Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

A comparative study of the effect of H+ and Si+ ion implantation on the hydrogenated amorphous silicon (a-Si:H) has been carried out in order to explore the interaction of hydrogen with the structural defects and to separate their contribution to the intrinsic compressive stress in the films. a-Si:H films were prepared by plasma-enhanced chemical vapor deposition. Raman scattering spectroscopy and infrared spectroscopy have been used to study the variations of the short range order of the silicon network and of the hydrogen bonding configuration, respectively. It has been suggested that the essential difference in the structural damage introduced by H+ and Si+ ion implantation could be related with the insertion of molecular hydrogen.

For investigation of luminescent centre profiles cathodoluminescence (CL) measurements are used by means of variation of the primary electron (PE) energy from Eo = 0.5 to 3 keV. Applying a constant incident power regime Eo x jo = const, the depth profiles of luminescent centres are deduced im comparable magnitude from the electron energy transfer profiles dE/dx.
Thermally grown SiO2 layers of thickness d = 500 nm have been implanted by Ge+-ions of energy 350 keV and doses 5x1015 to 5x1016 ions/cm2. Thus Ge profiles with a concentration maximum at the depth of about dm = 240 nm are expected. Afterwards the layers have been investigated partially "as implanted" and after different thermal annealing up to Ta = 1100 °C for one hour in dry nitrogen.
After thermal annealing, not only the typical violet luminescence (at 400 nm) of the Ge centers is strongly increased but also the luminescent centre profiles are sharpened and shifted in a characteristic manner from about 250 nm to 170 nm depth towards the surface.
In Ge-doped SiO2 layers the red (R) luminescence due to non-bridging oxygen hole centres (NBOHC) of the silica matrix is preserved, but the huge violet (V) band at 400 nm is attributed to twofold co-ordinated =Ge: centres as observed also in rutile-like GeO2 crystals. These centres in Ge+ implanted silica layers are especially developed during thermal annealing accompanied by Ge nanocluster formation, probably embedded in a GeO2 (or GeOx) surrounding within the silica matrix.

The effect of ion implantation on mechanical stress in a-Si:H films was studied with the aim of separating the contributions that the hydrogen content and structural defects make to the intrinsic compressive stress. The a-Si:H films were prepared by plasma-enhanced chemical vapour deposition. Silicon ions with an energy of 160 keV were implanted and the implantation-induced structural damage was studied by means of Raman backscattering spectroscopy. The stress in the films was compressive and its value correlated with the short and intermediate range orders. The results have shown that the value of compressive stress in the material could be lowered by changing the structural order of the silicon network without changing the hydrogen content.

Cathodoluminescence (CL) and its temperature-dose behaviour are presented for di•erent crystalline and amorphous modifications of SiO₂ and GeO₂ as well as for Ge-doped SiO₂ layers. The crystalline samples include four-fold coordinated Si and Ge in hexagonal quartz and quartz-like crystals, respectively, as well six-fold coordinated atoms in tetragonal rutile-like crystals. The detected luminescence bands, in general, are attributed to three optical active luminescence centres: the two-fold coordinated silicon ( =Si:) and germanium ( =Ge:) centre, respectively, the nonbridging oxygen hole centre (NBOHC) and the self trapped exciton (STE). The first ones, the oxygen deficient centres (ODC), are especially developed in both, in the tetragonal crystal rutile-like modifications as well as in glassy states. The huge violet luminescence in Ge-implanted SiO₂-layers is attributed to the two-fold coordinated Ge in the silica matrix.

Thermally grown SiO2 layers of thickness d = 500 nm have been implanted by Ge+-ions of energy 350 keV and doses 5x1015 to 5x1016 ions/cm2. Thus Ge profiles with a concentration maximum at the depth of about dm = 240 nm are expected. Afterwards the layers have been investigated partially as implanted and after different thermal annealing up to Ta = 1100 °C for one hour in dry nitrogen.
For investigation of the luminescent center profile cathodoluminescence measurements are used under variation of the primary electron energy Eo = 0.5...30 keV. Applying a constant incident power regime Eo x jo = const the depth profiles of luminescent centers are deduced in comparable magnitude from the electron energy transfer profiles dE/dx.
After thermal annealing, not only the typical violet luminescence (at 400 nm) of the Ge centers is strongly increased but also the luminescent center profile is redistributed in a characteristic manner towards the surface. This process should be described by Ge diffusion processes, precipitation and finally Ge nanocluster formation.

K+-meson production in pA ( A = C,Cu,Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Jülich accelerator. The complete momentum spectrum of kaons emitted at forward angles, ϑ≤12°, has been measured for a beam energy of Tp = 1.0 GeV, far below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus.

Higher integration in semiconductor technology causes the need for ultra-shallow junctions. Novel techniques are necessary to achieve abrupt and sharp profiles of dopants at high activation levels without significant diffusion of dopants. Because common RTP techniques are limited in temperature ramping speed, alternative methods for ultra-short time annealing are of great interest. In this paper we report on recent results from flash lamp annealing (FLA). Si (100) wafers were implanted with 500eV B+ ions to a fluence of 1015 cm-2. FLA was carried out at temperatures in the range 1100-1200°C with a soak time of 2-20ms using a bank of xenon flash-lamps. With this technique the final temperature is reached within one millisecond. Preheating of the samples from the rear side was performed at 250, 500 and 750°C by a bank of halogen lamps. For comparison conventional RTP was performed at 1100°C and 1200°C for the shortest reliable time of 1s and longer times up to 80 s. The boron diffusion and the dopant activation were investigated by secondary ion mass spectroscopy (SIMS) and spreading resistance profiling (SRP). The activated doses after FLA were as high as 20% of the implanted dose confined in a layer of only 60nm. The mechanical deformation induced to the samples due to the heat shock was investigated with X-ray reflection. The intensity of the specularly reflected beam (CuK radiation, scattering angle = 0.8°) is detected as a function of the incidence angle. The profile width and the distances between possible subsidiary peaks give integral values of the surface waveness.

Ion beam synthesis (IBS) is a versatile instrument to circumvent obstacles dictated by the thermal equilibrium. The basic steps to perform ion beam synthesis include ion beam irradiation with stoichiometric doses into a target kept at a certain temperature followed by another dedicated annealing step. On the other hand the actual EEPROM´s basing on floating gate transistors are driven to their limits of performance. An advanced very promising approach to circumvent these problems bases on the concept of Si-and Ge-nanoclusters embedded into silicon dioxide layers using IBS.
We have performed room temperature implantation of high fluences (3..9x1015 cm-2) of silicon and germanium into silicon dioxide layers with a thickness in the range 20-30 nm. This was followed by an annealing step at 950°C for 30 sec using Rapid Thermal Annealing (RTP). The microstructure and the electrical properties were investigated using a variety of methods. It will be shown that this type of processing leads to the formation of nanoclusters and the formation of trapping centres within the silicon dioxide layers. First device tests look promising.

