Microstructure, composition, and optical properties of PbTiO3 thin films prepared by the sol-gel method

Abstract

Crack-free and transparent PbTiO3 thin films with a perovskite structure were deposited on NaCl (100), Si(111), and fused quartz substrates by the sol-gel method. The crystal structure, morphology, domain structure, composition, and optical properties of the films were characterized by means of x-ray diffraction, transmission electron microscopy, scanning electron microscopy, x-ray photoelectron spectroscopy (XPS), and optical transmission spectrum. The films on Si and fused quartz substrates exhibit slight a axis preferred orientation, while the films on NaCl substrates show slight c axis preferred orientation. From XPS analysis, no residual carbon or other impurity element was detected on the films after 3 keV Ar+ cleaning. The chemical composition of the films was found to be stoichiometric. A great amount of absorbed oxygen exists on the surfaces of the films. In the fine-grained (≈150 nm) films, no 90° domains are present in most of the grains, while some grains show lamellar 90° domains. A large number of pores exist in the films and their sizes are in the range of 5–30 nm. The packing density of the film fired at 600 °C was estimated to be about 89.3% from its optical transmission spectrum. The film has a surface roughness Δd≈37.5 nm. The refractive index of the film is approximately 2.43 at 630 nm, and the absorption edge is at 321 nm.