Electron, concentration

Associative detaclunent reactions are important in controlling the electron concentration in the earth s mesosphere [75]. Reactions in which more than one neutral product are fonued also occur and are sometunes referred to as reactive detaclunent [76]. 

Above approximately 80 km, the prominent bulge in electron concentration is called the ionosphere. In this region ions are created from UV photoionization of the major constituents—O, NO, N2 and O2. The ionosphere has a profound effect on radio conmumications since electrons reflect radio waves with the same frequency as the plasma frequency, f = 8.98 x where 11 is the electron density in [147]. The... 

Diamond may never be used to make devices because it is nearly impossible to make it sufficiently n type, tliat is to obtain high electron concentration. Substitutional B is a good shallow acceptor, and interstitial Li has been reported to produce some n type conductivity. 

In a defect-free, undoped, semiconductor, tliere are no energy states witliin tire gap. At 7"= 0 K, all of tire VB states are occupied by electrons and all of the CB states are empty, resulting in zero conductivity. The tliennal excitation of electrons across tire gap becomes possible at T > 0 and a net electron concentration in tire CB is established. The electrons excited into tire CB leave empty states in tire VB. These holes behave like positively charged electrons. Botli tire electrons in the CB and holes in tire VB participate in tire electrical conductivity. 

Most of our ideas about carrier transport in semiconductors are based on tire assumption of diffusive motion. Wlren tire electron concentration in a semiconductor is not unifonn, tire electrons move diffuse) under tire influence of concentration gradients, giving rise to an additional contribution to tire current. In tliis motion, electrons also undergo collisions and tlieir temporal and spatial distributions are described by the diffusion equation. The... 

In many semiconductors employed for LEDs, and especially in mixed alloys, the direct and indirect minima ate separated by smaller energies than those of the purely direct and indirect semiconductors. As a result, finite electron concentrations exist within both minima. The total electron concentration, n, is given by equation 5 ... 

The equihbtium lever relation, np = can be regarded from a chemical kinetics perspective as the result of a balance between the generation and recombination of electrons and holes (21). In extrinsic semiconductors recombination is assisted by chemical defects, such as transition metals, which introduce new energy levels in the energy gap. The recombination rate in extrinsic semiconductors is limited by the lifetime of minority carriers which, according to the equihbtium lever relation, have much lower concentrations than majority carriers. Thus, for a -type semiconductor where electrons are the minority carrier, the recombination rate is /S n/z. An = n — is the increase of the electron concentration over its value in thermal equihbtium, and... 

Figure 5.4 The intrinsic conduction electron concentration as a function of temperature and band gap energy together with the values of the ionic diffusion coefficient which would provide an equal contribution to the conduction...

A guide to tire stabilities of inter-metallic compounds can be obtained from the semi-empirical model of Miedema et al. (loc. cit.), in which the heat of interaction between two elements is determined by a contribution arising from the difference in work functions, A0, of tire elements, which leads to an exothermic contribution, and tire difference in the electron concentration at tire periphery of the atoms, A w, which leads to an endothermic contribution. The latter term is referred to in metal physics as the concentration of electrons at the periphery of the Wigner-Seitz cell which contains the nucleus and elecUonic structure of each metal atom within the atomic volume in the metallic state. This term is also closely related to tire bulk modulus of each element. The work function difference is very similar to the electronegativity difference. The equation which is used in tire Miedema treatment to... 

The fee lattice of the coinage metals has 1 valency electron per atom (d °s ). Admixture with metals further to the right of the periodic table (e.g. Zn) increases the electron concentration in the primary alloy ( -phase) which can be described as an fee solid solution... 

From Eq. (18) the concentration of electrons, and according to Eq. (11) the concentration of holes also, depend on the lithium activity of the electrode phases with which the electrolyte is in contact. Since anode and cathode have quite different lithium activities, the electronic concentration may vary to a large extent and an ionically conducting material may readily turn into an electronic conductor. 

The experimental determination of the relationship between the electronic concentration and the partial pressure or activity of a component is commonly the best method to determine the type of disorder in a material. 

Improvement of the ionic current by fast transport in the electrodes. High electronic mobility and low electronic concentration favor fast chemical diffusion in electrodes by building up high internal electric fields [14]. This effect enhances the diffusion of ions toward and away from the solid electrolyte and allows the establishment of high current densities for the battery. 

Rule 1 Regions of high electron concentration (bonds and lone pairs on the central atom) repel one another and, to minimize their repulsions, these regions move as far apart as possible while maintaining the same distance from the central atom (Fig. 3.2). 

According to the VSEPR model, regions of high electron concentration take up positions that maximize their separations electron pairs in a multiple bond are treated as a single unit. The shape of the molecule is then identified from the relative locations of its atoms. 

Regions of high electron concentration—bonds to atoms and lone pairs attached to a central atom in a molecule— arrange themselves in such a way as to minimize mutual repulsions. 

Collisional Detachment. Reactions of negative ions in flames not containing hydrocarbons have not been widely studied, although OH -ion formation is important in flames containing high electron concentrations. The rate constant k l of the reaction... 

The practical importance of Reaction 4 stems from the fact that HC1 in rocket exhausts behaves as an electron scavenger, rapidly reducing electron concentrations. This fact, together with the above discussion, emphasizes the need for a more thorough investigation of the values of 4 and k 4. Detachment of electrons from Cl- through... 

We will first consider acid-base balances, then redox systems. Finally, we will illustrate in conclusion that both the ultimate H ion concentration (pH) and electron concentration (p8) result from interactions of biogeochemical cycles. 

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