Evidence of a critical film thickness for the early growth stage transition in YBa2Cu3O7-δ thin films

YBa2Cu3O7-delta thin films were grown by pulsed laser deposition on (100) SrTiO2 substrates with 0 and 5 degrees miscut angles along the [010] direction to observe and manipulate the growth at the early stages. For films on 0 degrees miscut substrates, the first 30 Angstrom of growth was by island nucleation, and the areal density of nuclei increased with the him thickness. The transition from island nucleation to growth was between 30 and 60 Angstrom. Islands grew larger with the film thickness for films thicker than 30 Angstrom while the areal density was dramatically reduced. For the films on 5 degrees miscut substrates, the step-flow growth and island nucleation competed with each other for film thicknesses up to 30 Angstrom. When the film thickness increased above 60 Angstrom, the step-flow mode was dominant and no islands were observed.