In the last years nanoclusters attracted much attention because of their outstanding properties for the use in opto- and microelectronics. As an example nanocrystal memories are a promising approach towards new scalable non-volatile memory structures [1, 2]. Because of their low programming voltages and the direct tunneling process for charging they overcome limitations of currently used flash EEPROM technologies. The simple structure and the possible process integration with only a few more additional process steps make this type of memory a well-suited candidate for applications in embedded systems. An effective method of producing nanoclusters in SiO2 is ion beam synthesis using Ge - or Si - implantation and subsequent annealing. This method allows the precise control over the distribution as well as the number of implanted ions and complies with common silicon technology.
This work is focused on the comparison of the properties of Si and Ge nanoclusters prepared by ion beam synthesis. Thin SiO2 films (20 and 30 nm,) were thermally grown on n-type (100) Si) and implanted with Ge+ (12 and 20 keV) and Si+ (6 and 12 keV) ions. Subsequently rapid thermal annealing was performed at 950°C for 30 s under a nitrogen atmosphere. Following that a poly-Si layer (300 nm) was deposited by LPCVD and subsequently doped with P+ ions. The poly-Si layer was etched to form the gate electrode of a MOS capacitor and several additional thermal treatment steps were carried out.

Microstructural investigations (XTEM, RBS and XPS) of Ge clusters showed dependent on the experimental conditions either only one volume cluster band or a two band structure consisting of one cluster band near the interface SiO2/Si and one volume band. All clusters were found in the amorphous state. As an example for 30 nm SiO2 layers implanted with 20 keV Ge+ ions to a dose of 5x1015 cm-2 show a sharp cluster band with a cluster density of 3.5x1011 cm-2 ( 50 %) in a distance of about 3 nm to the interface Si / SiO2. This structure is therefore of large interest for memory applications.
The process leading to the formation of this interface cluster band is based on the dynamics of the ion implantation. A model based on TRIM calculations, rate equation studies and 3D - kinetic Monte Carlo simulations explains this self organization process [3]. Small Si agglomerates are formed during implantation due to collisional mixing and near interface oxygen diffusion. During the annealing process they act as nucleation centers and diffusing Ge from the implanted Ge maximum is trapped at these centers and forms clusters. As a result a sharp - like cluster band is formed.

Charge storage effects of the MOS capacitors have been studied through I-V and high frequency C-V measurements after FN stress. For Ge implanted layers, samples containing bulk and interface clusters show larger programming window sizes but worse retention characteristics than samples with bulk clusters only. This means, that direct tunneling leads to a faster discharging of the clusters near the interface.
Memory effects of Ge and Si nanocrystal based memory structures were reported to be similiar in Ref. [2]. In our work however the behavior of Ge and Si nanocluster based MOS-capacitors was found to be different. The programming window using 6 V / 100 ms pulses for Ge based structures is larger than that for Si (2.0 V vs. 0.2 V).
In Fig. 1 investigations of the retention characteristics are shown. The samples have been stressed with pulses of 15 V / 10 ms. After the stress the samples were stored at a temperature of 250°C to get information about long term stability. The Si clusters show a large programming window even after 90 h storage at the elevated temparature. This implies, that Si clusters seem to be more promising for non-volatile memory applications. However, Ge clusters could be interesting for memory applications which do not require long retention times.

Surface alloying of Ti with Si has been performed with the use of high intensity pulsed plasma beams. In this technique, short, intense (1 µs, 3-4 J/cm²) plasma pulses serve as a source of heat to melt the near surface layer (up to 2 µm) of the Ti substrate togehter with a Si film (30 and 70 µg/cm²) pre-deposited on it. In the molten state, lasting a couple of microseconds, rapid diffusion of Si into Ti occurs leading to formation of new phases during rapid solidification of the molten surface layer. In the present work, an attempt has been undertaken to improve the mechanical properties of titanium via precipitation of hard stable phases in the Ti-Si system, is formed by the transient heat treatment. During subsequent annealing for 1 h at 800°C a fraction (14-43%) of Ti₅Si₃ transforms into TiSi. The presence of silicide precipitates in the near surface region layer of titanium increases dramatically its wear resistance.

Elastic recoil detection analysis has been used to study the interaction between the soda-lime glass substrates and the a-Si:H films. It has been established that H and Na ions penetrate from the near-surface region of the substrate into the deposited film. The results have shown that the influence of the substrate on the properties of a-Si:H can be strongly reduced by glass surface modification using the processes of ion exchange and ion extraction.

Since the end of the 1960's spreading resistance (SR) measurements have become a routinely used technique for determining charge carrier profiles in silicon. For wide band gap semiconductors however the application of this method is difficult because of the high barrier at the interface between probe tips and the semiconductor surface. In order to lower the barrier two different approaches can be taken. First, the material of the tips could be changed with respect to its work function. But there is a limited choice because of the required mechanical properties of the tips concerning high hardness and low brittleness. The other way is to lower the barrier by influencing the surface states of the semiconductor material. This is actually more promising.
A strong dependence of the SR values on the polishing material for beveling was reported in investigations for the wide band gap semiconductor GaAs [1]. For laser annealed 6H-SiC [2] and 3C-SiC [3] SR measurements have been reported, but very high measuring voltages (1 to 5 V) were used compared to the usual measurements on Si (10 mV). Ahmed et al. found an activation of more than 100% which points to problems in the interpretation of the measurement [2].

