Growth mode transition to pyramid from layer by layer of heteroepitaxial PbTiO₃ islands on a (001) vicinal SrTiO₃ substrate fabricated by hydrothermal epitaxy

The authors observed the surface morphology transition from the atomically flat two dimensional layer-by-layer mode to the three dimensional pyramidal mode of heteroepitaxial PbTiO₃ (PTO) islands synthesized by hydrothermal epitaxy by scanning electron microscopy and atomic force microscopy. Two types of (001) Nb–SrTiO₃ (NSTO) with the same step height, ∼0.25 and ∼1 μm terrace widths, were used for substrates. They found the critical island thickness at which the growth mode of PTO island was converted and its relation to the terrace width of the substrate. It is suggested that the relaxation of the misfit strain, which originates from out-of-plane lattice mismatch between the PTO island unit cell and the NSTO substrate step or somewhere interior of the film, has an effect on the PTO island growth mode transition.