Synthesis and optical properties of Ag/Au-TiO2 plasmonic composite thin films

Abstract

In this work, composite thin films based on titanium dioxide and noble metal nanoparticles (Ag, Au and bimetallic Ag/Au alloys) (Me-TiO2) were synthesized using the RF magnetron sputtering technique. The obtained thin films were characterized by TEM, SEM, XRD analysis, and Raman spectroscopy. It was observed that annealing in an argon atmosphere led to the crystallization of the initially amorphous as-deposited TiO2 matrix. The analysis of transmission spectra revealed that the composite thin films exhibited two light absorption regions: the first is local minima in the visible range associated with localized surface plasmon resonance (LSPR) phenomena; the second is light absorption due to the energy band gap. The study demonstrates the possibility of tuning these parameters in the composite films by changing the composition of the metal NPs. The LSPR minima for Ag-TiO2 and Au-TiO2 films were located at about 485 nm and 606 nm, respectively. In the composite thin films with bimetallic ∼Ag0.54/Au0.46 alloy nanoparticles, the position of the absorption peak was found to be at 555 nm. The energy band gap of these films also varies almost linearly, decreasing with an increase in the Au content, so that the largest value among the annealed Me-TiO2 composites was observed for the Ag-TiO2.