In this work the influence of mechanical processing, further annealing of the bevel and finally sputter cleaning on the SR measurements was investigated. The SiC - surface was beveled with a diamond emulsion on a rotating glass plate. Grain sizes of 1.0 µm and 0.1 µm were used. It was found that polishing with the smaller grain size leads to lower resistances. This is comparable to the results which are known for GaAs with Al2O3 emulsion from Ref. [1]. After beveling several of the samples were annealed under vacuum for 5 min at temperatures of 1300 to 1400°C. A modified thin layer (1 to 2 nm) at the surface was formed which resulted in a lowering of the barrier resistance. The measured resistance was lowered up to a factor of three but statistical variations increased.
In order to lower the barrier further, the influence of ion sputtering (Ar+, 2 keV) on the bevel before the measuring procedure was tested. The sputtering was carried out at a current density of 50 µAcm-2 for 300 s. During the process the temperature increased to 57 to 69°C. Subsequent SR measurements showed up to two orders of magnitude lower resistance. The shape of the depth profile remained the same and the statistical error of the SR dropped significantly. Samples with resistivities larger than 0.2 cm were not measurable after beveling but after subsequent sputtering. The resistivity range in which SR measurements can be carried out was extended to 3 cm. First investigations of SR depth profiles using this sputtering method show a very good reproducibility at remarkably small variations of the measured values.
The samples were implanted with Al+ at multiple energies of 450, 240, 115 and 50 keV to form a 500 nm thick homogeneously doped layer with plateau concentrations in the range of 5 1019 to 5 1021 cm-3. Various post annealing processes were carried out to cover a broad range of resistivities with the samples. Resistivities and mobilities were obtained from Hall measurements [4]. For SR profiling a SENTECH SR-210 device was used. The probe tips were made of sintered tungsten carbide with a tip diameter of 5 µm. The measuring voltage was kept constant at 10 mV allowing to measure resistance values up to 1 G . The highest spatial resolution of the apparatus was 5 nm and the probe tip load during the measurements 9 g.

References:

[1] G. Queirolo, J. Electrochem. Soc., 125 (10), 1672 (1978).
[2] S. Ahmed, C.J. Barbero and T.W. Sigmon, Appl. Phys. Lett. 66 (6), 712 (1995).
[3] J. A. Edmond, S.P. Withrow, W. Wadlin, R.F. Davis, Mat. Res. Soc. Symp. Proc.,
Vol. 77, 193 (1987).
[4] D. Panknin , H. Wirth, M. Mücklich, W. Skorupa, Mat. Sci. Engin. B56 (1999), in print

Ion beam synthesis (IBS) as a powerful tool for the modification of ultrathin layers allows the formation of functional nanostructured layers for micro- and optoelectronics. Such modified SiO2 layers are promising candidates for future non-volatile memory devices. Furthermore SiO2 layers containing nanostructures produced by IBS using group IV elements show strong blue-violet photo- and electroluminescence (EL) which is of great interest for novel optoelectronic devices.
In this paper we will report on our recent progress in the microstructural and electrical investigation of Ge and Si rich silicon dioxide layers. The group IV elements were implanted into thermally grown SiO2 layers to atomic concentrations of 0.3 .. 6% followed by different annealing steps. The microstructural properties were investigated using TEM, RBS and EDX. Electrical measurements using IV, Photo - IV and CV methods were focused on the injection and conduction mechanism as well as charge storage properties. The determined position of the charge centroid correlates well with the microstructural results. It will also be shown by a method combining IV and CV measurements that not only electron injection from the substrate but also hole injection from the top electrode takes place. A direct comparison of these results to the EL properties provides new impact in the understanding of the EL excitation mechanism.

In den hier beschriebenen Untersuchungen werden Nanostrukturen durch Ionenimplantation in thermisch auf einen Siliziumwafer (100, n-Typ) aufgewachsene SiO2 - Schichten erzeugt. Im Anschluß an die Ionenimplantation werden durch eine Temperung Strahlenschäden ausgeheilt und die Clusterbildung angeregt. Die so erhaltenen Nanocluster weisen Größen von 4 ... 6 nm auf. Als Frontkontakt der Lumineszenzstrukturen wird eine aufgesputterte transparente Indium-Zinnoxid (ITO) - Schicht lithographisch in kreisrunde Flächen von 0.2mm2 strukturiert. Der Rückseitenkontakt wird durch Al - Beschichtung der Wafersrückseite hergestellt.
Die Metall-Oxid-Halbleiter (MOS) - Anordnung mit clusterhaltigen Schichten wird durch eine zwischen der ITO - Deckelektrode und dem Si - Substrat angelegte Spannung zur Elektrolumineszenz (EL) angeregt. Die emittierte Lichtleistung hängt linear von der Anregungsleistung ab. Für Untersuchungen zur Photolumineszenz (PL) erfolgte die Anregung mit einer Xenon - Lampe bei einer Wellenlänge von 250 nm. Das Spektrum des emittierten Lichts liegt im blau/violetten Wellenlängenbereich und enthält zudem noch einen beträchtlichen UV - Lichtanteil. Die erzielten Leistungseffizienzen erreichen Werte bis zu 0.5%.
Ab Lichtleistungen von 10 nW, also bei ca. 5 µWcm-2 , ist das Licht mit bloßem Auge sichtbar. Maximale Lichtleistungen liegen derzeit bei einigen Hundert nW. Durch eine Verbesserung der Kantenpassivierung der Emitterstrukturen ist eine weitere Erhöhung der Betriebsleistung möglich.
Derzeit sind die für die Fluoreszenzanalyse verwendeten bioaktiven Substanzen nahezu alle auf die häufig verwendeten 633 nm - Laser optimiert. Es sind jedoch alternativ Farbstoffe, die blau/violett oder im UV angeregt werden können, verfügbar. Damit könnten derart integrierbare, in Siliziumtechnologie hergestellte Emitter - Strukturen in Lab-on-a-Chip Systemen Anwendung finden. Zudem wird eine ortsaufgelöste Anregung möglich, da die Lichtemitter mittels gängiger Photolithographie einfach strukturiert und dann durch entsprechende Chip - Ansteuerung gezielt geschaltet werden können. Eine kostengünstige Realisierung der Strukturen würde sogar die Verwendung als "Disposable" ermöglichen.

Im Vortrag werden die optischen und elektrischen Eigenschaften der Emitter vorgestellt. Ausgehend vom jetzigen Erkenntnisstand werden Anwendungen, wie z. B. ein integrierter Optokoppler, und Perspektiven siliziumbasierter Lichtemitter auf der Basis von Nanostrukturen aufgezeigt. Für zukünftige Applikationen sind dabei insbesondere Möglichkeiten der Einstellung der Wellenlänge durch geeignete Herstellungsvarianten interessant. Die internationalen Aktivitäten hinsichtlich der Realisierung von Si - basierten Lasern versprechen weitere interessante Aspekte für die Anwendung derartiger Strukturen.

Im Vortrag wird ein Überblick über mögliche Anwendungen Si-basierter Lichtemitter in der Biotechnologie vorgestellt. Dabei wird besonders auf die Anforderungen an den Emitter eingegangen.

