Dielectric confinement

The supporting medium (aqueous or organic solvents membrane-mimetic compartments) also has a profound influence on the optical and electro-optical properties of nanosized semiconductor particles. This dielectric confinement (or local field effect) originates, primarily, in the difference between the refractive indices of semiconductor particles and the surrounding medium [573, 604], In general, the refractive index of the medium is lower than that of the semiconductor particle, which enhances the local electric field adjacent to the semiconductor particle surface as compared with the incident field intensity. Dielectric confinement of semiconductor particles also manifests in altered optical and electro-optical behavior. 

Evidence for both quantum confinement in n(W03)-Nas6Y and dielectric confinement in n(WC>3)-Na56Y compared with n(W03)-H56Y can be found in both the optical and X-ray photoelectron spectra of these materials as one traverses the loading range n = 0-32, and alters the supercage cation respectively (Figure 9 and Table I). 

Takagahara T. (1993a), Effects of dielectric confinement and electron-hole exchange interaction on excitonic states in semiconductor quantum dots , Phys. Rev. B 47, 4569-4584. 

As the existence of a resonance behaviour can be explained by pure electromagnetic considerations, using as only ingredients macroscopic quantities that are the dielectric functions of the different media, the local field amplification phenomenon is often said to originate from dielectric confinement. 

One of the main consequences of dielectric confinement for the third-order nonlinear optical properties is the fact that the response of a composite medium can be very different in both sign and magnitude from the one of its constituents [73, 89, 94]. 

Semicondnctor particles at the nano scale are cnrrently nnder investigation as examples of non-molecnlar materials that show effects of qnantum and dielectric confinement. The chemical modification or snrface capping with... 

Diarra M, Niquet Y-M, Delerue C, Allan G (2007) Ionization energy of donor and acceptor impurities in semiconductor nanowires importance of dielectric confinement. Phys Rev B 75 045301... 

The first optical effect pointed out by Wang [13], and studied by computational simulations, is so-called dielectric confinement. Dielectric confinement is caused by the difference in refractive indices of a polymer medium (which has lower refractive index) and a semiconductor or metal particle (which usually has hi er refractive index). When illuminated by light, the field intensity near, at and inside the particle surface can be enhanced considerably compared to the inddent intensity becau of tte boundary established by the different refractive indices. This local ld enhancement eflect can have important con quences on photophysical and nonlinear optical properties of such polyn r-nancqmrtide systems. 

The measurement of surface forces calls for a rigid apparatus that exhibits a high force sensitivity as well as distance measurement and control on a subnanometre scale [38]. Most SFAs make use of an optical interference teclmique to measure distances and hence forces between surfaces. Alternative distance measurements have been developed in recent years—predominantly capacitive techniques, which allow for faster and simpler acquisition of an averaged distance [H, 39, 40] or even allow for simultaneous dielectric loss measurements at a confined interface. 

In most devices the liquid crystal molecules are confined between two thin walls which act as capacitor plates. This allows the determination of the dielectric properties of the liquid crystalline material through the simple relations... 

The effects of the intramicellar confinement of polar and amphiphilic species in nanoscopic domains dispersed in an apolar solvent on their physicochemical properties (electronic structure, density, dielectric constant, phase diagram, reactivity, etc.) have received considerable attention [51,52]. hi particular, the properties of water confined in reversed micelles have been widely investigated, since it simulates water hydrating enzymes or encapsulated in biological environments [13,23,53-59]. 

In this Section we want to present one of the fingerprints of noble-metal cluster formation, that is the development of a well-defined absorption band in the visible or near UV spectrum which is called the surface plasma resonance (SPR) absorption. SPR is typical of s-type metals like noble and alkali metals and it is due to a collective excitation of the delocalized conduction electrons confined within the cluster volume [15]. The theory developed by G. Mie in 1908 [22], for spherical non-interacting nanoparticles of radius R embedded in a non-absorbing medium with dielectric constant s i (i.e. with a refractive index n = Sm ) gives the extinction cross-section a(o),R) in the dipolar approximation as ... 

The observation of slow, confined water motion in AOT reverse micelles is also supported by measured dielectric relaxation of the water pool. Using terahertz time-domain spectroscopy, the dielectric properties of water in the reverse micelles have been investigated by Mittleman et al. [36]. They found that both the time scale and amplitude of the relaxation was smaller than those of bulk water. They attributed these results to the reduction of long-range collective motion due to the confinement of the water in the nanometer-sized micelles. These results suggested that free water motion in the reverse micelles are not equivalent to bulk solvation dynamics. 

Electromagnetic field of a surface plasmon is confined at the metal-dielectric interface and decreases exponentially into both media, Figure 6. 

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