Distribution of trap depths

There are many electrons in the sample, each in its own trap or in the conduction band (delocalized state), and there is a distribution of trap depths. The trap depths are not all the same because orientational disorder of the molecules provides a variety of polarization potential wells. Furthermore, an electron in a trap seems to couple with vibrational and librational modes of the trapping molecules. The optical absorption band of solvated electrons is very broad (Fig. 8). Part of the broadening might be caused by the distribution of trap depths, and part by the coupling with molecular modes. These parts are sometimes... 

In liquids where the trap depths are density dependences of electron mobilities are dominated by changes in the conduction band, not by the distribution of trap depths. In further development of the model we would ignore the possibility that localized states might lie above the delocalized level, and integrate Eq. (20) only over energies from zero to infinity. We would then need a formal couple between the values of E and a, which the present model does not have. 

Fig. 26. Screen filters contain pores of a uniform size and retain all particulates greater than the pore diameter at the surface of the membrane. Depth filters contain a distribution of pore sizes. Particulates entering the membrane are trapped at constrictions within the membrane. Both types of filters are rated 10...

Figure 9-19. Bund diagram of LPPP with hole traps and gold electrodes with Va<- vacuum level. Ec conduction band, Eva valence band. E, Fermi level. . baudgup energy. and , " trap depths. ,( ) trap distribution, X electron affmity, and All work function of the gold electrodes.

Whereas in good-conducting doped or polymeric dyes ft-or -type conductivity can be explained without difficulty by analogy with inorganic semiconductors, the p- and -type photoconductivity in insulating (intrinsic) dye films cannot be explained in this manner. It is necessary to take into consideration the existence of defect states (lattice defects, dislocations, impurities etc.) distributed at different depths in the forbidden zone between valence and conduction band these defect states are able to trap electrons and holes, respectively, with different probability 10,11,88),... 

In the inverted band a quite different pattern of intensity distribution is to be expected. In the pure crystal the topmost level alone is active it remains the strongest under all conditions. As the trap is deepened, some intensity moves from the topmost level downward through the band into the bottom level, which breaks out of the band and eventually becomes practically a localized state of the trapping molecule. Thus the presence of guest molecules awakens spectral activity in normally inactive levels, and should enable the extent and character of the pure crystal band structure to be studied experimentally. The point is illustrated in the diagrammatic spectra in Fig. 6, illustrating the transitions in one-dimensional mixed crystals for trap depths from zero (pure crystal) to d = 3.6. In each case the intensities are adjusted to make the lowest transition have unit intensity this... 

In the case of exponentially distributed traps, the effect of high fields on the trap depths (Poole-Frenkel effect) can be taken into account by the same procedure. The trapped hole density is modified and Eq. (3.40) changes to [38],... 

The triplet-triplet interaction, postulated to explain increased quantum yield of thin film organic LEDs, has been well known in EF of organic single crystals [2,21,41], One of the most spectacular manifestation of this type excitonic interactions is spatial distribution of EL emission (see Sec. 3.3). Interestingly, the EL light output resulting from the free-trapped carrier recombination (Oel) with respect to that underlain by free carriers recombination (Oel) does not depend on the trap depth [2]... 

Fig. 5.3 The spatial distribution of the positron density at the Ps formation stage when an external electric field E is imposed. efn is that part of the positron density that is bound within the blob and not biased by the external electric field. is the part perturbed by the field. The depth of the trapping potential is about several tenths of eV.

The fliox created by bubbles has been mathematically described in many ways, but all present theories are strongly dependent on assumptions regarding the nature of the bubble surface, the initial size spectra of the bubbles, and the distributions of bubbles with depth. A model that has been used to predict the effect of bubbles on gas saturation (Keeling, 1993, as modified from Fuchs et al, 1987) assumes that the full spectrum of bubble process can be described by a combination of two bubble transfer processes (Fig. 10.10). The first is the mechanism by which small bubbles, < 50 pim in diameter, completely collapse and inject their contents into the water. This mechanism has been called air injection or total trapping by bubbles. In this case flux of gas from the bubble depends only on the total volume of air transferred by these bubbles, which is described by an empirical transfer velocity, Vinj (mol m d atm ) and the mole fraction, X, of the gas in the air... 

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