Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Approved and published publications
Only approved publications

40533 Publications

Rare earth ion implantation for silicon based light emission: From infrared to ultraviolet (invited)

Skorupa, W.; Sun, J. M.; Prucnal, S.; Rebohle, L.; Gebel, T.; Nazarov, A. N.; Osiyuk, I. N.; Dekorsy, T.; Helm, M.

Using ion implantation different rare earth luminescent centers (Gd3+, Tb3+, Eu3+, Ce3+, Tm3+, Er3+) were incorporated into the silicon dioxide layer of a purpose-designed Metal Oxide Silicon (MOS) capacitor with advanced electrical performance, further called a MOS-light emitting device (MOSLED). The silicon dioxide layer did not contain silicon nanoclusters. Efficient electroluminescence was obtained from UV to infrared with a transparent top electrode made of indium-tin oxide. The electroluminescence properties were studied with respect to the luminescence spectra, decay time, impact excitation, cross relaxation (Tb3+), and power efficiency. Top values of the efficiency of 0.3 % corresponding to external quantum efficiencies well above the percent range were reached. The electrical properties of these devices such as current-voltage and charge trapping characteristics, were also evaluated. Moreover, we demonstrate photo- and electroluminescence in correlation to charge trapping characteristics for Er-rich MOSLEDs with a varying silicon cluster content. Finally, application aspects to the field of biosensing will be discussed.

Keywords: Silicon-based light emission; Ion implantation; Rare earth atoms

  • Contribution to proceedings
    MRS Spring Meeting, 29.03.2005, San Francisco, USA
    Materials Research Society Symposium Proceedings 866(2005) V4.1.1/FF4.1.1, V4.1.1/FF4
  • Invited lecture (Conferences)
    Materials Research Society Spring Meeting, 29.03.-01.04.2005, San Francisco, USA

Publ.-Id: 8187

Microarrays of silicon-based light emitters for novel biosensor and lab-on-a-chip applications

Rebohle, L.; Gebel, T.; Yankov, R.; Trautmann, T.; Skorupa, W.; Sun, J. M.; Gauglitz, G.; Frank, R.

We have demonstrated intense violet electroluminescence (EL) from thermally-grown SiO2 films containing Ge nanocrystals produced by ion beam synthesis. An outline is given of the electrical and optical characteristics of ITO/SiO2/Al light-emitting devices incorporating Ge nanocluster-rich oxide films. Optimization schemes based on the use of local oxidation of Si (LOCOS) have been developed and tested successfully. Arrays of 4 × 6 light-emitting devices with a diameter of 300 μm and spacing of 500 μm between the adjacent devices have been formed using standard lithography patterning. Bioanalyses have been carried out following fluorescent-based detection procedures. As distinct from the standard case of diagnostics in which the light source is typically a laser and the necessary spatial resolution is provided by a CCD camera, our light sources are small enough to immediately ensure high resolution while permitting their light emission to be detected by single inexpensive Si diodes. The relevance of the all-Si light sources to microarray, miniaturized sensor and lab-on-a-chip systems for point-of-care diagnostics is discussed. Finally, first EL spectra of Si-based light sources containing Tb are shown.

  • Optical Materials 27(2005), 1055

Publ.-Id: 8186

Nucleation control in FLASIC assisted short time liquid phase epitaxy by melt modification

Pezoldt, J.; Polychroniadis, E.; Stauden, T.; Ecke, G.; Chassagne, T.; Vennegues, P.; Leycuras, A.; Panknin, D.; Stoemenos, J.; Skorupa, W.

The influence of the different additions to the melt on the nucleation behavior during short time flash lamp processing was investigated. It was observed that germanium and carbon additions to the silicone melt led to an increase of the mass transport to the growing surface and to an increase of the nuclei size. In the case of germanium additions to the silicon melt an incorporation of germanium in the silicon substrate was observed.

  • Materials Science Forum 483-487(2005), 213-216

Publ.-Id: 8185

The effect of radio-frequency plasma treatment on the electroluminescent properties of violet light-emitting germanium implanted metal-oxide-semiconductor structures

Nazarov, A. N.; Vovk, J. N.; Osiyuk, I. N.; Tkachenko, A. S.; Tyagulskii, I. P.; Lysenko, V. S.; Gebel, T.; Rebohle, L.; Skorupa, W.; Yankov, R. A.

We have studied the effect of plasma treatment on both the electroluminescent (EL) properties of Ge-implanted light-emitting metal-oxide–silicon (MOS) devices and the charge trapping processes occurring therein. Under optimum conditions of plasma treatment, an appreciable increase in the device lifetime has been observed while maintaining unchanged the intensity of the light emission in the violet portion of the spectrum. These phenomena are believed to be associated with recovery of the oxide network resulting from a relief of internal mechanical stresses, and bond rearrangement that leads to a decrease in generation efficiency of electron traps, which are responsible for the device degradation.

  • Materials Science and Engineering B 124(2005), 458

Publ.-Id: 8184

Charge trapping in SiO2 layers implanted with rare earths and Ge ions

Prucnal, S.; Sun, J. M.; Cheng, X.; Skorupa, W.

Metal-oxide-silicon (MOS) structures containing different rare earth and germanium ions exhibit strong luminescence from 300 to 1540 nm.
It is very interesting from the viewpoint of the formation of silicon-based light-emitting devices. The different behaviour of charge trapping in Ge, Tb, Gd and Eu enriched SiO2 layer was studied under constant current regime. High-frequency (100 kHz) capacitors-voltage (C-V) characteristics exhibit a strong dependence of the charge trapping on the type of elements implanted into the SiO2 layer. The increase of the Eu concentration up to 3 percent leads to a shift of the C-V characteristics towards negative voltage in comparison with fresh samples, which reveals positive charge trapping. The capture cross section and the concentration of the different type of charge traps can also be strongly influenced by changing the annealing temperature and annealing time.

Keywords: charge trapping; Ge; rare earth

  • Lecture (Conference)
    Berlin 2005, "Physik seit Einstein", 04.03.-09.03.2005 Hinweise für Tagungsteilnehmer und Tagesübersicht, 04.-09.03.2005, Berlin, Germany

Publ.-Id: 8183

Charge trapping in SiO2 layers implanted with rare earth and Ge ions

Prucnal, S.; Sun, J.; Skorupa, W.; Nazarov, A.; Osiyuk, I.; Tyagulski, I.; Lysenko, V.

Metal-oxide-silicon (MOS) structures containing different rare earth and germanium ions exhibit strong luminescence from 300-1540 nm. This emission is very interesting from the viewpoint of the silicon-based light-emitting devices formation. Charge trapping behaviour in Ge and rare earth (Ce, Eu, Gd, Tb, Er and Tm) enriched SiO2 during high field electron injection corresponding to operation of the light-emission devices has been studied. Employing of constant current injection regime and high frequency C-V characteristics it was shown that embedment of rare earth impurities into dioxide matrix results in formation of similar system of charge traps with following capture cross section 2..3e-15 cm2 for electron and >1e-14 cm2 for holes. In various rare earths doping the amphoteric charge traps with distributed capture cross section in range from 1e-15 to 1e-17 cm2 is observed. Observed system of the traps is considerable different from one in the Ge implanted structures. For distributed traps an increase of injected current into the dielectric results in increase to positive charge trapping. Model of charge trapping in the defect shell located around rare earth inclusions inside of dioxide matrix is discussed.

Keywords: charge trapping; rare earth; EL

  • Poster
    Rare earth doped photonic materials, 31.05.-03.06.2005, Strasbourg, France

Publ.-Id: 8182

Miniaturised arrays of light-sources based on Silicon technology: A promising approach for novel sensors and Lab-on-a-Chip Systems

Gebel, T.; Rebohle, L.; Trautmann, T.; Yankov, R. A.; Skorupa, W.; Gauglitz, G.; Frank, R.

The recent progress in the fabrication of silicon-based light sources with a view to their application in miniaturized sensor and Lab-on-a-Chip systems is described. The core of an all-Si light emitting device is a SiO2 film containing ion-beam-synthesized nanoclusters. A brief account is given of the structural, electrical and optical properties of such nanocluster-rich oxide films. A notable feature of the devices so produced is their ability to exhibit intense UV, violet-to-blue or green electroluminescence depending on the ion-implanted species (rare earth elements or group-IV elements like Ge, Sn and Si). The fabrication of the devices is carried out in standard CMOS technology.
The relevance of the all-Si light sources to microarray and miniaturized sensor systems for point-of-care diagnostics and analysis is outlined.

Keywords: integrated silicon-based light sources; nanoclusters; microarrays; sensor systems

  • Contribution to proceedings
    Sensor 2005, 10.05.2005, Nürnberg, Germany
    Conference Proceedings Vol. 1, B1.4, 125-129

Publ.-Id: 8181

Optical and microstructural properties of doubly Ge–Si implanted SiO2 layers

Prucnala, S.; Cheng, X. Q.; Sun, J. M.; Kögler, R.; Zuk, J.; Skorupa, W.

Photoluminescence (PL) properties of 500 nm thick SiO2 films on Si substrate subjected to combined Ge–Si implantations have been studied: Sequentially 400 keV Ge+ and 200 keV Si+ ions were implanted into SiO2 to concentrations of 3% and 1–10%, respectively. As calculated using the SRIM 2000 code, under these conditions depth profiles of implanted species should be contained in the region 100–400 nm below the oxide surface. After the implantation, samples were annealed at temperatures ranging from 700 to 1100 °C, in order to obtain Si and Ge nanoclusters. A weak near UV luminescence peak at a wavelength of about 315 nm, a strong blue band at 400 nm and a near-infrared 780 nm band were observed for thus prepared samples. The optical emission was stable and reproducible. Diffusion of germanium towards the Si/SiO2 interface during the annealing process is suppressed by silicon ions additionally introduced into SiO2.

Keywords: Germanium; Silicon; Silicon dioxide; Double ion implantation; Photoluminescence

  • Vacuum 78(2005)2-4, 693-697

Publ.-Id: 8180

Microstructural characterization of 3C-SiC thin films grown by flash lamp induced liquid phase epitaxy

Ferro, G.; Panknin, D.; Polychroniadis, E. K.; Monteil, Y.; Skorupa, W.; Stoemenos, J.

In the so called FLASiC process, due to the transparency of the 3C-SiC, the irradiated energy is selectively absorbed at the SiC/Si interface where the most defected part of the 3C-SiC film exists. The Si at the interface melts up to a depth depending on the energy density of the flash pulse. Thus the lower part of the SiC film is dissolved into the melted Si substrate, then during the solidification phase separation occurs and the SiC is recrystallized forming high quality 3C-SiC trapezoidal pyramids (TPs) on the backside of the non-dissolved SiC film. 1. However due to significant Si mass transport the Si-surface is seriously undulated. Also the SiC film is mainly improved from the backside, which cannot be used for further epitaxial growth. For these reasons an improved method was developed with the aim, to (i) minimize the undulations of the Si substrate, and to (ii) improve the quality of the SiC film at the front interface. This method involves the deposition of a silicon overlayer (SOL) onto the SiC, followed by an additional SiC layer on the SOL. The new method is called i-FLASiC where the “i” stands for “inverse”.

  • Materials Science Forum 483-487(2005), 295

Publ.-Id: 8179

Photoluminescence of Er-doped SiO2 layers containing Si nanoclusters using dual ion implantation and annealing

Cheng, X. Q.; Sun, J. M.; Kögler, R.; Skorupa, W.; Möller, W.; Prucnal, S.

Er-doped SiO2 layers containing silicon nanoclusters were obtained by dual ion implantation and subsequent annealing. All the double beam implantations of Er and Si ion were sequentially and simultaneously performed at 900 and 200 keV to doses of 1.2×1015 and 8×1016/cm2, respectively. After these implantations, the samples were annealed at a temperature range of 800–1100 °C for 60 min to form Si nanoclusters in SiO2 layers. Er concentration and distribution in the matrix was confirmed by Rutherford backscattering spectrometry. Point defects induced by ion implantation were reduced and finally removed during increasing annealing temperature. Moreover, the simultaneous implantation creates more defects in the matrix than the sequential implantation. Interestingly, a photoluminescence of Er3+ ions excitation with a typical band at around 1.54 μm could be efficiently enhanced once Si nanoclusters form in SiO2 layers, which suggests an evident energy transfer process from Si nanoclusters to Er3+ ions.

Keywords: Erbium; Photoluminescence; Si nanoclusters; Dual ion implantation

  • Vacuum 78(2005)2-4, 667-671

Publ.-Id: 8178

Electromagnetic control of separated flows using periodic excitation with different wave forms

Cierpka, C.; Weier, T.; Gerbeth, G.

Time periodic Lorentz forces have been used to influence the separated flow on an inclined flat plate in deep stall at a Reynolds number of 10000. The influence of the control parameters effective momentum coefficient and excitation frequency as well as excitation wave form is discussed based on phase averaged PIV measurements. As expected, control authority depends strongly on momentum input and excitation frequency, but effects of the excitation wave form can be shown as well.

Keywords: flow control; Lorentz force; separation control

  • Invited lecture (Conferences)
    Conference on Active Flow Control 2006, 27.-29.09.2006, Berlin, Germany
  • Contribution to external collection
    King, Rudibert: Active Flow Control, Notes on Numerical Fluid Mechanics and Multidisciplinary Design (NNFM), Vol. 95, Berlin: Springer, 2007, 978-3-540-71438-5, 27-41

Publ.-Id: 8177

Lack of efficacy of imatinib in a patient with metastatic Leydig cell tumor

Froehner, M.; Beuthien-Baumann, B.; Dittert, D.-D.; Schuler, U.; Wirth, M. P.

Imatinib is a tyrosine kinase inhibitor with activity in gastrointestinal stromal tumor and a variety of other solid and hematological malignancies. Studies in vitro and in a mouse model suggested that the imatinib might also be active in malignant Leydig cell tumor. We report on the—to our knowledge—first treatment experiment with imatinib in a patient with metastatic Leydig cell tumor. Unfortunately, the tumor progressed during treatment.

Keywords: Imatinib; Leydig cell tumor; Testicular cancer; Metastases; Positron emission tomography

Publ.-Id: 8176

Defect engineering for ion beam synthesis of SOI structures

Kögler, R.; Mücklich, A.; Reuther, H.; Krecar, D.; Hutter, H.; Skorupa, W.

The simultaneous dual ipn implantation was recently shown to be an effective method to achieve better results from ion beam synthesis of SiC. The "in situ" generation of vacancies during implantation accomodates volume expansion due to phase formation and in this way increases the amount of synthesized material.
In this study different methods of introduction of vacancies are compared for the ion beam synthesis of a buried layer of SiO2 in Si (SOI structure).

Keywords: Ion beam synthesis; silicon on insulator; SOI; defect engineering

  • Poster
    E- MRS Rpring Meeting, 31.05.-03.06.2005, Straßbourg, Frankreich

Publ.-Id: 8175

Speciation of U(VI) in natural systems by advanced EXAFS analysis II. Application of MCTFA to solve the spatial structure of U(VI) sorption complexes on ferrihydrite

Ulrich, K.-U.; Rossberg, A.; Scheinost, A.

The motivation of this study was to investigate the binding structure of uranium attached to mine water colloids and sediments gained from an abandoned uranium mine currently being flooded. U LIII-edge EXAFS spectroscopy was applied to identify the oxidation state and the atomic coordination sphere of bound uranium. First results from shell fitting showed that U(VI) was coordinated by a mononuclear, inner-sphere complex to the edge of an Fe(O,OH)6 octahedron originating from 2-line ferrihydrite (Fh) which predominated the bulk solid phase. This is in accordance with [1].
However, a small spectral contribution at R+Δ ~2.4 Å in the Fourier transform (FT) of the EXAFS could not be explained. Therefore, synthetic U(VI)-Fh coprecipitates were prepared under varied chemical conditions in order to step by step rule out possible contributions of other constituents in the samples such as sulfur, silicon, and carbon. Interestingly, the FT peak was independent of the preparation conditions, i.e. it also appeared under CO2-free atmosphere and in absence of other ligands. Hence Monte Carlo Target Transformation Factor Analysis (MCTFA) [2] was employed to find a structural model consistent with both spectroscopic and experimental data. It was found that the FT peak originates from a third O-atom of the Fe octahedron at a radial distance of 2.84 Å which consistently explains the other atomic distances of the sorption complex calculated from the experimental data. This 3D topology is presented and discussed in comparison with the complex structure of U(VI) sorbed onto aluminum hydroxide gel.
By another set of sorption experiments the influence of carbonate was examined at different pH conditions under ambient air (pCO2 = 35.5 Pa) and increased CO2 atmosphere (pCO2 = 1014 Pa). It was shown by iterative factor analysis that two eigenvectors are sufficient to fully reproduce the measured spectra. One is given by the aforementioned binary complex structure, the other is represented by the UO2(CO3)34- aqueous complex suggesting accessory outer-sphere complexation of uranylcarbonate ions on ferrihydrite at elevated carbonate concentrations. Further research is needed to understand the complex topology in detail and to explain the role of steric influences by neighboring Fe octahedra of the adsorbent.

