IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Applied Surface Analysis Friday Sessions
       Session AS-FrM

Paper AS-FrM10
Use of Core- and Valence-Band XPS to Measure the Differences Among Similar Oxide and Mineral Phases

Friday, November 2, 2001, 11:20 am, Room 134

Session: Catalysis and Surface Reactivity
Presenter: F.S. Ohuchi, University of Washington
Authors: F.S. Ohuchi, University of Washington
G. Ghose, University of Washington
M.H. Engelhard, Pacific Northwest National Laboratory
D.R. Baer, Pacific Northwest National Laboratory
Correspondent: Click to Email
The three polymorphs of Al@sub 2@SiO@sub 5@, sillimanite, andalusite, and kyanite, are geologically important minerals. The differences in their stability relations depend critically on the differences in the chemical bonding of each polymorph of Al@sub 2@SiO@sub 5@, in which half of the Al-coordinations are 4-fold (tetrahedral) in sillimanite (stable at low P and high T), 5-fold (trigonal bipyramidal) in andalusite (stable at low P and high T), and 6-fold (octahedral) in kyanite (stable at low P and high T), whereas the other half of the Al atoms are in 6-fold (octahedral) and Si in 4-fold (tetrahedral) coordination in all three polymorphs. A challenge is whether we are able to measure such small differences using XPS technique, since bonding differences and electronic structures are fundamental to our understanding of their thermodynamical properties and stability relations. We have therefore undertaken an investigation using a state-of-the-art XPS system by measuring Al(2p), Si(2p), O(1s) core level spectra as well as valence band spectra. Introducing a novel charge neutralization technique, clear differences in each spectrum from three different polymorphs were identified, and the change in the valence band spectra were compared with ab-initio density of state calculations. This technique was further applied to other minerals, such as magnesium-silicates.