Erosion behaviour of ultrathin carbon layers and hydrogen retention in beryllium

Plasma-wall-interaction plays an important role on the way to technical feasibility of thermonuclear fusion. In this context, the erosion behavior of few nanometer thin amorphous carbon layers on different metallic substrates by energetic deuterium and helium ions is investigated. Several aspects of the interaction are distinguishable by XPS. Ion induced carbide formation is governed by kinematic intermixing of carbon and metal substrate. Several methods of quantification of XPS measurements are developed and discussed. Comparison of results from these methods with NRA measurements show that surface roughness and implantation of particles into the carbon layer and intermixing zone influence the XPS measurements, which are sensitive to parameters such as material density. The retention of 1 keV deuterium ions implanted into single crystalline and cleaned beryllium at room temperature is investigated by temperature programmed desorption (TPD). The residual BeO coverage was 0.2 ML. The retention is 78% at low fluences and saturates above a bombardment with a fluence of 2.1017 cm-2. The retained maximum areal density is 2.1017 cm-2. Above 900 K, no deuterium is retained in the sample. An onset of self diffusion is observed at this temperature and metallic beryllium from the bulk segregates though thin BeO layers on the surface. From deuterium desorption traces, retention mechanisms are obtained. The measured TPDspectra are modeled by TMAP7 and rate equations to obtain activation energies for the release processes. From these, binding energies for the system Be-D are derived. Up to a implantation fluence of 1.1017 cm-2, deuterium is trapped in ion induced defects in the beryllium lattice with binding energies of 1.69 eV and 1.86 eV and release temperatures of 770 K and 840 K, respectively. The occupation of these states shows a different isotope behavior for 1H and 2H. The states are filled by diffusion of deuterium at the end of its implantation trajectory. Above a implantation fluence of 1.1017 cm-2, local supersaturation and destabilization of the beryllium lattice leads to the formation of structural modifications. Deuterium is adsorbed on the surface of nanoscaled, closes voids in these areas. Energetic considerations show, that no molecular deuterium is formed under such circumstances. The binding energies of these states are 1.06 eV and 1.14 eV with release temperatures of 440 K and 470 K respectively. Implantation at substrate temperatures above 300 K lead to the formation of increasing amounts of BeD2, which decomposes at 570 K. The influence of a thin surface oxide coverage (1-3 ML BeO) is investigated. This shows, that none of the above mentioned binding states is limited by deuterium recombination. Deuterium bound to surface oxide is released at 680 K. (orig.)