Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Positron annihilation spectroscopy of thermally grown and deposited SiO2 films on silicon shows in a non-destructive manner that these films have a gradient in their density. The gradient is most pronounced for the oxide grown in dry oxygen. Oxidation in water-containing ambient results in an oxide with reduced gradient, similarly to the gradient in the deposited oxide. These observations are in accordance with earlier optical and other studies using stepwise etching or a set of samples of varying thickness. The effective oxygen charge, which is very likely one of the reasons for the difference in the W parameters of silica glass and quartz crystal, could be even higher at some localized configurations in the SiO2 films resulting in increased positron trapping.

Theoretical calculations of positron lifetimes, affinities and core electron contributions to Doppler broadening spectra are carried out for several phases (polymorphs) of SiO2. An interesting feature of SiO2 is that not all polymorphs have the same coordination of Si and O atoms, which also affects positron properties. The calculated quantities are compared with available experimental data and discussed with reference to SiO2/Si interfaces.

The Ninth International Workshop on Slow Positron Beam Techniques for Solids and Surfaces, SLOPOS-9, was held at Dresden, Germany, from 16 to 22 September 2001. This series is devoted to provide an informal platform of presentation and discussion of latest results in this quickly advancing field, covering such scientific topics as positron beam development and design, including intense beams and microscopes, developments in experimental and analytical techniques, positroni-defect interactions and defect structure, defect profiling in bulk and layered structures, positron implantation and thermalisation, positronic and other surface processes, surface modification and coatings, and positron atomic physics.

At the moment of printing the Program/Abstract (31 August), 92 persons from 20 countries all over the world had registered for participation. The program represented a careful balance of invited (12), oral (50), and poster (28) presentations, mixed with cultural events (welcome reception, visit to the superconducting accelerator ELBE (under construction at Rossendorf), excursion, and banquet). The awful terrorist attacks in the US on 11 September had a minor but noticeable impact on our conference. Several American colleagues had to cancel their participation for subjective or objective reasons, or could finally participate only in part due to unavailability of airline capacity in time. Four participants from other countries had to cancel their participation at the last minute for other reasons.

Finally, 86 persons from 18 countries participated in the workshop, and the program still consisted of 11 invited, 43 oral, and 28 poster contributions. The program was organised into 14 oral sessions, 2 poster sessions, and 2 round-table discussions. The last dealt with special aspects of positron sources, including intense ones, and the question of where to meet in 2004 for SLOPOS-10. The competition was decided in an open and direct vote in favour of Doha, Qatar. The participants of the
workshop expressed their feelings of great sadness and sympathy for those directly and indirectly involved in the terrorist attacks in the US in a book of condolence during the workshop. In our opinion, the decision to meet next time in Doha, Qatar underlines the internationality of science which may not be influenced by terrorist activities. The closing remarks given on behalf of all colleagues by Philip Sterne from Lawrence Livermore National Laboratory, USA confirmed that this workshop was an outstanding success both from the scientific program and from its infrastructure and stimulating atmosphere, including all the cultural events.

In total, 59 papers have been accepted for publication after extensive reviewing. For their cooperative and very conscientious work we are grateful to the referees. We would like to thank the editors of Applied Surface Science for giving continuity to the publication series of SLOPOS proceedings.

The location of the workshop in the new part of Germany, in Dresden, allowed us to keep the average costs per participant to an acceptable level. In addition, due to generous sponsorship from our local ministry it was possible to arrange the participation of 10 colleagues from eastern Europe. However, we would like to express our thanks to all the sponsors, and especially all un-named people at the venue, Forschungszentrum Rossendorf, and the locations of our cultural events who have been very involved in contributing to the overall success of the workshop.

