Investigating Optical Properties of Gold Nanorod Arrays

The plasmonic properties of a gold nanorod array surface can be tuned through modification of the surface parameters. To experimentally fabricate and investigate would be both resource and time expensive. This work utilises a finite element method (FEM) model to investigate the effect of varying parameters on the optical properties of the surface. Near-field coupling effects are considered within the nanorod array and between the array and gold underlayer. Increased coupling and blue-shifted resonance peaks occur for reduced array spacing and increased underlayer thicknesses red-shift resonance positions and increase overall extinction values. Nanorod geometry simulations show that larger diameters significantly blue-shift resonance peaks and increase local field enhancements throughout the array; whereas increasing height increases the extinction spectra and causes red-shift of resonance peaks. The results obtained for these investigations aid understanding of the electromagnetic interactions associated with the nanorod array which will benefit practical applications of the surface. Current experimental nanorod array geometries were investigated for plasmon-enhanced fluorescence (PEF) applications, with the maximum plasmonic signal and field enhancements occurring for 25x200nm array with 60nm spacing at fluorescent absorption and emission wavelengths. However, these significant field enhancements are localised to the surface of the nanorods rather than throughout the array so fluorescent molecules would have to be in contact with the surface to experience these enhancements.