Dissociative Chemisorption at Hyperthermal Energies: Benchmark Studies in Group IV Systems

We present a review of our recent work concerning supersonic molecular beam scattering of thin film precursors from the Si(100) and Si(111) surfaces. Both SiH4 and Si2H6 exhibit translationally activated dissociation channels at sufficiently high incident kinetic energies, (E┴) 0.5 eV. the dominant variables under our reaction conditions are the incident kinetic energy and the angle of incidence, whereas mean internal energy and substrate temperature play relatively minor roles. the former two variables couple to produce a universal relationship between the reaction probability and a scaled kinetic energy given by (E┴) = Eі[(l-Δ)cos2θі + 3Δsin2θі], where θі is the angle of incidence, a is a corrugation parameter, and 0 ≤ Δ ≤ 1. IN addition to the reaction probability, the reaction mechanism for Si2H6 is also dependent upon incident kinetic energy and surface structure, where a SiH4(g) production channel is observed on the Si(111)-(7x7) surface at low to moderate incident kinetic energies. the reactions of SiH3CH3 and PH3 provide convenient comparative examples. Methylsilane, reacting on a β-SiC surface, exhibits a translationally activated dissociation channel, similar to what is observed for SiH4 and Si2H6. Phosphine, on the other hand, exhibits the characteristics of trapping, precursor-mediated dissociative chemisorption. these results act to underscore the important role played by the frontier orbital topology, even at hyperthermal incident kinetic energies.