Surface-Based Control of Oxygen Interstitial Injection into ZnO via Submonolayer Sulfur Adsorption

Semiconductor surfaces offer efficient pathways for injecting native point defects into the underlying bulk. Adsorption of a suitably chosen foreign element serves to modulate the injection rate, even at small percentages of a monolayer. Through self-diffusion experiments using isotopic exchange with labeled oxygen, the present work demonstrates such behavior in the case of sulfur adsorption on <i>c</i>-axis Zn-terminated ZnO(0001), wherein the clean surface injects with exceptional efficiency. The experiments provide strong evidence that the injection sites comprise only a small fraction of the total surface atom density and that sulfur adsorption merely blocks those sites. Comparison with related systems shows this simple mechanism is surprisingly uncommon

Ethylene Hydrogenation over Pt/TiO₂: A Charge-Sensitive Reaction

Controlled charge transfer between a support and small metal particles provides unique opportunities to tune the activity of supported metal catalysts, as first proposed by Schwab [G. M. Schwab et al., <i>Angew. Chem</i>. <b>1959</b>, <i>71</i>, 101–104]. By controlling the thickness of polycrystalline anatase TiO₂ films, the TiO₂ carrier concentration can be manipulated by an order of magnitude. When 1 nm Pt particles are deposited on these TiO₂ films, the variation in the charge transfer between the TiO₂ support and the Pt particles is found to dramatically increase the ethylene hydrogenation activity. The sensitivity of ethylene hydrogenation to charge transfer was anticipated from the large effect of the Pt charge on the ethylene and ethylidyne adsorption energy, e.g., compared to CO and H. Our results demonstrate that the controllable Schwab effect provides a powerful tool to tune catalytic activity. An even larger effect can be expected for supported sub-nanometer clusters, and for the selectivity of hydrogenation reactions