Semiconductor and Oxide Nanocrystals

Attempts to organize nonspherical oxide nanocrystals have also met with reasonable success. Thus, tetrahedral CoO nanocrystals are foimd to organize into extended two-dimensional arrays [607], Prismatic BaCr04 nanocrystals assemble into a rectangular arrangement [513]. 

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Shape-Controlled Synthesis of Semiconductor and Oxide Nanocrystals... 

Rao CNR, Kulkami GU, Thomas PJ, Agrawal W, Gautam UK, Ghosh M (2003b) Nanocrystals of metals, semiconductors and oxides novel synthesis and applications. Curr Sci 85 1041-1045 Rao CNR, Kulkami GU, Thomas PJ (2005) Physical and chemical properties of nano-sized metal particles. In Nicolais L, Carotenuto G (eds) Metal-polymer nanocomposites. WUey, Hoboken, New Jersey, pp 1-36... 

The s)mthesis method in high-boiling solvents has been developed to obtain high quality nanocrystals of a number of metals, metal oxides, semiconductors, and inorganic salts. For rare earth compounds, the s)mthesis of rare earth oxides, phosphates and halides would be discussed in this and latter sections of this chapter. The s)mthesis route is considered as colloidal s)mthesis since the products are usually well dispersed NCs in the reaction solution or certain solvents, and the products could only be separated with particular techniques. 

Based on the above analysis, the development of metal oxides of nanometric dimensions can result in devices and materials with superior performance. However, these developments are directly related to the development of synthetic methods that allow for controlled particle size, particle morphology, and deposition. Once again, the bottom-up methods of wet chemical nanocrystal synthesis are apparently the most viable approach to achieve such control. Compared with the control attained in the synthesis of metal and 11-lV semiconductor nanocrystals, the control of metal oxide nanocrystals is still incipient, particularly insofar as the synthesis of complex metal oxide nanocrystals (oxides formed of more than one cation) is concerned. 

Nanocrystals and quantum dots of semiconductors and metal oxides comprising 1000-100,000 atoms. 

Properties of a nanocrystal can be influenced markedly by encasing it in a sheath of another material [531]. The material of the shell in such a core-shell structure can be a metal, semiconductor, or an oxide. The shell material helps to impart novel, desired properties on the nanocrystals. For example, defects prevalent in the surface states of semiconductor nanocrystals can be transferred to a buffer layer of the shell material to obtain better emission from the nanocrystals. We use the notation, core-shell to denote core-shell structures. We employ the following classification to describe the nature of the core and the shell semiconductor-semiconductor, metal-metal and metal-oxide, semiconductor-oxide and oxide-oxide. The classification is artificial in that the nanocrystals result from similar synthetic strategies. The motivation for carrying out the modification of the shell material, however, differs in each case. 

Hydrolyzable salts of metal ions are used for synthesis of corresponding oxides in colloidal form by their forced hydrolysis under hydrothermal conditions [322] or in high-boiling solvents (polyols) [323], Hydrolysis in nonaqueous solutions has been applied also to metal alkoxides [324] and diketonates [325], offering a convenient route to the uncapped nanoparticles. Synthesis of oxide nanocrystals has been directed to nonaqueous approaches [326-328] mostly inspired by the success of the synthesis of high quality semiconductor nanocrystals in nonaqueous media [329]. The quality of the nanocrystals yielded by these nonaqueous solution methods is generally better than that of the nanocrystals synthesized in aqueous solutions. 

Formation of Hollow Nanocrystals through the Nanoscale Kirkendall Effect. Science, Vol. 304, No. 5671, (April 2004), pp. 711-714, SSN 0036-8075 Yun, S.H. Wu, J.Z. Dibos, A. Gao, X. Karlsson, U.O. (2005). Growth of Indined Boron nanowire Bundle Arrays in an Oxide-Assisted Vapor-Liquid-Sohd Process. Applied Physics Letters, Vo. 87, No. 11, (September 2005), pp. 113109 (1-3), ISSN 0003-6951 Zhang, P.H. Crespi, V.H. (2002). Theory of B2O and BeB2 Nanotubes New Semiconductors and Metals in One Dimension. Physical Review Letters, Vol. 89, No. 

Nanocrystals are receiving significant attention for nano-electronics application for the development of future nonvolatile, high density and low power memory devices [1-3]. In nanocrystal complementary metal oxide semiconductor (CMOS) memories, an isolated semiconductor island of nanometer size is coupled to the channel of a MOS field effect transistor (MOSFET) so that the charge trapped in the island modulates the threshold voltage of the transistor (Fig. 1). 

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. 

Crystallization by reaction to form metals, semiconductors (e.g.. Si), and metal oxides including nanocrystals Supercritical fluid deposition... 

The reactions used for synthesis of II-VI (CdSe, CdTe), III-V (InP, InAs), and IV-VI (PbS, PbSe, PbTe) semiconductor nanocrystals are outlined by Schemes 3-5.4,17,30-32 The syntheses are carried out at high temperatures, and in the presence of long-chain alkylphosphines (trioctylphosphine,TOP), alkyl-phosphine oxides (trioctylphosphine oxide, TOPO), alkylamines (hexadecyl-amine, HD A), and alkylphosphonic acids as the stabilizing agents. 

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