The adsorption and incorporation of oxygen on Cu(100) and its reaction with carbon monoxide; comparison with Cu(111) and Cu(110)

Abstract

Ellipsometry, LEED, Auger electron spectroscopy and monitoring of work function changes have been used to study the interactions of O2 and N2O with a clean annealed Cu(100) surface and of the reaction of CO with sorbed oxygen. Gas pressures were in the range 10−7−10−4 Torr and crystal temperatures varied between 25–400°C. The initial interaction of oxygen with Cu(100) occurs in three stages. Oxygen chemisorbs with an initial sticking coefficient of ˜10−7 at room temperature and an apparent activation energy of 1.3−3.5 kcal/mol, depending on the substrate temperature. The first stage is the formation of a (√2 × √2)R45° LEED pattern up to a coverage of 0.5, which is converted with an apparent activation energy of 3.2 kcal/mol to a (√2 × 2√2)R45° structure at a coverage of 0.75 in the second stage. The work function increases inthe first stage in an amount of ˜300 meV, but decreases in the second stage to the value of the clean surface. In a third stage after an induction period further oxygen uptake could be registered only with ellipsometry. The apparent activation energy is 4.5 kcal/mol. The initial decomposition probability of N2O at room temperature is 5 × 10−5, its apparent activation energy 3.2 kcal/mol. The LEED patterns observed were the same as with O2. The sorbed oxygen can be removed at all coverages with CO. The reaction appears to follow Langmuir-Hinshelwood kinetics with an activation energy for the reaction COad + Oad → CO2 of 19–20 kcal/mol. A comparison is made with the data obtained for Cu(111) and Cu(110).