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

The interaction of O-2 with the Ag(111) surface was studied with scanning tunneling microscopy (STM) in the pressure range from 10(-9) Torr to 1 atm at room temperature and with X-ray photoelectron spectroscopy (XPS) up to 0.3 Torr O-2 in the temperature range from RT to 413 K. 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 0.01 Torr. In regions where the step density is high, the surface became rough under 0.01 Torr of O-2, 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 O-2 pressure, is kinetically hindered in the flat terrace areas but proceeds readily in regions with high-step density. (C) 2016 Elsevier B.V. All rights reserved.