Characterization Methods for Nanostructure of Materials

The 20th century was the so-called "age of new material synthesis" as shown in Fig. 5.1.1 (Adschiri, 2002). "Synthesis" of new substances had been essential to attain a new property for materials. However, in the recent R&D of material, keen attention is attracted on controlling material function by the material structure. Nanotechnology is a typical example of this stage of technology. In the control of material structure, "process" is regarded more important than "synthesis." For example, in the nanoparticle production, size and shape of particle significantly depend on the operating conditions of crystallization process. It was found that some semiconductor materials show strong photoluminescence and the wavelength can be controlled with its particle size ("quantum size effect"). With a same wavelength of excitation, a wide range of colors can be obtained by changing the particle size of the nanoparticles of CdSe, CdTe, CdS, etc., the so-called quantum dots (Medintz et al., 2005). Photonic crystal can be produced by self-assembly of nanomaterials (homoassembly) and the control of self-assembly phenomena is a critical issue of process design and operation. In the fabrication of ultraviolet laser (Tang et al., 1998, Kawasaki et al., 1998, Huang et al., 2001) and light-emitting diode (LED) (Tsukazaki et al., 2005) based on ZnO materials, laser molecular beam epitaxy is a powerful process to grow fine ZnO nanocrystals self-assembled and arrayed parallel on substrates. The next stage of the nanotechnology will be "programmed assembly" of nanomaterials because this is a foreseeable future target for the industries of various fields. In the device production by assembling the structured materials, "fabrication" is the key technology. Thus, science and technology for materials is being shifted from "synthesis" toward "processing" and "fabrication.".