Improved mechanical properties of sol-gel derived ITO thin films via Ag doping
School of Engineering
In this work, indium tin oxide (ITO) and silver doped ITO thin films at different Ag concentrations (i.e. 2, 4, 6 and 10 atomic%) were fabricated via a sol-gel spin coating technique. The thin film coatings were post annealed at 500 °C. Structural, mechanical, surface morphology, electrical and optical characteristics of the ITO and Ag-doped ITO thin films were studied as a function of Ag concentrations. XRD results are consistent with the presence of body centered cubic structure of the indium oxide polycrystalline phase with a new peak for Ag at 2θ ≈ 38.2°, indicating that by introducing Ag atoms they do not remarkably change the structural characteristics of the ITO films. FESEM images display the formation of ITO and Ag-doped ITO nanoparticles and the average crystallite size increases after annealing treatment as well as the incorporation of Ag concentration. The mechanical properties of the thin films were characterised by nanoindentation technique, with significant improvement observed through a combination of Ag doping and annealing treatment, which helps enhancing the effectiveness of the grain boundary in obstructing the displacement movements. The observed improvement in E and H is 14% and 28% respectively, with the hardness and Young’s modulus finally reaching 6.7 GPa and 148 GPa, respectively. Loading carrying capability and wear resistance are also enhanced by doping and annealing treatment. After annealing at 500 °C, the thin film coatings with the electrical resistivity of 2.4 × 10−4 Ω cm, carrier concentration of 6.8 × 1020 cm−3 and carrier mobility of 37 cm2/V s were achieved when the Ag doping level was 4 at.%. On the other hand, the maximum optical transparency was found to be 92% for both ITO and 2% Ag-doped ITO thin films after being annealed at 500 °C. The variation of optical constants, such as absorption coefficient, refractive index and extinction coefficient with different Ag concentrations, were also studied.