Surface Plasmons and Surface Enhanced Raman Spectra of Aggregated and Alloyed Gold-Silver Nanoparticles

Effects of size, morphology, and composition of gold and silver nanoparticles on surface plasmon resonance (SPR) and surface enhanced Raman spectroscopy (SERS) are studied with the purpose of optimizing SERS substrates. Various gold and silver films made by evaporation and subsequent annealing give different morphologies and compositions of nanoparticles and thus different position of the SPR peak. SERS measurements of 4-mercaptobenzoic acid obtained from these films reveal that the proximity of the SPR peak to the exciting laser wavelength is not the only factor leading to the highest Raman enhancement. Silver nanoparticles evaporated on top of larger gold nanoparticles show higher SERS than gold-silver alloyed nanoparticles, in spite of the fact that the SPR peak of alloyed nanoparticles is narrower and closer to the excitation wavelength. The highest Raman enhancement was obtained for substrates with a two-peak particle size distribution for excitation wavelengths close to the SPR

Tunable nano devices fabricated by controlled deposition of gold nanoparticles via focused ion beam

Cataloged from PDF version of article.In this paper, we present the fabrication procedures as well as the preliminary experimental results of a novel method for significantly simplified deposition of charged nanoparticles at specific patterns based on focused ion beam (FIB) technology. The deposition method relies on the implantation of positive gallium ions on an insulated material which creates the basis for attracting the nanoparticles to the substrate. In order to substantiate the theory two patterns were generated on a silicon on insulator (SOI) chip with an upper layer of silicon of 200 nm. The two patterns are as follows: resolution target – consisting of six squares and 400 nm 400 nm circular sinusoidal tunnel. In addition, we demonstrate the utilization and applicability of the aforementioned method in a tunable radiation nano device as well as show its experimental characterization. © 2009 Elsevier B.V. All rights reserved

Controlling the optical spectra of gold nano-islands by changing the aspect ratio and the inter-island distance: theory and experiment

The extinction spectrum of a dielectric film with periodic array of metallic islands of different shapes and different mutual distances was studied both theoretically and experimentally. It is shown, analytically, numerically and experimentally, that the positions of the surface plasmon resonances depend on the nano-structural details. We propose two ways of controlling plasmon resonance frequency: changing the aspect ratio of the elliptical (or rectangular) islands and changing their mutual distances. A new analytical asymptotic approach for calculating the optical properties of such plasmonic systems is developed. The results of our analytical and numerical studies are in good qualitative agreement with experiment