Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
The missing link: What can dynamo simulation learn from dynamo experiments?
Stefani, F.; Gerbeth, G.; Gundrum, T.; Avalos-Zuniga, R.;
Der homogene Dynamoeffekt in stömenden elektrisch leitfähigen Fluids ist verantwortlich für das Auftreten kosmische Magnetfelder, einschließlich des Erdmagnetfeldes. Nach Jahrzehnten ausschließlich analytisch-numerischer Untersuchungen wird der Dynamoeffekt seit 1999 auch in verschiedenen Laborexperimenten untersucht.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    FZD\FWS\2007\03

Publ.-Id: 9390 - Permalink


Kerne und Sterne - Vom Urknall, der Entstehung der chemischen Elemente und Experimenten im FZR
Wagner, A.;
Kerne und Sterne - Vom Urknall, der Entstehung der chemischen Elemente und Experimenten im FZR
  • Lecture (others)
    Lehrerfortbildung "Astrophysik", 17.02.2006, Dresden, Deutschland

Publ.-Id: 9389 - Permalink


BNL superconducting RF guns-technology challenges as ERL sources
Burrill, A.; Ben-Zvi, I.; Calaga, R.; Chang, X.; Hahn, H.; Kayran, D.; Kewisch, J.; Litvinenko, V.; Mcintyre, G.; Nicoletti, A.; Pate, D.; Rank, J.; Scaduto, J.; Rao, T.; Wu, K.; Zaltsman, A.; Zhao, Y.; Bluem, H.; Cole, M.; Falletta, M.; Holmes, D.; Peterson, E.; Rathke, J.; Schultheiss, T.; Todd, A.; Wong, R.; Lewellen, J.; Funk, W.; Kneisel, P.; Phillips, L.; Preble, J.; Janssen, D.; Nguyen-Tuong, V.;
The design, fabrication and commissioning of a 703.75 MHz SRF photoinjector with a retractable multi-alkali photocathode designed to deliver 0.5A average current at 100% duty factor is the present undertaking of the electron cooling group in the Collider Accelerator Division of Brookhaven National Labs. This photoinjector represents the state of the art in photoinjector technology, orders of magnitude beyond the presently available technology, and should be commissioned by 2007. The R&D effort presently underway, and the focus of this paper, will address the numerous technological challenges that must be met for this project to succeed. These include the novel physics design of the cavity, the challenges of inserting and operating a multi-alkali photocathode in the photoinjector at these high average currents, and the design and installation of a laser system capable of delivering the required 10s of watts of laser power needed to make this photoinjector operational. (c) 2005 Elsevier B.V. All rights reserved.
Keywords: energy recovery linac; high average current; superconducting RF; photoinjector design; ampere class; photocathode

Publ.-Id: 9387 - Permalink


Uranium as a stress factor in well aerated multispecies biofilms – A microsensor study of the O2 concentrations
Krawczyk-Bärsch, E.; Großmann, K.; Arnold, T.; Diessner, S.; Wobus, A.;
Multispecies biofilms were cultured on glass slides in a standard culture medium (Sifin; TN 117) under air atmosphere in annular rotating reactors [1] for two months to obtain a thickness of approximately 800 µm. The slides with the grown biofilms were removed from one reactor for microsensor studies in a flow cell. Two other reactors were fed with UO2(ClO4)2 to adjust the total uranium concentration in the culture medium to 1x10-5 mol/l and 1x10-6 mol/l, respectively, i.e. the biofilms in these reactors were exposed to uranium for three weeks before they were removed for additional microsensor studies. Concentration profiles of oxygen versus biofilm depths were measured in each biofilm by electrochemical microsensors with a tip diameter of 10µm. A motor-driven micromanipulator was used for moving downwards through the biofilm in 20 or 50µm steps. The microsensor results clearly showed a significant dependence of the O2 concentration on the presence as well as on the concentration of uranium. In the absence of uranium the O2 concentration in the well aerated biofilm decreased slightly due to the aerophile microbes, dominating this biofilm. In contrast, O2 concentrations in the biofilms, which were exposed to different concentrations of uranium, decreased with increasing uranium concentration. Apparently, uranium acted as a stress factor for the microbes. Since metals have a strong effect on oxygen consumption, decreases in oxygen concentration could be due to changes in microbial activities [2] as well as on the activation of microbial communities induced by the addition of uranium [3]. 16S rDNA gene sequence retrieval and FISH are currently in progress to provide information on the changes occurring in the biofilm community and the resulting influence on the O2 concentration profiles.

[1] Lawrence, J. R. et al., (2000) Journal of Microbiological Methods 42, 215-224.
[2] Viret, H. et al., (2006) Sci Total Environ. 367, 302-311.
[3] Geissler, A. et al., (2005) Geobiology 3, 275-285.
  • Poster
    International Symposium on Microbial Adaptation in Stress and Enviroment, 12.-14.04.2007, Marburg, Germany
  • Contribution to proceedings
    International Symposium on Microbial Adaptationin Stress and Enviroment, 12.-14.04.2007, Marburg, Germany, P30

Publ.-Id: 9386 - Permalink


Spectroscopic and microscopic characterization of uranium biomineralization in Myxococcus xanthus
Jroundi, F.; Merroun, M.; Arias, J. M.; Rossberg, A.; Selenska-Pobell, S.; González-Muñoz, M. T.;
In this work, synchrotron-based X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) studies were carried out to elucidate at molecular scale the interaction mechanisms of Myxococcus xanthus with uranium at different pH values. Extended X-ray absorption fine structure (EXAFS) experiments show that there are significant differences in the structural parameters of the U complexes formed by this bacterium at pH 2 and 4.5. At very low acidic pH of 2, the cells accumulated U(VI) as organic phosphate-metal complexes. However, at pH 4.5, the cells of this bacterium precipitated U(VI) as meta-autunite-like phase. TEM indicated that at pH 2 the uranium accumulates are located mainly at the cell surface. Whereas, at pH 4.5 the uranium precipitation takes place on the cell wall and within the extracellular polysaccharides (EPS) characteristic of this bacterium. Dead/live staining studies showed that 30% and 50% of the uranium-cell treated cell populations are alive at pH 2 and 4.5, respectively. The precipitation of uranium as mineral phase is possibly due to the acid phosphatase activity which was detected at both pH values. Precipitation of U as mineral phase may lead to more stable U(VI) sequestration that may be suitable for remediation uses. These observations, combined with the very high uptake capacity of this bacterium, imply that bacterial cells may significantly influence the fate of uranium in soils where these bacterial groups are mainly found.

