Colloidal nanoparticles materials

Asher, S. A., Crystalline colloidal array chemical sensing devices, In ACS PRF summer school on nanoparticle materials, June 6 18, 2004. Eastern Michigan University, Ypsilanti, MI, 2004... 

Materials development and synthesis is another important dual-use type of chemistry. Developments over the past few decades include a number of elec-troitic materials and their processing, fuel cells and batteries, photoresist and semiconductor synthesis, high-performance composites (structural components) and nanocomposite materials, colloidal nanoparticle technology, solid-state lasers, and light-emitting diodes. 

Finally, Mirkin and co-workers (137, 138) used a group of salen-Uke Schiff base ligands [bis(metallotridentate) Schiff base or BMSB] for the synthesis of metaHohgand-based CPs. Initial studies on these CPs were on colloidal nanoparticles of these materials, representing one of the earliest studies on CP or MOF nanoparticles (137, 138). Subsequent investigations showed that these amorphous nanoparticles could be transformed to a crystalline form by modifying the solvent conditions (132). 

To maximize fluorophore excitation and increase the fluorescence quantum yield, the spectral properties of the metal nanoparticles need to be optimized. While spherical colloidal nanoparticles of noble metals have been well known for many years, it is only recently that there has been an explosion of reports on the preparation and properties of anisotropically-shaped materials. As will be discussed in the following sections, a wide range of morphologies can be produced, including triangular nanoplates (nanoprisms), cubes, octahedra, nanowires, nanorods and bi-pyramids. The last few years have also seen major developments in our understanding of the growth processes involved, so that now it is possible to prepare many types of shaped p>articles in a controlled fashion. 

In many cases this approach may provide accurate and useful results, but there are also situations where it may not be particularly useful. A well-known class of materials that, moreover, constitutes a larger part of the systems that shall be discussed in this presentation, is that of clusters and colloids. These materials are intermediates between smaller molecules and extended, macroscopic solids. Typically, they contain from some 10s till several 100 000s of atoms. Often, they have only some few types of atoms with, in some cases, the exception of the surface, where ligands, that saturate dangling bonds, may occur. Thus, it may be assumed that the structure of these nanoparticles resembles that of small, finite parts of the infinite, crystalline material. However,... 

At the opposite of the molecular chemistry described until now, nanoparticles are reminiscent of heterogeneous catalysts. However, these colloid-derived materials have been shown to catalyze efficiently in water coupling reactions which have been previously described in pure homogeneous systems. For instance, poly(N-vi-nyl-2-pyrrolidine)-stabilized palladium nanopartides promote the Suzuki crosscoupling in aqueous media with high yields (see also Section 6.6) [87]. 

Chemical methods of material processing were known for years, existing in parallel with physical and other methods of film deposition. Recent advances in electron microscopy and scanning nanoprobe microscopy (STM, ATM) have revealed that some of the materials produced by the chemical methods have distinctive nanocrystalline structure. Furthermore, due to the achievements of colloid chemistry in the last 20 years, a large variety of colloid nanoparticles have become available for film deposition. This has stimulated great interest in further development of chemical methods as cost-effective alternatives to such physical methods as thermal evaporation magnetron sputtering chemical and physical vapor deposition (CVD, PVD) and molecular beam epitaxy (MBE). 

Interactions within the suspended material, such as colloidal nanoparticles [5, 6], and interactions between the suspended material and the substrate (see below). 

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