[1] Waite, T.D. et al. (1994) Geochim. Cosmochim. Acta 58, 5465-5478.
[2] Rossberg, A. et al. (2005) Anal. and Bioanal. Chem. 383, 56-66.

  • Lecture (Conference)
    ACTINET Kick-off Meeting, 13.-14.02.2006, Grenoble, France

Publ.-Id: 8174

Excess vacancies in SiGe

Kögler, R.

Experimental results on ion implantation into SiGe show a very high content of residual vacancy defects after annealing. On the other hand theory predicts a decreasing excess vacancy production in SiGe with increasing Ge content. The contribution adresses this problem.

Keywords: ion implantation; defects; SiGe; Si

  • Lecture (Conference)
    Germanium Workshop, 01.-02.12.2005, Brüssel, Belgien

Publ.-Id: 8173

X-ray investigations on NiMn films after ion beam irradiation

Cantelli, V.; von Borany, J.; Grenzer, J.

Magnetron sputtered film stacks of 5nm Ta/50(15)nm NiMn/20nm Fe19Ni81 /5nm Ta deposited at Si/SiO2 substrates were subsequently irradiated with He+ ions (30 keV, 1e15 - 3e16 cm-2). Using synchrotron X-ray diffraction and reflectivity, the transition from the paramagnetic NiMn phase to the chemically ordered, antiferromagnetic L10 phase during annealing was studied. The transformation to a dominating L10 ordered NiMn film takes place between 300-400°C irrespective of the irradiation. Ion irradiation at low fluences offers beneficial effects with respect to a reduction of the mosaicity for both, the NiMn and the permalloy film, and a smoothening of internal interfaces.

Keywords: magnetron sputtering; magnetic films; L10 ordering; ion irradiation

  • Lecture (Conference)
    6th Autumn School on X-ray Scattering from Surfaces and Thin Layers, 18.-21.09.2005, Smolenice, Slovakia

Publ.-Id: 8172

Zerstörungsfreie Charakterisierung modifizierter Glasoberflächen

Neelmeijer, C.

Die Kombination PIXE-RBS am externen Protonenstrahl wurde genutzt, um die Ursache einer ungeklärten Schichtbildung auf der Oberfläche eines Kirchenfensters von St. Marien in Rostock zu klären. Die zerstörungsfreien Analysen gaben den Hinweis, dass der gesuchte Effekt durch Wettersteinbildung erklärt werden kann, die infolge Abschattung durch Fassung des Glases in Bleiruten verzögert ablgelaufen ist.

Keywords: glass analysis; layer analysis; nondestructive analysis; external proton beam; PIXE; RBS

  • Contribution to external collection
    F. Martin: Glasmalerein in den Kirchen St. Jacobi, Greifswald, St. Marien und St. Nikolai, Rostock, Potsdam, Leipzig: Brandenburgische Akademie der Wissenschaften, 2005, 3-361-00594-9, 138-143

Publ.-Id: 8171

Master Curve testing on WWER-440 reactor pressure vessel steels

Viehrig, H.-W.; Murasov, M.

The Master Curve (MC) approach used to measure the transition temperature, T0, was standardized first-time in the ASTM Standard Test Method E1921 in 1997. The basic MC approach for analysis of fracture test results is intended for macroscopically homogeneous steels with a body centred cubic (ferritic) structure only. In reality, due to the manufacturing process, the steels in question are seldom fully macroscopically homogeneous.
Charpy size SE(B) specimens of base and weld metal from the WWER-440 Greifswald Unit 8 RPV were tested according to the ASTM test standard E1921-05. The measured fracture toughness values at brittle failure (KJc) of the specimen show a large scatter. In general the KJc values of the RPV weld and base metal follow the trend of the MC. For two base metals more than 5% of the KJc values lie below the 5% fracture probability line. It is therefore suspected that the investigated WWER-440 RPV base material is macroscopically inhomogeneous. In this paper, two recent extensions of the MC for inhomogeneous material are applied on these fracture toughness data and the nature of inhomogeneity was investigated.

Keywords: reactor pressure vessel steel; fracture toughness; Master Curve approach; inhomogeneous material; random inhomogeneity; maximum likelihood procedure; SINTAP procedure

  • Lecture (Conference)
    ASME Pressure Vessels and Piping Conference/ICPVT-11, 23.-27.07.2006, Vancouver, British Columbia, Canada,

Publ.-Id: 8170

On the nature of the coherent artifact

Lebedev, M. V.; Misochko, O. V.; Dekorsy, T.; Georgiev, N.

The coherent interaction of femtosecond laser pulses in the pump–probe regime has been experimentally studied in the time domain by monitoring light reflection from a tellurium single crystal. The optical response of the probed medium exhibits periodic variations at a frequency equal to that of the exciting laser radiation. Experimental dependences of the observed "coherent artifact" on the pump/probe intensity ratio, the number of accumulated pulses, and the mutual orientation of the polarization vectors of electromagnetic fields and the crystallographic axes are well described by the proposed phenomenological model.

  • Journal of Experimental and Theoretical Physics 100(2005), 272

Publ.-Id: 8169

InAsSb/GaAs hetero-epitaxial crystals studied by cyclotron resonance measurements

Drachenko, O.; Bansal, B.; Rylkov, V. V.; Galibert, J.; Dixit, V. K.; Leotin, J.

In this paper we present a compact terahertz cyclotron resonance (CR) spectrometer based on a GaAs/AlGaAs quantum cascade laser. We demonstrate high reproducibility as well as high precision in order of ~1% in the position of CR absorption and ~10% in amplitude. The spectrometer is, finally, used for measurements of InAsxSb1-x alloys with As concentration ranged between 0 and 6%.

  • Lecture (Conference)
    12-th International Conference on Narrow Gap Semiconductors, 03.-07.07.2005, Toulouse, France
  • Contribution to proceedings
    12-th International Conference on Narrow Gap Semiconductors, 03.-07.07.2005, Toulouse, France
    Proceedings of the 12th International Conference on Narrow Gap Semiconductors, Part II, 143-148

Publ.-Id: 8168

Predictions on ion-assisted synthesis of functional 1D-nanostructures using atomistic computer simulations

Röntzsch, L.; Heinig, K.-H.

Nanowires (NWs) and chains of nanocrystals (NCs) embedded in dielectrics or semiconductors are intensively studied for applications in photonics and nanoelectronics. CoSi2 NWs and NC chains are of particular interest for photonic functionalities of system-on-a-chip architectures because of their full CMOS compatibility, the low damping of surface plasmons at the CoSi2-Si interface, and the transparency of Si at the plasmon frequency. Here, we present predictions of atomistic computer simulations which describe the ion beam synthesis of CoSi2 NWs in Si and their thermally activated decay into chains of CoSi2 NCs. The simulations on focused ion beam (FIB) Co implantation is based on the binary collision codes TRIDYN and TRIM incorporating a convolution over the few tens of nanometer beam profile. The resulting 3D implantation profile serves as input for kinetic lattice Monte-Carlo simulations by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are predicted. From an evolutionary viewpoint, NW synthesis proceeds on a shorter time scale than its decay. The NW decay into a NC chain (“Rayleigh instability”) is driven by the minimization of interfacial free energy. Moreover, we demonstrate that the orientation of the Co implantation profile to the single crystalline Si matrix strongly influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the coherent CoSi2(111)/Si(111) interface, driving faceting forces may occur which accelerate the NW decay into a NC chain for FIB implantation not aligned with the Si-[110] orientation. Thus, intentional misalignment between the focused Co ion beam and the Si substrate is suggested as way to a controlled decay of the ion beam synthesized CoSi2 NW into a chain of monodisperse and equidistant CoSi2 NCs.

Keywords: Monte Carlo simulation; nanowire; CoSi2

  • Poster
    VEIT Summer School, 12.-16.09.2005, Sunny Beach, Bulgaria

Publ.-Id: 8167

Reaction pathways of ion beam synthesis and stability of monocrystalline nanowires

Röntzsch, L.; Heinig, K.-H.

We present results of atomistic computer simulations which predict the reaction pathways of the ion beam synthesis of single-crystalline nanowires embedded in a matrix and the disintegration of nanowires into a chain of nanoparticles which is driven by anisotropic surface energies.

Keywords: Monte Carlo; nanowire

  • Poster
    SEMINANO Conference, 10.-12.09.2005, Budapest, Hungary

Publ.-Id: 8166

Real-time in-situ analysis of target poisoning during reactive magnetron sputtering by nuclear reaction analysis and energy resolved mass spectroscopy

Güttler, D.; Abendroth, B.; Grötzschel, R.; Möller, W.

The effect of target poisoning is commonly observed in reactive magnetron sputtering, where a metallic target is sputtered in reactive gas atmosphere. This phenomenon can be described quite well in terms of sputter rate, reactive gas pressure and pumping speed, however the details of the processes on the target are not yet understood. In this work, an experimental setup is presented that combines energy resolved mass spectroscopy with quantitative in situ nuclear reaction analysis (NRA) of the reactive species target coverage. By adjusting the position of the magnetron, locally resolved information is obtained across the target surface. Experiments have been performed for the reactive deposition of TiN in an Ar/N2 gas mixture at varying process parameters, with special emphasis on the transition from metallic to poisoned target mode.
In the centre of the race track the nitrogen coverage is significantly smaller than on the remaining part of the target surface. The maximum amount of retained nitrogen significantly exceeds one adsorbed monolayer, which is attributed to nitrogen ion implantation and recoil implantation of adsorbed nitrogen.
The energy distribution of the neutral species is clearly composed from particles originating from the gas atmosphere and sputtered particles from the magnetron target. Significant differences in the energy distribution of the sputtered atoms are observed between the centre and the erosion zone of the target. The ratio of sputtered N/Ti atoms reflects characteristically the metallic or compound mode of operation.

Keywords: magnetron sputtering Titanium Nitride target poisoning NRA mass spectroscopy

  • Lecture (Conference)
    Tenth International Conference on Plasma Surface Engineering, 11.-15.09.2006, Garmisch, Deutschland

Publ.-Id: 8165

Ion irradiation through SiO2-Si interfaces: TEM study of self-organized Si nanocrystals applicable in nonvolatile memories

Röntzsch, L.; Heinig, K.-H.; Schmidt, B.

In recent years, immense effort has been devoted to the synthesis of Si nanocrystals (NCs) for multi-dot floating-gate MOSFETs. To assure optimum memory device characteristics, the Si NCs should be equal in size and equally distant from the transistor channel. This desired Si NCs structure can be fabricated in a two-step process of ion irradiation through a SiO2-Si interface and subsequent annealing [1,2]. Previously, the Si NCs could not directly been studied with XTEM because of the low mass contrast of Si NCs to SiO2 and their very small size of less than 3nm.
In this XTEM study we prove the validity of the Si NC formation process. For a mass contrast enhancement of the Si NCs we used Ge to decorate them: A thin Ge layer was embedded into the oxide. During annealing, diffusing Ge is captured by the Si NCs due to the favourable Si-Ge bond. Thereby, the Si NCs are alloyed resulting in Si1−xGex NCs which are equally aligned with the SiO2-Si interface in a tunnel distance of about 3nm. These structural results are in line with the eletronic device characteristics which are dicussed in the contributions of Heinig and Schmidt in this symposium.

  • Poster
    DPG Annual Meeting 2005, 04.-09.03.2005, Berlin, Germany

Publ.-Id: 8164

Synthesis and Radiopharmacological Characterisation of 86Y- and 68Ga-Labelled L-RNA Oligonucleotides as Molecular Probes for Positron Emission Tomography (PET)

Schlesinger, J.; Bergmann, R.; Klussmann, S.; Wüst, F.

Functionalisation of an L-RNA oligonucleotide with 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA) was performed using the N-succinimide ester 2. The DOTA-functionalised L-RNA oligonucleotide 3 was radiolabelled with the positron-emitting radiometals 86Y(III) and 68Ga(III) in radiochemical yields of 76 % and 93 %, respectively. Compound 4a represents the first example of an oligonucleotide labelled with the positron emitter 86Y. Biodistribution studies of the 86Y-radiolabelled L-RNA oligonucleotide 4a were performed in Wistar rats showing higher levels of radioactivity in the adrenal glands and kidneys. The low bone uptake (0.19 %ID/g after 60 min) is indicative of the high kinetic stability of the 86Y-DOTA chelate in vivo.

Keywords: 86Y; 68Ga; DOTA; L-RNA oligonucleotide; positron emission tomography (PET)

  • Letters in Drug Design & Discovery 3(2006)5, 330-335

Publ.-Id: 8163

Investigation of ultrathin tantalum based diffusion barrier films using AES and TEM

Dittmar, K.; Engelmann, H.-J.; Peikert, M.; Wieser, E.; von Borany, J.

Reliably acting diffusion barrier films are basically for the functionality of the copper inter-connect technology. Tantalum (Ta) and Tantalum nitride (TaN) are established materials for diffusion barriers against copper diffusion. In this study, the characterization of TaN like films produced using N+ plasma immersion ion implantation (PIII) was performed using Auger electron spectroscopy (AES). Chemical information was extracted from the Auger data using linear least square fit (LLS). The capability of the method in order to detect very little changes in the film composition dependent on small process changes was demonstrated. The nitrogen incorporation by PIII into high aspect ratio contact holes was proven using analytical TEM.

Keywords: AES; TEM; Tantalum nitride; Diffusion barrier; Plasma immersion ion implantation

  • Applied Surface Science 252(2005), 185-188

Publ.-Id: 8162

Ultra fine-grained metals prepared by severe plastic deformation: a positron annihilation study

Cizek, J.; Prochazka, I.; Kuzel, R.; Matej, Z.; Cherkaska, V.; Cieslar, M.; Smola, B.; Stulikova, I.; Brauer, G.; Anwand, W.; Islamgaliev, R. K.; Kulyasova, O.

Recent investigations of ultra fine-grained metals (Cu, Fe, Ni) performed within a Prague-Rossendorf-Ufa collaboration will be reviewed. The specimens were prepared by severe plastic deformation: the high-pressure torsion and equal channel angular pressing. Positron annihilation spectroscopy was used as the main method including (i) the conventional lifetime and the Doppler broadening measurements with 22Na and (ii) the slow-positron implantation spectroscopy with the Doppler broadening measurement. Other methods were also involved: transmission electron microscopy, X-ray diffraction, and microhardness. First, the mean grain size was determined and defects were identified in the as-deformed materials. Defects concentration and spatial distribution were studied in detail. Dislocations situated in distorted regions along grain boundaries, and a few-vacancy clusters distributed homogeneously inside dislocations-free grains, were observed in the ultra fine-grained Cu, Fe, and Ni. Subsequently, the thermal evolution of the ultra fine-grained structures during isochronal annealing was studied.

  • Open Access Logo Acta Physica Polonica A 107(2005), 745-752

Publ.-Id: 8161

Positron annihilation investigation and nuclear reaction analysis of helium and oxygen-implanted zirconia

Grynszpan, R. I.; Saude, S.; Anwand, W.; Brauer, G.

