Direct observation of hydride surface phases

Sakurai et al. [218] have used the atom probe field ion microscope [219] to make a direct study of hydride phases on silicon. Continuous field evaporation from 111 and 110 Si planes in the presence of hydrogen produced Si+, SiH+ and SiHj. Some Si atoms evaporate without forming hydrides to give Si+ SiH+ derives simply from the monohydride phase and SiHj from the dihydride. However, this latter comes from the 111 surface, whereas UPS data consistent with the presence of a dihydride came from 100 lxl. This apparent difference can be reconciled by the fact that some kink site atoms on 111 planes have two dangling orbitals per Si atom (as on 100 surfaces) and field evaporation occurs primarily at kink sites. 

With a disordered 311 surface, d.c. field evaporation produced Si+, SiH+ and, importantly, SiH4. If it is assumed that the disordered 311 surface has vacancies similar to those on the disordered 111 1 x 1, from which UPS data suggest Si atoms evaporate by the reaction 

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