Surface plasmons absorption

Michaelis and Henglein [131] prepared Pd-core/Ag-shell bimetallic nanoparticles by the successive reduction of Ag ions on the surface of Pd nanoparticles (mean radius 4.6 nm) with formaldehyde. The core/shell nanoparticles, however, became larger and deviated from spherical with an increase in the shell thickness. The Pd/Ag bimetallic nanoparticles had a surface plasmon absorption band close to 380 nm when more than 10-atomic layer of Ag are deposited. When the shell thickness is less than 10-atomic layer, the absorption band is located at shorter wavelengths and the band disappears below about three-atomic layer. 

Figure 21.6 Schematic illustration of the dynamics of the photoluminescence from the Au(0) i system. The inset shows the comparison of the Au(0) i surface plasmon absorption peak with the spectral distribution of the Au(0) i emission peakfor excitation at 3.14 eV (395 nm).

Adsorption of ions or molecules on metal clusters markedly affects their optical properties. It was shown that the intensity and the shape of the surface plasmon absorption band of silver nanometric particles, which is close to 380 nm, change upon adsorption of various substances [125]. The important damping of the band generally observed is assigned to the change of the electron density of the thin surface layer of the... 

Differences in surface plasmon absorption among various metals are clearly revealed by imagining the trajectories to be superposed onto the contour plot . Spherical silver and aluminum particles have intense surface plasmon absorption peaks because t" is small at the frequency where c is - 2, whereas gold... 

Surface plasmon absorption has been observed for small particles of several other metals, and many calculations have been published these are too... 

Fig. 83. Surface plasmon absorption band of a 1 x 10 4moldm-3 silver sol (O). Changes in absorption after electron donation (a) and positive hole injection (fc) by free radicals [506]...

For the same particles, the volume plasmon is located at very high energies (6-9 eV). The surface obviously plays a very important role for the observation of the surface plasmon resonance because it alters the boundary conditions for the polarizability of the metal and therefore shifts the resonance to optical frequencies. In this sense, the surface plasmon absorption is a small particle (or thin layer) effect but is definitely not a quantum size effect [14]. 

For the smallest of metallic nanoclusters with dimensions ca. < 2 nm, the surface plasmon absorption disappears. Since so few atoms comprise discrete nanoclusters of this size, the spacings between adjacent energy levels (referred to as the Kubo... 

Plasmonic nanostructures that are materials consisting of noble metal nanoparticles with sizes of 1-100 nm are known as specific substrates for surface enhanced Raman scattering and luminescence enhancement [1-4]. These effects are stimulated by the localized surface plasmon absorption (LSPA) and may be controlled by the change of metal nanoparticle sizes, their concentration and a substrate choice [5]. New opportunities for surface-enhanced effect realization and optimization are now discussed in connection with bimetallic nanostructures [6]. At the technological aspect one of the simplest types of a binary nanostructure is a stratified system made of two different monolayers, each is consisted of definite metal nanoparticles. The LSPA properties of these binary close-packed planar nanostructures are the subject of the paper. 

The curves 1-3 in Fig. 1 evidently show that for the two-layer silver-copper systems there is a strong optical density Increase over the spectral range X. 600-1200nm that overlaps the copper surface plasmon absorption band. 

The enhancement of surface plasmon absorption of metal nanoparticles may be a result of strong near-field coupling in the close-packed copper-silver nanostructure. The effect is more considerable at the spectral range outside of the copper interband absorption that is why it is not evident at the LSPA band of silver nanoparticles. At th e fi equency range near the LSPA band of copper nanoparticles, near-field coupling is not suppressed by die interband absorption so much and the LSPA enhancement is well seen. 

Lee, M., Kim, T.S., Choi, Y.S. Third-order optical nonlinearities of sol-gel-processed Au-SiO2 thin films in the surface plasmon absorption region. J. Non-Cryst. Solids 211, 143-149 (1997)... 

Keywords. Nanocrystals, Core-shell particles. Topology, Opals, Capsules, Surface plasmon absorption, Bragg diffraction. Arrays, Colloidal crystals... 

The optical behaviour of silver island films embedded in optical thin film materials has been studied by spectrophotometry. The silver cluster surface plasmon absorption line position and width strongly depend on deposition temperature and ambient material. Electron micrographs of the samples allow to establish the correlation between silver cluster geometry and optical behaviour. The first results of Rigorous Coupled Wave Approximation (RCWA) calculations reproduce the spectrophotometric experimental results. 

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