Hydrogen diffusion on Si(001) was investigated at the atomic scale by using a combination of laser-induced thermal heating and scanning tunnelling microscopy. In addition to the well-known diffusion path along the dimer rows, hydrogen diffusion across the rows was also observed. At a surface temperature of 1385K, the hopping-rate along this high-barrier inter-row diffusion pathway was 5.6 x 107/s, as compared with the intra-row hopping rate of 1.3 x 108/s. Thus, the diffusion of hydrogen on Si(001), which was strongly anisotropic below 700K, became almost isotropic at high temperatures.

Real-Space Investigation of High-Barrier Hydrogen Diffusion across the Dimer Rows of Si(001). C.H.Schwalb, M.Dürr, U.Höfer: Physical Review B, 2009, 80[8], 085317