Intrinsic charges, migration

An alternative picture of the conductivity of the electrons and holes in intrinsic semiconductors is to consider the electrons in the conduction band as migrating, as expected, toward the positive potential, and to consider the holes as discrete, positive charges migrating in the opposite direction. Although electrons are responsible for conduction in both cases, the hole formalism represents a convenient physical picture. 

At low temperatures, radiation-induced conductivity critically depends on the water content and appears only above the critical hydration levels 0.41 and 0.79 g/g for collagen and DNA, respectively [602, 603]. The critical hydration level for DNA corresponds to about 15 water molecules per phosphate group (F = 15). The effects of various additives on the conductivity evidence charge migration in the hydration shell of DNA [604]. At much lower hydrations (0.12 to 0.22g/g), conductivity of hydrated DNA shows exponential dependence on h [605], which may be attributed to the intrinsic semiconductivity of the DNA backbone. More detailed experimental studies of DNA hydration [606] show that radiation-induced conductivity starts not strictly atP =15 [602, 603] but via a sigmoid-like increase within hydration range from r = lltoF = 16 with subsequent stepwise increase at F 24. 

A Tafel-like behavior for the intrinsic redox behavior of the Li/Li+ could be measured, providing i0 values of 31.6 mA/cm2 (at 25°C) and (3 = 0.67 [89], These high values of the i0 of the Li/Li+ couple mean that the charge transfer resistance (/ CT) of Li electrodes is negligible compared with the surface film resistance (for Li+ migration). 

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