The talk gives an overwiew about current results from IV and CV investigations of Ge and Si implanted oxide layers. The electric properties of the devices and the investigation of memory parameters will be discussed.

Within a BUU type transport model we study φ meson production in subthreshold Ni+Ni and Ru+Ru reactions. For the first time we included in our model the elementary reaction channels φ+N, Δ → φ+N, π+N(1520)Δ+N and πρ → φ. In spite of a substantial increase of the φ multiplicities by these channels our results stay significantly below the preliminary experimental data.

Investigations of the elemental and phase composition, microstructure, microhardness and tribological properties of AISI M2 steel subjected to nitrogen and carbon plasma-immersion ion implantation (PIII) at different regimes arew presented

A new TOF-energy telescope was installed at the ERDA beamline of the Rossendorf 5 MV tandem accelerator. The TOF-system consists of a small MCP-start-detector using a 45° tilted C-foil and a large mirror-type MCP-stop-detector with a flight path of about 100cm. In order to reduce the energy straggling of recoils in the start and stop detector diamond-like carbon (DLC) foils with thicknesses in the range of 0.5 up to 1.0 mg/cm2 are used. The energy detector is a large solid-angle DE-E gas ionisation chamber. This chamber is position sensitive in the scattering plane and enables kinematic correction. The total solid angle of this TOF- energy telescope amounts to about 3.2 msr and is mainly limited by the size of the stop-MCP. The most important features and advantages of this combination are as follows:

• In contrast to conventional Si- energy detectors the ionisation chamber suffers no damage by heavy particles.
• The ionisation chamber enables very easy a kinematic correction in the range of ±0.05° of the scattering angle.
• There are different options to separate the detected particles according to their mass or to their atomic number and to use the energy information from the ionisation chamber or from the TOF.

Four different metals: Al, Cu, Ag and An have been used to produce four special multilayer samples to study the depth resolution of hydrogen. The layer structure of each sample was analysed using 2 MeV He Rutherford backscattering spectrometry, 4.5 MeV He elastic recoil detection (ERD) and 30 MeV F6+ HIERD. Moreover the hydrogen distribution was analysed in all samples using H(N-15, alphagamma)C-12 nuclear reaction analysis (NRA) with resonance at 6.385 MeV. The results show that the best depth resolution and sensitivity for hydrogen detection are offered by resonance NRA. The He ERD shows good depth resolution only for the near surface hydrogen. In this technique the depth resolution is rapidly reduced with depth due to multiple scattering effects. The 30 MeV F6+ HIERD demonstrated similar hydrogen depth resolution to He ERD for low mass metals and HIERD resolution is substantially better for heavy metals and deep layers.

The renormalization method of Bogoljubov-Parasiuk-Hepp-Zimmermann (BPHZ)
is used in order to derive the renormalized energy shift due to the
gauge invariant Källén-Sabry diagram of the two-photon vacuum
polarization (VPVP) as well as the self energy vacuum polarization
S(VP)E beyond the Uehling approximation.
It is outlined, that no outer renormalization is required for the
two-photon vacuum polarization and that only the inner renormalization
has to b e accomplished.
It is shown that the so-called nongauge invariant spurious term
is absent for a wide class of vacuum polarization (VP)
diagrams if one applies the widely used spherical expansion of bound
and free-electron propagator.
This simplifies significantly calculations in bound state quantum
electrodynamis.
As one result of our paper the use of the BPHZ-approach in bound
state QED is established.

In this report we present results of nitrogen PIII into 50 keV boron implanted austenitic stainless steel at 400°C and 40 kV. A surface layer of 90 nm consisting of expended austenite (lattice expansion 6.5%) and ferrite as well as containing 30 at% B was found. This layer was followed by another one containing expanded austenite with reduced expansion (lattice expansion 2.5%) before the base material was reached. Auger electron spectroscopy (AES) and X-ray diffraction (XRD) at variuos angels of incidence were used to obtain results. After annealing at 400°C for 5h further nitrogen diffusion, but no boron diffusion was observed.

Results of a combined analysis are presented for the production of ω and φ mesons in π reactions in the near-threshold region using a conventional "nonstrange" dynamics based on processes that are allowed by the nonideal ω-φ mixing. We show that the interferences of the t channel (meson exchange) and s, u channels (nucleon and nucleon-resonances) differ significantly for the ω and φ production amplitudes. This leads to a decrease of the relative yields, in comparison with the expectations based on a one-component amplitude with standard ω-φ mixing.
We find a strong and nontrivial difference between observables in ω and φ production reactions caused by the different roles of the nucleon and nucleon-resonance amplitudes. A series of predictions for the experimental study of this effect is presented.

Integral scaled coupled melt pool convection and vessel creep failure experiments are being performed in the FOREVER program at the Royal Institute of Technology, Stockholm. These experiments are simulating the lower head of a pressurized reactor vessel under the thermal load of a melt pool with internal heat sources. Due to the multi axial creep deformation of the three-dimensional vessel with a highly non-uniform temperature field these experiments offer an excellent opportunity to validate numerical creep models. A Finite Element model is developed and using the Computational Fluid Dynamic module, the melt pool convection is simulated and the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a new creep modeling procedure. Additionally, the material damage is evaluated considering the creep deformation as well as the prompt plasticity.
Pre- and post-test calculations of at least 4 FOREVER experiments have been performed successfully. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.
After analyzing the calculations, it seems to be advantageous to introduce a vessel support which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it is possible to install an absolutely passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down. This idea has been patented.

Ein großer Traum der Mikroelektronik ist die Realisierung von Lichtquellen in Silizium, da dieses Material die (billige) Grundlage der gängigen Mikroelektronik - Chips ist. Noch in den 80er Jahren erschien dies unmöglich, da Silizium als indirekter Halbleiter zur Lichtemission an sich ungeeignet ist. Teure und aufwendige andere Verfahren und Werkstoffe (z. B. Verbindungshalbleiter wie Gallium-Arsenid, Gallium-Nitrid, Silizium-Carbid usw.) werden derzeit für Leuchtdioden verwendet. Diese Technologien sind zwar weit entwickelt, vermögen aber eins nicht: die Integration einer solchen Lichtquelle in herkömmliche Chipstrukturen, also direkt auf einem Silizium - Chip in einem reinen Si- Herstellungsprozeß.
Seit Anfang der 90er Jahre kann mit dem Einzug der Nanotechnologien durch modifizierte Schichten und Strukturen im Nanometer - Bereich die bisherige Schranke des Siliziums überwunden werden: die in das Silizium oder in Siliziumdioxid eingebetteten Nanostrukturen können aufgrund ihrer speziellen Eigenschaften selbst zum Leuchten angeregt werden. Ein mögliches Verfahren zur Erzeugung derartiger Nanostrukturen ist die Ionenstrahlsynthese Durch die Verbindung von Ionenstrahl- und Temperverfahren können z. B. Nanocluster in SiO2 hergestellt werden. Derartige Schichten zeigen bei elektrischer Anregung eine blaue/violette Lumineszenz, die zudem auch noch einen beträchtlichen UV - Lichtanteil enthält. Der Beitrag gibt eine Übersicht über elektrische und optische Eigenschaften derart modifizierter Schichten und zeigt mögliche Anwendungen.

