Surface Microstructure of Ceramic Materials Investigated with the Atomic Force Microscope

The Atomic Force Microscope (AFM) is capable of directly imaging the morphology and microstructure of surfaces on a nanometer scale. In this thesis, the AFM was applied to a variety of ceramic systems, including the reconstruction and faceting behavior of the TiO_2 low index surfaces, the oxidation morphology of VC _{0.73}(100) at 500^ circC, and the morphology of clean and Pd dosed SnO_2 thin films on sapphire. Current theories which attempt to describe the contact mechanics of the tip-surface system are reviewed, and limitations such as various image artifacts are discussed. The faceting and reconstruction behavior of the TiO_2(110), (100), and (001) surfaces was examined. The growth of {011 } facets on the (001) surface below 900 ^circC is consistent with models of growth by surface diffusion. Theoretical facet profiles generated assuming {011} facets and a 400 A radius tip correctly predict image profiles. A distinctly different growth mode was observed above 1300^circC. The surface consists of flat regions separated by sharp ridges. The flat regions contain a step morphology consistent with the observation of {114} facets reported in previous studies. The profiles of the ridges are dominated by tip artifacts. On the (100) and (110) faces of TiO_2, surface features such as sputter cones, low aspect ratio facets, and ridges were observed which were not detected by electron spectroscopy or diffraction. The development of surface morphology with oxidation was studied on VC_{0.73}(100). Crystallites oriented in two orthogonal directions initially form on the surface. Electron diffraction identified the oxide as a VO_ x phase which is in registry with the VC_{0.73} (100) surface. The oxide is unstable and desorbs at temperatures above 1000^circC. Several cases of tip degradation and wear were evident, which at times resulted in sharper tips. The morphology of rf-sputter deposited SnO _2 films on r-cut sapphire was investigated. The sapphire substrates have atomically flat terraces ( ~830 A wide) separated by atomic height steps. Monocrystalline SnO_2(101) films grew epitaxially by diffusion to the sapphire step edges. Evaportion of 8 monolayers of Pd onto the SnO _2 film results in an even distribution over the surface. With annealing, the Pd overlyer coalesces into islands.