Theoretical studies of the optical properties of hollow spherical metallic nanoshells

We theoretically investigate the far-field and near-field optical properties originated from the surface plasmon resonance of hollow gold and silver single-shell nanospheres with inner radii ranging from 10 nm to 400 nm along with aspect ratio varying from 0.1 to 0.9 by means of numerical experiments on the basis of Mie scattering theory. We first address the extinction efficiency of both gold and silver nanoshells and show how variation trend of extinction efficieny is tuned by size effect and aspect ratio effect. We then demonstrate that resonance wavelengths of both hollow spheric metallic nanoshells are subject to both aspect ratio effect and size effect, where the size serves as a dominant role in determining the plasmon resonance wavelengths and is represented by inner radius of nanoshells. More importantly, in doing so, we reveal that how plasmon resonance wavelengths of the two types of metallic nanoshells behave in response to each distinct combination of aspect ratio and inner radius. Thirdly, we demonstrate the spectra of surface-enhanced Raman scattering of nanoshells with aspect ratio 0.9. In addition, we delineate that smallest nanoshells under this investigation hosts the largest enhancement factor and then shed light on the relationship between plasmon resonance wavelength and at which wavelength maxima enhancement factor happens.