Since irradiation affects in-service properties of zirconia, we investigated the fluence dependence on production and thermal stability of defects induced by helium and oxygen-ion implantation in single crystals of yttria-fully-stabilized zirconia. In either case, depth profiling by slow positron implantation spectroscopy (SPIS) detects a distribution of vacancy-type defects peaking at 60% of the projected ion range Rp. Owing to the saturation of positron-trapping occurring for low fluences, which depends on the ion mass, we could estimate a critical size of clusters ranging from 0.4 to 1.6 nm. The lack of SPIS-evidence of an open-volume excess at Rp is explained by the presence of over-pressurized gas bubbles. This assumption is confirmed by Nuclear Reaction Analysis of 3He concentration profiles, which shows that helium remains partly trapped at Rp, even after annealing above 400 °C.

Keywords: Ion-implantation; Zirconia; Radiation effects; Positrons

  • Nuclear Instruments and Methods in Physics Research B 241(2005), 526-530

Publ.-Id: 8160

Positron annihilation studies of microstructure of ultra fine grained metals prepared by severe plastic deformation

Cizek, J.; Prochazka, I.; Smola, B.; Stulikova, I.; Kuzel, R.; Cieslar, M.; Matej, Z.; Cherkaska, V.; Brauer, G.; Anwand, W.; Islamgaliev, R. K.; Kulyasova, O.

In the present work, positron annihilation spectroscopy (PAS) is employed for microstructure investigations of various ultra fine grained (UFG) metals (Cu, Ni, Fe) prepared by severe plastic deformation (SPD), namely high-pressure torsion (HPT) and equal channel angular pressing (ECAP): Generally, UFG metals prepared using both the techniques exhibit two kinds of defects introduced by SPD: dislocations and small microvoids. The size of the microvoids is determined from the PAS data. Significantly larger microvoids are found in HPT deformed Fe and Ni compared to HPT deformed Cu. The microstructure of UFG Cu prepared by HPT and ECAP is compared and the spatial distribution of defects in UFG Cu samples is characterized. In addition, the mircrostructure of a pure UFG Cu prepared by HPT and HPT deformed Cu+Al2O3 nanocomposite (GlidCop) is compared.

  • Materials Science Forum 482(2005), 207-210

Publ.-Id: 8159

Resonant impurity states in quantum wells and superlattices

Stehr, D.; Metzner, C.; Helm, M.

Introducing dopant atoms in quantum wells (QWs) and superlattices results in a random impurity potential in addition to the confinement in growth direction. As has recently been demonstrated, their hydrogenic levels form resonant states attached to each QW subband and finally develop into a novel type of impurity band in the case of superlattices [1].
Here we present detailed numerical studies of coupled double and quadruple QW structures with relatively low doping (few 1010cm−2 per layer), which can be seen as precursors to superlattices. By treating impurity and QW potential in a unified framework we exactly diagonalize the fully three-dimensional Schrödinger equation and calculate the infrared absorption spectrum. We find that, by varying the lattice temperature, the absorption spectrum changes dramatically, not only in its energetic resonances but also in its electronic origin. Analyzing the 3D - wavefunctions of the electronic states contributing to the final absorption spectra shows that at room temperature mainly delocalized states (intersubband states) contribute to the spectra, whereas at low temperature they are dominated by strongly localized states (impurity states). Hitherto unexplained experimental data of a quadruple QWsample are nearly perfectly reproduced by our calculation.
[1] D. Stehr et al., Phys. Rev. Lett., in print (2005).

  • Lecture (Conference)
    DPG Frühjahrstagung, Fachverband Halbleiterphysik, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8158

Deep-level defects in n-type 6H silicon carbide induced by He-implantation

Ling, C. C.; Chen, X. D.; Brauer, G.; Anwand, W.; Skorupa, W.; Wang, H. Y.; Weng, H. M.

Defects in He-implanted n-type 6H–SiC samples have been studied with deep-level transient spectroscopy. A deep-level defect was identified by an intensity with a logarithmical dependence on the filling pulse width, which is characteristic of dislocation defects. Combined with information extracted from positron-annihilation spectroscopic measurements, this defect was associated with the defect vacancy bound to a dislocation. Defect levels at 0.38/0.44 eV (E1/E2), 0.50, 0.53, and 0.64/0.75 eV (Z1/Z2) were also induced by He implantation. Annealing studies on these samples were also performed and the results were compared with those obtained from e–-irradiated (0.3 and 1.7 MeV) and neutron-irradiated n-type 6H–SiC samples. The E1/E2 and the Z1/Z2 signals found in the He-implanted sample are more thermally stable than those found in the electron-irradiated or the neutron-irradiated samples.

Publ.-Id: 8157

Deep level defects in 6H silicon carbide

Ling, C. C.; Chen, X. D.; Fung, S.; Beling, C. D.; Gong, M.; Ge, W. K.; Wang, J. N.; Brauer, G.

We have investigated the electrically active deep level defects in n-type 6H silicon carbide through the use of a series of complimentary spectroscopic techniques such as deep level transient spectroscopy, positron annihilation spectroscopy and photolumniescence. The deep level defects were created by neutron irrdiation, He implantation and electron irradiation with different energies. After analysis of the information gained from the different types of spectroscopy, as well as consideration of the defect creation and annealing behavior under different controlled environments, we provide experimental evidence for the microstructure of certain important deep level defects.

Keywords: 6H-SiC; electron irradiation; deep level defect; positron annihilation

  • Open Access Logo Physics 33(2004), 286-790

Publ.-Id: 8156

Deep level defects E1/E2 in n-type 6H silicon carbide induced by electron radiation and He implantation

Ling, C. C.; Chen, X. D.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Skorupa, W.; Gong, M.

6H-SiC samples subjected to He-implantation and e–-irradiation (Ee=0.2MeV–1.7MeV) were investigated by deep level transient spectroscopy (DLTS). E1/E2 were identified in the He-implanted and the e–-irradiated samples with Ee0.3MeV. Considering the minimum e– energy required to displace the atoms in the lattice, the E1/E2 creation was related to the C-atom displacement. Similar to previous reports, the peak intensity and the capture cross sections of E1/E2 anomalously varies from samples to samples. It was shown that these anomalies were due to the presence of a DLTS peak overlapping with the E1/E2 signals.

  • Contribution to proceedings
    27th International Conference on the Physics of Semiconductors (ICPS-27), 26.-30.07.2004, Melville/NY, USA
    Physics of Semiconductors, AIP Conference Proceedings 772/1, 99-100

Publ.-Id: 8155

Stress relaxation by ion bombardment in cubic boron nitride thin films

Abendroth, B.; Möller, W.; Gago, R.; Kolitsch, A.

Ion bombardment plays a special role in the deposition of cubic boron nitride (cBN) for hard coating applications. On one hand, low energy ion bombardment (100-500 eV) of the growing film surface is required to produce the hard cubic phase, on the other hand this implements extremely high compressive stresses (~10 Gpa) limiting film thickness and adhesion. Recently, high energy ion implantation (from keV to MeV range) has been successfully used to release the compressive stress in the films.
In this work the stress relaxation mechanism was investigated using the cantilever bending principle for in situ real time stress measurement during ion beam assisted deposition and Magnetron sputter deposition with simultaneous high energy ion bombardment. The amount of the relaxation is dependent on the product of the energy and the flux of the high energy ions. Using a variety of structural investigations, it can be shown that the relaxation takes place within the cBN grains, likely via the relaxation of interstitials. A relaxation due to the transformation of cBN to the more ductile hexagonal BN modification is less likely. This suggests a stress relaxation mechanism that is driven by a collisional relocation of strained film atoms due to high energy ion impact. A theoretical description of the stress relaxation based on TRIM simulation is presented and discussed. Assuming the stress in the layer to be proportional to the density of unrelaxed atoms, the calculation of the collisional relocation yield enables the calculation of a relative stress relaxation rate. The relocation yield is dependent on the incident ion energy and on the chosen relocation threshold energy. The experimental data are consistent with the model for different deposition parameters and processes for a relocation threshold energy of 5 eV.

Keywords: cubic boron nitride; stress relaxation; in situ stress measurement

  • Lecture (Conference)
    10th International Conference on Plasma Surface Engineering PSE 2006, 12.09.2006, Garmisch Partenkirchen, Deutschland

Publ.-Id: 8154

Effect of the annealing process on active properties of proton-exchanged optical waveguides in erbium-doped lithium niobate

Salavcova, L.; Spirkova, J.; Capek, P.; Novotna, M.; Vacik, J.; Mackova, A.; Kreissig, U.

We report about our study of the annealing effect on the resultant chemical composition of the APE (Annealed Proton Exchange) layers and their optical properties, with emphasis on their potential active function. The samples were annealed at various conditions and characterised by a number of nuclear analytic methods (NDP; ERDA; HIERDA) to investigate concentration profiles of the exchanged ions. The content of OH groups, which are undesirable in the active waveguiding layers owing to their effect of erbium excited state lifetimes shortening, was studied by IR absorption spectrometry. The waveguiding properties (number of guided modes, refractive index vs. depth profile) were measured by mode spectroscopy at 632.8 nm. We found out that hydrogen introduced to the surface layers of LiNbO3 by PE (Proton Exchange) moves deeper into the substrate during A (Annealing), lowering thus total refractive index increment. Consequently, the crystallographic phase of the exchanged layers changes towards the a-phase. The lowest amounts of OH groups were found when highest annealing temperatures were used; however, a limitation exists there as temperatures above 400°C cause degradation of the waveguiding properties.

Keywords: Lithium niobate; Erbium; Annealed proton exchange (APE); Optical waveguides

  • Open Access Logo Ceramics - Silikáty 49(2005), 86-90

Publ.-Id: 8153

Synthesis and characterization of boron-oxygen-hydrogen thin films at low temperatures

Music, D.; Kölpin, H.; Atiser, A.; Kreissig, U.; Bobek, T.; Hadam, B.; Mertens, R.; Schneider, J. M.

We have studied the influence of synthesis temperature on chemical composition and mechanical properties of X-ray amorphous boron–oxygen–hydrogen (B–O–H) films. These B–O–H films have been synthesized by RF sputtering of a B-target in an Ar atmosphere. Upon increasing the synthesis temperature from room temperature to 550 °C, the O/B and H/B ratios decrease from 0.73 to 0.15 and 0.28 to 0.07, respectively, as determined by elastic recoil detection analysis. It is reasonable to assume that potential sources of O and H are residual gas and laboratory atmosphere. The elastic modulus, as measured by nanoindentation, increases from 93 to 214 GPa, as the O/B and H/B ratios decreases within the range probed. Hence, we have shown that the effect of impurity incorporation on the elastic properties is extensive and that the magnitude of the incorporation is a strong function of the substrate temperature.

Keywords: amorphous materials; sputtering; machanical properties

  • Materials Research Bulletin 40(2005)8, 1345-1352

Publ.-Id: 8152

Efficient light emission from Si pn diodes and metal-oxide-semiconductor structures

Sun, J. M.; Skorupa, W.; Dekorsy, T.; Schmidt, B.; Helm, M.

Light emission from silicon has attracted considerable attention in the past few years due to the future potential in on-chip and inter-chip optical interconnects. This report reviews our current research work on efficient electroluminescence (EL) from silicon pn diodes and metal oxide semiconductor (MOS) devices. Efficient band edge EL with attractive power efficiencies up to 0.12 % has been observed in Si pn diodes prepared by boron implantation. We focus on the origin of the relatively high EL efficiency in Si pn diodes prepared by high-dose boron implantation, especially on the intriguing and anomalous increase of the EL for a temperature increase up to room temperature. EL from rare earth doped metal oxide semiconductor (MOS) devices was also studied using ion implantation of different rare earth luminescent centers (Gd3+, Tb3+, Eu3+, Ce3+, Tm3+, Er3+) into the silicon dioxide layers with a transparent top electrode made of indium-tin oxide. Strong EL was obtained from different rare earth centers in UV to infrared. The electroluminescence properties were studied with respect to the luminescence spectra, decay time, impact excitation, cross relaxation (Tb3+), and efficiency. Top external quantum efficiency above 15 % was obtained, which is comparable to the InGaN quantum well light emitting diodes

Keywords: electroluminescence; silicon; pn diode; rare earth; MOS structures

  • Invited lecture (Conferences)
    14th International Conference on Luminescence – ICL05, 2005, Beijing, July 25-29 China, WED_A_C02, 25.7.2005, Beijing, China

Publ.-Id: 8151

Modulation of the 1535 nm photoluminescence from Er-doped Si-rich silicon dioxide by field-induced quenching

Sun, J. M.; Skorupa, W.; Dekorsy, T.; Helm, M.; Rebohle, L.; Gebel, T.

Field-induced quenching of the efficient photoluminescence at 1535 nm was observed from Si-rich SiO2:Er thin films prepared by Er and Si co-implantation. The quenching effect was strongly enhanced by increasing the density of silicon nanoclusters at an electric field above 5 MV/cm. A modulation ratio of 0.37 was obtained at an electric field of 9 MV/cm for a 200 nm Er-doped Si-rich layer containing 0.24 % of Er atoms and 10% excess Si nanoclusters. The mechanism of the field-induced quenching of the photoluminescence was studied by simultaneously measuring the light intensity from nanolusters and Er3+ ions, the injection current and the electric field. The quenching mechanism could be attributed to the field induced separation of the excitons created in silicon nanoclusters and tunneling of carriers between the Er ions and silicon nanoclusters. This strong field quenching effect will be useful for controlling the optical gain in a Si-rich SiO2:Er waveguide amplifiers, but also for the small size optical modulator in silicon photonics.

Keywords: Field induced quenching; Erbium; silicon nanoclusters; silicon dioxide

  • Lecture (others)
    E-MRS 2005 Spring Meeting May 31 – June 3, 2005 Symposium D Materials science and device issues for future Si-based technologies, 31.05.-3.6.2005, Strasbourg, France

Publ.-Id: 8150

Efficent electroluminescence from Tb-implanted silicon metal-oxide-semiconductor devices

Sun, J. M.; Skorupa, W.; Dekorsy, T.; Helm, M.; Rebohle, L.; Gebel, T.

Strong green electroluminescence with brightness up to 2800 cd/m2 was obtained from indium-tin-oxide/SiO2:Tb/Si metal-oxide-semiconductor devices. The SiO2:Tb gate oxide was prepared by thermal oxidation followed by Tb+ implantation and annealing. Electroluminescence and photoluminescence properties were studied with variations of the Tb3+ ion concentration and annealing temperatures. The optimized device has a high external quantum efficiency of 16 % and a luminous efficiency of 2.1 lm/W. The excitation process of electroluminescence can be attributed to the impact excitation of the Tb3+ luminescent centers by hot electrons and the subsequent cross-relaxation from the 5D3 to 5D4 levels. Light emitting devices with micrometer size were demonstrated by the complementary metal-oxide-semiconductor technology.

Keywords: electrolumnescence; silicon dioxide; Terbium; MOS

  • Lecture (others)
    E-MRS 2005 Spring Meeting May 31 – June 3, 2005 SYMPOSIUM C Rare earth doped photonic materials, C-V.03, 31.05.-3.6.2005, Strasbourg, France

Publ.-Id: 8149

Forschungszentrum Rossendorf "Status report of FZR activities" / Status of Cathode System in FZR

Teichert, J.; Xiang, R.

kein Abstract vorhanden

  • Lecture (Conference)
    CARE Collaboration Meeting, 23.-25.11.2005, CERN, Switzerland

Publ.-Id: 8148

The Superconducting photoinjector at Rossendorf - Present status of the Rossendorf Superconducting RF Photo injector development

Teichert, J.

kein Abstract vorhanden

  • Invited lecture (Conferences)
    CARE Collaboration Meeting, 23.-25.11.2005, CERN, Switzerland


Publ.-Id: 8147

Effect of Ion Energy on Structure and Composition of Cathodic Arc Deposited Alumina Thin Films

Rosen, J.; Mraz, S.; Kreissig, U.; Music, D.; Schneider, J. M.

The effect of energy supplied to the growing alumina film on the composition and structure has been investigated by varying substrate temperature and substrate bias potential. The constitution and composition were studied by X-ray diffraction and elastic recoil detection analysis, respectively. Increasing the substrate bias potential from −50 to −100 V caused the amorphous or weakly crystalline films to evolve into stoichiometric, crystalline films with a mixture of the α- and γ-phase above 700 oC, and γ-phase dominated films at temperatures as low as 200 oC. All films had a grain size of <10 nm. The combined constitution and grain size data is consistent with previous work stating that γ-alumina is thermodynamically stable at grain sizes <12 nm [McHale et al., Science 277, 788 (1997)]. In order to correlate phase formation with synthesis conditions, the plasma chemistry and ion energy distributions were measured at synthesis conditions. These results indicate that for a substrate bias potential of −50 V, ion energies in excess of 100 eV are attained, both from a high energy tail and the accelerated ions with charge >1. These results are of importance for an increased understanding of the evolution of film composition and microstructure, also providing a pathway to γ-alumina growth at temperatures as low as 200 o C.

