Nanoparticles of noble metals: fabrication, characterization and applications

In principle, particles in nanometer scale have two important characteristics namely: 1) For most of their phenomena, the laws of classical physics can not be used, but we must apply laws and principles of quantum mechanics. Thus, optical, electrical and magnetic properties are different from their corresponding bulk materials, due to their quantum size effect. 2) By reducing their size, the surface to volume ratio (A/V) of the system increased. This leads to increase effective surface area that resulted in enhancement rate of physical and chemical processes on the surface, specially in rate of catalytic reactions. Moreover, their solvability is also increased. Therefore, these new properties of nanoparticles can provide new horizons in advanced technological and industrial applications. Due to rapid growth of nanoscience and nanotechnology as well as new applications of nanostructure materials, knowledge and detailed understanding of their principles, methods of synthesis and properties of these type of materials is necessary. In recent years, incorporation and addition of metallic and semiconductor nanoparticles in transparent dielectric media with aim of new applications has been investigated by many researchers. In addition, transparent thin films containing metallic nanoperticles possesses a plasmon absorption peak in visible region of electromagnetic spectrum. Therefore, by selecting a proper metal and controlling its particle size and concentration in a transparent media (SiO2, TiO2, WO3, Al2O3, ZnO and etc.), It can be used for different advanced applications including optical filters and switches, sensors, catalysts and solar cells. In this article, first, we will review different methods for nanoparticle synthesis and their applications. To synthesize noble metallic nanopartiles, we focus on several fabrication methods namely: RF co-sputtering, and Spin Coating. Some of the systems investigated in the past few years are including: Cu-SiO2, Ag-SiO2, Sol-Gel Au-SiO2, (Cu-Ag)-SiO2, (Cu-Au)-SiO2, (Ag-Au)-SiO2, Au-TiO2 and Au-WO3 . Then, we present some recent results obtained by our research group (1-3). Finally, we compare our results with very recent published data reported by other researchers (4,5).