Effect of beam energy and surface temperature on the dissociative adsorption of H2 on Si(001)

By: Dürr, M. B. Raschke, and U. Höfer

Journal of Chemical Physics 111, 10411 (1999)

Dissociative adsorption of H2 from a high-flux supersonic molecular beam on flat and vicinal Si(001) surfaces was investigated by means of optical second harmonic generation (SHG). The initial sticking coefficients for terrace adsorption varied between 10-8 and 10-4 . They revealed a strongly activated dissociation process, both with respect to the kinetic energy of the incident molecules (70 meV≤Ekin≤380 meV) and the surface temperature (440 K≤Ts≤670 K). The results indicate that dynamical distortions of Si surface atoms can lower the effective adsorption barriers from 0.8 +/- 0.2 eV to almost negligible values. Previously proposed defect-mediated processes can be ruled out as a major adsorption channel.