Nucleation and growth of primary nanostructures in SrTiO₃ homoepitaxy

SrTiO₃ nanoislands on SrTiO₃ (001) in a diffusion-limited growth regime were studied using in situ scanning tunneling microscopy (STM). The STM images revealed two characteristic features of nucleation stages. First, the minimum lateral size of the one-unit-cell (uc)-high SrTiO₃ islands was 4 × 4 uc². Second, one-dimensional SrTiO₃ islands of a 4 uc width grew along the crystal symmetry directions. These observations suggest that 4 × 4-uc² islands act as a minimum nucleation seed, and the addition of SrTiO₃ molecular species of the same width is the primary and dominant growth process in SrTiO₃ homoepitaxy. A close inspection of the surface of the substrate during the deposition process revealed possible connections between surface reconstruction and energetically favorable nucleation of SrTiO₃ islands.