Structure of Periodic Crystals and Quasicrystals in Ultrathin Film Ba-Ti-O

TL;DR

This paper models the structure of ultrathin Ba-Ti-O films, revealing quasicrystalline patterns and matching experimental STM images, advancing understanding of these complex thin-film structures.

Contribution

It introduces a detailed structural model of Ba-Ti-O thin films, including quasicrystalline arrangements, validated by simulated STM images matching experimental data.

Findings

Quasicrystal structure decorated with tiles: square, triangle, rhombus.

Simulated STM images match experimental patterns.

Ba atoms identified as bright protrusions in STM images.

Abstract

We model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO$_3$ thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O, and with Ba occupying the larger. mainly Ti$_7$O$_7$, pores. The quasicrystal structure is a simple decoration of three types of tiles: square, triangle and 30 degree rhombus, with edge lengths 6.85 Angstroms, joined edge-to-edge in a quasicrystalline pattern; observed crystalline Ba-Ti-O structures are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally, and identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.