no abstract delivered from author

The positron work function of 6H-SiC was determined to be –2.1±0.1 eV from an analysis of the energy spectrum of
positrons reemitted from the surface. The positron reemission yield, highest in the sample inserted into vacuum after
atmospheric exposure and cleaning with ethanol, was significantly reduced after sputtering with 3 keV, 125 µA min Ne+ ions.
The yield was not recovered even after annealing at 900 °C, presumably due to the stability of sputter induced defects.
Sputtering at lower energies caused a smaller decrease in the reemission yield that was largely recovered after annealing at 850 °C. Analysis using electron induced Auger electron spectroscopy and positron-annihilation-induced Auger electron spectroscopy indicated that the surface was Si enriched after sputtering and C enriched after subsequent annealing. Values of positron diffusion length and mobility in the unsputtered material were extracted from the dependence of the reemission yield on the beam energy. The application of SiC as a field-assisted positron moderator is discussed.

no abstract delivered from author

Slow positron implantation spectroscopy has been used to determine the surface and near surface defect profile in LiF after implantation with 100 keV argon ions for a range of fluences from 1013 to 1016 cm-2. The measured S-parameter is used to characterise the radiation damage as a function of depth. The spatial extent of the defect distributions was estimated by employing the computer program VEPFIT. Maximum lattice damage is shown to occur at incident positron energy of 4.0 keV for low doses and 5.0 keV for the high dose. This energy corresponds to a sample depth of about 200 nm. The positron annihilation spectroscopy results are correlated with optical absorption measurements on the crystals.

Slow Positron Implantation Spectroscopy (SPIS) is a nondestructive method whereby positrons of a predetermined energy are implanted into a solid. In a certain depth region they annihilate with electrons. The motion of the positron-electron pair prior to the annihilation causes a Doppler broadening of the photopeak. The Doppler broadening of the annihilation line, characterized by two lineshape parameters, is measured in dependence on the incident positron energy and thereby on the depth where the annihilation took place.
SPIS is well known for its sensitivity to vacancy-type defects in solids. For this reason, this method has been applied to investigate the damage created by implantation of Al+ ions into epitaxial 6H-SiC. Al+ was implanted at an energy of 200 keV and a fluence of 1x1015 cm-2. In order to minimize the implantation-induced damage the substrate temperature was varied from room temperature up to 800 oC in steps of 200 degrees. Depth dependent defect profiles were calculated from the measured lineshape parameters versus the incident positron energy using the software package VEPFIT [1]. These depth profiles show significantly deeper reaching defects as calculated by TRIM [2]: whereas TRIM calculations result in a maximum depth of vacancies of about 300 nm, the positron measurements show that multiple vacancy clusters can be found up to a depth of more than 1µm below the surface. In addition to the extraction of the depth distribution of the damage it was possible to estimate the size of the vacancy agglomerates from the positron data in dependence on the substrate temperature and the depth position. The size of the damage and its depth distribution will be compared for different substrate temperatures during implantation and it will be shown that the damage minimum is obtained at a substrate temperature of 190 oC.

[1] A. van Veen, H. Schut, J. de Vries, R. A. Hakvoort, and M. R. Ijpma, in Positron beams for solids and surfaces, edited by P. J. Schultz, G. R. Massoumi, J. P. Simpson (American Institute of Physics, New York, 1990), p. 171
[2] The Stopping and Range of Ions in Solids, eds. J. F. Ziegler, J. P. Biersack, and U. Littmark (Pergamon Press, NewYork, 1999)

Fullerene like carbon nitride (CNx) is a nanostructured material consisting of bent and intersecting graphitic layers. It combines the unique properties of being hard and elastic at the same time, which results in a fracture though and compliant material. Homogeneous well-structured fullerene like CNx thin films are commonly grown by DC reactive magnetron sputtering of graphite in an N2/Ar mixture. The nitrogen content in the films is fairly constant, limited due to the formation of volatile CN species at the substrate surface. Even though the composition is similar the structure and properties of these films can be varied over a very wide range in a comparatively narrow process window. This suggests that beside C and N ions and atoms other species like CN clusters might play an important role during growth. Here direct effects as growth templates or nucleation sites should be considered.

