THE TOPOLOGIES OF THE CLEAN AND HYDROGEN-TERMINATED C(100) SURFACES

The topologies of the clean and hydrogen-terminated C(100) surface have been studied via the SLAB-MINDO method. A symmetric dimer structure is predicted for both the clean C(100)2 x 1 and monohydride C(100)2 x 1:H surface reconstructions. The lowest energy configuration, however, is the dihydride which exhibits a (1 x 1) topology. Two steps in the hydrogen desorption process have been proposed: the so-called "fast" and "slow" steps corresponding to molecular and atomic desorption, respectively. The dimer structure is formed following molecular desorption from the C(100)1 x 1:2H configuration, whilst the dimer bond becomes a double bond when atomic hydrogen is desorbed from the monohydride C(100)2 x 1:H surface. The chemisorption energy of atomic hydrogen on the reconstructed clean C(100)2 x 1 surface is found to be 6.32 eV per surface atom and the barrier to further hydrogen chemisorption to form the dihydride C(100)1 x 1:2H structure, 1.48 eV per surface atom.