The kinetics of the interactions of O2 and N20 with a Cu(110) surface and of the reaction of CO with adsorbed oxygen studied by means of ellipsometry, AES and LEED

Abstract

Ellipsometry, LEED and Auger electron spectroscopy have been used to study the interactions of O2 and N2O with a clean annealed Cu(110) surface and the reaction of CO with adsorbed oxygen in the monolayer range. Gas pressures were in the range 10−8–10−4 Torr and crystal temperatures varied between 23–400°C. The changes in the ellipsometric angles Δ and ψ per oxygen atom upon adsorption and removal of oxygen depend on the coverage θ, the temperature and on the azimuth of the plane of incidence of the light beam. The kinetics of the chemisorption of oxygen is independent of the crystal temperature, initial sticking probability ≈ 0.2. The LEED data and the adsorption kinetics indicate an attractive interaction in the adsorbed layer in the [001] direction. The initial decomposition probability of N2O at room temperature is 0.15 and decreases with increasing temperature; the maximum coverage is 0.5 monolayer. The LEED patterns observed were the same as those with O2. The reaction probability of CO with adsorbed oxygen increases with decreasing oxygen coverage (order of magnitude 10−5, apparent activation energy 6 kcal/mol). This increase has been attributed to the operation of the Langmuir-Hinshelwood mechanism.