Keywords: Alumina; ion energy; plasma chemistry; composition; microstructure

  • Plasma Chemistry and Plasma Processing 25(2005)4, 303-317

Publ.-Id: 8146

Enhancement of the simulation of scaled vessel failure experiments by a recursive coupling of the thermal and mechanical FEM-models

Willschuetz, H.-G.

For the simulation of experiments investigating the behavior of the lower head of a nuclear power station in case of a core meltdown scenario like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model with 3 different physics environments is developed based on the code ANSYS® Multiphysics.
A thermal environment was build up including planar and contact elements for conductive heat transfer, additional surface elements to simulate convection and radiation from outer surface areas and a radiation matrix to account for internal radiative heat exchange. Normally a CFD-simulation would have been required for the natural convective heat transfer in the melt pool, but at very high internal Rayleigh numbers no turbulence model is capable for a correct simulation. Therefore an Effective Conductivity Convectivity Model (ECCM) was developed to simulate the heat transfer from the melt pool to its environment.
The resulting temperature field of the vessel wall is applied to the mechanical model. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied.
The third physics environment is a kind of fictitious physics environment: it uses hyperelasticity and contact to move the melt pool along with the creeping vessel wall.
In this paper problems on the numerical side are explained and differences between the results of a simple coupled and a kinematically coupled FE-simulation are highlighted. The final comparison with the experiments shows that the kinematically coupled model is closer to reality than the single step model.

Keywords: Fully Coupled Physics Environments; Effective Conductivity Convectivity Model; Creep and Plasticity of Pressure Vessel Steel

  • Contribution to proceedings
    International Youth Nuclear Congress, 18.-23.06.2006, Stockholm and Olkiluoto, Sveden and Suomi
    Proceedings on CD-ROM, paper 275
  • Lecture (Conference)
    International Youth Nuclear Congress, 18.-23.06.2006, Stockholm and Olkiluoto, Sveden and Suomi

Publ.-Id: 8145

Core design and transient analyses for weapons plutonium burning in VVER-1000 type reactors

Rohde, U.; Grundmann, U.; Kozmenkov, Y.; Pivovarov, V.; Matveev, Y.

The presented core calculations are aimed at the demonstration of the feasibility of weapon-grade plutonium burning in VVER-1000 type reactors with emphasis on safety aspects of the problem. Particular objectives of weapon-grade Pu burning are the net burning of fissile Pu isotopes in general, but also the conversion of the Pu vector of the fuel from weapon-grade to reactor plutonium. Three different fuel-loading options have been considered - full UO2 loading, mixed UO2 and MOX loading and full MOX loading. All considered cases meet the requirements on nuclear safety and design limits related to both normal operation and accident conditions. Two reactivity initiated accidents have been analyzed, caused by the ejection of the operational control rod group during 0.1 s and unauthorized withdrawal of the same control rod group with operational speed. The analyses have been performed for the beginning and the end of the fuel cycle. The maximum reactor power peak of 1.79 of the nominal reactor power was observed for the 2nd fuel-loading option (mixed loading). However, it does not cause an overheating of fuel rods.
The performed simulations demonstrated that the code DYN3D can be used for analyses of reactivity-initiated accidents in VVER type reactors with various fuel designs.
Feasibility of the VVER-1000 type reactor for burning weapon-grade Pu and changing its isotopic composition has been demonstrated.

Keywords: mixed oxide fuel; MOX; weapon-grade plutonium; core design; plutonium burning; plutonium vector; reactivity initiated accidents; nuclear safety; VVER-type reactors

  • Invited lecture (Conferences)
    Stand der Entwicklung für LWR Brennelemente und Auslegungsmethoden, 02.-03.03.2006, Dresden, Germany
  • Contribution to proceedings
    KTG-Fachtag "Stand der Entwicklung für LWR Brennelemente und Auslegungsmethoden", 02.-03.03.2006, Dresden, Germany
    CD-ROM Proceedings p. 265

Publ.-Id: 8144

Development of an optical wire-mesh tomograph for the study of multi-phase flows.

Schleicher, E.; Hampel, U.; Da Silva, M. J.; Zschau, J.; Futterschneider, H.; Zimmermann, W.

We introduce a novel optical wire-mesh tomograph for the investigation of multiphase flows. The sensor consists of an optical fibre matrix that covers the cross-section of a vessel or pipeline with fibres arranged in two distinct axial planes. Optical measurement is performed at the cross-points of the fibres where the cladding material is partially removed to enable light crossing from a fibre of the emitter plane to fibres of the receiver plane. A rapid optoelectronic processing unit enables the acquisition of cross-sectional images with frame rates above 10 kHz. We demonstrate the operation of the sensor for an oil-gas two-phase flow.

Keywords: optical fibre; wire-mesh tomograph; multiphase flow; oil-gas two-phase flow

  • Contribution to proceedings
    OPTO 2006, 30.05.-01.06.2006, Nürnberg, Germany
    Sensor+Test 2006, Proceedings, Wunstorf: AMA Service GmbH, 3-9810993-0-3, 115-119
  • Lecture (Conference)
    OPTO 2006, 31.05.2006, Nürnberg, Germany

Publ.-Id: 8142

Thermomechanische Modellierung eines Reaktordruckbehälters in der Spätphase eines Kernschmelzunfalls

Willschütz, H.-G.

Considering the late in-vessel phase of an unlikely core melt down scenario in a light water reactor (LWR) with the formation of a corium pool in the lower head of the re-actor pressure vessel (RPV) the possible failure modes of the RPV and the time to failure have to be investigated to assess the possible loadings on the containment. In this work, an integral model was developed to describe the processes in the lower plenum of the RPV. Two principal model domains have to be distinguished: The temperature field within the melt and RPV is calculated with a thermodynamic model, while a mechanical model is used for the structural analysis of the vessel wall.
In the introducing chapters a description is given of the considered accident scenario and the relevant analytical, experimental, and numerical investigations are discussed which were performed worldwide during the last three decades. Following, the occur-ring physical phenomena are analysed and the scaling differences are evaluated between the FOREVER-experiments and a prototypical scenario.
The thermodynamic and the mechanical model can be coupled recursively to take into account the mutual influence. This approach not only allows to consider the tem-perature dependence of the material parameters and the thermally induced stress in the mechanical model, it also takes into account the response of the temperature field itself upon the changing vessel geometry.
New approaches are applied in this work for the simulation of creep and damage. Using a creep data base, the application of single creep laws could be avoided which is especially advantageous if large temperature, stress, and strain ranges have to be covered. Based on experimental investigations, the creep data base has been de-veloped for an RPV-steel and has been validated against creep tests with different scalings and geometries.
It can be stated, that the coupled model is able to exactly describe and predict the vessel deformation in the scaled integral FOREVER-tests. There are uncertainties concerning the time to failure which are related to inexactly known material parame-ters and boundary conditions.
The main results of this work can be summarised as follows: Due to the thermody-namic behaviour of the large melt pool with internal heat sources, the upper third of the lower RPV head is exposed to the highest thermo-mechanical loads. This region is called hot focus. Contrary to that, the pole part of the lower head has a higher strength and therefore relocates almost vertically downwards under the combined thermal, weight and internal pressure load of the RPV.
On the one hand, it will be possible by external flooding to retain the corium within the RPV even at increased pressures and even in reactors with high power (as e.g. KONVOI). On the other hand, there is no chance for melt retention in the considered scenario if neither internal nor external flooding of the RPV can be achieved.
Two patents have been derived from the gained insights. Both are related to pas-sively working devices for accident mitigation: The first one is a support of the RPV lower head pole part. It reduces the maximum mechanical load in the highly stressed area of the hot focus. In this way, it can prevent failure or at least extend the time to failure of the vessel. The second device implements a passive accident mitigation measure by making use of the downward movement of the lower head. Through this, a valve or a flap can be opened to flood the reactor pit with water from a storage res-ervoir located at a higher position in the reactor building.
With regard to future plant designs it can be stated - differing from former presump-tions - that an In-Vessel-Retention (IVR) of a molten core is possible within the reac-tor pressure vessel even for reactors with higher power.

Keywords: Light Water Reactor; severe accident with core melt down; In-Vessel-Retention; recoursively coupled thermal and mechanical simulation; scaled experiments and prototypic scenario

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-447 2006
    ISSN: 1437-322X


Publ.-Id: 8141

Structural and magnetic modifications in Cr implanted Permalloy

Fassbender, J.; von Borany, J.; Mücklich, A.; Potzger, K.; Möller, W.; McCord, J.; Schultz, L.; Mattheis, R.

The static and dynamic magnetic properties, especially the magnetic damping behavior, have been investigated as a function of saturation magnetization in thin Permalloy films. Ion implantation doping with Cr in the percentage regime has been used to effectively reduce the Curie temperature and thus the saturation magnetization at room temperature. In order to understand the magnetic modifications the changes in stoichiometry but also the ion induced structural changes have been addressed. As a function of fluence first an improvement of the (111) fiber texture, then a lattice expansion and finally a partial amorphization of the interface near region of the Permalloy layer is found. The region of amorphization can be understood quantitatively by the concentration profiles as a function of depth in combination with irradiation induced damage formation. The magnetic properties change correspondingly. For increasing Cr doping a drop in saturation magnetization and a decrease of the uniaxial magnetic anisotropy is observed. For a fluence of 0.8 x 10^16 Cr/cm^2 (4 at.%) the magnetic damping parameter  increases by a factor of 7. This strong increase is mainly caused by the reduction of the saturation magnetization and the altered sample morphology.

Keywords: magnetism; ion implantation; doping; Curie temperature; saturation magnetization; magnetic anisotropy; magnetic damping; amorphization; TRIDYN

Publ.-Id: 8140

Systematics of magnetic dipole strength in the stable even-mass Mo isotopes

Rusev, G.; Schwengner, R.; Dönau, F.; Erhard, M.; Frauendorf, S.; Grosse, E.; Junghans, A. R.; Käubler, L.; Kosev, K.; Kostov, L.; Mallion, S.; Schilling, K. D.; Wagner, A.; von Garrel, H.; Kneissl, U.; Kohstall, C.; Kreutz, M.; Pitz, H. H.; Scheck, M.; Stedile, F.; von Brentano, P.; Jolie, J.; Linnemann, A.; Pietralla, N.; Werner, V.

The nuclides 92Mo, 98Mo and 100Mo have been studied in photon-scattering experiments by using bremsstrahlung. Dipole and quadrupole excitations in 92Mo were investigated in photon-scattering experiments at an electron energy of 6 MeV at the ELBE accelerator of the Forschungszentrum Rossendorf. Photon-scattering experiments on 98Mo and 100Mo were carried out at the Dynamitron accelerator of the Stuttgart University at electron energies from 3.2 to 3.8 MeV. Six dipole transitions in 98Mo and 19 in 100Mo were observed for the first time in the energy range from 2 to 4 MeV. Systematics of the magnetic dipole strength in the isotopic chain of the even-mass isotopes from 92Mo to 100Mo are discussed. The experimental results are compared with predictions of the shell model and with predictions of the quasiparticle-random-phase approximation in a deformed basis. The latter show significant contributions of isovector-orbital and isovector-spin vibrations.

Keywords: Photon scattering; Nuclear structure; Nuclear spectroscopy; Random phase approximation; Shell model

Publ.-Id: 8139

Effect of crystal orientation on self-assembled silicon nanostructures formed by electron beam annealing

Johnson, S.; Markwitz, A.; Rudolphi, M.; Baumann, H.; Kuo, P.-Y.; Blaikie, R.; Mücklich, A.

This paper discusses the growth of silicon nanostructures on silicon (100), (110) and (111) substrates by electron beam annealing. The nanofabrication procedure involves annealing of the untreated Si substrates at 1100°C for 15 s using a raster scanned 20 keV electron beam. Nanostructuring occurs as a result of kinetic amplification of the surface disorder induced by thermal decomposition of the native oxide. Pyramidal and truncated pyramidal nanocrystals were observed on Si(100) surface. The nanostructures are randomly distributed over the entire surface and square-based, reflecting the two-fold symmetry of the substrate surface. Similar square-based pyramidal structures with four equivalent facets are observed following nanostructuring of Si(110). With Si(111), nanostructure growth occurs preferentially along step-edges formed on the vicinal surface. Significant differences in nanostructure shapes formed on step-edges and terraces are related to the different growth mechanisms on the unreconstructed and 7x7 reconstructed domains respectively.

  • Journal of Applied Physics 97(2005), 94301

Publ.-Id: 8138

Formation of SiC-surface nanocrystals by ion implantation and electron beam rapid thermal annealing

Markwitz, A.; Johnson, S.; Rudolphi, M.; Baumann, H.; Mücklich, A.

SiC-surface nanostructures on silicon were produced by 10 keV carbon ion implantation into silicon followed by annealing to 1000°C for 15 s under high-vacuum conditions using a raster-scanned electron beam. Following implantation, an amorphous layer is produced which starts at the surface and extends 65 nm into the substrate. Following annealing, the implanted surface layer remains amorphous but becomes covered with semi-spherical crystalline features up to 300 nm in diameter. The nanocrystals have been confirmed to be SiC which, following nucleation, grow as a result of C and Si diffusion across the oxide free substrate surface during annealing.

  • Applied Physics Letters 86(2005), 013108-1

Publ.-Id: 8137

Defects in virgin and N+ ion-implanted ZnO single crystals studied by positron annihilation, Hall effect and deep level transient spectroscopy

Brauer, G.; Anwand, W.; Skorupa, W.; Kuriplach, J.; Melikhova, O.; Moisson, C.; von Wenckstern, H.; Schmidt, H.; Lorenz, M.; Grundmann, M.

High quality single crystals of ZnO in the as-grown and N+ ion-implanted states have been investigated using a combination of three experimental techniques - namely, positron lifetime/slow positron implantation spectroscopy accompanied by theoretical calculations of the positron lifetime for selected defects, temperature-dependent Hall (TDH) measurements and deep level transient spectroscopy (DLTS). The positron lifetime in bulk ZnO is measured to be (151 + 2) ps and that for positrons trapped in defects (257 + 2) ps. On the basis of theoretical calculations the latter is attributed to Zn+O divacancies, existing in the sample in both neutral and single negative charge states, and not to the Zn vacancy proposed in previous experimental work. From TDH measurements the concentrations of negatively-charged and neutral Zn+O divacancies are estimated to lie between 4 × 1015 and 6.3 × 1016 cm-3. DLTS revealed the creation of the defect E1 and an increase in concentration of the defect E3 after N+ ion implantation. Furthermore, a p-conducting layer is formed at the surface after the implantation/annealing procedure that can be used to inject holes during a DLTS measurement. In this way, the acceptor traps A2 and A3 with thermal activation energies of about 150 and 280 meV, respectively, have been detected for the first time by DLTS.

Keywords: zinc oxide; point defects; positron annihilation; N+ implantation; electron traps; acceptor traps; hole injection; Hall effect; DLTS; p-conducting ZnO

  • Physical Review B 74(2006), 045208

Publ.-Id: 8136

Fluid-structure interaction during artificially induced water hammers in a tube with bend – experiments and analyses

Altstadt, E.; Carl, H.; Prasser, H. M.; Weiß, R.

Experimental and numerical investigations of artificial water hammers in a pipe with a bend are presented. At FZR a cold water hammer test facility was used to measure the fluid pressures and the pipe wall stresses occurring during water hammers. The finite element code ANSYS® was used for the numerical analysis of the experiments. The focus was put on the local distributions of pressure and stress. It could be shown that the fluid pressure and pipe wall stress exhibit complex 3-dimensional structures, which is a consequence of the fluid-structure interaction. The highest stresses occur in the pipe bend. The pressure peak is lower than predicted by the extended Joukowsky formula.