Publ.-Id: 9385 - Permalink


Geochemical behavior of uranium in mine tailings at Freital, Germany: A μ-XRF, μ-XAFS and μ-XRD study
Scheinost, A.; Hennig, C.; Somogyi, A.; Martinez-Criado, G.; Knappik, R.;
- wird nachgereicht
  • Lecture (Conference)
    16th Annual V.M. Goldschmidt Conference 2006, 27.08.-01.09.2006, Melbourne, Australia
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 70(2006)18, A560

Publ.-Id: 9384 - Permalink


Defect profiles in B or P implanted Ge after Flash Lamp Annealing probed by Slow Positron Implantation Spectroscopy
Anwand, W.; Skorupa, W.; Schumann, T.; Posselt, M.; Schmidt, B.; Grötzschel, R.; Brauer, G.;
B+ and P+ ions were implanted into Ge wafers covered with an amorphous surface layer of 150 nm. After this, FLA in Ar atmosphere was used in order to realise three objectives:
- recrystallisation of the amorphous region on top of the Ge wafer
- electrical activation of the implanted ions
- reduction of diffusion processes during the FLA.
The heat treatment with Xenon flash lamps having a spectrum in the visible range of light and a pulse length of 3 or 20 ms allowed an ultra-short heating up of the near surface region. In this way, a modification of the structure of the amorphous layer containing the implanted range was possible. Depth profiles of defects, especially of the vacancy-type, were investigated by SPIS before and after FLA.
It will be shown that the remaining vacancy-type defect structure depends on the parameters of the process of heat treatment, and that these defects could not be completely removed by FLA.
These results will be compared with such from SRIM 2003 calculations (Stopping and Range of Ions in Matter) and Rutherford Backscattering Spectrometry.
Keywords: Ge, ion implantation, flash lamp annealing, vacancy-type defects, slow positron implantation spectroscopy
  • Lecture (Conference)
    3rd CADRES Ge Workshop, 23.01.2007, Gent, Belgium
  • Poster
    11th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-11), 09.-13.07.2007, Orleans, France

Publ.-Id: 9383 - Permalink


Organometallic 99mTc(III) ‘4+1’ Bombesin(7-14) Conjugates: Synthesis, Radiolabeling and In Vitro/In Vivo Studies
Künstler, J.-U.; Veerendra, B.; Figueroa, S. D.; Sieckmann, G. L.; Rold, T. L.; Hoffman, T. J.; Smith, C. J.; Pietzsch, H.-J.;
Bombesin (BBN) peptide exhibits high selectivity and affinity for the gastrin releasing peptide receptor (GRPr). The GRPr is over-expressed on many human cancer cell types, thus making BBN a potent delivery vehicle for radionuclide targeting. In this study, the biologically active minimal sequence BBN(7-14) was labeled using the novel Tc ‘4+1’ mixed-ligand system, [Tc(NS3)(CN-R)], in which Tc(III) is co-ordinated by a monodentate isocyanide linker bearing the peptide and the tetradentate, tripodal chelator, 2,2’,2’’-nitrilotriethanethiol (NS3). BBN(7-14) was N-terminally modified with Gly-Gly-Gly, ßAla and Ser-Ser-Ser spacer groups (X) and functionalized with 4-(isocyanomethyl)benzoic acid (L1) or 4-isocyanobutanoic acid (L2) resulting in a series of [M(NS3)(L-X-BBN(7-14))] conjugates (M = 99mTc, Re). The isocyanides ligand frameworks were introduced using novel bifunctional coupling agents. The spacer groups (X), the monodentate isocyanide units, and a tetradentate NS3 chelator bearing a pendant carboxylic acid (NS3COOH) were proposed as pharmacological modifiers. 99mTc-labeling was performed in a two-step procedure by first preparing 99mTc-EDTA/mannitol followed by reactions with the isocyanides and NS3 or NS3COOH ligand frameworks. The 99mTc-complexes were obtained with a radiochemical yield of 30 to 80% depending on the amount of the isocyanide (20 to 100 nmol) used. These new conjugates were purified by reversed-phased high performance liquid chromatography (RP-HPLC) to give a radiochemical purity of ≥ 95 %. The 99mTc-conjugates exhibited high in vitro stability (> 90 %, 24 h). Analogous nonradioactive Re-conjugates were synthesized and characterized by electrospray ionization mass spectrometry (ESI-MS). RP-HPLC analyses of the new Re-conjugates indicated that they exhibited identical retention times to the corresponding 99mTc-conjugates under identical HPLC conditions, demonstrating structural similarity between the two metallated species. The [Re(NS3)(L-X-BBN(7-14))] conjugates exhibited GRPr affinity in the nanomolar range as demonstrated by in vitro competitive binding assays using PC-3 human prostate cancer cells. In vitro internalization/externalization assays indicated that ~ 65% of [99mTc(NS3)(L2-βAla-BBN(7-14))] conjugate was either surface bound or internalized in PC-3 cells. Cell-associated activity for all other 99mTc-conjugates was below 20%. Biodistribution studies of [99mTc(NS3)(L-βAla-BBN(7-14))], L = L1, L2, in normal, CF-1 mice showed minimal accumulation in normal pancreas (a tissue expressing the GRPr in high density in rodent models) and rapid hepatobiliary elimination. Introduction of a carboxyl group onto the NS3 ligand framework had only minimal effects to increase renal excretion. Activity distribution and accumulation was highly dominated by the relatively lipophilic ‘4+1’ complex unit.
  • Bioconjugate Chemistry 18(2007), 1651-1661

Publ.-Id: 9382 - Permalink


Electromagnetic excitations in nuclei: from photon scattering to photodisintegration
Erhard, M.; Nair, C.; Beyer, R.; Grosse, E.; Junghans, A. R.; Klug, J.; Kosev, K.; Nankov, N.; Rusev, G.; Schilling, K. D.; Schwengner, R.; Wagner, A.;
In explosive nucleosynthesis temperatures are high enough for photodisintegration reactions to occur, e.g. leading to the production of p-process nuclei. In order to understand the reaction rates of element production and element disruption we started an experimental program at the new bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf. The bremsstrahlung facility and the detector setup are designed such that the scattering of photons from nuclei and the photodisintegration of nuclei around the particle separation energies can be studied under optimized background conditions. In activation measurements with bremsstrahlung at end-point energy from 10.0 to 16.5 MeV (g ,p), (g ,n) and (g ,a) reactions of 92,100Mo have been studied. Our activation yields can be described within a factor 2-3 or better with calculations using the cross sections from recent Hauser-Feshbach models.
  • Contribution to proceedings
    International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX, 25.-30.06.2006, Geneva, Swizerland
    PoS (NIC-IX) 056, Trieste: POS Proceedings of Science, ISSN 1824-8039
  • Lecture (Conference)
    International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX, 25.-30.06.2006, Cern, Schweiz

