Papers by Author: Reinhard Kögler

Abstract: The influence of helium on the mechanical properties of reduced-activation ferritic/martensitic Cr-steels under fusion-relevant irradiation conditions is still a concern. While the fact that He can influence the mechanical properties is well established [1,2], the underlying mechanisms are not fully understood [1,2]. In this work the effect of He and displacements per atom (dpa) on the irradiation-induced hardening of Eurofer97 at 300°C was studied. Self-ion irradiation was applied to simulate the neutron-irradiation-induced damage. Helium was implanted prior to (pre-implantation), simultaneously (dual-beam irradiation) or following the (post-implantation) self-ion irradiation to investigate the He effect. Nanoindentation was used in order to characterize the damage layer. Under the present conditions (300°C, 1 dpa, 10 appmHe) the observed hardening increased in the following order: single-beam Fe-ion irradiation/pre-implantation < simultaneous implantation < post-implantation. We conclude, that there is a significant interaction between damage and He. Additionally, Eurofer97 and ODS-Eurofer were irradiated with Fe ions up to 1 and 10 dpa to study the effect of the oxide particles on the irradiation-induced hardening. We have found a higher irradiation-induced hardening at 1 dpa for ODS-Eurofer but a steeper hardness increase per dpa up to 10 dpa for Eurofer97.

Abstract: Implantation of 18O into highly B-doped and undoped silicon provides the possibility to investigate the effect of B-doping and to distinguish the processes of in-diffusion and out-diffusion of oxygen by profiling of 16O and 18O, respectively. The simultaneous in- and outdiffusion of oxygen was observed at 1000°C under oxidizing conditions. For silicon, heavily Bdoped to concentrations of 􀀀 1019 B cm-3, oxygen tends to diffuse out toward the surface. Moreover, a fraction of the oxygen from both sources, implanted 18O and in-diffused 16O, also migrates deep into the substrate and is trapped far beyond the mean ion range RP in the depth of x
3RP at the so-called trans-RP gettering peak. In undoped silicon oxygen accumulation only takes place at vacancy-type defects introduced by ion implantation at a position shallower than RP. The mobility of oxygen implanted into B-doped Si is higher than for implantation into undoped Si. Highly mobile defects are suggested to be formed in B-doped silicon beside the common mobile interstitial oxygen, Oi, and the immobile SiOX precipitates. These I OXBY defects may involve selfinterstitials, I, and O and B atoms. The trans-RP peak appears due to the decay of these defects and the segregation of their constituents.

Abstract: SIMOX (Separation-by-Implantation-of-Oxygen) is an established technique to fabricate silicon-on-insulator (SOI) structures by oxygen ion implantation into silicon. The main problem of SIMOX is the very high oxygen ion fluence and the related defects. It is demonstrated that vacancy defects promote and localize the oxide growth. The crucial point is to control the distribution of vacancies. Oxygen implantation generates excess vacancies around RP/2 which act as trapping sites for oxide growth outside the region at the maximum concentration of oxygen at RP. The introduction of a narrow cavity layer by He implantation and subsequent annealing is shown to be a promising technique of defect engineering. The additional He implant does not initiate oxide growth in the top-Si layer of SOI.

Abstract: Different methods of defect engineering are applied in this study for ion beam synthesis of a buried layer of SiC and SiO2 in Si. The initial state of phase formation is investigated by implantation of relatively low ion fluences. He-induced cavities and Si ion implantation generated excess vacancies are intentionally introduced in the Si substrate in order to act as trapping centers for C and O atoms and to accommodate volume expansion due to SiC and SiO2 phase formation. Especially the simultaneous dual implantation is shown to be an effective method to achieve better results from ion beam synthesis at implantation temperatures above 400oC. For SiC synthesis it is the only successful way to introduce vacancy defects. The “in situ” generation of vacancies during implantation increases the amount of SiC nanoclusters and improves crystal quality of Si in the case of SiO2 synthesis. Also the pre-deposition of He-induced cavities is clearly advantageous for the formation of a narrow SiO2 layer. Moreover, in-diffusion of O by surface oxidation can substitute a certain fraction of the O ion fluence necessary to obtain a buried homogeneous SiO2 layer. The results show that defect engineering for SiC and SiO2 synthesis is working. However, the implementation of a single action is not sufficient to achieve a significant improvement of ion beam synthesis. Only an optimized combination of the different versions of defect engineering can bring about pronounced better results.