Local geometric and electronic structure of oxides using scanning tunneling microscopy/spectroscopy

Abstract

The potential of scanning tunneling microscopy (STM) and related scanning probe microscopies is amply demonstrated by the geometric increase in the number of papers utilizing the techniques that are published each year. The power of STM derives, not only from imaging capabilities, but also from associated spectroscopies which can provide local information about the density of states and work function. Although the technique has been applied to a wide range of metal and semiconductor surfaces, application to large bandgap materials such as oxides is difficult. We demonstrate the successful application of STM/STS to oxides with an analysis of the effect of reduction mechanism on the geometric and electronic structure of TiO2 (110). The structure of defects in oxides is critical in that it affects many properties of practical interest including catalysis, photoelectrolysis, and electron transport. The presence of defects can affect the local cation valence, such that the variation of d-orbital occupation results in a range of electronic properties, from insulating to semiconducting in nature. STM/STS is the ideal tool to probe the structure of these defects.