CdSe particles

Coulomb blockade effects have been observed in a tunnel diode architectme consisting of an aluminum electrode covered by a six-layer LB film of eicosanoic acid, a layer of 3.8-nm CdSe nanoparticles capped with hexanethiol, and a gold electrode [166]. The LB film serves as a tunneling barrier between aluminum and the conduction band of the CdSe particles. The conductance versus applied voltage showed an onset of current flow near 0.7 V. The curve shows some small peaks as the current first rises that were attributed to surface states. The data could be fit using a tunneling model integrated between the bottom of the conduction band of the particles and the Fermi level of the aluminum electrode. 

The products are usually crystalline, avoiding the need for a high temperature post-treatment [64]. Gautam et al. [65] has introduced an inexpensive, low boiling solvent under solvothermal conditions in the presence of dodecanethiol as a capping agent, using cadmium stearate as a source monodispersed 3 nm CdSe particles can be prepared. 

Transmission electron microscopy (TEM) has been an underutilized yet valuable too in particle size characterization of MC particles in LB films. Monolayer films of trioctylphosphine oxide-capped CdSe (18), spread as a monolayer on an aqueous subphase, were transferred to a TEM grid. A close-packed hexagonal arrangement of 5.3-nm (cr —4%) crystallites was found. TEM images were also obtained for HMP-stabilized CdS incorporated in BeH/octadecylamine films (79) and for CdS formed under an amine-based surfactant monolayer and transferred to a TEM grid (14). In one study, direct viewing of CdS and CdSe particles made from Cd2+-FA films on TEM grids was not possible due to poor phase contrast between the particles and the film (30). Diffraction patterns were observed, however, that were consistent with crystalline (3-CdS or CdSe. Approximately spherical particles of CdSe could... 

Another possibility that could explain the effect of illumination is a change in the electric double layer surrounding the CdSe particles, either adsorbed on the substrate or in the solution, which could lower a potential barrier to adsorption and coalescence, as suggested previously for film formation from Se colloids under illumination [93]. Partial coalescence would reduce the blue spectral shift due to size quantization. However, the spectral shape is not expected to undergo a fundamental change in this case. The photoelectrochemical explanation therefore appears more reasonable. 

Single-compartment DHP and DODAB (5) vesicles Size-quantized CdSe particles generated in situ in vesicles... 

Figure 4. Schematic description of the preparation of capped CdSe particles by arrested precipitation in reverse micelles,...

The third study on the fluorescence mechanism to be inspected in some detail was published in 1992 by Brus and co-workers [39]. They prepared 3.2-nm CdSe particles with a standard deviation below 8%. By separating... 

The emission spectra of nanoparticles of semiconductors such as CdSe and CdTe, known as quantum dots, depend on size. Quantum confinement of electrons within a particle increases the electronic bandgap with decreasing particle size, so that a series of different sized CdSe particles emits a rainbow of colors. 

Although the possible formation mechanism of nanocrystalline cadmium selenide is not very clear in ethylenediamine (en) by y-iiradiation, the formation process of CdSe particles in en is similar to that of CdS in water. So drawing an analogy with the formation mechanism of sulfides in aqueous system, a possible process of reactions is speculated ... 

Figure 3.16 Small-angle X-ray scattering data from bare 4.2 nm CdSe particles (a) overgrown by 0.65 (b) through 5.3 (e) monolayers ofZnS. From Ref. [274].

Fig. 4 (a) TEM micrograph of core-shell stmctures of CdSe nanoparticles stabilized with ELP. (b) HR-TEM micrograph of CdSe nanoparticles synthesized inside the ELP matrix, (c) TEM micrograph of individual ELP-CdSe fibres the CdSe nanoparticles appear as dark spots inside the ELP matrix, (d) Histogram of the CdSe particle diameter. A Gaussian fit yields a mean particle diameter of 4.2 nm and a standard deviation of 0.53 nm. (e) TEM micrograph of ELP-CdSe nanofibres. Reprinted with permission from Fahmi et al. [34]. Copyright, 2010, Wiley-VCH... 

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