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 Ts near 660 K, and with the monohydride species (SiH) near Ts=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 Ts 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.