Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Liquid metal ion source-produced germanium ions for maskless ion implantation
Ganetsos, T.; Aidinis, C.; Bischoff, L.; Mair, G. L. R.; Teichert, J.; Panknin, D.; Popadopoulos, I.;
We report on a prelimery investigation on the maskless implantation of Ge ions into Si for the production of Si 1-x Gex microstructures. The technique employs a focused ion beam system using a liquid metal alloy ion source. Closely spaced simple structures down to about 1 µm in width, with well-defined boundaries, have been produced. On some of these structures, spreading resistance measruements were carried out.
Keywords: Si 1-x Gex microstructures, focused ion beam
  • Journal of Physics D: Appl. Phys. 34 (2001) L 11 - L13

Publ.-Id: 3746 - Permalink


A study of the temperature dependence of the energy spread and energy deficit of a Ge ++ ion beam produced by a liquid metal alloy ion source
Aidinis, C. J.; Mair, G. L. R.; Bischoff, L.; Papadopoulos, I.;
This work involves an extensive study of the dependence on temperature (T) of the energy spread Delta E 1/2 and the potential energy deficit of the energy distribution of the Ge ++ beam produced by a liquid metal alloy ion source. The liquid metal alloy is Au77Ge14Si9. Differnces between consecutive sets of measurements were found but the energy spread versus temperature measurements agree remarkably well with a recent model that predicts Delta E 1/2 ~ T 1/2 . However, some questions involving the results either remain unsolved or are tentatively answered.
Keywords: Liquid metal alloy ion source, energy stread, energy deficit, temperature dependence
  • Journal of Physics D: Appl. Phys. 34 (2001) L14 - L 16

Publ.-Id: 3745 - Permalink


Alloying of silicon on Ti6Al4V using high-intensity pulsed plasma beams
Richter, E.; Piekoszewski, J.; Prokert, F.; Stanislawski, J.; Walis, L.; Wieser, E.;
Tianium and his alloys are widely used in medical applications, e.g. for artifical joints, dental prosthesis, teeth and so on. However, it these metals have to be coated with ceramic facing, some stability problems in the ceramic-titanium system arise due to the strong affinity of titanium to oxygen, which causes a reduction of the ceramic oxide. It is known that this reduction effect can be mitigated by alloying titanium or its alloys with a small amount of silicon using, e.g. an ion implantation technique. In the present work, we report the results of a new approach to alloying silicon to Ti6Al4V using high intensity pulsed plasma beams. The feasibility to from the silicide Ti5Si3 with grain size larger as 75 nm is demonstrated. This silicide has the highest melting point (2130 °C) among of all stable phases in the Si-Ti system.


Keywords: pulsed plasma beams, surface treatment, slicides
  • Vacuum 63 (2001) 523-527

Publ.-Id: 3741 - Permalink


Alloying of Pd into Ti by Pulsed Plasma Beams
Werner, Z.; Piekoszewski, J.; Barcz, A.; Grötzschel, R.; Prokert, F.; Stanislawski, J.; Szymczyk, W.;
Pd-Ti alloy surface layers in Ti formed by N- and Ar-plasma alloying of Pd films deposited by pulse erosion of Pd electrode tips were studied by RBS, XRD, SIMS, and gravimetric analysis. Layers of a thickness up to 2 µm and concentration up to 40% Pd at the surface were obtained. Pd is present as a solute in hcp alpha-Ti and as TiPd and TiPd3 phases. The Pd profiles follow gaussian distribution although no simple theoretical model can account for this behaviour.
Keywords: pulse plasma treatment, surface alloys, corrosion protection
  • Nuclear Instruments and Methods in Physics Research B 175-177 (2001) 767-771

Publ.-Id: 3740 - Permalink


Influence of the process parameters on the properties of hydrogenated amorphous carbon thin films deposited using ECR plasma
Piazza, F.; Arnal, Y.; Grambole, D.; Herrmann, F.; Kildemo, M.; Lacoste, A.; Relihan, G.; Golanski, A.;
A uniformly distributed multipolar microwave plasma reactor using electron cyclotron resonance at 2.45 GHz (600 W) was used to deposit a-C:H thin films at RT. C2H2 was used as precursor gas. Single crystal <100> Si and CR39 allelic resin substrates were RF biased to a negative voltage within the range between -10 and -200 V. The influence of the process parameters (gas flow and substrate bias) on the growth rate and hydrogen content have been investigated in detail. Optical parameters (optical gap ET, index of refraction n and extinction coefficient k) were measured using spectroscopic ellipsometry. The resonant (6.385 MeV) nuclear reaction: 1H(15N, alpha gamma)12C was used to determine the hydrogen content. For the C2H2 pressure range of 0.6 < P( C2H2) < 1.1 mTorr the optical parameters remain constant within the limits of experimental uncertainty. The sp3 content is seen to vary monotonically as a function of pressure and to be reaching a maximum of about 40% for 0.6 < P( C2H2) < 0.7 mTorr. The variation of the substrate bias within the range from -10 V to -190 V (at P( C2H2) = 0.6 mTorr) has no measurable impact neither on the deposition rate nor on the hydrogen content. The corresponding average values of ET and n remain stable (ET = 1.83 ± 0.11 eV, n = 2.12 ± 0.04). However, an increase in the bias is followed by a significant decrease of the extinction coefficient k and of the absorption tail width E0 . The observed evolution of k and E0 suggests that the sp2 clustering mode may be related to the substrate bias.

Keywords: carbon, thin films, hard coatings, optical properties, plasma processing
  • Poster
    EMRS'2000, 30. May - 2. June 2000, Strasbourg, France
  • Thin Solid Films 383(2001), 196-199

Publ.-Id: 3739 - Permalink


Thermodynamik der Wasserstoffabsorption in BaZr0.85 Y0.15O2.925/H2O
Groß, B.; Beck, C.; Engeldinger, J.; Grambole, D.; Herrmann, F.; Hempelmann, R.;
Dünne Schichten des Protonenleiters BaZr0.85 Y0.15O2.925/H2O (BZY15) wurden durch mehrfache Tauchbeschichtung mit einer mittleren Dicke von 900 nm hergestellt. Weiterhin wurden mikrokristalline und Nano-Pulver, mit Teilchengrößen zwischen 8 nm und 20 nm, präpariert.
Film- und mikrokristalline Proben wurden mit Wasserstoff, durch dissoziative Wasserdampfabsorption unter definierten Bedingungen, beladen. Die absoluten Wasserstoffkonzentrationen wurden mit der kernphysikalischen 15N Ionenstrahltechnik bestimmt. Mit einem Zweizustandsmodell, basierend auf Fermi-Dirak-Statistik, wurden die thermodynamischen Daten der Wasserdampfabsorption bestimmt [1].
Durch impedanzspektroskopische Messungen an gepressten und gesinterten mikrokristallinen Pulvern konnte die Bulkleitfähigkeit ermittelt werden. Aus der Kombination der Leitfähigkeit, den absoluten Protonenkonzentrationen und den protonischen Transportzahlen, bestimmt in Konzentrationszellenexperimenten, konnte der Leitfähigkeits-Diffusionskoeffizient des Bulkmaterials berechnet werden.
Weitere impedanzspektroskopische Messungen wurden an größenkontrolliert hergestellten Nano-Pulvern durchgeführt, um den Einfluss der Kristallgröße auf die protonische Leitfähigkeit zu ermitteln [2].

Literatur:
[1] B. Groß, J. Engeldinger, D. Grambole, F. Herrmann und R. Hempelmann,
Phys. Chem. Chem. Phys. 2 (2000) 297-301
[2] Ch. Beck, W. Härtl und R. Hempelmann,
J. Mater. Res. 13 (1998) 3174
  • Lecture (Conference)
    99. Hauptversammlung der Deutschen Bunsengesellschaft für Phys. Chemie, 1. - 3. Juni 2000, Würzburg

Publ.-Id: 3738 - Permalink


Application of new materials for integrated low-energy ignition elements in airbag systems - characterization and simulation
Weiß, U.; Löbner, T.; Geßner, T.; Hoyer, W.; Grambole, D.;
The direction of current research activities by international producers of ignition elements for airbag systems is developing cheap elements which are possible to be integrated into an ignition microsystem. These integrated ignition element is the most important actuator in the whole airbag system.
In conformity with the integration of ignitor structure and electronic parts Si became the basic material. Related materials were selected for functional coatings.
The investigations involved preparation, characterization, testing, simulation and reliability of the functional coatings for ignition structures.
Poly-Si was used as reference material to compare our results with the literature. Furthermore hydrides of titanium, zirconium and hafnium were investigated. Optimaly conversions of the metallic coatings (deposited by sputtering) after a heat treatment in a hydrogen atmosphere could be observed by X-Ray Diffraction and the nuclearphysical 15N-method (Figure 1).
After a heat treatment (110°C, on air) the evaluation of stability over the time was performed by analysing the sheet resistance for TiHx- and HfHx - probes. The divergence of the resistance values related to the start value (without heat treatment) amounts 5% for TiHx and 1% for HfHx. Accordingly to /1/ the thermal stability of the metal hydrides increases from Ti to Hf.
To obtain suitable design parameters for the ignition elements, a coupled electrical and thermal simulation was performed by the commercial ANSYS FEM program.
Figure 2 shows an example of the good agreement between the curves of the simulated thermal behavior and the measured current.


/1/ Streb, Wasserstoff in den Metallen Titan, Zircon und Hafnium, Thesis, Frankfurt am Main, 1984
/2/ Weiß U., Löbner B., Abschlußbericht SIFA-MST, "Schneller Anzünder", Januar 1999
/3/ Weiß U., Dünnschichtanzündelement für pyrotechnische Wirkmassen, Patent DE 19721929
  • Lecture (Conference)
    3rd Int. Conf. and Poster Exhibition Micro Materials (MicroMat 2000), 17. - 19. April 2000, Berlin, Germany

Publ.-Id: 3736 - Permalink


Lattice destruction during micro-channeling measurements
Herrmann, F.; Grambole, D.; Grötzschel, R.;
The degree of postimplantation damage in various semiconductor crystals depends on the dose rate applied. In particular strong effects have been observed at dose rates up to 1019 cm-2s-1 which are typical for focused ion beam (FIB) devices with sub-µm beam diameters. For a systematic study of such damages a nuclear microprobe must be employed for RBS/channeling measurements. But the fluence of the analysing beam of light ions is here orders of degree higher than usually in RBS/C experiments. Therefore the damage generation by the analysing beam must be considered.
We have studied the near-surface damage accumulation at room temperature in 6H-SiC by H, He and Li ions of various energies both for channeling and random incidence.
The fluence dependence of the regular damage, observed with beams in the MeV region, is much smaller than that with low and medium energies. The damage level observed by RBS/C seems to saturate at a cmin value far below unity. The calculated ratios of Rutherford cross section to deposited nuclear energy [SRIM 2000] for H, He, and Li ions predict lowest damage per backscattering yield for H ions at the lower energy end. But in the case of µm beam dimensions the lattice damage by the proton beam due to swelling, bubble formation, precipitation etc. exceeds by far the regular ballistic disorder and is higher than in the case of He or Li ions of the same energy.
  • Poster
    7th Intern. Conference on Nuclear Microprobe Technology and Applications, Bordeaux, France, Sept. 2000

Publ.-Id: 3733 - Permalink


Optical properties of ta-C:H films deposited by ECR plasma using acetylene as precursor gas
Piazza, F.; Arnal, Y.; Lacoste, A.; Relihan, G.; Kildemo, M.; Grambole, D.; Herrmann, F.; Golanski, A.;
A uniformly Distributed Multipolar Microwave plasma reactor using Electron Cyclotron Resonance at 2.45 GHz was used to deposit ta-C:H (DLC) films on silicon substrates at RT. The influence of the acetylene initial pressure (0.3 - 1.1 mTorr) and of the substrate bias (from -10 V to -190 V) on the DLC growth and structure has been investigated using spectroscopic ellipsometry. It is shown that the maximum sp3 content of about 40% (atomic) may be reached for the acetylene pressure of 0.6 - 0.7 mTorr. It is also shown that although the bias voltage has no measurable impact on the optical gap it has a significant influence on the extinction coefficient and the behaviour of the absorption tails. The results suggest that the sp2 clustering mode and the sp2 cluster size distribution are bias controlled.
  • Poster
    7th International Symposium on Trends and Applications of Thin Films (TATF' 2000), 27.-30.03.2000, Nancy, France
  • Contribution to proceedings
    7th Int. Symp. on Trends and Appl. of Thin Films (TATF' 2000), 27.-30.03.2000, Nancy, France
    Proceedings of TATF' 2000, 376-378

Publ.-Id: 3732 - Permalink


Phase analysis in alpha-Fe after high-dose Si ion implantation by depth-selective conversion-electron Mössbauer spectroscopy (DCEMS)
Walterfang, M.; Kruijer, S.; Dobler, M.; Reuther, H.; Keune, W.;
Si+ ions of 50 keV in energy were implanted into a-Fe (95% 57Fe) with a nominal dose of 5x10E17 cmE-2.
  • Hyperfine Interactions 126 (2000) 219-222

Publ.-Id: 3731 - Permalink


Studies of carbon ion self-implantation into hydrogenated amorphous carbon films
Khan, R. U. A.; Grambole, D.; Silva, S. R. P.;
The properties of polymer-like amorphous hydrogenated carbon thin films with low defect density have been studied. These films were implanted with carbon ions with a dose range of 1012 - 1016 cm-2. The purpose of the study is to investigate the effects of ion beam damage on this type of film. Optical absorption measurements observe a narrowing of the optical band gap, suggesting the introduction of a large number of defect states subsequent to the implantation resulting in the broadening of the band tails, only after a threshold ion dose of 1015 cm-2. Nuclear reaction analysis suggests also a reduction in the hydrogen content of the film which coincides with film thinning.


Keywords: Amorphous carbon; Defect; Hydrogen; Ion implantation
  • Diamand and Related Materials 9 (2000) 657 - 679

Publ.-Id: 3730 - Permalink


Reliable micro-measurement of strontium is the key to cracking the life-history code in the fish otolith
Markwitz, A.; Grambole, D.; Herrmann, F.; Trompetter, W. J.; Dioses, T.; Gauldie, R. W.;
The fish otolith is a calcium carbonate (usually aragonite) crystal that crows continuously by accretion over the life of the fish and unlike bone is not continuously re-metabolised. Consequently, the otolith has long been regarded as a potential store of information about the life history of an individual fish, and this information is encoded in the deposition pattern of trace elements in the otolith. The code has been difficult to crack. However, recent developments have show that: (1) Sr is one of the few non-mobile trace elements in the otolith; and (2) the pattern of Sr deposition summarises the effects of environment changes that affect the growth rate of the otolith crystal. The remaining difficulties in cracking the chemical code in the otolith have hinged about making reliable micro-measurements of the stable Sr content at spatial resolutions of 10 µm or less; this interval represents about 4-6 days of otolith growth in most species of fish. This paper describes high beam resolution 2 µm linear measurements, and 6 µm square measurements over narrow windows of about 300µm square, and links these micro-measures to macro-measures of 2D maps of the entire surface of sections of otoliths up to 5 mm square at beam resolutions of 25 µm square. The otoliths used in this study are from the Jurel, or Peruvian Jack mackerel, Trachurus murphyi (Carangidae: Teleostei).