Plasma analysis was carried out during this study in order to investigate the presence, number, and energy of clusters consisting of C and N and their possible effects upon the growing film. A number of techniques, such as spatially resolved wire and ion probe measurements and energy selective mass spectrometry were used to characterize the composition and energetic conditions of a N2/Ar DC sputtering plasma in front of a single graphite target, depending on discharge current, total pressure and gas composition.

In dieser Arbeit wurde das Master-Curve (MC)-Konzept zur Charakterisierung der Zähig-keitseigenschaften über die Wanddicke eines Blockes aus Reaktordruckbehälterstahl ASTM A533B Cl. 1 angewendet. Es handelt sich dabei um das IAEA-Referenzmaterial JRQ. Die Prüfung von SENB-Proben mit Charpy-Geometrie erfolgte bei quasi-statischer und dynami-scher Belastung. Dynamisch wurden die Proben mit einem instrumentierten Pendelschlag-werk bei einer Schlaggeschwindigkeit von 2,8 m/s und quasi-statisch mit einem servohydrau-lischen Prüfsystem bei 0,2 mm/min geprüft. Im unterem Bereich des Duktil-Spröd-Übergangs (DBT) sind beim Versagen der Proben durch Spaltbruch Bruchzähigkeitswerte KJc nach ASTM E1921 ermittelt und ausgewertet worden. Die Berechnung der Referenztemperaturen T0 erfolgte nach der Multi-Temperatur (MT)-Methode des Master-Curve-Konzeptes. Zum Vergleich zu diesen bruchmechanischen Referenztemperaturen sind zusätzlich konventionelle Charpy-V-Übergangstemperaturen ermittelt worden.
Der Temperaturbereich für die Ermittlung gültiger KJcd-Werte mit dem instrumentierten Kerbschlagbiegeversuch wird bei kleinen Werten durch die Messung der wahren Schlagkraft (3J-Kriterium) bestimmt und zu höheren Werten durch das Gültigkeitskriterium nach ASTM E1921 begrenzt. Bei den realisierten Schlaggeschwindigkeiten von 2,8 m/s reicht der Gültig-keitsbereich für die KJcd-Werte von ca. 80 MPam1/2 bis 160 MPam1/2.
Der Verlauf der bei quasi-statischer und dynamischer Belastung ermittelten und nach dem Master-Curve-Konzept auf eine Probengröße von 25,4 mm (1T) umgerechneten KJc-1T-Werte folgt der Master-Curve. Eine direkte Anwendung der Master-Curve auf modifizierte Charpy-Test-Bedingungen ist nach den Ergebnissen dieser Arbeit möglich. Die Belastungsgeschwin-digkeit beeinflusst deutlich die Referenztemperatur T0. Die mit einer Belastungsgeschwindig-keit von 2,8 m/s ermittelten dynamische Referenztemperaturen T0dy liegen ca. 74 K höher als das quasi-statisch ermittelte Äquivalent T0st. Sie liegen auch höher als die Charpy-V-Übergangstemperaturen. Das Ergebnis ordnet sich in die in der Literatur für unterschiedliche Belastungsgeschwindigkeiten angegebenen Spanne der Erhöhung von T0 von 30 bis 120 K ein.
Die Ergebnisse zeigen, dass mit den dynamischen Referenztemperaturen wie auch mit den quasi-statischen Referenztemperaturen unterschiedliche Materialzustände charakterisiert wer-den können. Master-Curve-Referenztemperaturen und Charpy-V-Übergangstemperaturen zeigen den gleichen Verlauf über die Wanddicke des untersuchten RDB-Stahlblockes mit starken Unterschieden im Gefüge an den Randlagen und in der Blockmitte. In der Blockmitte ist das Gefüge des untersuchten RDB-Stahls sehr inhomogen und die in der ASTM E1921-97 genannte Mindestprobenzahl von 6 reichte zur Ermittlung von T0 nicht aus. Bei der Anwen-dung der MT-Methode waren mindestens 8 Proben notwendig, um eine gültige T0 zu erhalten. Die Anwendung der MT-Methode ist der Eintemperaturmethode vorzuziehen. Sowohl bei quasi-statischer Belastung als auch bei dynamischer Belastung wurde ein geringer Einfluss der Prüftemperatur auf die T0 ermittelt.

