Optical Properties of Coupled Nanoparticles

Another example of recent work is the demonstration of non linear optical properties of Cu nanoparticles in an ITO matrix.62 This is an example of a structure that can be obtained fully by solution processing. Coupled with this is the observation of enhanced surface plasmons in some nanoparticles, which potentially produces tailorable, non linear optical properties.63 This effect can... 

An intense femtosecond laser spectroscopy-based research focusing on the fast relaxation processes of excited electrons in nanoparticles has started in the past decade. The electron dynamics and non-linear optical properties of nanoparticles in colloidal solutions [1], thin films [2] and glasses [3] have been studied in the femto- and picosecond time scales. Most work has been done with noble metal nanoparticles Au, Ag and Cu, providing information about the electron-electron and electron-phonon coupling [4] or coherent phenomenon [5], A large surface-to-volume ratio of the particle gives a possibility to investigate the surface/interface processes. 

A key issue in nanostructured materials is the dipole coupling between nanocrystals which will cause the optical properties of a nanocrystal ensemble to become like those of the bulk material. There has been extensive investigation of the interactions between particles embedded within media for a range of boundary conditions. We have found that the effective dielectric function given by Eq. (10), based on the Maxwell-Garnett model [1] is very accurate for quite dense nanocrystal arrays. In practice, one measures the transmittance of a thin film of the dense nanoparticle based film. Conventional solutions are simply... 

Through the silica coating procedure described, the optical properties of both dilute and concentrated dispersions of metal nanoparticles can be modulated. The influence of the silica shell on the optical properties has been described in detail, and shown to promote noticeable shifts of the plasmon band position in dilute systems, while coupling absorption and scattering in concentrated systems, which gives rise to rich, concentration-dependent optical behavior. 

Next, the role of the external dielectric medium on the optical properties of these surface-confined nanoparticles is considered. Just as it is difficult to decouple the effects of size and shape from one another, the dielectric effects of the substrate and external dielectric medium (i.e., bulk solvent) are inextricably coupled because together they describe the entire dielectric environment surrounding the nanoparticles. The... 

Molecular plasmonics involves the interaction between molecules and plasmonics systems such as metal nanoparticles. Such interaction is always mediated by electromagnetic (EM) fields, which determine how the optical properties of the molecules are modified by the presence of the plasmonics system, and vice versa. In this chapter, we shall describe the origin of the coupling and how the relevant quantities can be calculated. In particular regimes... 

In continuum electrodynamics, an optical system is represented as a collection of discretization grids, each of which is characterized by its electric permittivity and magnetic permeability which are uniquely determined by the material properties. By solving Maxwell s equations or the coupled dipole-field equations in either the time or frequency domain, any macroscopic optical property of interest can be numerically determined subject to the desired boundary conditions. Since the continuum models are typically scale invariant, they are applicable to arbitrarily large systems. However a limitation in the description of metal nanoparticles is that grid sizes on the order of a few nanometers are necessary for convergence of the numerical methods, so this places an... 

In-between the two limits is the interesting regime where one must study electrochemistry produced by nanoclusters. Nanoparticles linked by ligands show a spectrum completely different from that when they are apart. This phenomenon is the basis of several biosensing schemes. The analytical theory of the optical properties of dimers is challenging. The coupled-dipole approximation (where each nanoparticle is modelled as a dipole and their interaction is dipole-dipole) is limited to very small nanoparticles. In practice, nanoparticles of dimension 20-50 nm have a significant quadrupolar... 

Nanoparticles, which often show enhanced catalytic abilities [32, 33] unusual optical properties [34], and novel quantum size effects [35], have been widely used in fields such as catalysis [36, 37], sensing [38], optoelectronics [39], and microelectronics [40]. Nanoparticle catalysis is industrially and experimentally important because a large variety of C-C coupling [41] and alcohol oxidation [32] can be effectively catalyzed by nanoparticles. In this part, we will present a brief review on recent advances in supported nanoparticle heterogeneous catalysts on various mesoporous materials. Heterogeneous nanoparticle catalysts have several... 

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