Keywords: Nuclear microprobe; Elemental mapping; Sr measurements; Fish otoliths; Environmental; Trachurus murphyi PACS classification codes: 07.78.+s; 61.72.Ss; 89.60.+x
  • Nuclear Instruments and Methods in Physics Research B 168 (2000) 109-116

Publ.-Id: 3728 - Permalink


The surface grating on GaAs(001) characterized by conventional and synchrotron X-ray methods
Mazur, K.; Sass, J.; Eichhorn, F.; Turos, A.;
The investigation by means of triple crystal X-ray diffractometry and synchrotron reflectivity measurements were performed in two different kinds of laterally structured samples: (i) the simple surface grating created by photolithography methods (the surface grating were of the same material as the substrate) and (ii) stepped surface created by the intentionally off-oriented surface. The X-ray triple crystal arrangement allows us to measure reciprocal space maps of the scattered intensity, separating the intensity contributions of the scattered truncation rods on the first kind of samples. The synchrotron non-specular reflectivity measurements at ESRF were essential for proving the existence of stepped surfaces and examination of their structure.
Keywords: GaAs, high-resolution X-ray diffraction, X-ray reflectivity, surface grating, reciprocal space map
  • Lecture (Conference)
    XVIII Conference on Applied Crystallography, September 4 - 7, 2000, Wisła (Poland)
  • Lecture (Conference)
    Vortrag (Konferenzbeitrag): XVIII Conference on Applied Crystallography, September 4 - 7, 2000, Wisła (Poland)

Publ.-Id: 3727 - Permalink


Laterally structured surfaces of GaAs(001) characterized by conventional and synchrotron X-ray methods
Mazur, K.; Sass, J.; Eichhorn, F.; Turos, A.;
The samples with different laterally structured surfaces were investigated by means of triple crystal X-ray diffractometry and synchrotron reflectivity measurements. Studies including surface grating created by photolithography methods (the surface grating were of the same material as the substrate) and stepped surface created by the intentionally off-oriented surface were performed. The X-ray triple crystal arrangement allows us to measure reciprocal space maps of the scattered intensity, separating the intensity contributions of the scattered truncation rods on the first kind of samples. The synchrotron non-specular reflectivity measurements at ESRF were essential for proving the existence of stepped surfaces and examination of their structure.
Keywords: GaAs, high-resolution X-ray diffraction, X-ray reflectivity, surface grating, reciprocal space map
  • Poster
    19th European Crystallographic Meeting (ECM19), August 25-31, 2000, Nancy (France)

Publ.-Id: 3726 - Permalink


Strain and SiC crystallite formation in carbon implanted silicon
Eichhorn, F.; Schell, N.; Mücklich, A.; Matz, W.; Kögler, R.;
SiC formation by implantation of C ions into silicon is not a single-step process [1]. The implantation results in an elastic distortion of the Si host lattice and in a formation of crystalline SiC particles or their prestages depending on ion fluence and thermal conditions.
One part of the samples was prepared by implantation of C ions with an energy of 195 keV into Si (001) wafers at fluences varying from 5E15 ions/cm2 to 4E17 ions/cm² and temperatures between room temperature and 800°C. The other part was produced by implantation of 3.25E17 /cm² of C (45 keV) ions at 500 °C and a subsequent annealing at 1200°C for 2 h. The whole fluence was applied as well in one step as in three steps, respectively. The maximum of the carbon content lies in a depth of 130 nm for ions with an energy of 45 keV and at 570 nm for ions with an energy of 195 keV, respectively.
The growth of the SiC particles and the strain in the Si matrix and its relaxation were studied with different x-ray scattering techniques: high-resolution diffraction, wide-angle diffraction for the phase identification [2], grazing incidence diffraction for particle size determination, reciprocal space mapping (RSM) and texture studies for revealing the orientation alignment of the particles to the matrix. Mostly the use of Synchrotron radiation was necessary in order to have a clearly detectable signal in spite of the very small volume part of SiC. Furthermore, high resolution diffraction for strain studies requires radiation with a low divergence. The material research goniometer of the Rossendorf Beamline (ROBL) at the ESRF Grenoble [3] enables such studies which allow to follow the early stage of phase formation.
From the measurements it can be stated:
1. At the lowest ion fluence a significant Si lattice expansion on the order of 1E-3 is observed. However, no crystalline SiC precipitates were found.
2. Intermediate ion fluences and temperatures generate very small SiC particles (pre-stages) with enhanced lattice spacings in relation to the value of 3C-SiC. Due to the SiC particle formation the strain in the Si lattice is reduced.
3. Finally, for the highest fluences and temperatures crystalline 3C-SiC particles are found. The SiC lattice itself is only negligible strained if the phase formation occurs during a high-temperature implantation process.
4. As it was revealed by RSM and texture studies the SiC crystallites are aligned to the Si host lattice in such a way that the cubic crystallographic axes of matrix and particles coincide within an accuracy of 2.5° to 5°. A narrower distribution of the SiC crystallite orientation is formed by implantation at higher temperatures. Elevated temperature during implantation is supposed to be more effective in forming an aligned crystallite distribution than a subsequent annealing even at higher temperature.
[1] M. Deguchi et al., Jap. J. Appl. Phys. 31, 343 (1992)
[2] F. Eichhorn et al., J. Appl. Phys. 86, 4184 (1999)
[3] W. Matz et al., J. Synchrotron Rad. 6, 1076 (1999)

Keywords: SiC, Si, ion beam synthesis, X-ray diffraction, lattice strain, texture study, synchrotron X-rays
  • Lecture (Conference)
    5th Biennial Conference on High Resolution X-ray Diffraction and Topography XTOP-2000;, September 13 - 15, 2000, Ustron-Jaszowiec (Poland)

Publ.-Id: 3725 - Permalink


Structural relation between Si and SiC formed by carbon ion implantation
Eichhorn, F.; Kögler, R.; Mücklich, A.; Schell, N.; Matz, W.;
SiC ion beam synthesis by implantation of C ions into Si is a multiple-step process. In our experiments C ion implantation was performed at TII = RT ... 800 °C to a C concentration in the range of 0.3 to 33.5 at% into Si and SIMOX substrates. SiC phase formation and the related lattice strain were studied by different synchrotron X-ray scattering techniques using ROBL at ESRF Grenoble and by transmission electron microscopy:
1. Low ion fluences result in a Si lattice expansion in the order of 1E-3.
2. Intermediate ion fluences and temperatures generate small SiC pre-cursors with enhanced lattice spacings and reduced strain in the Si lattice.
3. High fluences and temperatures form 3C-SiC crystallites with three types of orientation:
- random-like orientation
- fibre texture with axis parallel to the surface normal with a mean orientation spread of 6°
- high alignment to the Si matrix: SiC<001> || Si<001> and SiC<110> || Si<110> due to a partial coherent growth of SiC in the Si matrix. The orientation spread is in the range from 2° to 5°.
Ion beam synthesis of SiC in Si at elevated temperatures favours the growth of highly oriented crystallites.

Keywords: SiC, Si, ion beam synthesis, X-ray diffraction, texture study, synchrotron X-rays
  • Poster
    E-MRS2001 Spring Meeting, June 5 - 8, 2001, Strasbourg (France)

Publ.-Id: 3724 - Permalink


Der Freie-Elektronen-Laser in Dresden/Rossendorf und seine Anwendungen in der Infrarot-Spektroskopie von Halbleitern und anderen Systemen
Helm, M.;
Am Forschungszentrum Rossendorf wird zur Zeit ein Freie-Elektronen-Laser (FEL) gebaut, der Ende 2001 betriebsfertig sein soll. Mittelfristig soll ein Wellenlängenbereich von 5-200 um überstrichen werden können. Ich möchte einen Überblick über dieses Projekt geben, mit Darstellung der angeschlossenen experimentellen Infrastruktur. Desweiteren möchte ich über die möglichen spektroskopischen Anwendungen sprechen, die im Prinzip alle Systeme mit niederenergetischen Anregungen (10-100 meV) betreffen. Der Schwerpunkt dabei wird, gemäß meines Erfahrungshintergrundes, auf dem Gebiet der Halbleiter-Quantenstrukturen liegen.
Keywords: semiconductors, free-eelctron-laser, infrared spectroscopy
  • Lecture (others)
    Seminarvortrag Universität Giessen (25.01.2001)

Publ.-Id: 3723 - Permalink


Elektronen in künstlichen Halbleiterstrukturen: vom Modellsystem für Quantenmechanik und Festkörperphysik zum Quantenbauelement
Helm, M.;
please contact the author
Keywords: semiconductors quantum structures
  • Lecture (others)
    Kolloquium an der TU Dresden (23.01.2001)

Publ.-Id: 3722 - Permalink


Structure refinement of the silicon carbide polytypes 4H and 6H: unambiguous determination of the refinement parameters
Bauer, A.; Reischauer, P.; Kräusslich, J.; Schell, N.; Matz, W.; Götz, K.;
The atomic positions of the silicon carbide polytypes 6H and 4H differ slightly from an ideal tetrahedron. These small deviations can be investigated by X-ray diffraction of so-called "quasiforbidden" reflectios, which are very sensitive to the extremly small variations in the structure.
Keywords: SiC; atomic structure; synchrotron X-ray diffraction
  • Acta Cryst. A57 (2001) 60-67

Publ.-Id: 3721 - Permalink


Formation of the phases Ti3Al and TiAl by high dose implantation of Aluminium into Titanium
Tsyganov, I. A.; Wieser, E.; Matz, W.; Mücklich, A.; Reuther, H.;
formation of buried intermetallic Ti-Al-phases by high doose Al implantation
Keywords: ion implantation; titanium; X-ray diffraction, TEM, AES
  • Contribution to proceedings
    1st International Congress on Radiation Physics and Chemistry of Condensed Matter, High Current Electronics, and Modifikation of Materials with Particle Beams and Plasma Flows, Tomsk, Russia, Sept. 14 - 29, 2000

Publ.-Id: 3720 - Permalink


Modification of Titanium by ion implantation of Calcium and/or Phosphorus
Tsyganov, I. A.; Wieser, E.; Matz, W.; Reuther, H.; Oswald, S.; Pham, M. T.; Richter, E.;
study of implantation treatment of Ti with Ca and P for improving hydroxylapatite formation
Keywords: ion implantation, hydroxylapatite, X-ray diffraction; AES
  • Contribution to proceedings
    1st International Congress on Radiation Physics and Chemistry of Condensed Matter, High Current Electronics, and Modifikation of Materials with Particle Beams and Plasma Flows, Tomsk, Russia, Sept. 14 - 29, 2000

Publ.-Id: 3719 - Permalink


Rossendorfer Beamline ROBL in Grenoble: Synchrotronstrahlung für Ökologie- und Materialforschung
Matz, W.;
Übersicht über ROBL / ausgewählte Ergebnisse
  • Lecture (others)
    Tag der offenen Tür des FZR, 16. September 2000

Publ.-Id: 3718 - Permalink


Influence of thermal treatment and cyclic plastic deformation on the defect structure in ultrafine-grained nickel
Thiele, E.; Bretschneider, J.; Hollang, L.; Schell, N.; Holste, C.;
Ultrafine-grained nickel samples were submitted to thermal treatment and cyclic plastic deformation in order to investigate the stability of the defect structure. Investigations by means of synchrotron radiation diffraction revealed that the mean volume expansion, long-range and short-range internal strains are diminished in consequence of the cyclic plastic deformation.
Keywords: ultrafine-grained nickel, cyclic plastic deformation, synchrotron X-ray diffraction, internal strains
  • Contribution to proceedings
    In: T. C. Lowe and R. Z. Valiev (eds.) Investigations and Applications of Severe Plastic Deformation, Proceedings of NATO Advanced Research Workshop, Moscow, Aug. 2 - 6 1999; Kluwer Academic Publishers, (2000) 173-178

Publ.-Id: 3717 - Permalink


Change of internal strains in ultrafine-grained nickel due to cyclic plastic deformation
Thiele, E.; Hecker, M.; Schell, N.;
Ultra-fine grained nickel samples were cyclically deformed at room temperature and at 200°C. The mean grain size of about 200 nm, determined by SEM and from the broadening of synchrotron diffraction profiles remained nearly constant, whereas the spectrunm of internal strains changed in consequence of the cyclic deformation. The relation between the profile shape ans asymmetry and the {hkl} reflection type suggests the existence of long range granular stresses in the original ufg samples.
Keywords: ultrafine-grained nickel, cyclic plastic deformation, synchrotron X-ray diffraction, diffraction profile analysis, internals strains and stresses
  • Materials Science Forum 321-324 (2000) 598-603

Publ.-Id: 3716 - Permalink


Characterisation of crystallinity of SiC-surface layers produced by ion implantation
Theodossiu, E.; Baumann, H.; Klimenkov, M.; Matz, W.; Bethge, K.;
Carbon implantations into silicon were carried out in order to form thin surface layers of SiC. Single crystalline <100> silicon samples were implanted with 40 keV 13C ions with a fluence of 3.8x1017 ions/cm2 and subsequently thermally treated under high vacuum conditions at different temperatures using a 20 keV electron beam. The isotope 13C offers the advantage to measure the carbon redistribution caused by the thermal treatment process with the nuclear resonance reaction analysis. The crystallinity of the SiC surface layers is studied by X-ray diffraction and transmission electron microscopy measurements. A polycrystalline 3C-SiC surface layer with a low content of 6H-SiC grains is formed with a thickness of about 70 nm. The analysis of high resolution TEM micrographs from the interface region shows obviously that the 6H-SiC phase coexists with the 3C-SiC modification in SiC layer.



