference)
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-9340
Publ.-Id: 9340


Issues In Flash Lamp Annealing

Smith, M. P.; Seffen, K. A.; Mcmahon, R. A.; Skorupa, W.
Review of recent work presented at the MRS Spring Meeting at San Francisco
Keywords: Flash lamp annealing, simulation
  • Lecture (others)
    Seminar bei der Fa. Mattson, 21.04.2006, Fremont, Ca, USA

Permalink: https://www.hzdr.de/publications/Publ-9339
Publ.-Id: 9339


Flash Lamp Processing for Conductive ITO Layers

Skorupa, W.; Anwand, W.; Schumann, T.; Voelskow, M.; Luethge, T.; Adam, D.
Vortrag anlässlich eines vertraulichen Projekttreffens bei der Creavis-Degussa AG
Keywords: ITO layers, Flash lamp annealing
  • Lecture (Conference)
    Summer School Nanotronics 2006, 11.-13.09.2006, Marl, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9338
Publ.-Id: 9338


Advanced Thermal Processing of Semiconductor Materials in the msec-Range

Skorupa, W.
Vortrag anlässlich der Begutachtung eines japanischen Grossprpojektes
Keywords: Flash lamp annealing, silicon carbide, silicon
  • Lecture (others)
    Projekttreffen OSTEC Advanced Quantum Beam Project, 27.09.2006, FZ Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9337
Publ.-Id: 9337


Efficiency and Stability Issues of MOSLED´s made by RE Ion Implantation

Skorupa, W.; Prucnal, S.; Sun, J. M.; Helm, M.; Rebohle, L.; Gebel, T.; Nazarov, A.; Osiyuk, I.; Tjagulski, I.; Zuk, J.
Combining silicon-based electronic circuits with optoelectronic functionality is one of the key challenges for the future semiconductor technology. Such work must not only be devoted to the wavelength of 1.54 µm because there are more applications needing light sources from all the UV to IR wavelength range. In our work we employed ion beam processing to embed different rare earth (RE) luminescent centers (Gd3+, Ce3+, Tm3+, Tb3+, Eu3+, Er3+) into the silicon dioxide layer of a purpose-designed Metal-Oxide-Silicon-based Light Emitting Diodes (MOSLEDs) with advanced electrical performance. Efficient electroluminescence was obtained from UV to infrared with a transparent top electrode made of indium-tin oxide. The distinct differences in efficiency of the various rare earth atoms will be discussed as well as problems of electrical stability of such devices due to hot electron injection and charge trapping phenomena. Several developments for improving the device stability will be proposed related to charge compensation and elimination of the defects in SiO2.
Keywords: Silicon-based light emitter, ion implantation, rare earths, electroluminescence, Metal-Oxide-Silicon-based Light Emitting Diodes (MOSLEDs), hot electron injection, charge trapping
  • Invited lecture (Conferences)
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-9336
Publ.-Id: 9336


Thermally Induced Deformation and Stresses During Millisecond Flash Lamp Annealing

Smith, M. P.; Seffen, K. A.; Mcmahon, R. A.; Anwand, W.; Skorupa, W.
A flash lamp has been proposed for annealing wafers with diameters approaching 100 mm.
The equipment applies a pulse, with duration 0.5 ms to 20 ms, resulting in large transient thermal
gradients in the wafer. In this paper, we present a model for the thermal reaction of this process
and its effect upon the mechanical behaviour, in order to predict stresses, shape changes and to
capture practical phenomenon, such as bifurcation of deformation modes. We then use the
model to follow changes in the expected response consequent on altering process conditions, as
well as exploring important issues associated with scaling to large wafer sizes. The model is
further used to predict material yielding leading to permanent deformations. This work presents
the first description of the thermo-mechanical response of wafers to flash lamp annealing in the
millisecond time regime and is therefore fundamental to the use of this technique in the
fabrication of semiconductor devices.
Keywords: Stress, Wafer, Flash lamp annealing
  • Contribution to proceedings
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA
    Materials Research Society Symposium Proceedings 912, 912-C04-08
  • Lecture (Conference)
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-9335
Publ.-Id: 9335


Process Control During Liquid Phase Rerowth of 3C-SiC on Si Substrates

Smith, M. P.; Voelskow, M.; Mcmahon, R. A.; Muecklich, A.; Anwand, W.; Skorupa, W.
Flash lamp annealing in the millisecond regime of heteroepitaxial silicon carbide on silicon structures involves melting the Si below the SiC layer, but the deep facetted nature of the solid-liquid interface leads to unacceptable surface roughness. This paper describes a method of controlling melting by implanting a high dose of carbon or germanium at a controlled depth below the Si/SiC interface, which significantly alters the melting characteristics of the silicon. Results confirm the effectiveness of these approaches for increasing surface uniformity, making liquid phase processing compatible with standard device fabrication techniques. A thermal model has also been developed to describe this process and results indicate that the theoretical work is consistent with the experimental evidence. The model is a valuable tool for predicting onset of melting, maximum temperatures and process windows for liquid phase epitaxy.
Keywords: Silicon carbide, Silicon, Heteroepitaxy, Liquid phase epitaxy, Flash lamp annealing
  • Contribution to proceedings
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA
    Materials Research Society Symposium Proceedings 911, 0911-B08-0
  • Lecture (Conference)
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-9334
Publ.-Id: 9334


Thermal and Stress Modeling for the Flash Lamp Crystallization of Amorphous Silicon Films

Smith, M. P.; Mcmahon, R. A.; Seffen, K. A.; Panknin, D.; Voelskow, M.; Skorupa, W.
Thin poly-crystalline silicon films are attractive for the fabrication of active matrix liquid crystal displays. We investigate the use of flash lamp annealing to crystallize amorphous silicon layers on glass substrates as a low cost manufacturing route. In this process amorphous silicon (a-Si) can be crystallized by solid phase crystallization (SPC) or in the super lateral growth (SLG) regime. We present a thermal model incorporating the phase transitions during annealing; providing a valuable tool for optimizing the process conditions. Another consideration is the evolution of stress resulting from the transient thermal loading of the substrate material. Results are presented for various substrate geometries and important scalability issues are addressed.
Keywords: polycrystalline silicon, flash lamp annealing, amorphous silicon on glass, active matrix liquid crystal displays
  • Contribution to proceedings
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA
    Materials Research Society Symposium Proceedings 910, A 21-15
  • Lecture (Conference)
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-9333
Publ.-Id: 9333


Deactivation of Li by vacancy clusters in ion-implanted and flash-annealed ZnO

Borseth, T. M.; Tuomisto, F.; Cristensen, J. S.; Skorupa, W.; Monakhov, E.; Svensson, B. G.; Kuznetsov, A.
Li is present in hydrothermally grown ZnO at high concentrations and is known to compensate both n- and p-type doping due to its amphoteric nature. However, Li can be manipulated by annealing and ion implantation in ZnO. Fast, 20 ms flash anneals in the 900–1400 °C range result in vacancy cluster formation and, simultaneously, a low-resistive layer in the implanted part of the He- and Li-implanted ZnO. The vacancy clusters, involving 3-4 Zn vacancies, trap and deactivate Li, leaving other in-grown donors to determine the electrical properties. Such clusters are not present in sufficient concentrations after longer (1 h) anneals because of a relatively low dissociation barrier ~2.6±0.3 eV, so ZnO remains compensated until Li diffuses out after 1250 °C anneals.
Keywords: flash annealing, ion implantation, zinc oxide, lithium, vacancy cluster
  • Physical Review B 74(2006), 161202(R)

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Permalink: https://www.hzdr.de/publications/Publ-9332
Publ.-Id: 9332


Engineering of radiation defects and Li by flash anneals in ion-implanted ZnO

Borseth, T. M.; Cristensen, J. S.; Monakhov, E.; Svensson, B. G.; Kuznetsov, A.; Tuomisto, F.; Skorupa, W.
Li is present in hydrothermally grown ZnO at high concentrations and is known to compensate both n- and p-type doping due to its amphoteric nature. However, Li can be manipulated by annealing and ion implantation in ZnO. Fast, 20 ms flash anneals in the 900–1400 °C range result in vacancy cluster formation and, simultaneously, a low-resistive layer in the implanted part of the He- and Li-implanted ZnO. The vacancy clusters, involving 3-4 Zn vacancies, trap and deactivate Li, leaving other in-grown donors to determine the electrical properties. Such clusters are not present in sufficient concentrations after longer (1 h) anneals because of a relatively low dissociation barrier ~2.6±0.3 eV, so ZnO remains compensated until Li diffuses out after 1250 °C anneals.
Keywords: zinc oxide, lithium, flash annealing, ion implantation, vacancy cluster, doping
  • Lecture (Conference)
    4th International Workshop on ZnO and Related Materials, 03.-06.10.2006, Gießen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9331
Publ.-Id: 9331


Blitzlampen-Prozessieren: Stress und Oberflächen-Schmelzen bei Silizium

Skorupa, W.
Überblick zu Stress und Oberflächen-Schmelzen bei Silizium infolge Blitzlampen-Prozessierens
Keywords: Flash lamp annealing, silicon, ion implantation
  • Invited lecture (Conferences)
    Deutsches Nutzertreffen Kurzzeitausheilung, 23.11.2006, Villach, Österreich

Permalink: https://www.hzdr.de/publications/Publ-9330
Publ.-Id: 9330


Silicon MOS light emitters by rare earth doping

Skorupa, W.
Review of recent results regarding Silicon MOS light emitters using rare earth doping
Keywords: Silicon-based light emitter, rare earth, doping
  • Invited lecture (Conferences)
    1st Optence workshop on silicon photonics, 10.11.2006, Mainz, Germany

Permalink: https://www.hzdr.de/publications/Publ-9329
Publ.-Id: 9329


High dose high temperature ion implantation of Ge into 4H-SiC

Kups, T.; Weih, P.; Voelskow, M.; Skorupa, W.; Pezoldt, J.
A box like Ge distribution was formed by ion implantation at 600 C. The Ge concentration was varied from 1 to 20 %. The TEM investigations revealed an increasing damage formation with increasing implantation dose. No polytype inclusions were observed in the implanted regions.
Keywords: 4H-SiC, Ge, solid solution, ion implantation, transmission electron microscopy
  • Materials Science Forum 527(2006), 851-854
  • Lecture (Conference)
    ICSCRM 2005, 18.-23.09.2005, Pittsburgh, USA

Permalink: https://www.hzdr.de/publications/Publ-9328
Publ.-Id: 9328


Millisecond annealing with flash lamps: tool and process challenges

Gebel, T.; Rebohle, L.; Fendler, R.; Hentsch, W.; Skorupa, W.; Voelskow, M.; Anwand, W.; Yankov, R.
Sub-second annealing is one of the key issues to meet the requirements of the 45 nm technology node according to the ITRS roadmap. Therefore, over the past decade there has been great interest in techniques such as laser and flash lamp annealing (FLA). In addition, advanced ultra-fast annealing shows promise for technologies that are not directly related to Si device processing. The main reason for using FLA in alternative applications is the reduced thermal budget because of the short annealing time, which enables one to achieve high temperatures (> 500°C) in the near-surface region while keeping the substrate bulk relatively cold. This is of particularly high importance for the development of novel polymer-based electronics and flexible solar cell technologies, where the substrates cannot withstand temperatures in excess of 150°C. An overview of theoretical simulations and related results from FLA experiments for a variety of layered systems is given. The influence of the flash duration and intensity on the heat distribution and the resulting physical properties is considered. Design and performance issues of the FLA tools depending on the specific uses and technical requirements are addressed. Furthermore, topics covered include high-throughput applications e.g. for roll-to-roll production of polymer substrates. Results of a prototype tool for multi-flash processing up to a frequency of 1 Hz using a pulse duration of 1 ms are also discussed.
Keywords: Flash lamp annealing, Silicon device processing, roll-to-roll production, polymer substrates, sub-second annealing
  • Contribution to proceedings
    14. International Conference on Advanced Thermal Processing of Semiconductors (RTP 2006), 10.-13.10.2006, Kyoto, Japan
    Proceedings, RTP 2006, Piscataway, New York, USA: Institut of Eletrical and Electronics Engineers, 1-4244-0648-X
  • Invited lecture (Conferences)
    14. Int. Conf. on Advanced Thermal Processing of Semiconductors, 10.10.2006, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-9327
Publ.-Id: 9327


Thermische Prozesse im msec-Bereich für Elektronik und Photonik

Skorupa, W.
Vortrag über die jüngsten Entwicklungen und Experimente am FZD zur Blitzlampentemperung
Keywords: Blitzlampen-Temperung, Silizium, ITO, Siliziumkarbid
  • Lecture (others)
    Seminar am Institut für Bio- und Nanosysteme des Forschungszentrums Jülich, 16.10.2006, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9326
Publ.-Id: 9326


Mikro-Nano-Piko: Elektronik und Photonik erobern das Nichts

Skorupa, W.
Es wird über Entwicklungen in der Elektronik und deren Übergang in Photonikanwendungen berichtet.
Keywords: Lichtemitter, Blitzlampen-Temperung
  • Lecture (others)
    Technologietag der FDP-Fraktion am Sächsischen Landtag, 18.05.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9325
Publ.-Id: 9325


Ausgründung einer GmbH aus dem FZD aus der Perspektive eines Wissenschaftlers

Skorupa, W.
Vortrag zu den Arbeiten am FZD sowie zu den Erfahrungen mit der Ausgründung einer GmbH aus dem FZD
Keywords: Lichtemitter, Blitzlampenausheilung
  • Lecture (others)
    Treffen mit Mittelstandsvereinigung Saxonia der sächsischen FDP, 09.06.2006, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9324
Publ.-Id: 9324


Advanced Thermal Processing of Semiconductor Materials in the msec-Range

Skorupa, W.
Sub-second annealing is one of the key issues to meet the requirements of the 45 nm technology node according to the ITRS roadmap. Therefore, over the past decade there has been great interest in techniques such as laser and flash lamp annealing (FLA). In addition, advanced ultra-fast annealing shows promise for technologies that are not directly related to Si device processing. The main reason for using FLA in alternative applications is the reduced thermal budget because of the short annealing time, which enables one to achieve high temperatures (> 500°C) in the near-surface region while keeping the substrate bulk relatively cold. This is of particularly high importance for the development of novel polymer-based electronics and flexible solar cell technologies, where the substrates cannot withstand temperatures in excess of 150°C. An overview of theoretical simulations and related results from FLA experiments for a variety of layered systems is given. The influence of the flash duration and intensity on the heat distribution and the resulting physical properties is considered. Design and performance issues of the FLA tools depending on the specific uses and technical requirements are addressed. Furthermore, topics covered include high-throughput applications e.g. for roll-to-roll production of polymer substrates. Results of a prototype tool for multi-flash processing up to a frequency of 1 Hz using a pulse duration of 1 ms are also discussed.
Keywords: silicon, flash lamp annealing
  • Lecture (others)
    Institutsseminar, 07.06.2006, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9323
Publ.-Id: 9323


Visokotemperaturnaja implantazia ionov N+ i Al+ v 6H-SiC pri visokich dosach

in Russian
Yankov, R.; Voelskow, M.; Kreissig, U.; Kulikov, D. V.; Pezoldt, J.; Skorupa, W.; Truschin, Y. V.; Charlamov, V. S.; Zigankov, D. N.
the effect of high temperature high dose nitrogen and aluminium implantation into 6H-SiC is investigated
Keywords: implantation high dose
  • Pisma v Zhurnal Tekhnicheskoi Fiziki 23(1997)16, 6

