Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

High resolution IBA analysis of spin dependent tunnel junctions

Barradas, N. P.; Da Silva, M. F.; Soares, J. C.; Kreissig, U.; Arnoldbik, W. M.; Cardoso, S.; Freitas, P. P.

Spin dependent tunnel junctions are of technological interest for applications in magnetic non-volatile random access memories due to their large tunneling magnetoresistance effect and low junction resistance-area product. Typical structures are Si/Al2O3 600Å/Ta 70Å/NiFe 70Å/CoFe 30Å/AlxNyOz t/CoFe 40Å/MnIr 200Å/Ta 30Å, with t=6-30 Å, annealed to temperatures up to 400ºC. The properties of these junctions are strongly influenced by the layer thicknesses and composition, and change on annealing. Standard technology for integrated circuits requires annealing at 400-450ºC, and an understanding of the changing magnetic properties of the tunnel junction requires detailed knowledge of the behavior of the different interfaces. We performed Rutherford backscattering (RBS) experiments at a grazing angle of incidence to achieve high depth resolution for the transition metals signal. The composition of the AlxNyOz layers was determined with Heavy Ion Elastic Recoil Detection Analysis. We also performed heavy ion RBS experiments for improved mass resolution. The thickness and composition of the individual layers is determined, and a high sensitivity to diffusion and layer intermixing is achieved.

  • Modern Physics Letters B, Vol. 15, 28/29 (2001) 1288-1296

Permalink: https://www.hzdr.de/publications/Publ-4759
Publ.-Id: 4759


Elementanalytik dünner Schichten mit MeV-Ionenstrahlen

Grötzschel, R.

Übersicht über Methoden der Materialanalytik an Beschleunigern

Keywords: IBA

  • Lecture (others)
    Institutsseminar IFW Dresden

Permalink: https://www.hzdr.de/publications/Publ-4758
Publ.-Id: 4758


Ion beam analysis of thin films with heavy MeV ions

Grötzschel, R.; Klein, C.; Kreissig, U.; Mäder, M.


Among the wide choice of physical analysis methods to characterise thin and ultra thin films both Rutherford backscattering spectrometry (RBS) and the elastic recoil atom spectrometry (ERDA) have a unique feature. The binary elastic scattering at the Coulomb potential of the involved nuclei can be described analytically by the Ruther-ford cross section formula. This allows an easy and accurate determination of quan-tities like area densities of elements or composition of thin films.
For the detection of all light elements ERDA with heavy incidence ions of energies
> 1 MeV/u is the method of choice. As recoil atom spectrometers heavy ion detec-tors are used which provide not only the energy signal but also particle identification and position information for kinematical corrections, which is particularly necessary at large acceptance angles. We use at the Rossendorf 5 MV tandem Bragg peak ioni-sation chambers, dE-E-ionisation chamber telescopes, time-of-flight (TOF) spectrome-ters or combinations of those. The specific merits and drawbacks of these detectors are discussed. A common feature is the moderate energy resolution dE/E of roughly 0.01. This is the limiting parameter for the obtainable depth resolution. To overcome this limit magnetic spectrometers have to be used which enable depth resolutions in the order of monolayers. We have installed at the tandem a QQDS spectrometer for ERDA with variable dispersion, which is shortly described.
An analogue situation we have in the case of RBS. Despite of many physical advanta-ges of heavy incidence ions [1] mostly He ions are used due to the fact that the energy resolution of solid state detectors decreases with increasing Z of the detected particles. When using magnetic spectrometers for RBS it is possible to profit fully from the high stopping powers of heavy ions. Thus depth resolutions of one monolayer can be achieved. We have installed a magnetic spectrometer of the simple Browne-Buechner type at the 3 MV Tandetron for RBS. The first results with this instrument are discussed.

[1] D.J.O´Connor, T.Chunyu, Nucl. Instr. And Meth. B 36 (1989) 178

Keywords: Ion Beam Analysis; Heavy Ions

  • Lecture (Conference)
    Conf. ION 2002, Kazimirz Dolny, Poland, June 10 - 13, 2002

Permalink: https://www.hzdr.de/publications/Publ-4756
Publ.-Id: 4756


Interplay of Equilibrium and Nonequilibrium Phenomena in the Nuclear Liquid-Gas Phase Transition

Zwieglinski, B.; Odeh, T.; Gross, C.; Schwarz, C.; Bassini, R.; Begemann-Blaich, M.; Fritz, S.; Gaff-Ejakov, S. J.; Gourio, D.; Imme, G.; Iori, I.; Kleinevoss, U.; Kunde, G. J.; Kunze, W. D.; Lynen, U.; Maddalena, V.; Mahi, M.; Moroni, A.; Möhlenkamp, T.; Müller, W. F. J.; Nociforo, C.; Ocker, B.; Petruzzelli, F.; Pochodzalla, J.; Raciti, G.; Riccobene, G.; Romano, F. P.; Saija, A.; Sann, H.; Schnittker, M.; Schüttauf, A.; Seidel, W.; Serfling, V.; Sfienti, C.; Trautmann, W.; Trzcinski, A.; Verde, G.; Wörner, A.; Xi, H. F.

Energy spectra of protons emitted by the target residue in Au+Au collisions at 1 GeV/u reveal two
components with different slopes attributed to preequilibrium and equilibrium emission. The relative
contribution of the latter decreases rapidly with excitation energy, so that its presence becomes not
apparent for the highest energy bins. It is argued therefore, that equilibrium may not be reached on
the gas branch of the caloric curve. The nuclear liquid-gas phase transition thus belongs to the
category of nonequilibrium phase transitions for which the concepts developed in synergetics, such as
self-organized criticality, provide the proper framework.

  • Nucl. Phys. A 681 (2001) 275

Permalink: https://www.hzdr.de/publications/Publ-4755
Publ.-Id: 4755


Fragment Isotope Distributions and the Isospin Dependent Equation of State

Tan, W. P.; Li, B.-A.; Donangelo, R.; Gelbke, C. K.; van Goetherm, M.-J.; Liu, X. D.; Lynch, W. G.; Souza, S.; Tsang, M. B.; Verde, G.; Wagner, A.; Xu, N. S.

Calculations predict a connection between the isotopic composition of particles emitted during an energetic nucleus-nucleus collision and the density dependence of the asymmetry term of the nuclear equation of state (EOS). This connection is investigated for central 112Sn+112Sn and 124Sn+124Sn collisions at E/A=50 MeV in the limit of an equilibrated freezeout condition. Comparisons between measured isotopic yields ratios and theoretical predictions in the equilibrium limit are used to assess the sensitivity to the density dependence of the asymmetry term of the EOS. This analysis suggests that such comparisons may provide an opportunity to constrain the asymmetry term of the EOS.

  • Phys. Rev. C 64 (2001) 051901

Permalink: https://www.hzdr.de/publications/Publ-4754
Publ.-Id: 4754


Effects of QED and Beyond from the Atomic Binding Energy

Soff, G.; Bedniakov, I.; Beier, T.; Erler, F.; Goidenko, I. A.; Jentschura, U. D.; Labzowski, L. N.; Nefiodov, A. V.; Plunien, G.; Schützhold, R.; Zschocke, S.

Atomic binding energies are calculated at utmost precision. A report on the current status of
Lamb-shift predictions for hydrogenlike ions, including all quantum electrodynamical corrections to first
and second order in the fine structure constant alpha is presented. All relevant nuclear effects are
taken into account. High-precision calculations for the Lamb shift in hydrogen are presented. The
hyperfine structure splitting and the g factor of a bound electron in the strong electromagnetic field of a
heavy nucleus is considered. Special emphasis is also put on parity violation effects in atomic systems.
For all systems possible investigations beyond precision tests of quantum electrodynamics are
considered.

  • Hyp. Int. 132 (2001) 75

Permalink: https://www.hzdr.de/publications/Publ-4753
Publ.-Id: 4753


Time Scales in Spectator Fragmentation

Schwarz, C.; Fritz, S.; Bassini, R.; Begemann-Blaich, M.; Gaff-Ejakov, S. J.; Gourio, D.; Gross, C.; Imme, G.; Iori, I.; Kleinevoss, U.; Kunde, G. J.; Kunze, W. D.; Lynen, U.; Maddalena, V.; Mahi, M.; Möhlenkamp, T.; Moroni, A.; Nociforo, W. F. J. M. C.; Ocker, B.; Odeh, T.; Petruzzelli, F.; Pochodzalla, J.; Raciti, G.; Riccobene, G.; Romano, F. P.; Saija, A.; Schnittker, M.; Schüttauf, A.; Seidel, W.; Serfling, V.; Sfienti, C.; Trautmann, W.; Trzcinski, A.; Verde, G.; Wörner, A.; Hongfei, X.; Zwieglinski, B.

Proton-proton correlations and correlations of
p-a, d-a, and t-a
from spectator decays following 197$Au + 197Au
collisions at 1000 AMeV have been measured with an highly efficient detector hodoscope.
The constructed correlation functions indicate a moderate expansion and low breakup densities similar to
assumptions made in statistical multifragmentation models. In agreement with a volume breakup
rather short time scales were deduced employing directional cuts in proton-proton correlations.

  • Nucl. Phys. A 681 (2001) 279

Permalink: https://www.hzdr.de/publications/Publ-4752
Publ.-Id: 4752


Ion acoustic microscopy for imaging of buried structures based on a focused ion beam system

Akhmadaliev, C.; Bischoff, L.; Teichert, J.; Kazbekov, K.; Köhler, B.

An intensity modulated focused ion beam (FIB) which is hitting the surface of a solid, leads to a small temperature variation in the near subsurface region which is sufficient for thermal elastic wave generation. The measurement of these waves can be used for analysis and imaging of surface as well as subsurface structures in the material. The modified FIB equipment IMSA-100 working with 35 keV Ga+ and Au+ ions and a current of about 3 nA was employed to obtain acoustic images from structures on silicon and glass targets. The acoustic signals were detected using a PZT transducer delivering an output voltage of 50 - 100 nV. The modulation frequency was varied in the range of 60kHz - 170kHz. The obtained lateral resolution of the ion acoustic images at these frequencies was about 15 µm on silicon and about 7µm on glass. We are going to increase the modulation frequency up to MHz range in order to reach sub-micron resolution.

Keywords: intensity modulated focused ion beam; thermal elastic wave generation

  • Lecture (Conference)
    DPG Tagungen 2001, Hamburg March 26 - 30

Permalink: https://www.hzdr.de/publications/Publ-4751
Publ.-Id: 4751


Temperature Dependence of the Electronics Characterization and mass spectra of Liquid Metal Alloy Ion Sources

Ganetsos, T.; Mair, G. L. R.; Bischoff, L.

This is a comprehensive study of the characteristics of an AuGeSi and CoNd Liquid Metal Alloy Ion Source (LMAISs) [1]. Such characteristics include current-voltage curves and ion beam mass-spectra. A careful investigation has been undertaken where the temperature is one of the main variable experiment parameters [2]. Theoretical models support the experimental results.
[1] P.D. Prewett and GLR. Mair, "Focused Ion Beams from Liquid Metal Ion Sources", Research Studies Press, Taunton, Somerset, UK, 1991
[2] L. Bischoff, J. Teichert, Th. Ganetsos and GLR. Mair
J. Phys. D: Appl. Phys. 33 (2000) 692.

Keywords: Liquid Metal Alloy Ion Source (LMAISs); mass-spectra; I-V curves; temperature

  • Lecture (Conference)
    IFES 2001, 47th International Field Emission Symposium. July 29 - Aug. 3, 2001, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-4750
Publ.-Id: 4750


Investigation of elastic waves generation in a solid target by a pulsed ion beam

Akhmadaliev, C.; Bischoff, L.

The generation of elastic waves in solids during irradiation with pulsed ion beams is investigated. There are two main mechanisms of the elastic wave emission. First is a simple momentum transfer from the beam particles to the target atoms. Also the heating of the material yields an acoustic wave due to a local thermal expansion. Other effects, like a change of the density, local amorphization, charging up of the target near the surface etc. can also generate elastic waves.
The measurements are carried out using a IMSA-100 focused ion beam (FIB) system and a 3 MV-TANDETRON accelerator. The energy of the FIB is 30-35 keV at a current of 1-3nA and a spot size of about 1mm. On the accelerator a current of some mA and energies up to some MeV with Au+, Ge2+, Si2+, Si3+and Si4+ ions and beam pulse duration of some microseconds were used. The elastic waves is registered by a piezoelectric sensor on the back surface of the sample. Then the signal is amplified and digitized on a PC. The dependence of the amplitude of the acoustic signal in silicon, titanium, brass and aluminum are measured for different beams. The change of the charge state of the ions up to 6 shows no significant influence. The amplitude depends on the power of the beam linearly at low current densities. These elastic waves can be used for acoustic imaging of surface and buried structures in a scanning ion acoustic microscope.

Keywords: elastic waves; pulsed ion beams; scanning ion acoustic microscope

  • Lecture (Conference)
    DPG Tagungen 2002, Regensburg March, 11 - 15, 2002, O 30.8

Permalink: https://www.hzdr.de/publications/Publ-4749
Publ.-Id: 4749


Solidified liquid metal ion sources - formation of a nanoemitter for electron field emission

Knapp, W.; Bischoff, L.; Teichert, J.