Publ.-Id: 9381 - Permalink


A new module-assisted synthesis of the versatile, bifunctional labelling agent [18F]SFB: From radiochemistry to applications.
Mäding, P.; Füchtner, F.; Bergmann, R.; Pietzsch, J.; Hultsch, C.; Wüst, F.;
kein Abstract verfügbar
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 49(2006), 223-225
  • Lecture (Conference)
    13th Workshop of the Central European Division e.V. of the International Isotope Society (IIS), 16.-17.06.2005, Bad Soden, Deutschland

Publ.-Id: 9380 - Permalink


Hyperon production in the channel pp -> K+ Lambda p near the reaction threshold
Abd El-Samad, S.; Bilger, R.; Böhm, A.; Brinkmann, K.-T.; Clement, H.; Dshemuchadse, S.; Eyrich, W.; Erhardt, A.; Fanara, C.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Geyer, R.; Hauffe, J.; Hassan, A.; Herrmann, P.; Hesselbarth, D.; Jakob, B.; Kilian, K.; Koch, H.; Kress, J.; Kuhlmann, E.; Marcello, S.; Marwinski, S.; Metzger, A.; Michel, P.; Möller, K.; Morsch, H. P.; Naumann, L.; Roderburg, E.; Schamlott, A.; Schönmeier, P.; Schulte-Wissermann, M.; Schroeder, W.; Steinke, M.; Stinzing, F.; Sun, G. Y.; Wächter, J.; Wagner, G. J.; Wagner, M.; Wilms, A.; Wirth, S.; Zielinski, U.;
Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at three different beam momenta pbeam=2.59, 2.68 and 2.85 GeV/c (corresponding to excess energies of var epsilon=85, 115 and 171 MeV). Total cross-sections were deduced to be 7.4±0.5 μb, 8.6±0.6 μb and 16.5±0.4 μb, respectively. Differential observables including Dalitz plots were obtained. From the investigation of the Dalitz plot at pbeam=2.85 GeV/c a dominant contribution of the N*(1650)-resonance to the reaction mechanism was found. In addition the pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution even 171 MeV above threshold.
Keywords: Associated strangeness production; Total cross-section; Angular distribution; Dalitz plot

Publ.-Id: 9379 - Permalink


Status of the superconducting 3 1/2 cell SRF gun in Rossendorf
Arnold, A.; Staufenbiel, F.;
  • Lecture (Conference)
    CARE Annual Meeting 2006, 15.-17.11.2006, Frascati, Rom, Italy

Publ.-Id: 9378 - Permalink


Simultaneous formation of two ripple modes on ion sputtered silicon
Keller, A.; Roßbach, S.; Facsko, S.; Möller, W.;
The amorphized surface of Si(100) sputtered with low energy ions at moderate temperature was found to develop two perpendicular ripple patterns overlaying each other. The evolution of these patterns was studied over a wide range of fluence. Coarsening of both ripple modes was observed, showing a similar time dependence with a coarsening exponent of 1/z ~ 0.08. In the high fluence regime, the surface enters a steady state with both ripple modes still present.

Publ.-Id: 9377 - Permalink


Equilibrium concentration and diffusivity of vacancies and self-diffusion in Ge: An atomistic study
Geßner, H.; Posselt, M.;
We developed an improved Stillinger-Weber-type potential for Ge by adjusting the three-body parameters in such a manner, that the potential yields the correct lattice constant and the correct cohesive energy, and the melting point and other properties are reproduced satisfactorily. Using this potential, the temperature dependence of equilibrium concentration and diffusivity of vacancies as well as the contribution of vacancies to self-diffusion are investigated by atomistic simulations and thermodynamic considerations. The enthalpies and entropies of formation and migration are calculated. Similar investigations are performed for self-interstitials in order to check whether their contribution to self-diffusion can be neglected, as shown experimentally. Finally, the self-diffusion coefficient and the equilibrium concentration of vacancies determined by the simulations are compared with experimental data from the literature.
Keywords: Ge, vacancy, equilibrium concentration, diffusivity
  • Lecture (Conference)
    CADRES Ge Workshop, 23.01.2007, Ghent, Belgium

Publ.-Id: 9376 - Permalink


N-doping by P implantation into pre-amorphized Ge and subsequent annealing: P diffusion, solid-phase-epitaxial regrowth and P activation
Posselt, M.; Schmidt, B.; Anwand, W.; Grötzschel, R.; Skorupa, W.; Heera, V.; Gennaro, S.; Bersani, M.; Giubertoni, D.;
P and As are considered the most suitable n-dopants in Ge. However, because of diffusion and deactivation effects it is difficult to achieve highly-n-doped Ge by ion implantation and subsequent annealing. We investigated high fluence P implantation into pre-amorphized Ge and subsequent annealing. The thickness of the amorphous layer was varied by implanting Ge at different energies. In all cases the main part of the as-implanted P profiles is located within this layer. Both RTA and flash-lamp annealing were employed. Considering samples with amorphous layers of different thickness enables detailed investigations of P diffusion in amorphous and crystalline Ge and solid-phase epitaxial regrowth during the post-implantation annealing. The thickness of the amorphous layers and the quality of the regrown crystalline Ge were monitored by RBS/C. The chemical depth profiles of P and the donor depth distributions were measured by SIMS and SRP, respectively. The results indicate that P diffuses much faster in amorphous Ge than in crystalline Ge. It is assumed that the P diffusivity in amorphous Ge shows a concentration dependence similar to that in crystalline Ge. The solid-phase epitaxial regrowth occurs already at the lowest thermal budget used in this work. It causes a considerable P redistribution and, presumably, the incorporation of P into crystalline Ge at concentrations above the equilibrium solubility.
Keywords: Ge, n-doping, ion implantation, annealing
  • Lecture (Conference)
    CADRES Ge Workshop, 23.01.2007, Ghent, Belgium

Publ.-Id: 9375 - Permalink


Damage accumulation in nitrogen implanted 6H SiC: Dependence on the direction of ion incidence and on the ion fluence
Zolnai, Z.; Ster, A.; Khanh, N. Q.; Battistig, G.; Lohner, T.; Gyulai, J.; Kotai, E.; Posselt, M.;
The influence of crystallographic orientation and ion fluence on the shape of damage distributions induced by 500 keV N+ implantation at room temperature into 6H SiC is investigated. The irradiation was performed at different tilt angles between 0 and 4 with respect to the 0001 crystallographic axis in order to consider the whole range of beam alignment from channeling to random conditions. The applied implantation fluence range was 2.5 1014 3 1015 cm 2. A special analytical method, 3.55 MeV 4He+ ion backscattering analysis in combination with channeling technique (BS C), was employed to measure the disorder accumulation simultaneously in the Si and C sublattices of SiC with good depth resolution. For correct energy to depth conversion in the BS C spectra, the average electronic energy loss per analyzing He ion for the 0001 axial channeling direction was determined. It was found that the tilt angle of nitrogen implantation has strong influence on the shape of the induc! ed disorder profiles. Significantly lower disorder was found for channeling than for random irradiation. Computer simulation of the measured BS C spectra showed the presence of a simple defect structure in weakly damaged samples and suggested the formation of a complex disorder state for higher disorder levels. Full-cascade atomistic computer simulation of the ion implantation process was performed to explain the differences in disorder accumulation on the Si and C sublattices. The damage buildup mechanism was interpreted with the direct-impact, defect-stimulated amorphization model in order to understand damage formation and to describe the composition of structural disorder versus the ion fluence and the implantation tilt angle.
Keywords: ion implantation, SiC, damage accumulation
  • Journal of Applied Physics 101(2007), 023502