Permalink: https://www.hzdr.de/publications/Publ-9322
Publ.-Id: 9322


Industrial Application of Gamma Ray CT

Hampel, U.; Bieberle, A.; Schleicher, E.; Hoppe, D.; Zippe, C.
Gamma ray CT is a powerful tool for the measurement of phase fraction distributions in thermal hydraulic systems and process diagnostics applications. Challenging process and plant conditions, such as high pressures and temperatures, opaque metallic vessels or machine parts as well as thermally unsteady and electromagnetically noisy environments limit the range of applicable measurement techniques in real processes. Gamma ray CT is a non-invasive technique and can be applied without major modification of the process facility. The tomography equipment is still not too bulky and complex to enable industrial measurements outside the laboratory. Recently our group has developed a high resolution gamma ray CT system that comprises a Cs-137 isotopic source (165 GBq activity, 622 keV photon energy) and a 320 channel scintillation detector that employs highly compact and robust avalanche photo detector technology in combination with fast LYSO scintillation crystals. The detector is operated in gamma photon counting mode. The spatial resolution of the detector is 2 mm. For measurements at industrial facilities we further devised a tomograph gantry that consists of a vertical translational and a rotational motor driven unit for tomographic scans at different axial planes of an object. The vertical operating range is approximately 1800 mm and objects of up to 900 mm diameter can be scanned.
Keywords: gamma ray CT, computed tomography
  • Contribution to proceedings
    International Conference on Multiphase Flow ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Proceedings of the International Conference on Multiphase Flow 2007, Paper No. PS/_10
  • Lecture (Conference)
    International Conference on Multiphase Flow ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-9321
Publ.-Id: 9321


Anwendung der Elektronenstrahltechnik zur ultraschnellen Tomographie von Mehrphasenströmungen

Hampel, U.; Fischer, F.; Mattausch, G.
Computertomographie (CT) auf der Basis von Röntgen- und Gammastrahlung stellt ein attraktives Messverfahren zur Untersuchung von Mehrphasenströmungen dar. Die Messung erfolgt dabei berührungslos und hat somit keine Rückwirkung auf die Strömung. Die Strahlung ermöglicht einen Blick in undurchsichtige Gefäße und durchdringt trübe oder intransparente Fluide, Supensionen, Emulsionen und Feststoffschichten ohne Probleme. Da die Strahlungsausbreitung geradlinig erfolgt, sind scharfe Abbildungen verborgener Strukturen möglich. Bisher wird die Computertomographie als bildgebendes Messverfahren hauptsächlich in der Medizin aber auch in der zerstörungsfreien Werkstoffprüfung eingesetzt. Seit einiger Zeit gibt es vielfältige internationale Bestrebungen, computertomographische Messverfahren für die Untersuchung von Mehrphasenströmungen verfügbar zu machen.
Das Prinzip der Elektronenstrahltomographie eignet sich für die Untersuchung schneller Strömungsvorgänge. Dabei ist es allerdings erforderlich, die Bildrate eines derartigen CT-Scanners über die in der Kardiobildgebung üblichen 50 Bilder pro Sekunde hinaus auf mindestens 1000 Bilder pro Sekunde zu steigern. Am Institut für Sicherheitsforschung am Forschungszentrum Dresden-Rossendorf wird derzeit daran gearbeitet, die Elektronenstrahltomographie als messtechnisches Tool für die Untersuchung von Zweiphasenströmungen im Forschungsschwerpunkt Sicherheit und Betriebsverhalten nuklearer Anlagen bzw. zu Zwecken der Entwicklung und Validierung von Zweiphasen-CFD-Codes verfügbar zu machen. Mit der Entwicklung eines optimierten ultraschnellen Elektronenstrahl-CT-Scanners mit eigenem Elektronenstrahlerzeuger und halbkreisförmiger Targetgeometrie wurde nunmehr am Forschungszentrum Dresden-Rossendorf ein nächster wichtiger Schritt in Richtung einer universell einsetzbaren Elektronenstrahl-CT für Strömungsuntersuchungen beschritten. In naher Zukunft wird dieses Messverfahren Anwendung bei der Untersuchung von Wasser-Wasserdampf-Strömungen in einer Rohrleitung mit 50 mm Innendurchmesser finden. Die Untersuchungen werden an der am Forschungszentrum Dresden-Rossendorf betriebenen Mehrzweck-Thermohydraulik-Versuchsanlage TOPFLOW durchgeführt.
Keywords: electron beam tomography
  • Contribution to external collection
    in: Jahresbericht 2006, Fraunhofer Institut für Elektronenstrahl- und Plasmatechnik, München: Fraunhofer, 2007, 57-58

Permalink: https://www.hzdr.de/publications/Publ-9320
Publ.-Id: 9320


Positron and deuteron depth profiling in He-3-implanted electrum-like alloy

Grynszpan, R. I.; Baclet, N.; Darque, A.; Flament, J. L.; Zielinski, F.; Anwand, W.; Brauer, G.
In spite of previous extensive studies, the helium behavior in metals still remains an issue in microelectronics as well as in nuclear technology. A gold–silver solid solution (Au60Ag40: synthetic gold-rich electrum) was chosen as a relevant model to study helium irradiation of heavy metals. After helium-3 ion implantation at an energy ranging from 4.2 to 5.6 MeV, nuclear reaction analysis (NRA) based on the 3He(d,p)4He reaction, was performed in order to study the thermal diffusion of helium atoms. At room temperature, NRA data reveal that a single Gaussian can fit the He-distribution, which remains unchanged after annealing at temperatures below 0.45 of the melting point. Slow positron implantation spectroscopy, used to monitor the fluence dependence of induced defects unveils a positron saturation trapping, which occurs for He contents of the order of 50–100 appm, whereas concentrations larger than 500 appm seem to favor an increase in the S-parameter of Doppler broadening. Moreover, at high temperature, NRA results clearly show that helium long range diffusion occurs, though, without following a simple Fick law.
  • Applied Surface Science 252(2006), 3252-3255

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Permalink: https://www.hzdr.de/publications/Publ-9318
Publ.-Id: 9318


Modification of Solid Surfaces by Slow Highly Charged Ions: Effects of Highly Confined Excitation

Heller, R.; Facsko, S.; Kost, D.; Zschornack, G.
Due to their high amount of potential energy highly charged ions induce various changes in morphology and electronic structure of solid surfaces [1,2]. The potential energy which is the sum of the ionization energies of all removed electrons, is released on a very small localized area of a few nm2 and in very short times of tens of fs. Hence the power density deposited into the surface can reach values of up to 1014 Wcm−2 depending on the ions incident charge state. The changes in surface topology depend strongly on the electronic excitation in the surface and its lateral and longitudinal confinement. Focus of our investigations is the interaction of slow HCIs with surfaces that have a high confinement of excitation. Such surfaces are mainly all kind of insulators, but also samples with an additional confinement due to a layered structure. In this case the electron transfer between different layers is suppressed and the interacting system becomes quasi two dimensional. Investigations were performed at the Rossendorf Two Source Facility, an ion beam facility consisting of two sources: a 14.5 GHz ECR ion source and an Electron Beam Ion Source, the Dresden EBIT [3]. Ions of both sources are decelerated by a common deceleration unit to suppress kinetic effects during ion surface interaction. The combination of these both sources offers ions of various charge states (up to q = 44 for Xe), species (He, Ne, Ar, Xe, C, N, O) and kinetic energies (<q · 100 eV to q · 25 keV). We present scanning probe microscopy studies of surface modifications induced by single ion impacts. HOPG, MICA and ultra thin SiO2 layers were irradiated with ions of argon (charge states q = 1...16) and xenon (charge states q = 1...40). The diameter and the height of created nano structures wer e investigated in dependence on the ion charge state for both ion species. Additional to SPM investigations Raman spectroscopy of HOPG before and after irradiation was performed to get information about structural changes induced by the HCI impact.
Keywords: Highly Charged Ions, Surface Interaction, HOPG, Excitation, STM
  • Poster
    13th International conference on the Physics of Highly Charged Ions (HCI), 28.08.2006, Belfast, Nord Irland

Permalink: https://www.hzdr.de/publications/Publ-9317
Publ.-Id: 9317


The Rossendorf Two Source Facility – A Device for the Observation of the Interaction of Slow Highly Charged Ions with Surfaces

Heller, R.; Facsko, S.; Kost, D.; Zschornack, G.
The interaction of slow highly charged ions with solid surfaces is mainly characterized by the high amount of potential energy stored in the ions and discharged on the surface. Thereby the potential energy is the sum of the ionization energies of all removed electrons. While the kinetic energy of an ion scales linearly with the charge state, its potential energy grows rapidly with each removed electron. Figure 1 shows the ionization energy and the resulting potential energy of iron ions of different charge states. The ion bombardment of solid surfaces with HCIs can lead to various changes in surface morphology [1-4]. The Rossendorf Two Source Facility presents a world wide unique ion beam facility consisting of two ion sources and providing ions of adjustable charge state and kinetic energy. These two sources are: a 14.5 GHz-Electron-Cyclotron-Resonance (ECR) ion source (Super Nanogan / Pantechnik) and an Electron Beam Ion Trap (Dresden EBIT / Leybold Vacuum Dresden GmbH) operating at room temperature [5,6,7].
Keywords: highly charged ions, surface interaction, nano dots, STM, HOPG
  • Contribution to proceedings
    International Doctoral Seminar 2006, 23.04.2006, Smolenice, Slowakia

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Permalink: https://www.hzdr.de/publications/Publ-9316
Publ.-Id: 9316


Extraktion hochgeladener Ionen aus der Dresden EBIT im Überlaufregime

Heller, R.; Zschornack, G.
For the first time the production and the extraction of highly charged ions from the Dresden EBIT using the so-called leaky mode, an operating mode with a continuous ion extraction (DC) at fixed axial trap potantial was investigated. Measurements of the ion output current at a Faraday cup directly behind the source were done with integral ion currents of up to 1.5nA depending on the source parameters. Also the charge state distribution of the extracted ions at leaky mode was investigated. It was shown, that ions of argon gas can be extracted up to a charge state of q=17 with an ion current of 1pA (DC) and xenon ions up to a charge state of q=21 with currents of about 0.5pA (DC).
Keywords: highly charged ions, leaky mode, EBIT
  • Contribution to proceedings
    28. EAS-Tagung - Energiereiche atomare Stöße, 06.-10.02.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9315
Publ.-Id: 9315


Ioneninduzierte Nanostrukturen

Möller, W.
  • Lecture (others)
    Festkolloquium, 06.12.2006, Cottbus, D

Permalink: https://www.hzdr.de/publications/Publ-9314
Publ.-Id: 9314


Mechanisms of target poisoning during reactive sputtering of TiN

Möller, W.
  • Invited lecture (Conferences)
    BELVAC Symposium on Reactive Sputter Deposition, , Belgium, 30.11.2006, Ghent, Belgium

Permalink: https://www.hzdr.de/publications/Publ-9313
Publ.-Id: 9313


Ion induced stress release – by thermal or collisional spikes?

Möller, W.
  • Lecture (others)
    Thin Film Workshop, 17062006, Linköping, Sweden

Permalink: https://www.hzdr.de/publications/Publ-9312
Publ.-Id: 9312


Ion irradiation for generation and control of nanostructures

Möller, W.
  • Lecture (others)
    Seminar, 10.01.06, Prag, CZ

Permalink: https://www.hzdr.de/publications/Publ-9311
Publ.-Id: 9311


Kontinuumsgleichungen zur Beschreibung ionenstrahlinduzierter Nanostrukturen

Facsko, S.
  • Lecture (Conference)
    Workshop "Ionenstrahlphysik und Nanotechnologie", 16.05.2006, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9310
Publ.-Id: 9310


Properties of thin films grown on periodically corrugated surfaces

Facsko, S.; Keller, A.; Liedke, O.; Fassbender, J.ORC; Möller, W.
  • Lecture (others)
    Seminar, 30.05.2006, Konstanz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9309
Publ.-Id: 9309


Changing carbon films by highly charged ions

Facsko, S.; Som, T.; Wilhelm, R.; Heller, R.; Möller, W.
Carbon films exist in a variety of modifications ranging from soft amorphous carbon film (a-C) to hard diamond-like carbon (DLC) films [1]. Due to their diverse proper-ties carbon films are technologically important materials, especially for protective, biomedical, or field emission coatings. In addition, special forms such as fullerene-like films have attracted the scientific interest for their special structure. Many of the properties of the carbon films are intrinsically related to their nanostructure which in turn is strongly related to the existence of sp2 and sp3 hybridized phases.
The nanostructure of the carbon films depends strongly on the preparation conditions but are as well modified by the irradiation with ions. Irradiation with single charged heavy ions at high energy normally turns the films amor-phous reducing the amount of sp3 and sp2 hybridized phases [2]. Here, we present systematic studies of irradia-tion of carbon films by highly charged argon and xenon ions with low kinetic energy.
Keywords: highly charged ions, carbon films
  • Poster
    International Workshop on Inelastic Ion-Surface Collisions (IISC-16), 17.-22.09.2006, Hernstein, Österreich

Permalink: https://www.hzdr.de/publications/Publ-9308
Publ.-Id: 9308


Periodic surface patterns induced by low energy ion erosion

Facsko, S.; Keller, A.; Rossbach, S.; Möller, W.
In the series of self-organized processes for the fabrication of nanostructures the pattern forma-tion during ion erosion of surfaces has attracted much interest in the last years. In the continuous sputtering process, induced by the bombardment with low-energy ions, periodic surface patterns appear in form of ripples under off-normal incidence or arrays of hexagonally ordered dots at normal incidence. The dimension of the pattern is related to the size of the typical collision cas-cade and lies in the range of ten to tens of nanometers, depending on ion energy. The self-organization mechanism relies on the interplay between a surface instability caused by the sput-tering, and surface diffusion processes. Regular ripple and dot array morphologies have been produced in this way on very different materials including semiconductors, insulators, and met-als, demonstrating the universality of the mechanism.
Keywords: Nanostructures
  • Lecture (others)
    Seminar, 15.12.2006, Göttingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9307
Publ.-Id: 9307


Thermal phase transformation and perpendicular exchange coupling of Co nanocrystals embedded in ZnO

Zhou, S.; Potzger, K.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
Recently, due to the potential application in spintronics, ferromagnet-semiconductor hybrid structures have attracted huge research attention [1]. Large magnetoresistance was observed in GaAs consisting MaAs nanocrystals formed by ion implantation [2] and in granular ZnO/Co systems [3]. Very recently, wide-band-gap semiconductors (GaN, ZnO and TiO2) doped with transition metals were reported to be diluted magnetic semiconductors with Curie temperatures above room temperature [4]. However, the origin of the observed ferromagnetism is still controversial, e.g. ferromagnetic clusters, or extrinsic reasons. In this work, Co nanocrystals (NCs) were formed inside ZnO my means of ion beam synthesis. The Co NCs are crystallorgraphically oriented inside ZnO. The magnetic properties, e.g. anisotropy and blocking temperature can be tuned by annealing. In the as-implanted and annealed (823 K) samples, hcp-Co or co-existing of hcp and fcc Co NCs have been found and show superparamagnetism. After annealing at 923 K, the sample exhibits a much higher blocking temperature and shows a perpendicular exchange bias effect, which indicates the formation of a Co/CoO core/shell structure. The system of ZnO semiconductor consisting of crystallorgraphically oriented Co NCs could be a promising hybrid for spin-injection.
1. H. Ohno, Semicond. Sci. Technol. 17, 275 (2002).
2. P. J. Wellmann, et al., Appl. Phys. Lett. 73, 3291 (1998).
3. A. B. Pakhomov, et al., J. Appl. Phys. 95, 7393 (2004).
4. A. H. MacDonald, et al., Nature Materials 4, 195 (2005).
Keywords: ZnO, magnetic semiconductor, Co nanocrystals
  • Lecture (Conference)
    71. Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.03.2007, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-9306
Publ.-Id: 9306


Structural investigations of magnetic nanocrystals embedded in semiconductors using synchrotron radiation x-ray diffraction

