Atomic-Site-Specific Surface Valence-Band Structure from X-Ray Standing-Wave Excited Photoemission

Abstract

X-ray standing wave (XSW) excited photoelectron emission was used to measure the site-specific valence band (VB) for 1 ⁄2 monolayer (ML) Pt grown on a SrTiO3 (001) surface. The XSW induced modulations in the core level (CL) and VB photoemission from the surface and substrate atoms were monitored for three hkl substrate Bragg reflections. The XSW CL analysis shows the Pt to have an f cc-like cube-on-cube epitaxy with the substrate. The XSW VB information compares well to a density functional theory calculated projected density of states from the surface and substrate atoms. Overall, this work represents a novel method for determining the contribution to the density of states by valence electrons from specific atomic surface sites.

Atomic-Scale Interface for Pt Nanoparticles on SrTiO3 (001)

“…39 This Pt−O interaction was also observed to affect the site-specific valenceband structure as reported in our previous XSW-XPS study of the AD Pt/STO interface. 22 Our current results provide a more complete description of the strong metal−support interaction through Pt−O bond at the interface, not only on the particle surface. Moreover, we found the interface O structure evolution appeared in the oxidation process at a lower temperature than 400 °C (see Figure S13), which means the interface O structure affects the Pt atomic structure.…”

“…To quantitatively determine the fraction of Pt occupying each site, α, and the height z of each site, a global least-squares fit is used to compare the model-predicted Fourier components to the four ( hk l) measured Fourier components: ,, F H = f H e 2 π i P H = e − 2 true( π σ d H true) 2 true[ α A e 2 π i bold-italicH · r A + α B e 2 π i bold-italicH · r B + α c true( e 2 π i bold-italicH · r bold-italicC bold1 + e 2 π i bold-italicH · r bold-italicC bold2 true) true] …”

“…Previous scanning probe microscopy work showed strong metal–support interaction on the oxide adlayer for Pd nanocrystals supported on SrTiO 3 (001). , The metal film growth kinetics confirmed Pt has high oxygen affinities due to interfacial bonding, which leads to Pt adsorption sites directly above O atoms . This Pt–O interaction was also observed to affect the site-specific valence-band structure as reported in our previous XSW-XPS study of the AD Pt/STO interface . Our current results provide a more complete description of the strong metal–support interaction through Pt–O bond at the interface, not only on the particle surface.…”

“…From this analysis, the Pt atoms show an upward displacement of 0.7 to 0.8 Å after the reaction. To quantitatively determine the fraction of Pt occupying each site, α, and the height z of each site, a global least-squares fit is used to compare the model-predicted Fourier components to the four (hkl) measured Fourier components: 13,20,22 F f e e e e e e…”

“…This earlier study focused on the atomic-site-specific valence-band structure. 22 X-ray Standing Wave Analysis of Surface Oxygen Atomic Distribution. For O 1s, we observed a double peak for all reflection geometries (see Figure S7).…”