Nanoparticle Optics:  The Importance of Radiative Dipole Coupling in Two-Dimensional Nanoparticle Arrays

Abstract

In this paper, the electromagnetic interactions between noble metal nanoparticles are studied by measuring the extinction spectra of two-dimensional arrays of Au and Ag cylinders and trigonal prisms that have been fabricated with electron beam lithography. The nanoparticles are typically 200 nm in diameter and 35 nm in height; both hexagonal and square array patterns have been considered with lattice spacings that vary from 230 to 500 nm. The extinction spectra typically have a maximum in the 700-800 nm region of the spectrum, and this maximum blue shifts as lattice spacing is reduced, having typically a 40 nm decrease in λ max for a 100 nm decrease in lattice spacing. The results are similar for the different noble metals, array patterns, and nanoparticle shapes. The extinction spectra have been modeled using coupled dipole calculations, and the observed spectral variations are in good qualitative agreement with experimental data. Moreover, the computational analysis indicates that the blue shifts are due to radiative dipolar coupling between the nanoparticles and retardation effects. These effects result in a net depolarization of the dipole couplings for lattice spacings of 200-500 nm.

Surface-Enhanced Raman Spectroscopy

“…In this body of work, field enhancement has been studied as a function of nanoparticle aspect ratio and shape (20,21), extremely large SERS enhancement has been predicted in small nanoparticle assemblies (22,23), and interesting optical phenomena that occur in extended arrays of nanoparticles have been uncovered (24,25).…”

Highly doped semiconductor plasmonic nanoantenna arrays for polarization selective broadband surface-enhanced infrared absorption spectroscopy of vanillin

“…Different interaction regimes in nanoparticle arrays have been identified in the literature, based mainly on examples of metallic, often Au and Ag nanoparticles [41][42][43][44][45][46]. Near-field interactions arise for gaps between antennas in the range of several tenths of nanometers.…”

“…Near-field interactions arise for gaps between antennas in the range of several tenths of nanometers. These spacings being small compared to optical and IR wavelengths, the interaction is often treated in an electrostatic framework of coupled dipoles [43], or alternatively by the plasmon hybridization model [44]. Near-field interactions can be excluded for the presented HDSC nanoantenna arrays as the spacing between antennas is in the micrometric range.…”

Effect of Solvent Refractive Index on the Surface Plasmon Resonance Nanoparticle Optical Absorption

“…1 Frequency of these resonances depend on particle size, shape, composition, and optical properties of local environment in which the nanoparticles are immersed. [1][2][3][4][5][6][7] The size effect has been experimentally studied for particles embedded in polymer films, [8][9][10][11] partially oxidized Si matrix, 12 and for silver clusters interacting with another metal, semiconductor or dielectric cluster. 13 Solvent effects on the excitation spectra of periodic arrays of silver nanoclusters in water, 14 fabricated by nanosphere lithography, 4 modified with alkanethiol self assembly monolayers, 15 and silica coated gold nanoparticles 16 17 have also been thoroughly investigated.…”