Zhou, S.; Potzger, K.; von Borany, J.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
Traditional electronics can be greatly stimulated by a combination of magnetic and semiconducting properties where spins provide an additional freedom degree. Recently theoretical works predict that some semiconductors (e.g. ZnO, GaN, TiO2, and Si) doped with transition metal (TM) are diluted magnetic semiconductors (DMS) [1]. In DMS materials, TM ions are substituted onto cation sites of the host semiconductor and are coupled with free carriers via indirect interaction resulting in ferromagnetism. However most experimental works have only concentrated on reporting high Tc and interpreted the observed ferromagnetism in terms of DMS without detail structural characterization. In this work, we have prepared magnetic ZnO, TiO2 and Si samples doped with TM by implantation, and correlated their magnetic and structural properties [2-5]. By synchrotron radiation x-ray diffraction, Fe, Ni, Co and Mn-silicide nanocrystals are observed in our samples, and are responsible for the magnetism. Depending on their crystalline structure, those nanocrystals are crystallographically oriented with respect to the host matrix. The structural information is well agreeable with the magnetic properties measured by SQUID. Additionally due to their orientation nature (crystallographically oriented or randomly oriented with respect to the host crystal), these nanocrystals in some cases are very difficult to detect by a simple Bragg-Brentano scan. This nature results in the pitfall of using XRD to exclude secondary phase in DMS materials.
References
[1] T. Dietl, et al, Science 287, 1019 (2000).
[2] K. Potzger, Shengqiang Zhou , et al, Appl. Phys. Lett. 88, 052508 (2006).
[3] Shengqiang Zhou, et al., J. Appl. Phys. 100, 114304 (2006).
[4] Shengqiang Zhou, et al., to be published at Phys. Rev. B (2007).
[5] Shengqiang Zhou, et al., to be published at J. Phys. D: Appl. Phys. (2007).
Keywords: synchrotron radiation x-ray diffraction, diluted magnetic semiconductor, magnetic nanocrystals
  • Poster
    The 17th ESRF Users Meeting, 05.-08.02.2007, Grenoble, France
  • Lecture (Conference)
    Nanospintronic design and realization 2007, 21.-25.5.2007, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9305
Publ.-Id: 9305


Buoyancy driven flow in the VeMix test facility

Vaibar, R.; Sühnel, T.
Buoyancy driven flow is often presented in many engineering application such as mixing process of fluids with different density. The aim of our study is to simulate mixing processes that are relevant in safety analyses of nuclear reactors. The boron dilution problem is one such safety issue analysis.
Borated and unborated water are of different densities and may be of the diffenrent temperatures, what causes additional density defferences. The degree of mixing of low and high borated coolant is a critical issue with respect to reactivity insertion into the reactor core. As nuclear reactor geometries are complex, the mixing process not widely understood and the influence of the buoyancy is small, a very simple vertical test facility was chosen for validation of numerical models of the mixing process. A new source term, which consists of a sum of the component turbulent density fluxes, is defined for the turbulent model and in this case is based on the definition turbulent kinetic energy.
Keywords: buoyancy driven turbulence, turbulence two-equation model
  • Lecture (Conference)
    Seminar on Numerical Analysis and Tutorial - SNA'07, 22.-26.01.2007, Ostrava, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-9304
Publ.-Id: 9304


Non-Fermi-Liquid Behavior in CeCoIn5 Near the Superconducting Critical Field

Movshovich, R.; Capan, C.; Ronning, F.; Bianchi, A.; Pagliuso, P. G.; Bauer, E. D.; Sarrao, J. L.
We measured specific heat and resistivity of heavy fermion CeCoIn5 at and above the superconducting critical field with field in [001] (Hc2 = 5 T) and [100] directions (Hc2 = 12 T), and at temperatures down to 50 mK. At the critical fields the data show Non Fermi Liquid (NFL) behavior down to the lowest temperatures. With increasing field the data exhibit crossover from NFL to Fermi liquid behavior at the lowest temperatures. Analysis of the scaling properties of the specific heat, and comparison of both resistivity and the specific heat with the predictions of a spinfluctuation theory suggest that the NFL behavior is due to incipient antiferromagnetism (AF) in CeCoIn5, with the quantum critical point in the vicinity of Hc2. Below Hc2 the AF phase which competes with the paramagnetic ground state is superseded by the superconducting transition. To separate the quantum critical point HQCP from the superconducting critical field Hc2 we performed a series of Sn-doping and hydrostatic pressure studies. Sn-doping appears not to be able to separate HQCP and Hc2. Preliminary resistivity in magnetic field measurements under hydrostatic pressure indicate that the QCP point moves inside the superconducting phase in the H-P plane with increasing field.
  • AIP Conference Proceedings 850(2006), 711

Permalink: https://www.hzdr.de/publications/Publ-9303
Publ.-Id: 9303


Plasma immersion ion implantation for surface modification

Shevchenko, N.
In the present work the surface processes during oxygen PIII and the microstructure and properties of the modified surface layers were studied. The samples were examined by X-ray diffraction analysis, Auger electron spectroscopy, atomic force microscopy, spectroscopic ellipsometry and corrosion and blood compatibility tests. Oxygen PIII at an ion energy of 40 keV and a substrate temperatures below 300°C results in the formation of a transparent rutile TiO2 surface layer with a Ni content down to below 1 at%. This layer prevents from corrosion and out-diffusion of Ni ions. Biocompatibility tests show a largely superior in vitro blood compatibility compared to the untreated samples.
Keywords: PIII, NiTi alloy, microstructure, surface
  • Lecture (others)
    Boston Scientific project meeting, 03.-05.05.2006, Maple Grove, Minnesota, USA

Permalink: https://www.hzdr.de/publications/Publ-9302
Publ.-Id: 9302


Heavy Ion ERDA at the 5 MV Tandem Accelerator in Rossendorf

Kreissig, U.
The different particle separating detection techniques used in Rossendorf to perform ERD analysis are described. Special emphasis was drawn on the TOF-E-telescope and all the experience which was collected with this detector. Some examples with real TOF-E-spectra are presented and discussed.
  • Lecture (others)
    Seminar of the Nuclear Physics Institute, 25.07.2006, Rez, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-9301
Publ.-Id: 9301


Portable THz cyclotron resonance spectrometer

Drachenko, O.; Leotin, J.; Schneider, H.; Helm, M.
In this paper we present a very compact THz cyclotron resonance (CR) spectrometer based on far IR quantum cascade lasers emitting at 11.4mkm and ~15mkm.
The CR spectrometer is schematically shown on the Figure 1. It incorporates an interchangeable GaAs/AlGaAs quantum cascade laser placed below the bottom edge of the magnet, where the absolute value of magnetic field is as low as 15 T when the maximum field of 70T is reached in the centre. Emitted light is collected by ZnSe microlens, guided through the stainless steel waveguide, and focused on the sample installed in the centre of the magnetic field coil. Transmitted light is then focused on the Si doped boron blocked impurity band (Si:B BIB) photodetector placed above the coil to minimize the value of magnetic field acting on the detector. The waveguide is purged with helium to avoid air condensation. The QCL source is driven by short current pulses 1mks long with amplitude ~2 Amps remaining constant during magnetic field shot. An appropriate repetition rate of the order of 3-4 kHz was chosen to avoid thermal degradation of the intensity. We record 4 signals during the magnetic field pulse: voltage drop across the laser, current through the laser, response of the photodetector, and, finally, magnetic field value. We use fast 100 MHz acquisition card with an onboard memory sufficient for 1s full speed acquisition. Especially designed software then removes useless points, corresponding to the absence of laser emission or regions of instability due to transient processes in the long power supply lines. Possible distortions due to QCL heating and modulation of its intensity by magnetic fields are avoided by normalisation of the signal with the sample installed by the signal without sample.
Keywords: Cyclotron resonance, High magnetic fields
  • Lecture (Conference)
    Détecteurs et Emetteurs de Radiations THz à semiconducteurs, 06.-07.12.2006, Université Montpellier II, Place Eugène Bataillon,, France

Permalink: https://www.hzdr.de/publications/Publ-9300
Publ.-Id: 9300


Fast THz time-domain spectrometer

Drachenko, O.; Winnerl, S.; Schneider, H.; Helm, M.
In this paper we present a concept of a THz time-domain spectrometer to be used in millisecond pulsed magnets with 24 mm clear bore. The design is based on fiber coupled semiconductor antennas, both for THz light emission and detection, gated with ultrafast femtosecond laser pulses. Both, THz emitter and detector are installed inside the magnet bore, close to the sample. The laser pulses gating the emitter and the detector are guided from outside by optical fibers (Fig.1). A fast acquisition rate is achieved due to implementing recently developed asynchronous optical sampling (ASOPS) technique that requires no mechanically moving parts. We employ two different Ti:sapphire oscillators with slightly different repetition rates (F and F+Δ) to gate the emitter and detector (fig. 1). As a result, the lasers produce two pulses with a time delay linearly ramped between zero and 1/F. The beat frequency Δ determines time delay scan rate.
We will present the design of the emitter/detector system, first results of THz spectra recorded with this system, and discuss the critical issues, such as the type of the fibers employed. In the future it will be possible to investigate the broadband-THz properties of semiconductors and other solids in pulsed high magnetic fields. In addition, the ASOPS laser system can of course be employed for pump-probe spectroscopy at the 750-850 nm laser wavelengths.
Keywords: THz time-domain, asynchronous optical sampling (ASOPS)
  • Lecture (Conference)
    Semiconductor sources and detectors of THz frequencies - Détecteurs et Emetteurs de Radiations TéraHertz à Semiconducteurs, 06.-07.12.2006, Université Montpellier II, Place Eugène Bataillon,, France

Permalink: https://www.hzdr.de/publications/Publ-9299
Publ.-Id: 9299


The Effect of High Magnetic Field on the Photoresponse of Si:B Structures with Blocked Conductivity in the Impurity Band

Aronzon, B. A.; Drachenko, A. N.; Ryl’Kov, V. V.; Leotin, J.
The dependence of photoconductivity on the magnetic field has been studied for Si:B blockedimpurity- band (BIB) structures with the boron impurity concentration of ~10^18 cm^–3 in the active layer. Measurements were performed in the magnetic field B up to 30 T with the pulse length of 0.8 s in the temperature range T = 4.2–9 K, under irradiation of structures with the room-temperature background with ~10^16 photons/(cm^2s) intensity. It is established that, in the longitudinal configuration and with the magnetic field parallel to the electric field, the photocurrent decreases as B increases, mainly due to a decrease in the hole multiplication factor M in the magnetic field and/or an increase in the activation energy for hopping conductivity in the active layer. At T= 4.2 K, the photocurrent can drop by a factor of several tens. At the same time, at low bias voltage Vb , when M≈1, and at higher temperatures, T≈9 K, the photocurrent decreases no more than twofold in the field of ~30 T. It is found also that in the transverse configuration (with the magnetic field perpendicular to the electric field), the effect of the magnetic field on the photoresponse of a structure significantly increases (more than by an order of magnitude at T= 4.2 K). This fact can be explained by the accumulation of carriers in the blocking (undoped) layer of a BIB structure, which is related to increasing time of the hole flight across this layer due to high mobility of holes and strong bending of their trajectories in the transverse configuration.
Keywords: Si doped Boron Blocked impurity band photodetector, high magnetic field

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Permalink: https://www.hzdr.de/publications/Publ-9298
Publ.-Id: 9298


Charge storage in silicon-implanted silicondioxide layers examined by scanning probe microscopy

Beyer, R.; Beyreuther, E.; von Borany, J.; Weber, J.
Ion beam synthesis is a promising technique to generate embedded nanoclusters in thin insulating layers for prospective memory devices. At present the electronic structure of clusters in oxide layers and the respective charge storage mechanism are not well understood. Moreover, it is still unclear, whether cluster-related or damage-related states in the silica network are predominant. Here, we report on the charge trapping in silicon implanted SiO2 layers using scanning capacitance microscopy and scanning force microscopy.
Silicondioxide layers on (100) oriented silicon with a thickness of 25nm were silicon implanted with different doses and subsequently annealed at high temperatures (1050°C/1150°C). Charge injection into the insulating layer was accomplished by applying a bias between the conductive probing tip and the substrate. Local as well as scanning injection in quadratic areas was performed in the contact mode. Scanning capacitance microscopy images taken at different times after injection show the charge patterns and their retention characteristics. For a quantitative estimate of the trapped oxide charge densities the peak shifts of the local dC/dV curves were evaluated. The strongest trapping effect was found for heavily silicon-implanted (2e16cm-2) SiO2 on p-substrate. Complementary information about local charge trapping was obtained from scanning force microscopy images. Sequences of voltages with different polarity were used to study the trapping/ detrapping kinetics and allowed a comparison of the degradation and the programmability of the different oxide layers.
Keywords: Scanning capacitance microscopy; Silicon oxide; Charge trapping; Ion beam synthesis

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Permalink: https://www.hzdr.de/publications/Publ-9297
Publ.-Id: 9297


The influence of alternating magnetic fields on structure formation in Al-Si alloys during solidification

Willers, B.; Dong, J.; Metan, V.; Smieja, F.; Eckert, S.; Eigenfeld, K.
Solidification experiments were carried out using binary Al-Si alloys and the technical alloys AlSi9Cu3 and AlCu4TiMg. In this paper we present results obtained from solidification in a cylindrical container made from stainless steel exposed to rotating or travelling magnetic fields, respectively. The container bottom is positioned on a water-cooled copper chill allowing a directional solidification by a vertical heat flux. In parallel, the solidification in sandcasting was studied as well. Local temperatures were determined during the solidification process using a set of thermocouples. Our results disclose that the forced convection causes distinct modifications of the temperature and the concentration field. The electromagnetic stirring promotes the columnar-to-equiaxed transition (CET) and causes a considerable grain refinement. Modifications of the grain structure and effects of macrosegregation are discussed with respect to the flow field.
Keywords: solidification, Al-Si alloys, magnetic field, convection, dendritic growth
  • Contribution to proceedings
    5th Decennial International Conference on Solidification Processing, 23.-25.07.07, Sheffield, United Kingdom
    Proceedings of the 5th Decennial International Conference on Solidification Processing, Sheffield, 978-0-9522507-4-6, 168-171
  • Lecture (Conference)
    5th Decennial International Conference on Solidification Processing, 23.-25.07.2007, Sheffield, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-9296
Publ.-Id: 9296


Synthesis of nanostructures with ion beams

Heinig, K.-H.
An extended review will be given on the synthesis and modification of nanostructures using ion beams. The lecture is devided in two parts: The first hour will be used to discuss the impact of ion beam solid interactions on the thermodynamics of phase separation (nucleation, growth, Ostwald ripening, coalescence). It will be shown that the nonequilibrium steady-state under ion irradiation results in reaction pathways of the system which differs considerably from conventional thermodynamics (e.g. inverse Ostwald ripening, nanoparticle shape change, surface structure formation). The second hour will be used to demonstrate the full CMOS compatibility of ion beam processing. The ion beam is a well-controllable tool for selforganization of structures on the nanoscale. As an example, the ion beam synthesis of self-aligned Si nanocrystal layers in the gate oxide of MOS transistors will be discussed. Such layers are applied as discrete charge storage centers in an advanced version of FLASH memories.
Keywords: nanostructures, ion beam synthesis, fundamentals, advanced processing, phase separation, self-organisation, modeling, atomistic simulations
  • Invited lecture (Conferences)
    Nanotechnology Research Forum, 16.-20.10.2006, Ankara, Turkey

