CdSe semiconductor particles

Kamat, P. V. Gopidas, K. R. Dimitrijevic, N. M. Picosecond charge transfer processes in ultrasmall CdS and CdSe semiconductor particles, Mol. Cryst. Liq. Cryst. 1990, 183, 439. 

A higher level of size and morphology control in the incipient semiconductors has been accomplished in reversed micelles prepared from cadmium AOT [614] and from mixtures of cadmium AOT and sodium AOT [615] or, alternatively, by arresting particle growth by surface derivatization [592, 621, 622]. Indeed, surface derivatization of semiconductor clusters was first reported for particles in reversed micelles [621] the reversed micelles act to confine precursor ions and to control the growth of the semiconductor particles. Conditions are typically arranged so that, initially, there is no more than one metal ion (say Cd2+) per water pool. Addition of a heptane solution of bis(trimethylsilyl) selenium resulted in the formation of size-quantized metal selenide particles (say CdSe) in the reversed micelles. This solution could be evaporated to dryness and the resultant particles could be reconstituted in a hydrocarbon solvent Alternatively, addition of metal (say Cd2+) ions to the reversed-micelle-entrapped metal selenide particles, followed by the addition of alkyl(trimethylsilyl)selenium, RMSiMe3, led to the formation of alkyl-capped... 

The special effects associated with materials made up of nanosized particles are also due to non-local interactions. Such effects were first noticed in the field of micro-electronics during efforts to decrease the size of devices to quasi one-dimensional or zero-dimensional structures [236]. One possibility for obtaining zero-dimensional structures is the inclusion of spherical semiconductor particles in a transparent dielectric medium. Such isolated microcrystals, typically of nanometer size are known as quantum dots. Best-known examples include particles of CdS and CdSe isolated in silicate glasses. 

We note that zeolites have also been used as hosts for a number of other intriguing "nanocomposites", for example in the field of encapsulated quantum-size semiconductor particles such as Se, CdS, CdSe, PbS, and GaP.3h32,33,34,35 phe encapsulation of metals such as Bi, Hg, Sn and Ga in zeolites has been described by Bogolomov.36 These studies demonstrate the enormous versatility of zeolite host systems for studies and control of structural/electronic relationships. 

A very important step toward a better understanding of the electronic properties of layered semiconductor particles is presented in the same article. In the framework of the effective mass approximation, the authors modeled the optical transition of CdSe crystallites with small inclusions of... 

Quantum dots (QDs) are nanosized semiconductor particles of group II-VI or III-V main group elements with diameters of less than 10 nm [123]. These were first characterized in 1983 by Brus [124] as small semiconductor spheres in a colloidal suspension. QDs due to their nanoscale dimensions are subject to strong quantum confinement, which results in unique optical properties. Thus, in the last two decades, synthesis of QDs has attracted a lot of attention and generated a large number of publications [125]. A variety of methods have been proposed and implemented for synthesis of QDs. Of these methods, colloidal synthesis is the most accessible method for producing QDs suspended in solution. Colloidal synthesis of CdSe QDs is shown in Fig. 4. A cadmium compound is heated to 320°C... 

Nanocrystalline particulate films, which exhibit pronounced quantum size effects in three dimensions, are of great interest due to applications in solar cell (108-112) and sensor (57, 113-115) applications. They exhibit novel properties due to not only the SQE manifested by individual nanoparticles but also the total surface area. Unlike MBE and MOCVD methods used to prepare quantum well electrodes, these electrodes can be prepared by conventional chemical routes described in Section 9.5.2.2. For example, II-VI semiconductor particulate films were prepared by using low concentrations of precursors and by controlling the temperature of the deposition bath. Nodes demonstrated the SQE for CdSe thin films deposited by an electroless method (98). The blue shift in the spectra of CdSe films has been demonstrated to be a function of bath temperature. As described in Section 9.5.2.1, electrodeposition of semiconductors in non-aqueous solvents leads to the formation of size-quantized semiconductor particles. On a single-crystal substrate, electrodeposition methods result in epitaxial growth (116, 117), and danonstrate quantum well properties. 

Metallic nanoparticles are either spherical metal or semiconductor particles with nanometer-sized diameters. Similar to nanoparticles nanocrys-tal (NC) or nanocrystallite term is used for nanoparticles made up of semiconductors. Generally semiconductor materials from the groups II-VI (CdS, CdSe, CdTe), III-V (InP, InAs) and IV-VI (PbS, PbSe, PbTe) are of particular interest. Metal Based nanoparticle are used for nanoscale transistors, biological sensors, and next generation photovoltaics [3]. 

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