431227 Control of Oxygen Defect Surface Injection in ZnO Via Sub-Monolayer Sulfur Adsorption

Monday, November 9, 2015: 9:30 AM
251D (Salt Palace Convention Center)
Ming Li, Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL and Edmund G. Seebauer, Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana-Champaign

Native oxygen defects within metal oxide semiconductors such as ZnO affect the material’s performance in applications for photovoltaics, nanoelectronics, gas sensing, and photocatalysis. Previous work in this laboratory has shown that the semiconducting metal oxides surfaces can be used to manipulate the concentrations and spatial distributions of bulk oxygen defects, particularly oxygen vacancies. The interaction chemistry between bulk point defects and reactive sites on semiconductor surfaces is comparable in richness to the reactions of surfaces with gases. The present work discusses a novel mechanism of controlling oxygen defect injection in c-plane ZnO(0001) through surface active sites blocking with sub-monolayer sulfur adsorption. Oxygen diffusion rates were measured by exposing single-crystal ZnO to isotopically labeled oxygen (18O2) gas. Sulfur was deposited controllably via an electrochemical cell and characterized in situ by Auger Electron Spectroscopy (AES). The resulting diffusion profiles were measured by secondary ion mass spectrometry (SIMS). Kinetic parameters were extracted by fitting the diffusion profiles with a previously derived mass transport model. The preliminary data shows that sulfur adsorption decreases the oxygen defect injection rate by roughly three times through affecting the injection flux, which points to a site blocking model. Subsequent temperature and pressure dependence study will help us gain insights into detailed injection kinetic pathways.

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