Void Nanoparticles

In this last section we will have a look at hollow nanoparticles with a particular attention focused on metal-dielectric core-shell 

Moreover the dielectric function of the void metallic nanoparticles here presented, are corrected by including the surface damping term (see Sec. 2.3] into the bulk dielectric function. 

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Here we consider cubically shaped void nanoparticles (see inset of Fig. 3.18), with external side /i and internal side Ij the thickness of the metallic "wall" is t = (/i — I2) /2. 

The production of fatty acid-capped silver nanoparticles by a heating method has been reported [115]. Heating of the silver salts of fatty acids (tetradecanoic, stearic, and oleic) under a nitrogen atmosphere at 250°C resulted in the formation of 5-20-nm-diameter silver particles. Monolayers of the capped particles were spread from toluene and transferred onto TEM grids. An ordered two-dimensional array of particles was observed. The oleic acid-capped particle arrays had some void regions not present for the other two fatty acids. 

Dendrimer-protected colloids are capable of adsorbing carbon monoxide while suspended in solution, but upon removal from solution and support on a high surface area metal oxide, CO adsorption was nil presumably due to the collapse of the dendrimer [25]. It is proposed that a similar phenomena occurs on PVP-protected Pt colloids because removal of solvent molecules from the void space in between polymer chains most likely causes them to collapse on each other. Titration of the exposed surface area of colloid solution PVP-protected platinum nanoparticles demonstrated 50% of the total metal surface area was available for reaction, and this exposed area was present as... 

Because no single homogeneous phase could fulfill these conflicting needs simultaneously, CLs require composite morphologies that consist of several interpenefrafing phases. A minimum of fwo distinct phases is needed, including a solid phase of nanoparticle catalyst (Pt) and electronically conducting substrate (carbon) and a liquid water phase in the void spaces of the substrate for diffusion and permeation of protons, water, and reactant molecules. 

This chapter deals with the selective preparation, TEM/EXAFS/XPS characterization and catalysis of mono- and bimetallic nanowires and nanoparticles highly ordered in silica FSM-16, organosilica HMM-1 and mesoporous silica thin films. The mechanism of nanowire formation is discussed with the specific surface-mediated reactions of metal precursors in the restraint of nanoscale void space of mesoporous silica templates. The unique catalytic performances of nanowires and particles occluded in mesoporous cavities are also reviewed in terms of their shape and size dependency in catalysis as well as their unique electronic and magnetic properties for the device application. 

One of the first examples of mesoscopic-macroscopic two-dimensional ordering within a structure involved a bacterial superstructure formed from the co-aligned multicellular filaments of Bacillus subtilis that was used to template macroporous fibers of either amorphous or ordered mesoporous silica [82], The interfilament space was mineralized with mesoporous silica and, following removal of the organic, a macroporous framework with 0.5 pm wide channels remained. Mesoporous silica channel walls in this hierarchical structure were curved and approximately 100 nm in thickness. Dense, amorphous walls were obtained by replacing the surfactant-silicate synthesis mixture with a silica sol solution. The difference in the mode of formation between porous and non-porous wall structures was explained in terms of assembly from close-packed mesoporous silica coated bacterial filaments in the former compared to consolidation of silica nanoparticles within interfilament voids in the latter. 

Reported volume resistivities for printed patterns formed from commercial silver-based inks are higher than that of bulk silver. This occurrence reflects the fact that sintered ink patterns contain non-ideal defects such as incomplete particle-to-particle contact, incomplete sintering between contacting particles, residual porosity, and the presence of non-conductive additives. The morphology and extent of void formation in two representative sintered silver nanoparticle inkjet inks are illustrated in Fig. 1. 

Use of high-k nanoparticles — Analogous to the nanoparticle conductors discussed previously, it may be possible to print high-k dielectrics using nanoparticles. To date, there have been significant difficulties in producing such films with low leakage, since there tend to be substantial defects such as voids, cracks, etc., in such films. 

Use of high-k nanoparticles in polymer dispersions — To solve the void and cracking issue, it is possible to disperse nanoparticles in a polymer matrix. The drawback is that this typically limits the actual dielectric constant boost to fractional amounts, since it is difficult to achieve significant mass loading of the nanoparticles within the polymer, resulting in a final film with only a small fraction of nanoparticle additive. 

The presence of SDS in the clay matrix permits to deposit a large amount of Au nanoparticles only on the edge of the clay and in voids created by ultrasonic treatment. (Fig. 2B) The SAXS and WAXS patterns of this composite (Fig. 1C) clearly indicate the formation of an intercalated structure and an increase of the interlamellar space between the clay layers up to 1.81 nm and 6.7 nm. 

Naturally occurring nanomaterials exist in a variety of complex forms. In this chapter a short set of definitions will be stated for clarity. Nanocrystals are single crystals with sizes from a few nm up to about 100 nm. They may be aggregated into larger units with a wide spectrum of microstructures. Nanoparticles are units of minerals, mineraloids or solids smaller in size than 100 nm, and composed of aggregated nanocrystals, nanoclusters or other molecular units, and combinations of these. Nanoclusters are individual molecular units that have well-defined structure, but too small to be true crystals. Al and ZnsSs solution complexes are types of nanoclusters with sizes from sub nanometer to a few nm. Nanoporous materials are substances with pores or voids of nanoscale dimensions. These materials can be single crystals, such as zeolites or... 

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