A study of the O/Ag(111) system with scanning tunneling microscopy and x-ray photoelectron spectroscopy at ambient pressures

Abstract

The interaction of O2 with the Ag(111) surface was studied with scanning tunneling microscopy (STM) in the pressure range from 10−9Torr to 1atm at room temperature and with X-ray photoelectron spectroscopy (XPS) up to 0.3Torr O2 in the temperature range from RT to 413K. STM images show that the Ag(111) surface topography is little affected in regions with large flat terraces, except for the appearance of mobile features due to oxygen atoms at pressures above 0.01Torr. In regions where the step density is high, the surface became rough under 0.01Torr of O2, due to the local oxidation of Ag. Various chemical states of oxygen due to chemisorbed, oxide and subsurface species were identified by XPS as a function of pressure and temperature. The findings from the STM images and XPS measurements indicate that formation of an oxide phase, the thermodynamically stable form at room temperature under ambient O2 pressure, is kinetically hindered in the flat terrace areas but proceeds readily in regions with high-step density.