Keywords: ion implantation, silicon carbide, 6H-SiC, NRRA, XRD, TEM
  • Phys. Stat. Sol. (a) 182 (2000) 653-660

Publ.-Id: 3715 - Permalink


X-ray structure characterization of barriers for Cu metallization
Mattern, N.; Hecker, M.; Fischer, D.; Wenzel, C.; Schell, N.; Matz, W.; Engelmann, H.; Zschech, E.;
The possibilities and limitations of X-ray scattering techniques are discussed for the structure analysis of Ta-N barriers for Cu metallization.
Keywords: X-ray diffraction; Ta barriers; synchrotron radiation
  • Microelectronics Reliability 40(2000) 1765-1770

Publ.-Id: 3714 - Permalink


Dissociative water vapour absorption in BaZr0.85Y0.15O2.925/H2O: pressure-compositions isotherms in terms of Fermi-Dirac statistics
Groß, B.; Engeldinger, J.; Grambole, D.; Herrmann, F.; Hempelmann, R.;
Thin films of proton-conducting BaZr0.85Y0.15O2.925 perovskite-type ceramics, prepared in a sol-gel process by multiple dip-coating on silicon single crystal wafers, and powder samples, prepared by the conventional carbonate route, were charged with hydrogen by dissociative water absorption at definite values of water vapour pressures and temperatures. The absolute content of the absorbed hydrogen was determined ex situ at room temperature using the 15N nuclear resonance reaction analysis. From the resulting water vapour pressure-hydrogen composition isotherms the absorption enthalpies and entropy were caculated, using our two site model, based on Fermi-Dirac statistics.
  • Phys. Chem. Chem. Phys., 2000, 2, 297-301

Publ.-Id: 3713 - Permalink


Application of the Tikhonov Regularization Method to the EXAFS analysis of UO2(H2AsO4)2 x H2O
Zayarnaya, T.; Reich, T.; Hennig, C.; Funke, H.;
We consider the possibility to determine structural parameters from partial pair correlation functions (PCF's) for UO2(H2AsO4)2 x H2O assuming that its crystal structure is unknown. Since UO2(HAsO4) x 4H2O is chemically similar to UO2(H2AsO4)2 x H2O, we wanted to investigate whether the scattering characteristics calculated by FEFF-8 for the uranium hydrogen arsenate with a known crystal structure are transferable for the analysis of the uranium dihydrogen arsenate.
The Tikhonov regularization method was applied to solve the inverse ill-posed problem of finding up to three partial PCF's from one EXAFS spectrum of UO2(H2AsO4)2 x H2O. From the U L3-edge EXAFS spectrum, we determined the U-U, U-As, and U-O PCF's. The As-As, As-U, and As-O PCF's were received from the As K-edge EXAFS spectrum. The interatomic distances obtained for the first and in several cases also for the second coordination shell of all pairs are in agreement with recently published crystallographic values. This demonstrates that the Tikhonov regularization method is a powerful tool for the structural analysis of samples for which only chemical information (oxidation state, elemental composition, type of ligands) is known.

* Corresponding author: zayarnaya@imp.uran.ru
  • Lecture (Conference)
    Actinide-XAS-2000 Workshop Proceedings, Grenoble, Sept. 10.-12.2000

Publ.-Id: 3711 - Permalink


EXAFS Study of U(VI) Compounds: A New Approach to Data Analysis
Babanov, Y. A.; Zayarnaya, T.; Reich, T.; Funke, H.;

The regularization method is applied to determine three partial pair correlation functions (PCF) from one EXAFS spectrum. The mathematical procedure is discussed and applied to the EXAFS analysis of UO-2(HAsO4) x 4H2O.
The measurements were performed at the Rossendorf Beamline (ROBL) at the ESRF in Grenoble. The As K-edge and the U L3-edge absorption spectra were recorded in transmission mode at temperatures of 41 K and 15 K, respectively. From the U L3-edge EXAFS spectrum, we obtain the PCF's of the pairs U-U, U-As, and U-O and determine the structural parameters for the first and the second coordination shells of each pair. The PCF's of the pairs As-U, As-As, and As-O are obtained from the As K-edge EXAFS spectrum.










  • Lecture (Conference)
    Actinide-XAS-2000 Workshop Proceedings, Grenoble Sept. 10-12., 2000

Publ.-Id: 3710 - Permalink


Tetraaquatrinitratoeuropium(III) dihydrate
Stumpf, T.; Bolte, M.;
In the title compound, [Eu(NO3)3(H2O)4]·2H2O, the Eu atom is ten co-ordinated by three bidentate nitrates and four water molecules. Furthermore, two water molecules are included in the crystal structure forming a complicated network of hydrogen bonds. [Eu(NO3)3(H2O)4]·2H2O is isostructural with other lanthanide analogues.

Acta Cryst. (2001) E (submitted)
  • Acta Cryst. E

Publ.-Id: 3709 - Permalink


Development of bubble size distributions in vertical pipe flow by consideration of radial gas fraction profiles
Lucas, D.; Krepper, E.; Prasser, H.-M.;
A new method for the prediction of the development of the bubble size distribution along the flow path is presented. It combines models for bubble coalescence and break-up with the calculation of radial gas fraction profiles. This model bases on the assumption of the equilibrium of the forces acting on a bubble perpendicularly to the flow direction. A large number of bubble classes is considered and the radial profile of the liquid velocity is taken into account.

The results of the model are compared with experimental data for a number of gas and liquid volume flow rates. The experiments were performed at a vertical test loop in Forschungszentrum Rossendorf (inner diameter 51.2 mm) using a wire mesh sensor. The sensor enables the determination of void distributions in the cross section of the loop. A special evaluation procedure supplies as well bubble size distributions as local distributions of bubbles within a predefined interval of bubble sizes.
  • Lecture (Conference)
    4th International Conference on Multiphase Flow, New Orleans, May 27 - June 1, 2001, Conference-CD, Paper 378
  • Contribution to proceedings
    4th International Conference on Multiphase Flow, New Orleans, May 27 - June 1, 2001, Conference-CD, Paper 378

Publ.-Id: 3708 - Permalink


Acid Rock Drainage samples from an abandoned Zn-Pb-Ag mine investigated by XAS
Moll, H.; Zaenker, H.; Richter, W.; Brendler, V.; Reich, T.; Hennig, C.; Rossberg, A.; Funke, H.; Kluge, A.;
In the aqueous environment of abandoned ore mines, iron sulphide ore crystals play a key role in the sulphide oxidation and water mineralization process occurring there. Highly miner-alised, red-coloured solutions are formed by weathering of ore particles which causes acid rock drainage (ARD). Major cationic components (>1 g/l) of the ARD solution under study were Zn, Fe, Mg, Al, and Mn. Important minor components were toxic heavy metals, e.g. As, Cu, Pb, and Cd. This XAS investigation deals with the in-situ characterisation of the near-order surrounding of As in ARD solutions containing colloidal particles as well as with the determination of the particle mineralogy. The atomic surrounding of Fe and As in ARD samples is compared to those found in model compounds. The presented study is an example for the broad applicability of X-ray absorption spectroscopy (XAS) techniques to environmental research.
Keywords: XAS, EXAFS, particles, Fe, As, ARD
  • Poster
    11th ESRF Users' Meeting, Grenoble, 16-21 February 2001 Workshop, Satellite to the ESRF Users' Meeting Environmental Studies Using Neutron and Synchrotron Facilities

Publ.-Id: 3707 - Permalink


Ion Beam Synthesis of SiC-Diamond-Heterostructures
Heera, V.;
Both, silicon carbide (SiC) and diamond are wide band gap semiconductors with excellent electronic properties. Unfortunately, there has been only limited success in producing n-type regions in diamond or p-type regions in SiC. On the other hand, n-type doping of SiC by nitrogen (N) implantation and p-type doping of diamond by boron (B) implantation are well-established processes. Therefore, it is an obvious idea to combine the materials in order to exploit this complementary behavior for the fabrication of p-n-heterojunctions or n-type regions in insulating diamond. Preliminary experiments have shown that ion beam synthesis could be a suitable process for the production of SiC-diamond-heterostructures in microscopic regions. There are two ways to achieve these heterostructures: (i) diamond formation by high dose carbon (C) implantation in crystalline SiC and (ii) SiC formation by high dose silicon (Si) implantation in natural diamond. The implantation must be carried out at elevated temperatures (> 700°C) in order to avoid accumulation of implantation damage. Epitaxial, nm-sized diamond or SiC precipitates with spherical or platelike shape, respectively, are formed inside the host crystals by the ion beam synthesis.
Keywords: SiC, diamond, ion implantation, phase formation, ion beam synthesis
  • Compound Semiconductor 7 (2001) No. 3, 43

Publ.-Id: 3706 - Permalink


Three VVER-1000 Tests Suitable for the Validation of Coupled Neutronic / Thermal-hydraulic Codes
Danilin, S.; Ilieva, B.; Khalimonchuk, V.; Mittag, S.; Weiß, F.-P.;
In the first test, carried out in the NPP Balakovo-4 (Russia), one of the two working feed water pumps was turned off at nominal power. The control system automatically reduced the reactor power down to 45 % of the nominal level. The coolant heat-up decreased proportionally to the power reduction. In the secondary circuit, the pumping power of the second feed water pump was increased in order to compensate some part of the missing feed water flow. In the following, the power of the second pump was reduced again to match the decreasing thermal power of the primary circuit. Corresponding changes in the steam generator water levels were observed. - The initiating event for a transient observed in the Zaporoshye-6 VVER-1000 (Ukraine) was the degradation of the turbo-generator power from 1000 MW down to the house load level of 50 MW. The reaction of the core control system and the behaviour of the primary circuit were similar to that in the Balakovo case. Immediately after the drastic reduction of the load level, the turbine started increasing its rotation speed. In order to prevent turbine damage, the steam control valves immediately reduced the steam flow to the turbine. Thus the turbine speed was stabilized, but the main steam header pressure started increasing. The turbine bypass valves were opened reducing the pressure quickly to its previous level. - The third test was carried out in the NPP Kozloduy-6 (Bulgaria). At 90 % of nominal power, two neighbouring main coolant pumps were switched off. The power was reduced to 35 %. Immediately after the transient initiation, the pressure in the primary circuit began to drop. All four pressurizer heaters started working to stabilize pressure. - The data measured in the three tests are useful for the validation of coupled codes.
  • Lecture (Conference)
    NEA/NSC Workshop on the Preservation of Experimental Integral Reactor Physics Data, 18-19 May 2000, Budapest, Hungary

Publ.-Id: 3705 - Permalink


Validation of coupled neutron-kinetic/thermal-hydraulic codes for VVERs
Mittag, S.; Kliem, S.; Weiß, F.-P.; Kyrki-Rajamäki, R.; Hämäläinen, A.; Langenbuch, S.; Danilin, S.; Hadek, J.; Hegyi, G.; Kuchin, A.; Panayotov, D.;
Three-dimensional hexagonal reactor dynamic codes have been developed for VVER type reactors and coupled with different thermal hydraulic system codes. Under the auspices of the EU's Phare programme, these codes have been validated against real plant transients by the participants from several countries. Data measured during tests in the Balakovo-4 VVER-1000 and the Loviisa-1 VVER-440 have been analysed by the codes. Critical boron concentrations, 3-D core power distributions, time behaviour of total fission power, coolant temperatures and pressures were the main parameters utilised in the validation. Good accuracy of the results was generally achieved, comparable to the measurement accuracy. The confidence in the results of the different code systems has increased and the consequences of certain model changes could be evaluated.
  • Lecture (Conference)
    Proc. of Tenth Symposium of AER on VVER Reactor Physics and Reactor Safety, Moscow, Russia, September 18-22, 2000, 763-781
  • Contribution to proceedings
    Proc. of Tenth Symposium of AER on VVER Reactor Physics and Reactor Safety, Moscow, Russia, September 18-22, 2000, 763-781

Publ.-Id: 3704 - Permalink


19F(p,p'gamma)19F and 18O(p, gamma)19F gamma-ray interferences studied on liquids
Grambole, D.; Neelmeijer, C.; Noll, K.; Herrmann, F.;
The interference effects for the 110 keV and 197 keV gamma-ray lines of the nuclear reactions 19F(p, p'gamma)19F and 18O(p, gamma)19F were studied quantitatively. For this, thick liquid targets were examined by PIGE using an external proton beam of 3.4 MeV energy. Several grades of dilutions were prepared from 76.3% 18O enriched H2O and from 1000 ppm F standard NaF solution. From this, a data base was obtained in order to extrapolate the 110 keV and 197 keV gamma-ray yields of the 18O(p, gamma)19F reaction for a target of water containing 0.2 % 18O. As a result it was obtained that, for fluorine in oxygen-rich materials, the reaction 19F(p, p'gamma)19F allows minimum detection limits of (1.06 ± 0.12) at.ppm and (1.85 ± 0.2) at.ppm for the 110 keV and 197 keV gamma-rays, respectively.
Keywords: PIGE; Fluorine; Oxygen-18; External beam; Liquid target
  • Nuclear Instruments and Methods in Physics Research B 161-163 (2000) 269-274

Publ.-Id: 3703 - Permalink


Verfahren zur Dotierung von Siliziumkarbid-Halbleiterbereichen
Heera, V.;
Der Erfindung liegt die Aufgabe zu Grunde, mit geringerem Aufwand in der Tiefe homogen dotierte SiC-Halbleiterbereiche mit einem schmalen Übergangsbereich zum Substrat zu erzeugen.
  • Patent
    Patentanmeldung 100 62 212.7
  • Patent
    DE 100 62 212 C1

Publ.-Id: 3701 - Permalink


Verfahren zur Herstellung von integrierten Abtastnadeln
Schmidt, B.; Bischoff, L.; Eng, L.;
Aufgabe der Erfindung ist es, ein Verfahren zu schaffen, das die Erzeugung von miniaturisierten, integrierten Abtastnadeln, bestehend aus Support, Biegebalken und hohler Nadelspitze mit und ohne Apertur, erlaubt und die somit bevorzugt für den Einsatz in der SNOM geeignet sind.
  • Patent
    DE 100 57 656 C1
  • Patent
    EP 1 209 689 A2
  • Patent
    EP 1 209 689 B1

Publ.-Id: 3700 - Permalink


Steuereinrichtung für einen Kühlkreislauf
Willschütz, H.-G.;
Der Erfindung liegt die Aufgabe zugrunde, eine Steuereinrichtung für einen Kühlkreislauf vorzuschlagen, die sicher und einfach auch bei einem schweren Störfall eine Kühlung des Reaktordruckbehälters sicherstellt. Dabei soll auf den Einsatz von Fremd-energie verzichtet werden.
  • Patent
    DE 100 41 779 C1
  • Patent
    WO 02/17331 A1

