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Organization of Metal Nanoparticles for Surface-Enhanced Spectroscopy: A Difference in Size Matters

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journal contribution
posted on 20.02.2016, 08:41 by Reshmi Thomas, R. S. Swathi
We consider the organization of spherical gold nanoparticles from monomers to dimers to trimers and use the finite difference time domain (FDTD) method to explore their utility as substrates in surface-enhanced spectroscopy (SES). We investigate homodimers with 20 nm diameter (d) particles as the monomers and symmetric trimers with a special geometry wherein a d = 40 nm particle is introduced between the two monomeric particles of the homodimer. The optical extinction spectra and the electric field profiles of these assemblies for various separations between the metal particles (s = 3, 6, 9, 12, 15, and 40 nm) are compared with those of the monomers to determine the extent of plasmon coupling. The estimated surface-enhanced Raman scattering (SERS) enhancement factors for a typical probe in the vicinity of these nanostructures suggest that the symmetric trimers have two types of hot spots, with the hottest spot giving rise to an enhancement as high as ∼1.0 × 107 for s = 3 nm. The symmetric trimers support large electric fields in the vicinity with an interesting gradation within a single trimer and are found to be more efficient than homotrimers. Organized arrays of nanoparticles fabricated from such nanostructures could be more interesting substrates for SES experiments than those of uniform size.