Effect of beam energy and surface temperature on the dissociative adsorption of H2 on Si„001..

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 and 10. 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 0.860.2 eV to almost negligible values. Previously proposed defect-mediated processes can be ruled out as a major adsorption channel. © 1999 American Institute of Physics. @S0021-9606~99!70747-6#