Publ.-Id: 9374 - Permalink


Azaspirovesamicols-Regioselective Synthesis and Crystal Structure Analysis of a Novel Class of Vesamicol Analogues as Potential Ligands for the Vesicular Acetylcholine Transporter
Wenzel, B.; Bats, J. W.; Scheunemann, M.; Steinbach, J.;
This report describes the high regioselectivity of nucleophilic epoxide ring-opening reactions which resulted in two of four possible regioisomers of N-benzoyl- (5a and 5b) and N-fluorobenzoylazaspirovesamicol derivatives (6a and 6b), respectively. Based on structural information obtained from X-ray crystal structure analyses of 5a and 5b the mode of epoxide ring-opening is discussed

Publ.-Id: 9373 - Permalink


Photocathode Laser for the Superconducting Photo Injector at the Forschungszentrum Rossendorf
Will, I.; Klemz, G.; Teichert, J.; Staufenbiel, F.;
We report on the design of the photocathode laser for a superconducting RF gun, which is presently under development at the Forschungszentrum (FZ) Rossendorf. This laser is foreseen to drive the RF gun in CW mode with up to 1 nC bunch charge. It generates pulses of 12...14 ps duration with 500 kHz repetition rate and 0.8 μJ pulse energy at 263 nm wavelength. This should provide sufficient pulse energy for generation of bunches with 1 nC charge using caesium telluride photocathodes. Due to two active modelockers in the laser oscillator, the latter operates in tight synchronism to the RF master oscillator of the linac. The laser consists of a short-pulse oscillator, a pulse picking Pockels cell, a regenerative amplifier and a wavelength conversion unit. The latter converts the infrared laser radiation to the ultra-violet (UV). This unit turns out to be a particularly critical element of such a photocathode laser driving a RF gun in CW mode.
  • Contribution to proceedings
    28th International Free Elektron Laser Conference FEL 2006, 27.08.-01.09.2006, Berlin, Germany
    Proceedings of FEL 2006, BESSY, 978-3-9809534-3-6, 564-566
  • Poster
    28th International Free Electron Laser Conference FEL 2006, 27.08.-01.09.2006, Berlin, Germany

Publ.-Id: 9372 - Permalink


3-1/2 Cell Superconducting RF Gun Simulations
Beard, C. D.; Rogers, J. H. P.; Teichert, J.; Staufenbiel, F.;
A 3-1/2 cell superconducting RF photocathode gun is being developed at Forschungszentrum Rossendorf to produce a high peak current, low emittance electron beam. This technology is essential to the realisation of many large scale facilities. The gun is designed for CW operation mode with 1 mA current and 9.5 MeV electron energy, and it will be installed at the ELBE superconducting electron linear accelerator. The gun will have a 3-1/2 cell niobium cavity operating at 1.3 GHz. The cavity consists of three cells with TESLA geometry and a specially designed half-cell in which the photocathode will be placed. Typical ERL-based projects require ~100 mA average current, and therefore suitable upgrade paths are required. Simulations have been carried out to evaluate the design and to determine suitable upgrades for higher current operation. Simulations of alternative cathode surface shapes are presented. Several couplers have been identified that can provide higher power to the cavity, whose integration and suitability has been verified. All the investigations that have identified possible solutions to higher current operation are discussed in this report.
  • Contribution to proceedings
    European Particle Accelerator Conference EPAC 2006, 26.-30.06.2006, Edinburgh, GB
    EPAC 2006 Proceedings, 92-9083-278-9, 2481-2483

Publ.-Id: 9371 - Permalink


Benchmark proposal for stratified horizontal two-phase flow phenomena
Höhne, T.; Vallee, C.;
Two-phase flow in the primary circuit of a PWR:LOCA scenarios Relevant example of stratified two-phase flow regime for Computational Fluid Dynamics validation:
Slug flow regime characterized by:acceleration of the gaseous phase, transition of fast liquid slugs
Aims of the numerical simulations:
feasibility study of numerical prediction of slug flow with multiphase flow models built in a commercial code (ANSYS-CFX) to prove the understanding of the general fluid dynamic mechanism leading to slug flow
Keywords: slug flow, two phase flow, stratified flow, cfd
  • Invited lecture (Conferences)
    German CFD Network, 9th Meeting,, 25.-26.01.2007, Köln, Deutschland

Publ.-Id: 9370 - Permalink


Modelling and regrowth mechanism of flashlamp processing of SiC-on-silicon heterostructures
Smith, M.; Mc Mahon, R.; Voelskow, M.; Skorupa, W.; Stoemenos, J.;
This paper describes the development of a thermal model for flashlamp processing of 3C-SiC on silicon. The model is a numerical solution of the enthalpy equation, using a modified Crank-Nichelson scheme to combine accurate prediction of melt depths with resonable computation times.
Keywords: FLASiC flashlamp annealing thermal modelling 3C-SiC
  • Material Science Forum 457-460(2004), 333-338

Publ.-Id: 9369 - Permalink


Ion beam doping of 6H-SiC for high concentration p-type layers
Panknin, D.; Skorupa, W.; Wirth, H.; Voelskow, M.; Mücklich, A.; Anwand, W.; Brauer, G.; Gonzalez-Verona, O.; Perez-Rodriguez, A.; Morante, J. M.;
Results of an extensive study concerning implantation, annealing and electrical activation of Al and B layers of 6H-SiC are presented. With increasing implantation temperature the implantation induced damage decreased. After annealing dislocation loops are observed in Al implanted layers whereas loops and precepitates are found in B implanted layers. For good electrical properties amorphization must be avoided. Using flash lamp annealing hole concentration is measured for Al doping whereas for B doping a limited hole concentration is observed.
Keywords: ion implantation SiC defects annealing electrical activation
  • Solid State Phenomena 69-70(1999), 391-396

