How heteroepitaxy occurs on strontium titanate

In traditional models of heteroepitaxy, the substrate serves mainly as a crystalline template for the thin-film lattice, dictating the initial roughness of the film and the degree of coherent strain. Here, performing in situ surface x-ray diffraction during the heteroepitaxial growth of LaTiO ₃ on SrTiO ₃ (001), we find that a TiO ₂ adlayer composed of the (√ 13 × √ 13) R33.7° and (radic 2 × √ 2) R45.0° reconstructions is a highly active participant in the growth process, continually diffusing to the surface throughout deposition. The effects of the TiO ₂ adlayer on layer-by-layer growth are investigated using different deposition sequences and anomalous x-ray scattering, both of which permit detailed insight into the dynamic layer rearrangements that take place. Our work challenges commonly held assumptions regarding growth on TiO ₂ -terminated SrTiO ₃ (001) and demonstrates the critical role of excess TiO ₂ surface stoichiometry on the initial stages of heteroepitaxial growth on this important perovskite oxide substrate material.