Supersonic molecular beam studies of the dissociative chemisorption of GeH₄ and Ge₂H₆ on the Ge(100) and Ge(111) surfaces

The reaction probabilities of GeH₄ and Ge₂H₆ on the Ge(100) and Ge(111) surfaces have been measured as a function of substrate temperature, incident kinetic energy, and angle of incidence employing supersonic molecular beam scattering techniques. At sufficiently large incident kinetic energies (E_i>1 eV) both GeH₄ and Ge₂H₆ react by direct dissociative chemisorption on both surfaces examined, with the reaction probability increasing approximately exponentially with increasing (scaled) incident kinetic energy. At moderate kinetic energies (E_i∼-0.4 eV), however, Ge₂H₆ reacts by a precursor-mediated mechanism on Ge(100), as demonstrated by a decrease in the reaction probability with either increasing substrate temperature or incident kinetic energy. Interestingly, under similar conditions, no evidence is found for precursor-mediated adsorption of Ge₂H₆ on the Ge(111) surface. The reaction of Ge₂H₆ does not exhibit a GeH₄ production channel on either Ge(100) or Ge(111) for the conditions examined here. The results obtained at high incident kinetic energies (>1 eV) are well described by a statistical model based upon a Rice-Ramsperger-Kassel-Marcus (RRKM) framework. The moderate incident kinetic energy results for Ge₂H₆ on Ge(100) are well described by a model that assumes reaction via a trapping, precursor-mediated mechanism.