THE HYDROGEN INVENTORY IN PLASMA EXPOSED GRAPHITE SURFACES

The trapping of hydrogen in graphite was investigated during exposure to an rf-discharge. The target placed in the wall of the rf-reactor wa s investigated in-situ by ion beam analysis. The hydrogen inventory wa s found to be twice as high as expected from ion beam implantation exp eriments in the similar energy range less than or equal to 200 eV, Als o an enhanced ion induced desorption by the energetic analyzing beam w as observed. This leads to the conclusion that a buildup of a hydrogen rich C:H-layer is formed by the simultaneous impact of thermal and en ergetic (less than or equal to 200 eV) hydrogen, A model is presented which explains the formation of the C:H-layer by a stitching process o f methyl radicals forming on the surface, Time resolved trapping measu rements were performed to test for a transient uptake of hydrogen duri ng plasma exposure. No such phenomenon could be detected below 600 K. Also the supposition that metallic impurities are responsible for a dy namic inventory at room temperature could be disproved.