Control of Ultraviolet Surface Plasmon Absorption of Al Nanoparticles by Changing Particle Size, Shape, Interaction, and Medium Dielectric Constant

Abstract

Growing interests to extend the nanotechnology based on plasmonics with tunable absorption band in the ultraviolet (UV) region require materials which are natural abundance and cost-effective and can open up new possibilities of device applications. Al is one such material which shows strong absorption in UV region. For understanding the shift of surface plasmon resonance (SPR) band of Al nanoparticles (NPs) due to change of particle size, shape, separation, and medium dielectric constant, systematic theoretical studies have been carried out using a simple model. A prominent deep-UV SPR absorption peak (~ 218 nm) has been observed for spherical non-interacting NPs of radius of 20 nm embedded in silica. This peak is seen to blue-shift with decrease in NP radius due to mainly surface-electron damping by the radiation effects. For other cases, a large redshift (in UV region) of the SPR peak has been seen as a function of shape parameter (K), inverse of interaction parameter (1/β), and dielectric constant of surrounding medium. For interacting NPs, the observed redshift of the SPR band has been found to decay exponentially with increase in 1/K and can be explained as due to the increased interaction of the electric fields between NPs. For prolate spheroid NPs, a linear variation of SPR band corresponding to longitudinal oscillations of free electrons of the NPs with increase in 1/β has been seen. Finally, correlations between (i) K and interparticle separation and (ii) β and aspect ratio have been established for the physical realisation of K and β, and practical applications of Al NPs as plasmonic devices.