Titanium surfaces were treated by exposing them to a beam of sodium ions. Sodium titanate was shown to be incorporated within the oxidic titanium surface. The ion- implanted surfaces were examined for their reactivity by immersion in a simulated body fluid, which showed the formation of surface-bound hydroxyapatite. The surface was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and optical and electron microscopy. The surface hydroxyl concentration was determined using the nuclear reaction 1H(15N,alpha, gamma)12C. Surface-related parameters that may affect hydroxyapatite nucleation are discussed in term of the electrical double layer.

Measurements of exclusive pp ® NKY reactions with beam momenta in
the range 2.5÷3.2 GeV/c are underway at COSY using the Time-of-Flight spectrometer TOF.
The high granularity of the detector, which covers almost the full phase space, allows to measure
differential distributions and total cross sections as well.
Moreover the hyperon polarization can be studied either with polarized beam
or target. Some preliminary results at different energies are given.

The electrical conductance of a-Si:H is studied in films deposited on ion-exchanged optical waveguides in glass substrates. The effect of chemical composition of the near-surface region of the waveguide is considered from the viewpoint of the electrical instability of a-Si:H related with the penetration of Na ions from the substrate into the film. The optical waveguides have been prepared by Ag+-Na+ or K+-Na+ thermal or field-assisted ion exchange in soda-lime glass (SLG). The Na concentration in the near-surface region of the glass substrate has been established by means of elastic recoil detection analysis (ERDA). The obtained results demonstrate the possibility of reduction of electrical instability of a-Si:H films deposited on optical waveguides in glass. It is shown that in some cases an additional Na depletion of the near-surface region is necessary to avoid Na contamination of the a-Si:H films.

The behaviours of implanted hydrogen in Ti225 alloy is investigated in this work. Hydrogen ion beam implantation was used to load hydrogen into the sample. Resonant Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA) were applied to obtain the depth profiles of hydrogen versus implantation dose. Two kinds of hydrogen have been found in the samples, one is as quasi-mobile and another is chemically bonded hydrogen. Three hydrogen precipitation stages, which relate to the different chemical states of hydrogen, are determined. Using X-Ray Diffraction (XRD), the hydride phase transformation from solid solution in titanium to titanium hydride (TiH1) and then titanium dehydrate (TiH2) tetragonal structure has been observed. The change is dose dependent in the implantation dose range between 2x1016 and 6x1017 H/cm2. The phase transformation from TiH1 to TiH2 occurs at an implantation dose greater than 1x1017 H/cm2 but finishes at a dose of 6x1017H/cm2 with the saturation of hydrogen concentration at about 23 at. %. The inhomogeneous planar distribution of the hydrogen was also observed using both scanning micro-probe ERDA and Scanning Electron Microscopy (SEM).

We report the first polarization transfer measurements for exclusive hyperon production reactions.
The normal spin transfer coefficient D_NN for
pp®pK⁺K^- L is large and negative for
forward L production at a beam momentum of 3.67GeV/c, a result
qualitatively consistent with expectations for a mechanism dominated by kaon-exchange and rescattering.
The sign of D_NN is opposite to that observed in the fragmentation regime for
inclusive L production at much higher energies.