Permalink: https://www.hzdr.de/publications/Publ-9295
Publ.-Id: 9295


Nucleation and nanostructure formation at mixed interfaces

Heinig, K.-H.; Schmidt, B.; Müller, T.; Roentzsch, L.
Interfaces between two immiscible phases A and B are rather abrupt at thermodynamic equilibrium. A compositional mixing of the interface over a thickness of several nanometers can be achieved by ion irradiation. The interface reforms during thermal treatment of this nonequilibrium state, thereby following an interesting reaction pathway: Phase separation at the former interface position occurs via spinodal decomposition, while the supersaturation in the tails of the mixing profil leads to nucleation and growth of nanocluster layers. The two nanocluster layers are narrow and separated from the recovered abrupt interface by zones denuded of the impurity phase. This kind of heteronucleation and nanostructure growth has been studied by comprehensive atomistic computer simulations as well as experimentally, especially for the Si/SiO2 interface. In collaboration with industry, this nanoluster layers where functionalised as discrete charge storage centers in nonvolatile (FLASH) memories.
Keywords: nanostructure synthesis, interface, ion beam mixing, phase separation, self-organisation, kinetik lattice Monte-Carlo simulation
  • Lecture (Conference)
    International Workshop on Polymorphism in Condensed Matter, 13.-17.11.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9294
Publ.-Id: 9294


Doubly-stacked Si dots in SiO2 formed by ion beam mixing – a way to improve retention of nanocrystal memories

Heinig, K.-H.; Roentzsch, L.
Nonvolatile nanocluster (NC) memories fabricated by Si ion implantation/irradiation of SiO2 gate oxides have some key parameters which are superior to those of state-of-theart devices [1-3]. However, data retention is below industrial requirements. Former studies have proven that a doubly-stacked nanocluster structure can improve retention by several orders of magnitude [4]. However, it is difficult to fabricate pairs of NCs where a big NC is located above a smaller ones. Additionally, the NCs of a pair must have a narrow intercluster spacing, and the smaller NCs must be located just a few nm above the Si substrate. Here, based on atomistic process simulations, a novel fabrication technique of selfaligned doubly-stacked Si NCs will be presented. It is assumed that a layer of large (<10nm) Si NCs is placed on top of ~10nm thermal oxide by a conventional (e.g. CVD) technique. This structure is covered by a control oxide. Tiny (~3 nm), self-aligned NCs between the large NCs and the substrate form during annealing after energetic ion irradiation. As described in ref. [5], ion beam mixing at Si/SiO2 interfaces results in the formation of tiny NCs. Here, mixing from the substrate and the large NCs lead to selective formation of tiny NCs below the large NCs. The stability of this CMOS-compatible processing for memory fabrication will be evaluated.
[1] B. Schmidt, K.-H. Heinig et al., Nucl.Instr.Meth. B242, 146 (2006).
[2] P. Dimikratis et al., J.Phys.Conf.Ser. 10, 7 (2005).
[3] T. Müller, K.-H. Heinig et al., Appl. Phys. Lett. 85, 2373 (2004).
[4] R. Ohba et al., IEEE Trans. El. Dev. 49, 1392 (2002).
[5] K.-H. Heinig et al., Appl. Phys. A 77, 17–25 (2003).
Keywords: nanostructures, FLASH memory, silicon, silica, ion irradiation, self-organization, modeling, computer simulation
  • Poster
    15th International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Taormina, Italy

Permalink: https://www.hzdr.de/publications/Publ-9293
Publ.-Id: 9293


Nanostructure growth and modification with ion beams

Heinig, K.-H.
Nanocluster ensembles and nanowires can be synthesised in surface layers of various substrates by high dose ion implantation. A detailed understanding of the complex processes like ion deposition and subsequent phase separation has been achieved by atomistic computer simulations. This understanding helps to tailor nanostructures for applications. Examples are the synthesis of very narrow Si nanocluster layers in SiO2 for nanodot memories and of ion-beam-shaped metallic nanorods for photonics. Recently it has been demonstrated that ion beams can be also used to change properties of nanostructures drastically. Thus, at elevated temperatures, irradiation of nanocluster ensembles results in a narrowing of the size distribution, which can be described as “inverse Ostwald ripening”. Irradiation of single-crystalline but chemically disordered nanostructures assists chemical ordering of alloys like FePt, which has a very high magnetic anisotropy and is, therefore, a favorite material for future magnetic recording.
Keywords: nanostructures, ion beam synthesis, phase separation, modeling, atomistic computer simulation
  • Lecture (others)
    Physikalisches Kolloquium, I. Physikalisches Institut der RWTH Aachen, 25.01.2006, Aachen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9292
Publ.-Id: 9292


Growth and modification of nanostructures with ion beams

Heinig, K.-H.
Nanocluster ensembles and nanowires can be synthesised in surface layers of various substrates by high dose ion implantation. Atomistic computer simulations lead to a detailed understanding of ion deposition and subsequent precipitation [1]. Recently it has been demonstrated that ion beams can be also used to change properties of nanostructures drastically. Thus, at elevated temperatures, irradiation of nanocluster ensembles results in a narrowing of the size distribution, which can be described as “inverse Ostwald ripening” [2]. Irradiation of single-crystalline but chemically disordered nanostructures assists chemical ordering of alloys like FePt, which has a very high magnetic anisotropy in its well-ordered state and is, therefore, a favorite material for future magnetic recording [3]. And finally, metallic nano-spheres in SiO2 can be shaped into rods or even wires by high-energy ion irradiation. This contribution will review theoretical studies and atomistic computer simulations on the phenomena listed above. It will be shown that all this phenomena have a common origin, the competition between two driving forces: (i) ion beam induced disordering (interface mixing, defect generation, …) which drives the system far from equilibrium and (ii) thermally activated processes like diffusion and phase separation which drives the system back towards the thermodynamic equilibrium.
[1] M. Strobel, K.-H. Heinig, W. Möller, Phys. Rev. B 64, 245422 (2001); T. Müller, K.H. Heinig, and W. Möller, Appl. Phys. Lett. 81, 2373 (2002); T. Müller, K.H. Heinig et al., Appl. Phys. Lett. 85, 2373 (2004).
[2] K.-H. Heinig et al., Appl. Phys. A 77, 17–25 (2003).
[3] H. Bernas, J.-Ph. Attane, K.-H. Heinig et al., Phys. Rev. Lett. 91, 077203 (2003).
Keywords: nanostructures, ion implantation, ion irradiation, modeling, computer simulation
  • Invited lecture (Conferences)
    International Workshop on Nanostructured materials (Nanomat2006), 21.-23.06.2006, Antalya, Turkey

Permalink: https://www.hzdr.de/publications/Publ-9291
Publ.-Id: 9291


Thermal instability of copper nanowires

Toimil-Molares, M. E.; Karim, S.; Sigle, W.; Heinig, K.-H.; Röntzsch, L.; Trautmann, C.; Cornelius, T. W.; Neumann, R.
Copper nanowires have been fabricated by electrochemical deposition into hollows, which are formed by selective etching of swift heavy ion tracks in thin foils. After removal of the matrix. the free copper nanowires are heated to about 500 °C, whre they decay into chains of nanodots. It is proven that the nanowires decay well below the melting temperature of copper is due to the Rayleigh instability. Copper nanowires fabricated in polycarbonate foils are covered by polymer rests after matrix removal. We call them metal wires within Carbon NanoTubes (CNT). In situ annealing in a transmission electron microscope (TEM) reveals an interesting evolution of these nanostructures: Surface minimization leads to a copper droplet formation at one of the openinigs of the CNT. The emtying of the CNT accelerates with the inverse droplet volume. Modeling results in an analytical description as well as in atomistic computer simulations, which are in excellent agreement with the experiment. This well-defined process could be used to measure materials parameters at the nanoscale.
Keywords: nanostructure, swift heavy ion irradiation, carbon nanotube, nanowire, copper, modelling, computer simulation
  • Poster
    Gordon Research Conference "Electrodeposition", 30.07.-04.08.2006, New London, NH, USA

Permalink: https://www.hzdr.de/publications/Publ-9290
Publ.-Id: 9290


Shaping of nanometals by swift heavy ions

Dawi, E.; Mink, M.; Heinig, K.-H.; Toulemonde, M.; Nordlund, K.; Vredenberg, A.
Metal nanorods and nanowires have great potential in a wide range of fields, because of their tunable (by shape and size) optical and magnetic properties. We present and discuss an unique way for producing perfectly parallel nanorods and -wires that are embedded in a solid. Starting from monodisperse spherical Au nanocolloids (15-50 nm diameter) in a silica matrix we show that the colloids are shaped controllably into rods -- and at later stages -- wires under heavy-ion irradiation above a threshold energy loss of ~6keV/nm. The threshold coincides with the formation of a continuous molten ion track, as follows from ion track temperature calculations. Nanowires of ~10nm diameter with lengths up to several hundred nanometer form and align parallel to the ion beam in the fluence regime of 1014-1015 ions/cm2. Based on experiments with different colloid sizes and concentrations we conclude that all Au nanospheres initially elongate into nanorods, with their long axis along the ion track. Above a critical fluence (e.g. 1x1014/cm2 for 54 MeV Ag) individual nanorods disintegrate while others continue to grow by uptake of the atoms of the disintegrated particles. This novel type of ripening process is corroborated by 3D kinetic Monte Carlo simulations.
Based on atomistic simulations we suggest that the lengthening is a result of thermocapillarity, which drives material of a gold nanosphere that is touched by an ion track from the hot equator to the colder pole regions. Temperature gradients of several billions Kelvin per cm can be reached, conditions that are similar to femtosecond laser processing of Au layers [1] where frozen nanojets have been observed.
[1] F. Korte, J. Koch, and B.N. Chichkov, Appl.Phys. A 79 (2004) 879-881
Keywords: nanostructure, high-energy ion irradiation, shaping, gold, silica, nanowires, modeling, kinetic Monte-Carlo simulations
  • Lecture (Conference)
    15th International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Taormina, Italy

Permalink: https://www.hzdr.de/publications/Publ-9289
Publ.-Id: 9289


Mechanisms of swift-heavy-ion-assisted shaping of Au nanospheres into wires and their subsequent “Ostwald ripening”

Heinig, K.-H.; Vredenberg, A.; Toulemonde, M.; Nordlund, K.
At the IBMM conference 2004 (Monterey), Arjen Vredenberg has shown for the first time that Au nanospheres embedded in a SiO2 layer change their shape significantly under swift heavy ion irradiation. At fluences of a few 1014cm-2, Au spheres of 15 nm diameter transform into rods. They become even a few hundert nm long wires at higher fluences. Several Au nanospheres are consumed for the formation of such long wires. The ion efficiency of shaping increases linearly with the electronic energy transfer to the SiO2 matrix, starting at a threshold of about 6 keV/nm. Because optical and magnetic properties of metal nanoparticles depend strongly on shape anisotropy, ion beam shaping may have potential for tuning nanomaterials in fields like photonics or magnetic data storage. Here we present models and atomistic computer simulations on ion beam shaping. Ion beam shaping occurs if the ion track temperature exceeds the SiO2 melting temperature, which was concluded from calculations of radial temperature-time profiles of ion tracks. Using the solubility (several ppm) and the high diffusivity of Au in molten silica, the “ripening” of the wires can be attributed to anisotrope, spatio-temporal limited Au diffusion in ion tracks, as it was proven by atomistic simulations. Thermocapillarity has been identified as a huge force elongating Au nanoparticles in SiO2 at the sub-picosecond timescale. Kinetic Monte Carlo simulations reproduce the experimental shape evolution. Preliminary molecular dynamics studies introduce the correct kinetics and explain the low fluence necessary for ion beam shaping.
Keywords: nanostructure, high-energy ion irradiation, gold, silicon, shaping, modeling, computer simulation
  • Lecture (Conference)
    15th International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Taormina, Italy

Permalink: https://www.hzdr.de/publications/Publ-9288
Publ.-Id: 9288


Optical and compositional analysis of functional SiOxCy:H coatings on polymers

Martin-Palma, R. J.; Gago, R.; Torres-Costa, V.; Fernandez-Hidalgo, P.; Kreissig, U.; Martinez Duart, J. M.
At present, optical polymers are increasingly replacing glass in several applications, including the field of ophthalmic lenses. In the present work, protecting and optical SiOxCy:H coatings have been deposited by Plasma Enhanced Chemical Vapor Deposition onto polymeric substrates at low temperature from hexamethyldisiloxane (HMDSO) and oxygen precursors. The best mechanical properties are obtained for composition graded SiOxCy:H layers, in which the O2/HMDSO ratio is varied during deposition. The optical properties of the protective layers, in particular the spectral behavior of the refractive index and extinction coefficient, have been calculated from the transmittance and reflectance spectra. Elastic Recoil Detection Analysis was used to obtain information about the elemental composition of the layers as a function of the deposition parameters.
Keywords: Silicon oxycarbide; Optical coating; Visible spectrometry; Plasma-enhanced CVD; Elastic recoil detection
  • Thin Solid Films 515(2006), 2493-2496

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Permalink: https://www.hzdr.de/publications/Publ-9287
Publ.-Id: 9287


Shaping of nanometals by high energy ion beams

Vredenberg, A.; Dawi, E.; Mink, M.; Heinig, K.-H.; Toulemonde, M.; Nordlund, K.; Kuronen, A.
Metal nanorods and nanowires have great potential in a wide range of fields, because of their tunable (by shape and size) optical and magnetic properties. We present a new and unique way of producing nanorods and -wires, embedded in a solid, that are aligned in the same direction. Starting from spherical Au nanocolloids in a silica film we will show that the colloids are shaped controllably into rods and -at later stages- wires by irradiation with an MeV heavy ion beam. The ion-beam induced anisotropy (from a spherical colloid to a rod) is caused by the highly anisotropic ion track: a long, few nm diameter cylinder of highly excited material. The colloids elongate and form rods with their long axis in the direction of the ion beam. The mechanism of this deformation is still under investigation, but we will discuss possible origins, involving anisotropy in mechanical or mass balance gradients. We will also discuss the potential of these individually shaped nanoparticles in applications such as nano(bio-)sensors, upconverters for solar cells, magnetic nanodevices, smart optical materials with negative index of refraction (left-handed materials.
Keywords: nanostructures, shaping, nanowire, high-energy ion irradiation, gold, silica, modeling, computer simulation
  • Invited lecture (Conferences)
    MRS Fall Meeting 2006, Symposium "Self Assembly of Nanostructures Aided by Ion- or Photon-Beam Irradiation---Fundamentals and Applications", 27.-29.11.2006, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-9285
Publ.-Id: 9285


Synthesis of aligned nanowire arrays by shaping of nanometals with swift heavy ions – modelling and atomistic simulations

Heinig, K.-H.; Vredenberg, A.; Toulemonde, M.; Nordlund, K.
The functionality of nanoparticles can be extended by shape anisotropy. Thus, for future hard disks, rod-like nanomagnets are more resistant against thermally activated spin flipping than spheres, and, for photonics, light is guided as surface plasmon-polariton along a chain of rods with less damping than along a chain of spheres. Recently it has been shown [1] that Au nanospheres embedded in SiO2 can be shaped into rods (and even wires) by swift heavy ion irradiation. The underlying mechanisms are largely unknown. Van Dillen has proven [2] that the Trinkaus model [3], which describes successfully the ion beam shaping of dielectrics/semiconductors, can not be applied to ion beam shaping of metal nanoparticles. Here, a consistent mechanism of ion beam shaping and nanowire ripening will be presented. Using the temperature-time profiles of ion tracks in SiO2 as delivered by Toulemonde [4], atomistic computer experiments performed with kinetic Monte-Carlo and Molecular Dynamics codes reproduce the experimental results [5]. Our comprehensive numerical studies facilitate a further optimisation of ion beam shaping.
[1] A. Vredenberg et al., IBMM2004 Conf., Monterey (USA), Sept5 - 10, 2004.
[2] T. van Dillen, Int. Workshop “Ion Beam Shaping”, Amsterdam (Netherlands), Dec17, 2004.
[3] H. Trinkaus, J. Nucl. Mater. 223, 196 (1995).
[4] M. Toulemonde, Nucl. Instr. and Methods B66/67, 903 (2000), and private comm..
[5] K.-H. Heinig, talk OO7.5 at the MRS2005 Fall Meeting, Nov28-Dec01, 2005, Boston (USA).
Keywords: nanostructures, shaping, high-energy ion-irradiation, gold, silica, modeling, computer simulations
  • Lecture (Conference)
    E-MRS IUMRS ICEM Spring Meeting 2006, Symposium "Science and Technology of Nanotubes and Nanowires", 29.05.-02.06.2006, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-9284
Publ.-Id: 9284


