Ultrasoft pseudopotential total energy calculation based on density functional theory (DFT) with generalized gradient approximation (GGA) have been used to investigate (1) the possible energy pathway for direct dissociative adsorption of GeH4 onto both Si(001) and Ge(001) surfaces to evaluate their gas–surface reactivity in comparison with measured gas–surface reactivity using supersonic molecular beam techniques and (2) the coupling of internal distortion of GeH4 with SiSi dimer distortion on Si(001) and GeGe dimer distortion on Ge(001) surfaces, respectively, at their transition states to understand how experimental variables such as incident kinetic energy of GeH4 and substrate temperature govern their gas–surface reactivity. Firstly, our calculated transition state structures strongly indicate the gas–surface reactivity for direct dissociative adsorption of GeH4 onto both Si(001)-(2×2) and Ge(001)-(2×2) surfaces increases with both incident kinetic energy and substrate temperature. But the increase of gas–surface reactivity with increasing substrate temperature, i.e. inducing thermal vibration, is not as significant as that with increasing incident kinetic energy of GeH4, i.e. inducing bond-breaking distortion. Secondly, our evaluated gas–surface reactivity for direct dissociative adsorption of GeH4 onto Si(001) is approximately a factor of 6 better than that onto Ge(001). This calculated result is in reasonable agreement with its counterpart (approximately a factor of between 10 and 2 depending on the incident kinetic energy) derived from measured gas–surface reactivity using supersonic molecular beam techniques. Finally, we attribute this higher evaluated gas–surface reactivity for the direct dissociative adsorption of GeH4 onto Si(001) surface in comparison with that onto Ge(001) surface to (1) the less energy conversion from incident kinetic energy of GeH4 to the energy of internal distortion of GeH4 at the transition state and (2) the more populated vibrational levels of SiSi dimer on Si(001) surface than that of GeGe dimer on Ge(001) surface provided by the same substrate temperature to reach their transition states.
Relation:
Journal of Molecular Structure : Theochem 635(1-3), pp.115-124
