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

Abstract

Morphology change in rutile TiO 2 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 TiO 2 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 TiO 2 films, smooth surface changed to island structure. In addition, the morphology of TiO 2 film on α-Al 2O 3(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 TiO 2 islands at annealing temperature (∼1073 K) and subsequent quenching (∼1.3 K/s). Formation process of TiO 2 particles on α-Al 2O 3(0 0 0 1) substrates is modeled based on instability of substrate at elevated temperatures.