Nanocrystal semiconductors

We begin our discussion of nanocrystals in diis chapter widi die most challenging problem faced in die field die preparation and characterization of nanocrystals. These systems present challenging problems for inorganic and analytical chemists alike, and die success of any nanocrystal syndiesis plays a major role in die furdier quantitative study of nanocrystal properties. Next, we will address die unique size-dependent optical properties of bodi metal and semiconductor nanocrystals. Indeed, it is die striking size-dependent colours of nanocrystals diat first attracted... 

An equally important challenge for nanocrystal assembly is the fonnation of specific nanocrystal arrangements in solution. By using complementary DNA strands as tethers, Mirkin et al [102, 103] fonned aggregates of gold nanocrystals with specific sizes Alivisatos et al also used DNA to stmcture semiconductor nanocrystal molecules, though in this case the molecules contained only a few nanocrystals placed controlled distances from each other [104, 105 and 106]. The potential applications of biomolecular teclmiques to this area of nanoscience are immense, and the opportunities have been reviewed in several recent publications [107, 108, 109 and 110]. 

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. 

Peng Z G, Wickham J and Alivisatos A P 1998 Kinetics of ll-VI and lll-V colloidal semiconductor nanocrystal growth focusing of size distributions J. Am. Chem. Soc. 120 5343... 

Sachleben J R ef a/1998 Solution-state NMR studies of the surface structure and dynamics of semiconductor nanocrystals J. Phys. Chem. B 102 10 117... 

Brus L E 1993 NATO ASI School on Nanophase Materials ed G C Had]lpanayls (Dordrecht Kluwer) Allvisatos A P 1996 Semiconductor clusters, nanocrystals and quantum dots Science 271 933 Heath J R and Shlang J J 1998 Covalency In semiconductor quantum dots Chem. See. Rev. 27 65 Brus L 1998 Chemical approaches to semiconductor nanocrystals J. Phys. Chem. Solids 59 459 Brus L 1991 Quantum crystallites and nonlinear optics App/. Phys. A 53 465... 

Goldstein A N, Echer C M and Alivisatos A P 1992 Melting in semiconductor nanocrystals Science 256 1425... 

Peng, X. G. (2003). Mechanisms for the Shape-control and Shape-Evolution of Colloidal Semiconductor Nanocrystals. Adv. Mater., 15,459-463. 

Rogach, A. L. Nagesha, D. Ostrander, J. W. Giersig, M. and Kotov, N. A. (2000). "Raisin Bun"-Type Composite Spheres of Silica and Semiconductor Nanocrystals. Chem. Mater., 12, 2676-2685. 

PBE dendrons coordinate to the surface of II-VI semiconductor nanocrystals (e.g., CdSe [33] and CdSe/ZnS core/shell structure [34, 35]) to modulate the photoluminescence of the nanocrystals [32]. Trioctylphosphine oxide (TOPO)-capped II-VI semiconductor nanocrystals of several-nanometers diameter have been synthesized by a pyrolysis reaction of organometallics in TOPO [33-35]. The capping ligand (TOPO) can be replaced by stronger ligands such as thiol compounds [36], suggesting that dendrons bearing sulfur atom(s) at the focal point replace TOPO as well. 

Penner RM (2001) Hybrid electrochemical/chemical synthesis of semiconductor nanocrystals on graphite. In Hodes G (ed) Electrochemistry of Nanostructures, Wiley-VCH,... 

Erley G, Gorer S, Penner RM (1998) Transient photocurrent spectroscopy Electrical detection of optical absorption for supported semiconductor nanocrystals in a simple device geometry. Appl Phys Lett 72 2301-2303... 

Peng X, Wickham J, Ahvisatos AP (1998) Kinetics of 11-VI and III-V colloidal semiconductor nanocrystal growth Focusing of size distributions. J Am Chem Soc 120 5343-5344... 

Doose, S., Tsay, J. M., Pinaud, F. and Weiss, S. (2005) Comparison of photophysical and colloidal properties of biocompatible semiconductor nanocrystals using fluorescence correlation spectroscopy. Anal. Chem., 77, 2235-2242. 

Alivisatos, A. P. (1996) Perspectives on the physical chemistry of semiconductor nanocrystals. J. Phys. Chem., 100, 13226-13239. 

Verberk, R., Oijen, A. V. and Orrit, M. (2002) Simple model for the power-law blinking of single semiconductor nanocrystals. Phys. Rev. B, 66, 233202-1-233202-4. 

Tang, J. and Marcus, R. A. (2005) Diffusion-controlled electron transfer processes and power-law statistics of fluorescence intermittency of nanoparticles. Phys. Rev. Lett, 95, 107401-1-107401-4 Tang, J. and Marcus, R. A. (2005) Mechanisms of fluorescence blinking in semiconductor nanocrystal quantum dots./. Chem. Phys., 123,054704-1-054704-12. 

Semiconductor nanoparticles have been intensively studied because of their properties of quantum size effects [54]. A number of synthetic techniques have been reported and their characteristics have been studied by various spectroscopic methods [55, 56]. However, magnetic field effects (MFEs) on the photoelectrochemical properties of semiconductor nanocrystals had not until now been reported. 

Maenosono, S., Dushkin, C. D., Saita, S. and Yamaguchi, Y. (2000) Optical memory media based on excitation-time dependent luminescence from a thin film of semiconductor nanocrystals. Jpn. J. Appl. Phys., 39, 4006- 12. 

Ito, Y, Matsuda, K. and Kanemitsu, Y. (2007) Mechanism of photoluminescence enhancement in single semiconductor nanocrystals on metal surfaces. Phys. Rev. B, 75, 033309. 

Verberk, R., Chon, J. W. M., Gu, M. and Orrit, M. (2005) Environment-dependent blinking of single semiconductor nanocrystals and statistical aging of ensembles. Physica E, 26, 19-23. 

High-Temperature Crystallization The size-tunable optical and electronic properties of semiconductor nanocrystals are attractive for a variety of optoelectronic applications. In solution-phase crystallization, precursors undergo chemical reaction to form nuclei, and particle growth is arrested with capping ligands that... 

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