Metal nanoparticles optical properties

K. L. Kelly, T. R. Jensen, A. A. Lazarides and G. C. Schatz, Modeling metal nanoparticle optical properties,... 

Noble metal nanoparticles can go beyond acting as labels recent advances show that changes in nanoparticle optical properties can act as the signal transduction mechanism in chemosensing and biosensing events. Van Duyne and coworkers have exploited the extreme LSPR sensitivity of NSL-fabricated nanoparticles to changes in local refiactive index in order to sense small molecules, amino acids, proteins, and antibodies. The LSPR shifts systematically to lower energies as the local dielectric constant increases ... 

The optical properties of metal nanoparticles have traditionally relied on Mie tlieory, a purely classical electromagnetic scattering tlieory for particles witli known dielectrics [172]. For particles whose size is comparable to or larger tlian tire wavelengtli of the incident radiation, tliis calculation is ratlier cumbersome. However, if tire scatterers are smaller tlian -10% of tire wavelengtli, as in nearly all nanocrystals, tire lowest-order tenn of Mie tlieory is sufficient to describe tire absorjDtion and scattering of radiation. In tliis limit, tire absorjDtion is detennined solely by tire frequency-dependent dielectric function of tire metal particles and the dielectric of tire background matrix in which tliey are... 

Bimetallic nanoparticles, either as alloys or as core-shell structures, exhibit unique electronic, optical and catalytic properties compared to pure metallic nanopartides [24]. Cu-Ag alloy nanoparticles were obtained through the simultaneous reduction of copper and silver ions again in aqueous starch matrix. The optical properties of these alloy nanopartides vary with their composition, which is seen from the digital photographs in Fig. 8. The formation of alloy was confirmed by single SP maxima which varied depending on the composition of the alloy. 

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. 

Nanosize particles (e.g., metals, semiconductors, etc.) are of continuing interest because they possess fascinating catalytic, electronic, and optical properties. Larger particles decorated with smaller nanoparticles on their surface are of interest because of their potential use as heterogeneous catalysts and their relevance in electronic and optical sensor applications as well as surface-enhanced Raman scattering [39,72-75]. 

The physical properties of metal nanoparticles are very size-dependent. This is clear for their magnetic properties, for which the shape anisotropy term is very important. This is also true for the optical properties of nanoparticles displaying plasmon bands in the visible range (Cu, Ag, Au) and for 111-V... 

Kelly, K.L., Coronado, E., Zhao, L.L. and Schatz, G.C. (2003) The optical properties of metal nanoparticles the influence of size, shape, and dielectric environment. The Journal of Physical Chemistry B, 107, 668-677. 

The optical, semiconductor, and electrical properties of metallic nanoparticles including potential applications in a number of fields have been reviewed in Chapter 5 of Schmid s recent book [60]. 

The synthesis of bimetallic nanoparticles is mainly divided into two methods, i.e., chemical and physical method, or bottom-up and top-down method. The chemical method involves (1) simultaneous or co-reduction, (2) successive or two-stepped reduction of two kinds of metal ions, and (3) self-organization of bimetallic nanoparticle by physically mixing two kinds of already-prepared monometallic nanoparticles with or without after-treatments. Bimetallic nanoparticle alloys are prepared usually by the simultaneous reduction while bimetallic nanoparticles with core/shell structures are prepared usually by the successive reduction. In the preparation of bimetallic nanoparticles, one of the most interesting aspects is a core/shell structure. The surface element plays an important role in the functions of metal nanoparticles like catal5dic and optical properties, but these properties can be tuned by addition of the second element which may be located on the surface or in the center of the particles adjacent to the surface element. So, we would like to use following marks to inscribe the bimetallic nanoparticles composed of metal 1, Mi and metal 2, M2. 

Surface composition and structure of bimetallic nanoparticles are crucially important for their catalytic property as well as their optical property. IR measurement of CO adsorbed on surface metals (CO-IR) is utilized for this purpose. CO is adsorbed on metals not only on-top sites but also in two-fold or three-fold sites, depending on the kinds of metals and their surface structures. The dramatical changes of wavenumber of adsorbed CO occurs depending on the binding structure [177-181]. 

An LCD is a ubiquitous electronic display. Now, it is widely distributed among human daily life, like mobile phones, TV, and personal computers. The LCD has, however, a drawback, i.e., slower response than a plasma display or an electroluminescene display. Recently we have first succeeded in combination of a nanoparticle technology with the LCD technology, which realized fast response of the LCD [45,235,236]. Thus we have found a phenomenon, i.e., a frequency modulation of the LCD doped with metallic nanoparticles. Since the frequency modulation, or electro-optic property depends on the kind of metals, we have prepared AgPd bimetallic nanoparticles protected with a typical liquid crystal molecule, 4-cyano-4 -pentylbiphenyl (5CB) to investigate the electro-optic property [45,235,236]. 

Metal nanoparticles have been actively synthesized for applications as catalysts, sensors, adsorbents, analytical probes and optical data storages [1-7]. This is due to the fact that the physicochemical properties of metal nanoparticles can be... 

Metal nanoparticles (NPs), which represent an important family of nanoscale objects with unique electronic, optical, catalytic, and magnetic properties, are distinctly different from both molecular and bulk materials. In the following we... 

The photoluminescence of these nanoparticles has very different causes, depending on the type of nanomaterial semiconductor QDs luminescence by recombination of excitons, rare-earth doped nanoparticles photoluminescence by atom orbital (AO) transitions within the rare-earth ions acting as luminescent centers, and metallic nanoparticles emit light by various mechanisms. Consequently, the optical properties of luminescent nanoparticles can be very different, depending on the material they consist of. 

When the size of metals is comparable or smaller than the electron mean free path, for example in metal nanoparticles, then the motion of electrons becomes limited by the size of the nanoparticle and interactions are expected to be mostly with the surface. This gives rise to surface plasmon resonance effects, in which the optical properties are determined by the collective oscillation of conduction electrons resulting from the interaction with light. Plasmonic metal nanoparticles and nanostructures are known to absorb light strongly, but they typically are not or only weakly luminescent [22-24]. 

Synthesis of novel materials with desired and tunable physical and chemical properties continues to draw wide interest. Nanomaterials with a variety of shapes and sizes have been synthesized as they offer numerous possibilities to study size and shape-dependent variations of electronic, optical, and chemical properties. Nanomaterials of a particular element show drastic differences in physical and chemical properties when compared with the bulk state. For example, bulk gold, a metal that is insoluble in water can be made dispersible when it is in the nanoparticle form. There are drastic changes in the optical properties as well. Bulk gold appears yellow in color, but when it is in the nanoparticle form with an average core diameter of 16 nm, it appears wine red. Likewise, the chemistry of gold, such as catalysis, also shows a drastic change when the constituent units are in the nanometer range. 

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