Properties of Nanocrystals

N and R represent nuclearity and radius, respectively. The values of the exponents a and /3i are normally 1 and respectively. The scaling law describes the experimental observations on ionization energy and charging energy reasonably well. When the size of clusters becomes extremely small (say less than 10-12 metal atoms), the clusters act like molecules with different energy level manifolds. 

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This section will outline the simplest models for the spectra of both metal and semiconductor nanocrystals. The work described here has illustrated that, in order to achieve quantitative agreement between theory and experiment, a more detailed view of the molecular character of clusters must be incoriDorated. The nature and bonding of the surface, in particular, is often of crucial importance in modelling nanocrystal optical properties. Wlrile this section addresses the linear optical properties of nanocrystals, both nonlinear optical properties and the photophysics of these systems are also of great interest. The reader is referred to the many excellent review articles for more in-depth discussions of these and other aspects of nanocrystal optical properties [147, 148, 149, 150, 151, 152, 153 and 1541. 

Some of the most interesting recent work in the optical properties of nanocrystals involves the study of single nanocrystals rather than ensembles, using near-field optical teclmiques. These relatively new optical methods can... 

V. COLLECTIVE PROPERTIES OF NANOCRYSTALS SELF-ORGANIZED IN 2D AND 3D SUPERLATTICES... 

C. Electron Transport Properties of Nanocrystals Either Isolated or Self-Assembled in 2D and 3D Superlattices... 

Burda C, Chen X, Narayanan R, El-Sayed MA. 2005. Chemistry and properties of nanocrystals of different shapes. Chem Rev 105 1025-1102. 

Eustis, S., and El-Sayed, M. A. (2006). Why gold nanoparticles are more precious than pretty gold Noble metal surface plasmon resonance and its enhancement of the radiative and nonradiative properties of nanocrystals of different shapes. Chemical Society Reviews 35 209-217. 

ND particles with diameters about 4 nm have 20% of the total number of atoms on the surface. Because the physical properties of nanocrystals are strongly size-dependent, it is crucial to control and accurately measure the crystal size. To some extent, ND crystal size can be controlled by the synthesis conditions, for example, the volume of the detonation chamber [79]. However, it is not something that can be easily changed. Therefore, ND suppliers provide powders of a size that they can... 

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 structure and composition of a nanocrystalline surface may have a particular importance in terms of chemical and physical properties because of their small size. For instance, nanocrystal growth and manipulation relies heavily on surface chemistry [261]. The thermodynamic phase diagrams of nanocrystals are strongly modified from those of the bulk materials by the surface energies [262]. Moreover, the electronic structure of semiconductor nanocrystals is influenced by the surface states that He within the bandgap but are thought to be affected by the surface reconstruction process [263]. Thus, a picture of the physical properties of nanocrystals is complete only when the structure of the surface is determined. 

The review by Yoffe [106] provides a good account of the optical properties of nanocrystals in compound semiconductors (see also [89]). 

In the recent years doped semiconductor nanocrystals are widely investigated including their intrinsic properties and the properties modified by inqjurities [1, 2], Quantum confinement effects are well known to modify the electronic properties of nanocrystals when their diameter is comparable to or smaller than the diameter of the bulk exciton [1-3], Moreover, early results onZnS.Mn nanocrystals [4] show that the position of the Mn emission band is slightly shifted from that of the bulk material. The authors of Ref. [4] also claimed that the Ti level lifetime of manganese ions in nanocrystals reduced by five orders of magnitude as compared to the bulk material. However, recent reports do not confirm this statement [5], Fvuther studies of luminescence in doped nanocrystals are necessary. 

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. 

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