Publ.-Id: 9368 - Permalink


The Radiation Source ELBE at Forschungszentrum Rossendorf
Michel, P.;
The radiation source ELBE (Electron Linac of high Brilliance and low Emittance) at Forschungszentrum Rossendorf is based on a superconducting linac that produces a high power continuous wave (cw) electron beam up to 40 MeV and 1 mA. The linac is used to drive two free-electron lasers producing infrared radiation from 5 to 150 microns wavelength. Additionally, from several conversion targets MeV-bremsstrahlung (< 20 MeV) and X-rays (10-100 keV) from electron channelling are generated. In the future even neutron and positron beams will be available at ELBE. The used superconducting RF accelerator technology and details of the machine instrumentation, in particular the electron beam diagnosis will be described.
  • Lecture (Conference)
    DPG - Tagung, 27.-31.03.2006, Dresden, Germany

Publ.-Id: 9367 - Permalink


Nanoscaled semiconductor heterostructures for CMOS transistors formed by ion implantation and hydrogen transfer
Popov, V.; Tyschenko, I.; Cherkov, A.; Voelskow, M.;
Abstract: Using bulk silicon can be ended for planar 22 nm technological node due to silicon mobility limitation. New type of substrates needs for further scaling in CMOS microelectronics. We speculate that these new type of materials will be semiconductor heterostructure on insulator (HOI) compatible with current silicon planar CMOS technology. In this work an effect of interface mediated endotaxial (IME) growth of thin semiconductor film at Si/SiO2 bonded interface was experimentally observed and investigated for the first time. Joint semiconductor material stack obtained by hydrogen transfer of one layer material (silicon) and second one (germanium or indium antimonide) placed on amorphous silicon dioxide film is presented. First of all thin film dual layer Si-Ge heterostructure properties were considered. Si-Ge HOI structures were obtained using Ge ion implantation in dioxide with followed Ge segregation to the interface between directly bonded silicon and silicon dioxide wafers. The method is also compatible with A3B5 thin film formation, as was shown for InSb film. Thermodynamic, kinetic and lattice mismatch parameter influences on IME process are considered.
Keywords: hydrogen transfer silicon films implanted impurities segregation endotaxy
  • Lecture (Conference)
    NATO ARW Conference "Nanoscaled SOI Structures and Devices", 15.-19.10.2006, Sudak/Krim, Ukraine
  • Contribution to external collection
    in: Nanoscaled Semiconductor-on-Insulator structures and Devices, Dordrecht: Springer Netherlands-Dordrecht, 2007, 9781402063800

Publ.-Id: 9366 - Permalink


Ion beam synthesis of 4H-(Si1-xC1-y)Gex+y solid solutions
Pezoldt, J.; Kups, T.; Voelskow, M.; Skorupa, W.;
4H-(Si1-xC1-y)Gex+y solid solutions with a Ge incorporation on lattice site from 0.7 to 2.5 percent were formed by ion beam synthesis. The concentration was varied from 1 to 20 % by implanting Ge at 600 C. The implanted samples were annealed at 1300 C in a rapid thermal processing equipment.
Keywords: implantation Ge into SiC RTA RBS
  • Lecture (Conference)
    EXMATEC 06, 15.-17.05.2006, Cadiz, Spain

Publ.-Id: 9365 - Permalink


Silicon-Germanium Heterostructure-on-Insulator formed by Ge+ Ion Implantation and Hydrogen Transfer
Popov, V. P.; Tyschenko, I.; Cherkov, A.; Voelskow, M.;
Using bulk silicon can be ended for 32 nm technological nodes. New type of substrates needs for further scaling in CMOS microelectronics. We speculate that these new type of materials will be semiconductor heterostructure on insulator (SHI) compatible with current silicon planar CMOS technology. Joint semiconductor material stack placed on cheap amorphous dioxide is presented. First of all thin film SiGe heterostructure properties is considered. It was obtain using Ge ion implantation in dioxide with followed Ge segregation to the directly bonded interface between silicon and silicon dioxide wafers. The method is also compatible with A3B5 thin film formation.
Keywords: Si-Ge heterostructures ion implantation
  • Lecture (Conference)
    210th Electrochemical Society Meeting, 29.10.-03.11.2006, Cancun, Mexico
  • ECS Transactions 3(2006)7, 303-307

Publ.-Id: 9364 - Permalink


Development of a Superconducting RF Photoinjector
Teichert, J.;
A superconducting rf photo electron injector (SRF gun) is under development at the Forschungszentrum Rossendorf. The project aims at several issues: improvement of the beam quality for the ELBE superconducting electron linac, demonstration of feasibility of this gun type, investigation of critical components, and parameter studies for future application (BESSY-FEL, 4GLS). The design layout of the SRF photo-injector, the parameters of the superconducting cavity and the expected electron beam parameters are presented. The SRF gun has a 3+1/2-cell niobium cavity working at 1.3 MHz and will be operated at 2 K. The three full cells have TESLA-like shapes whereas the half-cell has an special form obtained from numerical optimization. In the half-cell a Cs2Te photocathode is situated which will be cooled by liquid nitrogen. In 2005, the main parts for He cryostat like vacuum vessel, cryogenic and magnetic shields were fabricated. Test benches for the cathode cooling system and the cavity tuner were assembled and the measurements performed. The photo cathode preparation lab has been arranged, and the diagnostic beam line has been designed. After delivery of the Nb cavity, its rf properties were measured. The cavity was tuned and its chemical treatment is started.
  • Lecture (Conference)
    DPG - Tagung, 27.03.2006, Dresden, Germany

Publ.-Id: 9363 - Permalink


Effect of elevated substrate temperature on growth, properties, and structure of indium tin oxide films prepared by reactive magnetron sputtering
Rogozin, A.; Vinnichenko, M.; Shevchenko, N.; Vazquez, L.; Mücklich, A.; Kreissig, U.; Yankov, R. A.; Kolitsch, A.; Möller, W.;
The paper correlates the growth and structure formation with the properties of indium-tin-oxide (ITO) films fabricated by pulsed reactive magnetron deposition onto amorphous substrates held at elevated temperatures ranging from RT to 510 °C. The evolution of the microstructure is consistent with the well-known structure zone model. The temperature dependence of the film texture is described with consideration of the interplay between the shadowing and surface diffusion processes. It is shown that deposition at elevated temperatures lowers the crystallization threshold and is more effective in reducing resistivity than the post-deposition vacuum annealing at comparable temperatures. The films grown at a substrate temperature of 400 and 510 °C have the lowest resistivity of 1.2*10^-4 Ohm•cm, the highest free electron density of 1.2 - 1.0*10^21 cm^-3, and mobility of 35 - 42 cm^2•V^-1•s^-1 while showing the strongest (222) texture with the largest grain size.
Keywords: indium-tin-oxide, reactive pulsed magnetron sputtering, electrical properties, texture
  • Journal of Materials Research 22(2007)8, 2319-2329