Die Realisierung von Lichtquellen auf Silizium-Basis erschien noch in den 80er
Jahren unmöglich. Lichtemitter aus Verbindungshalbleitern hingegen sind
technologisch sehr weit entwickelt, vermögen aber eins nicht: die Integration in
herkömmliche Chipstrukturen, also direkt auf einem Silizium - Chip. Seit Anfang
der 90er Jahre kann mit dem Einzug der Nanotechnologien durch modifizierte
Schichten und Strukturen im Nanometer - Bereich diese bisherige Schranke des
Siliziums überwunden werden: Aufgrund ihrer speziellen Eigenschaften können in
einem reinen Si - Herstellungsprozeß erzeugte Nanostrukturen zum Leuchten
angeregt werden. Im Vortrag werden aktuelle Trends der siliziumbasierten
Lichtemission vorgestellt und Anwendungsfelder beschrieben, u. a. die mögliche
Verwendung integrierter optischer Strukturen in Lab-on-Chip Systemen für die
Biotechnologie.

Der Vortrag gibt einen Überblick über aktuelle Entwicklungen im Bereich der Si-basierten Lichtemission. Insbesondere wird ein integrierter Optokoppler vorgestellt und es werden mögliche Anwendungsgebiete aufgezeigt.

Stellar nuclear reactions, generally occurring at energies well below the Coulomb barrier, have extremely low cross sections posing a very difficult task for theri determination using the usual promt gammy-ray detection method. We describe here the application of the highly sensitive Accelerator Mass Spectrometry technique (AMS) as an alternative method for the determination of the resonance strenghts of the ²⁵Ma(p,gamma) reaction, by off-line counting of the produced ²⁶Al nuclei.

Zur Unterstützung des Bedienungspersonals bei der Prozessführung komplexer heterogener Hydrierprozesse in Batch-Reaktoren (Rührkesselreaktoren) wurde ein Online-Monitoring-System (MoSys) entwickelt. Die Industrieerprobung erfolgte im Rahmen eines entwickelten Batch-Informations-Management-Systems (BIMS), das in einem separaten Industrie-PC implementiert und über den Terminalbus in die vorhandene Automatisierungstechnik einer Mehrzweckanlage der Degussa AG eingebunden wurde. Neben den Online-Konzentrationsprofilen für das Edukt, das Endprodukt und ein summarisches Zwischenprodukt lieferte MoSys Informationen zur Umsatzgeschwindigkeit und zur verbleibenden Restdauer bis zum Ende der Hauptreaktion, ohne dass eine chemische Online-Prozessanalytik zwingend notwendig ist. Die Betriebserfahrungen von zwei Produktionskampagnen zeigten, dass das BIMS/MoSys stabil und zuverlässig arbeitete und die Konzentrationsprofile gut mit den erwarteten Konzentrationsverläufen übereinstimmten.
Ferner bietet BIMS/MoSys dem Prozessexperten die Möglichkeit, betrieblichen Nutzen zu ziehen, z. B. durch

• Einsparung einer chemischen Online-Prozessanalytik,
• Erweiterung und Archivierung des bestehenden Prozesswissens,
• bessere Reproduzierbarkeit der Produktqualität bei komplexen Batch-Prozessen,
• verbesserte Prozessführung durch die genauere Ermittlung anlagen- und prozessspezifischer Kenngrößen (H2-Verbrauch, Energieverbrauch, Produktausbeute, unerwünschte Zwischen- oder Nebenprodukte),
• Fehler- und Ursachenanalyse anhand der archivierten Batches,
• Rückverfolgbarkeit von Batches bei Problemen (z. B. Qualitätsbeanstandungen),
• Aufbau eines automatisierten Batch-Reports.

The deuteron charge - exchange reaction pD → n(pp) for the low values of momentum transfer and small excitation nergies of final pp - pair is considered in the framework of Bethe - Salpeter approach. The method of calculation of the observables is developed for the case, when the pp - pair is in ¹S₀ - state. The methodical numerical calculations of the differetial cross sections and tensor analysing powers are presented. The reaction under consideration is predicted to be a solid base for construction of the deuteron tensor polarimeter at high energies, and also to obtain some additional information about elementary nucleon - nucleon charge - exchange amplitude.

Die Glaskorrosion, hervorgerufen durch Umwelteinflüsse, ist eine ernstzunehmende Gefährdung vor allem für wertvolle historische Glasobjekte. Zur zerstörungsfreien Charakterisierung eines Glases werden drei ionenstrahlanalytische Techniken (PIXE, PIGE, RBS) in einer simultanen Messung mit dem externen, an Luft ausgeführten, Protonenstrahl kombiniert. Spezielle Auswerteprozeduren ermöglichen die Bestimmung der chemischen Zusammensetzung und die Beurteilung des Korrosionszustandes des Objektes. Neben Hinweisen auf die kunstgeschichtliche Einordnung können daraus vorsorgliche Empfehlungen für die Aufbewahrung besonders gefährdeter Gläser abgeleitet werden. Die Anwendung des Verfahrens wird an zahlreichen Glasobjekten aus dem Kunstgewerbemuseum Dresden und dem Kunstmuseum Düsseldorf demonstriert.

Excited states in the N=Z + 1 nucleus ⁷³Kr have been investigated using the ⁴⁰Ca(³⁶Ar,2pn) and ⁴⁰Ca(⁴⁰Ca,α2pn) reactions at 145 and 160 MeV, respectively. γ-rays were detected using the Gammasphere array and events were re corded in coincidence with charged-particle and neutron detectors.
The three previously observed bands were extended to high spin, and a new unfavored positive-parity band has been observed. The alignment characteristics and decay properties of the bands are all consistent with large-deformation prolate rotation, with no clear evidence for oblate bands or shape coexistence. This is quite different from neighboring ^72,74Kr, indicating a strong shape-stabilizing role for the valence neutron. The experimental results are compared to extended total Routhian surface, cranked Nilsson Strutinsky, and cranked relativistic mean-field calculations. The results suggest that the paired calculations lack some important physics. Neutron-proton correlations may be the missing ingredient. There is also evidence for an unusual band crossing in the negative-parity bands, which may in dicate the presence of T = 0 pairing correlations. At high spin all the models can reproduce the experimental data.

