SURFACE-COMPOSITION MODIFICATIONS OF CARBIDES AND DOPED GRAPHITES DUETO D-BOMBARDMENT( ION)

Surface composition modifications due to D+ ion bombardment with energ ies between 10 eV and 1 keV at temperatures ranging from 300 K to 1000 K and the consequences for the sputtering yields and chemical erosion have been investigated for SIG, TiC and graphites doped with 10 at.% Si or 10 at.% Ti. At D+ ion energies below about 100 eV, a steady-stat e surface enrichment of the metal has been observed both in the carbid es and in the doped graphites. The maximum enrichment was nearly 100 a t.% in SiC, about 75 at.% in TiC and about 70 at.% and 60 at.% in Si- and Ti-doped graphite, respectively. In SiC the temperature and the io n energy dependence of the Si surface enrichment reflects the chemical erosion, i.e. the surface depletion of carbon. The surface enrichment of the metal in TiC is caused by the threshold energy of 33 eV for Ti sputtering by D+ irradiation. In both doped graphites after D+ bombar dment, the development of a cone structure has been observed. The tops of these cones consist of Si- or Ti-rich grains shielding the underly ing graphite material from erosion. Thus, the steady-state metal surfa ce enrichment under D+ bombardment can be explained by considering the surface topography and the metal surface enrichment of the correspond ing carbide.