XPS comparison between nanocrystalline γ-alumina and a new high pressure polymorph

High surface area, nano-phase materials exhibit many interesting properties quite different from their bulk counterparts, and are the focus of much technical investigation and engineering development based on these properties. Earlier experiments using X-ray diffraction have indicated that a new phase of alumina exists upon non-hydrostatic compression of 67 nm particles of γ-alumina to above 35 GPa and quasi-hydrostatic compression to pressures over 50 GPa. This phase is quenchable on decompression to 0 GPa, allowing for additional analysis that are unmanageable in the diamond anvil cell (DAC). For the present paper, imaging X-ray photoelectron spectroscopy (XPS), which is ideally suited for surface chemistry measurements of the small samples required in the DAC, is used. The collection of Bremsstrahlung excited Auger electrons in combination with photoelectrons allows for a better comparison of chemical shifts, through the Auger parameter. No dramatic change was observed, as is the case with many alumina polymorphs, but slight differences between the gamma phase and the new high-pressure phase are noted, supporting the earlier X-ray results. Additionally, an extremely low adventitious carbon level was observed on a γ-phase sample and is discussed.