Solidified liquid metal ion sources (LMISs) operating with Au alloy wetted hair-pin emitters can be used as high-intensity electron point sources with nanometer dimension for electron field emission application. A nanoemitter tip on a solidified LMIS emitter can be formed by quenching during ion emission mode. I-V characteristics and the performance of the electron emitting LMIS are presented.

Keywords: Solidified liquid metal ion sources; electron emitting; nanoemitter tip

  • Lecture (Conference)
    12th International Summer School on Vacuum, Electron and Ion Technologies VEIT2001, September 17 - 21, 2001, Varna, Bulgaria Vacuum

Permalink: https://www.hzdr.de/publications/Publ-4748
Publ.-Id: 4748


Optical Pattern Formation in a-SiC:H Films by Ga+ Ion Implantation

Bischoff, L.; Teichert, J.; Kitova, S.; Tsvetkova, T.

The optical modification effect of Ga+ ion implantation in a-SiC:H films has been studied. As a result of the implantation a well expressed "darkening" effect (i.e. absorption edge shift to the longer-wavelength/lower-photon-energy region) has been registered. It is accompanied by a remarkable increase of the absorption coefficient up to 2 orders of magnitude in the measured photon energy range (1.5-3.1 eV). The optical contrast thus obtained (between implanted and unimplanted regions of the film material) has been made use of in the form of optical pattern formation by computer operated Ga+ focused ion beam. Possible applications of this effect in the area of sub-micron lithography and high-density optical data storage have been suggested with regard to the most widely spread focused micro-beam systems based on Ga+ liquid metal ion sources. The physical basis for the advantages in cases of applications in adverse environments have also been discussed.

Keywords: a-SiC:H films; optical modification; Ga+ ion implantation; focused micro-beam

  • Lecture (Conference)
    12th International Summer School on Vacuum, Electron and Ion Technologies VEIT2001, September 17 - 21, 2001, Varna, Bulgaria
  • Vacuum 69 (2003) 73-77

Permalink: https://www.hzdr.de/publications/Publ-4747
Publ.-Id: 4747


Promoted hydroxyapatite nucleation on titanium ion implanted with sodium

Pham, M. T.; Maitz, M. F.; Matz, W.; Reuther, H.; Richter, E.; Steiner, G.

Precipitation of hydroxyapatite on titanium from aqueous solution offers the possibility of creating biologically active coatings for bone fixated implants by mimicking the physiological properties of the bone. While solution-related factors have been well established, the research into surface-related stimuli for promoting hydroxyapatite nucleation is still underway. In the present work titanium surfaces were pretreated by implantation of sodium ions yielding sodium titanate incorporated within the surface layer with concentration, depth distribution, and morphology depending on the parameters of the ion implantation and the subsequent thermal treatment. Such ion-implanted surfaces were observed to promote hydroxyapatite nucleation and growth from simulated body fluid. Surface properties were studied using spectroscopic and microscopic methods. The mechanisms of heterogeneous nucleation of hydroxyapatite were discussed in terms of the electrical double layer.

Keywords: Apatit; Titanium; sodium; simulated body fluid

  • Thin Solid Films 379 (2000) 50-56

Permalink: https://www.hzdr.de/publications/Publ-4746
Publ.-Id: 4746


Ion beam treatment of titanium surfaces for enhancing deposition of hydroxyapatite from solution

Maitz, M. F.; Pham, M. T.; Matz, W.; Reuther, H.; Steiner, G.; Richter, E.

Surface coating with hydroxyapatite (HA) is a common way to improve the osseointegration of orthopaedic and dental titanium-based materials. The main problems with current techniques are changes in composition during heating and poor adhesion to the surface. An alternative method is deposition of HA onto an activated surface out of a solution.
The present work studies the surface treatment involving ion implantation of Na into Ti to induce a modification in chemistry and morphology, showing sodium titanate incorporated within the surface layer with concentration, depth distribution, and morphology depending on the parameters of the ion implantation. Such ion-implanted Ti surfaces actively induce heterogeneous precipitation of HA from a simulated body fluid containing physiological concentrations of calcium and phosphate ions. This is compared with the activation by NaOH etching. The growth of bone forming cells on the pure Na implanted surface is oriented without an increased bone formation. Cell growth on the NaOH etched surface is reduced. After deposition of HA on both surfaces cell the growth pattern was improved.

Keywords: hydroxyapatite; cell culture

  • Lecture (Conference)
    European Materials Research Society. 2001 Spring Meeting, 05.-08.06. 2001, Strasbourg, France
  • Biomol Engineer 19: 271-274 (2002)
  • Contribution to proceedings
    European Materials Research Society. 2001 Spring Meeting, 05.-08.06. 2001, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-4745
Publ.-Id: 4745


Deposition of Ti based coatings with different surface structure and chemistry for medical devices

Maitz, M. F.; Mukherjee, S.; Pham, M. T.; Richter, E.

Titanium alloys with small amounts of Aluminium and Vanadium are by now the favourite base materials for orthopaedic implants for their good biocompatibility, but stainless steel is wider in use because of its lower material costs and easier handling. By Metal Plasma Immersion Ion Implantation and Deposition (MPIIID) coatings of Ti, TiN, TixAl1-x, and TixAl1-xN layers were deposited on mirror polished stainless steel with a different process parameters, i.e. the bias voltage was changed systematically.
Coatings produced with a bias voltage of -2000 V had a roughness up to 70 nm, whereas those with zero bias voltage were much smoother (6 nm). In coatings with higher voltage the ration Ti : Al shifted to Ti. Rat one marrow cells were seeded out on these surfaces in a serum free medium. After 5h cell spreading and organisation of the cytoskeleton was best on the smoother samples with best spreading on Ti and TixAl1-xN with 0 bias voltage. There was no significant necrosis as measured by lactate dehydrogenase release within 5 h, but up to 25% pyknotic and fragmented cell nuclei as signs of apoptosis. This behaviour was different for the different samples, but there was no correlation with the surface roughness or chemistry. The effect of the medium, direct induction of apoptosis by the coating or apoptotic cell death due to inhibited adhesion by roughness or surface chemistry will be discussed.

Keywords: Titanium nitride; Titanium aluminum nitride; biocompatibility

  • Poster
    EMRS Spring Meeting 18.-21.06.2002. Strasbourg, France http://www-emrs.c-strasbourg.fr/2002_Book_Abs/02_Prog_Rv2.pdf
  • Contribution to proceedings
    EMRS Spring Meeting 18.-21.06.2002. Strasbourg, France http://www-emrs.c-strasbourg.fr/2002_Book_Abs/02_Prog_Rv2.pdf

Permalink: https://www.hzdr.de/publications/Publ-4744
Publ.-Id: 4744


Synthesis of polyurethane coating with drug compounds on metal stents

in Russian

Romanova, V. A.; Begishev, V. P.; Guenzel, R.; Maitz, M.; Kondyurin, A. V.; Kondyurina, I. V.

Russisches Abstrakt siehe Download

Keywords: Stents; polymer; drug release

  • Poster
    Conference "Oligomers 2002", Chernogolovka, Russia, 9.-14. September 2002

Permalink: https://www.hzdr.de/publications/Publ-4743
Publ.-Id: 4743


Ionenbehandlung von Gefäßstents erhöhen Blutkompatibilität und Röntgenkontrast

Maitz, M.; Pham, M. T.

Gefäßstents werden nach der Aufweitung eines arteriosklerotisch verengten Herzkranzgefäßes eingebracht und sollen den erneuten Verschluss des Gefäßes verhindern. Sie stellen einen der wesentlichen Fortschritte in der Kardiologie des letzten Jahrzehnts dar. Durch sie konnte die Zahl der teuren und belastenden Bypass-Operation wesentlich gesenkt und die Aufenthaltsdauer der Patienten im Krankenhaus verkürzt werden.

Trotz des heute millionenfachen Einsatzes dieser filigranen Metallgeflechte, werden von den anwendenden Ärzten noch eine Reihe von Verbesserungen gewünscht, die eine genaue Kenntnis der Körperreaktionen und eine Materialbehandlung mit modernen Methoden erfordern.

Die Gefäßstents werden unter Röntgenkontrolle eingesetzt und auch radiologisch beurteilt. Die dünnen Stahl- oder Nickel-Titan-Drähte, aus denen der Stent besteht, bieten nur einen unbefriedigenden Röntgenkontrast. Durch die Aufbringung einer einige Mikrometer (µm) dicken Schicht eines Metalls hoher Ordnungszahl kann der Röntgenkontrast der Drähte erhöht werden. Dabei bieten sich Metalle wie Tantal an, die ähnlich wie das aus der Orthopädie bekannte Titan eine sehr stabile Oxidschicht ausbilden und dadurch auch gut biokompatibel sind.

Eine gute Haftung der Schicht auf dem Untergrund ist hier besonders wichtig, weil abgelöste Anteile der Schicht sonst mit dem arteriellen Blutstrom in das feinere Gefäßnetz der Herzmuskulatur transportiert werden und dort einen Verschluss herbeiführen würden. Die aufgebrachte Schicht darf keine inneren Spannungen aufweisen, die bei den erforderlichen Schichtdicken ansonsten zu Lamellierung sowie beim Aufweiten des Stents zur Rissbildung führen würden. Die Aufbringung dieser Schicht wird am Forschungszentrum Rossendorf durch Metallplasma Ionenimplantation und -abscheidung erreicht, wobei die Haftfestigkeit durch eine Zwischenschicht vermittelt ist.

Ein weiteres noch nicht befriedigend gelöstes Problem bei Gefäßstents ist die Aktivierung der Blutgerinnung und ein Wachstumsreiz auf die innerste Gefäßschicht. Diese beiden Reaktionen können zum Verschluss des Stents führen und sind eine der Ursachen, warum im Vergleich zur Bypass-Operation noch häufig eine Nachbehandlung nötig ist. Auch hier ist Tantal ein gutes Metall für die Beschichtung, weil es mit der Oxidschicht eine sehr gute Blutverträglichkeit aufweist, die wie bei Titan durch die Implantation weiterer Ionen wie Phosphor, Stickstoff, Kalzium noch verbessert werden kann.

  • Dresdner Transferbrief 9(4/2001): 12 (2001)

Permalink: https://www.hzdr.de/publications/Publ-4742
Publ.-Id: 4742


Principles of biomaterials testing

Maitz, M.

no abstract delivered from author

Keywords: Biomaterials; testing

  • Lecture (others)
    Southwest Jiaotong University, Institute of Biomaterials & Surface Engineering, Chengdu, December 14, 2001

Permalink: https://www.hzdr.de/publications/Publ-4741
Publ.-Id: 4741


The MatMed Database

Maitz, M. F.

no abstract delivered from author

Keywords: database; materials in medicine; MatMed; EC Project

  • Lecture (others)
    MatMed EU Project meeting, Rhodos May 09-11, 2001

Permalink: https://www.hzdr.de/publications/Publ-4740
Publ.-Id: 4740


Principles of Biological Testing of Implant Materials

Maitz, M. F.

no abstract delivered from author

  • Lecture (others)
    Kyiv Taras Shevchenko University, Faculty of Physics, May 03, 2001

Permalink: https://www.hzdr.de/publications/Publ-4739
Publ.-Id: 4739


Grundlagen der Gerinnungsaktivierung an Fremdmaterialien

Maitz, M. F.

Die Blutgerinnung ist ein komplex regulierter Vorgang. Es gibt eine Reihe von Faktoren, die die Gerinnung initiieren können. Beteiligt sind die Proteasen der Gerinnungskaskade, Blutplättchen, die Endothelzellen der Gefäßwand und verschiedene Proteine, die an Oberflächen adsorbiert sind. Die Ursachen der Blutgerinnung liegen allgemein an geänderten Strömungsverhältnissen, erhöhter Gerinnungsfähigkeit des Blutes und an den Oberflächen.
Die Aktivierung der Blutgerinnung ist meist bei Implantaten im Blutstrom nicht gewünscht. Der Schwerpunkt dieser Übersicht liegt darauf, wie durch veränderte Oberflächeneigenschaften die direkte Aktivierung der plasmatischen Blutgerinnung, Aktivierung von Blutplättchen und der Endothelzellen unterdrückt werden können. Dabei werden physikalische Eigenschaften wie die Oberflächenrauhigkeit und Oberflächenenergie optimiert, biochemisch funktionelle Gruppen auf der Oberfläche aufgebracht, als lokale Pharmaka werden Heparin und Hirudin als gerinnungshemmende Substanzen angewandt, Thrombozyten-Rezeptorblocker und antiproliferative Medikamente sind in vorklinischen oder klinischen Studien. Weiter wird darauf gesetzt, eine intakte Endothelschicht zu erreichen, indem das Endothelwachstum auf der Oberfläche gefördert wird oder Endothelzellen auf den Implantatoberflächen in vitro im Sinn von Tissue Engineering zu züchten.

Keywords: Hemocompatibility; clotting cascade

  • Lecture (Conference)
    3. Thüringer Biomaterial-Kolloquium, Jena, November 09, 2001
  • Contribution to external collection
    3. Thüringer Biomaterial-Kolloquium, Jena, November 09, 2001

Permalink: https://www.hzdr.de/publications/Publ-4738
Publ.-Id: 4738


Ta implantation and deposition for increased X-Ray visibility and hemocompatibility of vascular stents

Maitz, M. F.; Günzel, R.; Pham, M. T.; Langping, W.; Chu, P.; Richter, E.

