Effects of annealing and quenching treatments on reconstruction of rutile thin films on sapphire substrates

Morphology change in rutile TiO2 thin films on sapphire substrates prepared by pulsed laser deposition under reduced oxygen environment was investigated as a function of film thickness, temperature and cooling treatments with atomic force microscopy, X-ray diffraction and scanning electron microscopy equipped with X-ray spectroscopy (SEM/EDX). The deposited TiO2 was determined as epitaxially grown rutile films whose crystallographic correlation with substrates was (1 0 0)rutile//(0 0 0 1)sapphire. As increasing thickness of TiO2 films, smooth surface changed to island structure. In addition, the morphology of TiO2 film on α-Al2O3(0 0 0 1) varied drastically by annealing treatment from 973 to 1123 K. In case of ∼5 nm thickness films, morphology strongly depended on annealing and cooling treatments. We found interesting order structure of TiO2 islands at annealing temperature (∼1073 K) and subsequent quenching (∼1.3 K/s). Formation process of TiO2 particles on α-Al2O3(0 0 0 1) substrates is modeled based on instability of substrate at elevated temperatures.