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

• Published in: Journal of physical chemistry. C Vol. 116; no. 41; pp. 21982 - 21991
• Main Authors: Thomas, Reshmi, Swathi, R. S
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 18-10-2012
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Nanocrystals and nanoparticles; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures; Physics; Nanoparticles; Gold; Particle size; Time domain method; SERS; Electric field effects; High field; Plasmons; Spherical particle; Arrays; Extinction index; Finite difference method
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp3086914

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.