Semiconducting particles, particle

Finally, it was possible to build up the first stand-alone room-temperature singleelectron junction by depositing a semiconducting particle directly onto the tip of a very sharp electrode, avoiding in this case the use of an STM microscope, and it was possible to observe the coulomb staircase in such a system (Facci et al. 1996). 

It is possible that colloidal photochemistry will provide a new approach to prebiotic syntheses. The work described previously on redox reactions at colloidal ZnS semiconductor particles has been carried on successfully by S. T. Martin and co-workers, who studied reduction of CO2 to formate under UV irradiation in the aqueous phase. ZnS acts as a photocatalyst in the presence of a sulphur hole scavenger oxidation of formate to CO2 occurs in the absence of a hole scavenger. The quantum efficiency for the formate synthesis is 10% at pH 6.3 acetate and propionate were also formed. The authors assume that the primeval ocean contained semiconducting particles, at the surface of which photochemical syntheses could take place (Zhang et al 2007). 

Each printed TFT element is composed of nanoscale conducting, dielectric, or semiconducting particles. The electrical performance of the printed transistors and printed integrated circuits is dependent on the uniformity of the... 

The membrane-mimetic approach has the potential of providing superior size, morphology, and monodispersity control for ceramic particles. The relatively meager amount of published work in this area [826-834] (see Table 11) is rather surprising. Vigorous and sustained activities, inspired by biomineralization [15-18] and modeled on the incorporation of metallic, catalytic, and semiconducting particles into membrane-mimetic compartments, are fully expected. 

It should be noted that the given sensor is much more sensitive than a sensor based on composite films CuS-polyvinyl alcohol prepared by a classical liquid-phase method [88]. In these films the sensor effect is caused by increase in probability of tunnel transitions between CuS semiconducting particles owing to increase in macroscopical dielectric permeability of a hydrophilic matrix absorbing water from the surrounding atmosphere [88]. 

For instance, a high porosity can increase the extent of adsorption of certain molecules, but at the same time, the internal surface of the pores is not fully irradiated so that the density of photoproduced active species inside the pores can be lower than on the external surface. Photons are not only absorbed but also reflected and scattered by the semiconducting particles, whether they are in the form of powders or films. Consequently, the texture, surface rugosity, and agglomeration of particles affect the fraction of photons that are absorbed and therefore are potentially useful for photocatalytic chemical transformations. In addition, scattering depends on the refractive index of the medium and is therefore very different depending on whether Ti02 is exposed to air or liquid water. 

Light with supraband gap energy absorbed by a semiconducting particle (e.g., Ti02) can excite an electron from its valence band to the conduction band. This process also creates a positive hole in the valence band, which is an oxidizer and may react with adjacent oxygenated species to produce OH radicals. At the same time, the excited electron is capable of directly or indirectly reducing species in contact with the semiconductor. Such phenomena are electrochemical in nature—they are under intense study for application in the environmental remediation arena where they are globally called photocatalysis. 

When the particle sizes of semiconducting materials become smaller than about 100 A. their band gap energies become larger. The band structure aillapses, and discrete energy levels appear. Therefore, such small (and size quantized) semiconducting particles show a remarkable blue shift and clear structure in their absorption spectra. 

These can cause short circuits or entrapment of the electrolyte. Entrapment of electrolyte in the deposit, with or without enrichment of additives, will lower the cathode quality. Codeposition of electrolyte impurities can lead to cathode contamination. A nodule forms when a conductive or semiconductive particle remains on the cathode surface. The deposit will then grow around the particle encasing it. The nodular growth can be initiated by several factors. The nodule becomes larger with the continuation of electrolysis and more contaminated with slime particles. Nodules can also lead to short circuits. The local current efficiency can vary depending on the inhibitors and local current density. This can also result in rough deposits, if the current efficiency increases with current density. 

The rate of photocorrosion depends on the size of the semiconducting sulfide particles. 

From molecular clusters to semiconducting particles -high nuclearity Cu-Se clusters... 

Sillars. R.W. Properties of dielectric containing semiconducting particles of various shapes. J. Inst. Electr. Eng. 1937. 80. 378. 

S. Joly, R. Kane, L. Radzilowski, T. Wang, A. Wu, R. Cohen, E. Thomas, M. Rubner, Multilayer nanoreactors for metallic and semiconducting particles, Langmuir 16 (2000) 1354-1359. 

R. W. Sillars, The Properties of a Dielectric Containing Semiconducting Particles of Various Shapes. Inst Electr Eng 1937, 80, 378-394. 

A similar device made use of a dispersion of semiconducting particles in an insulating fluid. Winslow in 1947 first patented such a fluid made by mixing fine silica particles in oil. This fluid flowed easily under ordinary conditions but gelled when a strong electric field, about 2 kV mm, was applied across it. Winslow showed by microscopic stndy that strings of particles were formed between the electrodes when the voltage was imposed. 

Other materials derived from clay-organic systems include small semiconductor nanoparticles (CdS, for instance), which are extremely interesting in terms of new nanoelectronic and optoelectronic devices. The functionalization of sepio-lite using 3-MPTMS (see Sec. VI.A) allows complexation of Cd ions by thiol-cation interactions (200). These materials are potentially very attractive for their quantum dot properties, because it can be expected that treatment with H2S gas or Na2S solutions could produce semiconducting CdS particles of nanosized dimensions. In addition, such systems would be of interest in terms of photocata-lytic activity, such as for the generation of H2 from isopropanol, as was observed for MCM mesoporous silica that was functionalized in a similar way (230). 

The microstructure of the semiconducting particles and the surface composition, both of which are characterized by the crystallite size D, the grain-size distribution, and the coagulation structure, all subject to some control through the inclusion of additives,... 

Photoactivity is known to depend strongly on the life of positive holes in other words, the recombination of positive holes with excited electrons, before the reaction with H2O to give OH radicals, has to be avoided. Loading of fine metallic or semiconductive particles (e.g., Ag [79], Pt [80-83], Nb203 [84], CdS and 81283 [85],... 

There are some further aspects which must be considered when photochemical diodes are used. When a metal (catalyst) is deposited on a semiconductor, then frequently a Schottky barrier instead of an ohmic contact is formed at the semiconductor-metal interface. In this case, the latter junction behaves as a photovoltaic system by itself, which may determine or essentially change the properties of the photochemical diode. The consequences have been discussed in detail in [14, 27]. Frequently, colloidal semiconducting particles have been used, their size being much smaller than the thickness of the space charge region expected. 

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