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 5.6x10(7) s(-1) comparable to the intrarow hopping rate of 1.3x10(8) s(-1). Thus, diffusion of hydrogen on Si(001), which is strongly anisotropic below 700 K, becomes almost isotropic at high temperatures.