Self-aligned doubly-stacked Si dots fabrication for improved data retention of nanocrystal memories

Heinig, K.-H.; Roentzsch, L.
Nonvolatile nanocluster (NC) memories fabricated by Si ion implantation/irradiation of SiO2 gate oxides have some key parameters which are superior to those of state-of-the-art devices [1-3]. However, data retention is still below industrial requirements. Former studies have proven that a doubly-stacked nanocluster structure can improve retention considerably [4]. However, it is difficult to fabricate NC pairs with a precise intercluster spacing at a precise distance above the Si substrate. Here, based on atomistic process simulations, a novel fabrication technique of self-aligned doubly-stacked Si NCs will be presented. It is assumed that a layer of large (<10nm) Si NCs is placed on top of ~10nm oxide by a conventional (e.g. CVD) technique. This structure is covered by a control oxide. Tiny (~3nm),self-aligned NCs between the large NCs and the substrate form during annealing after energetic ion irradiation. As described in ref.[5], ion beam mixing at Si/SiO2 interfaces results in Si NCs growth. Here, mixing from the substrate and large NCs lead to selective NC formation below the large NCs. The stability of this CMOS-compatible processing will be evaluated.
[1] B. Schmidt, K.-H. Heinig et al., Nucl.Instr.Meth. B242, 146 (2006).
[2] P. Dimikratis et al., J.Phys.Conf.Ser. 10, 7 (2005).
[3] T. Müller, K.-H. Heinig et al., Appl. Phys. Lett. 85, 2373 (2004).
[4] R. Ohba et al., IEEE Trans. El. Dev. 49, 1392 (2002).
[5] K.-H. Heinig et al., Appl. Phys. A 77, 17–25 (2003).
Keywords: Nanostructures, silicon, silica, ion-irradiation, self-organization, modeling, kinetic Monte-Carlo simulation
  • Lecture (Conference)
    E-MRS IUMRS ICEM Spring Meeting 2006, Symposium "Silicon Nanocrystals for Electronic and Sensing Applications", 29.05.-02.06.2006, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-9283
Publ.-Id: 9283


CMOS compatible bottom-up approach of multi-dot floating-gate nonvolatile memory fabrication.

Heinig, K.-H.; Schmidt, B.; Mueller, T.; Roentzsch, L.; Stegemann, K.-H.
Scalability and performance of current FLASH memories could be improved substantially by novel devices based on multi-dot floating gate MOSFETS. Until today, ten years of research effort have been devoted to Tiwari`s idea [1] to replace the poly-silicon floating-gate of FLASH memories by a layer of Si nanocrystals. Although several groups and companies developed test-devices, a breakthrough was not achieved due to two main reasons: (i) The CMOS compatible fabrication of the layer of nanocrystals remains a great challenge (monolayer of monodisperse Si nanocrystals of high density, which has to be embedded in the gate oxide at a controlled tunnel distance of a few nm above the Si channel). (ii) The retention of the test-devices did not reach the industrial standard. Here, we present a CMOS compatible bottom-up approach of a multi-dot floating-gate nonvolatile memory fabrication which is based on ion-beam mixing of Si-SiO2 interfaces [2]. By energetic Si ion irradiation through the poly-Si gate and the gate oxide into the Si substrate, a SiOx layer forms in the interface region. During post-irradiation annealing, the flat Si/SiO2 interface rebuilts rapidly by spinodal decomposition and interface area minimization. However, in the tail of the mixing profile, Si excess nucleates in the gate oxide layer forming Si nanocrystals. These nanocrystals are separated from the substrate by a few nm thin SiO2 layer which is free of Si excess. Experimental and atomistic computer simulation studies of this bottom-up approach will be presented. Electrical characteristics of devices, which were fabricated in an industrial environment, will be shown. Predictions to overcome the main drawback in view of applicability as memory devices, i.e. the data retention of only a few months at room temperature, will be discussed.
[ 1] S. Tiwari et al., IEEE Int. Electron Devices Meeting Technical Digest, 521–524 (1995).
[ 2] K.-H. Heinig, T. Müller, B.Schmidt, M. Strobel, W. Möller, Appl. Phys. A 77, 17–25 (2003).
Keywords: nanostructures, silicon, silica, ion-irradiation, self-organization, FLASH memory, modeling, process simulation
  • Lecture (Conference)
    MRS Spring Meeting 2006, Symposium "Science and Technology of Nonvolatile Memories", 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-9282
Publ.-Id: 9282


Predictive process simulation of Si nanocluster layer formation by low-energy ion implantation

Heinig, K.-H.; Mueller, T.; Schmidt, B.
Memory cells consisting of a metal-oxide-semiconductor field-effect transistor (MOSFET) with a charge-storage floating-gate made of silicon nanocrystals (ncs) are promising candidates for high-storage density low-power memory applications. The information is stored in the floating gate that can be charged and discharged either from the control gate or from the channel of the transistor. Floating gates consisting of Si ncs have been fabricated through the use of different deposition techniques. The multi-dot layer in the very thin gate oxide can be fabricated CMOS-compatibly by ion beam synthesis (IBS) [1]. Here, we present theoretical studies on IBS of multi-dot layers
consisting of Si nanocrystals (NCs) [2]. The NCs are produced by ultra low energy Si ion implantation, which causes a high Si supersaturation in the shallow implantation region. During post-implantation annealing, this supersaturation leads to phase separation of the excess Si from the SiO2. Kinetic lattice Monte Carlo simulations of Si phase separation have been performed and compared with EFSTEM images [3]. It has been predicted theoretically that the morphology of the multi-dot Si floating gate changes with increasing ion fluence from isolated, spherical NCs to percolated spinodal Si pattern. These patterns agree remarkably with EFSTEM images. However, the predicted fluence for spinodal pattern is lower than the experimental ones. Because oxidants of the ambient atmosphere penetrate into the asimplanted SiO2, a substantial fraction of the implanted Si is lost due to oxidation.
[1] K.-H. Heinig, T. Müller, B.Schmidt, M. Strobel, W. Möller, Appl. Phys. A 77, 17–25 (2003).
[2] T. Müller, K.H. Heinig, and W. Möller, Appl. Phys. Lett. 81, 2373 (2002).
[3] T. Müller, K.H. Heinig, W. Möller, C. Bonafos, H. Coffin, N. Cherkashin, G. Assayag, S. Schamm, G. Zanchi, A. Claverie, M. Tencé, C. Colliex, Appl. Phys. Lett. 85, 2373 (2004).
Keywords: nanostructures, silicon, silica, low-energy ion implantation, non-volatile memory, modeling, phase separation, process simulation
  • Poster
    MRS Spring Meeting, Symposium "Science and Technology of Nonvolatile Memories", 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-9281
Publ.-Id: 9281


Experimente an der Versuchsanlage ROCOM zur Bestimmung der minimalen Borkonzentration bei postulierten Störfällen mit kleinem Leck im heißen Strang

Kliem, S.; Sühnel, T.
Die in diesem Bericht dokumentierten Ergebnisse sind vertraulich.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    FZR\FWS\2006\03
    75 Seiten

Permalink: https://www.hzdr.de/publications/Publ-9280
Publ.-Id: 9280


Ion beam shaping of nanometals: process modeling and atomistic simulations of extreme conditions

Heinig, K.-H.; Vredenberg, A.; Toulemonde, M.; Nordlund, K.
Recently, a novel type of ion-beam induced deformation of metal nanoobjects has been found. Under heavy ion irradiation, Au nanospheres in a silica matrix first elongate into rods. At higher fluences they combine into nanowires that continue to grow during irradiation. Such anisotropically shaped metal nanoparticles may have great potential in a wide range of fields. For example, nanorods exhibit a split plasmon resonance, with one of the bands shifting into the infrared. Arrays of such particles have a great potential as nanophotonic guides in the (infra)red, an important telecom wavelength regime, but outside the range of plasmon resonances of spherical metal particles. Here, we present a model and atomistic computer simulations of this ion beam shaping. The experimental lower threshold for ion beam shaping of 6 keV/nm ion energy deposition along the ion track coincides with the theoretically required energy for melting of SiO2 in the ion track of a few nanometer diameter. Heating occurs on a timescale of a few tens of fs. Thus, temperature gradients of several billion Kelvin per cm can be reached. The Au nanosphere experiences such an extreme environment if it is touched by an ion track. These extreme conditions are similar to femtosecond laser processing of Au layers where frozen nanojets have been observed. Laser-induced nanojet formation and ion beam shaping have obviously the same driving force: Based on atomistic simulations we prove that thermocapillarity drives material of a Au nanosphere, which is touched by an ion track, from the hot equator to the colder pole regions(Thermocapillarity is the driving force for the wellknown Marangoni effect). Additionally, the transiently extreme high temperature in the molten SiO2 ion track dissolves Au, which diffuses fast and precipitates during cooling into tiny Au clusters. Superposition of tracks leads to a highly anisotropic “track diffusion” transport of Au from short nanorods to longer ones, which can be considered as a special case of Ostwald ripening.
Keywords: nanostructure processing, high-energy ion irradiation, gold nanowires, silica, extreme conditions, kinetic Monte-Carlo simulations, thermocapillarity
  • Lecture (Conference)
    MRS Spring Meeting 2006, Symposium "Materials in Extreme Conditions", 20.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-9279
Publ.-Id: 9279


In-situ observation o Ni-Ti thin film growth by synchrotron radiation scattering

Martins, R. M. S.; Braz Fernandes, F. M.; Silva, R. J. C.; Beckers, M.; Schell, N.
A sputter deposition hamber inserted into the six-circle Huber diffractometer of the materials research station of the ROssendorf BeamLine (ROBL-CRG) at ESRF allowed to perform in-situ experiments during film growth of Ni-Ti. It is equipped with Kapton windows for X-Ray Diffraction (XRD) and specular Reflectivity (XRR) measurements. By following in situ the evolution of the structure of the growing film, we reveal intermediate “states” which cannot be seen/revealed ex situ , because those states ocurred only during the growth but were no longer visible after deposition. Vertical Bragg-Brentano large-angle scattering geometry was employed to study the different trends of structural transformations taking place during deposition. Ni-Ti films exhibiting a non-uniform phase content across the film thickness could be produced by varying the power of co-sputtering Ni-Ti plus Ti. A significant decrease of IB2{110}/IB2{200} was observed when a bias of -45 V was applied.
  • Materials Science Forum 514-516(2006), 1588-1592

Permalink: https://www.hzdr.de/publications/Publ-9278
Publ.-Id: 9278


Visualisation of the concentration distribution and the flow field in solidifying metallic melts by means of X-ray radioscopy

Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.
Capabilities of the X-ray attenuation contrast radioscopy will be demonstrated to provide a real-time diagnostic technique of the melt flow during solidification of Ga-In alloys. Directional solidification processes of binary metallic Ga-In alloys were visualised using a microfocus X-ray tube. The X-ray facility provided shadow radiographs at spatial resolutions of about 10 µm at frame repetition rates of 25 Hz. The optical flow approach has been adapted to determine the velocity of the liquid, the mass transport and the dendritic growth rate in the mushy zone from translocations of concentration contour lines appearing during the image sequence. Buoyancy-driven flow patterns were found ahead of the solidification front at length scales much larger than the dendrite spacing.
  • Contribution to proceedings
    5th Decennial International Conference on Solidification Processing, 23.-25.07.2007, Sheffield, UK
    Proceedings of the 5th Decennial International Conference on Solidification Processing, Sheffield, 978-0-9522507-4-6, 311-315
  • Lecture (Conference)
    5th Decennial International Conference on Solidification Processing, 23.-25.07.2007, Sheffield, UK

Permalink: https://www.hzdr.de/publications/Publ-9277
Publ.-Id: 9277


Charge trapping phenomena in high-efficiency metal-oxide-silicon light-emitting diodes with ion-implanted oxide

Nazarov, A.; Osiyuk, I.; Tyagulskii, I.; Lysenko, V.; Prucnal, S.; Sun, J.; Skorupa, W.; Yankov, R. A.
This work focuses on the processes of charge trapping in SiO2 layers doped with either rare-earth impurities or Ge. Diode SiO2/Si structures incorporating such oxide layers exhibit efficient electroluminescence (EL) in the spectral range of UV to IR. Analyses of the charge trapping and the variation of the EL intensity during electron injection enable three injection levels to be identified (low, medium and high). The nature of specific hole trapping at the medium injection level is discussed.
Keywords: rare-earth doping, charge trapping, light-emitting diodes, electroluminescence
  • Journal of Luminescence 121(2006)2, 213-216

Permalink: https://www.hzdr.de/publications/Publ-9276
Publ.-Id: 9276


Characterization of Ga-Bi Liquid Metal Alloy Ion Source

Akhmadaliev, C.; Pilz, W.; Bischoff, L.
Liquid metal alloy ion sources (LMAIS) are now of increasing interest in mass-separated focused ion beam (FIB) systems where a variety of projectile ions can be used. Typically, these can be focused into diameters of the order of 10 nm, with current densities of several A/cm2 giving probe currents of 1 pA -30 nA.
A Gallium-Bismuth LMAIS with melting point temperature of 222°C has been studied. The ion source was based on a mechanical treated Ta emitter. The emission characteristics of the source were investigated. From a detailed analysis of the source mass spectra as a function of emission current, the mechanism of single and double-charged ions emission is established. Good agreement is obtained comparing these results with Swanson’s investigations of a pure Bi source.
GaBi LMAIS allows to provide FIB structuring of a silicon substrate using either shallow donor ions (Bi) or acceptors ions (Ga) without changing the ion source.
Keywords: Focused ion beam, liquid metal ion source, shallow donor
  • Lecture (Conference)
    The European Focused Ion Beam Users Group Meeting(EFUG), 02.10.07, Wuppertal, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9275
Publ.-Id: 9275


Low energy Ar ion accelerated diffusion of interstitial nitrogen

Abendroth, B.; Abrasonis, G.; Möller, W.; Ma, X. X.
Interstitial N diffusion under low energy (700 eV) Ar+ bombardment at 673 K in ion beam nitrided austenitic stainless steel is investigated. Ar+ ion bombardment increases the N mobility in depths far beyond the ion penetration depth, resulting in an increased broadening of the N depth profile as a function of Ar+ flux. This effect cannot be explained by any established mechanism of radiation-enhanced diffusion. An explanation based on quasiparticle-enhanced mobility is proposed.
  • Lecture (Conference)
    13. Workshop "Oberflächentechnologie mit Plasma- und Ionenstrahlprozessen", 14.-16.03.2006, Mühlleithen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9274
Publ.-Id: 9274


Simulations of FZR adiabatic air-water data with CFX-10

Krepper, E.; Lucas, D.; Shi, J.-M.; Prasser, H.-M.
The CFD simulation of an adiabatic gas-liquid flow requires an adequate characterisation of the momentum exchange between the phases. This report describes the CFX simulation of adiabatic air/water bubbly flow in a vertical pipe and the comparison to experimental results for several test conditions that were obtained in FZ-Rossendorf. The measured cross sectional distribution of the gas volume fraction enables the validation of the applied models for the momentum exchange between the liquid and the gaseous phase. The drag bubble force determines the flow resistance in flow direction and influences the gas volume fraction for given superficial gas and liquid velocities. The non drag forces, namely the lift-, the wall- and the turbulent dispersion forces act perpendicularly to the flow direction and influence the cross sectional gas volume fraction distribution. Their correct simulation is important, since they have an essential influence on the flow regime.
In the report the model approaches for the drag and the non drag bubble forces are described. Several tests gained at MT-Loop that show low gas volume fractions are presented. These can be described by only one dispersed gaseous phase having a certain bubble size. These experiments are therefore suited for the validation of the non drag force models.
Increasing the gas injection rate, a bubble size distribution including bubble coalescence and fragmentation has to be considered. The paper describes the concept of the inhomogeneous MUSIG model, which is implemented in CFX-10. Several tests from MT-Loop and from TOPFLOW are presented to demonstrate the applicability of the model.
The simulations are intended for the comparison to other CFD models e.g. in the NURESIM-CFD platform.
Keywords: Two phase flow, CFD, drag forces, non drag forces, population balances, experiments, model validation
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    NURESIM-SP2-TH-D2.2.3.1 (June 2006)
    22 Seiten

