The distribution of localized electronic states in atactic polystyrene

Abstract

The steady-state charge level reached after repeated contact of a single metal with a film of atactic polystyrene has been interpreted previously in terms of electron injection from the metal into the polymer. The charge level is a function of film thickness, the particular contacting metal, and the particular metallic film substrate. In this study different metals are contacted to the same film until a steady-state condition is reached for each metal. The net charge level at the end of the contact sequence is found to be approximately equal to the sum of the previously measured single-metal charge levels for an initially charge-neutral film and is independent of the order of the metals in the sequence. Therefore, charge injection does not follow a simple energetic relationship between the Fermi level of the metal and the energy of a surface or bulk band or localized level of the polymer. Rather, each metal communicates with a discreet portion of the distribution of localized polymeric electronic states. The energy selective feature of the charge-injection process converts the contact charge-exchange experiments into a spectroscopic tool for the study of the localized polymeric states. As a result the localized electronic-state distribution of the polymer can be derived for a range of electron energies related to that spanned by the Fermi levels of the contacting metals.