The trapping of electrons in polystyrene

The trapping of electrons in polystyrene has been studied, using an electron beam to inject a short pulse of charge into the free surface of the thin polymer film and a second electron beam to monitor the surface potential of the film. The surface potential is proportional to trapped charge density, and the time-derivative of this potential is a measure of the current flow, which is proportional to the rate of detrapping of the electrons. The electrons in shallow traps rapidly become detrapped, and electrons located in deeper traps experience longer trapping times. Detrapped electrons either are swept out of the polymer, or drift until they are retrapped. Retrapping appears to be negligible in films of 3 to 5 μm thickness of purified polystyrene. The release of electrons from traps in the polymer is analyzed in terms of a time-dependent demarcation energy, E_m, which is related to elapsed time. The time dependence of current is thus related to the energy distribution of traps in the polymer, and by plotting the function tdV/dt versus In(v₀t ), a plot of the trap distribution versus energy is obtained. This distribution characterizes the electron-trapping properties of the polymer