Permalink: https://www.hzdr.de/publications/Publ-9273
Publ.-Id: 9273


Progress report on the simulation of the plunging jet configuration. EU projetc NURESIM Deliverable D2.1.3.1 (June 2006)

Bodèle, E.; Lucas, D.
This progress report presents the preliminary work done for the numerical prediction of the plunging jet configuration. It consists in the definition of the most appropriate numerical configuration which should permit to obtain the most realistic behaviour of the gas below the free liquid surface. Several numerical domain (mesh and boundary conditions), numerical assumptions (steady state or transient calculations) and numerical models (mainly the effects of the non drag forces acting on the gas phase) have been tested. This report presents the most realistic numerical results and concludes on the most appropriate numerical domain and assumptions for the following tasks.
Keywords: plunging jet, Pressurized Thermal Shock (PTS), non drag forces, numerical simulation, CFX
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    0039 Seiten

Permalink: https://www.hzdr.de/publications/Publ-9272
Publ.-Id: 9272


Synthesis report on work package 2.1: Pressurized Thermal Shock (PTS)

Lucas, D.
This report summarizes the results of the first 18 months period of the NURESIM project for the workpage 2.1 “Pressurized Thermal Shock (PTS)”. It mainly bases on the deliverables supplied by the partners involved in this workpage. In the Introduction chapter some more general information on the PTS issue is given, which should help to clarify the integration of the single activities. Since the PTS scenario involves different flow situations, for which also different modelling approaches are necessary, the contributions are sorted according to these flow situations. The relations of the work done to the general aim of the NURESIM project, which is to establish a new code platform, is indicated by assigning the activities to 6 different types. The present status PTS workpage is in agreement with the planning of the NURESIM project, the expected results were met by the deliverables. The work done leads to an improvement of the simulation capabilities regarding a PTS flow situation, but caused by the complexity of the issue it will still be a long way to enable reliable predictions for the whole process from such simulations.
Keywords: PTS
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    FZR\FWS\2006\06
    19 Seiten

Permalink: https://www.hzdr.de/publications/Publ-9270
Publ.-Id: 9270


Mass separated FIB applications from alloy liquid metal ion sources

Bischoff, L.; Akhmadaliev, C.
During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range ion species other than gallium are needed. Therefore alloy liquid metal ion sources (LMIS) were developed. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of an FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current I, ion mass m and emitter temperature T. For singly charged ions a predicted dependence of the energy spread, DE µ I2/3 m1/3 T1/2 found for Ga could be reasonable confirmed. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-OrsayPhysics especially for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB obtained from a Co36Nd64 alloy LMIS was applied for the ion beam synthesis of CoSi2 micro-structures down to 60 nm. Additionally, the possibility of varying the current density of the FIB by changing the pixel dwell-time was used for investigations of radiation induced damage and its dynamic annealing in Ge, Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. Especially this direct patterning 3D technique was used for the fabrication of various kinds of micro-tools.
All these examples underline the importance of FIBs in modern research and the new possibilities opened up by a mass separated system applying a broad spectrum of ion species.
Keywords: FIB; alloy LMIS; micropatterning; tools; CoSi2
  • Invited lecture (Conferences)
    FIB User Meeting 2006, 18.-19.05.06, Fufeau, France

Permalink: https://www.hzdr.de/publications/Publ-9269
Publ.-Id: 9269


Sicherheit von Kernkraftwerken - Beiträge des Forschungszentrums Dresden-Rossendorf

Willschütz, H.-G.; Weiß, F.-P.
Zur Zeit werden weltweit über 440 Kernkraftwerke im kommerziellen Leistungsbetrieb eingesetzt. Die überwiegende Mehrheit sind sogenannte Leichtwasserreaktoren (LWR). Das Risiko, dass es beim Betrieb von LWR der heutigen Generation zu einem schweren Unfall (engl. Severe Accident, SA) mit partiellem oder vollständigem Abschmelzen des Reaktorkerns kommt, ist gering. Es lässt sich aber trotz umfangreicher Sicherheitsvorkehrungen nicht vollständig ausschließen.
Bei der Entwicklung und Auslegung von Kernkraftwerken wurde von Beginn an ein erhöhtes Sicherheits- beziehungsweise Schutzkonzept verfolgt, weil bekannt war, dass das radioaktive Inventar, das aus den während des Betriebs entstehenden Spalt- und Aktivierungsprodukten besteht, nicht unkontrolliert freigesetzt werden darf. Es wurde daher von vornherein ein sogenanntes Mehrstufenkonzept („defence-in-depth“) eingeführt, um die in jeder technischen Anlage auftretenden Störungen innerhalb des Kraftwerks zu beherrschen und Unfälle auszuschließen.
Das Mehrstufenkonzept besteht heute aus 4 Ebenen. Die Ebenen 1 bis 3 – Normalbetrieb, Betriebsstörungen und Auslegungsstörfälle – wurden bereits bei der Reaktorauslegung berücksichtigt und dienen der Störfallverhinderung beziehungsweise der Störfallvermeidung. Zur Vermeidung und Begrenzung von schweren Unfällen ist mit dem sogenannten „anlageninternen Notfallschutz“ nachträglich die 4. Ebene eingeführt worden.
Die Wirksamkeit des Defence-in-Depth wird zum einen durch die technische Auslegung sichergestellt. Zum anderen durch die Umsetzung der sogenannten Sicherheitskultur. Die Sicherheitskultur stellt die Gesamtheit der Eigenschaften und Einstellungen von Personen und Organisationen dar, die dafür sorgt, dass dem sicheren Anlagenbetrieb die höchste Priorität zukommt.
Ein Pfeiler der Sicherheitskultur ist die Sicherheitsforschung. In diesem Vortrag werden zwei Beispiele der aktuellen Arbeiten im Forschungszentrum Rossendorf zu sicherheitsrelevanten Fragestellungen behandelt: die sogenannten Borverdünnungstransienten und die Kernschmelzerückhaltung im Reaktordruckbehälter.
Ein kurzer Überblick über die Historie der verschiedenen Kernkraftwerksgenerationen und die Erläuterung der wesentlichen Eigenschaften der aktuell in Bau befindlichen dritten Generation sowie der heute in der internationalen Forschung betrachteten zukünftigen Reaktortypen (Generation IV) schließen den Vortrag ab.
Keywords: Safety of Nuclear Power Plants, Defence in Depth, Saftey Research, Boron Dilution Transients, In Vessel Retention, Generation III, Generation IV
  • Invited lecture (Conferences)
    Vortragsreihe des VDI, Dresdner Bezirksverein - Arbeitskreis Energietechnik, 06.02.2007, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9268
Publ.-Id: 9268


Application of a Mass Separated Focused Ion Beam

Bischoff, L.; Akhmadaliev, C.; Pilz, W.; Schmidt, B.
During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range ion species other than gallium are needed. Therefore alloy liquid metal ion sources (LMIS) were developed. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of an FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current I, ion mass m and emitter temperature T. For singly charged ions a predicted dependence of the energy spread, DE µ I2/3 m1/3 T1/2 found for Ga could be reasonable confirmed. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-OrsayPhysics especially for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB obtained from a Co36Nd64 alloy LMIS was applied for the ion beam synthesis of CoSi2 micro-structures down to 60 nm. Additionally, the possibility of varying the current density of the FIB by changing the pixel dwell-time was used for investigations of radiation induced damage and its dynamic annealing in Ge, Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. Especially this direct patterning 3D technique was used for the fabrication of various kinds of micro-tools.
All these examples underline the importance of FIBs in modern research and the new possibilities opened up by a mass separated system applying a broad spectrum of ion species.
Keywords: FIB; alloy LMIS; micro - and nanostructures
  • Poster
    1. FIB Workshop, Focused Ion Beams In Research, Science and Technology May 22 – 23, 2006, IFW Dresden, Germany, 22.-23.05.06, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9267
Publ.-Id: 9267


Mn containing alloy LMIS for Spintronics

Akhmadaliev, C.; Pilz, W.; Bischoff, L.
Magnetic ions such as Mn are of increasing interest for the structuring of diluted magnetic semiconductors, e. g. spin-based optoelectronics in III-V as well as II-VI materials. Only a few Mn alloy liquid metal ion sources (LMIS) for nano-patterning are reported, so an Au-Si-Mn or an Au-Ge-Mn sources were used in mass separated FIB applications. The Mn-Ge alloy LMIS (melting temperature of 720°C) showed a stable operation at emission current of 2 - 30 µA. The slope of the I-V characteristic curve was ~0.11 µA/V at a heating current of about 2.6 A.
Keywords: LMIS, focused ion beam
  • Poster
    The European Focused Ion Beam Users Group Meeting(EFUG), 02.10.06, Wuppertal, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9266
Publ.-Id: 9266


Formation of CoSi2 nanowires and nanochains in silicon by direct FIB writing

Akhmadaliev, C.; Bischoff, L.; Schmidt, B.; Mücklich, A.
A Focused Ion Beam (FIB) equipped with a CoNd alloy liquid metal ion source was used for the formation of cobalt disilicide nanowires and nanochains by an ion beam synthesis process. Co ions at 60 keV were implanted into silicon (111) and (100) substrates at 400-450°C followed by a two-step annealing at 600°C and 1000°C. During the FIB patterning of the samples using a digital scanning system the dose, the pixel dwell time and the relaxation time between the irradiation cycles were varied. The FIB spot size was in the range of 40 nm. The formation of long, stable nanowires occurs along the favoured <110>-crystal direction. The misalignment of the FIB trace relative to this direction leads to a decay of the wire into shorter ones or to the formation of chains of single-crystalline nanoparticles. Nanowires of 20-80 nm diameter and lengths up to 50 microns were obtained. Imaging of nanostructures was done in-plane by SEM, AFM and TEM. Cross-sections through nanowires were prepared by conventional Ga FIB milling across the nanowire. Further efforts will be concentrated in a better control of the nanowires growth, in the characterization of the electrical properties and in the fabrication of nanodevices.
Keywords: Cobalt disilicide, nanowire, focused ion beam
  • Lecture (Conference)
    DPG-Tagung 2006, 27.-31.03.06, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9265
Publ.-Id: 9265


Efficient oxidation protection of gamma-TiAl alloys by ion implantation of halogens

Yankov, R. A.; Richter, E.; Donchev, A.; Schütze, M.
In this work, gamma-TiAl samples have been rendered highly oxidation-resistant by plasma immersion ion implantation using various Cl- or F-containing precursor gases. PI3 processing has been preceded by beamline ion implantation of either Cl or F because of the well-established nature of the process. Implanting F gives better results. Further work has involved the co-implantation of F and Si to study the combined effect of these elements on the alloy’s high temperature behavior.
Keywords: Titanium aluminides, ion implantation, oxidation resistance
  • Lecture (Conference)
    International Conference on Ion Beam Modification of Materials, Taormina, Sicily, Italy, 18 – 22 September 2006, 18.-22.09.2006, Catania, Sicily, Italy

Permalink: https://www.hzdr.de/publications/Publ-9264
Publ.-Id: 9264


FIB assisted silicide nanowires formation in silicon

Akhmadaliev, S.; Bischoff, L.; Schmidt, B.
Focused Ion Beam (FIB) is one of the most suitable tools for sub-µm structure fabrication, modification and investigation. Combining FIB and self organization processes during ion beam synthesis a reduction of the FIB written structures can be provided. The Rossendorf FIB system allows the operation with a Ga liquid metal ion source (LMIS) as well as with a CoNd alloy LMIS. Formation of CoSi2 nanoparticles and nanowires in silicon was investigated using Co++ ions from the CoNd LMIS. Si(111) and Si(100) samples were implanted with a fine focused cobalt ion beam at elevated sample temperatures as well as at room temperature. Subsequent annealing steps lead to the formation crystalline CoSi2 long nanowires with diameter down to 10-20 nm in the crystalline substrate. These structures were analyzed using SEM and AFM. Two main mechanisms of the nanowires formation have been observed: via coalescence of the implanted Co nanoparticles with following Oswald ripening and via diffusion of Co atoms during annealing into “linear defects” induced by FIB irradiation. Further efforts are concentrated in increasing of reproducibility of nanowire growth and then the fabrication of nanodevices.
Keywords: Cobalt disilicide, nanowire, focused ion beam, ion beam synthesis
  • Lecture (Conference)
    E-MRS Spring Meeting 2006, 29.05.-02.06.06, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-9263
Publ.-Id: 9263


Improvement of the oxidation behavior of TiAl-alloys by treatment with halogens

Donchev, A.; Richter, E.; Schütze, M.; Yankov, R.
The paper addresses the enhancement of the oxidation resistance of gamma-TiAl alloys with the aim of making them suitable for applications at temperatures in excess of 750 °C. Improvements in the oxidation resistance have been achieved by ion-implanting halogens, notably Cl and F, which favors the formation of an adherent protective alumina scale. Additional results are presented pertinent to the high-temperature creep behavior of the halogen-implanted alloys.
Keywords: Titanium aluminides, Ion implantation, Halogens, Oxidation, Creep
  • Intermetallics 14(2006)10-11, 1168-1174

Permalink: https://www.hzdr.de/publications/Publ-9262
Publ.-Id: 9262


Dampfgehaltsmessung in Brennelementbündeln mittels hochauflösender Gammatomographie

Bieberle, A.; Kronenberg, J.; Hampel, U.
Für die Bestimmung des Dampfgehaltes in Brennelementbündeln wurde ein hochauflösendes Gammatomographie Messsystem am Forschungszentrum Dresden - Rossendorf entwickelt und erste Testmessungen an der Testanlage KATHY der Firma AREVA NP GmbH in Karlstein durchgeführt. Gegenstand des Vortrages ist die Vorstellung des Messsystems und erste Ergebnisse, die im Rahmen meiner Promotionsvorhabens entstanden sind.
Keywords: Gamma Tomographie
  • Lecture (others)
    Kompetenzzentrum Ost für Kerntechnik - Doktorandenseminar, 15.12.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9261
Publ.-Id: 9261


Gamma ray computed tomography for fast rotating objects

Bieberle, A.; Hampel, U.
Recently, we have developed a high resolution gamma ray computed tomography system to analyze processes at hydro dynamic and multi phase flow facilities non-invasively. Typically, the measurement system consisting of a collimated isotopic source and a gamma ray detector is rotated around the object of investigation to record projections from different angle positions in one plane. In our case we use Cs137 with an activity of about 165 GBq. For fast rotating objects our developed measurement system is arranged in a fixed position and the stir of the object is used. By cyclically read-out of the measurement system’s electronic the number of projections per revolution can be determined. A trigger signal that is also included in the data transfer indicates a full revolution. That information is important for the later data processing if the object is rotating non-uniformly and thus the number of projections per revolution differs. After the recording the data of one projection can be resorted in a matrix – called sinogram - to the corresponding angle position column. Typical applications areas are the behaviour analysis of hydro dynamic couplings and the determination of gas fraction in a stirrer vessel reactor. Therefore we developed a new electronic that is compatible to the existing digital unit and realizes a periodical read-out of our 320 single detector arc every 40 µs. That means for an object that is rotating with 1500 rpm 1000 projections can be recorded per revolution.
Keywords: high speed gamma ray tomography
  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography, 03.-06.09.07, Bergen, Norway, IPS01
  • Lecture (Conference)
    5th World Congress on Industrial Process Tomography, 03.-06.09.07, Bergen, Norway