Keywords: Fluid-structure interaction; water hammer; Finite element method

Publ.-Id: 8135

Wechselwirkung zwischen Corium und Reaktordruckbehälter - Experimente, Versagensmodus, Versagenszeitpunkt

Willschütz, H.-G.; Alstadt, E.; Weiß, F.-P.

In-Vessel-Retention, betrachtetes Stadium, Debrisbett in der Bodenkalotte: Kühlbarkeit/Nichtkühlbarkeit (IKE-Arbeiten), mögliche Schmelzekonfigurationen, Fragestellungen.
Übersicht der Experimente: mechanisches Werkstoffverhalten, Wärmeübergang vom Schmelzepool, Materialwechselwirkung zwischen Corium und Stahlwand, integrale Experimente.
Versagensarten: thermisches Versagen, thermomechanisches Versagen, Versagensort und –form, Auswirkung auf Schmelzeaustrag.
Analysetools: bekannte Modelle, Vorgehensweise im FZR.
Versagenszeitpunkt / mögliche Gegenmaßnahmen
Ausblick: aktuelles Projekt BMWA Nr. 150 1279, weiterführende Fragestellungen.

Keywords: Nuclear Power Plant; Severe accident with core meltdown; Interaction between corium and reactor pressure vessel wall; investigation of failure modes

  • Invited lecture (Conferences)
    Workshop: Corium - Eigenschaften, Wechselwirkungen und Beherrschungskonzepte, 09.-10.02.2006, Köln, Germany
  • Contribution to proceedings
    Workshop: Corium - Eigenschaften, Wechselwirkungen und Beherrschungskonzepte, 09.-10.02.2006, Köln, Germany
    Proceedings on CD-ROM, Paper P03

Publ.-Id: 8134

Annealing of indium tin oxide films by electric current: properties and structure evolution

Rogozin, A.; Shevchenko, N.; Vinnichenko, M.; Seidel, M.; Kolitsch, A.; Möller, W.

As a new method of indium tin oxide (ITO) annealing in vacuum, direct electric current flow through the film is proposed. ITO films of about 170 nm thickness were produced by reactive pulsed magnetron sputtering. During annealing at constant electric power, the film resistance, free electron density and structure evolution were monitored in situ. Compared to conventional isothermal annealing, the current annealing is more efficient with a noticeable reduction of the thermal budget and a decrease of the kinetic exponent of the crystallization. Electrical inhomogeneities of the film, which produce locally overheated regions, are discussed as potential reason for the acceleration of the crystallization process.

Keywords: indium tin oxide; annealing by electric current; reactive pulsed magnetron sputtering; in situ x-ray diffraction; in situ spectroscopic ellipsometry; activation energy; resistivity; optical properties

  • Applied Physics Letters 89(2006)6, 061908

Publ.-Id: 8133

Experimental study of interactions between suboxidized corium and reactor vessel steel

Bechta, S. V.; Khabensky, V. B.; Granovsky, V. S.; Krushinov, E. V.; Vitol, S. A.; Gusarov, V. V.; Almiashev, V. I.; Lopukh, D. B.; Tromm, W.; Bottomley, D.; Fischer, M.; Piluso, P.; Miassoedov, A.; Altstadt, E.; Willschütz, H.-G.; Fichot, F.

One of the critical factors in the analysis of in-vessel melt retention is the vessel strength. It is, in particular, sensitive to the thickness of intact vessel wall, which, in its turn, depends on the thermal conditions and physicochemical interactions with corium.
Physicochemical interaction of prototypic UO2-ZrO2-Zr corium melt and VVER vessel steel was examined during the 2nd Phase of the ISTC METCOR Project. Rasplav-3 test facility was used for conducting four tests, in which the Zr oxidation degree and interaction front temperature were varied; in one of the tests, stainless steel was added to the melt.
Direct experimental measurements and posttest analyses were used for determining corrosion kinetics and maximum corrosion depth (i.e. the physicochemical impact of corium on the cooled vessel steel specimens), as well as the steel temperature conditions during the interaction, and finally the structure and composition of crystallized ingots, including the interaction zone. The minimum temperature on the interaction front boundary, which determined its final position and maximum corrosion depth was ~1090°С. An empirical correlation for calculation of corrosion kinetics has been derived.

Keywords: Corium-steel interaction; physicochemical properties; in vessel melt retention; reactor pressure vessel

  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants (ICAPP) 2006, 04.-08.06.2006, Reno, United States
    Proceedings on CD-ROM, paper 6054, 1355-1362

Publ.-Id: 8132

Materialforschung für sichere Kernkraftwerke

Altstadt, E.

Es wird ein Überblick zu den Aspekten der Materialsicherheit in der Kerntechnik gegeben. Im Mittekpunkt der Betrachtungen steht der Reaktordruckbehälter von Leichtwasserreaktoren. Im FRZ angwendete Methoden zur Mikrostrukturanalyse und zur Bruchmechanik werden erläutert.

Keywords: Reactor pressure vessel; Material Safety; Small Angle Neutron Scattering; Fracture Mechanics

  • Lecture (others)
    Ringvorlesung des Materialforschungsverbundes Dresden für das Studium generale der Technische Universität Dresden, 25.01.2006, Dresden, Germany

Publ.-Id: 8131

Aufbau eines Versuchsplatzes für die Positronen-Emissions-Tomographie

Würschig, T.

Die Positronen-Emissions-Tomographie (PET) hat sich als bildgebendes Verfahren in der klinischen Routine sowie der medizinischen, biologischen und pharmazeutischen Forschung etabliert.
Daraus ergibt sich die Notwendigkeit, Mediziner sowie Physiker und Ingenieure mit der speziellen Ausrichtung auf multidisziplinäre Forschungsgebiete der Biologie und Medizin bzw. medizintechnischen Anwendungen im Rahmen ihrer Ausbildung möglichst praxisnah mit dieser Technik vertraut zu machen. Zu diesem Zweck soll ein Versuchsplatz für die PET aufgebaut werden, an welchem die allgemeinen Prinzipien der Computertomographie (CT), die Grundlagen der PET sowie die PET als kernphysikalisches Multiparameter-Messverfahren vermittelt werden. Für die Realisierung dieser Aufgabenstellung gibt es folgende Vorgaben:

  • Der Tomograph besteht aus zwei kommerziellen, in Koinzidenz betriebenen, ortsempfindlichen Szintillationsdetektoren.
  • Zum Gewinnen vollständiger Projektionsdatensätze wird ein Computer gesteuertes Bewegungssystem für die Translation und die Rotation verwendet.
  • Die Signalverarbeitung basiert auf Standardmodulen der kernphysikalischen Messtechnik.
  • Zur Gewährleistung einer flexiblen, den unterschiedlichen Anforderungen genügenden Auswertung erfolgt die Speicherung der Daten im Listen-Modus.
  • Die tomographische Rekonstruktion mittels gefilterter Rückprojektion ist in die laufende Messung (Online-Betrieb) integriert. Daneben besteht
die Möglichkeit, die Daten auch nach der Messung in unterschiedlichen Konfigurationen zu rekonstruieren (Offline-Betrieb).
Diese Diplomarbeit soll zudem als Grundlage für das zu erstellende Lehrmaterial fungieren. Dabei wird zuerst auf die Anwendung und Entwicklung der PET eingegangen (Abschnitt 1.1). Im zweiten Kapitel werden die für die PET notwendigen Grundbegriffe erklärt sowie die physikalischen und mathematischen Prinzipien und Wirkungsweisen dargestellt. Daran anschließend wird im dritten Kapitel der Aufbau des PET-Versuchsplatzes beschrieben, wobei auch näher auf die einzelnen ausgewählten Komponenten eingegangen wird. Im vierten Kapitel werden systemspezifische Größen für den Versuchsplatz hergeleitet. Darauf folgend wird in Kapitel 5 die Software detaillierter vorgestellt. Die Ergebnisse der durchgeführten Messungen sind im sechsten Kapitel zu finden. Dabei handelt es sich sowohl um Messungen zur Charakterisierung des Messplatzes als auch um vollständige tomographische Rekonstruktionen von Punktquellen. Abschließend werden die Besonderheiten und Merkmale des aufgebauten Tomographen nochmals zusammengefasst sowie ein Ausblick gegeben (Kapitel 7).
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-445 2006
    ISSN: 1437-322X
  • Lecture (Conference)
    DPG Frühjahrstagung, 13.-15.03.2006, Heidelberg, Deutschland


Publ.-Id: 8130

Ion beam synthesis of Fe nanoparticles in MgO and YSZ

Potzger, K.; Reuther, H.; Zhou, S.; Mücklich, A.; Grötzschel, R.; Eichhorn, F.; Liedke, M.; Fassbender, J.; Lichte, H.; Lenk, A.

In order to prepare epitaxially oriented Fe nanoparticles embedded below the surface of an oxide single crystalline host material the method of ion beam synthesis has been explored for MgO(001) and YSZ(001). At a fixed implantation energy and fluence the implantation temperature has been varied between *room temperature* and 1273 K. It was found, that for MgO substrates the fraction of metallic Fe increases up to a maximum of 60% (at 1073 K) as a function of implantation temperature, whilst the Fe depth profile remains the same. The Fe nanoparticles are nonmagnetic at room temperature exhibiting fcc structure. They show a mean diameter of 5 nm and an exclusive orientation relationship to the host. In YSZ the fraction of metallic Fe increases with increasing implantation temperature reaching 100% at 1273 K. However, the nanoparticles formed are of bcc structure with a mean diameter of 13 nm located mainly close to the sample surface. The ferromagnetic behavior is reflected by a magnetic hyperfine field of 330 kOe and a hysteretic magnetization reversal. Electron holography measurements have been carried out in order to visualize the stray field of the particles.

Keywords: MgO; YSZ; magnetic nanoparticles; ion beam synthesis; mossbauer spectroscopy

  • Lecture (Conference)
    Frühjahrstagung des Arbeitskreises Festkörperphysik zusammen mit der Condensed Matter Division der EPS (DPG-Tagung), 26.-31.03.06, Dresden, Deutschland

Publ.-Id: 8129

Fe doped ZnO – a diluted magnetic semiconductor?

Potzger, K.; Zhou, S.; Reuther, H.; Mücklich, A.; Eichhorn, F.; Talut, G.; Herrmannsdörfer, T.; Bianchi, A.; Fassbender, J.

The fabrication of diluted magnetic semiconductors (DMS) by transition-metal (TM) doping of ZnO has attracted tremendous interest within the last 3 years. However, there are still vivid discussions if the ferromagnetic state stems from Zener-interaction between diluted TM ions or from magnetic secondary phases. In order to prove or exclude the possible formation of TM-secondary phases in ZnO we have investigated iron doping, since Fe-ZnO (n-type) DMS are theoretically predicted to exhibit ferromagnetism [1].
For these investigations Fe-ions have been implanted with an ion energy of 180 keV (projected range Rp=80 nm) at 250 K and 620 K into ZnO single crystals. Two fluences of either 0.4 or 4x1016 ions per cm2 were chosen which correspond to 0.5 and 5 at%, respectively. The samples were characterized by CEMS (conversion electron Mössbauer spectroscopy), XRD (X-ray diffraction) using synchrotron radiation, RBS (Rutherford back scattering), TEM (transmission electron microscopy) and SQUID (superconducting quantum interference device) magnetometry.
For the as implanted sample a high solubility of Fe was found. The ionic states are 2+ and 3+ but none of the ionic fractions could be clearly determined to occupy substitutional lattice sites. The sample implanted at high fluence and 620 K exhibits ferromagnetic behavior at room temperature as was observed by CEMS and SQUID. However, CEMS and XRD measurements confirm that the origin of the ferromagnetic behavior is due to Fe-nanocluster formation. These nanoclusters show the magnetic moment and hyperfine field of metallic bcc-Fe. For samples implanted at 250 K and a low fluence also a ferromagnetic behavior could be detected at room temperature. No secondary phase formation occurs suggesting the formation of a diluted magnetic semiconductor (DMS)

[1] K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys. 40, L334 (2001)

Keywords: Diluted magnetic semiconductors; Ion beam doping; ZnO

  • Lecture (Conference)
    364. Heraeus Workshop on Nanoscale Magnets - Top-Down meets Bottom-Up, 04.-06.01.2006, Bad Honnef, Deutschland

Publ.-Id: 8128

Control of magnetic damping by means of Ni implantation in thin Ni81Fe19 layers

Fassbender, J.; McCord, J.

The static and dynamic magnetic properties of 20 nm thick Ni81Fe19 films have been investigated as a function of Ni ion fluence up to 1x10^16 Ni/cm^2 (5 atom-%). The implantation has been performed at 30 keV in order to implant the Ni ions in the center of the ferromagnetic layer and to achieve a rather homogeneous energy distribution throughout the film. With increasing ion fluence the saturation magnetization and the effective magnetic anisotropies (static and dynamic) are reduced by about 80%. However, the effective magnetic damping is drastically enhanced for higher ion fluences. Starting at a pure permalloy value of alpha= 0.008 a 7-fold increase to alpha= 0.058 is found for a fluence of 0.8x10^16 Ni/cm^2. This increase can be explained mainly by the drop in saturation magnetization in connection with structural changes. In addition ion implantation in an applied magnetic field allows the setting of the uniaxial anisotropy direction irrespective of the initial orientation for fluences as low as 5x10^13 Ni/cm^2.

Keywords: magnetism; ion implantation; magnetization dynamics; magnetic damping; permalloy; anisotropy

  • Poster
    Joint European Magnetics Symposium, 26.-30.06.2006, San Sebastian, Spanien

Publ.-Id: 8124

Exchange bias on rippled substrates

Liedke, M. O.; Rossbach, S.; Facsko, S.; Hillebrands, B.; Fassbender, J.

The interface between ferromagnet (FM) and antiferromagnet (AFM) plays a crucial role for the exchange bias phenomenon. This is mainly because monoatomic steps, islands or point defects give rise to uncompensated spins at the interface which serve as the origin of exchange bias. The number of monoatomic steps and thus the magnitude of the induced uniaxial anisotropy can easily be varied by means of Ar+ ion erosion. Depending on the primary energy and the angle of incidence a rippled surface with a well defined periodicity (20 – 100 nm) and peak to valley height (2 – 5 nm) can be created. On top of this surface the exchange bias system 5 nm Ni81Fe19 coupled to 10 nm Fe50Mn50 has been prepared. The interface corrugation remained throughout the whole layer stack. By means of a field annealing cycle the exchange bias direction has been initialized either along or perpendicular to the ripple direction, which causes to align the uniaxial and unidirectional anisotropy contributions either parallel or perpendicular to each other. For both cases the magnetic easy- and hard-axes remain the same because the uniaxial anisotropy contribution is much larger than the unidirectional one. However, if the exchange bias is initialized along (perpendicular to) the ripple direction the easy-axis (hard-axis) magnetization reversal loop is shifted. In order to evaluate this behavior in more detail a complete angular dependency of the magnetization reversal behavior has been investigated in both cases and compared to simulations based on a Stoner-Wohlfarth coherent rotation model. A good agreement between experimental data and simulations is found.
M. O. L. acknowledges the financial support from the European Communities Human Potential Program NEXBIAS under Contract No. HPRN-CT2002-00296.

Keywords: magnetism; exchange bias; magnetic anisotropy; ion erosion; ripples

  • Poster
    3rd Joint European Magnetic Symposia, 26.-30.06.2006, San Sebastian, Spanien
  • Poster
    International Colloquium on Magnetic Films and Surfaces, 14.-18.08.2006, Sendai, Japan
  • Poster
    Workshop on Properties of ultrathin magnetic films, 06.-09.09.2006, Bialowieza, Polen

Publ.-Id: 8123

Exchange bias on rippled substrates – step induced uniaxial versus unidirectional anisotropy

Liedke, M. O.; Rossbach, S.; Facsko, S.; Hillebrands, B.; Fassbender, J.

