Hydrogen-induced semimetal-semiconductor transition of two-dimensional ErSi2 detected by electron energy loss spectroscopy

Using high-resolution electron energy loss spectroscopy, we find that two-di men sio nal ErSi2 silicide epitaxially grown on Si(111) undergoes a semimetal-semiconductor transition upon atomic H dosing. Passivation of the Si top layer already inferred from previous photoemission work is directly demonstrated and provides further evidence of the similarity between the silicide surface atomic structure and the ideal Si(111) termination. Nevertheless, in contrast with the latter case it is shown by using simple chemical bonding and electron counting arguments that saturation of the Si dangling bonds cannot explain by itself the semiconducting nature of the hydrogenated silicide. Possible mechanisms that might account for the observed transition are discussed.