Varieties of Quantum Dots

The ultimate fabrication technique of QDs should produce significant amounts of sample, with such a high control of QD size, shape and monodispersity that singleparticle properties would not be affected by sample inhomogeneity. To date, ensembles of QDs produced by the best available techniques still show a behavior that derives from a distribution of sizes, although this field is evolving very rapidly. In the fabrication of QDs, different techniques may lead to different typologies. Notably, 

1 eV= 1.602 X lO J. The experimental values were obtained by the Alivisatos group by recording the absorption spectra of CdSe QDs of different sizes and determining their size using transmission electron microscopy. 

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SLI is not specific to molecular eigenstates, but universal to the superposition of any eigenstates in a variety of quantum systems. It is thus expected as a new tool for quantum logic gates not only in MEIP but also for other systems such as atoms, ions, and quantum dots. SLI also provides a new method to manipulate WPs with fs laser pulses in general applications of coherent control. 

Bottom The broad color spectrum of quantum dots that is now available. These nanoscale particles can be functionalized and attached to a variety of different chemical species for tagging purposes. The great advantages of quantum dots are that they can all be excited at the same wavelength and are very resistant to photobleaching. 

Nanoscale materials present many interesting opportunities and promises as semiconductor device scaling reaches fundamental limits in the near future. Such materials have novel properties that are of interest in a variety of applications— applications not limited to semiconductors. Over the last decade several methods have been developed for the self-assembly of quantum dots and nanocrystals, with varying degrees of control over size and properties. Chemical self-assembly is particularly promising for inexpensive, bulk manufacturing of such materials. 

Cadmium sulfide is one of the chemical species that have been synthesized through microemulsions by a large number of research groups under a variety of conditions. The apparent reason behind this choice is the application of quantum dots of CdS and similar compounds in luminescent devices etc., but also for theoretical understanding. 

Chemical and electrochemical techniques have been applied for the dimensionally controlled fabrication of a wide variety of materials, such as metals, semiconductors, and conductive polymers, within glass, oxide, and polymer matrices (e.g., [135-137]). Topologically complex structures like zeolites have been used also as 3D matrices [138, 139]. Quantum dots/wires of metals and semiconductors can be grown electrochemically in matrices bound on an electrode surface or being modified electrodes themselves. In these processes, the chemical stability of the template in the working environment, its electronic properties, the uniformity and minimal diameter of the pores, and the pore density are critical factors. Typical templates used in electrochemical synthesis are as follows ... 

The disadvantages of organic dyes (low photostability, insufficient brightness, short lifetimes, etc.) have resulted in competition from luminescent metal-ligand complexes, semiconductor nanoparticles (Quantum Dots), and conjugated polymers. These new materials show advanced performance in a variety of applications... 

Whenever the commercially available particles do not match the operator s requirements, a variety of possibilities exist in order to modify the particles from company suppliers. Similarly to other doped beads the dyes [92] or quantum dots [107, 108] can be physically entrapped into magnetic beads by swelling or are covalently bound to the surface of the particles. If localization of the dye on the particle surface is desired or if the polarity of dye and/or matrix polymer does not allow the irreversible entrapment of the dye in the bulk polymer, a covalent attachment of the dye is preferable [109, 110]. Even the covalent binding of whole fluorescent nanoparticles to magnetic microparticles is possible, as shown by Kinosita and co-workers who investigated the rotation of molecular motors [111]. 

As was demonstrated, a variety of polymeric materials are used for preparation of dye-doped beads. Dye-doped silica beads are also extremely popular due to their chemical robustness, biocompatibility and simplicity in preparation and further functionalization of the surface [55]. Thus, polymeric, silica and Ormosil beads (which occupy intermediate position) are widely used as nanosensors and labels. On the other hand, quantum dots possess much higher cytotoxicity which often limits their application in biological systems. 

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