Adsorption of H, CH 3, CH 2 and C 2H 2 on 2 × 1 restructured diamond (100) : Theoretical study of structures, bonding, and migration

Abstract

Surface properties of clean and hydrogenated diamond (100) have been calculated using the atom superposition and electron delocalization molecular orbital (ASED-MO) and ASED-band methods. For the clean surface, dimerization and 2 × 1 restructuring are predicted. The monohydrogenated surface maintains the 2 × 1 structure but with elongated surface CC dimer bonds. The dihydrogenated surface takes a 1 × 1 structure but, because of steric crowding, is not as stable. These findings support the interpretations of recently obtained experimental results of Hamza et al. They are also analogous to the well established properties of clean and hydrogenated Si(100). CH 3 and CH 2 migration energy barriers in the presence of H vacancies on the monohydrogenated surface are calculated to be high for CH 3 but low enough for CH 2 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 can bind strongly by bridging two adjacent hydrogen vacancy sites on the monohydrogenated surface. This structure is not likely to be involved in the growth mechanism.