Abstract
The adsorption of NH 3 on a clean Si(111)7 × 7 reconstructed surface and the effect of vacuum annealings of the NH 3-saturated surface have been studied by low energy electron diffraction, Auger electron spectroscopy and photoemission yield spectroscopy. The analysis of the surface order, of the nitrogen coverage and of the workfunction, ionization energy and filled surface state band changes upon NH 3 exposure or annealing temperatures gives the following results: the adsorption is dissociative into NH 2 + H and occurs in a two-step process, a fast one with an initial sticking coefficient equal to one up to half saturation, then a much slower one. At saturation, 10 ± 1 NH 3 molecules per 7 × 7 unit cell are adsorbed, the NH 2 radicals occupying the 7 rest atom dangling bonds plus three sites on the average which are attributed to the presence of steps or missing adatoms. Annealings lead to a two-step process, first a hydrogen desorption from 450 °C to 700 °C then a surface nitridation beyond 800 °C.
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