Nanocrystal organizations

Figure 8.3. Schematic illustration of the various metal nanocrystal organizations...

In this chapter, we discuss the structure and stability of mesoscopic organizations of nanocrystals in one, two and three dimensions, obtained by using a variety of surfactants. We also examine certain unusual organizations such as clusters of nanocrystals and microcolloidal crystals. Collective properties of nanocrystal organization are presented. 

The way in which the nanocrystals organize themselves depends critically on the core diameter, the nature of the ligand, substrate and even the dispersive medium used [101]. Thiolized metal nanocrystals readily arrange into two-dimensional arrays on removal of the solvent [29]. Using suitable methods, they can also be put into one-dimensional organization in the form of strings or assembled in a stepwise fashion in a three-dimensional superlattice (see Figure 4.8). 

In this chapter we discuss the physical and chemical properties of metal nanocrystals, with emphasis on size-dependent properties. The ability of nanocrystals to form mesoscopic organizations in one, two, and three dimensions is also examined. Collective properties of nanocrystal organization are presented. 

It has been proposed that self-similarity in metal nanocrystal organization would manifest in the form of a giant cluster whose shape and size are direct consequences of the nanocrystals themselves [114]. The invariance of the shell effects in metal nanocrystals with scaling is shown schematically in Figure 1.16. 

The fact that the physical properties of nanocrystal organizations could be different from that of the isolated particles is being realized. Pellets of monodis-perse nanocrystals, obtained by the use of bifunctional ligand that binds to more than one nanocrystal or by applying pressure on dried nanocrystalline matter, have been used for electrical transport measurements [130-133]. Pellets made of small Au and Pd nanocrystals exhibit nonmetallic behavior with specific conductivities in the range of 10 Q cm [130-132]. The conductivity, however, increases dramatically with an increase in the diameter of the nanocrystals. An insulator metal transition has indeed been reported from pellets made of -12.5-... 

Fig. 3.1. TEM images of Au nanocrystals organized into (a) ribbons and (b) thicker strands on the DNA backbone. The inset illustrates schematically the relationship between the DNA chains and the Au nanocrystals (reproduced with permission...

Table 13. Schematic representation of most limiting cellulose nanocrystals organizations...

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