Publ.-Id: 3699 - Permalink


Abstützvorrichtung für Stahlbehälter
Willschütz, H.-G.;
Der Erfindung liegt die Aufgabe zugrunde, eine Abstützvorrichtung vorzuschlagen, mit der eine vertikale Unterstützung des Stahlbehälters im Falle von außergewöhnlich hoher Temperatur und/oder Druck gewährleistet wird, ohne die Kühlung des Stahlbehälters zu beeinträchtigen.
  • Patent
    DE 100 41 778 A1
  • Patent
    WO 02/16821 A2
  • Patent
    De 100 41 778 C2

Publ.-Id: 3698 - Permalink


Einrichtung zur lokalen Bestimmung von Strömungsgeschwindigkeiten
Eckert, S.; Witke, W.; Gerbeth, G.;
Der Erfindung liegt die Aufgabe zugrunde, eine Einrichtung zur Messung von Strömungsgeschwindigkeiten vorzuschlagen, die auch in nichttransparenten Fluiden einsetzbar ist und keinen Einschränkungen bei kleinen Geschwindigkeitswerten, turbulenten Geschwindigkeitsschwankungen, hohen Temperaturen und der Richtung der Strömung unterliegt.
  • Patent
    Patentanmeldung 100 37 331.3
  • Patent
    DE 100 37 331 C1

Publ.-Id: 3697 - Permalink


Schaltungsanordnung zur Erzeugung positiver und negativer pulsförmiger Magnetfelder
Krug, H.; Eckert, D.;
Der Erfindung liegt die Aufgabe zugrunde, insbesondere große Anlagen für positive und negative pulsförmige Magnetfelder mit deutlich geringerem Aufwand herstellen zu können.
Die Erfindung geht aus von einer Schaltungsanordnung, die im Wesentlichen aus einer Kondensatorbatterie, einer Hochfeldspule, einer Schutzdrossel, einem Thyristorschalter, einer Crowbardiode, einem Crowbarwiderstand und mehreren Trennkontakten besteht.
  • Patent
    DE 100 30 566 A1
  • Patent
    DE 100 30 566 C2
  • Patent
    WO 01/98792 A1

Publ.-Id: 3696 - Permalink


Verfahren und Anordnung zur kontaktlosen Bestimmung von räumlichen Geschwindigkeitsverteilungen in elektrisch leitfähigen Flüssigkeiten
Stefani, F.; Gerbeth, G.; Gundrum, T.; Eckert, S.; Cramer, A.;
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren und eine Anordnung zur Bestimmung von räumlichen Geschwindigkeitsverteilungen in elektrisch leitfähigen Flüssigkeiten vorzuschlagen, die für alle Geschwindigkeitskomponenten reproduzierbare Ergebnisse garantieren und in denen jeglicher Kontakt mit der Flüssigkeit oder den sie einschließenden Wänden vermieden wird.
  • Patent
    Patentanmeldung 100 26 052.7
  • Patent
    DE 100 26 052 C2
  • Patent
    WO 01/90762 A1

Publ.-Id: 3695 - Permalink


Mechanisms of pit coarsening in ion erosion of fcc(111) surfaces: A kinetic 3D lattice Monte-Carlo study
Strobel, M.; Heinig, K.-H.; Michely, T.;
An atomic simulation approach toion erosion of fcc(111) surfaces is presented. In a fully 3D kinetic lattice Monte-Carlo model thermodynamically activated processes like adatom, step-edge or surface vacancy diffusion are combined with ballistic eects due to single ion impacts, i.e. sputtering, adatom and surface vacancy generation. In the course of erosion nucleation of surface vacancy islands, their growth, both laterally and vertically, and subsequent coarsening of these pits is observed. For removal of up to theta = 6 monolayers the evolution of the surface is characterized in terms of the roughness and height-height-correlation function. The simulation results are discussed with respect to low-energy noble gas ion erosion experiments of Pt(111) surfaces [M. Kalff, et al., Surf. Sci., preceding paper]. By explicitly tuning specifc atomic transitions within the simulation it is demonstrated, that forbidden thermal adatom generation does hardly in uence the surface evolution. Suppressed step-edge diffusion, however, considerable slows down pit coarsening and impedes pit shape relaxation, emphasizing the importance of this smoothening process in ion erosion.
  • Surface Science 486 (1-2) Jul 2001 p.136-156

Publ.-Id: 3694 - Permalink


Modeling and XPS Study of Precipitation and Oxidation of Ge in Ge+ implanted SiO2 layers
Borodin, V.; Heinig, K.-H.; Schmidt, B.; Oswald, S.;
During annealing at 950°C in an oxidizing ambient, the redistribution of Ge in Ge+ implanted SiO2 layer is influenced by the germanium oxidation. Crystalline clusters precipitate immediately after sample heating. During the annealing an oxidation front proceeds into the layer, consuming crystalline clusters and leaving behind glassy precipitates barely visible by XTEM.
Sputtering depth profiling in conjunction with the x-ray photoelectron spectroscopy analysis was applied in order to identify the chemical state of both the precipitated Ge and that dissolved in the silicon dioxide matrix. For a reliable interpretation of the measured data, modeling of the physical processes involved in the depth profiling XPS technique was performed. It is shown that the depth profiling by ion beam sputtering causes collisional mixing of the subsurface region, which modifies the XPS signal. The results indicate possible improvement of the depth profiling XPS method to be used in future experiments.
  • Nuclear Instruments and Methods in Physics Research B, 178 May 2001 p. 115-119

Publ.-Id: 3693 - Permalink


Ion irradiation of gold inclusions in SiO2: experimental evidence for inverse Ostwald ripening
Rizza, G.; Strobel, M.; Heinig, K.-H.; Bernas, H.;
When sub mm size gold inclusions in SiO2 are irradiated with MeV gold ions, a ring of nanometer-size clusters is formed in their immediate vicinity. The size, density and radial distribution of these nanoclusters was determined. Our observations are in agreement with a recent prediction that in a driven system, under appropriate ion beam and temperature conditions, the steady-state solute concentration's dependence on precipitate size may be opposite to that expected from the equilibrium Gibbs-Thomson relation. Kinetic Monte-Carlo simulations account for additional experimental results: the irradiation-induced increase in solute concentration can promote nucleation of additional precipitates around the first ring. The latter finding contradicts the usual assumption that ion beam mixing hinders nucleation.
  • Nuclear Instruments and Methods in Physics Research B 178: 78-83 MAY 2001

Publ.-Id: 3690 - Permalink


3D Kinetic Lattice Monte-Carlo Simulations of Ion Erosion of fcc(111) Surfaces
Strobel, M.; Heinig, K.-H.; Michely, T.;
In high-dose ion implantation nanoclusters can be formed in a rather well-controlled manner as a function of implantation parameters like ion fluence, ion flux and substrate temperature. According to our current understanding of ion beam synthesis the evolution of nanoclusters is determined by the competition between ballistic and thermodynamic effects. While standard thermodynamics, i.e. the phase transition from a supersaturated solid-solution to second-phase precipitates via homogeneous nucleation and growth, gives a reasonable explanation for a variety of observed nanostructures, under irradiation conditions ballistic processes can modify the phase-ordering kinetics dramatically. By incorporating collisional mixing with the standard thermodynamical kinetic Monte-Carlo model, analytical predictions of irradiation effects of nanoclusters, e.g. inverse Ostwald ripening, are discussed.
Keywords: Ion erosion, fcc(111) surfaces, Kinetic lattice Monte-Carlo modeling
  • Nuclear Instruments and Methods in Physics Research B 178: 105-108 MAY 2001

Publ.-Id: 3689 - Permalink


Shape evolution of oxidized silicon V-grooves during high dose ion implantation
Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.;
The evolution of the shape of oxidized V-grooves on (001) Si under high-dose Ge+ ion irradiation has been studied experimentally as well as theoretically. The shape of the V-grooves changes due to sputtering, re-deposition and swelling. An integro-differential equation has been derived which takes into account these 3 effects. The equation where solved numerically for the experimental conditions. Experimentally, V-grooves where formed by anisotropic etching and dry oxidation. XTEM images of as-oxidized
and as-implanted V-grooves where compared. The theoretically predicted SiO2 layer thickness reduction as well as the predicted surface shape change agree nicely with XTEM images. It is shown that sputtered material accumulates at the bottom of the V-grooves. At the same time implanted species accumulate in the bottom region of V-grooves, which can result in the formation of a very thin wire during subsequent annealing.
  • Nuclear Instruments and Methods in Physics Research B 178: 109-114 MAY 2001

Publ.-Id: 3688 - Permalink


Shape evolution of oxidized silicon V-grooves during high dose ion implantation
Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.;
The evolution of the shape of oxidized V-grooves on (001) Si under high-dose
Ge+ ion irradiation has been studied experimentally as well as
theoretically. The shape of the V-grooves changes due to sputtering,
re-deposition and swelling. An integro-differential equation has been
derived which takes into account these 3 effects. The equation where solved
numerically for the experimental conditions. Experimentally, V-grooves where
formed by anisotropic etching and dry oxidation. XTEM images of as-oxidized
and as-implanted V-grooves where compared. The theoretically predicted SiO2
layer thickness reduction as well as the predicted surface shape change
agree nicely with XTEM images. It is shown that sputtered material
accumulates at the bottom of the V-grooves. At the same time implanted
species accumulate in the bottom region of V-grooves, which can result in
the formation of a very thin wire during subsequent annealing.
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3687 - Permalink


3D Kinetic Lattice Monte-Carlo Simulations of Ion Erosion of fcc(111) Surfaces
Strobel, M.; Heinig, K.-H.; Michely, T.;
In high-dose ion implantation nanoclusters can be formed in a rather well-controlled manner as a function of implantation parameters like ion fluence, ion flux and substrate temperature. According to our current understanding of ion beam synthesis the evolution of nanoclusters is determined by the competition between ballistic and thermodynamic effects. While standard thermodynamics, i.e. the phase transition from a supersaturated solid-solution to second-phase precipitates via homogeneous nucleation and growth, gives a reasonable explanation for a variety of observed nanostructures, under irradiation conditions ballistic processes can modify the phase-ordering kinetics dramatically.
By incorporating collisional mixing with the standard thermodynamical kinetic Monte-Carlo model, analytical predictions of irradiation effects of nanoclusters, e.g. inverse Ostwald ripening, are discussed.
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3686 - Permalink


Ion irradiation of gold inclusions in SiO2: experimental evidence for inverse Ostwald ripening
Rizza, G.; Strobel, M.; Heinig, K.-H.; Bernas, H.;
When sub mm size gold inclusions in SiO2 are irradiated with MeV gold ions, a ring of nanometer-size clusters is formed in their immediate vicinity. The size, density and radial distribution of these nanoclusters was determined. Our observations are in agreement with a recent prediction that in a driven system, under appropriate ion beam and temperature conditions, the steady-state solute concentration's dependence on precipitate size may be opposite to that expected from the equilibrium Gibbs-Thomson relation. Kinetic Monte-Carlo simulations account for additional experimental results: the irradiation-induced increase in solute concentration can promote nucleation of additional precipitates around the first ring. The latter finding contradicts the usual assumption that ion beam mixing hinders nucleation..
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3685 - Permalink


Inverse Ostwald ripening under ion irradiation
Heinig, K.-H.; Strobel, M.;
The steady-state behavior of plain interfaces and nanoclusters (NCs) under
ion irradiation has been studied analytically as well as by kinetic
Monte-Carlo (MC) simulations. In the two-phase system mixing of A-type atoms
into phase B region leads to a strong increase of the solute concentration
at low irradiation temperatures. For NCs the ion irradiation induced
elevated solute concentration depends on their sizes. The analytical form of
this size dependence is identical to that of NCs in equilibrium, i.e. it is
given by the Gibbs-Thomson relation. However, in contrast to equilibrium,
small NCs have a lower increase in solute concentration than larger ones.
This may result in a dramatically change of the evolution of NC ensembles:
The driven system can get a negative capillarity length for its interfaces
with the consequence of mass transport from large NCs to smaller ones, i.e.
inverse Ostwald ripening is observed. Thus, it is predicted theoretically
that a broad size distribution can be made narrow by ion irradiation. At
conditions not being too far from equilibrium this behavior has been proven
by a computer experiment. The MC simulations predict in addition to the
analytical result that at very high fluxes or low temperatures large NCs can
disintegrate due to the formation of smaller ones by nucleation.

Keywords: Ion irradiation, nanoclusters, non-equilibrium, Ostwald ripening, theory
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3684 - Permalink


Atomistic Study of the Evolution of Nanoclusters in Ion Beam Synthesis
Strobel, M.; Heinig, K.-H.; Möller, W.;
Ion implantation is an established tool to synthesize or to modify buried low-dimensional nanostructures (e.g. nanoclusters), which have become the basis of numerous technological applications. According to our current understanding of ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. In this work it is shown, that a sound understanding of the diffusional interaction dynamics of nanoclusters can be achieved by kinetic 3D lattice Monte-Carlo simulations. In particular, the exploitation of the cluster size-concentration dependence (the Gibbs-Thomson relation) under pure thermal or ion irradiation conditions provides a wealth of physical information relevant for ion beam synthesis. Furthermore, evidence is presented, that within a certain parameter window of irradiation conditions collisional mixing induced nucleation of nanoclusters occurs.
Keywords: Ion beam synthesis, nanoclusters, nucleation, Ostwald ripening, collisional mixing, kinetic lattice Monte-Carlo modeling
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3683 - Permalink


Modeling and XPS Study of Pricipitation and Oxidation of Ge in Ge+ implanted SiO2 layers
Borodin, V.; Heinig, K.-H.; Schmidt, B.; Oswald, S.;
During annealing at 950oC in an oxidizing ambient, the redistribution of Ge in Ge+ implanted SiO2 layer is influenced by the germanium oxidation. Crystalline clusters precipitate immediately after sample heating. During the annealing an oxidation front proceeds into the layer, consuming crystalline clusters and leaving behind glassy precipitates barely visible by XTEM. Sputtering depth profiling in conjunction with the x-ray photoelectron spectroscopy analysis was applied in order to identify the chemical state of both the precipitated Ge and that dissolved in the silicon dioxide matrix. For a reliable interpretation of the measured data, modeling of the physical processes involved in the depth profiling XPS technique was performed. It is shown that the depth profiling by ion beam sputtering causes collisional mixing of the subsurface region, which modifies the XPS signal. The results indicate possible improvement of the depth profiling XPS method to be used in future experiments.
Keywords: Germanium, oxidation, silicon dioxide, X-ray photoelectron spectroscopy, modeling
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3682 - Permalink


Morphology Evolution during Ion Erosion of fcc(111) Surfaces: A 3D Kinetic Lattice Monte-Carlo Study
Strobel, M.; Heinig, K.-H.; Michely, T.;
Ion Erosion ...
  • Lecture (Conference)
    12th Int. Conf. Ion Beam Modifications of Materials (IBMM2000), Canela, Brazil, September 3 - 8, 2000

Publ.-Id: 3681 - Permalink


Nanocluster Evolution under Ion Irradiation
Heinig, K.-H.; Strobel, M.; Rizza, G.;
An ensemble of nanoclusters embedded in a substrate evolves during thermal annealing by coarsening or Ostwald ripening, and, if the concentration of cluster material is sufficiently high, coalescence.
In this contribution it will be shown that by ion irradiation the evolution of nanoclusters can be modified or even dramatically changed. (i) Ion irradiation increases due to collisional detachments of atoms from clusters the steady-state solubility. Thus, cluster evolution is accelerated or happens at lower temperatures. (ii) Collisional detachment of atoms from nanoclusters is more efficient for large clusters than for small ones. This dependence on cluster size is opposite to that predicted by the Gibbs-Thomson law for thermally activated detachment. The "inverse" behaviour results in "Inverse Ostwald Ripening", i.e. a broad size distribution becomes narrower during annealing under ion irradiation. (iii) Under intense ion irradiation large clusters can evaporate and new nanoclusters will nucleate. A steady-state mean size, which is dependent on ion flux and temperature, can be found.
The new results listed above were predicted by an analytical theory and have been proven by kinetic lattice Monte-Carlo simulations and preliminary experiments.

