Semiconductor nanocrystal electronic

MR Silvestri, J Schroeder. Pressure-tuned and laser-tuned Raman-scattering in II-VI semiconductor nanocrystals—Electron-phonon coupling. Phys Rev B 50 15,108-15,112, 1994. 

Tang, J. and Marcus, R. A. (2005) Diffusion-controlled electron transfer processes and power-law statistics of fluorescence intermittency of nanoparticles. Phys. Rev. Lett, 95, 107401-1-107401-4 Tang, J. and Marcus, R. A. (2005) Mechanisms of fluorescence blinking in semiconductor nanocrystal quantum dots./. Chem. Phys., 123,054704-1-054704-12. 

High-Temperature Crystallization The size-tunable optical and electronic properties of semiconductor nanocrystals are attractive for a variety of optoelectronic applications. In solution-phase crystallization, precursors undergo chemical reaction to form nuclei, and particle growth is arrested with capping ligands that... 

Charge transport through an array of semiconductor nanocrystals is strongly affected by the electronic structure of nanocrystal surfaces. It is possible to control the type of conductivity and doping level of quantum dot crystals by adsorbing/desorbing molecular species at the nanocrystal surface. As an... 

Vanmaekelbergh, D. Liljeroth, P. 2005. Electron-conducting quantum dot solids novel materials based on colloidal semiconductor nanocrystals. Chem. Soc. Rev. 34 299-312. 

Colloidal CdS particles 2-7 nm in diameter exhibit a blue shift in their absorption and luminescence characteristics due to quantum confinement effects [45,46]. It is known that particle size has a pronounced effect on semiconductor spectral properties when their size becomes comparable with that of an exciton. This so called quantum size effect occurs when R < as (R = particle radius, ub = Bohr radius see Chapter 4, coinciding with a gradual change in the energy bands of a semiconductor into a set of discrete electronic levels. The observation of a discrete excitonic transition in the absorption and luminescence spectra of such particles, so called Q-particles, requires samples of very narrow size distribution and well-defined crystal structure [47,48]. Semiconductor nanocrystals, or... 

Quantum size effects in semiconductor nanocrystals became an important field of research in the 1980s, when a number of groups, notably those of Brus at Bell Labs and Henglein at the Hahn Meitner Institute, published seminal papers on the effects of the size of semiconductor colloids on their optical properties and correlated crystal size with changes in electronic band structure. 

Electronic absorption spectroscopy has played a pivotal role in the development of methods for synthesizing pure semiconductor nanocrystals. Nanocrystal sizes, size distributions, growth kinetics, growth mechanisms, and electronic structures have all been studied in detail using electronic absorption spectroscopy. 

The size-dependent properties of nanoparticles differ greatly from the corresponding bulk materials. An example is the size quantization phenomenon commonly observed in II-VI and III-V inorganic semiconductor nanocrystals.6 During the intermediate transition towards that of the bulk metal (usually between 2 and 20 nm), localization of electrons and holes in a confined volume causes an increase in its effective optical band gap as the size of the nanoparticle decreases, observed as a blue shift in its optical spectrum. Bms predicted that there should also be a dependence on the redox potential for these same classes of quantum dots.7 Bard and coworkers showed this experimentally and have reported on the direct observation between the... 

It is assumed that deeply trapped holes, h+ff, are chemically equivalent to surface-bound hydroxyl radicals. Weakly trapped holes, on the other hand, that are readily detrapped apparently posses an electrochemical potential close to that of free holes and can therefore be considered to be chemically similar to the latter. Their shallow traps are probably created by surface imperfections of the semiconductor nanocrystals. From these traps the charge carriers recombine or they are transferred by interfacial charge transfer to suitable electron acceptors or donors adsorbed at the surface of the semiconductor. 

Figure X. Density of states for metal (a) and semiconductor (b) nanocrystals. In each case, the density of states is discrete at the band edges. The Fermi level is in the center of a band in a metal, and so kT may exceed the electronic energy level spacing even at room temperatures and small sizes. In contrast, in semiconductors, the Fermi level lies between two bands, so that the relevant level spacing remains large even at small sizes. The HOMO-LUMO gap increases in semiconductor nanocrystals of smaller sizes.

Theoretical calculations of the electronic structure of metal and semiconductor nanocrystals throw light on the size-... 

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