Identification of atomic adsorption site by means of high-resolution photoemission surface core-level shift: oxygen on Ru(1010)

Oxygen adsorption on Ru(10 (1) over bar 0) is studied using the evolution o f the 3d(5/2) photoemission surface core-level shift as a function of cover age. We show that the measurements are sensitive to changes occurring to at oms in both the first and the second layer. This permits a direct demonstra tion that oxygen adsorbs on this surface in the three-fold hexagonal close- packed site. In addition, the role of the ruthenium second layer in the ads orption process is discussed in terms of the oxygen-metal interaction and h eat of adsorption. (C) 2000 Elsevier Science B.V. All rights reserved.