Kinetics of oxygen adsorption and initial oxidation on Cu(110) by hyperthermal oxygen molecular beams

Moritani, Kosuke*; Okada, Michio*; Teraoka, Yuden; Yoshigoe, Akitaka ; Kasai, Toshio*

Oxygen adsorption and subsequent oxide formation on Cu(110) using a hyperthermal oxygen molecular beam (HOMB) has been investigated using SR-XPS. The O-uptake curves, which were determined from the evolution of O-1s peaks, indicate that simple Langmuir type kinetics can describe dissociative adsorption of O with an incident energy (Ei) below 0.5eV under oxygen coverage of 0.5 ML. The reaction order dependence on Ei implies two competing dissociation mechanisms, trapping-mediated and directly-activated adsorption. Oxidation at oxygen coverage larger than 0.5 ML proceeds rather effectively using highly energetic HOMB at Ei larger than 1.0 eV. The surface CuO formed with highly-energetic HOMB incidence decomposes with desorbing subsurface oxygen even at room temperature. This indicates that HOMB can induce a meta stable surface structure that cannot be produced in the thermal equilibrium process.