X-ray 3D atomic imaging of Pt nanocrystals supported on SrTiO$_{3}$(001)

Ultrathin metal or metal-oxide layers deposited onto oxide surfaces have wide applications in catalysis, chemical sensing and electronics. For sub-monolayer Pt deposited on the 2x1 SrTiO$_{3}$(001) surface, atomic-force microscopy shows the formation of nanoparticles and X-ray standing wave (XSW) atomic imaging shows that these nanoparticles are composed of Pt face-centered-cubic nanocrystals with cube-on-cube epitaxy coherent to the substrate unit cell. The phase sensitivity of the XSW allows for a direct measurement of the interface offset between the two unit cells along the c-axis. Different Pt coverages lead to differences in the observed XSW image of the interfacial structure, which is explained by the Pt-Pt interaction becoming stronger than the Pt-substrate interaction as the coverage is increased from 0.2 to 0.6 ML. Proposed atomic-scale interface models are based on a published double-layer TiO$_{2}$ terminated structure for the 2x1 SrTiO$_{3}$(001) surface and density functional theory.