Nanometer-sized metal particles

Dependence of the electric field distribution in the double layer on particle size [Zhdanov and Kasemo, 2002 Chen and Kucemak, 2004a, b], which, according to Zhdanov and Kasemo, should result in an increase in the rates of electrochemical reactions on nanometer-sized metal particles. 

Summary Materials containing uniform, nanometer-sized metal particles homogeneously dispersed in a Si02 matrix, with a variable metal loading, were prepared by the sol-gel processing starting from metal salts, alkoxysilanes of the type X(CH2)nSi(OR)3 and, optionally, Si(OR)4. 

Composites containing nanometer-sized metal particles of a controllable and uniform size in an insulating ceramic matrix are very interesting materials for use as heterogeneous catalysts and for magnetic and electronic applications. They show quantum size effects, particularly the size-induced metal-insulator transition (SIMIT) [1],... 

Tsai, K.-L. and Dye, J.L., Synthesis, properties, and characterization of nanometer-size metal particles by homogeneous reduction with alkalides and electrides in aprotic solvents, Chem. Mater., 5, 540,1993. 

Particles produced in the gas phase must be trapped in condensed media, such as on solid substrates or in liquids, in order to accumulate, stock, and handle them. The surface of newly formed metallic fine particles is very active and is impossible to keep clean in an ambient condition, including gold. The surface must be stabilized by virtue of appropriate surface stabilizers or passivated with controlled surface chemical reaction or protected by inert materials. Low-temperature technique is also applied to depress surface activity. Many nanoparticles are stabilized in a solid matrix such as an inert gas at cryogenic temperature. At the laboratory scale, there are many reports on physical properties of nanometer-sized metallic particles measured at low temperature. However, we have difficulty in handling particles if they are in a solid matrix or on a solid substrate, especially at cryogenic temperature. On the other hand, a dispersion system in fluids is good for handling, characterization, and advanced treatment of particles if the particles are stabilized. 

Scheme 12.1.8 Formaiion of nanometer-sized metal particles protected by polymer.

The possibility to obtain a uniformly dispersed composite powder was shown for the a-Fe-Al203 system where metal particles with an average size of 55 nm were formed in an amorphous/nano alumina matrix.18 Other studies attempting to obtain dense bulk composites based on the sol-gel route using conventional pressure-assisted sintering ( 1400°C and an applied force of 10 MPa) resulted in a coarse microstructure.16 However, if reaching theoretical density is not a necessary requirement, a porous ceramic microstructure containing nanometer-sized metal particles can be used as a catalytic material.19 Certain combinations of composite materials demand... 

The initial interest in ceramic matrix nanocomposites arose from reports by Niihara and co-workers indicating enhanced mechanical properties due to the presence of ceramic (SiC) particles.53 With the development of various processing routes to introduce nanometer-sized metal particles in a ceramic matrix, variations in functional (i.e. magnetic) properties are possible. In the following we briefly review the microstructurally dependent properties, with emphasis on the possible mechanisms leading to improved properties and using SiC-reinforced alumina as a point of comparison. 

Surface plasmons, or surface plasmon polaritons, are surface electromagnetic waves that propagate inside a metal along a metal/dielectric (or metal/ vacuum) interface their excitation by light is surface plasmon resonance (SPR) for planar surfaces or localized surface plasmon resonance (LSPR) for nanometer-sized metal particles. 

Up to now we have considered unreconstructed, defect-free low-index surfaces, where all surface atoms have the same geometric environment. In the real world, large defect-free terraces of low-index surfaces are the exception rather than the rule, and in nanometer-sized metal particles (clusters) such as those found in industrial catalysts a significant fraction of all surface atoms sit at steps, edges or corners and therefore have lower coordination than those in the terraces. There are many indications that such sites are more reactive than terraces [59],... 

J. Hodak a. Henglein G. V. Martian D, Photophysics of Nanometer Sized Metal Particles Electron-Phonon Coupling and Coherent Excitation of Breathing Vibrational Modes./. Phys. Chem. B 2000, 304, 9954-9965. 

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. 

Given that two-nanometer sized metal particles cannot reside within the zeolite supercages, we measured only the magnetic moiety of reduced nickel on the outer surface of zeolite matrix. It is seen from these results that the share of metal nickel present as small particles less than 2 nm in size decreases dramatically on diminishing the amount of metal loaded. Of course, these estimates correspond also the concentrations of oxide precursors initially hosted in the supercages but only their bottom limit, and the real content of oxide component present as the cage-hosted nanoclusters may be substantially higher. 

The full reduction of the metal oxide enables one to prepare composite materials consisting of nanometer-sized metallic particles dispersed in a Li20 matrix. The nanodimensional size of the metal particles is instrumental in making the reactions highly reversible. Conversion reactions are not limited to metal oxides, as it is now clear that there are a number of other systems that can be used, including sulfides, nitrides, phosphides, and fluorides. For a binary metal compound (MX ), with X = F, O, S, N, these reactions proceed as follows ... 

Yes, through a pseudocapacitive process such as is the case for V2O5, or through conversion reactions where the metal oxide is converted into nanometer-sized metallic particles dispersed in a Li20 matrix. 

Chamberlain TW, Zoberbier T, Biskupek J, Botos A, Kaiser U, Khlobystov AN. Formation of uncapped nanometer-sized metal particles by decomposition of metal carbonyls in carbon nanotubes. Chem Sci 2012 3 1919-24. 

Hydrogen gas exhibits high miscibility with CO2 and is a very desirable reducing agent for producing nanometer-sized metal particles in the water-in-SCCO2 microemulsion [52]. 

J. H. Hodak, A. Henglein, and G. V. Hartland, Photophysics of nanometer sized metal particles electron-phonon coupling and coherent excitation of breathing vibrational modes, J. Phys. Chem. B 104, 9954-... 

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