Morphological and in situ local refractive index change induced tuning of the optical properties of titania coated porous gold nanoparticles

Porous nanoparticles are very popular because of their high surface/volume ratio; moreover, they have stronger plasmonic properties than their solid counterparts. Due to these properties, these are potential candidates in optical, or even in ophthalmological applications. We prepared porous gold nanoparticles on SiO 2 / Si as well as on sapphire substrates with solid-state dewetting–dealloying methods. In this work, we studied the morphological and optical properties of porous gold nanoparticles coated with a thin ( ∼ 7 nm) TiO 2 layer using the plasma-enhanced atomic layer deposition method. We show that heat treatments can be used to tune the optical properties of titania coated porous gold hybrid nanoparticles in a wide range of wavelengths. The change in the optical properties is induced by the TiO 2 phase transformation, which also initiates a change in the local refractive index, and assisted by the decrease of the melting point of Au on the nanoscale.