A TDS study of D adsorption on terraces and terrace edges of graphite (0001) surfaces

Adsorption of thermal (2000 K) D atoms on (0001) surfaces of various highly oriented pyrolytic graphite (HOPG) and natural graphite substrates was studied under ultra high vacuum (UHV) conditions with thermal desorption spectroscopy (TDS). D chemisorption on terrace and terrace edge sites of graphite (0001) surfaces was identified. Recombinative desorption of D adsorbed on terraces was observed between 400 and 600 K. The analysis of TD spectra from various graphite surfaces reveals the existence of three desorption states intrinsic to graphite (0001), and proposed as being due to adsorbate structures composed of one (monomer) and two neiahbouring (dimer) chemisorbed D atoms, and aggregates thereof (mixed). The dimer structure is supposed to exhibit higher stability than the monomer. Reaction of D with terrace edges leads to the formation of CD, CD(2) and CD(3)-groups at edge C atoms. These groups decompose during heating between 790 and 1300 K via release of gaseous D(2) and CD(x), C(2)D(x) and C(3)D(x)-hydrocarbons. (C) 2003 Elsevier Ltd. All rights reserved.