Growth mode study of heteroepitaxial $PbTiO_3$ island on (001) $Nb-SriTiO_3$ fabricated by means of Hydrothermal epitaxy

Abstract

Heteroepitaxial structures based on perovskite oxides have been widely used to study for engineering applications. In particular, perovskite lead titanate $[PbTiO_3(PTO)]$ has been extensively investigated due to their great potentials of high Curie temperature, low dielectric constant, and high spontaneous polarization. Recently, ferroelectric lead titanate thin films have been fabricated for their researches and applications by MOCVD, PLD, sol-gel method and etc. One of them, Hydrothermal epitaxy, is known an eminent technique for producing fine, high purity, and homogeneous ferroelectric heteroepitaxial thin film and is proper to understand an initial stage of its growth and microstructure. In this study, we synthesized single-crystal PTO micro-sized island films (Islands) on a miscut (001) $Nb-SrTiO_3$ (NSTO) substrate by means of hydrothermal epitaxy. From the investigation of Atomic Force Microscopy, two-dimensional islands with various sizes from hundreds of nanometers to a few micrometers were observed. Moreover, we confirmed that the overall morphology of heteroepitaxial PbTiO3 island was transformed from smooth surface to stepped pyramidal surface with increasing island thickness, terrace width and step edge waviness of substrate. 3D islands having stepped pyramidal surface was observed to grow in spiral mode. Besides, we estimated the critical boundary for morphologic transition from 2D layer-by-layer growth to 3D pyramidal growth through the experimental plot and discovered one unit of terrace in spiral was proportional to the terrace-width of substrate. Our results provide a modeling on the flat-to-pyramid transition in (001) PTO/NSTO heteroepitaxial structure as well as support for researches and nano-structural applications of ferroelectric single-crystal.