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

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Abstract
Dissociativeadsorption of H 2 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 ⩽E kin ⩽380 meV ) and the surface temperature (440 K ⩽T s ⩽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.