Structural, optical and electronic properties of Ag–TiO₂ nanocomposite thin film

Abstract

Nanocomposite thin films of Ag nanoparticles in TiO₂ matrices were synthesised by RF magnetron co-sputtering and characterised by X-ray diffraction (XRD), Rutherford back scattering (RBS) spectrometry, UV–Vis, high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The composition of Ag was varied from 0 to 45 at.%. The thickness and the concentrations of Ag in the nanocomposite thin film were revealed by RBS. XRD analysis confirmed that the TiO₂ matrix is in anatase phase and shows change in phase with Ag concentration. The UV–visible absorption spectroscopy revealed low-intense and broad surface plasmon resonance (SPR) peak at ~500 nm for the thin film with 33 at.% Ag content that was red-shifted to ~525 nm with increasing its intensity for 45 at.% of Ag. The red shift in SPR peak understood by Maxwell–Garnett theory and explained further nonexistence of SPR by interparticle separation from HR-TEM images and crystallinity. This HR-TEM image analysis confirmed the formation of Ag nanoparticles, and average radii were ~5, 12, 15 nm. The Tauc plot reveals reduction in band gap from 3.05 to 2.25 eV with increase in Ag content. Above results are understood based on the XPS analysis which shows a strong interaction between the Ag nanoparticle and TiO₂. This decrease in band gap was advantageous to enhance the properties like photocatalytic and bioactivities through SPR.