Plasmon assisted high ultraviolet to visible broad band photosensitivity in lateral Ag NPs-TiO2 nanocomposite film

Noble metal-TiO2 composite films attract great attention because of the extension of its spectral absorption in the visible range due to surface plasmon resonance. Among them, Ag-TiO2 composite is considered to be an ideal candidate for the visible light photosensitivity because of narrow energy distribution of plasmonic hot electrons in Ag and the high density of states in the TiO2 conduction band. Here, we report high broad band photosensitivity from ultraviolet (UV) to visible wavelength of sol-gel grown TiO2 film decorated with Ag nanoparticles (NPs) in a simple planar photoconductive geometry. In addition to UV light, Ag NPs-TiO2 composite film (for 1 nm Ag) shows very high photosensitivity values of-105 and-104 and responsivity values of 0.1 A/W and 7x10(- 3) A/W at 10 V bias for 680 nm and 550 nm illuminations respectively while pristine TiO2 show photosensitivity values of 6x10(2 )and 3.3x10(2) and responsivity values of 2.4x10(-4) A/W and 6.6x10(- 5) A/W for both the visible illuminations. A highly enhanced broad band photosensitivity due to transfer of plasmonically generated hot electrons from Ag to TiO2 is quite interesting without having any device fabricated. The photosensitivity values for Ag NPs for 3 nm and 6 nm layer thicknesses on TiO2 decrease because of coalescence of metal NPs on surface which acts as scattering center and/or light shielding.

Automated summary

This study investigates the photosensitivity of Ag-TiO2 composite films and finds that the combination of Ag nanoparticles on TiO2 films enables high broad band photosensitivity from UV to visible wavelength. The transfer of hot electrons from Ag nanoparticles to TiO2 enhances the overall photosensitivity. However, the thickness increase of Ag nanoparticles on TiO2 affects the photosensitivity negatively due to aggregation of the metal particles.