Effects of adventitious impurity adsorption on oxygen interstitial injection rates from submerged TiO2(110) and ZnO(0001) surfaces

Abstract

Low bond coordination of surface atoms facilitates the injection of oxygen interstitial atoms into the bulk near room temperature from the clean surfaces of semiconducting metal oxides when exposed to liquid water, opening new prospects for postsynthesis defect engineering and isotopic fractionation. The injection rate and penetration depth vary considerably under identical experimental conditions, however, with the adsorption of adventitious carbon suggested as the cause. For water-submerged rutile TiO2(110) and wurtzite ZnO(0001), this work bolsters and refines that hypothesis by combining the isotopic self-diffusion measurements of oxygen with characterization by x-ray photoelectron spectroscopy and atomic force microscopy. Adventitious carbon likely diminishes injection rates by poisoning small concentrations of exceptionally active surface sites that either inject O or dissociate adsorbed OH to injectable O. These effects propagate into the penetration depth via the progressive saturation of Oi traps near the surface, which occurs less extensively as the injected flux decreases.