Dissociative adsorption of O2 on Cu(001)-(2√×√)-O was shown to induce Cu2O epitaxial islands on the surface. The initial dissociative sticking probability of O2 on Cu(001)-(2√×√)-O scaled with the total translational energy of incident O2, suggesting that the interaction potential was highly corrugated. The sticking probability decreased with increasing translational energy of incidence and increased with increasing surface temperature. For lower translational energy of incident O2 (⩽130 meV), the velocity distribution of the scattered molecules was of nonshifted Maxwellian-type, indicating trapping desorption. The translational temperature of the trapping desorption was lower than the surface temperature and increased linearly with surface temperature, suggesting that there was no barrier for desorption. Neither thermal desorption experiments nor velocity distribution analysis of the trapping desorption showed any evidences of recombination desorption. These results were interpreted as an activated dissociation via a trapping precursor. The activation barrier for dissociation was estimated as 330 meV. The angular distribution of the trapping desorption was fitted well by cos2 θ, which was in contrast to the expectation of a cosine angular distribution based on the detailed balance arguments. The discrepancy may have been attributable to preferential consumption of the parallel momentum of the trapped O2 for dissociation and imbalance between adsorbing and desorbing O2 flux.

In exploring the dynamics of dissociative chemisorption of O2 on clean and O-covered Cu(001), we demonstrate that the chemisorption is very sensitive to uniaxial tensile stress within an elastic limit. The stress enhances the dissociative chemisorption on clean Cu(001) when the translational energy of incident O2 is below 250 meV, and suppresses it when the energy is above 250 meV. In the case of an oxygen-covered Cu(001)- (2squareroot2 x squareroot2) surface, the dissociative adsorption probability of O2 decreases as the stress increases. The effect of external stress on the O2 dissociation dynamics is different between clean and O-covered surfaces.

There are two distinctive channels in the dissociation reaction of O2 on Si(001)-(2 x 1): a trapping-mediated channel and a direct-activated channel. Externally applied tensile strain along the <110> direction on the (001) surface is found to suppress the dissociation via a direct-activated channel and to enhance that via a trapping-mediated channel in the temperature range between 200 and 300 K. It has been demonstrated that the dissociation dynamics involving elementary processes such as inelastic scattering and trapping, desorption and/or dissociation from a trapping precursor, and direct dissociation are sensitively influenced by the strain to change the branching ratio of the dissociation reaction.

We have investigated the initial oxidation process of Cu(001) surface and the role of translational energy of incident O 2 on the initial oxidation using supersonic molecular beam techniques. In the initial oxidation, the Cu(001) surface is oxidized in a layer by layer manner up to one monolayer, followed by forming the Cu 2 O epitaxial islands on the layer. At the initial stage of the layer by layer oxidation, a direct activated dissociation of O 2 is a dominant process and the process is promoted by the increasing translational energy of incident O 2 . At the stage of the subsequent oxidation in which the Cu 2 O islands are formed on the oxide layer, dissociative adsorption of O 2 proceeds by thermal activation via a trapping precursor and the process is promoted by the decreasing translational energy of the incident O 2 and/or by increasing surface temperature. Our results demonstrate that the initial oxidation can be controlled by the adjustment of the translational energy of incident O 2 .