SUPERSONIC MOLECULAR-BEAM STUDIES OF THE DISSOCIATIVE CHEMISORPTION OF GEH4 AND GE2H6 ON THE GE(100) AND GE(111) SURFACES

zThe reaction probabilities of GeH4 and Ge2H6 on the Ge(100) and Ge(11 1) 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 k inetic energies (E(i)> 1 eV) both GeH4 and Ge2H6 react by direct disso ciative chemisorption on both surfaces examined, with the reaction pro bability increasing approximately exponentially with increasing (scale d) incident kinetic energy. At moderate kinetic energies (E(i) similar to 0.4 eV), however, Ge2H6 reacts by a precursor-mediated mechanism o n Ge(100), as demonstrated by a decrease in the reaction probability w ith either increasing substrate temperature or incident kinetic energy , Interestingly, under similar conditions, no evidence is found for pr ecursor-mediated adsorption of Ge2H6 on the Ge(111) surface. The react ion of Ge2H6 does not exhibit a GeH4 production channel on either Ge(1 00) or Ge(111) for the conditions examined here. The results obtained at high incident kinetic energies (>1 eV) are well described by a stat istical model based upon a Rice-Ramsperger-Kassel-Marcus (RRKM) framew ork. The moderate incident kinetic energy results for Ge2H6 on Ge(100) are well described by a model that assumes reaction via a trapping, p recursor-mediated mechanism. (C) 1996 American Institute of Physics.