The Optical Properties of Metal Nanoparticles:  The Influence of Size, Shape, and Dielectric Environment

Abstract

The optical properties of metal nanoparticles have long been of interest in physical chemistry, starting with Faraday's investigations of colloidal gold in the middle 1800s. More recently, new lithographic techniques as well as improvements to classical wet chemistry methods have made it possible to synthesize noble metal nanoparticles with a wide range of sizes, shapes, and dielectric environments. In this feature article, we describe recent progress in the theory of nanoparticle optical properties, particularly methods for solving Maxwell's equations for light scattering from particles of arbitrary shape in a complex environment. Included is a description of the qualitative features of dipole and quadrupole plasmon resonances for spherical particles; a discussion of analytical and numerical methods for calculating extinction and scattering cross-sections, local fields, and other optical properties for nonspherical particles; and a survey of applications to problems of recent interest involving triangular silver particles and related shapes.

Calculated Absorption and Scattering Properties of Gold Nanoparticles of Different Size, Shape, and Composition: Applications in Biological Imaging and Biomedicine

“…[61][62][63] At the same time, well-established theoretical tools based on the Mie theory 64 and the discrete dipole approximation (DDA) 65 method have been readily exploited for a quantitative study of the nanoparticle optical properties of different size, shape, composition, and aggregation state, etc. 2,36,[66][67][68][69][70][71][72][73] In this paper, we use Mie theory and the DDA method to calculate the absorption and scattering efficiencies and optical resonance wavelengths of gold nanospheres, silica-gold nanoshells, and gold nanorods, for various nanoparticle dimensions, so as to aid the selection of nanoparticles for specific biomedical applications. The calculated optical cross-sections of all three nanoparticle classes are found to be a few orders of magnitude higher than those for conventionally used absorbing and fluorescent dyes.…”

Controllable Cobalt Oxide/Au Hierarchically Nanostructured Electrode for Nonenzymatic Glucose Sensing

“…This creates a charge separation with respect to the lattice [2,15]. The confined conduction band electrons in the small particle volume then begin to move in phase with the radiation plane wave excitation, creating a coherent electromagnetic (EM) response which strengthens both the near field energy and the optical extinction associated with the nanoparticle surface [16,17]. The optical extinction, or maximum intensity of the oscillation frequency, is composed of both scattering (elastic and radiative) and absorption (inelastic and non-radiative) efficiencies [14,17].…”

“…The effective radiative damping of a dipolar plasmon will be proportional to the nanoparticle volume where smaller nanoparticles will have intrinsic, or thermoelastic, damping as their dominant decay mechanism [9,20]. For nanoparticles with diameters greater than 50 nm radiative damping will dominate [16,21].…”

“…This can be achieved largely through geometric design [2,16,17,[46][47][48][49][50][51]. While many structures exhibit suitable enhancement of their EM field in response to incident light, their lack of symmetry results in multiple resonances due to non-degenerate electronic transitions [52,53].…”

“…In this case the facet energies of the hexagonal close packed (HCP) structure of the cobalt template are known to increase 0001 < 10-10 < 10-11 < 11-20 < 10-12 < 11-21 with respective energies of 131,140,149,155,156,163 (meV/Å 2 ) [109]. This means that the oxidation and generation of Kirkendall voids were initiated on the [11][12][13][14][15][16][17][18][19][20][21] plane of the cobalt lattice.…”