Oxidation state sensitive 3D atomic mapping of oxide-supported catalysts through X-ray Standing Wave (XSW) excited X-ray photoelectron spectroscopy (XPS)

XSW excited XPS was used to study the hydroxylated surface of rutile TiO₂ (110) single crystal, where the excess unpaired electrons of the hydroxyls play a critical role in surface chemistry and photocatalytic processes. The experiments were performed at APS DND-CAT 5IDC using a 7 keV incident beam. The hydroxylated O 1s binding energy was 2.4 eV higher than that of the bulk-like O atoms and was found to have a different XSW coherent fraction and position. Summation of these Fourier components for 3 symmetry inequivalent hkl Bragg peaks generate a chemical state sensitive 3D atomic map of oxygen. We also studied monolayer coverages of vanadium oxide (catalytic material) supported on the same surface. Collecting V, O and Ti 1s XPS signals as we scanned across a Bragg peak at different stages of a redox reaction allowed tracking of surface sites for chemically distinct V atoms, important for understanding their catalytic behaviour. These results coupled with DFT calculations will give unique insights into this as well as other related oxide supported catalysts.