The surface kinetics of hydrogen adsorbed on vicinal Si(001) surfaces, misoriented towards the [110] direction, is investigated by means of optical second-harmonic generation. Following the selective saturation of the double-height $D_{\mathrm{B}}$ steps by exposing the surface to a well-defined dose of molecular hydrogen, the transition from this nonequilibrium to an equilibrium hydrogen distribution is monitored in the temperature range between 580 and 730 K. A thermally activated diffusion process with a barrier of $1.7\pm 0.15\mathrm{eV}$ associated with the step depletion is observed. From measurements of the equilibrium hydrogen coverage the steps are found to be energetically favored with a ${\mathrm{H}}_2$-chemisorption energy difference of $\sim 0.2\mathrm{eV}$ between step and terrace sites.

• Received 22 June 1998

DOI:https://doi.org/10.1103/PhysRevB.59.2783