Noble metal nanoparticles properties

Noble metal nanoparticles dispersed in insulating matrices have attracted the interest of many researchers fromboth applied and theoretical points of view [34]. The incorporation of metallic nanoparticles into easily processable polymer matrices offers a pathway for better exploitation of their characteristic optical, electronic and catalytic properties. On the other hand, the host polymers can influence the growth and spatial arrangement of the nanoparticles during the in situ synthesis, which makes them convenient templates for the preparation of nanoparticles of different morphologies. Furthermore, by selecting the polymer with certain favorable properties such as biocompatibiHty [35], conductivity [36] or photoluminescence [37], it is possible to obtain the nanocomposite materials for various technological purposes. 

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. 

Hydrocarbonyl compounds, lanthanide complexes, 4, 4 ( -Hydrocarbyl)bis(zirconocene), preparation, 4, 906 Hydrocarbyl-bridged cyclopentadienyl-amido complexes, with Zr(IV), 4, 864 Hydrocarbyl complexes bis-Cp Ti hydrocarbyls reactions, 4, 551 structure and properties, 4, 551 synthesis, 4, 542 cobalt with rf-ligands, 7, 51 cobalt with rf-ligands, 7, 56 cobalt with ]4-ligands, 7, 59 cobalt with rf-ligands, 7, 71 heteroleptic types, 4, 192 homoleptic types, 4, 192 into magnetic metal nanoparticles via ligand stabilization, 12, 87 via polymer stabilization, 12, 87 into noble metal nanoparticles... 

Jain PK, Huang X, El-Sayed IH, El-Sayed MA. Review of some interesting surface plasmon resonance-enhanced properties of noble metal nanoparticles and their applications to biosystems. Plasmonics 2007 2 107-18. 

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. 

Surface-enhanced Raman scattering (SERS) is a powerful tool for characterization, sensing and quantitation of variety of chemical, environmental and biological analytes at trace concentrations [1]. The considerable enhancement of SERS is attributed to highly concentrated local electric fields in the structures with closely spaced noble metal nanoparticles (NPs). An engineering of novel nanostructures for SERS with advanced properties is of immediate interest for experimentalists. 

In the first case where metal surfaces provide active oxygen species to the support contact structure is not critical. The second case is often observed when supported metal catalysts are prepared by coprecipitation or sol-gel methods. Noble metals whose oxides are more stable than Pt oxides such as Pd and Ir are more readily buried in the bulk of metal oxide supports, and the metal oxide overlayers of a thickness of about a few monolayers are modified in their electronic and redox properties by underlying noble metal nanoparticles to become active at lower temperatures. 

In the first part, emphasis will be put on the linear optical properties of dielectric media doped with noble metal nanoparticles. Indeed, the study of the linear response is definitely needed to further explore the nonlinear one. We will then introduce the fundamentals of the theoretical tools required to understand why and how people inquire into the third-order nonlinear properties of nanocomposite materials. In the second part, experimental results will be presented by first examining the different nonlinear optical phenomena which have been observed in these media. We will then focus on the nanoparticle intrinsic nonlinear susceptibility before analysing the influence of the main morphological factors on the nonlinear optical response. The dependence of the latter on laser characteristics will finally be investigated, as well as the crucial role played by different thermal effects. 

LINEAR OPTICAL PROPERTIES OF NOBLE METAL NANOPARTICLES AND NANOCOMPOSITE MEDIA... 

Whatever the degree of approximation used in evaluating the effective nonlinear susceptibility of a composite medium, it can be seen in Eqs. (22), (23) or (27) that the result depends on the product of two complex quantities One linked with the medium morphology and composition (the local field factor), the other linked with the nonlinear optical properties of the metal inclusions themselves (the intrinsic third-order susceptibility, Xm ) - inasmuch as the own contribution of the host matrix to the whole nonlinear response still remains negligible. We will focus here on the second factor. It is noteworthy that very few theoretical work has been accomplished regarding the value of Xm for noble metal nanoparticles after the pioneering smdies of Flytzanis and coworkers [79, 80, 89, 90]. Moreover, as will be underlined below, their results may not be used in every experimental situation as they are. 

Whereas the majority of experimental works has been focused on silica-, glass-or alumina-embedded noble metal nanoparticles, or aqueous colloidal solutions, a few ones have dealt with other kinds of matrices, either amorphous (BaO [177], BaTiOj [164, 167], Bi.()., [178], Nb.O, [179], TiO. [180, 181], ZrO. .. [167]) or crystalline (BaTiOj [164, 182, 183], BiT) [184], LiNbOj [185], SrTiOj [172], ZnO... [186]). A direct comparison of the nonlinear properties from one matrix to another is difficult to carry out, since all other parameters should be kept constant while tuning the wavelength as to match the SPR maximum. 

Electrically conductive polymers are perspective materials in modern technologies because of their potential applications as chemical sensors, catalysts, microelectronic devices, etc. [1]. The interest to new hybrid nanostructured materials based on polymer matrix with poly-7t-conjugated bonds and noble metals nanoparticles constantly increases. This is reasoned by a wide spectrum of new optical and electrophysical properties [2]. 

The optical absorption properties of noble metal nanoparticles in the visible range of the electromagnetic spectrum are determined by the effect of the boundary condition of the coherent electron oscillations as well as by d ip electronic transitions. Very small gold nanoparticles (d<2 nm), as well as bulk gold do not show a localized surface plasmon absorption band As discussed earlier (see Fig. 16.5), gold nanorods... 

Probing plasmonic resonances using low-loss electron energy loss spectroscopy has proved particularly useful for studying the optical properties of noble metal nanoparticles. Single particle plasmonic studies are an important tool to understand the role of size, shape and local environment on the exact nature of plasmonic excitations that might be complicated by dispersity of these traits when using bulk techniques. 

SPR is a unique property of plasmonic or noble metal nanoparticles such as gold nanoparticles. This unique property offers multimodalities for medical applications due to photon confinement to a small particle size and enhancing all radiative and nonradiative properties of the nanoparticles [77]. 

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