Thin Pt films on the polar SrTiO 3(1 1 1) surface: an experimental and theoretical study

Abstract

We have examined the growth of thin Pt films on the polar SrTiO 3(1 1 1) surface using both experimental and theoretical methods. Pt films were grown on both as-received and treated substrates using electron-beam evaporation, and then were characterized with X-ray and low-energy electron diffraction and atomic force microscopy. The nature of the substrate surface strongly influences the crystallinity and microstructure of the Pt films. We find that for well-treated, crystalline SrTiO 3(1 1 1) substrates we obtain crystalline Pt(1 1 1) films. In addition, the first few layers strongly replicate the surface structure of the substrate. XRD results demonstrate that even the best films exhibit two distinct in-plane domains separated by 60°, equivalent to the existence of inversion domains. Density functional theory (DFT) calculations were performed for 1–4 monolayers of Pt on both terminations of SrTiO 3(1 1 1). These calculations find that two energetically equivalent stacking sequences are possible for the second monolayer of Pt, corresponding to the observed 60° domains. We propose that these stacking faults are the source of the observed domains in crystalline Pt(1 1 1) films grown on polar SrTiO 3(1 1 1) surfaces. Finally, the DFT calculations corroborate the observation that the structures and growth modes of the first few monolayers are coupled strongly to the substrate, yet the films quickly relax to bulk-like Pt arrangements and homoepitaxial growth modes.