A NEW INTERPRETATION OF THE BINDING-ENERGIES IN X-RAY PHOTOELECTRON STUDIES OF OXIDES

Films and coatings applied to different substrates are often various types of oxides. The latter are employed for a number of reasons with particular emphasis on their lack of chemical and electrical porosity. It is generally important therefore to have some measure of the physical and chemical integrity of the resulting oxide films and their interfaces with the substrate. The latter is often realized by using X-ray photoelectron spectroscopy or electron spectroscopy for chemical analysis. In order to accomplish this, it is common practice to utilize the (now generally well accepted) binding energy data from the literature to verify and expand upon one's results. Unfortunately, close scrutiny reveals a number of major discrepancies in these literature results for certain key oxides. Thus, for example, a significant portion of the literature reports the Al 2p level of Al2O3 at similar to 75.7 +/- 0.3 eV, whereas many others specify similar to 74.0 +/- 0.2 eV. Perhaps the greatest difficulty with this observation is that it can be shown that, based upon their respective methods of analysis, both results are equally valid. In the present investigation, we examine the extent and nature of this problem. We have discovered that there are particular types of oxides that exhibit this dichotomy in binding energies, whereas others do not. The role played by bonding and morphology in these differences is explored, as is the effect of the different methods of binding energy determination. Finally, we shall describe how the mechanism of the growth of oxides is the principal ''culprit'' and a lack of understanding of the latter and its electronic implications may lead many to an incorrect interpretation of ''true'' binding energies.