Surface properties of clean and hydrogenated diamond (100) were calculated using the atom superposition and electron delocalization molecular orbital methods. For the clean surface, dimerization and 2 x 1 restructuring were predicted. The monohydrogenated surface maintains the 2 x 1 structure but with elongated surface CC dimer bonds. The dihydrogenated surface takes a 1 x 1 structure but, because of steric crowding, was not as stable. These findings support the interpretations of recently obtained experimental results of Hamza et al. They were also analogous to the well established properties of clean and hydrogenated Si(100). CH3 and CH2 migration energy barriers in the presence of H vacancies on the monohydrogenated surface were calculated to be high for CH3 but low enough for CH2 that surface migration might occur under low pressure diamond growth conditions. Because of electron promotion to the π* orbital, acetylene does not form a strong bond to a surface radical site, but it could bind strongly by bridging two adjacent hydrogen vacancy sites on the monohydrogenated surface. This structure was not likely to be involved in the growth mechanism.

Adsorption of H, CH3, CH2 and C2H2 on 2 x 1 Restructured Diamond (100). Theoretical Study of Structures, Bonding, and Migration. Mehandru, S.P., Anderson, A.B.: Surface Science, 1991, 248[3], 369-81