The thickness effect on lspr spectra of au-nanorod coated tio₂ and sio₂ studied by mnpbem

We have studied the effect on localized surface plasmon resonance (LSPR) of Au-nanorod (AuNR) coated TiO₂ (Au@TiO₂) and SiO₂ (Au@SiO₂). The length and diameter of AuNR are 70 nm and 20 nm, respectively. For this purpose, then AuNR was coated by TiO₂ and SiO₂ with thickness varying from 2nm to 20nm with increment 2nm. The LSPR exhibited two modes, transverse mode (TM) and longitudinal mode (LM) as commonly was found in a rod-shaped particle. Interestingly, the peak of extinction red-shift as the thickness increased both TM and LM. Increasing volume and refractive index around AuNR contributed to red-shift, therefore the rate of decreasing energy TiO₂ faster than SiO₂. Furthermore, we have also observed the peak of LSPR extinction curve of Au@TiO₂ have a similar trend to Au@SiO₂ as the thickness increased, but its beginning to decrease at ∼8nm. In the LM, for a given thickness, we found the peak of extinction curve Au@TiO₂ show more than one peak present around ∼2-3nm and ∼8nm. However, only one peak happened in Au@SiO₂. In a sense, Au coated TiO₂ can be fully utilized to enhance photocatalytic activity under visible light of AuNR and useful in photocatalytic activity, on the other hand, SiO₂ plays an insignificant role for a certain limit thickness under visible light-near-infrared.