Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles

Metallic nanoparticles (NPs) can strongly absorb the incident light and produce enhanced localized electric field when the frequency of the incident light is in phase with coherent oscillation of conduction electrons in them. This characteristic feature of metallic NPs can be tuned by changing parameters such as size, shape, polarization direction of incident light and refractive index of medium. Although plasmonic properties of larger size nanoparticles are extensively investigated, little has been done on smaller sized particles in the size range of 3 to 10 nm. By reducing the size, band structure of the metalic particles discretizes, leading channeling plasmon properties of the NPs from classical to quantum regime. In this work, plasmonic properties of the spherical silver (Ag) NPs in the size range of 3 to 20 nm has been investigated using both quantum and classical model. We performed theoretical calculations using normal Mie theory, and studied size and surrounding medium effects on the absorption efficiency, LSPR energy peak shift and field enhancement of the samples. The results indicate that the quantum model is able to predict blue shift of LSPR peak with decreasing size of the samples from 10 to 3 nm while the classical model fails to observe this effect.