Oxygen-driven rearrangement of Ag and Au monolayers on W(110) studied by photoemission spectroscopies

Exposure of Ag or Au monolayers deposited on W(1 1 0) to molecular oxygen leads to the formation of admetal double layers and open W patches covered with atomic oxygen. We have studied this rearrangement process in its dependence on admetal coverage, oxygen exposure and substrate temperature employing valence band and core-level photoemission. We present experimental evidence that the first reaction step, dioxygen dissociation, occurs through the closed Ag monolayer on W(1 1 0). Subsequent site-exchange processes lift Ag atoms into the second layer. We compare the restructuring of Ag layers with the one of Au layers. While the basic mechanism appears to be similar, we observe a different dependence on sample temperature during oxyen exposure. (C) 2001 Elsevier Science B.V. All rights reserved.