Ripples with a periodicity of 35 nm and a height of 2 nm were formed on a Si(001) substrate
by means of Ar+ ion erosion. The primary energy was 500 eV and the angle of incidence 70° with respect to the surface normal. One of the main characteristics of such a surface is the large step density which is usually only achieved for vicinal miscut substrates. After ripple preparation a 0.5 nm Pt buffer layer and a 5 nm Permalloy (Ni81Fe19) ferromagnetic layer were deposited by means of molecular beam epitaxy. In order to allow for an easy comparison between ferromagnetic layer and exchange biased system on half of the sample a 10 nm Fe50Mn50 antiferromagnetic layer was deposited. Then the whole sample was covered by a 2 nm Cr protection layer. Additional AFM images confirmed that the ripple structure remains throughout the whole layer system.

The magnetization reversal behavior of the ferromagnetic layer and the exchange bias system was then investigated by means of magneto-optic Kerr effect (MOKE). The Permalloy layer itself exhibits already a uniaxial anisotropy of Ku = 3.74×104 erg/cm3 which was determined from the saturation field HS of the hard-axis magnetization reversal curve. This value is already about 20 times larger than the uniaxial anisotropy observed in Permalloy films deposited on flat substrates. Since no field annealing has been performed only a strongly enhanced coercivity with respect to the Permalloy film is found. This is due to the coupling of the ferromagnetic layer to the antiferromagnetic layer. Two additional field annealing procedures have then been performed in order to set the exchange bias direction either along or perpendicular to the ripple direction. Since the uniaxial anisotropy contribution is much larger than the unidirectional one the easy- and hard-axes remain the same. However, if the exchange bias is set along the ripple direction a shift of the easy-axis loop is found. In contrast, if the exchange bias field is set perpendicular to the ripple direction the hard-axis loop is shifted. In order to evaluate this behavior in more detail a complete angular dependency of the magnetization reversal behavior has been investigated in both cases and compared to simulations based on a Stoner-Wohlfarth coherent rotation model. A good agreement between experimental data and simulations is found.

Keywords: magnetism; exchange bias; ripples; magnetic anisotropy; ripple formation; ion erosion

  • Lecture (Conference)
    International Magnetics Conference, Intermag 2006, 08.-12.05.2006, San Diego, USA

Publ.-Id: 8122

EXAFS investigation of U(VI) and U(IV) aquo chloro complexes with a newly developed spectro-electrochemical cell

Hennig, C.; Tutschku, J.; Rossberg, A.; Bernhard, G.; Scheinost, A.

The coordination of the U(IV) and U(VI) ions as a function of the chloride concentration in aqueous solution has been studied by U LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The oxidation state of uranium was changed in situ using a gas-tight spectro-electrochemical cell, specifically designed for the safe use with radioactive solutions. For U(VI) we observed the complexes UO2(H2O)52+, UO2(H2O)4Cl+, UO2(H2O)3Cl20 and UO2(H2O)2Cl3 with [Cl] increasing from 0 to 9 M, and for U(IV) the complexes U(H2O)94+, U(H2O)8Cl3+, U(H2O)6-7Cl22+ and U(H2O)5Cl3+. The distances in the U(VI) coordination sphere are U-Oax = 1.760.02 Å, Oeq = 2.410.02 Å and U-Cl = 2.710.02 Å, the distances in the U(IV) coordination sphere are U-O = 2.410.02 Å and U-Cl = 2.710.02 Å.

Keywords: EXAFS; aquo chloro complexes; uranium; U(VI); U(IV); spectro-electrochemistry

  • Poster
    ESRF Users' Meeting 2006, 07.-8.2.2006, Grenoble, France

Publ.-Id: 8121

Comparison of complexed species of Eu in Alumina-bound and free Polyacrylic Acid. A spectroscopic study.

Montavon, G.; Hennig, C.; Janvier, P.; Grambow, B.

The speciation of Eu complexed with polyacrylic acid (PAA) and alumina-bound PAA
(PAAads) was studied at pH=5 in 0.1M NaClO4. Structural parameters were obtained from 7F0→5D0 excitation spectra measured by Laser Induced Fluoresence ectroscopy as well as from Eu LIII edge Extended X-ray Absorption Fine Structure (EXAFS) spectra. The mode of coordination was also investigated by Infra Red pectroscopy. To elucidate the nature of the complexed species, Eu-acetate complexes were used as references. The spectroscopic techniques show that two carboxylate groups with 2-3 (EuPAA) and 4-5 (EuPAAads) hydration water molecules are coordinated to Eu in the first coordination sphere. For EuPAAads, the coordination between carboxylate groups and Eu appears to be bidendate. A similar coordination is probable for EuPAA but the EXAFS data indicate a sligthly distorted coordination. The results show that the degree of freedom of carboxylate groups is not the same for free or adsorbed PAA. For PAA, the degree of freedom is constrained by the flexibility of the methylene chain. When PAA is adsorbed on alumina, the polymer chains cannot any more be treated as independent chains. One may rather assume formation of aggregates that form an organic layer at the mineral surface presenting a complex arrangement of carboxylate groups.

Keywords: polyacrylic acid; Eu; spectroscopic study; speciation; adsorption; ternary system

  • Journal of Colloid and Interface Science 300(2006), 482-490

Publ.-Id: 8120

Structure investigation of uranium in aqueous solution under reduced conditions

Hennig, C.

The presentation refers to the application of a spectroelectrochemical cell for X-ray absorption spectroscopy to structure investigations under reduced conditions. The spectro-electrochemical cell will be used at the Rossendorf Beamline in Grenoble/France.

Keywords: Actinides; XAFS; Rossendorf beamline

  • Invited lecture (Conferences)
    Research Reactor Institute, Kyoto University, 19.01.2006, Kyoto, Japan

Publ.-Id: 8119

X-ray absorption spectroscopy as tool for speciation and structure analysis of actinides in solution

Hennig, C.

The contribution comprises an introduction in X-ray absorption spectroscopy and several typical examples of speciation and structure analysis. XAFS sectroscopy is a appropriate method to study structure sequences of solution species.

Keywords: XAFS; actinides; ROBL beamline

  • Invited lecture (Conferences)
    Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 17.01.2006, Tokyo, Japan

Publ.-Id: 8118

Entwicklung eines 3D Neutronentransportcodes auf der Basis der Ray-Tracing-Methode und Untersuchungen zur Aufbereitung effektiver Gruppenquerschnitte für heterogene LWR-Zellen

Beckert, C.; Rohde, U.

Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert.
Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (bzw. Moderator mit geringerer Dichte) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: linearer Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void (bzw. Moderator geringerer Dichte) umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.

Keywords: Reactor physics; calculational methods; neutron transport; transport methods; Monte Carlo method; ray tracing; cross sections; cell calculation; absorber rod; void

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-446 2006
    ISSN: 1437-322X


Publ.-Id: 8117

Annealing of the indium tin oxide films with an electrical current

Rogozin, A.; Shevchenko, N.; Vinnichenko, M.; Seidel, M.; Kolitsch, A.; Möller, W.

Indium tin oxide (ITO) films were grown by reactive middle frequency magnetron sputtering. Postdeposition annealing of transparent and conductive ITO films was performed with an electrical current in vacuum and air. The electrical power released by the current into the film during annealing was maintained at a constant level. The film structure and properties were characterized in situ by synchrotron produced X-ray diffraction, spectroscopic ellipsometry and resistance measurements.
The XRD data demonstrate transformation of the as-deposited amorphous film structure in to
crystalline during annealing. The films annealed in vacuum show two-stage decrease in the film resistance: first in amorphous state and second during crystallization. Increasing the electrical power of annealing hastens the onset of the second stage and reduces its total time. Resistance of the films annealed in air have three-stage behaviour: the resistance decreases at the beginning, then it starts to increase and finally, it decreases again. The experimental results are discussed in the terms of oxygen vacancy generation and tin donor activation.
Comparison of these results with data obtained during annealing of the indium oxide film without tin doping demonstrates significance of tin donor activation on the film resistance during crystallization process.
The mass analysis of the gas fractions escaping the ITO film during subsequent annealing in vacuum of the samples annealed already in air and vacuum was carried out. It is established that the samples annealed in air contain approximately one order of magnitude higher amount of water in comparison to the samples annealed in vacuum. This result shows that the water absorption deteriorates the improvement of the film resistance during annealing in air.

Keywords: ITO; annealing; electric current; film resistivity

  • Poster
    13th International Congress on Thin Films; 8th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, 19.-23.06.2005, Stockholm, Sweden

Publ.-Id: 8116

Mass dependence of nuclear isotopic temperature for binary and ternary fission.

Andronenko, M. N.; Andronenko, L. N.; Neubert, W.

Method of Temperature Distributions based on isotope thermometers has been suggested and applied to determine nuclear temperatures related to spontaneous and neutron induced fission process. Binary and ternary fission modes show a pronounced difference for the mean temperature. Target mass dependence of nuclear temperatures is in agreement for both modes of fission process but in contradiction to one for high energy fragmentation.

Keywords: will be included

  • Other report
    Gatchina, Russia: Preprint St. Petersburg Nuclear Physics Institute, PN PI - 2643, 2005
    21 Seiten

Publ.-Id: 8115

Improved Monte Carlo Methods with Application to Borehole Logging Simulations

Legrady, D.

Monte Carlo simulation is the most accurate method in general for nuclear particle transport calculations. The convergence properties are, however, often outstandingly poor. The efficiency can be enhanced by replacing the simulation by a statistically equivalent calculation by modifying the sampling algorithms by so-called variance reduction techniques. One way of achieving such aim is the adjoint Monte Carlo method, where particle interactions are simulated in reverse. The Midway Monte Carlo method combines a regular Monte Carlo forward simulation with an adjoint one on a virtual surface separating source and detector resulting in an enhanced convergence rate. The coupling of forward and ajoint calculations is a statistically evaluation of a bilinear surface integral of the radiation current and the adjoint function in every phase-space variable.
This doctorate thesis develops and applies the time dependent form of the Midway Monte Carlo method to a pulsed neutron-photon oil well logging tool. Full analysis is given on the accuracy and convergence properties of the coupling possibilities and of the efficiency increase for such an application. Additionally, the theoretical framework of the adjoint simulation of scintillation detectors (Pulse Height tallies) has been developed.
The thesis concludes that the Midway Monte Carlo method delivers a user-friendly general variance reduction tool with high efficiency improvement, moreover the application of conventional variance reduction techniques can further enhance the efficiency. On the downside the reliability of the delivered answer and confidence intervals are often poor for time dependent simulations. Also, the method requires high computer memory capacity for the current standards.

Keywords: Monte Carlo; Midway; Adjoint; Well logging; Borehole logging; pulse height; neutron; photon; time dependent

  • Book (Editorship)
    (Signatur: 518.2/4/1:1) Delft: Delft University Press, 2005
    140 Seiten
    ISBN: 90-407-2614-0

Publ.-Id: 8114

Potential energy retention of slow highly charged Ar-Ions into solid surfaces -a calorimetric measurement-

Kost, D.; Facsko, S.; Keller, A.; Grötzschel, R.; Möller, W.

Highly charged ions (HCIs) carry a large amount of potential energy, which is defined as the sum of the binding energies of all electrons that are removed from the atom. In the case of low velocities of the ions this energy can exceed the kinetic energy of the ions. Retaining such a large energy in a very small surface area of typically about 1-10nm^2 and in a very short interaction time of typically 5-10 fs an enormous power flux of 10^13 W/cm^2 is given. Here the mechanisms of energy dissipation are not completely understood yet. A fraction of energy is released by emission of electrons and photons, the other part is retained in the surface. Micro-calorimetric techniques provide some advantages for the measurement of the energy retention. We used this technique to determine the fraction of the retained potential energy in collisions of argon ions of charge states from Ar+ to Ar9+ with atomically clean surfaces of Si. We measured values between 0.7 and 0.8 for the fraction of the retained energy. This values are compared with earlier measurements on a copper surface. The potential energy retention coefficient for silicon is about three times larger than in case of the copper surface.

  • Lecture (Conference)
    25th Brandt-Richie Workshop on Particle Penetration Phenomena and Excitations of Solids: Electronic Interactions at Surfaces, 10.-13.04.2005, Gainesville, USA

Publ.-Id: 8113

Magnetic domains and magnetization reversal of ion-induced magnetically patterned RKKY-coupled Ni81Fe19/Ru/Co90Fe10 films

Kuepper, K.; Fassbender, J.; Bischoff, L.; Mattheis, R.; Fischer, P.

Pure magnetic patterning by means of ion beam irradiation of magnetic thin films and multilayers result often from a post deposition local modification of the interface structure with only minor effects on the film topography. In the study presented here a 60 keV fine focused Co ion beam was used to change the coupling in a Ni81Fe19/Ru/Co90Fe10 structure from antiferromagnetic to ferromagnetic on a micron scale. Thereby an artificial structure with locally varying interlayer exchange coupling and therefore magnetization alignment is produced. High-resolution fullfield x-ray microscopy is used to determine the magnetic domain configuration during the magnetization reversal process locally and layer resolved dueto the element specific contrast in circular x-ray dichroism. In the magnetically patterned structure there is in addition to the locally varying interlayer exchange coupling across the Ru layer also the direct exchange coupling within each ferromagnetic layer present. Therefore the magnetization reversal behaviour of the irradiated stripes is largely influenced by the surrounding magnetic film.

Keywords: magnetic patterning; ion irradiation; x-ray magnetic circular dichroism (XMCD); x-ray microscopy

  • Poster
    ALS Users' Meeting 2005, 20.-22.10.2005, Berkeley, USA
  • Poster
    364. WE-Heraeus-Seminar Nanoscale Magnets - Top down meets Bottom up, 04.-06.01.2006, Bad Honnef, Germany
  • Poster
    DPG - spring meeting of the Division Condensed Matter, 26.-31.03.2006, Dresden, Germany

Publ.-Id: 8110

Plasma-immersion ion-implanted nitinol surface with depressed nickel concentration for implants in blood

Maitz, M.; Shevchenko, N.

Ion implantation into nitinol had been shown previously to decrease the surface nickel concentration of this alloy and produce a titanium oxide layer. Nothing is known yet about the blood compatibility of this surface and the suitability for implants in the blood vessels, like vascular stents. Nickel depletion of superelastic nitinol was obtained by oxygen or helium plasma-immersion ion implantation. The latter leads to the formation of a nickel-poor titanium-oxide surface with a nanoporous structure, which was used for comparison. Fibrinogen adsorption and conformation changes, blood platelet adhesion, and contact activation of the blood clotting cascade have been checked as in vitro parameters of blood compatibility; metabolic activity and release of cytokines IL-6 and IL-8 from cultured endothelial cells on these surfaces give information about the reaction of the blood vessel wall. The oxygen-ion-implanted nitinol surface adsorbed less fibrinogen on its surface and activated the contact system less than the untreated nitinol surface, but conformation changes of fibrinogen were higher on the oxygen-implanted nitinol. No difference between initial and oxygen-implanted nitinol was found for the platelet adherence, endothelial cell activity, or cytokine release. The nanoporous, helium-implanted nitinol behaved worse than the initial one in most aspects. Oxygen-ion implantation is seen as a useful method to decrease the nickel concentration in the surface of nitinol for cardiovascular applications.

Keywords: nitinol; ion implantation; nickel depletion; titanium oxide; blood compatibility

  • Journal of Biomedical Materials Research Part A 76A(2006)2, 356-365

Publ.-Id: 8109

Oxygen implanted NiTi surfaces for biomedical application

Shevchenko, N.; Richter, E.; Maitz, M. F.; Möller, W.

no abstract delivered from author

Keywords: PIII; biomedical; NiTi; surface

  • Poster
    8th International Workshop on Plasma Based Ion Implantation and Deposition, 18.-22.09.2005, Chengdu, China

Publ.-Id: 8108

Structure and properties of oxygen implanted NiTi surfaces

Shevchenko, N.; Richter, E.; Pham, M.-T.; Maitz, M. F.

The memory shape and superelastic NiTi alloy for biomedical implants and devices has the drawback of the high nickel concentration of 50 at%. Plasma immersion ion implantation (PIII) for improved corrosion resistance and surface nickel depletion of NiTi has been suggested. In the recent work it could be shown that oxygen PII implantation (ion energy of 20 keV and fluence of 1e17 – 1e18 cm-2) can reduce the Ni concentration in 50-100 nm surface layers to concentration below 1 at%. This effect is combined with a Ni enriched layer below the Ni depleted surface layer, what suggests a reactive process as mechanism. Grazing incidence X-ray diffraction analysis revealed the formation of rutile TiO2 phase in the surface layer and perhaps Ni4Ti3 in the Ni enriched layer. The effect of ion fluence and implantation temperature on element profiles, phase composition, layers thickness has been systematically investigated.
The nickel depleted TiO2 layer prevents corrosion and out-diffusion of Ni ions. The oxygen ion implanted NiTi surface had a superior blood compatibility in vitro compared to untreated NiTi.

