Charge Density at Oxide Surfaces

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The primary focus of the proposed research is to obtain experimental measurements of charge density changes at surfaces, with a particular emphasis on polar oxide surfaces. For the oxide surfaces, the charge transfer at the surface between the metal cation and oxygen will be measured from precision electron diffraction measurements. In addition, the redistribution of charge density will also be measured. These measurements will be compared to quantum-mechanical calculations, primarily using density functional techniques, done both as part of this effort and with theoretical collaborators. Questions of interest include how covalency and ionicity change at the surface, as well as rehybridization of the d-electrons and valence changes. Simultaneous with this work, ancillary data which may be significant in its own right on the character of steps on oxide surfaces will also be obtained, for instance step structures on antiferromagnetic NiO (111) surfaces. A continuing effort, albeit at a smaller scale, will be development of direct methods for surfaces. The idea is to test whether statistical methods such as multivariant statistical analysis or principle component analysis can be applied to the end product of direct methods, greatly simplifying the final analysis. If this concept works, it would have potential applications in other areas, for instance protein crystallography.