ORIGIN OF THE SEMIMETAL-TO-SEMICONDUCTOR TRANSITION OBSERVED IN 2-DIMENSIONAL ER SILICIDE UPON H EXPOSURE - EVIDENCE OF 2 CHEMISORPTION SITES

Chemisorption of atomic hydrogen on two-dimensional p(1 x 1) ErSi2 sil icide epitaxially grown on Si(111) has been studied with angle-resolve d photoemission (ARP) and high-resolution electron energy-loss spectro scopy (HREELS). The existence of two H chemisorption sites correspondi ng to Si-H and Er-H bonds in the ErSi2 silicide is clearly established . These two sites per unit cell are found to be closely related and, f or stability reasons, must be filled concomitantly rather than sequent ially upon atomic H exposure. Their saturation explains the semimetal- to-semiconductor transition observed upon adsorption of atomic H. (C) 1997 Elsevier Science B.V.