Interaction of H (D) atoms with surfaces of glassy carbon:: adsorption, abstraction, and etching

The interaction of thermal (2000 K) H and D atoms with glassy carbon (GC) surfaces was investigated in ultrahigh vacuum environment using thermal desorption and reaction kinetics mass spectroscopy. Virgin GC surfaces (not previously subjected to stationary etching by H atoms) exhibit a remarkably low reactivity with respect to adsorption of D. The saturation coverage of D on GC is about a factor of ten smaller than on (0 0 0 1) graphite surfaces (HOPG or natural single crystal). Thermal desorption spectra indicate that D atoms on virgin GC surfaces are adsorbed on distorted graphite basal planes, i.e. the recombinative desorption features of D on GC between 400 and 600 K are broadened as compared to those measured on graphite. Upon heating of D-covered virgin GC surfaces, CD3 surface groups desorb between 500 and 1000 K. Stationary etching of GC by a flux of H atoms is most efficient around 600 K, as was previously observed on other carbon materials, a-C:H thin films and graphite, and as expected from the etching mechanism on C substrates. GC surfaces repeatedly etched by H exhibit an increasing density of C atoms located at edge sites which are capable to adsorb D via formation of sp(n) C-D bonds. D from these sites desorbs recombinatively around 830 K and competitive desorption Of C-2 deuterocarbons at 780 K occurs. The graphite-like fraction of the surface is unaffected by etching. Abstraction of D on virgin GC by H exhibits the same phenomenology as on graphite: Eley-Rideal mechanism and large abstraction cross-section at small D coverages. (C) 2003 Elsevier Ltd. All rights reserved.