EARLY STAGES OF CU GROWTH ON B-SI(111)ROOT-3 X ROOT-3R30-DEGREES

The presence of boron atoms in a subsurface layer provides a high chemical stability to the B-Si(111) square-root 3 x square-root 3 R30-degrees surface (hereafter referred to as the B square-root 3) and confers to it unexpected new properties regarding subsequent deposition of semiconductor or metal atoms. In this study, we report on the early stages of Cu deposition on the B square-root 3 and compare it to the growth on the 7 x 7 substrate using Auger, LEED and EELS characterizations. Different growth behaviours are observed for RT deposition, but striking differences for high temperature deposition revealed the different electronic and chemical properties of the two substrates. For boron concentrations, corresponding to B/Si ratio > 0.02 in Auger, the quasi "5 x 5" is never obtained up to coverages corresponding to 15 equivalent monolayers of deposited Cu, whereas the EEL spectrum of the substrate remains unchanged. Parallel Auger growth curves indicate a Volmer-Weber growth suggesting that under these conditions Cu does not wet the surface. All these results clearly indicate that a strong modification of the interaction between Cu and Si atoms occurs at the surface of the B square-root 3 substrate. This result is interpreted in terms of large electronic charge transfer between Si surface atoms and B atoms underneath which changes drastically the chemical properties of the substrate.