Quantum dots nanoclusters

One of the striking features of NANOM TMC -200 ) is a domination of quantum dots, nanoclusters and carbon nanotubes at different aspects. Their unique properties extensively studied last years have led to an avalanche of theoretical and experimental papers. Properties of these nanostructures have been predicted and often tested for wide range applications extending from more or less traditional fluorescent marks and elements of nanophotonics to unique nanocontainers, thermal nanoantennas and elements for spintronics and quantum computing. Many examples can be found in this book collecting invited reviews and short notes of contributions to the Conference. 

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 catalytic chemistry of M° depends on the elementary properties of M and on the structure and size of the M° nanoclusters ( quantum dots ) [2]. S may play a role as a reactivity enhancer of M°/S as a whole (co-catalytic role) and/or as a promoter of its catalytic chemoselectivity (promotional role) [3,4]. 

Dendrimers can be used to effectively coat and passivate fluorescent quantum dots to make biocompatible surfaces for coupling proteins or other biomolecules. In addition, the ability of dendrimers to contain guest molecules within their three-dimensional structure also has led to the creation of dendrimer-metal nanoclusters having fluorescent properties. In both applications, dendrimers are used to envelop metal or semiconductor nanoparticles that possess fluorescent properties useful for biological detection. 

Keywords Fluorescent marker Nanoclusters Nanodots Nanoscale metal Quantum dots... 

The materials described in this chapter are denoted in the literature mostly as metal clusters or metal nanoclusters . However, the terminology metal clusters spans various scientific disciplines and has consequently multiple meanings, including plasmonic nanoparticles and various nanosized metallic structures. Therefore alternative names have been given, although they are at the moment supported only by a fraction of the scientific community quantum clusters [26], nanodots [27], metal quantum dots [25] and superatoms [28]. 

Fig. 5 Photostability of fluorescent Au nanoclusters (AuNC DHLA) compared with semiconductor quantum dots (polymer-coated QD 520 from Invitrogen) and organic fluorophores (fluorescein, rhodamine 6G) [12]...

H. Noglik and W. J. Pietro, Chem. Mater., 7, 1333 (1995). Surface Functionalization of Cadmium Sulfide Quantum Confined Semiconductor Nanoclusters. 2. Formation of a Quantum Dot Condensation Polymer. 

Semiconductor nanoclusters (quantum dots) possess chemical and physical properties that differ substantially from those of the analogous bulk solids [36-38]. Quantum dots have been synthesized using hosts such as zeolites [39], porous glass [40], micelles [41], membranes [42], and anionic polymers [43]. The synthesis and characterization of CdS quantum dots in dendrimer hosts have been studied [44-48]. Here, two PAMAM dendrimers are used one is G3.5 with surface carboxyl group and the other is G4 with surface amino group. Mixing solutions of Cd2+ and S2 in pure methanol result in a yellow precipitate of... 

STM is ideally suited to characterize the morphology of nanostructures grown on single-crystal substrates. The self-organization of nanoclusters with a preferential size distribution on semiconductor surfaces is being exploited to form quantum dots, and a huge number of studies in this technologically important field have been conducted. Here, however, we provide two examples that relate to catalysis and electrocatalysis. 

During the past decade, a new focus has developed. It was found that semiconductor particles can be made so small, typically into the nanometer size regime, that a quantum confinement effect occurs [6-15]. Particles of this size are often referred to as nanoclusters, nanoparticles, quantum dots, or Q-particles. The structures of these nanometer-sized semiconductor clusters are usually similar to those of the bulk crystals, yet their properties are remarkably different. With the proper surface-capping agents, clusters of varying sizes can be isolated as powders and redissolved into various organic solvents just like molecules. The availability of this new class of materials allows us to study the transition of a material from molecule to bulk solid, as well as its various properties and applications. 

A study of formation and modification of Ge quantum dots (QD) in Si is the actual problem due to perspectives to apply Ge/Si nanostructures in optoelectronic devices [1], To obtain nanoclusters with specified properties it is important to control sizes and density of Ge QDs. The modification of Ge nanocluster sizes is reached [2,3] by variation of temperature and growth rate, change of interfacial mechanical stresses, creation of buffer layers, insertion of impurities as nucleation centres, and stimulation of island growth by ion beams. In this paper, modification of Ge QDs by pulsed laser radiation was studied by Raman spectroscopy. 

Figure 12.29 shows the I-V characteristics of thin specimen at room temperature, and 253 K were observed by high current source measure unit and plotted by using Metrics Interactive Characterization Software. The overall nature of I-V characteristics is an apparent indicator of the formation of localized energy levels in the host background. The formation of localized energy level may be attributed due to 3-D confinement of quantum dot-like ionic nanoclusters within the dielectric substrate. 

Laser annealing of Ge/Si heterostructures with Ge quantum dots (QDs) embedded in the depth of 0.15 and 0.3 pm has been studied. The samples were irradiated by 80-nanosecond ruby laser pulses. The irradiation energy density was near the melting threshold of Si surface. The nanocluster structure was analyzed by Raman spectroscopy. Changes in the composition of QDs are observed for both types of samples. The decrease in dispersion of nanocluster sizes after laser irradiation is obtained for samples with QDs embedded in 0.3 pm depth. The numerical simulation shows that the maximum temperature in the depth of QDs bedding differs by -100 K. This difference is likely to lead to different effects of laser annealing of heterostructures with QDs. 

A ruby laser pulsed irradiation of Ge/Si heterostructures with Ge nanoclusters (quantum dots) at the irradiation energy density near the melting threshold of Si surface has been studied by means of Raman spectroscopy and by numerical simulation of the laser-induced processes. Two types of the structures have been tested. They differ mainly in the depth of nanoclusters occurence (0.15 and 0.3 pm). From the RS analysis one may conclude that laser irradiation results in different changes of QD properties. The decrease of QD size dispersion is observed in the samples with QDs at 0.3 pm, this effect is not observed in the samples with QDs at 0.15 pm. The numerical simulation of laser heating shows that the QDs are in a molten state for the same time, but the induced temperatures of nanoclusters for the two depths differ by -100 K. This result indicates that qualitatively different effects of the laser irradiation may be connected with different temperatures of QDs during laser irradiation. 

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