THERMOSTIMULATED SWITCHING IN THIN POLYMER-FILMS

The paper presents results of a study on a new kind of instability obs erved in thin poly(3,3'-phthalidylidene-4,4'-biphenylylene) films, nam ely, thermostimulated switching. This occurs at 265 K as a result of h eating at a certain rate. After switching the sample transits to a met allic state. Investigations of the polymer dielectric loss and IR spec trum under similar heating regimes show the existence of relaxation ex citations at this temperature. Another range of excitations is detecte d at 190 K. According to IR spectra, in the low temperature range, exc itation of nonvalence aromatic distortion oscillations of the C-H bond s take place, whereas C=C double bonds are excited in the high tempera ture range. Dependence of the intensity of excitations on film thickne ss and heating regime allows us to suggest that they are associated wi th the thermostimulated ionization of trapping states. The model of po laron lattice formation is discussed as a possible explanation of the observed dielectric-metal transition.