ROLE OF HYDROGEN IN SYNCHROTRON-RADIATION-STIMULATED EVAPORATION OF AMORPHOUS SIO2 AND MICROCRYSTALLINE SI

We report on the photostimulated evaporation of amorphous SiO2 and microcrystalline Si by synchrotron radiation in ultrahigh vacuum and in H-2 ambients up to 0.08 Torr. For a-SiO2, the evaporation was slowed by introduction of H-2, which suggests that the highly efficient decomposition process is hindered by hydrogen termination (-OH species formation). For mu-c-Si, the evaporation rate in ultrahigh vacuum was strongly affected by the degree of crystallization. The evaporation rate doubled with introduction of 0.08 Torr H-2. Hydrogenation of the surface (SiHx species formation) slightly reduces the activation barrier for evaporation.