The migration of atomic H upon the (111) 7 x 7 surface was investigated by monitoring optical second-harmonic diffraction from a sub-monolayer grating of adsorbed H. With the aid of sub-micron grating periods, it was possible to measure surface diffusivities of less than 10-14cm2/s. A thermally activated diffusion process was identified which could be described by:

D(cm2/s) = 1 x 10-3exp[-1.5(eV)/kT]

Surface Diffusion of Hydrogen on Si(111)7×7. G.A.Reider, U.Höfer, T.F.Heinz: Physical Review Letters, 1991, 66[15], 1994-7