Thin Pt films on the polar SrTiO3(111) surface : an experimental and theoretical study

We have examined the growth of thin Pt films on the polar SrTiO3(111) surface using both experimental and theoretical methods. Pt films were grown on both as-received and treated substrates in a UHV chamber using electron beam evaporation, and they 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 SrTiO3(111) substrates we obtain crystalline Pt(111) 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. DFT calculations were performed for 1 to 4 monolayers of Pt on both terminations of SrTiO3(111). 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(111) films grown on polar SrTiO3(111) 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.