Contact charge exchange

The purpose of this paper is the presentation of a brief overview of recent literature in which new models of electronic states in polymers and molecular solids have been proposed (, 2, 5-16). Since localized (e.g., molecular-ion) states seem prevalent in these materials, I indicate in Sec. II the physical phenomena which lead to localization. Sec. Ill is devoted to the description of a model which permits the quantitative analysis of the localized-extended character of electronic states and to the indication of the results of spectroscopic determinations of the parameters in this model for various classes of polymeric and molecular materials. I conclude with the mention in Sec. IV of an important practical application of these concepts and models The contact charge exchange properties of insulating polymers ( 7, 17, 18, 19). 

An important practical problem idiich requires for its solution the concepts developed in the preceeding section is that of contact charge exchange between insulators. Long viewed in terms of the traditional semiconductor model (, 32), charge injection and motion in high polymers have successfully eluded quantitative interpretation until the recognition in recent years ( 5, 18,... 

Observations that contact charge exchange can be quite rapid relative to the dielectric relaxation times (63. 69, 152), and the demonstration that "clean" polymers have well defined sets of surface states (, 58, 70), suggest that these latter may be more important than bulk states for charging of dielectrics (.62). On the other hand, Williams (7 1, 72) has shown that one can make bulk states accessible on a ten millisecond time scale by "doping" dielectrics to induce a bulk conductivity of the order of 10 1 1 sie/cm, and this approach has found useful applications (73). 

The relationship between the chemical properties of the polymers in question and the steady-state contact charge exchange is embedded in t ai i eters characteristic of the... 

In this paper the development and major applications of a new relaxation-localization model of electronic states in molecular solids have been briefly outlined. This model affords a detailed description of valence-electron photoemission spectra which, moreover, have been utilized to verify explicitly several of its important predictions. It provides a similar description of DV absorption spectra and electron-transfer processes. Inadequate experimental data are available in these cases, however, to test the model critically. Finally a phenomenological version of the model has been shown to provide a quantitative description of steady-state contact charge exchange in polymers and to constitute a link between this charge exchange and the molecular architecture of pendant group polymers. 

---