Keywords: Nitinol; PIII; oxide layer; surface properties

  • Poster
    13th International Congress on Thin Films /8th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, 19.-23.06.2005, Stockholm, Sweden

Publ.-Id: 8107

Real-time investigations of ITO film structure evolution during annealing

Shevchenko, N.; Rogozin, A.; Vinnichenko, M.; Cantelli, V.; Kolitsch, A.; Möller, W.

The real-time in-situ evolution of the ITO film structure during annealing was continuously investigated by synchrotron X-ray diffraction at ROssendorf Beam Line (ROBL), which is located at the European Synchrotron Radiation Facility in Grenoble, France. The amorphous ITO films are produced by reactive pulsed middle frequency dual magnetron sputtering on the Si substrates covered with SiO2. The post-deposition annealing in vacuum of ITO samples was carried out with the ROBL UHV annealing chamber equipped with a hemispherical Be dome at two annealing modes: termal annealing (at constant temperature within the range of 200 - 240 °C) and annealing with an electrical current (at constant electrical power within the range of 1.25 – 2.0 W). In both experiments the resistivity behavior of the ITO film was monitored in situ by the four point probe technique or direct electrical measurement.
The evolution of XRD peaks of crystalline In2O3 phase with annealing time was shown. The time dependence of XRD peak integral intensity has the typical S-like shape. Using the Kolmogorov–Avrami–Johnson–Mehl equation for the dependence of the crystalline fraction on the annealing time, the kinetic parameters of crystallization process were determined. The value of kinetic exponent n is within the range of 2-3 for the thermal annealing and within the range of 1-2 for the annealing with an electrical current. The activation energy for the crystallisation at thermal annealing was found as 1.5 +/- 0.2 eV, whereas the activation energy at electrical current annealing was determined as 0.8 +/- 0.1 eV. It could be suggested that an electrical current stimulates the crystallization process.

Keywords: ITO; in-situ XRD; crystallization; activation energy

  • Lecture (Conference)
    13th International Congress on Thin Films /8th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, 19.-23.06.2005, Stockholm, Sweden

Publ.-Id: 8106

Optimized List-Mode Acquisition and Data Processing Procedures for ACS2 Based PET Systems

Langner, J.; Bühler, P.; Just, U.; Pötzsch, C.; Will, E.; van den Hoff, J.

PET systems using the acquisition control system version 2 (ACS2), e.g. the ECAT Exact HR PET scanner series, offer a rather restricted list-mode functionality. For instance, typical transfers of acquisition data consume a considerable amount of time. This represents a severe obstacle to the utilization of potential advantages of listmode acquisition. In our study, we have developed hardware and software solutions which do not only allow for the integration of list-mode into routine procedures, but also improve the overall runtime stability of the system.
We show that our methods are able to speed up the transfer of the acquired data to the image reconstruction and processing workstations by a factor of up to 140. We discuss how this improvement allows for the integration of list-mode-based post-processing methods such as an event-driven movement correction into the data processing environment, and how list-mode is able to improve the
overall flexibility of PET investigations in general. Furthermore, we show that our methods are also attractive for conventional histogram-mode acquisition, due to the improved stability of the ACS2 system.

Keywords: Dynamic data acquisition; list mode; data processing; ACS2; ECAT Exact HR+; positron emission tomography

Publ.-Id: 8105

Structural evolution on thermal cycling in Ti-rich NiTi SMA

Paula, A. S.; Canejo, J. P. H. G.; Schell, N.; Braz Fernandes, F. M.

Shape-memory alloys (SMA) represent a class of metallic materials that has the capability of recovering a previously defined initial shape when subjected to an adequate thermomechanical treatment. Annealing of a Ti-rich Ni–Ti alloy has been followed by in situ high temperature diffraction in order to register the texture as well as the microstrain/microstress evolution. This type of study is relevant to the envisaged applications, because the type of preferential orientation and the corresponding anisotropic response of the material conditions contributes to the success of the SMA application. In the present study we have tested the feasibility of high temperature pole figures determination at ROBL (BM20) at the ESRF, and we have shown that there is a relation between the preferential orientation changing and the structural evolution taking place during annealing.

Keywords: Keywords: Shape-memory alloy; Texture; In situ high temperature X-ray diffraction

  • Nuclear Instruments and Methods in Physics Research B 238(2005)1-4, 111-114

Publ.-Id: 8104

Porous surface of NiTi alloy produced by plasma ion implantation

Shevchenko, N.; Muecklich, A.; Richter, E.; Maitz, M. F.

For several applications a nanoporous surface layer of titanium oxide on titanium or NiTi is desired, e.g. for surface-increase for catalytical or electrochemical applications, or as carrier in a drug release system. This application requires interconnected pores with the size in the same order of magnitude as the drug molecule, few nanometers. A possibility to produce such a nanoporous structure is seen in the high dose ion implantation of a non reactive gas, which aggregates to nano-bubbles. To our knowledge this type of treatment has not yet been done with the superelastic or memory shape NiTi alloy.
Helium ion implantation of the NiTi and Ti samples was performed by means of plasma immersion ion implantation at following parameters: ion energy of 20 keV, ion fluence of ~1e18 cm -2, substrate temperature (100 – 400 °C). The implanted layers were examined by elastic recoil detection analysis, Auger electron spectroscopy, grazing incidence X-ray diffraction analysis, atomic force microscopy and transmission electron microscopy.
The He+-implanted region of NiTi samples contains a Ni depleted surface layer of TiOx, a Ni enriched zone with fine Ni4Ti3 crystallites and a nanoporous amorphous layer. Structure and morphology of these layers after etching in 1% HF acid were studied in order to characterize a deeper porous layer. An influence of implantation temperature on Ni transport from surface to the deeper layers and nanoporous layer formation are discussed.

Keywords: NiTi; nanoporous; surface; PIII

  • Poster
    European Materials Research Society Spring Meeting (E-MRS), 31.05.-03.06.2005, Strasbourg, France

Publ.-Id: 8103

Structural in situ studies of shape memory alloy (SMA) Ni–Ti thin films

Martins, R. M. S.; Schell, N.; Silva, R. J. C.; Braz Fernandes, F. M.

Ni–Ti SMA thin films formed by sputtering have been attracting great interest as powerful actuators in microelectromechanical systems (MEMS) such as micro-valves, micro-fluidic pumps and micro-manipulators. Successful implementation of Ni–Ti micro-actuators requires a good understanding of the relationship among processing, microstructure and properties of Ni–Ti thin films. At the ROssendorf BeamLine (ROBL-CRG) at ESRF, we carried out a series of experiments that clearly illustrate the benefit of in situ studies, not only during annealing, but also during sputtering. The in situ sputtering experiments during film growth were performed using a magnetron sputter deposition chamber installed into the six-circle diffractometer of the materials research station. This facility allowed us to follow, almost in ‘‘real time’’, the structural evolution of the deposited thin films as a consequence of changing deposition parameters.

Keywords: Keywords: Structure and morphology; Deposition by sputtering; In situ X-ray diffraction

  • Nuclear Instruments and Methods in Physics Research B 238(2005)1-4, 319-322

Publ.-Id: 8102

Determination of absolute defect concentrations forsaturated positron trapping – deformed polycrystalline Ni as a case study

Krause-Rehberg, R.; Bondarenko, V.; Thiele, E.; Klemm, R.; Schell, N.

Positrons may be used in many cases to determine defect densities of vacancies and dislocations. In case of saturated positron trapping, i.e. all positrons are getting trapped, only a lower-limit estimation can be given. However, a combination of positron back-diffusion measurements using a monoenergetic positron beam in combination with conventional lifetime spectroscopy can be used to overcome the problem of saturated positron trapping. As a case study, this combination was used for the determination of dislocation densities in polycrystalline nickel samples of highly varying dislocation density. Saturated positron trapping into dislocations and small voids was observed. The total positron trapping rate was calculated from the positron diffusion length obtained by back-diffusion experiments. The trapping rates of the two defects were finally obtained using the decomposition of lifetime spectra. The results were found in good agreement with those determined by the analysis of synchrotron Bragg-diffraction profiles, measured on the same set of samples. From the comparison of both techniques, the positron trapping coefficient was found to be ldisl = 3.9 ± 0.3 cm2/s for a high density of dislocations in Ni.

Keywords: Keywords: Positron annihilation; VEPAS; Dislocation density; Nickel; Specific trapping rate; Bragg-diffraction profiles

  • Nuclear Instruments and Methods in Physics Research B 240(2005)3, 719-725

Publ.-Id: 8101

Investigation of the formation and phase transitionof Ge and Co nanoparticles in a SiO2 matrix

Cantelli, V.; von Borany, J.; Mücklich, A.; Schell, N.

The evolution of ion beam synthesized Co and Ge nanoclusters into a SiO2 matrix during annealing processes has been investigated by X-ray diffraction and transmission electron microscopy. Remarkable differences have been found between Ge and Co clusters behaviour. For Ge implanted SiO2 films, a clear influence of near-surface Ge oxidation and nanoclusters melting has been established. Annealing at temperatures around 1000 C leads to the formation of small (diameter 5 nm) nanocrystals. Classical Ostwald ripening mainly drives the clusters thermodynamical growth. On the contrary, for Co-implanted SiO2 films, a jump-like transition in nanoclusters evolution has been established at about 800 °C. A homogenous distribution of small (diameter 4 nm) amorphous clusters is transformed into a bimodal clusters profile, characterised by large (diameter between 20 and 40 nm) nanocrystals near the surface and a region of smaller clusters (diameter 7 nm) in depth. During Co nanoclusters formation the influence of nanoclusters melting can be neglected.
PACS: 81.07.Bc; 61.10.Eq; 68.37.Lp; 66.30.Pa

Keywords: Keywords: Nanoclusters; Ion-beam synthesis; Cobalt; Germanium; Silicon dioxide

  • Nuclear Instruments and Methods in Physics Research B 238(2005)1-4, 268-271

Publ.-Id: 8100

Novel and Efficient Preparation of Precursor [188Re(OH2)3(CO)3]+ for the Labeling of Biomolecules

Park, S. H.; Seifert, S.; Pietzsch, H.-J.

A novel and efficient method for preparing 188Re(I) tricarbonyl precursor [188Re(OH2)3(CO)3]+ has been developed by reacting [188Re]perrhenate with Schibli’s kit in the presence of borohydride exchange resin (BER) as a reducing agent and an anion scavanger. The precursor was produced in more than 97% yield by reacting a solution of tetrahydroborate exchange resin (BER, 3 mg), borane-ammonia (BH3âNH3, 3 mg), and potassium boranocarbonate (K2[H3BCO2], 3 mg) in 0.9% saline with a solution of sodium perrhenate (Na188ReO4) with up to 50 MBq and concentrated phosphoric acid (85%, 7 íL) at 60 °C for 15 min. HPLC and TLC revealed 0% unreacted [188Re]-perrhenate ion and <3% of colloidal 188ReO2. Since the precursor is produced with high radiochemical purity and labeling efficiency under the milder conditions than those required for the conventional reducing agents, the latter can be replaced.

  • Bioconjugate Chemistry 17(2006), 223-225

Publ.-Id: 8099

Synthesis of Azolyl Carboximidamides as Ligands for Zn(II) andCu(II): Application of the Zn(II) Complexes as Catalysts for theCopolymerization of Carbon Dioxide and Epoxides

Walther, M.; Wermann, K.; Lutsche, M.; Günther, W.; Görls, H.; Anders, E.

A series of novel S,N-heterocyclic (thiazolyl) substituted carboximidamides 3 and 4 was synthesized in yields up to 82% from specific triazinium salts 1 and primary or secondary amines 2 which additionally bear pyridine or imidazole units. These carboximidamides are used as tailor-made ligands for the complexation of Cu(II) and Zn(II). The coordination behavior of 3 and 4 and the properties of the resulting metal complexes are affected a significant extent especially by the nature of these amine substituents. The most important structural feature of the novel complexes is that the ligation of the metal cations is achieved by a 1,3,5-triazapentadienyl anion system, compare the X-ray structure of the model complex Cu-4d. Analogous Zn(II) complexes 5, 6a, 6b, 6c, 7a, and 7b were obtained from carboximidamides 3, 4a, 4b, 4c, 4d, and 4e after reaction with diethylzinc. Interestingly, these Zn(II) complexes possess an intrinsic activity to catalyze the copolymerization of cyclohexene oxide and carbon dioxide to give polycarbonates 15 (TON up to 113; Turn Over Number: moles of substrate 14 consumed per moles of zinc. Molecular weights: up to 206â103 Da). Contaminations of 15 by polyethers are produced only in remarkably small amounts.

  • Journal of Organic Chemistry 71(2006)4, 1399-1406

Publ.-Id: 8098

Real time in situ diagnostics of PVD growth using synchrotron radiation

Andreasen, K. P.; Bøttiger, J.; Chevallier, J.; Schell, N.

For specific applications of hard coatings, the microstructure (or nanostructure) has to be tailored for optimum performance. This requires information about the mechanisms of growth and the connection between the microstructure and the deposition parameters. In order to obtain this knowledge, in situ real time growth studies of magnetron-sputtered thin films were carried out. A growth chamber, equipped with two magnetrons and Kapton windows for X-ray diffraction and reflectivity, was mounted on a six-circle goniometer at a synchrotron beam line at ESRF in Grenoble. As an example, X-ray diffraction measurements were carried out in situ during growth of TiN to follow the development of the microstructure. Recrystallization was identified as the mechanism which controlled the development of texture. The driving force for these texture changes arose from minimalization of the sum of the surface energy and the strain energy of the individual grains. As another example, the heteroepitaxial growth of TiN on MgO(001) was studied. Bragg–Brentano as well as grazing-incidence in-plane wide angle scattering was used to establish the pseudomorphic growth of TiN to the underlying MgO(001). Using real-time specular X-ray reflectivity, layer-by-layer growth was observed, with the surface roughening decreasing with an increase in the deposition temperature. The growth of nanocrystalline Au was also investigated. Among the results we found that changes in the (111) fiber texture arose from grain rotations.

Keywords: Keywords: In situ diagnostics; X-ray diffraction; Magnetron; Gold; Titanium nitride; Nanostructure

  • Surface & Coatings Technology 200(2005), 1-6

Publ.-Id: 8096

A Low Energy Ion Beam Line for Highly Charged Ions

Zschornack, G.; Landgraf, S.; Großmann, F.; Kentsch, U.; Ovsyannikov, V. P.; Schmidt, M.; Ullmann, F.

An ion beam line is presented, which is designed to study the interaction of highly charged ions with matter, especially solid surfaces. The highly charged ions are produced in a room temperature electron beam ion trap, the Dresden EBIT. This device delivers bare nuclei up to elements with an atomic number of about 28, and neon-like ions up to about Z=80. After leaving the trap the ion beam containing several neighbouring ion charge states passes through standard ion optics elements before entering an analysing magnet for separating a certain ion charge state. In a following deceleration unit, which will be integrated soon, the ions can be slowed down to a definite kinetic energy of a few eV. The characteristic of the HCI beam is presented, combined with ion extraction spectra of selected elements detected by a Faraday cup after passing through an analysing magnet.

Keywords: Highly Charged Ions; Electron Beam Ion Trap

  • Vacuum 78(2005)2-4, 319-323

Publ.-Id: 8095

Experimente zur CFD-Validierung für horizontale Zweiphasen-Strömungen

Vallee, C.

Zur Weiterentwicklung und Validierung von CFD-Codes bei Zweiphasen-Strömungen wurden am Forschungszentrum Rossendorf zwei horizontale Luft/Wasser-Strömungskanäle aufgebaut. Die Teststrecken, mit unterschiedlichem rechteckigen Querschnitt, wurden für den Einsatz optischer Messverfahren aus Acrylglas konstruiert. Die Versuche fanden bei Umgebungsdruck und -temperatur statt.

