Site-specific valence-band of Pt monolayer on SrTiO₃ (001) via X-ray standing wave excited photoelectron emission

Platinum is widely used as a heterogeneous catalyst in chemical production. The interfacial atomic behavior of the Pt/support structure in redox processes remains ambiguous. In this work, X-ray standing wave (XSW) excited photoemission was used to measure the site-specific valence band for a Pt monolayer (ML) grown on a SrTiO₃ (001) substrate (Pt/STO). The Pt ML was grown by pulsed laser deposition. XSW measurements were performed at the Diamond Light Source I09 beamline on the as-deposited, oxidized and reduced surfaces, where we found that ½ of the Pt was correlated with the substrate lattice. The XSW induced modulations in the core and valence photoemission signals from the surface and substrate atoms were monitored while scanning through three different hkl substrate Bragg peaks. This information was then compared to the DFT projected density of states from the surface and substrate atoms. We find that the Pt region of the valence-band shows the biggest redox-induced changes. Furthermore, this higher activity is primarily attributed to the portion of Pt that is uncorrelated with the substrate lattice.