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

Oxygen adsorption and subsequent oxide formation on Cu(110) using a hyperthermal oxygen molecular beam (HOMB) were investigated using X-ray photoelectron spectrometry. The O-uptake curves, which were determined from the evolution of the O-1s peaks, indicate that simple Langmuir type kinetics can describe dissociative adsorption of O(2) with an incident energy (E(i)) below 0.5 eV under Theta < or = 0.5 ML. The reaction order dependence on E(i) implies two competing dissociation mechanisms, trapping-mediated and directly activated adsorption. Oxidation at Theta > or = 0.5 ML proceeds rather effectively using highly energetic HOMB at E(i) > or = 1.0 eV. The azimuthal dependence of the sticking probability during the effective oxidation using HOMB incidence suggests that the added rows, which consist of the Cu-O structure, shade the reactive hollow sites in the trough where oxygen penetrates into the subsurface. The surface Cu(2)O formed with highly energetic HOMB incidence decomposes with desorbing subsurface oxygen even at room temperature, demonstrating that HOMB can induce a metastable surface structure that cannot be produced in the thermal equilibrium process.