Study of CeO XPS spectra by factor analysis: reduction of CeO 2 2

The evaluation of the reduction state of CeO2 by XPS is still controversial because of the presence of more than 10 peaks in the Ce 3d.photoemission spectra due to Ce3q and Ce4q, some of them at similar binding energies. This makes difficult conventional fitting using nonlinear least-square NLLSF.methods with Gaussian–Lorentzian curves that require the knowledge of the number of bands. In the present work, we have tried to overcome this problem using factor analysis FA., a method that has been applied with success to other spectroscopic problems. In order to obtain confident results for the individual shapes of the components, the basis for a correct quantification.we have combined target testing TT. and iterative target transformation factor analysis ITTFA.. We have shown that the combined use of these two methods results in a more accurate evaluation ca. "2%.of the reduction state of partially reduced CeO2. The election of the ‘‘real factors’’ corresponding to Ce4q and Ce3q species is discussed in detail. q2000 Elsevier Science B.V. All rights reserved