Metallic nanoparticles 614 INDEX

Bragg mirrors on periodic stacks of layers Periodic stacks of metal nanoparticles or dielectric layers with alternating high and low refractive index produce a desired reflectance of the mirror that depends on the thickness and the refractive index of the layers in the stack 16,17... 

Khlebtsov NG, Trachuk LA, Mel nikov AG (2005) The effect of the size, shape, and structure of metal nanoparticles on the dependence of their optical properties on the refractive index of a disperse medium. Optics Spectrosc 98 77-83... 

Interaction of biomolecules with the surface of metallic nanoparticles may also result in local changes in refraction index. This in turn may result in delicate modification of plasmon resonance frequency and yield detectable analytical signal [138],... 

However, this assumption is not necessarily justified. Even for a well-faceted nanoparticle there are a number of nonequivalent adsorption sites. For example, in addition to the low-index facets, the palladium nanoparticle exhibits edges and interface sites as well as defects (steps, kinks) that are not present on a Pd(l 1 1) or Pd(lOO) surface. The overall catalytic performance will depend on the contributions of the various sites, and the activities of these sites may differ strongly from each other. Of course, one can argue that stepped/kinked high-index single-crystal surfaces (Fig. 2) would be better models (64,65), but this approach still does not mimic the complex situation on a metal nanoparticle. For example, the diffusion-coupled interplay of molecules adsorbed on different facets of a nanoparticle (66) or the size-dependent electronic structure of a metal nanoparticle cannot be represented by a single crystal with dimensions of centimeters (67). It is also shown below that some properties are merely determined by the finite size or volume of nanoparticles (68). Consequently, the properties of a metal nanoparticle are not simply a superposition of the properties of its individual surface facets. 

These difficulties have stimulated the development of defined model catalysts better suited for fundamental studies (Fig. 15.2). Single crystals are the most well-defined model systems, and studies of their structure and interaction with gas molecules have explained the elementary steps of catalytic reactions, including surface relaxation/reconstruction, adsorbate bonding, structure sensitivity, defect reactivity, surface dynamics, etc. [2, 5-7]. Single crystals were also modified by overlayers of oxides ( inverse catalysts ) [8], metals, alkali, and carbon (Fig. 15.2). However, macroscopic (cm size) single crystals cannot mimic catalyst properties that are related to nanosized metal particles. The structural difference between a single-crystal surface and supported metal nanoparticles ( 1-10 nm in diameter) is typically referred to as a materials gap. Provided that nanoparticles exhibit only low Miller index facets (such as the cuboctahedral particles in Fig. 15.1 and 15.2), and assuming that the support material is inert, one could assume that the catalytic properties of a... 

Several strategies were appUed to produce samples for TEM and kinetic studies [8, 21], but only one route is presented here (Fig. 15.3). Noble metal nanoparticles were grown via metal evaporation on a crystalline soluble substrate (e.g., NaCl(OOl)), leading to an epitaxial growth of particles with regular shape and well-developed low-Miller index facets (Fig. 15.3). Thereafter, the metal particles were embedded in a thin (25 nm) amorphous oxide fdm, before the metal-oxide system was lifted off the substrate via flotation in water [8, 18, 20, 31]. 

Abstract Nanophotonic stractures exhibit a large variety of effects on the nanoscale that can be used for biosensing in a biochip format. The resonance nature of these structures then allows high sensitivity to analytes, gases, or other external index perturbations down to the order of 10 refractive index unit. In this chapter, several configurations of nanophotonic structures and their use for sensing are reviewed with special emphasis on grating-based resonant strucmres, metallic nanoparticle, and nano apertures. 

Composite materials formed by nanometer-sized metal particles embedded in dielectrics have a growing interest o wing to the large values of fast optical Ken-susceptibility, whose real part is related to the intensity-dependent refractive index 2 [ ] Ion implantation has been shown to produce a high density of metal nanoparticles (MN) in glasses [2], The high-precipitate volume fraction and small size of MN leads to giant value of the [3]. This stimulates an interest in the use of ion implantation to fabricate nonlinear optical materials. 

The problem of designing new polymer-based composite materials containing metal nanoparticles (MNPs) is of current interest, particularly in the fabrication of magnetooptic data storages, picosecond optical switches, directional connectors, and so on. The nonlinear optical properties of these composites stem from the dependence of their refractive index on incident light intensity. This effect is associated with MNPs, which exhibit a high nonlinear susceptibility of the third order when exposed to ultrashort (picosecond or femtosecond) laser pulses [1]. 

Metal nanoparticles with very high positive standard reduction potential ( °) values are easily reduced. These metal particles are said to be noble and there remains a possibility of finding them even in their elemental stage in the Earth s crust. One such example is gold with an value of + 1.52 V. So, the ° value is an index of nobility for metals in particular. The reduction of noble metal ions by the bottom-up approach thus becomes easy, which gives birth to metal nanoparticles if the stabilization of particles takes place at a proper nanostage. On the other hand, metals like Ni and Cu are difficult to reduce. This is a case where resin support can really help their reduction, which is otherwise difficult to achieve. This may be explained by... 

The very first studies of mesoporous silicon noted the different colors of anodized and so-called stain films (Uhlir 1956 Turner 1958 Archer 1960). Uhlir referred to his surfaces as having a matte black, brown or red deposif (Uhlir 1956). Turner commented that several orders of interference colors can be seen as the film thickens (Turner 1958). The first use of such colored silicon in the late 1950s was in p-n junction delineation (lies and Coppen 1958 Whoriskey 1958 Robbins 1962). Porous silicon, with its lower refractive index than solid silicon, induces optical interference effects as etched films on wafers. A colorimetric analysis for layer thicknesses below 500 nm, at quantified porosities, showed that interference color directly related to the optical thickness of anodized singlelayer structures (Lazarouk et al. 1997). Figure 1 shows examples for stain-etched p + wafers. The visual color of a given layer can be further changed by plasmonic effects of deposited metal nanoparticles (Lublow et al. 2012) or through controlled oxidation of the silicon skeleton. 

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 ... 

Finally, the dependence of the position and peak intensity of the extinction spectrum of the noble metal nanoparticles, due to nanoSPR, on the refractive index of the surroimding medium has also been exploited for biosensing. Gold or silver... 

---