Objectives: Coronary stents are seen as the most important step in cardiology of the decade, as they reduce the risk of restenosis after angioplasty and the risk of a second invasive procedure. But still problems concerning occlusion by restenosis or thrombosis have to be overcome, and x-ray contrast of the thin wires has to be improved. The suggested way is coating of the stents with tantalum which is known for its good biocompatibility and hemocompatibility, and its high x-ray absorption.
Deposition of tantalum on stainless steel, the basis of the stent material, is not trivial with common techniques, because of poor adhesion of tantalum. Plasma immersion ion implantation and plasma ion deposition of tantalum are promising ways to create an adherent tantalum layer.
Methods: Tantalum was deposited on flat samples of stainless steel in an argon plasma, 1A Magnetron currency, WHF = 1000 W and 5µs pulse time. Various voltages, bias voltages, pulse counts and temperatures were used.
The adhesion of the tantalum layer was measured in a scratch test. Potentiodynamic corrosion measurement was performed with 0.05M H2SO4 as an electrolyte.
For blood compatibility the activation of freshly prepared blood platelets on the surface was investigated and the clotting time with standard plasma was measured.
Results: For thin coatings (< 1µm) the result of the scratch test was 250mN as a promising result. The coating showed very high corrosion resistance with a corrosion potential between 225 mV and 355 mV and corrosion current densities between 20 nA and 40 nA cm-2.
Results of thrombocyte adhesion, thrombocyte activation and blood clotting time will be presented.
Production of thicker coatings caused problems because of internal stress in the coating.
Conclusion: Coating of stainless steel with tantalum by plasma ion deposition is a good means to increase corrosion resistance and blood compatibility. The production of a thick layer with increased X-ray contrast needs further work.

Keywords: vascular stent; tantalum; coating; radiopacity; x-ray contrast; hemocompatibility

  • Lecture (Conference)
    5th Asian Symposium on Biomedical Materials, Hongkong, December 9-12, 2001
  • Contribution to proceedings
    5th Asian Symposium on Biomedical Materials, Hongkong, December 9-12, 2001

Permalink: https://www.hzdr.de/publications/Publ-4737
Publ.-Id: 4737


Hydroxyapatite precipitation on Na implanted titanium

Maitz, M. F.; Pham, M. T.; Matz, W.; Reuther, H.; Steiner, G.; Richter, E.

Objectives: Titanium is known for its good biocompatibility as an implant material. But a structural integration of a foreign material into the body is known only for hydroxyapatite because of its osteoconductive properties. Surface coating of titanium with hydroxyapatite by means of plasma spraying is the current technique to improve the osteointegration of implants. Problems with this method are the high thickness and limited adhesion of the apatite coating on titanium. Further there are changes in crystallinity of the apatite due to the heating process. A surface preparation that spontaneously induces hydroxyapatite nucleation on its surface is desired.
Methods: By ion beam implantation of Na (3 x 1017 ions cm-1, 50 keV) in titanium a sodium titanate surface was created. Hydrolysis of this layer in deionidised water resulted in formation of TiOH. By incubation in simulated body fluid a hydroxyapatite layer was precipitated on the surface. The human osteosarcoma cell line was seeded out on samples after hydrolysis and after hydroxyapatite precipitation. Reference samples were untreated or activated by soaking in hot NaOH. After 3, 14, and 28 days samples ware investigated for cell growth, alkaline phosphatase activity and calcification.
Results: Cell growth on Na implanted hydrolysed samples was decreased compared with pure titanium at any time. After hydroxyapatite precipitation cell growth after two weeks and four weeks was significantly higher on Na implanted samples than on untreated or NaOH treated samples. Without previous hydroxyapatite deposition only on NaOH treated samples a production of hydroxyapatite could be detected, after hydroxyapatite precipitation there was also better calcification by the cells. Alkaline phosphatase did not differ significantly in the cells on the different substrates.
Conclusion: Na ion implantation in titanium can activate the surface for hydroxyapatite nucleation out of aqueous solutions. The surface without further treatment is too reactive for direct cell contact. After a calciumphosphate deposition on the surface the growth of bone forming cells is enhanced.

Keywords: Apatit; Simulated Body Fluid

  • Lecture (Conference)
    5th Asian Symposium on Biomedical Materials, Hongkong, December 9-12, 2001
  • Contribution to proceedings
    5th Asian Symposium on Biomedical Materials, Hongkong, December 9-12, 2001

Permalink: https://www.hzdr.de/publications/Publ-4736
Publ.-Id: 4736


Surface stimuli to precipitating hydroxyapatite on titanium

Pham, M. T.; Maitz, M. F.; Grambole, D.; Herrmann, F.; Reuther, H.; Richter, E.

no abstract delivered from author

Keywords: hydroxyapatite; titanium; simulated body fluid

  • Journal of Materials Science Letters 20 (2001) 295-296

Permalink: https://www.hzdr.de/publications/Publ-4735
Publ.-Id: 4735


Principles of Biological Testing of Implant Materials

Maitz, M.; Günzel, R.

no abstract delivered from author

Keywords: Biomaterials; biocompatibility testing

  • Lecture (others)
    City University of Hong Kong, 9.-14. November 2000

Permalink: https://www.hzdr.de/publications/Publ-4734
Publ.-Id: 4734


The MatMed database

Maitz, M.

no abstract delivered from author

Keywords: MatMed; EU-Projekt; Materials in Medicine

  • Lecture (others)
    MatMed Workshop, Brehna bei Leipzig, Deutschland, 08.05.2002

Permalink: https://www.hzdr.de/publications/Publ-4733
Publ.-Id: 4733


Aspekte der Implantatmaterial-Organismus-Wechselwirkung

Maitz, M.

Seminarvortrag ohne Abstract

Keywords: Biomaterial

  • Lecture (others)
    Physik, Univ Regensburg, 08.12.2000 http://www.physik.uni-regensburg.de/forschung/gk_nichtlin/vortraege.html

Permalink: https://www.hzdr.de/publications/Publ-4732
Publ.-Id: 4732


Quantum Mechanical Approach to Planar Electron Channeling in a Hypersonic Field (II) - Resonant Influence on the Radiation

Grigoryan, L. S.; Mkrtchyan, A. R.; Mkrtchyan, A. H.; Khachatryan, H. F.; Wagner, W.; Piestrup, M. A.

The spectral intensity of the radiation emitted by a planar channeled
electron in a single crystal excited by a longitudinal hypersonic
wave propagating along the channeling direction has been calculated
for the energy range 10 MeV£E£100 MeV.
It has bben found that the hypersound can excite inverse transitions
through which the transversal energy of the channeled electron is increased.
These transitions have a resonant nature and can lead to a considerable
intensification of the electron channeling radiation.

  • Radiation Effects & Defects in Solids 153 (2001) 307

Permalink: https://www.hzdr.de/publications/Publ-4731
Publ.-Id: 4731


Quantum Mechanical Approach to Planar Electron Channeling in a Hypersonic Field (I)

Grigoryan, L. S.; Mkrtchyan, A. R.; Mkrtchyan, A. H.; Khachatryan, H. F.; Wagner, W.; Piestrup, M. A.

The wave function of an electron 10 MeV £E£100 MeV
planar channeled in a longitudinal hypersonic superlatice has been found.
Conditions for the resonant influence of the acoustic waves on the quantum states of the electron were deduced.
The expression obtained for the wave finction is applicable at resonance.

  • Radiation Effects & Defects in Solids 153 (2001) 289

Permalink: https://www.hzdr.de/publications/Publ-4730
Publ.-Id: 4730


Resonant Influence of Hypersound on the Radiation of an Axially Channeled Electron

Grigoryan, L. S.; Mkrtchyan, A. R.; Mkrtchyan, A. H.; Khachatryan, H. F.; Wagner, W.; Piestrup, M. A.

The spectral intensity of the radiation emitted by an axially channeled
electron in a single crystal excited by a longitudinal hypersonic wave
propagating along the channeling direction has been calculated for the
energy range 10 MeV £E£100 MeV.
It has been shown that under the influence of acoustic vibrations excited
in the single crystal a resonant intensification of the electron
channeling radiation, a variation of its spectral distribution as well as inverse
radiative transitions are possible.

  • Radiation Effects & Defects in Solids 153 (2001) 221

Permalink: https://www.hzdr.de/publications/Publ-4729
Publ.-Id: 4729


Der Fokussierte Ionenstrahl in der Nanotechnologie

Bischoff, L.

Die Arbeit mit dem Fokussierten Ionenstrahl (focused ion beam = FIB) wird vorgestellt und erläutert. Beginnend mit den Ionenquellen (Flüssigmetall, - Flüssiglegierungs- Ionenquellen) über die Ionenoptik bis hin zu anlagenspezifischen Teilen werden Funktionsweise und Parameter dargestellt. Verschiedene Beispiele der Anwendung dieser hochauflösenden Strukturierungstechnik, speziell in der Nanotechnologie, werden aufgezeigt und insbesondere die Flexibilität und Vielseitigkeit dieser modernen Ionenstrahltechnik demonstriert.

Keywords: Focused Ion Beam; Liquid Metal Ion Source; Ion Optics; Nanotechnology

  • Lecture (others)
    DFG-Graduierten-Kolleg "Sensorik" (GK 51) Technische Universität Dresden, Dec. 5, 2001

Permalink: https://www.hzdr.de/publications/Publ-4728
Publ.-Id: 4728


Resonant Influence of a Longitudinal Hypersonic Field on the Radiation from Channeled Electrons

Grigoryan, L. S.; Mkrtchyan, A. R.; Mkrtchyan, A. H.; Khachatryan, H. F.; Prade, H.; Wagner, W.; Piestrup, M. A.

The wave function of a planar/axially channeled electron with energy 10 MeV≤E≤1 GeV under the influence of a longitudinal hypersonic wave excited in a single crystal is calculated. Conditions for the resonant influence of the hypersonic wave on the quantum state of the channeled electron are deduced. Expressions for the wave function that are applicable in the case of resonance are obtained.
Angular and spectral distributions of the radiation intensity from the planar/axially channeled electron are also calculated. The possibility of significant amplification of channeling radiation by a hypersonic wave is substantiated. It is found that the hypersound can excite inverse radiative transitions through which the transversal energy of the channeled electron is increased. These transitions have a resonant nature and can lead to a considerable intensification of the electron channeling radiation. In the case of axial channeling, the resonance radiation is sustained also by direct radiative transitions of the electron.

  • Nucl. Instr. Meth. B 173 (2001) 184

Permalink: https://www.hzdr.de/publications/Publ-4727
Publ.-Id: 4727


Ion acoustic imaging of microstructures using a focused ion beam system

Akhmadaliev, C.; Bischoff, L.; Teichert, J.; Kazbekov, K.

: An intensity modulated focused ion beam (FIB) which is hitting the surface of a solid, leads to a small temperature variation in the near subsurface region which is sufficient for thermal elastic wave generation. The measurement of these waves can be used for analysis and imaging of surface as well as near subsurface structures in the material. The modified FIB equipment IMSA-100 working with 35 keV Ga+ and Au+ ions and a current of about 3 nA was employed to obtain acoustic images from structures on silicon, aluminum and glass targets. The acoustic signals were detected using a PZT transducer delivering an output voltage of 50 - 100 nV. The modulation frequency was varied in the range of 60kHz - 1MHz. The obtained lateral resolution of the ion acoustic images at 80kHz was about 16 µm on silicon and about 7µm on glass and at 632 kHz it decreases to 7 µm and 3 µm respectively.

Keywords: ion acoustic effect; focused ion beams; buried structures; imaging

  • Lecture (Conference)
    3rd International Conference on Nuclear and Radiation Physics June 4 - 7, 2001, Almaty, Republic of Kazakstan

Permalink: https://www.hzdr.de/publications/Publ-4726
Publ.-Id: 4726


Quantum-Mechanical Approach to Planar Positron Channeling in a Longitudinal Hypersonic Field

Grigoryan, L. S.; Mkrtchyan, A. R.; Mkrtchyan, A. H.; Khachatryan, H. F.; Prade, H.; Wagner, W.; Piestrup, M. A.

The wave function of a planar-channeled positron with energy
10 MeV£E£100 MeV
under the resonant influence of hypersound is calculated.
It is found that the longitudinal hypersound changes the spectral
distribution of the channeling radiation significantly.
With decreasing wavelength ls of the hypersound,
starting from ls=lE,
where lE is the characteristic
length related to one transverse oscillation of the channeled positron,
a new type of radiative transition occurs.
It is characterized by the stimulated enhancement of transverse
energy of the positron at channeling (inverse radiative transition).
When ls approaches lE/2 the inverse
transitions show a resonant behaviour.

  • Nucl. Instr. Meth. B 173 (2001) 132

Permalink: https://www.hzdr.de/publications/Publ-4725
Publ.-Id: 4725


Direct fabrication of Ordered Polymer nanocavity Arrays from Surface-Modified ion- nanostructured silicon Templates

Azzaroni, O.; Schilardi, P. L.; Gago, R.; Vázquez, L.; Salvarezza, R. C.

