Real-space investigation of high-barrier hydrogen diffusion across the dimer rows of Si(001)

Hydrogen diffusion on Si 001 has been investigated on the atomic scale by means of a combination of laser-induced thermal heating and scanning tunneling microscopy. In addition to the well known diffusion path along the dimer rows, hydrogen diffusion across the rows was observed. At a surface temperature of 1385 K, the hopping rate of this high-barrier interrow diffusion pathway is 5.6 107 s−1 comparable to the intrarow hopping rate of 1.3 108 s−1. Thus, diffusion of hydrogen on Si 001 , which is strongly anisotropic below 700 K, becomes almost isotropic at high temperatures.