Trap-modulated band mobility

In the nonpolar liquids exhibiting a high electron drift mobility, the condition Pef Pet is fulfilled. The trapped electrons can be considered as temporary negative ions and ions always have a much smaller mobility as compared to quasifree electrons. We may then neglect the second term of the r.h.s. of Equation 74 and obtain 

Solutions of biphenyl in tetramethylsilane represent an example where the electron mobility is modulated by the formation of temporary negative ions due to electron attachment to the solute molecules. The electron mobility in tetramethylsilane at room temperature is about 100 cm V s The electrons are considered to be quasifree and to move in a conduction band. If biphenyl, Ph2, is dissolved electron attachment and subsequent thermally activated detachment occurs  

The equilibrium constant K for this equilibrium is given by ki(Ph)/k2. The higher the concentration of biphenyl, (Ph), the more the equilibrium is shifted toward the right-hand side. 

While in pure TMSi, the electron mobility is almost independent of temperature in the interval concerned, the mobility in the solution shows a strong dependence of temperature, although the absolute values are quite high and are indicative of transport in the delocalized state (see Table 14). According to Equation 75, the electron 

Data from Warman, J.M., deHaas, M.R, and Hummel, A., 5th Int. Conf. on Conduction and Breakdown in Dielectric Liquids, Noordwijkerhout, Goldschvartz, J.M., Nie ssen, A.K., and Boone, W, Eds., Delft University Press, 

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In this section we shall discuss simple models of electron transport. Some more detailed considerations will be presented in Chapter 7. Basically, three cases will be described here (1) electrons moving in delocalized states (motion in the conduction band) (2) trap-modulated motion in delocalized states and (3) hopping mobility. The three modes of transport are depicted schematically in Figure 35. 

In Section 3.11.2 we discussed the phenomenological model of electron transport in the conduction band of tetramethylsilane modulated by trapping by biphenyl. Such a model can be generalized for the electron transport in low mobility hydrocarbons, as, for instance, n-hexane. Localized electrons have been detected by their optical absorption. The traps in hydrocarbons are assumed to be structural voids which upon occupation by an electron increase further in depth. The electrons are only partially localized in these traps (Schiller et al., 1973). By thermal activation they... 

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