Effective number, of carriers

Fig. 154. Effective number of carriers per unit cell, Neff (co), as a function of energy. The effective mass was assumed to be equal to the free-electron mass. The inset shows the low-energy region with an expanded scale. Reproduced by permission of the American Physical Society from K. Lee, A. J. Heeger, and Y. Cao, Phys. Rev. B 48, 14884 (1993). Copyright 1993, American Physical Society.

From the saturation value above 1.2 eV, the effective number of carriers per unit cell, involved in the intraband Drude-like con-... 

Fig. 2. (top) Optical conductivity spectra of Lai-xSrxTiOs and Yi-xCaxTiOs as a function of changing bandfilling n (=1 - x) (from [74]). (bottom) Effective number of carriers Neu as a function of x for Yi-xCaxTiOs (left) and effective mass parameter F = m /m - 1 as a function of bandfilling (right) [65]... 

Fig. 6, (top) Hole-concentration p (=1 - x) dependence of the effective number of carriers Neff for Lai-xSrxTiOa and Yi-xCaxTiOa [74], (bottom) The parameter C as a function of the electron correlation strength, where C is the rate at which the Drude-like response changes with bandfilling [64]... 

Fig. 8. (top) Optical conductivity spectra for NdNiOa at various temperatures, (bottom) Effective number of carriers Neff and the magnetic moment as a function of temperature [157]... 

Morrison (31) has compared measurements of the Hall effect and of the resistance. The Hall voltage is inversely proportional to the average concentration of carriers in the material (24), and so, for zinc oxide, will be inversely proportional to the concentration of carriers in the large grains (Fig. 2) of the material. Figure 3 shows an example in which the resistance and the inverse of the Hall voltage measured on a sintered sample of zinc oxide are plotted as functions of the time. This illustrates that the number of carriers in the bulk of the sample may remain relatively constant, while the conductance varies widely, all at constant temperature. 

The conductance is proportional to the number of carriers in the neck (as was shown above) and to the mobility of these carriers. Thus, unless one makes the unusual assumption that the bulk properties of the neck are very different indeed from those of the grain, or that the bulk electron mobility varies widely with time at a constant low temperature, the conductivity must be controlled by surface effects. 

Partially filled bands of collective-electron states support metallic conductivity. The electrical conductivity is defined as the ratio of current density J = nev to electric field strength, E, where n is the number of carriers of charge e per unit volume and v is their average velocity. Since the average force on a charged particle is eE = m v/r, where r is the mean time between collisions and m is the effective mass, it follows that... 

In TOF experiments (Fig. 2b), a small number of carriers are generated by short pulses of strongly absorbed light. Under the effect of a constant... 

Although the introduction of the highly dissociative salt group proved to be effective in increasing the number of carrier ions, the increase of the salt fraction significantly elevated the Tg. The characteristics of salt turned dominant by increasing the salt fraction, as mentioned above. Since the carrier ions can migrate faster in... 

The number of carriers collected (in an external circuit, for example) versus those optically generated defines the quantum yield (C>), a parameter of considerable interest to photochemists. The difficulty here is to quantify the amount of light actually absorbed by the semiconductor since the cell walls, the electrolyte and other components of the assembly are all capable of either absorbing or scattering some of the incident light. Unfortunately, this problem has not been comprehensively tackled, unlike in the situation with photocatalytic reactors involving semiconductor particulate suspensions where such analyses are available [204-207]. Pending these, an effective quantum yield can still be defined. 

Fig. 18 Effective density of carriers N b vs. the number of spin vortices. Error bars indicate standard deviations of Meir calculated from five nominally lowest energy states used in the calculations for Fig. 17...

The study of such a large number of carriers allowed for the elucidation of the effect of both the amount of carrier in the membrane, as well as the effect of the ligand nature on the observed selectivities. It was thus concluded that the selectivity was influenced by the size of the constituent R groups, suggesting steric hindrance in the penta-coordination of the corresponding ionophores by analyte anions. 

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