For calculations of Lower Head Failure experiments like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model is developed based on the code ANSYS®. The CFD module is used to calculate the thermodynamics. The resulting temperature field of the vessel wall is applied to the mechanical model. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied.
After post-test calculations for the FOREVER-C2 experiment, pre-test calculations for the forthcoming experiments are performed. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios. After analyzing the results of the calculations, it seems to be advantageous to provide a vessel support, which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it may be advantageous to install a passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down.

A unique parameterization of secondary (thermal) dilepton and photon yields in heavy-ion experiments at CERN-SPS is proposed. Adding those thermal yields to background contributions the spectral shapes of the CERES/NA45, NA38, NA50, HELIOS/3 and WA98 data from experiments with lead and sulfur beams can be well described.

Im WWER-Prototyp-Reaktor WWER-2 des KKW Rheinsberg ist ein umfangreiches Bestrahlungsprogramm zur Untersuchung der Anfälligkeit von WWER-Reaktordruckbehälterstählen und -schweißwerkstoffen gegen Neutronenversprödung durchgeführt worden. Bestrahlt wurden insgesamt 21 verschiedene Chargen derartiger Materialien. Vergleichend wurden auch ASTM-bezogene Druckbehälterstähle in das Programm einbezogen. Zur Charakterisierung der bestrahlungsbedingten Änderungen wurden Charpy-Kerbschlagbiegeversuche, Zugversuche, Härtemessungen, bruchmechanische Versuche und Neutronenkleinwinkelstreuexperimente herangezogen. In jedem Fall sind die für die Neutronenversprödung typischen Eigenschaftsänderungen, wie Erhöhung der Übergangstemperaturen, Absenkung der Kerbschlag-Hochlagenenergie und Härte- bzw. Festigkeitssteigerung, nachgewiesen worden. Der Effekt wächst mit der Neutronenfluenz, zeigt aber darüber hinaus beträchtliche stahlmarken- bzw. chargenabhängige Unterschiede. Ein wichtiger Einflussparameter ist der Gehalt an Kupfer und Phosphor, der aber allein die unterschiedliche Versprödungsempfindlichkeit nicht erklären kann.
Vergleicht man die Ergebnisse des Bestrahlungsprogrammes Rheinsberg mit der Vorhersage auf der Basis der im russischen Normenwerk verankerten Vorhersagegleichungen, so wird in etlichen Fällen auch für Werkstoffe, die innerhalb der WWER-Spezifikation liegen, das Verhallten nicht konservativ vorausgesagt. Damit werden Schwächen im System der russischen Vorhersageprozeduren aufgedeckt.

Glass treated on its surface with silver compounds and an aluminosilicate, such as ochre or clay, at higher temperatures (between 550 and 650°C) accepts a wide variety of a yellow colour. It is the aim of this study to investigate the parameters of the manufacturing process affecting the final colour of silver stained glass and to correlate them with the final colour and colour intensity. Therefore, defined mixtures of ochre and a silver compound (AgCl, AgNO₃, Ag₂SO₄, Ag₃PO₄, Ag₂O) were prepared and applied on soda-lime glass. The firing process was modified within the range from 563 to 630°C and glass samples were analysed after treatment with energy dispersive X-ray fluorescence analysis (EDXRF), scanning electron microscopy (SEM/EDX), transmission electron microscopy (TEM), as well as ion beam analysis (IBA) with an external beam. Within the scope of IBA simultaneous measurements using particle-induced X-ray emission (PIXE), particle-induced gamma-ray emission (PIGE), and Rutherford backscattering spectrometry (RBS) were carried out in order to obtain the thickness of the Ag-rich surface layer and the depth distribution of Ag. By means of TEM the microstructure of the silver particles was visualised. XRF results show that the lowest amount of Ag could be detected on glass samples treated with silver stain mixtures containing AgCl and Ag₂O. A low kiln temperature (e.g. 563°C) results in a higher silver concentration at the surface and lower penetration depths. Furthermore, the results obtained with SEM/EDX at cross-sections of the glass samples could be confirmed by PIXE, PIGE, RBS, and TEM.

Excited states in ⁷⁰Br were populated in the ⁴⁰Ca(³²S,pn) reaction at E_beam = 80-100 MeV and the ⁴⁰Ca(³⁶Ar, αpn) reaction at E_beam = 145 MeV. The resulting gamma decay was detected using the Gammasphere array triggered by a 30-element neutron detector. The cross-bombardment allowed the unambiguous assignment of levels to ⁷⁰Br, comprising a total of 32 states built both on the J^π=0⁺ ground state and a previously known J^π=9⁺ isomer, which is located at an excitation energy of 2293 keV by the observation of linking transitions. The structures are discussed within the context of the two-quasiparticle plus rotor model, the IBM-4 model and the cranked Nilsson-Strutinsky formalism. The nonobservation of a doublet of J = 0, T = 1 and J = 1, T = 0 states at low excitation in ⁷⁰Br is indicative that T = 0 proton-neutron pairing strength is weak in comparison to T = 1 pairing.

The effect of ion beam mixing on the formation of tantalum-silicon contacts was studied. Silicon implantation into 50 nm Ta layers on n+-Si (100) was carried out at temperatures from 150 to 500°C and fluences between 1x1015 and 1x1017 Si/cm². To characterize the microstructural changes Auger electron spectroscopy (AES), X-ray diffraction and cross-sectional transmission electron microscopy (TEM) were used. The contact resistance was measured before and after implantation using the four-point Kelvin method. Implantation at low temperature (~150°C) leads to the formation of an amorphous Ta-Si interface-layer. The width of the mixed layer increases linearly with implanted dose and temperature. Substrate amorphisation up to a depth of about 200 nm results in an increase of the contact resistance. An improved contact resistance was achieved by implantation with 5x1016 Si/cm² at 400°C. TaSi2 formation at the interface was observed in this case.

