Geometrical modifications and tuning of optical and surface plasmon resonance behaviour of Au and Ag coated TiO2 nanotubular arrays

A protocol for surface structuring and shape modifications of anodized TiO2 nanotubes by controlling the electric field is presented. The shape and size control of nanotubes is essential in order to achieve more control over optical and electronic properties of nanotubes such as effective band gap, light absorption capabilities, photoelectrochemical response, Raman properties, as well as appearance of the localized states. A surface plasmon resonance (SPR) study was performed using these newly developed nanotubes. It was observed that noble metal treated nanotube assemblies exhibit a 'slow photon effect' and plasmon-exciton interaction. Such a 'slow photon' effect is highly advantageous to improve photoelectrochemical (PEC) performance and quantum efficiency if plasmonic PEC activity is coupled with it in the SPR region. The FDTD simulations of tilted nanotubes suggest that the maximum surface field confinement can be realized for a lower bend angle of 8 degrees and this confinement diminishes when inclination of the nanotubes increases further.