Ion-beam nanopatterned silicon has been used as template for the direct molding of polymeric materials. The silicon surface was chemically modified by octadecyltrichlorosilane before molding in order to allows easy polymer release. This fabrication process allows us to produce a nanocavity polymer array from a nanodot structured silicon template with a lateral and vertical resolutions of 50 nm and 5 nm, respectively. Both, the use of the nanopatterned silicon template and tapping mode atomic force microscopy at low tip-sample interaction forces allow us to determine not only the lateral and vertical resolution of this new method but also the error involved in the transfer process, which results to be of 1nm. Thus. the new method fulfils the requirements of serial nanofabrication trends that requires sub-100 nm lateral resolution and sub-10nm vertical resolution involving only a few and very simple steps during the whole nanofabrication process. Besides, the method displays a proved high fidelity in the molding process showing its potential applications as a direct nanofabrication route for future information storage technologies.

  • Poster
    The IUVSTA Workshop #35 on “Pattern formation and atomic processes in epitaxial growth and ion erosion” June 9-13 2002, Trofaiach, Austria

Permalink: https://www.hzdr.de/publications/Publ-4724
Publ.-Id: 4724


X-ray absorption studies of the bonding structure of B-C-N compounds

Jiménez, I.; Gago, R.; Caretti, I.; Albella, J. M.

Although cubic BCN compounds are desired for their attractive mechanical properties, the synthesis in thin film form of these compounds normally yields amorphous material containing different local structures like trigonal bonding (hexagonal structure), tegragonal bonding (cubic structure) and formation of B12 icosahedra. X-ray absorption (XANES) spectroscopy is a well suited technique to analyse the local structure of these amorphous coatings and discern between formation of single phase or multiple phase and ternary compounds or mixtures of binary grains. We have synthesized a variety of ternary BCN compounds by using Ion Beam Assisted Deposition (IBAD) techniques using B4C, B and C solid evaporation sources with concurrent ion bombardment from mixtures of N2, Ar and CH4 gases. In this way, hydrogenated and hydrogen-free BCN compounds with various compositions are obtained. The bonding structure of the different compounds is discussed in connection with the sample preparation method.

Keywords: Nitrides; BCN; XANES; bonding structure

  • Poster
    13th European Conference on Diamond, Diamond-like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide, 8-13 September 2002, Granada (Spain)

Permalink: https://www.hzdr.de/publications/Publ-4723
Publ.-Id: 4723


Evaluation of the Two-Photon Self-Energy Correction for Hydrogenlike Ions

Goidenko, I. A.; Labzowski, L. N.; Nefiodov, A. V.; Plunien, G.; Soff, G.; Zschocke, S.

We report on the recent evaluation of the two-photon electron self energy to all orders in the
interaction with the Coulomb field of the nucleus. With the present results at hand the major theoretical
uncertainty is diminished, which provides predictions of the ground-state energy with a relative
accuracy of about 10(-6) for the hydrogenlike uranium and lead systems. This allows for
high-precision tests of quantum electrodynamics (QED) in strong fields that are expected to be
experimentally available in the near future.

  • Hyp. Int. 132 (2001) 397

Permalink: https://www.hzdr.de/publications/Publ-4722
Publ.-Id: 4722


Radiative Corrections in Highly Charged Ions and Tests of QED in Strong Electric and Magnetic Fields

Goidenko, I. A.; Labzowski, L. N.; Nefiodov, A. V.; Jentschura, U. D.; Plunien, G.; Zschocke, S.; Soff, G.

To provide predictions of the Lamb shift of highly charged ions on the level of accuracy of about
10(-6) has been achieved after exact results for the contributions of all two-photon self-energy
diagrams have been performed. We report on the present status of our Lamb-shift calculations
including all QED-corrections of first- and second-order in the finestructure constant a and all
relevant nuclear effects. An excellent agreement between the most recent experimental data for Lamb
shift of the ls-ground state in hydrogenlike uranium can be stated. This can serve as a sensitive test
of QED in the strongest electric fields accessible in nature. In a second part of this article we report
about an all-order numerical evaluation of the one-photon selfenergy at low nuclear charge (Z =
1,...,5). A sensitive comparison of our numerical approach with analytical approach to the one-photon
selfenergy confirms the consistency of these two different approaches (numerical and analytic) to very
high precision.

  • Phys. Src. T 92 (2001) 426

Permalink: https://www.hzdr.de/publications/Publ-4721
Publ.-Id: 4721


Spectroscopy in the Z=49 108,110In isotopes: Lifetime measurements inshears bands

Chiara, C. J.; Fossan, D. B.; Janzen, V. P.; Koike, T.; Lafosse, D. R.; Lane, G. J.; Mullins, S. M.; Paul, E. S.; Radford, D. C.; Schnare, H.; Sears, J. M.; Smith, J. F.; Starosta, K.; Vaska, P.; Wadsworth, R.; Ward, D.; Frauendorf, S.

Excited states have been populated in In-108 and In-110 in complementary
backed- and thin-target experiments, using the Stony Brook and the 8
pi Ge-detector arrays. The level schemes for both isotopes have been
extended and modified, including the first observation of DeltaI = 2
bands in In-110. Lifetimes of states in four DeltaI = 1 bands and one DeltaI = 2
band have been measured using the Doppler-shift attenuation method.
Experimental total angular momenta and reduced transition strengths for
the DeltaI = 1 bands have been compared with tilted axis cranking
predictions for shears bands with configurations involving one proton
g(9/2) hole and one or three valence quasineutrons from the h(11/2) and
g(7/2)/d(5/2) orbitals. The DeltaI = 2 bands have been compared with
principal axis cranking predictions for configurations with two g(9/2)
proton holes and a g(7/2) or d(5/2) proton and one- or three-quasineutron
configurations involving the h(11/2) and g(7/2)/d(5/2) orbitals. In
general, there is good overall agreement for both the angular momenta and reduced
transition strengths. The DeltaI = 1 and DeltaI = 2 bands have large
J((2))/B (E2) ratios as expected for the shears mechanism. The B (M1) strengths
deduced for the DeltaI = 1 bands show a decreasing trend as a function
of spin, which is also a feature of the shears mechanism. Configuration
assignments have been made for most observed bands based on comparisons
with theory and systematics of neighboring nuclei.

  • Phys. Rev. C 64 (2001) 054314

Permalink: https://www.hzdr.de/publications/Publ-4720
Publ.-Id: 4720


Emission of Unstable Clusters from Hot Yb Compound Nuclei

Charity, R. J.; Sobotka, L. G.; Cibor, J.; Hagel, K.; Murray, M.; Natowitz, J. B.; Wada, R.; El Masri, Y.; Fabris, D.; Nebbia, G.; Viesta, G.; Cinausero, M.; Fioretto, E.; Prete, G.; Wagner, A.; Xu, H.

Neutrons and isotopically resolved light charged particles have been detected in coincidence with evaporation residues produced in the reaction E/A = 11 MeV 60Ni+100Mo. Multiplicities of evaporated particle-unstable clusters have been determined from correlations in the emission of these light particles. The decay of the short-lived 5He and 8Be (E* = 3.04 MeV) states was found to be affected by the Coulomb field of the compound nucleus in accordance with theoretical estimates. The contributions to the measured kinetic-energy distributions of stable fragments from the sequential decay of the unstable clusters was examined. Overall, the contributions from secondary fragments do not greatly influence the spectral shapes and specifically the location of the spectral peaks are not significantly shifted down in energy due to the presence of these secondary fragments. Therefore contrary to the suggestion of Charity et al.
[Phys. Rev. C 56, 873 (1997)], the lower peak energy of the experimental α-particle spectrum as compared to standard statistical-model calculations cannot be attributed to sequential α-particles from 5He and other clusters. Only for the extreme "subbarrier" regions of the α-particle, deuteron, 6,7Li, and 8Be spectra was the sequential contribution found to be dominant. Statistical-model calculations incorporating large initial deformations are shown to provide enhancements in the yield of low-energy fragments which are roughly appropriate for all the detected isotopes. This suggests that the origin of the sub-barrier enhancements may be a result of evaporation from highly deformed systems which are either produced dynamically during the fusion process or by thermal shape fluctuations.

  • Phys. Rev. C 63 (2001) 024611

Permalink: https://www.hzdr.de/publications/Publ-4719
Publ.-Id: 4719


Klonogenes Zellüberleben von Keratinozyten und Fibroblasten nach Bestrahlung mit weichen Röntgenstrahlen.

Brankovic, K.; Slonina, D.; Panteleeva, A.; Pawelke, J.; Dörr, W.

Weiche Röntgenstrahlung wird in der diagnostischen Radiologie, aber auch in der Strahlentherapie angewandt. In der vorliegenden Untersuchung wurde die Wirkung weicher Röntgenstrahlen (25 kV) bzw. Referenzröntgenstrahlung (200 kV) für verschiedene Zelllinien (3T3/NIH Mausfibroblasten, V-79 Hamsterfibroblasten, primäre neonatale Haut-Keratinozyten des Menschen) verglichen. Zusammenfassend zeigen Fibroblasten ein vemindertes klonogenes Zellüberleben nach Bestrahlung mit weichen Röntgenstrahlen im Vergleich zu 200 kV Röntgenstrahlen. Dieser Unterschied geht einher mit einer Abnahme des alpha-Wertes und einer Zunahme von beta. Demgegenüber zeigen Keratinozyten keine deutliche Veränderung des
Zellüberlebens. Hier findet sich jedoch eine Zunahme von alpha.

  • Exp. Strahlenther. Klin. Strahlenbiol., Vol. 10 (2001) 71-75

Permalink: https://www.hzdr.de/publications/Publ-4718
Publ.-Id: 4718


Evidence for chiral symmetry in the mass A ~ 130 region

Beausang, C. W.; Hecht, A. A.; Zyromski, K. E.; Balabanski, D.; Barton, C. J.; Caprio, M. A.; Casten, R. F.; Cooper, J. R.; Hartley, D.; Krücken, R.; Novak, J. R.; Zamfir, N. V.; Zhang, J.; Dönau, F.

Two new DI = 1 bands in the N = 75, doubly-odd nuclei 136Pm and 138Eu
are reported. These bands have been assigned the same
ph11/2h11/2
structure as the yrast band and show some of the features expected
from predicted chiral twin bands.

  • Nucl. Phys. A 682 (2001) 394

Permalink: https://www.hzdr.de/publications/Publ-4717
Publ.-Id: 4717


Three-dimensional linear stability analysis of lid-driven MHD cavity flow

Shatrov, V.; Mutschke, G.; Gerbeth, G.

We present numerical results of a linear 3-D stability analysis of a square lid-driven cavity flow under the influence of an external magnetic field which is directed parallel to the lid. For Reynolds numbers up to Re * 7800 the 2-D hydrodynamic flow is steady. The Lorentz force has a strong influence on the 2-D flow structure, thereby changing number, shape and strength of the eddies inside. The resulting 3-D stability behaviour is rather complex since it depends on the 2-D flow structure. Although increasing magnetic fields are able to damp 3-D instability, in a parameter region around Re = 3100, several branches of the neutral stability curve do exist. This leads to a non-monotonic behaviour of receptivity to 3-D disturbances as the strength of the magnetic field is increased.

  • Physics of Fluids (August 2003) Vol. 15, No. 8 , pp 2141-2151

Permalink: https://www.hzdr.de/publications/Publ-4716
Publ.-Id: 4716


Thin Films of Molecular Metals: TTF-TCNQ

Fraxedas, J.; Molas, S.; Figueras, A.; Jiménez, I.; Gago, R.; Auban-Senzier, P.; Goffman, M.

We present recent results on the characterization of highly-ordered polycrystalline thin films of the charge transfer salt TTF-TCNQ (TTF = tetrathiafulvalene, TCNQ = tetracyanoquinodimethane) prepared by thermal sublimation in high vacuum under different conditions. The increase in orientation and microcrystal size as a function of substrate and annealing temperatures is addressed. A consequence of such an increase is the reduction of the conductivity activation energy, which eventually leads to the observation of the Peierls transition by resistivity measurements. X-ray Absorption Near Edge Spectroscopy (XANES) studies performed with synchrotron radiation reveal directly the influence of charge transfer on unoccupied states near the Fermi level.

Keywords: Molecular metals; molecular organic materials; thin films; TTF-TCNQ; Peierls transition; synchrotron radiation

  • Journal of Solid State Chemistry 168 (2002) 384-389

Permalink: https://www.hzdr.de/publications/Publ-4715
Publ.-Id: 4715


Investigation of Al-implanted 6H- and 4H-SiC layers after fast heating rate annealings

Ottaviani, L.; Lazar, M.; Locatelli, M. L.; Monteil, Y.; Heera, V.; Voelskow, M.; Skorupa, W.

no abstract delivered from author

Keywords: SiC; Al Implantation; High Temperature Annealing

  • Appl. Surf. Sci. 184 (2001) 330-335

Permalink: https://www.hzdr.de/publications/Publ-4714
Publ.-Id: 4714


TEM Investigation of Si Implanted Natural Diamond

Pécz, B.; Barna, Á.; Heera, V.; Fontaine, F.; Skorupa, W.

no abstract delivered from author

Keywords: Diamond; Electron Microscopy; Ion Implantation; Phase Formation

  • Lecture (Conference)
    ECSCRM 2002, Kloster Banz, Germany, September 2000; Mater.Sci.Forum Vols. 353-356 (2001) 199-202
  • Contribution to external collection
    ECSCRM 2002, Kloster Banz, Germany, September 2000; Mater.Sci.Forum Vols. 353-356 (2001) 199-202

Permalink: https://www.hzdr.de/publications/Publ-4713
Publ.-Id: 4713


Bloch oscillations and their coupling to optical phonons

Dekorsy, T.

