The trapping of electrons in polystyrene

A thin polystyrene film is charged with a short pulse of low-energy electrons (2 keV). Most of these electrons are deeply trapped in the polymer; the remaining electrons are excited from shallow traps into conduction levels and are swept out of the polymer. At short times, when most of these shallow-trapped electrons are excited into the conduction levels, the current approaches the space-charge limit: hence a value for electron mobility is obtained. At long times (from about five seconds to thousands of seconds) the conduction process is dominated by the rate of excitation from deeper-lying trapping levels; the excitation of electrons from these traps can be analyzed in terms of a time-dependent demarcation energy that is related to elapsed time. The time dependence of current is thus related to the distribution of electron traps in the polymer.<>