The diffusion behaviour of hydrogen substitutional sites on Cl-terminated Si(100) surfaces was investigated at high temperatures using time-lapse scanning tunnelling microscopy. The latter showed that each hydrogen atom underwent Brownian motion within a monochloride dimer row. The position of a hydrogen substitutional site was directly exchanged with that of an immediate neighbouring chlorine atom in either the same dimer (intra-dimer diffusion) or in one of the two adjacent dimers in the same row (intra-row diffusion). Direct exchange diffusion in a two-dimensional lattice was experimentally observed. Analysis of the data at various temperatures yielded rather low attempt-frequencies and energy barriers; leading to the suggestion that the diffusion mechanism involved an intermediate low-energy molecular state. Density-functional theory calculations provided partial support for the proposed diffusion mechanism.

Possibility of Direct Exchange Diffusion of Hydrogen on the Cl/Si(100)-2 x 1 Surface. M.F.Hsieh, D.S.Lin: Physical Review B, 2009, 80[4], 045304