Bloch oscillations in semiconductor superlattices are an intriguing subject of electronic coherence in low dimensional semiconductor structures. The electronic coherence is destroyed by several scattering mechanisms, most important carrier-carrier scattering and carrier-phonon scattering. Especially in wide miniband superlattices with miniband widths larger than the LO phonon energy LO phonon emission is responsible for subpicosecond dephasing times. We investigate the dynamics of Bloch oscillations in GaAs/AlxGa1-xAs superlattices with large minibands tuned into resonance with LO phonons. The coherent excitation of coherent LO phonons via Bloch oscillations is observed at very low carrier densities. The peculiarities of the resonant excitation process are in agreement with theoretical considerations.

  • Invited lecture (Conferences)
    Second International Workshop on Quantum Nonplanar Nanostructures&Nanolectronics '02, Tsukuba, Japan, Sept. 9-11, 2002 (invited talk).

Permalink: https://www.hzdr.de/publications/Publ-4712
Publ.-Id: 4712


Investigation of Antimagnetic Rotation in 100Pd

Zhu, S.; Garg, U.; Afanasjev, A. V.; Frauendorf, S.; Kharraja, B.; Ghugre, S. S.; Chintalapudi, S. N.; Janssens, R. V. F.; Carpenter, M. P.; Kondev, F. G.; Lauritsen, T.

High spin states have been studied in the nucleus 100Pd with the aim of investigating the novel phenomenon of "antimagnetic rotation." A cascade of four "rotational-band-like" transitions is proposed as corresponding to antimagnetic rotation, based on the observed spectroscopic properties and a comparison with calculations in the configuration-dependent cranked Nilsson-Strutinsky formalism.

  • Phys. Rev. C 64 (2001) 041302

Permalink: https://www.hzdr.de/publications/Publ-4711
Publ.-Id: 4711


Electroproduction of Kaons and Light Nuclei

Zeidman, B.; Abbott, D.; Ahmidouch, A.; Ambrozewicz, P.; Armstrong, C. S.; Arrington, J.; Asaturyan, R.; Assamagan, K.; Avery, S.; Bailey, K.; Baker, O. K.; Beedoe, S.; Bitao, H.; Breuer, H.; Brown, D. S.; Carlini, R.; Cha, J.; Chant, N.; Christy, E.; Cochran, A.; Cole, L.; Collins, G.; Cothran, C.; Crowder, J.; Cummings, W. J.; Danagoulian, S.; Dohrmann, F.; Duncan, F.; Dunne, J.; Dutta, D.; Eden, T.; Elaasar, M.; Ent, R.; Ewell, L.; Fenker, H.; Fortune, H. T.; Fujii, Y.; Gan, L.; Gao, H.; Garrow, K.; Geesaman, D.; Gueye, P.; Gustafsson, K.; Hafidi, K.; Hansen, J. O.; Hinton, W.; Jackson, H. E.; Juengst, H.; Keppel, C.; Klein, A.; Koltenuk, D.; Liang, Y.; Liu, J. H.; Lung, A.; Mack, D.; Madey, R.; Markowitz, P.; Martoff, C. J.; Meekins, D.; Mitchell, J.; Miyoshi, T.; Mkrtchyan, H.; Mohring, R.; Mtingwa, S. K.; Mueller, B.; O'Neill, T. G.; Niculescu, G.; Niculescu, I.; Potterveld, D.; Price, J. W.; Raue, B. A.; Reimer, P. E.; Reinhold, J.; Roche, J.; Roos, P.; Sarsour, M.; Sato, Y.; Savage, G.; Sawafta, R.; Schiffer, J. P.; Segel, R. E.; Semenov, A.; Stepanyan, S.; Tadevosian, V.; Tajima, S.; Tang, L.; Terburg, B.; Uzzle, A.; Wood, S.; Yamaguchi, H.; Yan (Jlab), C.; Yan (Kent), C.; Yuan, L.; Zeier, M.; Zihlmann, B.

The A(e,e,K+YX reaction on H, D, 3He, and 4He was investigated in Hall C at CEBAF. Data were obtained for Q2≈0.35 and 0.5 GeV2 at 3.245 GeV. The missing mass spectra for both H and D are fitted with Monte-Carlo simulations incorporating peaks corresponding to Λ production on the proton and Σ production on both the proton and neutron. For D, the cross section ratio Σ0-≈2, and excess yield close to the thresholds for Λ and Σ production can be attributed to final-state interactions; models are compared to the data. The analysis of the data for the He targets is in a more preliminary state with broader quasi-free peaks resulting from the higher Fermi momenta. Evidence for bound Λ-hypernuclear states is seen and other structure may be present.

  • Nucl. Phys. A 691 (2001) 37

Permalink: https://www.hzdr.de/publications/Publ-4710
Publ.-Id: 4710


Characteristic Features of the Pseudogap and Superconducting States of YBa2Cu3O7 – x

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

The relaxation dynamics of the lattice and low-energy quasiparticles in a YBa2Cu3O7 – x superconductor are studied by the light reflection technique with femtosecond temporal resolution in a wide temperature range. It is shown that, for T > Tc, there exist two temperature regions with qualitatively and quantitatively different excitation dynamics, and the transition between these regions is of a hysteretic nature. It is also found that the character of changes observed in the charge carrier relaxation dynamics in the superconducting state testifies to the presence of an anisotropic gap with nodes at the Fermi surface.

  • JETP Letters, Volume 75, Issue 12, pp. 642-645 (2002).

Permalink: https://www.hzdr.de/publications/Publ-4709
Publ.-Id: 4709


Coupled Bloch-phonon oscillations in biased InGaAs/InAlAs superlattices

Först, M.; Kurz, H.; Dekorsy, T.; Leavitt, R. P.

The coupling of coherent Bloch oscillations to LO phonons is investigated in ternary
InGaAs/InAlAs superlattice. The coherent amplitudes of distinct superlattice phonon modes are selectively enhanced in resonance with the Bloch oscillations frequency.

  • Lecture (others)
    Quantum Electronics and Laser Sciences Conference (QELS) 2002, Long Beach, California, USA, May 19-24, 2002

Permalink: https://www.hzdr.de/publications/Publ-4708
Publ.-Id: 4708


Observation of a hysteretic pseudogap behavior via coherent phonons in high temperature superconductors

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

We investigate ultrafast reflectivity changes of a near-optimally doped YBa2Cu3O7-x (123) superconductor. The amplitude of coherently excited phonons show strong changes as a function of temperature above the superconducting transition temperature. These changes give evidence for two crossover temperatures within the pseudogap regime. In addition, these crossover temperatures exhibit a clear hysteretic behavior as a function of temperature.

  • Lecture (Conference)
    13th Conference on Ultrafast Phenomena, Vancouver, Canada, May 12-17, 2002

Permalink: https://www.hzdr.de/publications/Publ-4707
Publ.-Id: 4707


IR spectroscopic possibilities with the Rossendorf free-electron laser

Dekorsy, T.

The free-electron laser (FEL) facility at the Research Center Rossendorf will span the wavelength range from 5 µm to 150 µm. Driven by the superconducting linear accelerator ELBE (up to 40 MeV electron energies, bunch charge of 77 pC) the FEL will provide a continuous pulse train at 13 MHz with pulsewidths of 0.5 ps to 10 ps and pulse energies in the µJ range. These pulses will be used for time-resolved spectroscopy, nonlinear optics and optical near-field spectroscopy by three in-house groups working on semiconductors, bio-molecules and cells. We will describe the status of the FEL and of the experimental facilities. The combination of the FEL with high magnetic fields will represent unique experimental possibilities. These will be discussed with emphasis on semiconductor physics.

  • Lecture (others)
    1st Workshop on High Magnetic Fields, Dresden, June 20, 2002

Permalink: https://www.hzdr.de/publications/Publ-4706
Publ.-Id: 4706


Zeitaufgelöste Spektroskopie an Halbleiterheterostrukturen mit dem Freie-Elektronen Laser an ELBE

Dekorsy, T.

Die Grundlagen der zeitaufgelösten Spektroskopie an Halbleitern und Halbleiterheterostrukturen mit dem Freie-Elektronen Laser an ELBE werden erläutert mit Schwerpunkt auf der Dynamik von Intersubbandübergängen. Neben Anrege-Abfrage Experimenten mit einer Wellenenlänge (degenerate pump-probe) liefern Mehrfarben-Experimente mit synchronisierten Femtosekunden Lasern zusätzliche wichtige Informationen über elektronische Nichtgleichgewichts-Verteilungsfunktionen. Desweiteren werden die Techniken des Vier-Wellen Mischens und des spektralen Lochbrennens diskutiert, die bei der Beantwortung von Fragen nach inhomogenen/homogenen Verbreiterungen von Übergängen wichtig sind.

  • Lecture (others)
    ELBE Palaver, FZR, Nov. 1, 2001

Permalink: https://www.hzdr.de/publications/Publ-4705
Publ.-Id: 4705


Von der Femtosekunden Spektroskopie zur -Technologie

Dekorsy, T.

Die Entwicklung von Femtosekunden-Lasersystemen hat in den letzten Jahren einen rasanten Fortschritt gemacht. Vom Fernen Infrarot bis zur Röntgenstrahlung lassen sich auf einem optischen Tisch über nichtlineare optische Prozesse ultrakurze Pulse hoher Intensität erzeugen. Diese Laser erlauben die zeitliche Auflösung der wichtigsten Prozesse in Halbleitern, an Oberflächen, bei chemischen Reaktionen und in biologischen Systemen und sind damit zu einem wertvollen wissenschaftlichen Instrument geworden. Ihre Verknüpfung mit dem Freie-Elektronen Laser an ELBE ermöglicht weitere einzigartige spektroskopische Möglichkeiten.

Ich werde einige Beispiele meiner Arbeiten auf dem Gebiet der Femtosekunden-Spektroskopie kohärenter Anregungen in Halbleitern geben, insbesondere zur Anregung kohärenter Wellenpakete und Gitterschwingungen in Halbleiter Quantenstrukturen. Desweiteren werde ich auf Beiträge zur technologischen Entwicklung des Feldes, wie die Realisierung des kompaktesten Femtosekunden Lasers auf Festkörperbasis, und deren Anwendungen eingehen.

  • Lecture (others)
    Kolloquium des FZR, May 31, 2001

Permalink: https://www.hzdr.de/publications/Publ-4704
Publ.-Id: 4704


Coherent phonons

Dekorsy, T.

The excitation and detection of coherent phonon states in semiconductors
with femtosecond laser pulses reveals detailed insight into phonon dynamics on ultrashort time scales. I will review the generation mechanism responsible for
coherent phonon generation in different materials. I will present recent results on
the coupling of coherent electronic excitations to Bloch oscillations in superlattices
and the detection of phonon co-variances and their relation to squeezed phonon states.

  • Lecture (others)
    TU Wien, Austria, May 28, 2001

Permalink: https://www.hzdr.de/publications/Publ-4703
Publ.-Id: 4703


Coherent phonons and phonon co-variances

Dekorsy, T.

The excitation and detection of coherent phonon states in semiconductors
with femtosecond laser pulses reveals detailed insight into phonon dynamics on ultrashort time scales. I will review the generation mechanism responsible for
coherent phonon generation in different materials. I will present recent results on
the coupling of coherent electronic excitations to Bloch oscillations in superlattices
and the detection of phonon co-variances and their relation to squeezed phonon states.

Keywords: excitation and detection of coherent phonon states in semiconductors; coupling of coherent electronic excitations to Bloch oscillations in superlatices; detection of phonon co-variances; squeezed phonon states

  • Lecture (others)
    FOM Institute AMOLF, Amsterdam, Netherlands, Jan. 29, 2001

Permalink: https://www.hzdr.de/publications/Publ-4702
Publ.-Id: 4702


Ultrafast Dynamics of excitons in crescent-shaped GaAs quantum wires

Komori, K.; Yasuhira, T.; Wang, X. L.; Ogura, M.; Först, M.; Dekorsy, T.; Kurz, H.

Ultrafast exciton dynamics in crescent-shaped GaAs quantum-wires have
been investigated using pump-probe and Reflective-Electro-Optic-Sampling (REOS)
methods. The differential-reflectivity shows the exciton energy-shift and the subband-relaxation. Also ultrafast coherent dynamics are observed in the REOS measurement.

  • Poster
    Quantum Electronics and Laser Sciences Conference (QELS) 2001, Baltimore, MD, USA, May 6-11, 2001

Permalink: https://www.hzdr.de/publications/Publ-4701
Publ.-Id: 4701


Isoscalar-Isovector Interferences in pN®N e+ e- Reactions as a Probe of Baryon Resonance Dynamics

Titov, A. I.; Kämpfer, B.

The isoscalar-isovector (r-w) interferences in the exclusive reactions
p-p®ne+e-
and
p+n®pe+e-
near the w threshold leads to a distinct difference of the dielectron invariant
mass distributions depending on beam energy.
The strength of this effect is determined by the coupling of resonances to the nucleon
vector-meson channels and other resonance properties. Therefore, a combined analysis of the
se reactions can be usedas a tool for determining the baryon resonance dynamics.