Permalink: https://www.hzdr.de/publications/Publ-9260
Publ.-Id: 9260


PC driven etching system for emitter needle tips

Pilz, W.; Lange, H.; Akhmadaliev, C.; Zimmermann, L.; Bischoff, L.
The reproducible forming of emitter needle tips is a serious demand for the fabrication of liquid metal ion sources. The movement of the needle into the etch solution, for tungsten 1n NaOH is used, a PC driven step motor with an increment of 2 µm is used. Due to the adjustment of the motion as a function of height and time the optimum shape of the tip can be repeatable etched. This process is controlled on a monitor optically using a long distance microscope and a video system. Characteristic needle tips with a radius of a few micron are presented.
Keywords: emitter needle; liquid metal ion source; etching; PC control
  • Invited lecture (Conferences)
    1st Workschop on Ion Beams from L.M.I.S. and Applications, 03.12.06, Lamia, Greece

Permalink: https://www.hzdr.de/publications/Publ-9259
Publ.-Id: 9259


The statistical properties of paleomagnetic reversals: measurements and models

Sorriso-Valvo, L.; Carbone, V.; Stefani, F.; Nigro, G.
The spontaneous reversals of the geomagnetic field have recently been shown to own clustering properties. Poisson-like statistics (including non-stationary renewal processes) is indeed unable to describe some statistical properties observed in the data. Such statistical properties are thus used here to test some numerical models currently adopted to reproduce the geodynamo effect. Moreover, the model's parameters can be tuned in order to reproduce with the simulated reversals the same degree of deviation from Poisson statistics observed on the real data.
  • Open Access Logo Abstract in refereed journal
    Geophysical Research Abstracts 9(2007), 02863-02863

Permalink: https://www.hzdr.de/publications/Publ-9258
Publ.-Id: 9258


The application of alloy liquid metal ion sources in mass separated focused ion beams

Bischoff, L.; Akhmadaliev, C.; Pilz, W.
For special purposes like writing ion implantation or ion mixing in the micrometer- or sub-micrometer range different ion species are needed. Therefore alloy liquid metal ion sources (LMISs) are used. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of a FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, Ga38Bi62, Mn43Ge57, In50Ga50, Sn86Pb14 and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current, ion mass, charge state and emitter temperature and the abundance of the species, emitted from the tip, in the mass spectra.
Most of the alloy LMISs discussed above have been used in the Rossendorf FIB system IMSA-Orsay Physics especially for writing implantation to fabricate sub-micrometer pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi2 micro-and nanostructures. Additionally, the possibility of varying the current density with the FIB by changing the pixel dwell time was used for radiation damage investigations in Si, Ge and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume-loss method as well as used for patterning of different surface structures, i.e. in nano-functional films. Especially this technique was used for the fabrication of various kinds of micro-tools.
Keywords: alloy liquid metal ion sources; focused ion beam; nano-structures; implantation
  • Invited lecture (Conferences)
    1st WORKSHOP ON ION BEAMS FROM L.M.I.S. AND APPLICATIONS, 03.12.06, Lamia, Greece

Permalink: https://www.hzdr.de/publications/Publ-9256
Publ.-Id: 9256


Magnetic and superconducting properties of RuSr2GdCu2O8

Papageorgiou, T. P.; Casini, E.; Braun, H. F.; Herrmannsdörfer, T.; Bianchi, A. D.; Skourski, Y.; Wosnitza, J.; Freudenberger, J.
The high-temperature superconducor RuSr2GdCu2O8 (Ru1212) offers the rare opportunity to study how superconductivity develops in an already magnetically ordered state. In this compound the Ru moments order magnetically at TM 130 K and a G-type antiferromagnetic arrangement has been proposed from neutron-diffraction studies [1] with the spins aligned along the c axis. We have measured the magnetic-field dependence of the magnetization of Ru1212 at T < TM in fields up to B 50 T. At the lowest measuring temperature of 4.2 K no saturation of the magnetization was observed and at 50 T, assuming a Gd contribution of 7 μB/formula unit, the Ru contribution to the measured magnetic moment was estimated to be 2.1 μB/formula unit. This is consistent with a mixed-valence state of the Ru ions (Ru5+ and Ru4+) and in contrast to the neutron diffraction studies that estimate an ordered Ru moment of 1.18 μB. In the superconducting state of the sample (T < 50K) we show that the signature of a bulk Meissner state, diamagnetism, is absent. Nevertheless, we suggest that this could be the effect of the granular nature of the investigated samples. A discussion of the specific heat of Sr2GdRuO6, the precursor for the preparation of Ru1212, with respect to the reported specific heat of the latter compound strongly supports the claims that Ru1212 is a bulk superconductor.
  • Poster
    International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VIII (M2S-HTSC-VIII), 09.-13.07.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9255
Publ.-Id: 9255


Pressure dependence of the electronic properties of the quasi-two-dimensional organic superconductor β" - (BEDT-TTF)2SF5CH2CF2SO3

Ignatchik, O.; Hagel, J.; Wosnitza, J.; Pfleiderer, C.; Schlueter, J. A.; Mohtasham, J.; Gard, G. L.
We report on the pressure-dependent superconducting and transport properties of the quasi-two-dimensional organic superconductor beta"-(BEDT-TTF)2SF5CH2CF2SO3, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene (or ET for short). With increasing pressure the superconducting transition temperature, Tc, decreases monotonously. Superconducting traces can be observed up to 11.7 kbar; at higher pressures an insulating state appears. By use of Shubnikov-de Haas (SdH) and angular-dependent magnetoresistance oscillations the Fermi-surface topology as well as the effective masses were determined. Close to the insulating state a new SdH frequency can be resolved. The effective mass, mc, of the main orbit decreases approximately linear with pressure. By assuming a direct relationship between mc and the superconducting coupling parameter lambda, the pressure dependence of Tc can be well explained by the modi-fied McMillan equation. For all pressures in the metallic state the resistance can be described by R = R0 + AT2 at low temperatures. The coefficient A, however, is found to be not proportional to m2c as expected for a purely electronic origin of the T2 behavior.
  • Poster
    International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VIII (M2S-HTSC-VIII), 09.-14.07.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9254
Publ.-Id: 9254


Infrared pump-probe spectroscopy of carrier dynamics in semiconductor quantum structures

Helm, M.
no abstract available
Keywords: intersubband relaxation, infrared, quantum well, carrier dynamics, femtosecond
  • Invited lecture (Conferences)
    International Conference on Engineering Physics and 9th Vietnamese-German Seminar, 09.-11.10.2006, Hanoi, Vietnam

Permalink: https://www.hzdr.de/publications/Publ-9253
Publ.-Id: 9253


Electronic band structure and superconducting gap of YNi2B2C and LuNi2B2C

Bergk, B.; Ignatchik, O.; Bianchi, A. D.; Jäckel, M.; Wosnitza, J.; Perenboom, J.; Jobiliong, E.; Souptel, D.; Behr, G.; Canfield, P. C.
We present de Haas-van Alphen (dHvA) measurements of the nonmagnetic borocarbides YNi2B2C and LuNi2B2C. The measurements were carried out on high-quality crystals by the torque method in magnetic fields up to 33 T. The Fermi-surface topology has been measured in the normal state and compared with band-structure calculations. In the superconducting state below the upper critical field, Bc2, the dHvA-signal is strongly damped due to the opening of the superconducting gap, which allows to study the evolution of the superconducting gap. In order to investigate the symmetry of the order parameter we performed angle-dependent measurements
of this damping. We compare results from two differently grown kinds of crystals. The crystals produced by a zone-melting method show an abrupt vanishing of the dHvA signal at Bc2. In contrast, flux-grown crystals display a broader phase transition combined with a continuous decrease of the oscillation amplitude. The observed anisotrop of the dHvA-signal damping points to an anisotropic energygap in these materials.
  • Poster
    8th International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VIII (M2S-HTSC-VIII), 09.-14.07.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9252
Publ.-Id: 9252


The strongly correlated superconductor CeCoIn5: Evidence for the realization of a FFLO state

Bianchi, A. D.; Capan, C.; Movshovich, R.; Pagliuso, P. G.; Sarrao, J. L.
I will be reporting on specific-heat and thermal-conductivity measurements at low temperatures on the strongly correlated superconductor CeCoIn5 in magnetic fields close to the upper critical field Hc2. This system is a prime example for illustrating how in a strongly correlated electron system superconductivity emerges near a so-called quantum critical point (QCP). Close to this point the system fluctuates between a paramagnetic heavy-fermion state and an uncorrelated antiferromagnetically ordered metal. What makes CeCoIn5 special is the fact that just before the magnetic order is established at the QCP, superconductivity supersedes it. Several aspects of the superconductivity in CeCoIn5 are unconventional: On the one hand, the temperature dependence of the specific heat and thermal conductivity well below the critical temperature suggests lines of zeroes in the energy gap of the superconducting state. On the other hand, we observed a second phase inside the superconducting part of the temperature-magnetic field phase diagram close to Hc2. The limiting upper critical field to superconductivity in CeCoIn5 is set by the Pauli criterion, suggesting that this second phase is a Fulde-Ferrell-Larkin-Ovchinnikov state (FFLO). In the FFLO state, the superconducting wave function acquires an additional modulation. The FFLO phase is also of great interest to the astrophysics community, as it could describe the dense quark matter inside neutron stars, or quasars.
  • Invited lecture (Conferences)
    8th International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VIII (M2S-HTSC-VIII), 09.-14.07.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9251
Publ.-Id: 9251


“Recent developments at the Dresden High Magnetic Field Laboratory”

Wosnitza, J.; Bianchi, A. D.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S.
A high magnetic field laboratory for pulsed non-destructive fields up to 100 T is under construction at the Forschungszentrum Rossendorf, situated at the outskirts of Dresden, Germany. Besides the ultimate goal of a pulsed magnet reaching 100 T for a timescale of 10 ms in a bore of 20 mm, further large-scale magnets (e.g. 60 T, 0.5 s, 40 mm) are planned. The necessary energy for the pulsed coils will be provided by a world-unique 50 MJ capacitor bank working at 24 kV that became operational this year (2006) within a newly built laboratory building. As an outstanding feature of the laboratory, the intense light of a next-door free-electron-laser facility will enable unique high-field infrared spectroscopy. Dedicated coil-winding facilities allow a fast realization of novel self-designed pulsed coils with diameters up to 750 mm. After a thorough test period of the coil design, user-type coils for up to 65 T, 10 ms, and bore of 20 mm, made out of soft copper wire with Zylon reinforcement, have been wound and tested successfully with high-field pulses repeatedly. The first large-scale coil for magnetic fields above 70 T with 100 ms pulse length and 24 mm bore has been realized. A two-coil system for the decisive goal of 100 T is scheduled. First tests of these high-energy coils will be performed in the near future. Cryotechniques and different sample probes for a broad range of experimental techniques custom-designed for the variety of pulsed magnets will be readily available for users and own in-house research. The new Hochfeld-Magnetlabor Dresden (HLD) is planned to open as user facility in 2007.
  • Invited lecture (Conferences)
    Megagauss 2006, 05.-10.11.2006, Santa Fe, USA

Permalink: https://www.hzdr.de/publications/Publ-9250
Publ.-Id: 9250


Gamma ray CT – system for multiphase flow imaging

Bieberle, A.; Schleicher, E.; Hampel, U.
We present a recently developed gamma ray CT system that enables us to visualize rapidly rotating multi-phase distributions, such as in stirred chemical reactors and hydrodynamic machines. Transmission measurements with gamma rays or X-rays are often employed when the flow is confined in dense metal structures and the distribution of gas, liquid or solid suspensions have to be determined. For gamma ray tomography the object of investigation must be placed between an isotopic source and a detector that measures the attenuation of the radiation passing through the object. In the past our group developed a first gamma ray tomography device and supplied it successfully to rapidly rotating systems (Prasser 2003, Hampel 2005). The old system contains a detector made of 64 elements (BGO scintillation crystals and photo multipliers) and a pulse processing unit transferring projection data in 90 µs intervals. As isotopic source Cs137 was used with an activity of about 165 GBq. Our new high resolution gamma ray detector now comprises 320 single detector elements each with an active area of 2 mm by 8 mm. The detectors are made of avalanche photo diodes and lutetium yttrium orthosilicate (LYSO) scintillation crystals whose shape was optimized for a high gamma photon yield. All 320 elements produce weak negative voltage pulses that are shaped and amplified by a pulse processing unit which is built up fully parallel for all 320 channels. The signal processing unit contains also gain adjustable amplifiers, discrimination stages, and binary pulse counters. This allows energy discrimination of every detected gamma photon and thus dividing scattered from non-scattered photons. Data of one projection data set can now be transferred to a PC every 40 µs for 320 detectors periodically via USB2.0. This enables acquisition of 500 radiographic projections per revolution of objects rotating at 3000 rpm. To compound the sinogram a data matrix is initiated to zero. After each revolution the value of every detector element is added to the data matrix with respect to the current angle position in. The detailed procedure is described elsewhere (Prasser 2003, Hampel 2005). Figure 2 shows as an example the reconstructed image of a stirrer of 60 mm outer diameter rotating at 1500 rpm. The result was reconstructed using a standard filtered backprojection algorithm.
Keywords: phase flow imaging, gamma ray tomography
  • Contribution to proceedings
    International Conference on Multiphase Flow 2007, 09.-13.07.07, Leipzig, Germany
    Programme and Abstracts of the 6th International conference on Multiphase Flow, S7-Thu_C55
  • Lecture (Conference)
    International Conference on Multiphase Flow 2007, 09.-13.07.07, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-9248
Publ.-Id: 9248


A high-resolution gamma tomograph for void fraction distribution measurements in fuel element bundles

Bieberle, A.; Kronenberg, J.
We would like to present our recently developed high-resolution gamma ray measurement system for analyzing dry-out effect and determine void fraction distributions in sub-channels of electrically heated fuel element bundles at the thermal hydraulic test loop KATHY in Karlstein (AREVA NP GmbH, Germany). The instrumentation setup enables a non-invasive measurement of cross-sectional void fraction profiles through the pressure vessel for fuel element bundles under typical nuclear reaction conditions. The gamma ray tomography system consists of a Cs137 isotopic source with an activity of about 165 GBq and a detector arc containing 320 single elements. The source radiation is restricted to a flat fan beam with a tungsten collimator. The average spatial resolution of the system is 3 mm in plane and 8 mm axial. With a special gantry vertical positioning and continuous rotation of the measurement setup is realised which is necessary for a complete tomography in different planes. Typically, transversal scans require an approximate recording time of 25 minutes. Gamma ray tomography is a relative measurement method. To determine void fraction calibration measurements are recorded at zero and one hundred percent void fraction respectively. It is a challenge to develop a tomography measurement system that is non-sensitive to temperature changes, high humidity and electrical fields to scale the void measurement to the calibration data. Cross-sectional images are reconstructed by standard filtered back projection algorithms.
Keywords: gamma ray tomography, void distribution
  • Contribution to proceedings
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.07, Nagoya, Japan
    Proceedings of the ICONE15, Paper No. ICONE15-10440
  • Lecture (Conference)
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.07, Nagoya, Japan

Permalink: https://www.hzdr.de/publications/Publ-9247
Publ.-Id: 9247


High Peak Current Design of a superconducting Cavity for a SRF Photoinjector

Janssen, D.; Marhauser, F.; Volkov, V.
A 1.5-cell cavity for a superconducting RF gun has been designed and a magnetic RF mode for emittance compensation is applied. For a peak current of 125 A a transverse emittance of 1.8 mm mrad has been obtained.
  • Poster
    28 th Free Electron Laser Conference FEL 2006, 27.08.-01.09.2006, Berlin, Germany
  • Contribution to proceedings
    28 th Free Electron Laser Conference FEL 2006, 27.08.-01.09.2006, Berlin, Germany, 571-574

