Secondary Emission from Polymers

The available data on secondary emission yields from electron bombarded polymers was reviewed to identify those features they have in common with metals and inorganic insulators. As in the case of the more widely studied materials it was found that when the yield δ obtained at a bombarding electron energy Eo, is divided by the maximum yield δm, and plotted versus Eo/Eom' most of the data falls within a small range, i.e. on a "universal" curve. At high energies the yield is given by a simple power function δ = KE-n with n = 0.725 for all the materials and K ranging from 1.55 for teflon to 0.68 for kapton if E is in KeV. The value of K is found to decrease as the complexity of the repeating unit in the polymer increases. This can be expressed quantitatively as K = 10.64 (N/M) - 3.15 where N/M is the ratio of the number of valence electrons to the gram molecular weight of a monomeric unit. We also find that δm/Eom averages 9.5 for the polymers which is very close to the value of 9.6 reported for inorganic insulators. Using the semiempirical model of secondary emission we find that the yield coefficient is given by K = 12.1Eom1.725. Consequently it is possible to estimate the yield curve over the full range of interest if any one of the parameters δm' Eom or K are known.