  • Eur. Phys. J. A 12 (2001) 217-229

Permalink: https://www.hzdr.de/publications/Publ-4700
Publ.-Id: 4700


Visualization of vacancy type defects in the RP/2 region of ion implanted and annealed silicon

Peeva, A.; Koegler, R.; Skorupa, W.

Recently, a strong metal gettering in Si after ion implantation and annealing has been detected at depths between the surface and the projected ion range RP, indicating the presence of residual defects therein. The theoretical ballistic calculations ascribed the RP/2 effect to the excess vacancies resulting from the forward momentum transfer of the implanted ions into the silicon matrix. So far, the gettering centers for metals at RP/2 have been considered to be too small to be visible by Transmission Electron Microscopy (TEM). We show that the crucial point for visualization of the vacancy type defects at RP/2 by TEM is the specimen preparation technique. The very widely used conventional ion milling technique for TEM specimen preparation introduces damage on the surface of the XTEM specimen, which blurs the original defect structure at RP/2 and obscure it of being visualized. Only the TEM specimens prepared by cleaving reveals cavities at RP/2. Minimum damage production caused during the preparation of the TEM specimen using cleaving allows the imaging of the cavities at RP/2.

Keywords: Silicon; Gettering; Defects; Ion Implantation; Electron Microscopy

  • Nuclear Instruments and Methods in Physics Research B 206: 71-75 MAY 2003
  • Lecture (Conference)
    IBMM 2002 Conference, Kobe, Japan, 1-6 September 2002

Permalink: https://www.hzdr.de/publications/Publ-4699
Publ.-Id: 4699


Synthesis and Decay of Nanowires

Müller, T.

no abstract delivered from author

  • Lecture (others)
    Ionenstrahltreffen, Uni Augsburg, Germany, October 1-2, 2001

Permalink: https://www.hzdr.de/publications/Publ-4697
Publ.-Id: 4697


Chiral Doublet Structures in Odd-Odd N=75 Isotones: Chiral Vibrations

Starosta, K.; Koike, T.; Chiara, C. J.; Fossan, D. B.; Lafosse, D. R.; Hecht, A. A.; Beausang, C. W.; Caprio, M. A.; Cooper, J. R.; Krücken, R.; Novak, J. R.; Zamfir, N. V.; Zyromski, K. E.; Hartley, D. J.; Balabanski, D. L.; Zhang, J.; Frauendorf, S.; Dimitrov, V. I.

New sideband partners of the yrast bands built on the i
ph11/2nh11/2
configuration were identified in 55Cs, 57La, and 61Pm
N = 75 isotones of 134Pr.
These bands form with 134Pr unique doublet-band systematics suggesting
a common basis. Aplanar solutions of 3D tilted axis cranking
calculations for triaxial shapes define left- and right-handed chiral
systems out of the three angular momenta provided by the valence
particles and the core rotation, which leads to spontaneous chiral symmetry
breaking and the doublet bands. Small energy differences between the

  • Phys. Rev. Lett. 86 (2001) 971

Permalink: https://www.hzdr.de/publications/Publ-4696
Publ.-Id: 4696


Nanocluster Formation by Low-Energy Ion Implantation - Basic Mechanisms

Müller, T.; Heinig, K.-H.

no abstract delivered from author

  • Lecture (others)
    Projekttreffen, Uni Aarhus, Denmark, August 19-21, 2001

Permalink: https://www.hzdr.de/publications/Publ-4695
Publ.-Id: 4695


Template-Directed Ion Beam Synthesis of Ge Nanowires Using V-Grooves

Müller, T.; Heinig, K.-H.; Schmidt, B.

Guided self-organization of Ge nanowires in templates has been studied experimentally and theoretically. V-grooves formed in (001)Si by anisotropic etching with 30% KOH at 80°C. About 200 nm were grown on the (001)Si wafer surface and on the (111)Si V-groove sidewalls by oxidation at 1000°C in dry O2. The resulting SiO2-V-grooves were used as templates for the Ge nanowire fabrication. Ge+ ions have been implanted into the SiO2 at 70 keV with a fluence of 1017 cm-2. The theoretically predicted enrichment of Ge in the V-groove bottom during homogeneous ion implantation has been proven by analytic TEM (EDX). Annealing of Ge+ implanted samples in N2 leads to phase separation of Ge from the SiO2 matrix. Cross sectional TEM studies have confirmed the self-organization of a Ge nanowire in the SiO2 at the V-groove bottom, whereas only a thin layer of isolated Ge nanoclusters has been found in the V-groove side-walls. The kinetics of the wire formation during annealing was studied 3D Kinetic Lattice Monte-Carlo simulations. The comparison to experimental results reveals self-organization phenomena during phase separation, caused by nucleation, Ostwald ripening and coalescence. Moreover, the simulations were used to study the stability of very thin Ge nanowires against thermal fluctuations.

  • Lecture (Conference)
    Annual Meeting of the German Physical Society, Hamburg, March 26-30, 2001

Permalink: https://www.hzdr.de/publications/Publ-4694
Publ.-Id: 4694


Resonant and non Resonant K--Production in pp Reactions at 2.85 GeV

Ritman, J.; Balestra, F.; Bedfer, Y.; Bertini, R.; Bland, L. C.; Brenschede, A.; Brochard, F.; Bussab, M. P.; Choi, S.; Debowski, M.; Dressler, R.; Dzemidzic, M.; Faivre, J.-C.; Falomkin, I. V.; Fava, L.; Ferrero, L.; Foryciarz, J.; Fröhlich, I.; Frolov, V.; Garfagnini, R.; Grasso, A.; Grosse, E.; Heinz, S.; Ivanov, V. V.; Jacobs, W. W.; Kühn, W.; Maggiora, A.; Maggiora, M.; Manara, A.; Panzieri, D.; Pfaff, H.-W.; Piragino, G.; Pontecorvo, G. B.; Popov, A.; Salabura, P.; Tchalyshev, V.; Tosello, F.; Vigdor, S. E.; Zosi, G.

Inclusive and exclusive (i.e. via the f resonance) K- meson production
cross sections have been measured in proton-proton
reactions at Tbeam = 2.85 GeV. The inclusive K- cross section is
about a factor 20 lower than the K+ cross sections at the
same available energy above threshold.
The observed f/w cross section ratio is enhanced by about an order
of magnitude relative to naive predictions based upon the
Okubo-Zweig-Iizuka (OZI) rule.
Differential cross section results are presented which indicate significant contributions from higher partial
waves in the proton-proton entrance channel.

  • Nuclear Physics 69 (2001) 395

Permalink: https://www.hzdr.de/publications/Publ-4693
Publ.-Id: 4693


Coupled Bloch-phonon modes in superlattices

Ghosh, A. W.; Jönsson, L.; Wilkins, J. W.; Dekorsy, T.; Bartels, A.; Kurz, H.

Experiments and microscopic theoretical analysis show that the coupling of Bloch
oscillations with coherent longitudinal optical phonons in a GaAs/AlGaAs
superlattice leads to resonant coherent phonon excitation but no gap in the Bloch-phonon spectrum.

  • Lecture (Conference)
    Quantum Electronics and Laser Sciences Conference (QELS) 2001, Baltimore, MD, USA, May 6-11, 2001

Permalink: https://www.hzdr.de/publications/Publ-4692
Publ.-Id: 4692


Ordered quantum dot arrays via sputtering

Facsko, S.; Bobek, T.; Kurz, H.; Dekorsy, T.

The erosion of III -V compound semiconductors by low-energy Ar ions
under normal incidence leads to the formation of regular nanoscale
quantum dot arrays. We present the dependence of the formation
on ion energy for GaSb and compare them to simulations based on
a continuum equation.

  • Lecture (Conference)
    Gordon Conference "Material processes far from equilibrium", Meriden, NH, USA, July 1-6, 2001

Permalink: https://www.hzdr.de/publications/Publ-4691
Publ.-Id: 4691


Wavelength tunable femtosecoond Ti:sapphire ring laser with up to 1.5 GHz repetition rate

Bartels, A.; Dekorsy, T.; Kurz, H.

We demonstrate a wavelength-tunable Ti:sapphire femtosecond laser with a repetition
rate between 500 MHz and 1.5 GHz. A “half-Brewster-prism” is introduced into
the cavity to achieve tuning from 733 nm to 840 nm by tilting a cavity mirror.

  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2001, Baltimore, MD, USA, May 6-10, 2001

Permalink: https://www.hzdr.de/publications/Publ-4690
Publ.-Id: 4690


Ion-induced Formation of Quantum Dots

Kurz, H.; Facsko, S.; Bobek, T.; Dekorsy, T.

We review the mechanism of the ion-induced formation of nanoscale quantum dots on III-V semiconductor surfaces and their potential applications.

  • Lecture (Conference)
    APS March Meeting, Seattle, USA, March 12-16, 2001

Permalink: https://www.hzdr.de/publications/Publ-4689
Publ.-Id: 4689


Electroproduction of Kaons and Light Hypernuclei

Reinhold, J.; Abbott, D.; Ahmidouch, A.; Ambrozewicz, P.; Armstrong, C. S.; Arrington, J.; Asaturyan, R.; Assamagan, K.; Avery, S.; Bailey, K.; Baker, O. K.; Beedoe, S.; Bitao, H.; Boeglin, W.; Breuer, H.; Brown, D. S.; Carlini, R.; Cha, J.; Chant, N.; Christy, E.; Cochran, A.; Cole, L.; Collins, G.; Cochran, C.; Crowder, J.; Cummings, W. J.; Danagoulian, S.; Dohrmann, F.; Duncan, F.; Dunne, J.; Dutta, D.; Eden, T.; Elaasar, M.; Ent, R.; Ewell, L.; Fenker, H.; Fortune, H. T.; Fujii, Y.; Gan, L.; Gao, H.; Garrow, K.; Geesaman, D. F.; Gueye, P.; Gustafsson, K.; Hafidi, K.; Hansen, J. O.; Hinton, W.; Jackson, H. E.; Juengst, H.; Keppel, C.; Klein, A.; Koltenuk, D.; Liang, Y.; Liu, J. H.; Lung, A.; Mack, D.; Madey, R.; Markovitz, P.; Martoff, C. J.; Meekins, D.; Mitchell, J.; Miyoshi, T.; Mkrtchyan, H.; Mohring, R.; Mtingwa, S. K.; Mueller, B.; O'Neill, T. G.; Niculescu, G.; Niculescu, I.; Potterveld, D.; Price, J. W.; Raue, B. A.; Reimer, P. E.; Roche, J.; Roos, P.; Sarsour, M.; Sato, Y.; Savage, G.; Sawafta, R.; Schiffer, J. P.; Segel, R. E.; Semenov, A.; Stepanyan, S.; Tadevosian, V.; Tajima, S.; Tang, L.; Terburg, B.; Uzzle, A.; Wood, S.; Yamaguchi, H.; Yan, C.; Yan, C.; Yuan, L.; Zeidman, B.; Zeier, M.; Zihlmann, B.

Kaon electroproduction on hydrogen, deuterium and helium targets has been
measured at a beam energy of 3.245 GeV and four-momentum transfer, Q2, ranging
from 0.34 to 0.5 GeV. Associated hyperon production off a nucleon in the
deuteron exhibits a quasifree production mechanism.
Excess yield close to the respective thresholds for L and S
production is observed. This can be accounted for be final-state interaction
between the electroproduced hyperon and the spectator nucleon. The effects
predicted from three different hyperon-nucleon potentials are compared to
the data. The measurements on the helium targets is the first ever performed.
Very preliminary results are presented.

  • Nucl. Phys. A 684 (2001) 470

Permalink: https://www.hzdr.de/publications/Publ-4688
Publ.-Id: 4688


Deposition of thick cubic boron nitride thin films by dual ion beam deposition

Gago, R.; Kolitsch, A.; Möller, W.

In this work we report on the production of cubic boron nitride (c-BN) thin films by Dual Ion Beam Deposition (DIBD). The interest of this work is to search for an ion-beam-assisted deposition (IBAD) method able to produce thick (> 1 um) low-stress c-BN thin films and, hence, with potential industrial application. This is not applicable in the case of IBAD using electron beam evaporation, since the material contained in the liner limits the maximum process time and, in addition, the fact that boron sublimes, makes difficult a fine control over the evaporation rate. Our DIBD system is equipped with two commercial Kauffman-type ion guns. Boron atoms were sputtered by direct Ar+ bombardment of a 3” boron target. The ions impinge under an angle of 45° and are produced with a 3 cm beam-diameter ion gun. The growth process was assisted by concurrent bombardment from a mixture of argon and nitrogen ions extracted from a 5 cm beam-diameter ion gun. For the cubic phase growth, the substrate temperature and ion assisting parameters were chosen in order to reach the required momentum transfer per incoming atom [1]. The stress release was achieved by additional ion bombardment with medium-energy N2+ ions (35 keV) during the growth process [2].

REFERENCES:
[1] D.J. Kester, R. Messier, J. Appl. Phys. 72 (1992) 504.
[2] C. Fitz, A. Kolitsch, W. Möller, Appl. Phy. Lett. 80 (2001) 55.