Publ.-Id: 9361 - Permalink


Multimodal electronic-vibronic spectra of luminescence in ion-implanted silica layers
Fitting, H.-J.; Salh, R.; Schmidt, B.;
Thermally oxidized SiO2 layers of 100 and 500 nm thickness have been implanted by oxygen and sulfur ions with a dose of 3x1016 and 5x1016 ions/cm2, respectively, leading to an atomic dopant fraction of about 4 at.% at the half depth of the SiO2 layers. The cathodoluminescence spectra of oxygen and sulfur implanted SiO2 layers show besides characteristic bands a sharp and intensive multimodal structure beginning in the green region at 500 nm over the yellow-red region extending to the near IR measured up to 820 nm. The energy step differences of the sublevels amount on average 120 meV and indicate vibration associated electronic states, probably of O2-interstitial molecules, as we could demonstrate by a respective configuration coordinate model.
Keywords: ion implantation, SiO2, CL-luminesence
  • Journal of Luminescence 122(2007)SI JAN-APR, 743-746

Publ.-Id: 9360 - Permalink


Sorption Data Bases ("PA ready"): Proposed next steps towards a data base
Brendler, V.; Kienzler, B.; Lützenkirchen, J.;
- wird nachgereicht
  • Invited lecture (Conferences)
    2nd Annual FUNMIG Workshop, 21.-23.11.2006, Stockholm, Sweden

Publ.-Id: 9358 - Permalink


Mechanistische Sorptionsmodelle - gegenwärtiger Stand und Perspektiven für die Langzeitsicherheitsanalyse
Brendler, V.;
- wird nachgereicht
  • Invited lecture (Conferences)
    Vortrag bei der GRS Braunschweig, 14.07.2006, Braunschweig, Germany

Publ.-Id: 9357 - Permalink


Grundlagen der geochemischen Modellierung
Brendler, V.;
- wird nachgereicht
  • Invited lecture (Conferences)
    Seminar am Dresdner Grundwasserforschungszentrum (DGFZ) e.V., 15.09.2006, Dresden, Germany

Publ.-Id: 9356 - Permalink


Verlässliche Daten, Modelle und Codes für die Geochemie
Brendler, V.;
- wird nachgereicht
  • Invited lecture (Conferences)
    Festkolloquium für PD Dr. M. Richter, 20.10.2006, Leipzig, Germany

Publ.-Id: 9355 - Permalink


Thermodynamische Datenbasis für das Nahfeld: aktueller Stand
Brendler, V.;
- wird nachgereicht
  • Invited lecture (Conferences)
    2. Fachgespräch zur Radionuklidmigration bei PTKA, 25.-26.10.2006, Karlsruhe, Germany

Publ.-Id: 9354 - Permalink


Overview of Current Thermodynamic Databases
Brendler, V.;
- wird nachgereicht
  • Invited lecture (Conferences)
    12th ISSP - International Symposium on Solubility Phenomena and Related Equilibrium Processes, 23.-28.07.2006, Freiberg, Germany

Publ.-Id: 9353 - Permalink


SiGe heterostructures-on-insulator produced by Ge+-ion implantation and subsequent hydrogen transfer
Tyschenko, I. E.; Cherkov, A. G.; Voelskow, M.; Popov, V. P.;
Strong decrease in the carrier mobility of the nanometer-thick silicon films imposes a limitation on the application of silicon-on-insulator (SOI) structures in the current silicon planar CMOS technology. The formation of SiGe-heterostructures-on-insulator (HOI) is a way to increase the carrier mobility in the nanometer-scale layers. In this work, we present the results on the interface mediated endotaxial (IME) growth of thin Ge film from the Ge+-ion implanted SiO2 layer of the SOI structure.
Keywords: SOI, implantation
  • Lecture (Conference)
    XII Gadest Conference 2007, 14.-19.10.2007, Erice, Italy
  • Solid State Phenomena 131-133(2008), 143-147

Publ.-Id: 9352 - Permalink


Crystallization of InSb phase near the bonding interface of silicon-on-insulator structure
Tyschenko, I. E.; Cherkov, A. G.; Voelskow, M.; Popov, V. P.;
Bonding interface of SOI structure may be an effective sink for impurity atoms because of higher concentration of vacancies and microvoids on the cleavage planes. The behaviour of ion-implanted Sb and In atoms near the bonding interface of SOI structures was investigated as a function of annealing temperature.
Keywords: SOI, implantation, Sb, In
  • Lecture (Conference)
    XII Gadest Conference 2007, 14.-19.10.2007, Erice, Italy
  • Solid State Phenomena 131-133(2007), 137-142

Publ.-Id: 9350 - Permalink


Process control and melt depth homogenization for SiC-on-Si structures during flash lamp annealing by carbon implantation
Smith, M. P.; Mcmahon, R. A.; Voelskow, M.; Skorupa, W.; Stoemenos, J.; Ferro, G.;
Flash lamp annealing in the millisecond regime of heteroepitaxial silicon carbide on silicon structures involves melting the silicon below the SiC layer, but the deep faceted nature of the liquid-solid interface leads to unacceptable surface roughness. This paper describes a method of controlling melting by implanting a high dose of carbon at a controlled depth below the Si/SiC interface, which significantly alters the melting characteristics of the silicon. This technology has also been applied to SiC and Si multilayer heterostructures. Results confirm the effectiveness of this approach 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 the onset of melting, maximum temperatures, and process windows for controlled liquid phase epitaxy.
Keywords: silicon carbide, ion implantation, flash lamp processing, liquid phase processing, modelling

Publ.-Id: 9349 - Permalink


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. M.; Skorupa, W.;
This work is a comparative study of the processes of charge trapping in silicon dioxide layers doped with different rare-earth impurities (Gd, Tb, Er) as well as with Ge. Diode structures incorporating such oxide layers exhibit efficient electroluminescence (EL) in the spectral range from UV to IR.
Ion implantation was performed over a wide dose range using doses chosen to provide impurity concentrations of 0.1 to 3 at. % with the implant profiles peaking in the middle of the oxide. Post-implantation anneals were carried out at different temperatures. An ITO layer was employed as the transparent gate electrode for the implanted SiO2/Si light emitting diodes (LEDs).
Charge trapping was studied using an electron injection technique at constant current regime in the range of 1013 to 1021 e/cm2 with simultaneous measurements of the EL intensity. High-frequency C/V characteristics were used to control the net charge in the oxides. The I/V characteristics and the EL intensity vs. applied voltage were also measured.
Analysis of the charge trapping and the variation of the EL intensity during electron injection shows that the current density range can be conveniently divided in three portions: (i) low injection level, where electron/hole capture at traps with a large capture cross-sections and low EL intensity occurs; (ii) medium injection level corresponding to the main operation mode of the LEDs (odd hole trapping depending on the injected current level is observed); and (iii) high injection level (electrical quenching of the EL, which correlates with electron capture at traps of extremely small capture cross-sections of about 10-21 cm2 takes place). The parameters of the hole and electron traps are determined.
The nature of specific electron hole trapping at the medium injection level in RE doped MOSLEDs is discussed. Mechanisms of EL quenching at the high injection level are proposed.
Keywords: chare trapping, electroluminescence, ion implantation, light emitting diodes, rare earths, germanium
  • Lecture (Conference)
    European Materials Research Society (EMRS) Spring Meeting, 29.05.-02.06.2006, Nizza, France