Die erste Anlage wurde für Vorversuche genutzt: An dieser konnte die Instrumentierung getestet und weiterentwickelt werden. Es wurden optische Messungen mit einer Hochgeschwindigkeitskamera durchgeführt und mit dynamischen Druckmessungen synchronisiert. Aus den entstandenen Bildsequenzen wurde die Phasengrenzfläche durch eigenentwickelte Algorithmen ermittelt. Außerdem wurden Geschwindigkeitsfelder in einem Schwall mit PIV (Particle Image Velocimetry) gemessen.

Der zweite Testkanal profitierte von den Erfahrungen an der ersten Anlage: Seine Konstruktion wurde für die Validierung von CFD-Codes optimiert. Eine spezielle Einlaufkomponente sorgt für definierte und konstante Randbedingungen am Eintritt. Zudem kann die Kanallänge bis auf 14 m erweitert werden. Es werden erste qualitative Ergebnisse gezeigt, so zum Beispiel Visualisierungen verschiedener Strömungsformen.

Keywords: Horizontal two-phase flow; Slug flow; High-speed video observations; Image processing; PIV

  • Invited lecture (Conferences)
    Seminar des Lehrstuhl für Thermodynamik, 09.01.2006, Garching, München, Germany

Publ.-Id: 8094

Magic matching in semiconductor heterojunctions

Pecz, B.; Barna, Á.; Heera, V.; Skorupa, W.

Matching of m crystal planes of a grown layer to n planes of the substrate is observed in many cases, when the difference in the lattice parameters is large. This kind of magic matching is explained by coincidence planes. Two examples are shown in this paper. SiC grains perfectly oriented to the substrate were prepared by high temperature ion implantation of Si into natural diamond. Considering the (111) lattice planes and the cases, when 5 planes of SiC match to 6 planes in diamond, or 4 planes of SiC match to 5 planes in diamond, the misfit is reduced to about 2% in both cases having opposite signs. High resolution images taken at the SiC/diamond interface were investigated and both of the above mentioned domains were found. When we consider the regular distribution of the above two domains, i.e. matching of 9 SiC lattice planes to 11 diamond planes a misfit value below 0.1% is obtained. This explains how the ion beam synthesised SiC can grow epitaxially despite the huge difference in lattice parameters. GaN synthesised in GaAs by ion implantation is presented as another example where magic matching of 5:4 reduces the misfit to 0.8%. That value is low enough to be compensated by elastic deformation of the lattice, therefore the insertion of another domain is not needed.

Keywords: ion beam synthesis; heteroeptitaxy; SiC-diamond; GaAs-GaN; lattice matching; XTEM

  • Lecture (Conference)
    14th International Conference on Microscopy of Semiconducting Materials- MSMXIV, 11.-14.04.2005, Oxford, U. K.
  • Contribution to proceedings
    Microscopy of Semiconducting Materials, 11.-14.04.2005, Oxford, UK
    Proceedings of the 14th Conference, Berlin, Heidelberg, New York: Springer, 3-540-31914-X, 159-162

Publ.-Id: 8093

Dependence of the linewidth of planar electron channeling radiation on the thickness of the diamond crystal

Azadegan, B.; Wagner, W.; Pawelke, J.

Measurements of (110) planar channeling radiation have been performed at the radiation source ELBE at electron energies of 14.6, 17, 30 and 34 MeV using diamond crystals of thickness 42.5, 102, 168 and 500 micrometers. The influence of different line-broadening mechanisms on the spectral shape of radiation from the 1 - 0 transition has been investigated. The analysis bases on fitting a convolution of the intrinsic Lorentz-like line shape with a Gaussian-like multiple-scattering distribution to the measured spectra. The asymmetry parameter involved relates to the standard deviation of the multiple-scattering angle under channeling condition. Its dependence on the crystal thickness at channeling was found to be weaker than for nonchanneled particles. The deduced coherence lengths show no significant dependence on the electron energy.

Keywords: planar channeling radiation; linewidth; diamond; coherence length

  • Physical Review B 74(2006), 045209-1

Publ.-Id: 8092

Untersuchung der Verschiebung der bakteriellen Populationen in mit U(VI) inokulierten Bodenproben einer Uranabfallhalde mittels direkter molekularer Analysen

Tschikov, J.

wird nachgereicht

  • Other report
    Hochschule Anhalt: Köthen, 2005
    45 Seiten

Publ.-Id: 8091

"Böttger Stoneware" - Authentic or Not?

Neelmeijer, C.; Mäder, M.; Pietsch, U.; Ulbricht, H.; Walcha, H.-M.

The so-called "Böttger Stoneware", red porcelain invented by Böttger in the early 18th century, represents an independent development of high technological standard. In comparison to other ceramics Böttger stoneware is characterized by a high material density, consequently greater hardness and suitability for surface polishing. Hence museums show growing interest in obtaining objective criteria based on non-destructive methods of stoneware material analysis. In the present work the possibility of characteristic "fingerprints" for the different provenance of stoneware is tested by making use of ion beam analysis at the external proton beam, i.e. a proton beam on air.

Keywords: ceramics; Böttger; stoneware; material analysis; fingerprints; ion beam analysis; PIXE

  • Contribution to external collection
    Dagmar Hülsenberg: Ehrenfried Walther von Tschirnhaus Gesamtausgabe, Beiband, Leipzig: Sächsische Akademie der Wissenschaften zu Leipzig, 2003, 3-515-08464-9, 29-33

Publ.-Id: 8090

Schätze im Protonenlicht

Neelmeijer, C.; Mäder, M.

Glas kann korrodieren wie Metall. Wenngleich die Prozesse andersartig sind, das Resultat ist identisch. Umgebungsbedingte chemische Reaktionen zerstören die Materialien. Schadstellen an wertvollen Gemälden lassen sich restauratorisch festigen und ergänzen, für Unikate aus Glas besteht diese Chance nicht. Der Erhaltungszustand von Glasoberflächen kann bestenfalls eingefroren werden. Voraussetzung dafür ist, dass man ihn kennt und dass es möglich ist, die potentielle Gefahr umweltbedingter Schädigung für das einzelne Glasobjekt objektiv einzuschätzen. Selbst unter dem Schutz von Klimaanlagen in den Museen altern die Schätze aus Glas. Einige hochkarätische Pretiosen befinden sich heute bereits in einem außerordentlich kritischen Zustand. Das Schadensbild reicht von Trübung über feine Haarrisse und großflächige Rissnetze bis zur Schuppenbildung, der Ablösung von Glasschichten und den Verlust von Farbfassungen. Viele Objekte erscheinen, visuell beurteilt, heute noch in recht gutem Erhaltungszustand. Genau hier setzt die Entwicklung unserer präventiven Untersuchungsmethode ein, in Analogie zur lebensrettenden Krebsfrüherkennung bei Patienten. Ohne Probenahme gelingt es mittels zerstörungsfreier Materialanalyse solche Gläser aufzufinden, deren Zusammensetzung für Glaskorrosion kritisch ist. Für diese empfehlen wir dem Museum vorsorgliche Erhaltungsmaßnahmen.

Keywords: Glass; museum; deterioration; non-destructive analysis; PIGE; PIXE; RBS

  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-398 März 2004, 62-71
    ISSN: 1437-322X


Publ.-Id: 8089

Preventive ion beam inspection of glass treasures

Neelmeijer, C.; Mäder, M.

Art objects made of glass may undergo deterioration when exposed to environmental stress. Even in air conditioned museums, susceptible glass surfaces may decompose. Thus, their transparency is reduced and initial tiny surface cracks may result in irreplaceable loss of glass. Degradation takes place via ion exchange reactions between the silicate network and the humidity of the ambient atmosphere. Endangered glass objects in important collections should be studied using non-destructive analytical methods. In this regard, the advantage of ion beam analysis by simultaneous Particle Induced Gamma-ray Emission (PIGE), Particle Induced X-ray Emission (PIXE) and Rutherford Backscattering Spectrometry (RBS) in a non-vacuum facility is demonstrated. This paper is concerned with both the current condition of the glass surface and the composition of the bulk of the glass. The result of such ion beam examination enables the scientist to recommend suitable storage conditions. In addition, the non-destructive study provides scientists studying art objects with means of objective material identification, enabling them to reach conclusions with respect to particular glass technologies or proveniences.

Keywords: Glass; museum; deterioration; non-destructive analysis; ion beam analysis; PIGE; PIXE; RBS

  • Contribution to external collection
    Annemie Adriaens, Christian Degrini, JoAnn Cassar: Benefits of non-destructive analytical techniques for conservation, Brussels: COST Office, 2005, 92-898-0010-0, 99-108

Publ.-Id: 8088

IBA of iridescent Art Nouveau glass - comparative studies

Mäder, M.; Jembrih-Simbürger, D.; Neelmeijer, C.; Schreiner, M.

Simultaneous PIXE, PIGE, and RBS in air were employed to characterise the surface structure of iridescent Art Nouveau glass artefacts produced around 1900 by Tiffany, USA and Loetz, Austria. Using PIXE and PIGE, the chemical composition of the bulk glass and the overlays was determined in a non-destructive manner. Furthermore, the combination of PIXE and RBS enabled the layer structure of the analysed glasses (bulk, overlays, and iridescent layers) and the thicknesses of the thin layers in the near-surface domain to be determined. The measurement and evaluation procedure is demonstrated on blue iridescent glass fragments of Tiffany and Loetz by way of example. The initial results showing similarities but also differences in the layered glass structure of Tiffany and Loetz objects are presented.

Keywords: Ion beam analysis (IBA); Proton induced X-ray emission (PIXE); Proton induced γ-ray emission (PIGE); Rutherford backscattering spectrometry (RBS); Iridescent Art Nouveau glass; Tiffany; Loetz

  • Nuclear Instruments and Methods in Physics Research B 239(2005), 107-113

Publ.-Id: 8087

Three-dimensional modeling of EXAFS spectral mixtures by combining Monte-Carlo Simulations and Target Transformation Factor Analysis

Rossberg, A.; Scheinost, A.

wird nachgereicht

  • Poster
    15th Users Meeting, 08.-11.02.2005, Grenoble, France

Publ.-Id: 8086

Wavelet analysis of EXAFS Data

Funke, H.; Chukalina, M.; Hennig, C.; Rossberg, A.; Scheinost, A.

wird nachgereicht

  • Poster
    15th Users Meeting, 08.-11.02.2005, Grenoble, France

Publ.-Id: 8085

The Rossendorf Beamline for Actinide Research

Scheinost, A.

wird nachgereicht

  • Lecture (others)
    CEA, 11.05.2005, Valduc, France

Publ.-Id: 8084

Coolant mixing studies of natural circulation flows at the ROCOM test facility using ANSYS CFX

Höhne, T.; Kliem, S.

Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the ROCOM mixing test facility. The Rossendorf Coolant Mixing Model (ROCOM) was constructed for the investigation of coolant mixing in PWR. The ROCOM facility has four loops each with an individually con¬trol¬led pump. This allows to per¬form tests in a wide range of PWR flow conditions from natural con¬vec¬tion flow up to forced con¬vec¬tion flow at nominal flow rates including flow ramps. ROCOM is operated with wa¬ter at ambient tem¬pe¬ra¬tures because the re¬ac¬tor pressure ves¬sel (RPV) mock-up and its internals are made of perspex. The model has a linear scale 1:5 to the prototype, the water inventory in the loops is kept in scale 1:125 and the traveling time of the coolant is identical to the original reactor.

Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shifted towards the reactor pressure vessel (RPV). In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied. During inherent dilution the slug could have a higher temperature and a lower density. Additionally the boron content influences the fluid density. In ROCOM this density difference is adjusted by the addition of ethyl alcohol. The acquisition of the concentration fields is performed with high spatial and temporal resolution mea¬sure¬ments of the tracer con¬¬¬centration.

Experiments with 0 up to 2% density differences between the de-borated slugs and the ambient coolant were used to validate the CFD software ANSYS CFX. A Reynolds stress turbulence model was employed and a hybrid mesh consisting of 3.6 million nodes and 6.4 million elements was used. The Best Practice Guidelines were applied to ensure the quality of the calculations. In the calculations, the High-Resolution discretisation scheme of ANSYS CFX was used to discretize the convective terms in the model equations. A second-order implicit scheme was utilized to approximate the transient terms. The time step size was set to 0.1 s. The ethyl alcohol water, which had a lower density, was applied as a tracer. It was modelled with the multi-component model of ANSYS CFX. The ethyl alcohol water was modelled as a component with different density and viscosity compared to water.

Depending on the degree of density differences the experiments and CFD calculations show a more or less intense stratification in the cold leg and downcomer. The ANSYS CFX calculations show a good qualitative agreement with the data. At some local positions differences in the predicted and measured concentration fields occur. The obtained experimental and numerical results can be used for further studies of the core behaviour using coupled thermo-hydraulic and neutron-kinetic code systems.

Keywords: CFD; ROCOM; boron dilution; PWR

  • Contribution to proceedings
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS), 05.-09.09.2006, Garching, Germany
  • Lecture (Conference)
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS), 05.-09.09.2006, Garching, Germany

Publ.-Id: 8083

Neural correlates of anosognosia for cognitive impairment in Alzheimer's disease.

Salmon, E.; Perani, D.; Herholz, K.; Marique, P.; Kalbe, E.; Holthoff, V.; Delbeuck, X.; Beuthien-Baumann, B.; Pelati, O.; Lespagnard, S.; Collette, F.; Garraux, G.

We explored the neural substrate of anosognosia for cognitive impairment in Alzheimer's disease (AD). Two hundred nine patients with mild to moderate dementia and their caregivers assessed patients' cognitive impairment by answering a structured questionnaire. Subjects rated 13 cognitive domains as not impaired or associated with mild, moderate, severe, or very severe difficulties, and a sum score was calculated. Two measures of anosognosia were derived. A patient's self assessment, unconfounded by objective measurements of cognitive deficits such as dementia severity and episodic memory impairment, provided an estimate of impaired self-evaluative judgment about cognition in AD. Impaired self-evaluation was related to a decrease in brain metabolism measured with 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) in orbital prefrontal cortex and in medial temporal structures. In a cognitive model of anosognosia, medial temporal dysfunction might impair a comparison mechanism between current information on cognition and personal knowledge. Hypoactivity in orbitofrontal cortex may not allow AD patients to update the qualitative judgment associated with their impaired cognitive abilities. Caregivers perceived greater cognitive impairments than patients did. The discrepancy score between caregiver's and patient's evaluations, an other measure of anosognosia, was negatively related to metabolic activity located in the temporoparietal junction, consistent with an impairment of self-referential processes and perspective taking in AD.

Keywords: dementia; neuroimaging; cognition; awareness; evaluation; perspective taking; confabulation

Publ.-Id: 8082

Surface Passivation of Silicon Solar Cells by Amorphous Silicon/Silicon Nitride Dual Layers

Bentzen, A.; Ulyashin, A.; Suphellen, A.; Sauar, E.; Grambole, D.; Wright, D. N.; Marstein, E. S.; Svensson, B. G.; Holt, A.

We have investigated surface passivation of silicon by a dual structure consisting of a hydrogenated amorphous silicon thin film capped by a silicon nitride anti-reflection layer, both layers deposited by plasma enhanced chemical vapor deposition. The results show that a synergetic effect on the surface passivation properties is obtained from such a dual structure. Moreover, we find that the surface passivation can be significantly enhanced after a short anneal for temperatures up to about 500 °C, whereas anneals at higher temperatures result in degradation of the passivation properties. From nuclear reaction analyses of the as-deposited and annealed structures, the enhanced surface passivation experienced after annealing is indicated to be due to hydrogen release from the structure towards the silicon substrate, possibly followed by a redistribution of hydrogen and subsequent passivation of silicon dangling bonds in the sub-interface region.

Keywords: Surface Passivation; Amorphous Silicon; Silicon Solar Cells

  • Contribution to proceedings
    15th International Photovoltaic Science and Engineering Conference (PVSEC-15), 10.-15.10.2005, Shanghai, China, 316-317

Publ.-Id: 8081

Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.] [331.] [332.] [333.] [334.] [335.] [336.] [337.] [338.] [339.] [340.] [341.]