Quantum dot materials

Quantum computers, 77 61 Quantum dot materials, 22 142 Quantum dot PV cells, 23 44 Quantum dots... 

Related to the quantum well structures, "quantum dot" materials, or size-quantized semiconductor particles, have also been recognized to have nonresonant properties that are attractive. A series of small (< 30 A) capped (thiophenolate) CdS clusters has recently been shown to... 

Zeolites provide a novel host for the generation of semiconductor hyperlattices within their pore volume. The control of the connectivity between the clusters of semiconductor is unparalleled in any other host medium and so has allowed a detailed study of the optical consequences of such connectivity6. However, from the practical standpoint, such materials have some severe drawbacks - most notably the lack of single crystals of sufficient size to produce viable optical devices such as optical transistors or spatial light modulators. We have therefore moved on to look at more practical/processable quantum-dot materials such as semiconductor-doped porous glasses. 

Quantum dots are objects with sizes in all three directions equal to few nanometers. Such systems resemble molecules and the energy levels of electrons in them quantize. Energies of the transitions between these levels depend on quantum dots material and size, and those transitions are the base for the quantum dots laser radiation. 

J. Y. Kim, O. Voznyy, D. Zhitomirsky, E. H. Sargent, 25th Anniversary Article Colloidal Quantum Dot Materials and Devices A Quarter-Century of Advances. Advanced Materials 2013,25,4986-5010. 

Apart from the II-VI family of materials, the III-Vs are considered one of the most investigated quantum dot materials. Bawendi and co-workers have studied the mechanism for the formation of InP QDs by the reaction of indium (111) myristate, tris(trimethylsilyl)phosphine (TMS)3P and octyl-amine in sealed NMR tubes, analysing the intermediates using NMR spectroscopy. They concluded that InP QDs were formed due to ripening from non-molecular InP species due to the depletion of the phosphorus source in the initial nucleation step, whilst the presence of octylamine prevented the decomposition of the precursor due to solvation effects. 

The famous quantum dots are nanometer-size colloidal particles smaller than the exciton radius. These quantum dot materials are around 20 times brighter and more than 100 times more stable against photo-bleaching compared to organic fluorescent dyes. Within recent years these luminescent nano-particles found wide-spread use for multicolor staining, homogenous assays, and tissues imaging. 

S.M.M. Nelwamondo, M.J. Moloto, R.W.M. Krause, N. Moloto, Synthesis and characterization of alanine capped water soluble copper sulphide quantum dots. Material Letters 75 (2012) 161-164. 

S.V. Kershaw, M.T. Harrison, A.L. Rogach, A. Komowski, Development of IR-Emitting Colloidal II-VI Quantum-Dot Materials, IEEE. Select. Topics in Quantum Electronics 6 (2000) 534 543. 

Clusters are intennediates bridging the properties of the atoms and the bulk. They can be viewed as novel molecules, but different from ordinary molecules, in that they can have various compositions and multiple shapes. Bare clusters are usually quite reactive and unstable against aggregation and have to be studied in vacuum or inert matrices. Interest in clusters comes from a wide range of fields. Clusters are used as models to investigate surface and bulk properties [2]. Since most catalysts are dispersed metal particles [3], isolated clusters provide ideal systems to understand catalytic mechanisms. The versatility of their shapes and compositions make clusters novel molecular systems to extend our concept of chemical bonding, stmcture and dynamics. Stable clusters or passivated clusters can be used as building blocks for new materials or new electronic devices [4] and this aspect has now led to a whole new direction of research into nanoparticles and quantum dots (see chapter C2.17). As the size of electronic devices approaches ever smaller dimensions [5], the new chemical and physical properties of clusters will be relevant to the future of the electronics industry. 

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... 

Nanoclusters/Polymer Composites. The principle for developing a new class of photoconductive materials, consisting of charge-transporting polymers such as PVK doped with semiconductor nanoclusters, sometimes called nanoparticles, Q-particles, or quantum dots, has been demonstrated (26,27). 

The bromination of the phenyl group in TgPhg has been reported by He et al. but few characterization data were given. The product, Tg[C6H4-Br]g, obtained in a 60% yield was subject to Pd catalyzed arylations to form the first organic-based quantum dot-like materials (Figure 19). ... 

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 ... 

A number of zinc selenium complexes have now been characterized, with particular interest in the formation of zinc selenide semiconductors and quantum dots. In many cases analogous structures to those observed with thiol or thiolates are recorded. 77Se NMR is frequently used in characterization, and comparison with the sulfur equivalent is relevant. Zinc selenium compounds are of particular interest as precursors for metal/selenide materials and their relevance as models for selenocysteine-containing metalloproteins. 

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