Chemical composition analysis on historical objects of art and archaeology assists in clarifying their authenticity and provenience. In addition, special technologies of their manufacture can be elucidated. Knowledge on the chemical composition represents one of the fundamentals for conservation and preservation concepts for historic silicate materials. The ensemble of ion beam analytical techniques (IBA) using external beams is a tool if non-destructive investigation is required.
Glass corrosion caused by environmental attacks is a serious problem especially for valuable historic objects. This is because the glasses may lose their transparency and stability. Alterations proceeding on the glass surface include ion exchange processes where network modifiers such as potassium and calcium are replaced by hydrogen bearing species to form a hydrated silica-rich surface layer. In order to characterise the state of a glass object showing no visible effects of alteration or corrosion damage, three ion beam based techniques (PIXE, PIGE, RBS) are combined in simultaneous measurements at the Rossendorf external proton beam. Combining PIXE (Proton Induced X-ray Emission) and PIGE (Proton Induced Gamma-ray Emission) the yield of X- and g-radiation of the element Si is ideal to indicate thin leached layers. More extended regions can be characterised by external RBS (Rutherford Backscattering Spectrometry). For getting the composition of the glass bulk the PIXE spectra are treated using the GUPIX code taking into account the experimental findings about the surface corrosion state. The developed procedure allows evaluation of initial corrosion and the identification of glass materials which are sensitive to atmospheric corrosion processes. The analytical results may offer suggestions for storing sensitive glass objects under special atmospheric conditions.
The present contribution demonstrates the applicability and the advantages of IBA techniques by investigating three medieval glass beakers.

The equivalence of the covariant renormalization and the partial-wave
renormalization (PWR) approaches is proven explicitly for the
one-loop self-energy (SE) correction of a bound electron state in
the presence of external perturbation potentials.
No "spurious" correction terms to the noncovariant PWR scheme are
generated for Coulomb-type screening potentials and for external
magnetic fields.
It is shown that in numerical calculations of the SE with Coulombic
perturbation potential spurious terms result from an improper treatment
of the unphysical high-energy contribution.
A method for performing PWR utilizing the relativistic B-spline
approach for construction of the Dirac spectrum in external magnetic
fields is proposed.
This method is applied for calculating QED corrections to the
bound-electron g factor in H-like ions.
Within a level of accuracy of about 0.1 % no spurious
terms are generated in numerical calculations of the SE in magnetic fields

The dependence of the radiative energy loss of hard partons (E<10 GeV) on the initial thermodynamic parameters
is studied for deconfined matter to be expected at the Relativistic Heavy-Ion Collider (RHIC).
We demonstrate that the specific QCD radiation pattern with a nonlinear dependence of the energy
loss on the propagated distance leads to a strong increase of the energy loss with increasing initial
entropy of deconfined matter supposing its lifetime is less than the average time to pass through the medium.
This is in contrast to a parametrization with constant energy loss per unit length of propagation.
For a sufficiently high initial temperature a two-regime behavior of the energy loss as a function
of the initial parton momentum occurs. The angular structure of the energy loss of hard jets with
respect to the initial temperature is also discussed for RHIC conditions.

The centrality dependence of thermal parameters, characterizing the hadron multiplicities, is determined phenomenologically
for lead-on-lead collisions at CERN-SPS for a beam energy of 158 A GeV.
The strangeness equilibration factor shows a clear, approximately linear, increase with increasing centrality, while the freeze-out temperature and chemical potential remain constant.

Nanometer-sized SiC precipitates were synthesized at 450oC in Si by simultaneous dual beam implantation of C+ and Si+ ions and subsequent annealing. The results are compared with those of sequential dual beam implantation and of single beam implantation. Two types of SiC precipitates were found. Precipitates of type I with a diameter of d = 4 - 5nm consist of 3C-SiC epitaxially oriented with the Si matrix. They were formed already in the as-implanted state and do not grow further during subsequent annealing. The SiC precipitates of type II with d " 10nm are not oriented with the Si matrix and grow exclusively during the subsequent annealing. The high growth velocity, the misorientation in regard to the Si matrix and the lower concentration of type II precipitates can be explained by the assumption that these precipitates were formed in an amorphous substrate which modifies their interface energy.

The contribution reviewed the state of the art regarding the so called Rp/2 gettering effect. It was shown that ion implantation induced excess vacancies and their agglomerates are the origin of metal gettering in the Rp/2 region of ion-implanted Si. Metal atoms are gettered at the inner wall of the cavities. The removal of the excess vacancies by defect engineering avoids metal gettering at Rp/2. Interstitial-type defects (small clusters of interstitials) are as well present in the Rp/2 region. However, their gettering capability for metal impurities is much smaller than that of the vacancy-type defects.

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Positron implantation profiles have been investigated over a range of about 1 m on a gold solid solution containing 40 at.% of Ag, after helium implantation at 300 keV. The S parameter lineshape of the annihilation radiation, sensitive to both the size and the concentration of vacancy type defects, was measured after isochronal annealing up to 930 K. Depending on the incident energy of the positron, i.e. the distance between its mean implantation depth and the helium concentration maximum, several recovery stages were unambiguously observed attributed, respectively, to free vacancy migration (I), helium stabilization of larger defects (II) and competitive processes of bubble nucleation (III) and breaking up (IV). These latter mechanisms lead to the observation of a lineshape maximum at T=0.5Tm (melting point), already observed for nickel.

The reconstruction of the precipitation structure after solution treatment has been investigated by positron
annihilation spectroscopy. In this study the behaviour of samples taken from an aircraft "Airbus 300", being
in operation for 18 years, is compared to a reference material supplied by Alcoa. The results of position
annihilation spectroscopy show that there are no significant differences in both materials. This finding is in
agreement with the results obtained from other methods within the scope of the general research program
which points to a materials behaviour as predicted for a safe operation of this type of aircraft.

Sn films grown on silicon substrate by d.c. magnetron sputtering have been investigated by slow positron
implantation spectroscopy. As the substrate bias is one of the most important factors affecting the structure
of a sputtered film, films grown at various substrate bias (+80 V, 0 V, -80 V) are compared and their
properties are discussed.

The spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Jülich in spring 1998.
An initial scientific goal is to study K⁺-production in pA collisions at subthreshold energies far below the free NN-threshold at T_p=1.58GeV. This requires the identification of K⁺-mesons in a background of pions and protons, about 10⁶ times more intense.
In this paper the sophisticated detection system and the software procedures for kaon identification are described.
With the help of TOF, energy-loss and range measurements as well as the track information from wire chambers, it is possible to measure d²σ/dΩdp for deep subthreshold K⁺ production at beam energies down to T_p=1.0GeV.

