Modified optical characteristics of TiO2/Au/TiO2 thin composite films

摘要

We report the optical characteristics of the TiO2/Au-NPs/TiO2 composite thin films determined from the UV-Vis absorption spectroscopy and spectroscopic ellipsometry. The UV-Vis spectra indicated the enhanced optical absorption in the composite thin films in the range 1.6-3.0 eV. Spectroscopic ellipsometry was employed to determine the optical parameters of the composite films. The experimental results were fitted with hybrid model, which included Drude Lorentz model for Au layer and Urbach tail modified Tauc Lorentz model for TiO2 layers. The photoluminescence spectrum of the composite film clearly showed a weak emission band centered at 500 nm, which was absent in the pure TiO2 films. The extracted optical parameters manifested the generation of hot electrons at the Au/TiO2 interface due to Au surface plasmon (SP) modes, multiple interband transitions in Au in the energy range (1-4 eV) and a long Urbach tail (similar to 144 meV) in TiO2. These were direct indicators of hot electron scattering from the plasmon modes and their transfer to the TiO2 conduction band. The present study revealed that the plasmon exciton interactions in composite film can modify its optical properties.