  • Poster
    13th European Conference on Diamond, Diamond-like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide, 8-13 September 2002, Granada (Spain)

Permalink: https://www.hzdr.de/publications/Publ-4686
Publ.-Id: 4686


Hydrogen incorporation on CNx films deposited by ECR Chemical Vapor Deposition

Camero, M.; Gago, R.; Gómez-Aleixandre, C.; Albella, J. M.

Amorphous CNxHy films have been deposited by ECR-CVD from argon, nitrogen and methane gas mixtures. The composition and bonding environment of the films, consisting in one-dimensional polymeric chains with amine groups, have been studied by ERDA and IRS. By proper selection of the gas mixture composition, hydrogen incorporation in the films can be controlled. For low methane concentrations (CH4/(N2+CH4)<0.5) hydrogen atoms are predominantly joined as NHx radicals whereas for higher methane concentrations the CHx percentage in the films strongly increases. Furthermore, as the methane concentration increases, the substitution of NHx by larger size CHx radicals accounts for the decrease in the H content of the films, as detected by ERDA (Elastic Recoil Detection Analysis). The influence on the hydrogen incorporation of the argon content in the gas mixture has also been evaluated.

  • Diamond and Related Materials 12 (2003) 632-635
  • Poster
    13th European Conference on Diamond, Diamond-like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide, 8-13 September 2002, Granada (Spain)

Permalink: https://www.hzdr.de/publications/Publ-4685
Publ.-Id: 4685


Fine structure at the x-ray absorption pi* and sigma* bands of amorphous carbon: distorted trigonal and tetragonal bonding?

Jiménez, I.; Gago, R.; Albella, J. M.

X-ray absorption near edge spectroscopy (XANES) of amorphous carbon films shows a fine structure at the pi* and sigma* bands that is not present in the reference crystalline graphite and diamond materials. Thermal treatments of the amorphous carbon films in a vacuum induce clear changes in the fine structure, hence indicating that it is due to the presence of multiple bonding states. The intensity and energy position of the multiple pi* and sigma* states is directly correlated, confirming its origin as different bonding states of sp2 hybridized carbon atoms. The presence of the fine structure in amorphous carbon is interpreted as due to the presence of distorted trigonal and tetragonal bonding structures, in addition to the ideal hexagonal and cubic structures.

  • Diamond and Related Materials 12 (2003) 110-115
  • Lecture (Conference)
    4th SPECIALIST MEETING ON AMORPHOUS CARBON (SMAC 2002), 5-6 September 2002, Barcelona (Spain)

Permalink: https://www.hzdr.de/publications/Publ-4684
Publ.-Id: 4684


Direct molding of nanopatterned polymeric films: Resolution and errors

Azzarozi, O.; Schilardi, P. L.; Salvarezza, R. C.; Gago, R.; Vázquez, L.

The capability of the direct polymer molding method to transfer ordered nanopatterns from a surface-modified silicon template to polymeric materials, such as polystyrene (PS) and high-impact polystyrene (HIPS) is investigated by tapping mode atomic force microscopy (AFM). The lateral resolution of the method for both materials is 54 ± 1 nm while the vertical resolution is 56 ± 1 nm and 3 ± 1 nm, for PS and HIPS, respectively. This difference is explained by considering the different nanomechanical properties of the polymers. In contrast, HIPS surfaces are more resistant to the wear induced by the repetitive ‘‘reading’’ of the surface structure with the AFM tip.

  • Applied Physics Letters 82 (2003) 457-459
  • Virtual Journal of Nanoscale Science & Technology 7/4 (Compilation of links to selected articles covering a focused area of frontier research published by the American Institute of Physics and the American Physical Society)

Permalink: https://www.hzdr.de/publications/Publ-4683
Publ.-Id: 4683


Production of a+0-Mesons in the Production of a+0-Mesons in the Reaction pp ® da+0

Müller, H.

We investigate the reaction pp ® da0+ at COSY and SIS energies
together with accompanying background reactions and inclusive particle yields.
The a0+ is considered as a usual quark model state with two decay channels
a0+® K+[`(K0)] and a0+®p+ h.
Cross sections for a0+ production as well as for the corresponding nonresonant channels
pp ® dK+[` (K0)] and pp ®dp+hare compared.
Especially in case of the final channel dp +h
high statistics measurements are necessary to extract the a0+ signal from the nonresonant background.

  • Eur. Phys. J. A 11 (2001) 113

Permalink: https://www.hzdr.de/publications/Publ-4682
Publ.-Id: 4682


Deposition of TiN/AlN bilayers on a rotating substrate by reactive sputtering

Auger, M. A.; Gago, R.; Fernández, M.; Sánchez, O.; Albella, J. M.

A balanced dual-cathode reactive magnetron sputtering system has been developed, which allows the growth of TiN/AlN bilayers from pure titanium and aluminium targets in a mixture of argon and nitrogen gases. One important property of the TiN/AlN coatings is that they combine two important requirements for protective coatings: good adhesion properties of the TiN films and the chemical stability of the AlN films. The chemical composition of the grown layers has been studied by Auger electron spectroscopy (AES), elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS) techniques, and nitrogen incorporation in the nitrides has been correlated to the argonynitrogen ratio in the sputtering gas. Structural properties have been studied by X-ray diffraction (XRD), and the results showed the presence of cubic TiN and hexagonal AlN phases in the grown bilayer. Mechanical properties have been extracted from nano-indentation measurements, giving hardness values for TiN/AlN bilayer in the range of the reported values for TiN coatings.

Keywords: Reactive sputtering; Titanium nitride; Aluminium nitride

  • Surface and Coatings Technology 157 (2002) 26-33

Permalink: https://www.hzdr.de/publications/Publ-4681
Publ.-Id: 4681


X-Ray absorption study of the bonding structure of BCN compounds enriched in carbon by CH4 ion assistance

Gago, R.; Jimenez, I.; Kreissig, U.; Albella, J. M.

Ternary BCN compounds can be grown by B4C evaporation and concurrent N2/Ar ion assistance in both hexagonal and cubic structures, depending on the deposition parameters. However, the films are always carbon poor, with a maximum carbon content of approximately 10 at.% in hexagonal BCN, and 5 at.% of C in cubic BCN. In order to increase the carbon content in the films, we have added CH4 to the bombarding gas mixture. In the case of hexagonal structures, the additional carbon atoms are efficiently incorporated to the h-BCN without finding a solubility limit. For the cubic structures, the carbon enrichment induces a disruption of the structure and segregation into h-BCN and BxC domains.

Keywords: Nitrides; Carbides; Ternary BCN; X-Ray absorption near edge spectroscopy

  • Diamond and Related Materials 11 (2002) 1295-1299

Permalink: https://www.hzdr.de/publications/Publ-4680
Publ.-Id: 4680


On the bonding structure of hydrogenated carbon nitrides grown by electron cyclotron resonance chemical vapour deposition: towards the synthesis of non-graphitic carbon nitrides

Alonso, F.; Gago, R.; Jiménez, I.; Gómez-Aleixandre, C.; Kreissig, U.; Albella, J. M.

This work compares the composition and bonding structure of hydrogenated carbon nitride films (CNx:H) obtained by electron cyclotron resonance chemical vapour deposition (ECR-CVD) with those of hydrogen-free carbon nitrides (CNx) obtained by nitrogen ion beam assisted deposition (IBAD) of graphite.The composition and structure of the films was analysed by ion scattering techniques well suited to the detection of hydrogen, in addition to the more conventional infrared spectroscopy.The bonding structure was examined by X-ray absorption spectroscopy (XANES).The typical IBAD CNx films are graphitic with a N/C content below 0.3. However, the ECR-CVD films show a less graphitic bonding structure. The ECR-CVD films were synthesised in a conventional microwave ECR reactor (2.25 GHz, 875 Gauss, 250 W) using as precursor gases N2 and Ar in the reactor chamber, and CH4 directly in the deposition chamber.

Keywords: Electron cyclotron resonance chemical vapour deposition; hydrogenated carbon nitride, Bonding structure, X-Ray absorption spectroscopy

  • Diamond and Related Materials 11 (2002) 1161-1165

Permalink: https://www.hzdr.de/publications/Publ-4678
Publ.-Id: 4678


Binding and extraction of oxyanions by dendrimers and cryptands

Gloe, K.; Grotjahn, M.; Rambusch, T.; Wichmann, K.; Johannsen, B.; Spies, H.; Stephan, H.; Bharadwaj, P. K.; Chand, D. K.; Gorka, M.; Müller, W. M.; Vögtle, F.

  • Poster
    26 International Symposium on Macrocyclic Chemistry, Fukuoka/Japan, 15.-20.07.2001

Permalink: https://www.hzdr.de/publications/Publ-4677
Publ.-Id: 4677


Abtrennung von Uran aus wässriger Lösung durch Calixarene

Schmeide, K.

Abtrennung von Uranylionen aus Sicker- und Grundwässern mit uranophilen Calixarenen-Integrierter Umweltschutz in der Textilindustrie

  • Lecture (others)
    FWR - 21.8.2001

Permalink: https://www.hzdr.de/publications/Publ-4676
Publ.-Id: 4676


Structural Studies of Actinide Complexation with Humic Substances

Reich, T.; Sachs, S.; Schmeide, K.; Bubner, M.; Brendler, V.; Funke, H.; Geipel, G.; Hennig, C.; Roßberg, A.; Heise, K. H.; Bernhard, G.

kein Abstract

  • Lecture (Conference)
    Intern. Konferenz Actinides 2001, Hayama, Japan 4.-9-11-2001

Permalink: https://www.hzdr.de/publications/Publ-4675
Publ.-Id: 4675


Ions for materials research: surface modification and analysis at Rossendorf

Möller, W.

  • Lecture (others)
    Institute of Applied Physics, University of West Bohemia, Pilsen, CZ, 20.12.2001

Permalink: https://www.hzdr.de/publications/Publ-4674
Publ.-Id: 4674


Grundlagen der Ionen-Festkörper-Wechselwirkung

Möller, W.

  • Lecture (others)
    Sommerschule "Nukleare Sonden und Ionenstrahlen", Bad Blankenburg, 24.09.2001

Permalink: https://www.hzdr.de/publications/Publ-4672
Publ.-Id: 4672


Ionenstrahlen in der Materialforschung

Möller, W.

  • Lecture (others)
    FhI für Keramische Technologien und Sinterwerkstoffe, Dresden, 18.6.2001

Permalink: https://www.hzdr.de/publications/Publ-4671
Publ.-Id: 4671


Interaction of Actinides with the Predominant Indigenous in Äspö Aquifer

Moll, H.

kein Abstract

  • Lecture (others)
    Workshop University of Gotheburg, 16.-18.10.2001

Permalink: https://www.hzdr.de/publications/Publ-4669
Publ.-Id: 4669


Solvent Effects on Uranium(VI) Fluoride and Hydroxide Complexes Studied by EXAFS and Quantum Chemistry

Vallet, V.; Wahlgren, U.; Schimmelpfennig, B.; Moll, H.; Szabó, H.; Grenthe, I.

  • Inorg. Chemie 40, 3516-3525 (2001)

Permalink: https://www.hzdr.de/publications/Publ-4666
Publ.-Id: 4666


Seminar-Vortrag am Institut für Tieftemperaturphysik der TU Dresden (23.05.2002): Gateoxides with embedded Si-nanoclusters for memory applications - preparation by magnetron sputtering, electrical and optical characterization

Schmidt, J. U.

In silicon-nanocluster (Si-NC) memories, Si-NC embedded in the gate oxide of a MOSFET are used to store and release electrons thereby modifying the threshold of a transistor. This article describes the formation of its core functional structure, the Si-NC MOS memory capacitor, by annealing a SiO2/SiOX (x < 2) stack, deposited onto a thin direct tunneling oxide on silicon by a sputtering method. To achieve a high density of isolated Si-NC, both, the initial silicon excess in the SiOX layer and the thermal annealing treatment must be optimized. Optimum conditions are expected just at the end of the nucleation stage of the NC ensemble. Therefore the effect of various rapid thermal anneals (RTA) on SiOX/Si structures with different silicon excess x was investigated focusing on two optical methods: infrared absorption and photoluminescence (PL). The rate of nucleation and phase separation was found to depend strongly on both, silicon excess and annealing temperature. The characteristic size dependence of Si-NC PL was used to differentiate annealing regimes yielding NC ensembles being 'frozen' in the process of nucleation or in their growth/ripening phase respectively. Additionally, Si-NC MOS memory capacitors were prepared and characterized using both, optical and electrical tests. The devices prepared under optimized conditions yield a high flat-band shift and good charge retention characteristics.

Keywords: Silicon rich oxide; Silicon Nanocclusters; Photoluminescence

  • Lecture (others)
    Seminar-Vortrag am Institut für Tieftemperaturphysik der TU Dresden (23.05.2002)

Permalink: https://www.hzdr.de/publications/Publ-4665
Publ.-Id: 4665


Consequences of Neutron-Proton Pairing Correlations for the Rational Motion of the N=Z Nucleus 72Kr

Kelsall, N. S.; Wadsworth, R.; Wilson, A. N.; Fallon, P.; Macchiavelli, A. O.; Clark, R. M.; Sarantites, D. G.; Seweryniak, D.; Svensson, C. E.; Vincent, S. M.; Frauendorf, S.; Sheikh, J. A.; Ball, G. C.

