Interaction of H with epitaxial Er silicide layers on Si(111): adsorption versus absorption

Abstract

We present evidence from angle-resolved photoemission that a well-ordered H monolayer is chemisorbed on both two-dimensional (1 × 1) and bulk-like (√3 × √3)R30° Er silicide epitaxially grown on Si(111) when exposed to atomic H at room temperature. The data indicate a complete saturation of the Si surface dangling bonds in a geometry quite similar to the ideal Si(111)-(1 × 1)H surface. Most interestingly, in the case of bulk-like Er silicide it is found that H is not only adsorbed on but also absorbed in the layer, i.e. formation of a hydride takes place. H absorbed in the bulk-like (≥2 ML) films causes dramatic changes in their electronic structure and is the more tightly bound form in ultrathin (∼2 ML) films. The spectroscopic data suggest a model where H in bulk silicide passivates the internal Si dangling bonds related to the ordered array of Si vacancies formed in the graphite-like Si planes of defected (√3 × √3)R30° Er silicide.