Keywords: Ion irradiation, nanoclusters, annealing, Ostwald ripening, theory, computer simulation
  • Invited lecture (Conferences)
    12th Int. Conf. Ion Beam Modifications of Materials (IBMM2000), Canela, Brazil, September 3 - 8, 2000 (invited)

Publ.-Id: 3680 - Permalink


Synthese und Bearbeitung von Nanostrukturen mit Ionenstrahlen
Heinig, K.-H.;
Unter Ionenbestrahlung laufen in der Festkörperoberfläche Prozesse weitab vom thermodynamischen Gleichgewicht ab. Übliche Prozeßabläufe können umgekehrt werden (z.B. inverses Ostwaldreifen), und geordnete Strukturen können sich ausbilden (z.B. wave-ordered-structures). Im Vortrag werden hierzu experimentelle und theoretische Untersuchungen vorgestellt. Es wird u.a. gezeigt, wie Nanocluster in Ordnungszustände gebracht werden können, die für mikroelektronische und mikrooptsche Anwendungen hochinteressant sind.
Keywords: Ionenstrahlsynthese, Nanocluster, Computersimulation, Thermodynamik
  • Lecture (others)
    Friedrich-Schiller Universität Jena, Physikalisch-Astronomische Fakultät, Vortrag am 17. 11. 2000

Publ.-Id: 3679 - Permalink


Physico-chemical characterization of seaborgium as oxide hydroxide
Hübener, S.; Taut, S.; Vahle, A.; Dressler, R.; Eichler, B.; Gäggeler, H. W.; Jost, D.; Piguet, D.; Türler, A.; Schädel, M.; Jäger, E.; Brüchle, W.; Schimpf, E.; Kirbach, U.; Trautmann, N.; Yakushev, A.;
Seaborgium (element 106) was studied in comparison with tungsten in the O2-H2O(g)/SiO2(s)-system using high-temperature on-line isothermal gas chromatography. The 21-s nuclide 266Sg was produced in the 248Cm + 22Ne reaction at a beam energy of 119 MeV. The reaction products were continuously transported by a He(MoO3)-jet to the chromatography apparatus HITGAS. Group 6 element oxide hy-droxide molecules volatile at temperatures above 1000 K were formed at 1325 K by adding humid oxygen as reactive gas. 266Sg was unambiguously detected after gas chromatographic separation by measuring 266Sg-262Rf mother-daughter a-sf correlations. The experimental results demonstrate the volatility of seaborgium in humid oxygen, presumably as seaborgium oxide hydroxide as typical for both uranium (VI) and the group 6 elements.
Keywords: Seaborgium, group 6 elements, oxide hydroxide, reaction gas chromatography
  • Radiochimica Acta 89 (2001) 737-741

Publ.-Id: 3678 - Permalink


Elastic constants of diamond-like amorphous carbon films: the effect of internal stresses
Belov, A.; Jäger, H.-U.;
The extreme wear resistance and chemical inertness of tetrahedral, or
diamond-like, amorphous carbon (ta-C) make it a promising material for
wear-resistive mechanical coatings. The unique mechanical behaviour of ta-C
is related to the atomic structure of amorphous carbon and atomic scale
modeling becomes a valuable tool to study both growth mechanisms of ta-C
films and their mechanical properties. Here we report results of atomistic
calculations of elastic constants in ta-C films grown by a realistic
computer simulation of ion-beam deposition. The dependence of the elastic
constants on the ion energy is presented. Similar to the real as-grown
nonequilibrium (not annealed) ta-C films, the simulated structures possess
the high internal compressive stress, which can considerably effect on
elastic constants. An approach employed allows for the stress dependence of
elastic constants to be analysed. We demonstrate the variation of elastic
constants as a function of the internal stress, and therefore the
importance of nonlinear elastic properties in amorphous carbon.
Keywords: tetrahedral amorphous carbon, elastic constants, internal stresses
  • Lecture (Conference)
    E-MRS 2001 SPRING MEETING, June 5-8, 2001, Strasbourg (France), Symposium C: Protective Coatings and Thin Films

Publ.-Id: 3677 - Permalink


Structures of technetium and rhenium complexes
Leibnitz, P.; Reck, G.; Pietzsch, H.-J.; Spies, H.;
Investigations in the 99mTc chemistry are stimulated by the search for new radiopharmaceuticals for nuclear medical applications. To understand the coordination mode of Tc with various complexing agents, macroscopic studies of technetium coordination chemistry are often performed using the low energy ß-emitting radionuclide 99Tc, which has a much longer half life (t1/2 = 2.12 x 105 years) than 99mTc, in the mg level.
Investigations of Re coordination chemistry are done in conjunction with Tc studies because Re possesses chemical properties similar to those of Tc. For some chemical tasks, Re provides a non-radioactive alternative to work with Tc radioisotopes. In addition, 186Re and 188Re are of great interest to nuclear medicine as they possess nuclear properties favorable for use in therapeutic radiopharmaceuticals.
Our investigations of Tc and Re coordination chemistry are toward this goal. A large series of technetium and rhenium complexes resulted from this studies have been characterized by X-ray crystal structure determinations.
This survey covers the structural investigations performed by P.Leibnitz and G.Reck (BAM) from 1992 till now. It summarizes results obtained in the Rossendorf technetium group and is not intended to compete with the well-written reviews published so far.

Keywords: technetium complexes, rhenium complexes, oxotechnetium(V) complexes, oxorhenium(V) complexes, Tc(III) mixed ligand complexes, Re(III) mixed ligand complexes, X-ray structural analysis
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-311 2001

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Publ.-Id: 3676 - Permalink


Calculation of intrinsic stresses in amorphous carbon films grown by molecular dynamics simulation: from the atomic to the macroscopic scale
Belov, A.; Jäger, H.-U.;
We present a method of calculation and an estimate for the bulk intrinsic stress in nonequilibrium tetrahedral amorphous carbon (ta-C) films grown by a realistic atomic scale simulation of ion-beam deposition. The simulated films have a thickness of a few nanometers and reproduce the important features of the real as grown nonequilibrium (not annealed) structures such as the presence of a steady-state growth region with uniform properties, the large content of sp3 bonded atoms, and the high intrinsic compressive stress, which seriously limits the maximum thickness of films that can be deposited. Using slices from the nearly structurally uniform film region, a 3D periodic model was constructed for the bulk intrinsic stress calculation. Employing empirical interatomic potentials for carbon, atomic stresses as well as the bulk stresses were computed. The obtained value of the compressive stress for the transition from the graphitic-like carbon to ta-C is in a good agreement with experimental data for the stress threshold.
Keywords: tetrahedral amorphous carbon, thin films, intrinsic stress
  • Poster
    E-MRS 2001 SPRING MEETING, June 5-8, 2001, Strasbourg (France), Symposium A: Computational Materials Science Across Time and Length Scales

Publ.-Id: 3675 - Permalink


Erwärmung des Reaktordruckbehälters des Blocks 8 des KKW Greifswald bei der Zerlegung mittels Sägetechnik
Mössner, T.; Altstadt, E.; Böhmert, J.; Weiß, R.;
Die Arbeit untersucht das Erwärmungsverhalten des Reaktordruckbehälters des Blockes 8 des KKW Greifswald bei der Zerlegung in Ringabschnitte mit einer Bandsäge. Mit dem Programm ANSYS wurde dazu ein thermisches Finite-Elemente-Modell erstellt. Dieses Modell ist an Hand vorhandener Temperaturmessdaten abgeglichen worden. Mit dem abgeglichenen Modell wurden abschließend die auftretenden Maximaltemperaturen für den Sägevorgang ermittelt. Diese liegen bei höchstens 200 °C.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf, FZR-310 Januar 2001

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Publ.-Id: 3674 - Permalink


Riga Dynamo Experiment
Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.;
It is widely believed that almost all magnetic fields in a natural
environment are a result of the dynamo process -- field generation in a
moving nearly homogeneous fluid electroconducting material of celestial
bodies. Such are fields of the Earth, most of the planets, Sun, another
stars and even galaxies. The believe is based on the theory and numerical
simulation. Until very recently no direct laboratory experiment was
supporting this important point. We are not going to model in the laboratory
any particular celestial body. Our aim is to demonstrate the very idea -- by
intense stirring in a large volume of good electroconducting liquid one can
generate a magnetic field. As the working fluid we are using 2 qm of molten
sodium -- the best electroconducting liquid available. The fluid part of
celestial bodies is stirred by thermal and other types of natural
convection. In laboratory circumstances such stirring is much too slow.
Hence we are stirring sodium by an outside forced propeller consuming 150kW
of power. The propeller is producing an axisymmetric swirling flow inside a
prolongated annular vessel. When flowrate reaches 0.6 qmps or so the device
starts to generate magnetic field. The field pattern is nonaxisymmetric and
slowly (1.2 --1.5hz) rotates round symmetry axis. The overall rotation is
superimposed by turbulent fluctuations. The generation process is stable in
operational sense and results are reproducible. We report on two experiments
at the Riga dynamo facility. In November 1999, a slowly growing magnetic
field eigenmode was observed for the first time in a liquid metal
experiment. In July 2000, the magnetic field saturation regime was studied.
We sketch also the underlying theory in order to illuminate the background
of the Riga dynamo experiment.

  • Lecture (Conference)
    Lecture at European Geophysical Society, XXVI General Assembly, Nice (France), March 25-30, 2001

Publ.-Id: 3673 - Permalink


Validation of coupled neutron kinetic / thermal-hydraulic codes Part 2: Analysis of a VVER-440 transient (Loviisa-1)
Hämäläinen, A.; Kyrki-Rajamäki, R.; Mittag, S.; Kliem, S.; Weiss, F.-P.; Langenbuch, S.; Danilin, S.; Hadek, J.; Hegyi, G.;
Several three-dimensional hexagonal reactor dynamic codes have been developed for VVER type reactors and coupled with different thermal-hydraulic system codes. Under the auspices of the European Union's Phare programme these codes have been validated against real plant transients by the participants from 7 countries. Two of the collected five transients were chosen for validation of the codes. Part 1 of this article consists of validation against VVER-1000 reactor data. This second part is focussed to validation against measured data of `One turbo-generator load drop experiment' at the Loviisa-1 VVER-440 reactor. The experiment was performed just after plant modernisation and more measured data was available to validation than in normal operation of real plants. Good accuracy of the results was generally achieved comparable to the measurement accuracy. The confidence in the results of the different code systems has increased, and consequences of certain model changes could be evaluated.
  • Annals of Nuclear Energy 29 (2002) 255-269

Publ.-Id: 3672 - Permalink


Syntheses and Crystal Structure Determination of hexacoordinated Silicon-Complexes with Dimethylpyridines
Hensen, K.; Kettner, M.; Stumpf, T.; Bolte, M.;
Halogensilane, HSiCl3, forms with 3,4-dimethylpyridine in aprotic solvents a crystalline 1:2-compound which is stable at room temperature and readily soluble in CHCl3. Colourless crystals of the dicationic complex, [H2Si(3,4-dimethylpyridine)4]2+ 2Cl-×6 CHCl3 (verified by X-ray structure analysis) are obtained by dismutation of HSiCl3(3,4-di-methylpyridine)2 in CHCl3, within one week at room temperature. 29Si-NMR indicates that SiCl4 is generated as a second product. H2SiCl2 with 2,4-dimethylpyridine as well as MeHSiBr2 with 3,5-dimethylpyridine in aprotic solvents form 1:2-compounds stable at room temperature. X-ray structure analysis in both cases establish neutral-complexes with a hexacoordinated silicon atom.

  • Naturforschung 55b 2000 (901-906)

Publ.-Id: 3670 - Permalink


Halogen exchange and expulsion : ligand stabilized dihalogen silicon dications
Hensen, K.; Mayr-Stein, R.; Stumpf, T.; Pickel, P.; Bolte, M.; Fleischer, H.;
The first ligand stabilized SiCl22+ dications were synthesed using N-methylimidazole as co-ordinating ligand. The compounds SiCl4, SiBr2Cl2, and SiH2Cl2 form six-co-ordinated dicationic compounds of almost octahedral symmetry with similar structures which were investigated by single crystal X-ray analysis and density functional calculations. The structures exhibit particularly short dative Si-N bonds of about 1.90 C. Complexes crystallized from the same solvent are isostructural. A different solvent, though, leads to geometrical variations. It was also discovered that the halogen exchange process among mixed silicon tetrahalides occurs under much milder conditions than previously thought and proceeds with considerable speed even without a catalyst.

