Internal-state distributions of H2 desorbed from mono- and dihydride species on Si(100)

Abstract

Following adsorption of atomic hydrogen on Si(100)–(2×1), the surface is heated and the desorbed H₂ is detected via (2+1) resonance‐enhanced multiphoton ionization (REMPI). H₂ desorption correlated with the decomposition of dihydride groups on the surface (SiH₂) is detected at a surface temperature T_s near 660 K, and with the monohydride species (SiH) near T_s=780 K. Although the H₂ rotational distributions are nearly identical for the mono‐ and dihydride species, the vibrational distributions differ with roughly 0.2% and 1% of the population in H₂(v=1) for the monohydride and dihydride, respectively. The enhancement in the [H₂(v=1)]/[H₂(v=0)] population ratio over that of a thermal distribution at T_s is, however, roughly 20 times for both mono‐ and dihydride species. The results are interpreted within a model that assumes desorption proceeds through a common intermediate, which is identified as the dihydride.