High-spin states in the N = Z nucleus 72Kr were populated using
the 40Ca(36Ar,2p2n) reaction at a beam energy of 145 MeV.
The yrast band has been observed up to a tentative spin of 20 h.
Nonyrast rotational structures have also been observed for the first time.
The alignment of g9/2 protons and neutrons in the yrast band is observed to
be significantly delayed relative to the heavier even-even Kr isotopes.
Exact deformed cranked shell model calculations suggest that this could be due to the combined effect
of isovector (T = 1) and isoscalar (T = 0) neutron-proton pairing correlations.

  • Phys. Rev. C 64 (2001) 024309

Permalink: https://www.hzdr.de/publications/Publ-4657
Publ.-Id: 4657


Tritium depth profiling by AMS

Pilz, W.; Friedrich, M.; Bekris, N.; Glugla, M.; Kiisk, M.; Liechtenstein, V.; (Editors)

Tritium depth profiles in carbon have been determined at the Rossendorf AMS facilities during the past seven years. The samples have been cut from tiles of the inner walls of the fusion reactors ASDEX-upgrade Garching, JET Culham and TFTR Princeton. The high tritium content required a dedicated AMS facility to prevent any contamination of the versatile 3 MV Tandetron. It is based on an SF6-insulated 100 kV tandem accelerator equipped with a DLC stripper foil of about 1µg/cm². Depth profiles of deuterium and other light elements can also be measured in SIMS mode or AMS mode depending on concentrations.

Keywords: Mass spectrometry; Tritium; Fusion; Electrostatic accelerators

  • Contribution to proceedings
    proceedings of conference HIPAN02,Neptun,Romania,September 2-6,2002

Permalink: https://www.hzdr.de/publications/Publ-4656
Publ.-Id: 4656


Comparison of the scintillation properties of LSO:Ce manufactured by different laboratories and of LGSO:Ce.

Kapusta, M.; Moszynski, M.; Balcerzyk, M.; Braziewicz, J.; Wolski, D.; Pawelke, J.; Klamra, W.

We measured photoelectron yield, light output, decay times of the light pulses, cerium concentration, energy resolution and time resolution of LSO:Ce manufactured by different laboratories and LGSO:Ce. The LSO samples show excellent scintillation properties: high light output, close to 30,000 ph/MeV and good energy resolution of 7.3% FWHM for 137Cs gamma-source full energy peak. Time resolution measured in geometry fulfilling the PET scanners requirements is equal to 450 ps.
We also present results from the measurements with LGSO:Ce by Hitachi Chemical Co., which is of similar chemical composition to LSO. LGSO, at present stage of development, shows about 20% lower light output than LSO and energy resolution of 12.4% FWHM for 662 keV gamma-rays.
LSO crystals used in our studies posses similar in scintillation properties, although we suppose that the details of the productions method are different due to the differences in Ce concentration. LGSO is a new and very promising scintillator due to lower background radiation in comparison to LSO, but it features worse energy resolution and smaller number of photoelectrons.

  • IEEE Trans. Nucl. Sci. 47 (2000) 1341-1345

Permalink: https://www.hzdr.de/publications/Publ-4655
Publ.-Id: 4655


Probing Meson Spectral Functions with Double Differential Dilepton Spectra in Heavy-Ion Collisions

Kämpfer, B.; Pavlenko, O. P.

The double differential dilepton spectrum dN/ (dM2 dM^2)
at fixed transverse mass M^ allows a direct access to the vector meson spectral
functions. Within a fireball model the sensitivity of dN/ (dM2dM^2) against variations of both the in-medium properties of mesons and the dynamics of the fireball is investigated. In contrast to the integrated invariant-mass spectrum dN/dM2, in the spectrum dN/dM2dM^2 with fixed M^ the ω signal is clearly seen as bump riding on the ρ background even in case of strong in-medium modifications.

  • Eur. Phys. J. A 10 (2001) 101-107

Permalink: https://www.hzdr.de/publications/Publ-4653
Publ.-Id: 4653


Evidence for Chiral Symmetry in 136Pm and 138Eu

Hecht, A. A.; Beausang, C. W.; Zyromski, K. E.; Balabanski, D. L.; Barton, C. J.; Caprio, M. A.; Casten, R. F.; Cooper, J. R.; Hartley, D. J.; Krücken, R.; Meyer, D.; Newman, H.; Novak, J. R.; Paul, E. S.; Pietralla, N.; Wolf, A.; Zamfir, N. V.; Jing-Ye, Z.; Dönau, F.

High-spin states in the doubly odd N=75 nuclei Pm-136 and Eu-138 were populated following the Sn-116(Mg-24,p3n) and Cd-106(Cl-35,2pn) reactions, respectively. A new ΔI = 1 band is reported in Eu-138 and new data are presented for the recently reported band in Pm-136. Polarization and angular correlation measurements have been performed to establish the relative spin and parity assignments for these bands. Both bands have been assigned the same πh11/2νh11/2 structure as the yrast band and are suggested as candidates for chiral twin bands.

Permalink: https://www.hzdr.de/publications/Publ-4652
Publ.-Id: 4652


Detailed Spectroscopy of the Chiral-Twin Candidate Bands in 136Pm

Hartley, D. J.; Riedinger, L. L.; Riley, M. A.; Balabanski, D. L.; Kondev, F. G.; Laird, R. W.; Pfohl, J.; Archer, D. E.; Brown, T. B.; Clark, R. M.; Devlin, M.; Fallon, P.; Hibbert, I. M.; Joss, D. T.; Lafosse, D. R.; Nolan, P. J.; O'Brien, N. J.; Paul, E. S.; Sarantites, D. G.; Sheline, R. K.; Shepherd, S. L.; Simpson, J.; Wadsworth, R.; Jing-Ye, Z.; Semmes, P. B.; Dönau, F.

The chiral-twin candidate bands recently observed in 136Pm have been extended to high spins [I = (21)] using the Gammasphere γ-ray spectrometer and the Microball charged-particle detector array.
A more-detailed spectroscopy of the bands was possible, where the rotational alignments and B(M1)/B(E2) ratios confirm that both sequences have the πh11/2νh11/2 configuration. Particle-rotor calculations of intraband and interband transition
strength ratios of the chiral-twin bands are compared with experimental values for the first time. Good agreement was found between the predicted transition strength ratios and the experimental values, thus supporting the possible chiral nature of the configuration in πh11/2νh11/2
136Pm.

Permalink: https://www.hzdr.de/publications/Publ-4651
Publ.-Id: 4651


Symmetries of the Rotating Mean Field

Frauendorf, S.

The discrete symmetries of the rotating mean field lead to a variety of rotation
al bands with different sequences of spin and parity. We focus on the
breaking of chiral symmetry in rotating triaxial nuclei.

  • Acta Phys. Polonica B 32 (2001) 2661

Permalink: https://www.hzdr.de/publications/Publ-4650
Publ.-Id: 4650


Atomic Clusters as a Branch of Nuclear Physics

Frauendorf, S.; Guet, C.

The conduction electrons in clusters of simple metal atoms are approximatively i
ndependent and free. Nucleons in nuclei also behave as delocalized
and independent fermions. This generic behavior generates analogies between
metal clusters and nuclei, such as the shell structure, the shapes,
and the dipole vibration mode. However, there are also major differences
that arise from the presence of ions in metal clusters. Fission of nuclei and
clusters, and particle emission from them, reveal these differences.

  • Ann. Rev. of Nucl. and Part. Scien. 51 (2001) 219

Permalink: https://www.hzdr.de/publications/Publ-4649
Publ.-Id: 4649


Spontaneous Symmetry Breaking in Rotating Nuclei

Frauendorf, S.

The concept of spontaneous symmetry breaking is applied to the rotating mean field of nuclei. The description is based on the tilted-axis cranking model, which takes into account that the rotational axis can take any orientation with respect to the deformed density distribution. The appearance of rotational bands in nuclei is analyzed, focusing on weakly deformed nuclei at high angular moment um. The quantization of the angular momentum of the valence nucleons leads to new phenomena. Magnetic rotation represents the quantized rotation of the anisotropic current distribution in a near pherical nucleus. The restricted amount of angular momentum of the valence particles causes band termination. The discrete symmetries of the mean-field Hamiltonian provide a classification scheme of rotational bands. New symmetries result from the combination of the spatial symmetries of the density distribution with the vector of the angular momentum. The author discusses in detail which symmetries appear for a reflection-symmetric density distribution and how they show up in the properties of the rotational bands. In particular, the consequences of rotation about a nonprincipal axis and of breaking the chiral symmetry are analyzed. Also discussed are which symmetries and band structures appear for non-reflection-symmetric mean fields. The consequences of breaking the symmetry with respect to gauge and isospin rotations are sketched. Some analogies outside nuclear physics are mentioned. The application of symmetry-restoring methods to states with large angular momentum is reviewed.

  • Rev. Mod. Phys. 73 (2001) 463

Permalink: https://www.hzdr.de/publications/Publ-4648
Publ.-Id: 4648


Results from FOPI on Strangeness in Nuclear Matter at SIS Energies

Crochet, P.; Alard, J. P.; Andronic, A.; Averbeck, R.; Barret, V.; Basrak, Z.; Bastid, N.; Belyaev, I.; Bendarag, A.; Berek, G.; Caplar, R.; Cindro, N.; Devismes, A.; Dupieux, P.; Dzelalija, M.; Eskef, M.; Finck, C.; Fodor, Z.; Gobbi, A.; Grishkin, Y. L.; Hartmann, O.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Koczon, P.; Korolija, M.; Kotte, R.; Kowalczyk, M.; Kress, T.; Kutsche, R.; Lebedev, A.; Lee, K. S.; Leifels, Y.; Manko, V.; Merlitz, H.; Mohren, S.; Moisa, D.; Neubert, W.; Nianine, A.; Pelte, D.; Petrovici, M.; Plettner, C.; Rami, F.; Reisdorf, W.; de Schauenburg, B.; Schüll, D.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynka, K.; Smolyankin, V.; Somov, A.; Stockmeier, M. R.; Stoicea, G.; Vasilev, M.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Yang, J. T.; Yushmanov, I.; Zhilin, A.

Experimental data on charged kaon phase space distributions and strangeness sidewards
flow measured with the FOPI detector at SIS/GSI are presented.
Comparisons are made with the predictions of transport models investigating the in-medium
kaon-nucleon potential.

  • J. Phys. G: Nucl. Part. Phys. 27 (2001) 267

Permalink: https://www.hzdr.de/publications/Publ-4647
Publ.-Id: 4647


The halogen effect in the oxidation of intermetallic titanium aluminides

Schütze, M.; Schumacher, G.; Dettenwanger, F.; Hornauer, U.; Richter, E.; Wieser, E.; Möller, W.

Stoichiometric TiAl and two quasi-technical TiAl alloys were investigated in the temperature range of 800¯1000°C with regard to the halogen microalloying effect on oxidation resistance. The halogens Br, Cl, F and I were introduced into the material surface by ion implantation with different doses and energies before the thermogravimetric oxidation experiments were started. The results show that a very low "homeopathic" amount of these halogens at the oxide scale/metal interface activates a mechanism of selective Al-oxidation which changes oxidation behavior
from fast mixed titania/alumina kinetics to slow pure alumina kinetics. A model is described which explains this change in kinetics supported by quantitative data from thermodynamic calculations. The halogen microalloying effect offers a high potential for the improvement of oxidation resistance of TiAl alloys for technical applications.

Keywords: Intermetallics; Ion implantation; Chlorination; Interfaces; Selective oxidation

  • Corrosion Science 44 Issue 2 (2002) 303-318

Permalink: https://www.hzdr.de/publications/Publ-4646
Publ.-Id: 4646


On the Way to a Superconducting RF-Gun: First Measurements with the Gun Cavity

Barthels, E.; Büttig, H.; Gabriel, F.; Grosse, E.; Janssen, D.; Bushuev, A.; Karliner, M.; Konstantinov, S.; Kruchkov, S.; Myshkin, O.; Petrov, V.; Sedlyarov I, I.; Tribendis, A.; Volkov, V.; Sandner, W.; Will, I.; von Stein, P.; Vogel, H.; Matheisen, A.; Pekeler, M.; Thiel, C.

The parameters of a superconducting RF gun cavity have been measured in a test cryostat of DESY. A field strength of 31.8 MV/m at the cathode has been obtained.

  • Nucl. Instr. Meth. A 445 (2000) 408

Permalink: https://www.hzdr.de/publications/Publ-4645
Publ.-Id: 4645


Synthesis of epitaxial diamond grains in cubic SiC by high temperature carbon implantation

Pécz, B.; Tóth, L.; Heera, V.; Skorupa, W.

3C-SiC have been implanted with carbon ions at 60 keV to a dose of 3x10^17 and 1x10^18 cm^-2. All of the implantation experiments were carried out at elevated temperature in the range of 900°C-1200°C to study the phases, which are formed, when excess carbon is introduced into the SiC lattice. At 1100^C and at 1200°C small diamond grains are formed; these are embedded in the SiC and form perfectly oriented crystallites of a few nm size. Diamond is formed in SiC at 900°C as well, however, at high dose rate the impinging carbon ions can destroy the nucleated diamond grains.

Keywords: Ion beam synthesis; diamond; SiC

  • Contribution to external collection
    Inst. Phys. Conf. Ser. No 169 (2001) 367-370

Permalink: https://www.hzdr.de/publications/Publ-4644
Publ.-Id: 4644


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