Semiconductor quantum dots incorporation

Research on semiconductor nanoparticle technology by chemists, materials scientists, and physicists has already led to the fabrication of a number of devices. Initially, Alivisatos and co-workers developed an electroluminescence device from a dispersion of CdSe nanoparticles capped with a conducting polymer349 and then improved on this by replacing the polymer with a layer of CdS, producing a device with efficiency and lifetime increased by factors of 8 and 10, respectively. 0 Chemical synthetic methods for the assembly of nanocrystal composites, consisting of II-VI quantum dot polymer composite materials,351 represent one important step towards the fabrication of new functional devices that incorporate quantum dots. 

Silica particles have been exploited in virtually every assay or detection strategy that polymer particles have been used in for bioapplication purposes. Recently, fluorescent dye-doped silica nanoparticles have been developed by a number of groups that have similar fluorescence characteristics to quantum dot nanocrystals (Chapter 9, Section 10). Fluorescent silica nanoparticles can be synthesized less expensively than quantum dots due to the fact that the silica particles incorporate standard organic dyes (Ow et al., 2005 Wang et al., 2006) and are not dependent on making reproducible populations of semiconductor particles with precise diameters to tune emission wavelengths. 

Nanocrystal semiconductor memory (Tiwari et al., 1996) is another application based on the small capacitance of quantum dots (or nanocrystals, as they are often called in this context). In a conventional field effect transistor inversion is obtained by applying a suitable bias voltage to the gate. The incorporation of nanocrystals in the gate insulator would provide a means to apply a field offest by charging the quantum dots. Working devices have been successfully manufactured. 

In the fabrication of semiconductors, the composition of ternary and quaternary alloys can be strongly influenced by factors like the temperature and the duration of the annealing processes. For example, the sulfur content in CdSSe quantum dots increases with increasing temper temperature [48]. In the case of superlattices with very thin layer thicknesses, unwanted ternary or quaternary alloys can be formed by diffusion of the ions into the adjacent layer. Because of this, it is necessary to prove the material composition of the alloys after the growth. The behavior of the vibrational properties of a system with an incorporated element B in the crystal lattice AC is similar to the problem of the impurities The element B causes a distortion of the lattice because of the difference in the masses and, hence, of the appearance of new modes. With increasing... 

Coming back to incorporated luminescent species, the text to follow is divided in terms of the active luminescent species, that is, lanthanide ions and dyes. Of course many other important luminescent species, among them transition metal ions and semiconductor nanoparticles (quantum dots (QDs)), can be incorporated in OIH giving rise to several applications, but these will not be treated here. 

Semiconductor NCs have been incorporated into solar cells in different configurations, for example (a) photoelectrodes composed of quantum dot arrays, (b) metal-semiconductor photovoltaic cells,(c) NC-polymer solar cells and (d) quantum dot sensitized solar cells. This field has been the focus of intense research in recent years because of the possibility that quantum dot-based solar cells can overcome the Shockley-Queisser photoconversion limit. This possibility relies on two feasible processes hot carrier extraction and multiple exciton generation (MEG). 

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