  • J. Chem. Soc., Dalton Trans. 2000 (473-477)

Publ.-Id: 3669 - Permalink


Template-Directed Self-Assembly of Buried Nanowires and the Pearling Instability
Müller, T.; Heinig, K.-H.; Schmidt, B.;
The fabrication of more and more miniaturized electronic and photonic devices relies on new, ingenious methods for the fabrication of spatially controlled nanostructures. Examples are electronic devices based on semiconducting nanowires and photonic devices based on chains of metallic nanoclusters that guide light by coupled surface plasmons. In this contribution a template-directed ion beam synthesis of nanowires and regular nanocluster chains will be presented. As templates, V-grooves etched in (001)Si and subsequently oxidized are used. High fluence Ge+ implantation is carried out into the SiO2 layer at 70 keV. Thereby, the implanted Ge enriches themselves in the V-groove bottom to a critical amount, which may result in nanowire formation by nucleation, growth and coalescence during subsequent thermal treatment. TEM investigations indicate the formation of a nanowire buried in the SiO2 at the V-groove bottom. Kinetic lattice Monte Carlo simulations of the nanowire formation process were performed in order to understand the phase separation mechanism and results are compared to TEM images. Furthermore, it is shown that even ideal nanowires show a instability and form during long-lasting annealing equal-spaced and equal-sized nanoclusters "nanocluster chains" by self-organization.
Keywords: Nanowires, Ion Beam Synthesis, Pearling Instability, Nanocluster Chains
  • Poster
    European Materials Research Society Spring Meeting E-MRS 2001, Strasbourg, France, June 5-8, 2001
  • Material Scince and Engineering C 19 (2002) 209-213
  • Contribution to WWW
    arXiv:cond-mat/0108371 v1 23 Aug 2001

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Publ.-Id: 3667 - Permalink


Kinetics of Ion Beam Synthesis of Sn and Sb Clusters in SiO2 Layers
Spiga, S.; Ferrari, S.; Fanciulli, M.; Schmidt, B.; Heinig, K.-H.; Grötzschel, R.; Mücklich, A.; Pavia, G.;
In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (doses of 0.1-1 x 1016 cm-2) Sn implanation in 85 nm thick SiO2 followed by RTP annealing (800-1000°C for 30-300 under Ar or N2 dry ambient) leads to the formation of two cluster bands, near the SiO2 surface and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed in the middle of the oxide. Cluster-size distribution and cluster-crystallinty are related to implantation dose and annealing time. Low energy (10-12 kev) Sb and Sn implantation (doses 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed
Keywords: ion beam synthesis, nanoclusters, Tin, Antimony, ion implantation, silicon dioxide, Ostwald ripening, nonvolatile memory device
  • Contribution to external collection
    Mat. Res. Soc. Proc. vol. 647 (2001)

Publ.-Id: 3666 - Permalink


Kinetics of Ion Beam Synthesis of Sn and Sb Clusters in SiO2 Layers
Spiga, S.; Ferrari, S.; Fanculli, M.; Schmidt, B.; Heinig, K.-H.; Grötzschel, R.; Mücklich, A.; Pavia, G.;
In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (doses of 0.1-1 x 1016 cm-2) Sn implanation in 85 nm thick SiO2 followed by RTP annealing (800-1000°C for 30-300 under Ar or N2 dry ambient) leads to the formation of two cluster bands, near the SiO2 surface and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed in the middle of the oxide. Cluster-size distribution and cluster-crystallinty are related to implantation dose and annealing time. Low energy (10-12 kev) Sb and Sn implantation (doses 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed.
Keywords: ion beam synthesis, nanoclusters, Tin, Antimony, ion implantaion
  • Poster
    Materials Research Society 2000 Fall Meeting, Symp. O "Ion Beam Synthesis and Processing of Advanced Materials" , Boston, USA, Nov. 27-29, 2000
  • Contribution to proceedings
    Mat.Res.Soc.Symp.Proc. Vol. 647 (2001) O11.23 MRS2000 Fall Meeting, Symposium O: "Ion Beam Processing of Advanced Materials", Boston, USA, Nov. 27-29, 2000

Publ.-Id: 3665 - Permalink


Understanding ion beam synthesis of nanostructures: Modelling and atomistic simulations
Strobel, M.; Heinig, K.-H.; Möller, W.;
Ion implantation, specified by parameters like ion energy, ion fluence, ion flux and substrate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced, which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient in understanding nanocluster evolution. Various aspects of precipitate evolution during implantation, formation of ordered arrays of nanophase domains by focused ion implantation and compound nanocluster synthesis are discussed.
Keywords: ion beam synthesis, nanostructures, nanoclusters, ion implantation, ion beam mixing, Ostwald ripening, kinetic Monte-Carlo simulation
  • Contribution to external collection
    Mat. Res. Soc. Proc. vol. 647 (2001)

Publ.-Id: 3664 - Permalink


Successful nitriding of austenitic stainless steel: On the diffusion mechanism of nitrogen and on the role of the surface oxide layer.
Parascandola, S.; Möller, W.; Williamson, D. L.;
In the first part of this paper we present a quantitative trapping model that includes detrapping to describe the diffusion of nitrogen in austenitic stainless steel during successful nitriding. Calculated nitrogen depth profiles, assuming a diffusion pre-exponential factor D0 = 10-3 cm2/s, a diffusion activation energy Ed = 1.1 eV, and a detrapping activation energy Et2d = 1.45 eV, show good agreement with experimental nitrogen depth profiles
obtained from a sample that has been subsequently nitrided with 14N and 15N. The plausibility of a trapping mechanism is also supported by a number of phenomenological and thermodynamical arguments. In the second part of this paper we present a modelling approach for the evolution of the thickness of the surface oxide layer during successful nitriding. The approach bases on the assumption that the surface oxide layer thickness is completely controlled by the interplay of sputtering and oxidation and differentiates between oxide layer growth limited by diffusion and oxide layer growth limited by the rate of oxygen supply. The applicability of this approach is supported by experimental data obtained by real-time elastic recoil detection analysis during ion nitriding at different combinations of ion energy and oxygen partial pressure.
  • Lecture (Conference)
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan
  • Contribution to proceedings
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan

Publ.-Id: 3663 - Permalink


Understanding ion beam synthesis of nanostructures: Modeling and atomistic simulations
Strobel, M.; Heinig, K.-H.; Möller, W.;
Ion implantation, specified by parameters like ion energy, ion fluence, ion flux and substrate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced,
which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient
in understanding nanocluster evolution. Various aspects of
precipitate evolution during implantation, formation of
ordered arrays of nanophase domains by focused ion implantation
and compound nanocluster synthesis are discussed.
Keywords: ion beam synthesis, nanostructures, nanoclusters, ion implantation, ion beam mixing, Ostwald ripening, kinetic Monte-Carlo simulation
  • Invited lecture (Conferences)
    Materials Research Society 2000 Fall Meeting, Symp. O "Ion Beam Synthesis and Processing of Advanced Materials", Nov 27 - Dec 1, 2000, Boston, USA, Invited Talk

Publ.-Id: 3662 - Permalink


Evidence for a Soft Nuclear Equation-of-State from Kaon Production in Heavy Ion Collisions
Sturm, C.; Böttcher, I.; Debowski, M.; Förster, A.; Grosse, E.; Koczon, P.; Kohlmeyer, B.; Laue, F.; Mang, M.; Naumann, L.; Oeschler, H.; Pühlhofer, F.; Schwab, E.; Senger, P.; Shin, Y.; Speer, J.; Ströbele, H.; Surowka, G.; Uhlig, F.; Wagner, A.; Walus, W.;
The production of pions and kaons has been measured in Au+Au collisions at beam energies from 0.6 to 1.5 AGeV with the Kaon Spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.
Keywords: pion kaon Au+Au collisions K+ meson multiplicity nucleon nuclear equation-of-state.
  • Physical Review Letters 86 (2001) 39

Publ.-Id: 3661 - Permalink


Inverse Ostwald Ripening and Self-Organization of Nanoclusters due to Ion Irradiation
Heinig, K.-H.; Schmidt, B.; Strobel, M.; Bernas, H.;
Under ion irradiation collisional mixing competes with phase separation if the irradiated
solid consists of immiscible components. If a component is a chemical compound,
there is another competition between collisional forced chemical dissociation of the
compound and its thermally activated re-formation. Especially at interfaces between
immiscible components, irradiation processes far from thermodynamical equilibrium
may lead to unexpected phenomena. If the formation of nanoclusters (NCs) occurs
during ion implantation, the phase separation caused by ion implantation induced
supersaturation can be superimposed by phenomena caused by collisional mixing.
In this contribution it will be studied how collisional mixing during high-fluence ion
implantation affects NC synthesis and how ion irradiation through a layer of NCs
modifies their size and size distribution. Inverse Ostwald ripening of NCs will be
predicted theoretically and by kinetic lattice Monte-Carlo simulations. The
mathematical treatment of the competition between irradiation-induced detachment
of atoms from clusters and their thermally activated diffusion leads to a Gibbs-
Thomson relation with modified parameters. The predictions have been confirmed by
experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The
unusual behavior results from an effective negative capillary length, which will be
shown to be the reason for inverse Ostwald ripening. Another unexpected
phenomenon to be addressed is self-organization of NCs in a delta-layer parallel to
the Si/SiO2 interface. Such delta-layers were found when the damage level at the
interface was of the order of 1...3 dpa. It will be discussed that the origin of the delta-
layer of NCs can be assigned to two different mechanisms: (i) The negative interface
energy due to collisional mixing gives rise to the formation of tiny clusters of substrate
material in front of the interface, which promotes heteronucleation of the implanted
impurities. (ii) Collisional mixing in the SiO2 produces diffusing oxygen, which may be
consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes
denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si
excess promotes heteronucleation too. Independent of the dominating mechanism of
self-organization of a delta-layer of NCs, its location in SiO2 close to the
SiO2/Si interface makes it interesting for non-volatile memory application.
Keywords: Nanostructures, ion implantation, Ostwald ripening. nucleation, ion beam mixing, theory, kinetic lattice Monte-Carlo simulation, nonvolatile memory device
  • Contribution to external collection
    Mat. Res. Soc. Proc. vol. 647(2001) O14.6

Publ.-Id: 3660 - Permalink


Inverse Ostwald Ripening and Self-Organization of Nanoclusters due to Ion Irradiation, (invited talk MRS 2000 Fall Meeting, Boston, USA), Mat. Res. Soc. Proc., vol. 647
Heinig, K.-H.; Schmidt, B.; Strobel, M.; Bernas, H.;
Under ion irradiation collisional mixing competes with phase separation if the irradiated
solid consists of immiscible components. If a component is a chemical compound,
there is another competition between collisional forced chemical dissociation of the
compound and its thermally activated re-formation. Especially at interfaces between
immiscible components, irradiation processes far from thermodynamical equilibrium
may lead to unexpected phenomena. If the formation of nanoclusters (NCs) occurs
during ion implantation, the phase separation caused by ion implantation induced
supersaturation can be superimposed by phenomena caused by collisional mixing.
In this contribution it will be studied how collisional mixing during high-fluence ion
implantation affects NC synthesis and how ion irradiation through a layer of NCs
modifies their size and size distribution. Inverse Ostwald ripening of NCs will be
predicted theoretically and by kinetic lattice Monte-Carlo simulations. The
mathematical treatment of the competition between irradiation-induced detachment
of atoms from clusters and their thermally activated diffusion leads to a Gibbs-
Thomson relation with modified parameters. The predictions have been confirmed by
experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The
unusual behavior results from an effective negative capillary length, which will be
shown to be the reason for inverse Ostwald ripening. Another unexpected
phenomenon to be addressed is self-organization of NCs in a delta-layer parallel to
the Si/SiO2 interface. Such delta-layers were found when the damage level at the
interface was of the order of 1...3 dpa. It will be discussed that the origin of the delta-
layer of NCs can be assigned to two different mechanisms: (i) The negative interface
energy due to collisional mixing gives rise to the formation of tiny clusters of substrate
material in front of the interface, which promotes heteronucleation of the implanted
impurities. (ii) Collisional mixing in the SiO2 produces diffusing oxygen, which may be
consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes
denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si
excess promotes heteronucleation too. Independent of the dominating mechanism of
self-organization of a delta-layer of NCs, its location in SiO2 close to the
SiO2/Si interface makes it interesting for non-volatile memory application.
Keywords: nanostructures; nanoclusters; ion implantation; ion irradiation; Ostwald ripening; nucleation; self-organization; nonequilibrium thermodynamics; theory; kinetic lattice Monte-Carlo simulation; nonvolatile memory device
  • Invited lecture (Conferences)
    Materials Research Society 2000 Fall Meeting; Boston (USA), 27.11.-1.12.2000, invited talk
  • Mat.Res.Soc.Proc. 650 (2001) R9.6

Publ.-Id: 3659 - Permalink


A toy model for inverse dynamo theory
Stefani, F.; Gerbeth, G.;
We consider a simple model of inverse dynamo theory consisting of a spherically symmetric alpha^2-dynamo with unknown radial dependence of alpha. Using an evolutionary strategy, we try to reconstruct this radial dependence of alpha from a finite number of given data, e.g. from a few real or complex eigenvalues and/or from the assumption that the field is confined to the dynamo region. Although for planetary dynamos the direct applicability of our specific model is very limited, the principle of inversion is quite general and might be useful for cosmic dynamos as well as for the emerging laboratory dynamo community.
  • Physics of the Earth and Planetary Interiors 128, No. 1-4 (2001), pp. 109-124

Publ.-Id: 3658 - Permalink


Synthesis of S-([18F]fluoromethyl)-(+)-McN5652 as a potential PET radioligand for the serotonin transporter
Zessin, J.; Eskola, O.; Brust, P.; Bergman, J.; Steinbach, J.; Lehikoinen, P.; Solin, O.; Johannsen, B.;
The present study describes the synthesis of the [18F]fluoromethyl analogue of (+)-McN5652 ([18F]FMe-McN) as a new potential tracer for the serotonin transporter. In vitro binding studies have shown that FMe-McN displays only slightly lower affinity for the serotonin transporter (Ki=2.3 ± 0.1 nM) than (+)-McN5652 (Ki=0.72 ± 0.2 nM). The radiofluorinated tracer [18F]FMe-McN was prepared by reaction of normethyl (+)-McN5652 with the fluoromethylation agent [18F]bromofluoromethane in an overall radiochemical yield of 5 ± 1% (decay-corrected, related to [18F]fluoride) and with high specific radioactivity (200 - 2000 GBq/µmol at the end of synthesis).
Keywords: (+)-McN5652, [18F]fluoromethyl analogue, [18F]bromofluoromethane, serotonin transporter, positron emission tomography
  • Nuclear Medicine and Biology 28 (2001) 857-863

Publ.-Id: 3657 - Permalink


The Rossendorf CYCLONE 18/9 Facility - Four Years Experience in Operation and Maintenance -
Preusche, S.; Füchtner, F.; Steinbach, J.;
Our four years experience in operation and maintenance of the PET cyclotron "CYCLONE 18/9" is given. Improvements at the CYCLONE 18/9 are presented as well as results of the routine radionuclide production.
  • Poster
    CYCLONE 18/9 & 10/5 USER COMMUNITY 3. Workshop, February 04 - 06, 2001, Amsterdam, The Netherlands
  • Contribution to proceedings
    CYCLONE 18/9 & 10/5 USER COMMUNITY 3. Workshop, February 04 - 06, 2001, Amsterdam, The Netherlands

Publ.-Id: 3656 - Permalink


Radio fluorination and positron emission tomography (PET) as a new approach to study the in vivo distribution and elimination of the advanced glycation endproducts Nepsilon-carboxymethyllysine (CML) and Nepsilon-carboxyethyllysine (CEL)
Bergmann, R.; Helling, R.; Heichert, C.; Scheunemann, M.; Mäding, P.; Wittrisch, H.; Johannsen, B.; Henle, T.;

After synthesis of fluorine-18 labelled analogues by [18F]fluorobenzoylation at the alpha-amino group, biodistribution and elimination of individual advanced glycation endproducts, namely Nepsilon-carboxymethyllysine and Nepsilon-carboxyethyllysine, was studied in comparison to lysine in rats after intravenous injection using positron emission tomography (PET).
The [18F]radiofluorinated amino acids were fast distributed via the blood, followed by a rapid excretion through the kidneys. Elimination kinetics were similar for both AGEs and lysine. For CML and CEL, but not for lysine, a temporary liver accumulation could be observed, which was not connected with any metabolisation or enterohepatic circulation. No further accumulation in any tissues was observable, indicating that increased tissue levels of CML or CEL, which have been described for certain disorders, are exclusively derived from endogenous origin and should not depend on a dietary intake. Under uremic conditions, however, an impaired kidney function might result in a significant increase of the AGE-load of blood and tissues. PET based on 18F-labelled AGEs proved to be a promising tool to elucidate the physiological fate of post-translationally modified amino acids and to clarify the role of AGEs as possible "glycotoxins".

