Secondary electron emission coefficient from lexan: the low energy crossover
The energy location of the first crossover point of the secondary electron emission curve of the polymer insulator Lexan (polycarbonate) has been experimentally investigated. The secondary electron emission coefficient (SEEC) is the ratio of the number of secondary electrons leaving the surface to the number of incident primaries. At high and low energies the SEEC is less than one, between the energy extremes the SEEC is greater than one. The energy at which the (SEEC) is first equal to one is called the first crossover point.
The Lexan sample is treated as a parallel plate capacitor. The sign of the replacement current to the metalized back of the sample shows whether the SEEC is above or below one, and the incident electron energy is above or below the first crossover point. Successive choices of incident electron energy bracketed the first crossover point for Lexan, at about 44 eV.