Microstructural evolution of Au/TiO2 nanocomposite films: The influence of Au concentration and thermal annealing

Abstract

Nanocomposite thin films consisting of a dielectric matrix, such as titanium oxide (TiO2), with embedded gold (Au) nanoparticles were prepared and will be analysed and discussed in detail in the present work. The evolution of morphological and structural features was studied for a wide range of Au concentrations and for annealing treatments in air, for temperatures ranging from 200 to 800 ºC. Major findings revealed that for low Au atomic concentrations (at. %), there are only traces of clustering, and just for relatively high annealing temperatures, T ≥ 500 ºC. Furthermore, the number of Au nanoparticles is extremely low, even for the highest annealing temperature, T = 800 ºC. It is noteworthy that the TiO2 matrix also crystallizes in the anatase phase for annealing temperatures above 300 ºC. For intermediate Au contents (5 at.% ≤ CAu ≤ 15 at.%), the formation of gold nanoclusters was much more evident, beginning at lower annealing temperatures (T ≥ 200 ºC) with sizes ranging from 2 to 25 nm as the temperature increased. A change in the matrix crystallization from anatase to rutile was also observed in this intermediate range of compositions. For the highest Au concentrations (> 20 at.%), the films tended to form relatively larger clusters, with sizes above 20 nm (for T ≥ 400 ºC). It is demonstrated that the structural and morphological characteristics of the films are strongly affected by the annealing temperature, as well as by the particular amounts, size and distribution of the Au nanoparticles dispersed in the TiO2 matrix.