  • Nahrung/Food 45 (2001) 182-188

Publ.-Id: 3655 - Permalink


Biodistribution and catabolism of 18F-labeled neurotensin(8-13) analogs
Bergmann, R.; Scheunemann, M.; Heichert, C.; Mäding, P.; Wittrisch, H.; Kretzschmar, M.; Rodig, H.; Tourwé, D.; Iterbeke, K.; Chavatte, K.; Zips, D.; Reubi, J. C.; Johannsen, B.;

4-([18F]fluoro)benzoyl-neurotensin(8-13) (18FB-Arg8-Arg9-Pro10-Tyr11- Ile12-Leu13-OH, 1) and two analogs stabilized in one and two positions (18FB-Arg8Psi(CH2NH)Arg9-Pro10-Tyr11- Ile12-Leu13-OH, 2, 18FB-Arg8Psi(CH2NH)Arg9-Pro10-Tyr11-Tle12-Leu13-OH, 3) were synthesized in a radiochemical yield of 25 - 36% and a specific activity of 5 - 15 GBq/mmol. The peptides were evaluated in vitro and in vivo for their potential to image tumors, overexpressing neurotensin receptor 1 (NTR1) by positron emission tomography (PET). All analogs exhibited in vitro binding affinity in the low nanomolar range to NTR1-expressing human tumors, measured by quantitative receptor autoradiography, HT-29 and WiDr cells, and to sections of tumors derived from these cell lines in mice. The radiotracers were internalized in the cells in vitro, and the fluorinated peptides were able to mobilize intracellular Ca2+ of WiDr cells. In in vivo studies in rats and in mice bearing HT-29 cell tumors, only a moderate uptake of the radioligands into the studied tumors was observed, presumingly due to degradation in vivo and fast elimination by the kidneys. In comparison with the other analogs, the specific tumor uptake expressed as tumor-to-muscle relation was highest for the radioligand 3. The blood clearance of 3 was reduced by co-injection of peptidase inhibitors. The catabolic pathways of the radiofluorinated peptides were elucidated. The results suggest that the high binding affinity to NTR1 and the stabilization against proteolytic degradation are not yet sufficient for tumor imaging by PET.

Keywords: Neurotensin analogs, Positron emission tomography, F-18, Receptor binding, Tumor
  • Nuclear Medicine and Biology 29 (2002) 61-72

Publ.-Id: 3654 - Permalink


Evolution of Ion Beam Synthesized Au Nanoclusters in SiO2 under Ion Irradiation
Schmidt, B.; Heinig, K.-H.; Mücklich, A.;
The evolution of the mean size and the size distribution of Au nanoclusters (NCs) under high-energy ion irradiation has been studied. Au NCs were synthesized in a 480 nm thick SiO2 layer by 330 keV Au+ implantation and subsequent annealing at T = 1000 °C for 1h in dry O2. XTEM images show a 70 nm thick layer of Au NCs, being centered at the projected ion range Rp(330keV) = 100 nm, having a mean NC size of 5 nm at Rp, and resembling the broad LSW size distribution of diffusion controlled Ostwald ripening. Post-irradiation of the Au NCs by 4.5 MeV gold ions were used in order to tailor their size and size distribution. The high-energy Au+ irradiation were performed at 190...210 °C with a fluence of (0.5...1.0)x1016 cm-2. By the post-irradiation no gold was deposited into the SiO2 layer, the Au+ ions come to rest in the (001)Si substrate at Rp(4.5MeV) = 1 mm. XTEM images of the post-irradiated Au NCs show a strong decrease of their mean size as well as the width of their size distribution. The observed NC evolution under ion irradiation agrees with recent theoretical predictions and kinetic Monte-Carlo simulations.
Keywords: Ion beam synthesis, nanucluster, comuter simulation
  • Contribution to proceedings
    Materials Research Society, Symposium Proceedings Ion Beam Synthesis and processing of Advanced Materials Symposium held November 27-29, 2000, Boston, Massachusetts, U.S.A

Publ.-Id: 3653 - Permalink


Reflectivity and diffraction study of cross-beam pulsed laser deposited Co/Cu multilayers
Prokert, F.; Noetzel, J.; Schell, N.; Wieser, E.; Matz, W.; Gorbunov, A.;
Co/Cu multilayers were prepared by cross-beam pulsed laser deposition and characterised by high-angle X-ray diffraction as well as specular and off-specular reflection. Using synchrotron radiation at the K-edge energy of Co and Cu to enhance the scattering contrast, the study shows that the roughness of these multilayers is well described by the fractal model of self-affine structures. For the pulsed laser deposited layers an extremely large lateral correlation length, xi, of the vertically correlated interfacial roughness is found (xi >1 µm) which exceeds the xi-value of the uncorrelated roughness by about two orders. The interfaces are very jagged (roughness exponent, h, between 0.15 and 0.3). The root mean square roughness, sigma, of the Cu/Co and Co/Cu interfaces are of the same order compared with the values reported for sputtered layers.
Keywords: Surfaces and interfaces; Multilayers; Reflection spec.; Surface roughness; X-ray diffraction
  • Thin Solid Films, vol. 394 (1-2), (2001) p.164-173

Publ.-Id: 3652 - Permalink


Structure and magnetic properties of Co nanoclusters fabricated by ion beam synthesis in SiO2 films.
Klimenkov, M.; von Borany, J.; Matz, W.; Eckert, D.; Wolf, M.; Müller, K.-H.;
Abstract: Co nanoparticles fabricated by ion beam synthesis in SiO2 films were inve-stigated with TEM and SQUID technique. The variation of the thermal treatment enables the formation of Co nanoclusters of different sizes ranging from 2 to 40 nm. Small nanoclusters of about 2-3 nm are amorphous, whereas clusters above 7 nm show the configuration of cubic Co nanocrystals. Measurements of magnetization at tem-peratures between 2 K and 360 K reveal superparamagnetic behaviour for the small nanoclusters up to 3 nm and ferromagnetism for clusters above 7 nm .
Keywords: cobalt nanoclusters, magnetism, transmission electron microscopy, ion implantation
  • Applied Physics A elektron. Publikation vol.73 (2001) DOI 10.1007/s003330100915
  • Appl. Phys. A 74 (2002)571-575 (Druckversion)

Publ.-Id: 3651 - Permalink


Development of an Apparatus for Seaborgium Studies by High Temperature Gas Chromatography
Vahle, A.; Hübener, S.; Dressler, R.; Grantz, M.;
In preparation for the characterization of Sg as oxide hydroxide a new high temperature gas chromatography apparatus based on the OLGA design was developed. However, the time-consuming recluster step was replaced by direct deposition of species leaving the chromatographic column on metal foils. In test experiments with short-lived Mo isotopes a retention time of 9 s was determined for an isothermal temperature of 1270 K, sufficient to study Sg isotopes.
A model based on the theory of supersonic jet and on simple geometrical considerations reproduces the data of direct condensation experiments quite well.

Keywords: on-line gas chromatography, reaction gas chromatography, direct deposition, molybdenum oxide hydroxide, adsorption
  • Nuclear Instruments and Methods in Physics Research A 481 (2002) 637-645

Publ.-Id: 3650 - Permalink


Ion Beam Synthesis of Ge Nanowires
Müller, T.;
The formation of Ge nanowires in V-grooves has been studied experimentally as well as theoretically. As substrate oxide covered Si V-grooves were used formed by anisotropic etching of (001)Si wafers and subsequent oxidation of their surface. Implantation of 1E17 Ge+ cm^-2 at 70 keV was carried out into the oxide layer covering the V-grooves.
Ion irradiation induces shape changes of the V-grooves, which are captured in a novel continuum model of surface evolution. It describes theoretically the effects of sputtering, redeposition of sputtered atoms, and swelling. Thereby, the time evolution of the target surface is determined by a nonlinear integro-differential equation, which was solved numerically for the V-groove geometry. A very good agreement is achieved for the predicted surface shape and the shape observed in XTEM images. Surprisingly, the model predicts material (Si, O, Ge) transport into the V-groove bottom which also suggests an Ge accumulation there proven by STEM-EDX investigations.
In this Ge rich bottom region, subsequent annealing in N2 atmosphere results in the formation of a nanowire by coalescence of Ge precipitates shown by XTEM images. The process of phase separation during the nanowire growth was studied by means of kinetic 3D lattice Monte-Carlo simulations. These simulations also indicate the disintegration of continuous wires into droplets mediated by thermal fluctuations. Energy considerations have identified a fragmentation threshold and a lower boundary for the droplet radii which were confirmed by the Monte Carlo simulation.
The here given results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations as well as chains of equally spaced clusters with nearly uniform diameter.

Keywords: Ion Beam Synthesis, Nanowires, Surface Sputtering, Redeposition, Kinetic Monte Carlo Simulation
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-309 Januar 2001

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Publ.-Id: 3649 - Permalink


Strahlkopplung von Tandetron-Beschleuniger und Ionenimplanter zur Durchführung von Mehrstrahlexperimenten im Forschungszentrum Rossendorf
Tyrroff, H.; Richter, B.; Neumann, W.;
Im Sommer 1999 wurde im Forschungszentrum eine Zweistrahlführung in Betrieb genommen. Dieses System gestattet, Ionenarten aus unterschiedlichen Beschleunigern gleichzeitig in die Experimentierstationen zu lenken. In der Doppelimplantationsstation wird die Zweistrahlführung zur Synthese neuartiger Materialien genutzt. In der Analysestation wird die Zweistrahlführung in Kombination mit einem magnetischen Browne-Buechner-Spektrometer eingesetzt, um komplexe und hochgenaue Materialanalysen durchzuführen. Das System überträgt Ionen des gesamten Teilchen- und Energiespektrums von 3-MV-Tandetron-Beschleuniger und 500-kV-Ionenimplanter mit minimalen Intensitätsverlusten zu den Experimenten. Steuerung und Kontrolle von Beschleunigern, Strahlführung und Experiment erfolgen in einem hierarchischen Rechnernetz. Die hier beschriebene Zweistrahlanlage ist Teil eines Projekts zur umfassenden Kopplung von Basisgeräten des Forschungszentrums.
Keywords: Strahlkopplung, Tandetron-Beschleuniger, Ioneneimplanter, Mehrstrahlexperimente, Doppelimplantation, Oberflächenanalyse, ERD, RBS, Browne-Buechner-Spektrometer, Ionenoptik, Emittanz, Optimierung, magnetische Linsen, elektrostatische Linsen, Ablenkmagneten, Strahlenveloppen, Transmission, Energiebereich, Ionenart, Stromdichte, Strahlkontrolle, Testresultate.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-308 Januar 2001

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Publ.-Id: 3648 - Permalink


Verification of neutron transport calculations for nonstandard pressure vessel surveillance positions in the VVER-1000 Novovoronesh-5
Böhmer, B.; Konheiser, J.; Brodkin, E.; Egorov, A.; Vikhrov, V.; Zaritsky, S.; Polke, E.;
Activation measurements results at non-standard surveillance positions of the VVER-1000 Novovoronesh-5 have been used to verify neutron fluence calculations for pe-ripheral reactor regions with large flux gradients. Fluence integrals and activities of irradiated detectors and specimens had been calculated by three laboratories using different transport calculation methods: 2D/1D-SN synthesis, 3D-SN and the Monte Carlo method. The results obtained by different calculations and by activation measurements have been compared. The differences between measured and calculated activities as well as between the different calculation results were reasonable. Possible causes of discrepancies are discussed.
Keywords: neutron embrittlement, neutron fluences, neutron transport calculations, activation measurements
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Proceedings pp. 37-42
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Proceedings pp. 37-42

Publ.-Id: 3647 - Permalink


Intersubband Lasers and Detectors
Helm, M.;
The term “intersubband transitions” has been coined to describe optical transitions between confined electronic states in semiconductor quantum structures. In this lecture I will discuss the basic underlying physics of intersubband transitions in quantum wells and discuss their recent applications for real optoelectronic devices, as there are the quantum cascade laser (QCL) and the quantum well infrared photodetector (QWIP).

Concerning the physics, the basic concept of intersubband transitions appears extremely simple; yet a detailed understanding of all aspects, such as absorption strength and frequency, polarization dependence and linewidth, requires a careful consideration of band structure, many-body physics and electromagnetism.

The first observation of intersubband absorption was reported in 1974 in Si accumulation layers and 1985 in GaAs quantum wells. Since then, intense research has driven the development of high-sensitivity intersubband infrared detectors and focal-plane arrays, which are now commercially available. Intersubband lasers have been realized in 1994 and are now covering a spectral range from 4 to 17 m. I will discuss the physics and performance of these optoelectronic devices, also in comparison to conventional band-gap detectors and lasers.