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Permalink: https://www.hzdr.de/publications/Publ-9246
Publ.-Id: 9246


Kontrolle von Aluminium-Feinguss mittels Einsatz einer elektromagnetischen Induktionspumpe

Gerbeth, G.; Buchenau, D.; Eckert, S.; Galindo, V.; Willers, B.; Witke, W.
Die numerischen und experimentellen Arbeiten zur Auslegung und dem Test einer elektromagnetischen Pumpe zur Kontrolle des Füllprozesses beim Aluminium-Feinguss werden zusammen gefasst. Weiterhin wird über die industriellen Ergebnisse des Einsatzes eines statischen Magnetfeldes auf die Gussteilqualität berichtet.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    Abschlussbericht zum BMBF-Projekt 01 RW 0304, Dezember 2006

Permalink: https://www.hzdr.de/publications/Publ-9245
Publ.-Id: 9245


Density functional investigation of the (113)[-110] twin grain boundary in TiO2 anatase and its influence on magnetism in diluted magnetic semiconductors

Gemming, S.; Janisch, R.; Schreiber, M.; Spaldin, N. A.
Density-functional calculations were carried out for the (113)[-110] tilt grain boundary in the anatase modification of TiO2, with and without magnetic Co dopants. The boundary exhibits a low energy of 0.88 J/m^2 and no rigid translation of the grains. It is composed from four distinct structural units, and a deviation from the mirror-symmetric atom arrangement due to local relaxation is found. The analysis of the electronic structure indicates that the grain boundary is electronically inactive, because it introduces no boundary-specific states in the bulk band gap, and only minor differences between the valence band structures of the grain boundary and the pure bulk are obtained. The regular arrangement of the quite open structural units provides the possibility of doping the grain boundary with electronically or magnetically active elements, which is explored by doping the supercell with Co. In this diluted magnetic semiconductor the (113)[-110] grain boundary can enhance the ferromagnetic interaction by providing convenient bond angles for ferromagnetic superexchange.
Keywords: dilute magnetic semiconductor, oxide, grain boundary

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Permalink: https://www.hzdr.de/publications/Publ-9244
Publ.-Id: 9244


Untersuchung von Spektraleigenschaften kugelsymmetrischer alpha2-dynamos mit Techniken der Funktionalanalysis und Operatortheorie

Günther, U.; Stefani, F.; Gerbeth, G.
Zum besseren Verständnis natürlicher Dynamos und zur Datenauswertung und Auslegung von Dynamoexperimenten ist ein vertieftes Verständnis des Spektrums von Dynamooperatoren nötig. Dies gilt insbesondere für die Erklärung von Umpolungsprozessen des Erdmagnetfeldes, die sehr wahrscheinlich mit spektralen Phasenübergängen zwischen nicht-oszillierenden und oszillierenden Lösungen der Induktionsgleichung in engem Zusammenhang stehen. Der erste Schwerpunkt des Projektes lag auf spektraltheoretischen Grundlagenuntersuchungen einfacher Dynamomodelle mit kugelsymmetrischen helikalen Turbulenzparametern. Hier konnte gezeigt werden, dass der Differentialausdruck des entsprechenden Dynamo-Operators eine diskrete Symmetrie besitzt, welche es erlaubt, ihn für idealisierte Randbedingungen als selbstadjungierten Operator in einem Krein-Raum (einem Hilbert-Raum mit zusätzlicher indefiniter Metrik) zu behandeln. Dadurch besitzt er eine Vielzahl von Gemeinsamkeiten mit Hamilton-Operatoren der PT-symmetrisch erweiterten Quantenmechanik, welche sich ebenfalls als Operatortheorie in Krein-Räumen formulieren lässt. Viele dieser Parallelen wurden aufgezeigt, darunter das spektrale Verzweigungsverhalten zweiter und höherer Ordnung. Der zweite Schwerpunkt des Projektes lag auf der numerischen Behandlung des betrachteten einfachen Dynamomodells mit nichtlinearer Rückwirkung und Rauschen. Dabei konnte einerseits gezeigt werden, dass sich die typischen Eigenschaften von Umpolungen tatsächlich auf die Magnetfelddynamik in der Nähe spektraler Verzweigungspunkte zurückführen lassen. Andererseits wurde gezeigt, dass es eine starke Tendenz hochüberkritischer Dynamos gibt, sich in einen zu Umpolungen neigenden Zustand zu begeben, und dass sich die typischen Umpolungszeiten des Geodynamos ebenfalls auf die hohe Überkritikalität zurückführen lassen. Die bemerkenswerte Übereinstimmung der numerisch bestimmten Umpolungsmerkmale mit denjenigen des realen Geodynamos legen den Schluß nahe, dass der untersuchte Umpolungsmachanismus in der Nähe spektraler Verzweigungspunkte generischen Charakter hat und sich auch in komplizierteren Dynamomodellen identifizieren lassen sollte.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    Abschlussbericht zum DFG-Projekt Ge 682/12-2, Mai 2006

Permalink: https://www.hzdr.de/publications/Publ-9243
Publ.-Id: 9243


Fermi surfaces of the half heusler compounds Ce1-xLaxBiPt

Bianchi, A. D.; Wosnitza, J.; Kozlova, N.; Freudenberger, J.; Schultz, L.; Opahle, I.; Elgazzar, S.; Richter, M.; Goll, G.; von Löhneysen, H.; Yoshino, T.; Takabatake, T.
We report on the Fermi surface in the correlated half-Heusler compounds Ce1-xLaxBiPt. In CeBiPt, as well as in Ce0.95La0.05BiPt, we find a temperature-dependent Fermi-surface topology. In addition, we observe a field-induced change of the electronic band structure as discovered by electrical-transport measurements in pulsed magnetic fields. For magnetic fields above about 25 T, the charge-carrier concentration determined from Hall-effect measurements increases nearly 30%, whereas the Shubnikovde Haas (SdH) signal disappears at the same field [1]. In the non-4f compound LaBiPt the Fermi surface remains unaffected, suggesting that these features are intimately related to the Ce 4f electrons. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.
  • Poster
    International Conference on Magnetism (ICM), 20.-25.08.2006, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-9242
Publ.-Id: 9242


Magnetic properties of transition-metal nanoclusters on biological substrates

Herrmannsdörfer, T.; Bianchi, A.; Papageorgiou, T.; Pobell, F.; Wosnitza, J.; Selenska-Pobell, S.; Pollmann, K.; Merroun, M.
Compared to their bulk counterparts, micro- and nanogranular materials can reveal a diverse appearance of physical properties. In particular, their magnetic and superconducting behaviour can be drastically changed. Recently we have started to investigate transition metal clusters with a well defined grain size of 1 nm. These metal nanoclusters have been deposed on a regular square lattice of a biological template. In more detail, this template is a purified self-assembling paracrystalline surface layer (S-layer) of the bacillus sphaericus JG-A12 which exhibits square symmetry and is composed of identical protein monomers. The nucleation sites of the nanoclusters are most probably the pores of the S-layers. The S-layer proteins are capable of selective and reversible binding of high amounts of metals, making the S-layer also interesting for technological applications. The transition metal nanoclusters were investigated using EXAFS-spectroscopy and SQUID-magnetometry. First data of their magnetization at 0 < B < 7T and 1.8 K < T < 350 K reveal interesting magnetic properties. The Stoner enhancement factor of the d conduction-electron susceptibility in the Pd and Pt nano clusters is dramatically reduced compared to the one of bulk transition metals. In the case of granular Pt, the weakened magnetism of the 5d electrons is considered to play a crucial role for the occurrence of superconductivity by adjusting the balance between electron-phonon interaction and competing magnetic interactions observed for micron [1] and submicron [2] grain size powders. As the superconducting transition temperature has been observed to increase clearly with decreasing Pt grain size, we focus our interest also on the search of superconductivity in the transition metal nanoclusters.
  • Lecture (Conference)
    International Conference on Magnetism (ICM), 20.-25.08.2006, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-9241
Publ.-Id: 9241


Development of a prototype superconducting cw cavity and cryomodule for energy recovery

Mcintosh, P. A. B.; Dykes, C. D.; Todd, D. M.; Belomestnykh, B.; Liepe, S.; Medjidzade, M.; Padamsee, V.; Sears, H.; Shemelin, J.; Proch, V. D.; Buechner, A.; Michel, P.; Teichert, J.; Kimura, T.; Smith, T. I.; Byrd, J.; Corlett, J. N.; Li, D.
Energy Recovery LINAC (ERL) and LINAC-driven FEL proposals and developments are now widespread around the world. Superconducting RF (SRF) cavity advances made over the last 10 years for TESLA/TTF at 1.3 GHz, in reliably achieving accelerating gradients >20 MV/m, suggest their suitability for these ERL and FEL accelerators. Typically however, photon fluxes are maximised from the associated insertion devices when the electron bunch repetition rate is as high as possible, making CW-mode operation at high average current a fundamental requirement for these light sources. Challenges arise in controlling the substantial HOM power and in minimizing the power dissipated at cryogenic temperatures during acceleration and energy recovery, requiring novel techniques to be employed. This paper details a collaborative development for an advanced high-Q0 cavity and cryomodule system, based on a modified TESLA cavity, housed in a Stanford/Rossendorf cryomodule. The cavity incorporates a Cornell developed resistive-wall HOM damping scheme, capable of providing the improved level of HOM damping and reduced thermal load required.
  • Contribution to proceedings
    European Particle Accelerator Conference EPAC 2006, 26.-30.06.2006, Edinburgh, GB
    EPAC 2006 - Proceedings, 436

Permalink: https://www.hzdr.de/publications/Publ-9240
Publ.-Id: 9240


Crenarchaeota 1.1b and Firmicutes consortium recovered from a uranyl nitrate treated uranium waste sample and its possible role against the toxicity of uranium

Reitz, T.; Geissler, A.; Merroun, M.; Selenska-Pobell, S.
Supplementations of a sample collected from a depleted uranium mining waste pile with uranyl nitrate induced significant changes in microbial community structure during the first four weeks of incubation. At the later stages of the treatment, however, the initial composition of the community, indigenous for the untreated samples and consisting mostly of uranium sensitive populations, started to set up. This indicates that the added uranium was no longer bio-available, possibly due to the interactions of the induced at the first stages of the treatment uranium resistant populations with the added radionuclide. Studies on archaeal diversity demonstrated a strong shifting from the subgroup 1.1a to the subgroup 1.1b of the mesophilic soil Crenarchaeota within the first four weeks of the incubations.
Our efforts to cultivate representatives of this crenarchaeal group on specific enrichment media from the sample treated with uranyl nitrate under anaerobic (corresponding to the natural) conditions, resulted in the recovery of a consortium consisting of the mentioned 1.1b Crenarchaeota mixed with populations of Firmicutes, mainly of Clostridium spp. Clostridia can effectively interact with uranium and they can also fermentatively reduce nitrate to ammonium. Because an ammonia oxidizing activity was deduced on the basis of meta-genomic analyses for the closest relative to the stimulated in our case 1.1b populations, we speculate that the clostridia possibly supply the crenarchaeal members of the recovered synergetic consortium with ammonia. In addition, a Paenibacillus sp. isolate was cultivated from this consortium and its interactions with uranium were studied by using TEM and EDX analyses.
  • Poster
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 01.-04.04.2007, Osnabrück, Germany
  • Contribution to proceedings
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 01.-04.04.2007, Osnabrück, Germany
    Biospektrum, Das Magazin für Biowissenschaften, Tagungsband: Elsevier, 0947-0867, 193

Permalink: https://www.hzdr.de/publications/Publ-9239
Publ.-Id: 9239


Interaction mechanisms of bacterial strains isolated from uranium mining waste piles with U and Pb

Merroun, M.; Geissler, G.; Raff, J.; Hennig, C.; Selenska-Pobell, S.
Bacterial isolates belonging to two different groups of Gram-positive bacteria, namely to Arthrobacter sp. of Actinobacteria and to Bacillus sphaericus of Firmicutes were cultivated from a uranium mining waste pile near the town of Johanngeorgenstadt in Germany. We demonstrate that these two kinds of isolates possess different strategies to protect their populations from the toxicity of uranium. Transmission electron microscopy (TEM) analyses showed that the Arthrobacter sp. strains accumulated this radionuclide intracellularly, although a significant part of the uranium treated Arthrobacter sp. population remained radionuclide-free. X-ray absorption spectroscopy (XAS) studies demonstrated that uranium was mainly coordinated to bacterial organic phosphate groups in a monodentate binding mode.
In the case of the Bacillus sphaericus isolate JG-A12 uranium was bound on the cell surface by the bacterial surface layer (S-layer) protein. Extended x-ray absorption fine structure (EXAFS) spectroscopic analyses demonstrated that the radionuclide was complexed by carboxylic groups in a bidentate fashion and by phosphate groups in a monodentate fashion.
X-ray diffraction (XRD) analysis indicated that the growing cells of the arthrobacterial strains precipitated Pb as galena (PbS), whereas in non-growing conditions pyromorphite (Pb5(PO4)3Cl) phase was produced by the cells, alleviating probably the toxicity of Pb. TEM analyses showed that the pyromorphite precipitates were mainly located at the cell surface.
Because representatives of Arthrobacter and Bacillus were induced in uranium supplemented samples of the same uranium mining waste we suggest that these organisms play an important protective role for the natural bacterial community of the studied habitat.
  • Poster
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 01.-04.04.2007, Osnabrück, Germany
  • Contribution to proceedings
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 01.-04.04.2007, Osnabrück, Germany
    Biospektrum, Das Magazin für Biowissenschaften, Tagungsband: Elsevier, 0947-0867, 193

Permalink: https://www.hzdr.de/publications/Publ-9238
Publ.-Id: 9238


Bacterial response to sodium and uranyl nitrate treatments of uranium mining waste samples

Geissler, A.; Reitz, T.; Selenska-Pobell, S.
The response of bacterial community of a depleted uranium mining waste pile to increased concentrations of uranyl or sodium nitrate was studied in microcosm experiments under conditions corresponding to the natural. For this, the 16S rRNA- and the narG-gene retrievals were applied. Both retrievals demonstrated that at the early stages of the treatments with sodium nitrate a strong activation of nitrate reducing and denitrifying populations, mainly of Firmicutes and Betaproteobacteria, occurred that had overgrown the originally predominating in the untreated samples populations of Acidobacteria, Alpha-, and Deltaproteobacteria. The parallel treatments with uranyl nitrate demonstrated that only particular populations of the above mentioned induced Firmicutes and betaproteobacterial nitrate-reducers are uranium resistant. More significant was the stimulation in these samples of the gammaproteobacterial denitrifyers, able also to effectively interact with and to immobilize the added uranium. After longer incubations both kinds of treatments resulted in an establishment of populations characteristic for the original non-treated sample. The latter indicates that particular members of the natural bacterial consortium of the studied uranium waste site possess a high potential to deal with increased and toxic concentrations of uranium and nitrate, which usually co-contaminate these environments. In this way the diversity of the whole community which includes also uranium sensitive populations is kept unaffected. These results explain our previous finding that the bacterial communities of a large variety of uranium mining waste samples collected from the same site but from different depths and polluted with uranium to a different extend, exhibit almost the same structure.
  • Contribution to proceedings
    VAAM-Jahrestagung 2007, 01.-04.04.2007, Osnabrück, Germany
    Biospektrum, Das Magazin für Biowissenschaften, Tagungsband:: Elsevier, 0947-0867
  • Poster
    VAAM-Jahrestagung 2007, 01.-04.04.2007, Osnabrück, Germany

Permalink: https://www.hzdr.de/publications/Publ-9237
Publ.-Id: 9237


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