Intermediate metastable structure of the C(111)\/(1×1)H-C(111)\/(2×1) surface phase transition

The pathway of the (111)\ diamond surface transformation between the (2×1) π-bonded chain and the (1×1) bulk-terminated structures is investigated using the molecular-dynamics technique. The metastable surface structure that mediates the H adsorption-induced phase transition from the (2×1) to the (1×1) surface reconstruction, and the crucial role played by hydrogen in the stabilization of this intermediate structure, are proposed. Atomic configurations formed by adjacent CH bonds on the mostly (2×1) structure are responsible for the energy barrier separating the metastable phase from the hydrogen-terminated (1×1) structure. Calculated vibrational spectra for the various surface reconstructions are correlated with experimental observations of Chin et al. [Phys. Rev. B 45, 1522 (1992)]. The occurrence of the additional higher-frequency metastable peak, its intensity variation during hydrogen absorption, and possible reasons for the irreversible character of the surface transition are discussed based on the results of the molecular-dynamics simulation.