ABSTRACT:
The work functions of two polar surfaces of ZnO (wurtzite), i.e., O-(000–1) and Zn-(0001) are determined by photoelectron spectroscopy in ultrahigh vacuum or in the presence of oxygen or water vapor at near-ambient pressures, and by Kelvin probe in air. The work functions were also determined by Mott-Schottky analysis in aqueous or aprotic (acetonitrile) electrolyte solutions. The values obtained by different techniques and in different environments are much less scattered compared to the fluctuations, reported for TiO 2 (anatase or rutile). The Zn-(0001) surface has a smaller work function for all the solid/vacuum and solid/gas interfaces, and also in the acetonitrile electrolyte solution. Solely at the aqueous electrochemical interface, the difference is small or even opposite. We propose a hypothesis that the dissociative water adsorption on the O-(000–1) is responsible for this irregular downshift of the work function in aqueous medium.