Publ.-Id: 9348 - Permalink


The effect of potassium and fluorine implantation on the electroluminescence stability in Gd and Tb implanted SiO2 layers
Prucnal, S.; Sun, J. M.; Reuther, H.; Skorupa, W.;
Metal-Oxide-Silicon-based light emitting diodes (MOSLEDs) with Gd and Tb implanted SiO2 layers exhibit strong ultra violet and green electroluminescence (EL) at 316 nm and 541 nm, respectively. If amorphous SiO2 is bombarded with energetic ions, various types of defects are created as a consequence of ion-solid interaction and annealing processes (oxygen deficiency centres (ODC), non-bridging oxygen hole centres (NBOHC), E’-centres, etc.) leading to charge trapping effects during electrical excitation. Elimination or neutralisation of such defects is very important from the viewpoint of electrical stability of MOSLEDs. It will be demonstrated that (i) an additional fluorine implant into SiO2:Gd and SiO2:Tb layers leads to a decrease of E’-centres and ODC´s improving the efficiency of the MOSLEDs; and (ii), an additional potassium implant produces positive ions leading to a compensation effect for the negatively charged electron traps and, hence, to an reduced quenching of the EL efficiency and increased MOSLED lifetime .
Keywords: MOSLEDs, rare earths, electroluminescence, ion implantation, fluorine, potassium, nonbridging oxygen hole center, oxygen deficiency center, E'-center
  • Poster
    European Materials Research Society (EMRS) Spring Meeting, 29.05.-02.06.2006, Nizza, Frankreich

Publ.-Id: 9347 - Permalink


Recent progress in efficient electroluminescence from silicon-based light emitting devices made by ion beam processing
Sun, J. M.; Prucnal, S.; Potfajova, J.; Skorupa, W.; Schmidt, B.; Mücklich, A.; Helm, M.; Rebohle, L.; Gebel, T.;
This report reviews our recent progress on efficient electroluminescence (EL) from silicon pn junctions and rare earth doped metal-oxide-semiconductor light emitting devices (MOSLEDs) in the infrared to ultraviolet range [1-3]. Silicon pn diodes prepared by boron implantation have shown efficient band edge EL with a high efficiency above 0.15% at room temperature. A detailed study has shown that the anomalous increase of the EL intensity with increasing temperature comes from the release of free carriers by thermal ionization of bound excitons. They are trapped around locally enhanced p-type doping spikes formed by boron clustering at dislocations or fabricated by selective diffusion of boron through a patterned SiO2 mask layer.
Efficient EL from Er, Tb, Gd doped MOSLEDs at 1535, 541 and 316 nm with an high quantum efficiency of 14, 16.5, and 5 %, respectively, has been demonstrated in our MOSLEDs, which is comparable to that of III-V semiconductor devices. The EL properties of efficiency, decay time, and excitation cross-section were studied concerning cross relaxation at concentrations from 0.25 to 9% and clustering of rare earth dopants at annealing temperatures from 800 to 1100°C. Improving of the device stability is achieved by using double-stacked gate oxide layers, charge compensation and elimination of defects in SiO2 layers.
[1] J. M. Sun, W. Skorupa, T. Dekorsy , and M. Helm, J. Appl. Phys. 97, 123513 (2005)
[2] J. M. Sun, W. Skorupa, T. Dekorsy, and M. Helm, Appl. Phys. Lett. 85, 3387 (2004).
[3] J. M. Sun, T. Dekorsy, W. Skorupa, B. Schmidt, A. Mücklich, and M. Helm, Phys. Rev. B 70, 155316 (2004).
Keywords: electroluminescence, ion implantation, MOSLED, pn junction,rare earths, doping spike, boron clustering, decay time
  • Invited lecture (Conferences)
    European Material Research Society(EMRS) Spring Meeting 2006, 29.05.-02.06.2006, Nizza, France

Publ.-Id: 9346 - Permalink


Electrical activation of implantation-induced defects in ZnO by flash-annealing
Børseth, T. M.; Christensen, J. S.; Anwand, W.; Skorupa, W.; Svensson, B. G.; Kuznetsov, A. Y.;
In this project we study diffusion and electrical activation in lithium and helium implanted ZnO single crystal wafers with high resistivity using secondary ion mass spectrometry (SIMS), scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM), respectively. Li+ ions were implanted with an energy of 837 keV at a dose of 2x1015 cm-2, and He+ were implanted with an energy of 683 keV at a dose of 6x1015 cm-2 to ensure similar implantation depths and damage productions. The samples were then annealed using short 20 ms light flashes corresponding to temperatures of 900°C, 1200°C and 1400°C. After each annealing step the samples were characterized with SSRM/SCM and SIMS. In as-implanted samples, no changes in the initially high resistivity are observed in neither the Li- nor the He-implanted samples but after the thermal treatments a substantial decrease is observed in both sets of samples. This resistivity drop is most likely related to electrical activation of shallow implantation-induced defects or deactivation of compensating defects/impurities, as He in principle should be electrically inactive in any solid state material. No significant redistribution of the implanted ions is observed.
Keywords: zinc oxide. ion implantation, flash lamp annealing, electrical activation, SIMS, scanning spreading resistance microscopy, scanning capacitance microscopy
  • Lecture (Conference)
    15, Int. Conf. on Ion Beam Modification of Materials, 18.-22.09.2006, Catania, Italy

Publ.-Id: 9345 - Permalink


Formation of germanium shallow junction by Flash annealing
Satta, A.; D’Amore, A.; Simoen, E.; Anwand, W.; Skorupa, W.; Clarysse, T.; van Daele, B.; Janssens, T.;
We have investigated flash-lamp annealing (FLA) of germanium wafers doped with phosphorous and boron introduced in the crystal by ion implantation. Annealing was performed by using pre-heating at 400-450 oC in a conventional rapid thermal processing (RTP) unit and a fast (3-20 ms) FLA annealing at 800 oC or 900 oC. Diffusion of P is suppressed during the 800oC-20 ms FLA annealing, while concentration-enhanced diffusion occurs upon 900oC FLA anneals. At this higher temperature the FLA pulse time becomes a fundamental parameter, since the shortest FLA pulse (3 ms) causes less junction deepening and less P dose loss as compared to the longest (20 ms) pulse. Importantly, P activation seems to be enhanced by the FLA process.
The FLA process applied to B-doped pre-amorphized Ge layers does not show advantages as compared to a RTP conventional annealing. B diffusion and activation behavior are indeed similar for the millisecond annealing approach and for a conventional RTP combined with a solid phase epitaxial regrowth of the doped Ge layer.
In summary, the FLA technique holds a potential for the development of P shallow junctions in germanium wafers. However, junction stability following the FLA process is a concern and needs to be further investigated.
Keywords: ion implantation, germanium, flash lamp annealing, diffusion, activation, RTP

