H-induced surface restructuring on Si(100): Formation of higher hydrides

H-induced surface structures on Si(100) were studied using temperature-programmed-desorption mass spectroscopy and low-energy electron diffraction. It is shown that the (3×1) phase consists of mainly monohydride and dihydride structures, while the (1×1) phase is composed of a mixture of monohydride, dihydride, and trihydride surface species. The trihydride surface species is associated with the phase transition between the (3×1) and (1×1) surface phases, and liberates ${\mathrm{SiH}}_4$ and ${\mathrm{\beta }}_{3\mathrm{-}}$ ${\mathrm{H}}_2$ during thermal desorption, beginning at ∼200 K. For the fully saturated Si(100) surface, a saturation surface coverage of 1.9 monolayers (ML) H has been established at a Si(100) adsorption temperature of 210±10 K. These results suggest that the 1.9-ML saturation coverage of H on Si(100) involves the presence of ${\mathrm{SiH}}_3$(a) species, which leads to a (3×1)→(1×1) LEED pattern change. This is contrary to a model for the (1×1) surface involving a uniform ${\mathrm{SiH}}_2$(a) overlayer.