Keywords: infrared, laser, detector, intersubband
  • Invited lecture (Conferences)
    Invited talk at the "29th Int. School on the Physics of Semiconducting Compounds", Jaszowiec, Poland, June 2000

Publ.-Id: 3646 - Permalink


Miniband absorption in strongly coupled superlattices
Helm, M.;
please contact the author
Keywords: superlattice, infrared
  • Lecture (others)
    Seminarvortrag am Paul-Drude-Insitut für Festkörperelektronik (13.11.2000)

Publ.-Id: 3645 - Permalink


Infrarotspektroskopie von Halbleiterübergittern
Helm, M.;
Ich moechte einen Ueberblick ueber die optischen Eigenschaften von Halbleiteruebergittern im Infrarot- und THz-Spektralbereich geben, die ja im wesentlichen von Inter- und Intraminibanduebergaengen herruehren. Die theoretischen Ueberlegungen werden durch verschiedene experimentelle Resultate illustriert - z.B. Interminibandabsorption und ihre Anwendung zur Analyse der Elektronen Verteilungsfunktion oder thermisches "quenching" der Intraminibandabsorption. Abschliessend diskutiere ich die Erweiterung obiger
Messungen auf Uebergitter mit einem vertikalen elektrischen Feld, d.h. die Untersuchung von Wannier-Stark-Leitern und Bloch-Oszillatoren.
Keywords: superlattice, infrared
  • Lecture (others)
    Seminarvortrag am Institut für Technische Physik der Universität Erlangen (10.11.2000)

Publ.-Id: 3644 - Permalink


Elastic Properties of Diamond-Like Amorphous Carbon Films Grown by Computer Simulation of Ion-Beam Deposition Process
Belov, A.; Jäger, H.-U.;
Atomic-scale calculations were performed for the first time to investigate mechanical
properties of amorphous carbon films grown by a realistic simulation of ion-beam deposition process. The simulated films have a thickness of a few nanometers and reproduce the main structural features of real films, with the bulk content of sp3 bonded atoms varying from 35 to 95%, depending on the ion energy (E = 20-80 eV). Employing empirical interatomic potentials for carbon, the average bulk stresses as well as the atomic-level stress distributions were calculated and analysed. The bulk stresses were found to depend not only on the ion energy, but also on the film quality, in particular, on such structural inhomogeneities as local fluctuations of the sp3 fraction with the depth. The local variation of the bulk stress from the average value considerably increases as the local content of sp2 bonded atoms increases. Elastic constants of amorphous carbon films were also computed using the method of inner elastic constants, which allows for the stress dependence of elastic constants to be analysed. This investigation showed how the Young's modulus varies as a function of the lateral bulk stress in an amorphous film.

Keywords: amorphous carbon, thin films, computer simulation, molecular dynamics, mechanical properties, empirical potentials
  • Contribution to proceedings
    Materials Research Society Symposium Proceedings 648 (2001) P6.53.1-6

Publ.-Id: 3643 - Permalink


RESQUE: Dependence of Test Results from Reconstituted Specimens with Tolerance Deviations and Variation of End Block Materials
Viehrig, H.-W.; Richter, H.; Atkins, T.; van Walle, E.; Scibetta, M.; Valo, M. J.; Wootton, M. R.; Keim, E.; Debaberis, L.; Horsten, M.;
This paper continues the presentation of detailed results of the EU-sponsored RESQUE project. Within the RESQUE project it was planned to determine the dependence of Charpy-V test results on tolerance deviations and different end block materials in reconstituted specimens. The conventional Charpy-V parameters - the total impact energy, lateral expansion and shear fracture appearance - are not significantly affected by the effects of oversized dimensional variability. Disturbing load oscillations arise from some of the geometrical deviations. This influences the characteristic yield load, yield deflection and impact energy at load maximum. In comparison to the existing scatter there is no significant effect of the end block material on the main Charpy parameters and the characteristic loads.
Keywords: reactor pressure vessel steel, reconstituted specimens, stud welding, geometrical deviation, Charpy-V test, Charpy-V parameters, transition temperatures
  • Lecture (Conference)
    Small Specimen Test Techniques: Fourth Volume, ASTM STP 1418, M. A. Sokolov, J. D. Landes, and G. E. Lucas, Eds., ASTM International, West Conshohocken, PA, 2002, pp. 477 - 488.
  • Contribution to external collection
    Small Specimen Test Techniques: Fourth Volume, ASTM STP 1418, M. A. Sokolov, J. D. Landes, and G. E. Lucas, Eds., ASTM International, West Conshohocken, PA, 2002, pp. 477 - 488.

Publ.-Id: 3642 - Permalink


Dose Rate Calculations from Radioactive Vascular Stents: DPK versus exact MC approach
Gorodkov, S.; Möslang, A.; Vladimirov, P.;
Vascular stents activated with radioactive isotopes are planned to be used in clinical practice to prevent restenosis in human coronary arteries after balloon angioplasty. Medical stents are cylindrical meshes and their complex geometry is usually treated for energy dose calculation with approximate dose point kernel(DPK) approach. The important point missed in the DPK approach is the absence of the stent material and, hence, the absence of energy absorption inside the stent. We have performed a comparison between DPK and exact Monte Carlo calculations for some simplified stent models. It appears that DPK approximation significantly overestimates pike dose values especially for the case of gamma-emitting sources. We suggest DPK kernel normalization, which minimizes the difference at relatively far distances, while significant discrepancies near the stent surface still remain.
Keywords: vascular stent radioactive isotope medical application Dose Point Kernel(DPK) Monte Carlo EGS4
  • Poster
    Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation an Applications, Proceedings of the Monte Carlo 2000 Conference, Lisbon, 23.-26. October 2000, pp 467-472, Springer-Verlag Berlin Heidelberg New York, 2001, ISBN 3-540-41795-8
  • Contribution to proceedings
    Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation an Applications, Proceedings of the Monte Carlo 2000 Conference, Lisbon, 23.-26. October 2000, pp 467-472, Springer-Verlag Berlin Heidelberg New York, 2001, ISBN 3-540-41795-8

Publ.-Id: 3641 - Permalink


Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) Study of the Sorption of Cm(III) onto Smectite and Kaolinite
Stumpf, T.; Bauer, A.; Coppin, F.; Kim, I. J.;
The surface sorption process of Cm (III) onto smectite and kaolinite was investigated by time-resolved laser fluorescence spectroscopy (TRLFS) in the trace concentration range. We conclude that at low pH Cm(III) is sorbed onto kaolinite and smectite as an outer-sphere complex and retains its complete primary hydration sphere. With increasing pH, inner-sphere adsorption onto kaolinite and smectite occurs via the aluminol edge sites. The same evolution of the Cm(III)-clay surface species as a function of pH was observed for both minerals. Starting at a pH ³ 5, we observe the formation of a ºAl-O-Cm2+(H2O)5 surface complex, which is replaced by a second species at higher pH. The second surface complex may be a monodentate ºAl-O-Cm+(OH)(H2O)4 species or bidentate º(Al-O)2-Cm+(H2O)5 species. The Cm(III)/clay surface complexes are characterised by their emission spectra (peak maxima at 598.8 nm and 603.3 nm) and their fluorescence lifetime (both 110±7 µs). An important result for the mobility and bioavailability of radionuclides is that no incorporation of Cm(III) into the bulk clay structure was observed.
  • Environmental Science and Technology

Publ.-Id: 3640 - Permalink


Messung der Kondensatfilmdicken in einem dampfdurchströmten horizontalen Rohr
Li, W.; Hicken, E. F.; David, P. H.; Prasser, H.-M.; Baldauf, D.; Zschau, J.;
Im Mehrzweck-Thermohydraulik-Versuchsstand NOKO wurde die Wirksamkeit verschiedener passiver Sicherheitssysteme oder deren Komponenten untersucht. Passive Sicherheitssysteme besitzen keine Komponenten, die zur Funktionsfähigkeit Fremdenergie benötigen.
Bei Nachrechnungen der Experimente mit den waagerecht angeordneten Notkondensatorbündeln hatte sich ergeben, dass die verwendeten Rechenprogramme wohl die integral abgeführte Energie gut berechnen können; die lokalen Kondensationsraten auf der Innenseite der Rohre unterschieden sich bei den eingesetzten Programmen beträchtlich voneinander. Daher wurde im Rahmen einer Dissertation die Kondensation von Wasserdampf und eines Wasserdampf-Stickstoff-Gemisches auf der Innenseite eines waagerechten Rohres untersucht. Durch eine entsprechende Instrumentierung war die Dicke des Kondensatfilms sowie dessen Struktur zu ermitteln. In einem besonders instrumentierten Rohr des 2. Notkondensator-Bündels wurden hierzu Nadelsonden eingebaut, deren Eintauchtiefe mit Hilfe von Schrittmotoren verändert werden konnte. Diese beweglichen Nadelsonden wurden im wandnahen Bereich hin und her gefahren, um so die Filmdicke zu registrieren. Zusätzlich waren die Nadelsonden mit Thermoelementen ausgestattet, die gleichzeitig eine Messung der Temperaturverteilung in der Grenzschicht ermöglichten.

Keywords: emergency condenser, passive safety systems, steam condensation, two-phase flow, conductivity probes, heat transfer
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15./17. Mai 2001, Tagungsbericht S. 103-106.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15./17. Mai 2001, Tagungsbericht S. 103-106.

Publ.-Id: 3638 - Permalink


Spectroscopic Study of Cm(III)Sorption onto γ-Alumina
Stumpf, T.; Rabung, T.; Klenze, R.; Geckeis, H.; Kim, J. I.;
The surface sorption of Cm(III) onto aqueous suspensions of alumina is investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The experiment is performed under Ar atmosphere at ionic strength of 0.1 M NaClO4. pH is varied between 2 and 10 and the metal ion concentration between 2.7.10-7 and 4.5.10-5 mol/L. With increasing pH, two Cm(III)-alumina surface species are identified which are attributed to ºAl-O-Cm2+(H2O)5 and ºAl-O-Cm+(OH)(H2O)4. The two curium-alumina surface complexes are characterised by their emission spectra (peak maxima at 601.2 nm and 603.3 nm, respectively) and fluorescence emission lifetime (both 110 µs). In the concentration range investigated, the surface complex formation is not dependent upon the metal ion concentration but only on pH. Also the concentration ratio of the two surface species is found to be independent on the metal ion concentration. No spectroscopic evidence for the presence of "strong" and "weak" sites can be found at different surface coverages.
Keywords: Curium, Alumina, Surface complexation, TRLFS
  • Journal of Colloid and Interface Science 238, 219-224(2001)

Publ.-Id: 3637 - Permalink


Synthesis of Spatially Controlled Nanowires by Ion Implantation in V-Grooves on (001) Si-Surfaces
Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.;
The synthesis of spatially controlled Ge nanowires and nanoclusters by Ge+ ion implantation in oxidized V-grooves on (001) Si surfaces has been studied experimentally as well as theoretically. The V-grooves were prepared by anisotropic wet chemical etching and thermal oxydation. The SiO2-covered V-grooves were implanted with 70 keV Ge+ ions up to a fluence of 1017 cm-2. Ge accumulates within the SiO2 at the bottom of the V-groove which has been proven by analytical TEM (EDX-mapping). Theoretical studies have shown that the Ge accumulation is caused by the V-groove geometry, forward sputtering, and re-deposition. During subsequent annealing the redistributed Ge forms a nanowire by precipitation, ripening and coalesence. Kinetic lattice Monte Carlo simulations of the nanowire formation process show growth instabilities and self-organization phenomena.
Keywords: Ion beam synthesis, nanowires, computer simulation
  • Contribution to proceedings
    Materials Research Society, Symposium Proceedings Ion Beam Synthesis and processing of Advanced Materials Symposium held November 27-29, 2000, Boston, Massachusetts, U.S.A. Mat. Res. Soc. Symp. Proc. vol. 647 (2001) O10.2.1-6

Publ.-Id: 3635 - Permalink


Bericht der Herbsttagung der Studiengruppe für elektronische Instrumentierung vom 25. bis 27. September 2000 im Hahn-Meitner-Institut Berlin
Gabriel, F.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-305 November 2000

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Publ.-Id: 3634 - Permalink


Improving the understanding of ion-beam-induced defect formation and evolution by atomistic computer simulations
Posselt, M.;
The morphology of the as-implanted damage in silicon is investigated using a recently developed combination of time-ordered computer simulations based on the binary collision approximation (BCA) with classical molecular dynamics (MD) calculations. The method is applied to determine the type and the amount of defects formed within the first nanosecond after ion impact. The depth profile and the total number of different defect species (vacancies, interstitials, disordered atoms, etc.) produced on average per incident ion are calculated for B+ (15 keV), P+ (5, 10, 20, 30 keV), and As+ (15 keV) implantations. It is shown that the as-implanted defect structure depends not only on the nuclear energy deposition per ion but also explicitly on the ion mass. Therefore for each ion species the damage morphology exhibits characteristic features. For heavy ions the percentage of extended defects is higher than for light ions. In all cases investigated the number of free or isolated interstitials exceeds the amount of free vacancies. The results obtained allow a microscopic interpretation of the phenomenological model for the as-implanted damage employed in conventional BCA simulations in order to describe the dose dependence of the shape of ion range profiles. They can be also applied to get more realistic initial conditions for the simulation of the defect kinetics during post-implantation annealing.
Keywords: ion implantation, computer simulation, defects
  • Invited lecture (Conferences)
    MRS 2000 Fall Meeting, Boston, USA, November 27 - December 1, 2000 (invited talk)
  • Contribution to external collection
    Mat. Res. Soc. Symp. Proc. Vol. 647 (2001) pp. O2.1.1-O2.1.12

Publ.-Id: 3632 - Permalink


MHD Turbulence Measurements in a Sodium Channel Flow Exposed to a Transverse Magnetic Field
Eckert, S.; Gerbeth, G.; Witke, W.; Langenbrunner, H.;
The influence of a static transverse magnetic field on a turbulent sodium flow in a channel with a
rectangular cross section is investigated. The turbulence has been forced by mechanical means
employing a grid of cylindrical bars. Electric potential probes have been used to determine the
longitudinal component of the liquid velocity. The experiments cover a wide range of the
non-dimensional parameters Hartmann number (Ha < 3000) and the magnetic interaction parameter
(N < 800). Measurements of the turbulence intensity as a function of the magnetic interaction
number N will be presented and discussed. The measured spectra are essentially different from those
predicted according to the theory of two-dimensional turbulence.
Keywords: MHD turbulence, liquid metal channel flow, transverse magnetic field, local velocity, measurements, potential probes, velocity profiles, turbulence intensity, power spectra
  • International Journal of Heat and Fluid Flow, Vol. 22/3, 2001, 358-364

Publ.-Id: 3631 - Permalink


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