Publ.-Id: 9344 - Permalink


Germanium shallow junction formation by flash annealing
Satta, A.; D'Amore, A.; Simoen, E.; Janssens, T.; Clarysse, T.; Anwand, W.; Skorupa, W.;
We have investigated flash-lamp annealing (FLA) of germanium wafers doped with phosphorous and boron introduced in the Ge crystal by ion implantation. Annealing was performed by using pre-heating at 400-450 oC in a conventional rapid thermal processing (RTP) unit and a fast (3-20 ms) FLA annealing at 800 oC or 900 oC. Diffusion of P is suppressed during the 800oC-20 ms FLA annealing, while concentration-enhanced diffusion occurs upon 900oC FLA anneals. At this higher temperature the FLA pulse time becomes a fundamental parameter, since the shortest FLA pulse (3 ms) causes less junction deepening and less P dose loss as compared to the longest (20 ms) pulse. Importantly, P activation seems to be enhanced by the FLA process. The FLA process applied to B-doped pre-amorphized Ge layers does not show advantages as compared to a RTP conventional annealing. B diffusion and activation behavior are indeed similar for the millisecond annealing approach and for a conventional RTP combined with a solid phase epitaxial regrowth of the doped Ge layer.
In summary, the FLA technique holds a potential for the development of P shallow junctions in germanium wafers. However, junction stability following the FLA process is a concern and needs to be further investigated.
Keywords: germanium, ion implantation, flash lamp annealing, RTP, diffusion, electrical activation
  • Lecture (Conference)
    15. International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Catania, Italy

Publ.-Id: 9343 - Permalink


Flash lamp processing in the millisecond-range for Metal-Oxide-Silicon-based light emitting diodes
Prucnal, S.; Sun, J. M.; Muecklich, A.; Skorupa, W.;
The influence of different annealing processes (furnace annealing FA, rapid thermal annealing RTA and flash lamp annealing FLA) on the electroluminescence intensity, electric stability and point defect creation in SiO2 layers containing Gd atoms was investigated. The samples were annealed at different temperatures (from 800 to 10000C with the step 1000C for FA and from 10000C to 12000C with the step 500C for RTA and FLA). In the case of the peak at 316 nm which corresponds to Gd3+ the strongest EL intensity was observed from the sample annealed at 11000C after FLA. Increasing of the annealing temperature leads to a decreasing of the luminescence for each of annealing methods. The same effect was observed after increasing of the annealing time. In the case of defect formation under different annealing conditions an inverse situation was observed. Increasing of the annealing temperature and annealing time leads to an increase of the EL from oxygen deficiency centers (ODCs) An increase of the luminescence from defects at a simultaneous decrease of the luminescence from Gd at 316 nm can be explained by Gd-nanocluster creation in a-SiO2 during the annealing process.
Keywords: flash lamp annealing, silicon-based light emission, electroluminescence, ion implantation
  • Lecture (Conference)
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA

Publ.-Id: 9342 - Permalink


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

Publ.-Id: 9341 - Permalink


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

Publ.-Id: 9340 - Permalink


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

Publ.-Id: 9339 - Permalink


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

Publ.-Id: 9338 - Permalink


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

Publ.-Id: 9337 - Permalink


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

Publ.-Id: 9336 - Permalink


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

Publ.-Id: 9335 - Permalink


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

Publ.-Id: 9334 - Permalink


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

Publ.-Id: 9333 - Permalink


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)

Publ.-Id: 9332 - Permalink


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

Publ.-Id: 9331 - Permalink


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

Publ.-Id: 9330 - Permalink


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

Publ.-Id: 9329 - Permalink


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

Publ.-Id: 9328 - Permalink


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

Publ.-Id: 9327 - Permalink


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

Publ.-Id: 9326 - Permalink


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

Publ.-Id: 9325 - Permalink


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

Publ.-Id: 9324 - Permalink


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

Publ.-Id: 9323 - Permalink


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

Publ.-Id: 9322 - Permalink


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

Publ.-Id: 9321 - Permalink


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

Publ.-Id: 9320 - Permalink


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

Publ.-Id: 9318 - Permalink


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

Publ.-Id: 9317 - Permalink


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

Publ.-Id: 9316 - Permalink


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

Publ.-Id: 9315 - Permalink


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

Publ.-Id: 9314 - Permalink


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

Publ.-Id: 9313 - Permalink


Ion induced stress release – by thermal or collisional spikes?
Möller, W.;
  • Lecture (others)
    Thin Film Workshop, 17062006, Linköping, Sweden

Publ.-Id: 9312 - Permalink


Ion irradiation for generation and control of nanostructures
Möller, W.;
  • Lecture (others)
    Seminar, 10.01.06, Prag, CZ

Publ.-Id: 9311 - Permalink


Kontinuumsgleichungen zur Beschreibung ionenstrahlinduzierter Nanostrukturen
Facsko, S.;
  • Lecture (Conference)
    Workshop "Ionenstrahlphysik und Nanotechnologie", 16.05.2006, Berlin, Deutschland

Publ.-Id: 9310 - Permalink


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

Publ.-Id: 9309 - Permalink


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

Publ.-Id: 9308 - Permalink


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

Publ.-Id: 9307 - Permalink


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

Publ.-Id: 9306 - Permalink


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

Publ.-Id: 9305 - Permalink


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

Publ.-Id: 9304 - Permalink


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

Publ.-Id: 9303 - Permalink


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

Publ.-Id: 9302 - Permalink


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

Publ.-Id: 9301 - Permalink


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

Publ.-Id: 9300 - Permalink


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

Publ.-Id: 9299 - Permalink


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

Publ.-Id: 9298 - Permalink


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

Publ.-Id: 9297 - Permalink


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

Publ.-Id: 9296 - Permalink


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

Publ.-Id: 9295 - Permalink


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

Publ.-Id: 9294 - Permalink


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

Publ.-Id: 9293 - Permalink


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

Publ.-Id: 9292 - Permalink


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

Publ.-Id: 9291 - Permalink


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

Publ.-Id: 9290 - Permalink


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

Publ.-Id: 9289 - Permalink


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

Publ.-Id: 9288 - Permalink


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

Publ.-Id: 9287 - Permalink


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

Publ.-Id: 9285 - Permalink


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