The behaviour of hydrogen implanted into Ti225 alloy is studied in this work. The hydrogen depth profiles vs. different implantation doses and ion energies were measured with resonant Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA). The hydrogen diffusion to the surface at room temperature is found from the depth profiles which differ from their theoretical simulation due to a more complex diffusion and hydrogenation than described at present by theory. A rapid formation of titanium hydrides, i.e. TiH1 and TiH2 , is found in the implantation dose range between 6x1016 and 2x1017 H1/cm2 by X-ray diffraction. The phase transformation from TiH1 to TiH2 crystal structure starts after implantation of 1x1017 H1/cm2, and is finished at a dose of 6x1017H1/cm2 at which a saturation of the hydrogen concentration of about 23 at.% is found from the depth profiles. The titanium hydrides are inhomogeneously distributed in the sample. The hydrogen contour maps measured by the scan of micro-beam ERDA show dose-dependent inhomogeneities due to the hydride formation process. The radiation damage affects also the hydrogen concentration and out-diffusion. A defect-related trapping of hydrogen is observed by slow positron implantation spectroscopy (SPIS). The surface hydride layer on titanium acts as a highly effective barrier to oxygen. It is found that the oxidation ratio is strongly reduced already by implantation of only 2x1016 H1/cm2.

In order to investigate the hydrogen isotope accumulation at the erosion dominated inner walls of fusion experiments, several small carbon samples have been mounted in the inner wall tiles of the torus of the JET Joint Undertaking. After about 2.5 years of JET operation, including the extended D/T phase and the D/D cleaning phase, the samples have been removed and analysed by RBS, ERDA and AMS. In the near surface region only small T concentrations are measured. A much larger T concentration is found at depths between about 1 and 2 m. This may originate from energetic (~1 MeV) T which is produced during the D/D discharges and implanted to large depth. The lower energy (keV) T which is implanted during the D/T discharges became effectively removed from the inner wall, by isotope exchange with implanted D or H and/or by erosion of the wall. The total amount of T within a depth of about 2 m was found to be about 1-3×1013 T/cm2, while in a surface layer of about 0.5 m about 1-3×1012 T/cm2, about 2-4×1016 D/cm2 and about 4-9×1016 H/cm2 were measured.

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.

Übersicht über Methoden der Materialanalytik an Beschleunigern

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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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.

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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.

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.

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.

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Seminarvortrag ohne Abstract

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.

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.

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.

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.

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.

: 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.

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 l _s of the hypersound,
starting from l _s=l _E,
where l _E 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 l _s approaches l _E/2 the inverse
transitions show a resonant behaviour.

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.

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.

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.

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.

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.

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.

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.

Two new DI = 1 bands in the N = 75, doubly-odd nuclei ¹³⁶Pm and ¹³⁸Eu
are reported. These bands have been assigned the same
ph_11/2 nÄh_11/2
structure as the yrast band and show some of the features expected
from predicted chiral twin bands.

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.

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.

no abstract delivered from author

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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.

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.

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/Σ^-≈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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 R_P, indicating the presence of residual defects therein. The theoretical ballistic calculations ascribed the R_P/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 R_P/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 R_P/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 R_P/2 and obscure it of being visualized. Only the TEM specimens prepared by cleaving reveals cavities at R_P/2. Minimum damage production caused during the preparation of the TEM specimen using cleaving allows the imaging of the cavities at R_P/2.

no abstract delivered from author

New sideband partners of the yrast bands built on the i
p h _11/2 n h _11/2
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

no abstract delivered from author

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.

Inclusive and exclusive (i.e. via the f resonance) K^- meson production
cross sections have been measured in proton-proton
reactions at T_beam = 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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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⁺[`(K<sup>0</sup>)] and a<sub>0</sub> <sup>+</sup> ® p <sup>+</sup> h.
Cross sections for a<sub>0</sub> <sup>+</sup> production as well as for the corresponding nonresonant channels
pp ® dK<sup>+</sup>[` (K⁰)] and pp ®dp ⁺ h are compared.
Especially in case of the final channel dp ⁺ h
high statistics measurements are necessary to extract the a₀ ⁺ signal from the nonresonant background.

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.

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.

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.

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

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