The High Acceptance Di-Electron Spectrometer (HADES) is a detector arrangement combined with a superconducting toroid for lepton pair spectroscopy presently built up at GSI (Darmstadt). HADES is designed to cope with the high-multiplicity environment of heavy ion collisions at 1AGeV and intensities of up to 10⁸ beam particles per second and central event rates of 10⁵ s^-1. The detector has a geometrical acceptance of almost 50% for e⁺e^- pairs and a mass resolution of 0.8% for ρ and ω mesons. Four low-mass drift chamber systems, two before and two behind the magnet, serve for charged particle track reconstruction. Design aspects of the drift chambers and first results from beam tests are presented.

Titanium foil is employed for electron transparent windowsin the lectron beam dry scrubber process. The foil suffers corrsion, which limits the window life. Here, the examination of a palldium-coated window, prepared by ion beam assisted deposition and plasma source ion assisted deposition (PIIAD), after service in a pilot-scale plant is reported. Most significantly, the adhesion of the coating was reduced by the flue gas. Where the coating remained adherent, corrison was negligible. Elsewhere, general, intergranular and pitting corrosion occurred. A PSIAD coating provided the best performance.

A hybrid type of apparatus is described which eneables one to form a thin multi-layer film on the surface of any kind of solid substrate. In one process, the surface is treated with a high intensity pulse plasma beam which introduces the chosen kind of atoms into the near-surface layer of the substrate. In the second process, following the first without breaking the vacuum, the coating is formed by arc PVD process. Two examples of coatings formed on metallic and ceramic substrates are presented.

The design, construction and operation of a Compton back-scattering laser
polarimeter at the HERA storage ring at DESY are described.
The device measures the longitudinal polarization of the electron
beam between the spin rotators at the HERMES
experiment with a fractional systematic uncertainty of 1.6 %. A measurement
of the beam polarization to an absolute statistical
precision of 0.01 requires typically one minute when the device is operated
in the multi-photon mode.
The polarimeter also measures the polarization of each individual
electron bunch to an absolute statistical precision of 0.06 in
approximately five minutes.
It was found that colliding and non-colliding bunches can
have substantially different polarizations.
This information is important to the collider
experiments H1 and ZEUS for their future longitudinally polarized
electron program because those experiments use the colliding
bunches only.

The present investigation focuses on further development of the plasma based high voltage modulator for plasma immersion ion implantation (PIII) devices. The modulator produces high voltage pulses using grid controlled extraction of electrons from the plasma, which is used for the ion implantation. The operation features of the modulator in connection with an RF-plasma are described. The device is applied to implantations of stainless steel. The results indicate considerable hardness improvement, which confirm the practical use of the high voltage modulator.

The titanium hydrogenation process in the H2+ implanted Ti225 titanium alloy has been studied in this work. The Ti/H phase transformation from hydrogen solid solution (hcp) to gamma phase titanium hydride (TiH(γ)) with a primitive tetragonal structure and then to a titanium-dihydride (TiH2(x)) with a body centred tetragonal (bct) structure has been characterized by X-ray diffraction, NRA and ERDA. This process is very different from the usual hydrogenation mechanism, in which the delta phase titanium-dihydride (TiH2(δ)) with a face centred cubic (fcc) structure is always involved. Both of the TiH(γ) and TiH2(x) are rare phase, which are formed under extreme conditions. The TiH(γ) was considered to be a metastable phase in low hydrogen concentrated titanium, and the TiH2(x) phase has not yet been notated. The characteristics of the TiH2(x) are unclear, but it is very stable at room temperature and exists as a mixture state with the titanium. A saturated fraction of the hydride to titanium phase has been obtained as about 15% (H/Ti~0.3) in a H2+ implanted sample.

The damage accumulation in stabilized cubic ZrO2 single crystals irradiated with low-energy Ar ions was investigated,
combining Rutherford backscattering/channeling (RBS/C) and slow positron implantation (SPIS) spectroscopies. In the 3×1014¯1016 cm-2 range, the fluence dependence of the damage-induced dechanneling parameter (fD) exhibits three production stages (labeled 1, 2 and 3) already reported for ion-irradiated ceramics and attributed to the formation of small clusters and dislocation loops, either isolated or overlapping. Moreover, a precursory stage, never hitherto reported in RBS/C studies, is unveiled for fluences below 3×1014 cm-2. This "new" stage (labeled 0) is confirmed by SPIS and attributed to clustering of small vacancy-type defects. Although both techniques exhibit different specific sensitivities to defects, similarities in the fluence dependence allow to identify common limits to all observed damage production stages.

The X6CrNiTi1810 austenitic stainless steel samples nitrided by plasma immersion ion implantation at 300 °C/3 h are studied by slow positron implantation and conversion electrons Mössbauer spectroscopies completed with X-ray diffraction (XRD) measurements. The surface layers consist of N-Fe expanded austenite and -Fe2N nitride. The changes in hyperfine parameters and relative representation of both phases during the interrupted long-time annealing at 150 °C are discussed from the point of view of nitrogen migration and changes in defect structure.

The influence of bending stress on the hydrogen behaviour in titanium was investigated by elastic recoil detection analysis with a heavy ion microbeam (micro ERDA) and X-ray diffraction (XRD). The samples were made by hydrogen ion implantation into polished pure titanium sheets. Three-dimensional hydrogen distributions were obtained by scanning the microbeam over the sample using the depth information of ERDA. Inhomogeneous hydrogen distributions in the titanium were observed which vary with the depth. With mechanical bending of the samples the inhomogeneities increased in varied grade. The surface hydrogen loaded by surface polishing is stable, whereas the implanted hydrogen located inside of the sample is mobile under bending. These different hydrogen behaviours are relevant to the chemical states of hydrogen. Different titanium hydrides are formed by the different loading methods. An relatively unknown titanium dihydride phase (TiH2(x)) with a tetragonal texture was identified by XRD in the depth region of implanted hydrogen. It is less stable than the normal titanium-dihydride phase (TiH2(d)) observed in the surface region. The change of hydrogen distribution is related to the dehydrogenation of the TiH2(x) and TiH(g) under bending.

Ultra-fine grained copper prepared by high pressure torsion has been studied by means of slow positron implantation
spectroscopy with Doppler broadening measurement. In addition, conventional positron lifetime and Doppler broadening spectroscopy have been utilised. Defects present in the specimens were identified, their spatial distribution and depth profile have been determined. The results are discussed in correlation with those obtained by XRD and TEM.

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.

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.

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.