A.Yu. Zherebov

On the mutual influence of uniaxial pressure and electric field on the electronic instabilities in polydiphenylenephthalide

It is established that electric field and uniaxial pressure are interdependent, in particular in the vicinity of their threshold values and result in the alternation of the conduction state of the sample. There are three types of states: dielectric, semiconductive and metal-like. However their properties do not depend on the way these states were initiated. Pressure diminishes the threshold voltage of the electrical switching. Thus two kinds of switching which may affect each other are studied in polydiphenylphtalide. The term «switching» in this context implies that the dielectric-metal phase transition takes place not in the entire volume of the polymer, but in its separate regions, i.e. channels

Thermostimulated switching in thin polymer films

Abstract The paper presents results of a study on a new kind of stability observed in thin poly(3,3′-phthalidylidene-4,4′-biphenylene) films, namely, thermostimulated switching. This occurs at 265 K as a result of heating at a certain rate. After switching the sample transits to a metallic state. Investigations of the polymer dielectric loss and IR spectrum under similar heating regimes show the existence of relaxation excitations at this temperature. Another range of excitations is detected at 190 K. According to IR spectra, in the low temperature range, excitation of nonvalence aromatic distortion oscillations of the CH bonds take place, whereas CC double bonds are excited in the high temperature range. Dependence of the intensity of excitations on film thickness and heating regime allows us to suggest that they are associated with the thermostimulated ionization of trapping states. The model of polaron lattice formation is discussed as a possible explanation of the observed dielectric-metal transition.

On the influence of trapping states on electronic instabilities in polydiphenylenephthalide

Abstract A phenomenon of switching with memory in polydiphenylenephthalide (PDP) films is studied. The existence of a practically continuous spectrum of the states of polymer film from a dielectric ‘off’ to a metal-like ‘on’ is established. The switching time is less than 0.1 μs. It is shown that highly conducting channels appear as a result of switching. Their diameter is 0.1 μm or less and conductivity ranges from 10 to 10 5 Ω −1 cm −1 . This effect is only observed in pristine PDP films less than 3 μm thick. By virtue of the investigations of thermostimulated currents and optical absorption spectra it is established that thin polymer films differ from thick ones in their much higher concentration of trapping states. Simulation of such states in thick PDP films by doping showed that a critical concentration of these states must be achieved in order to realize the switching effect, no matter what the nature of the states. Analysis of the results obtained allows us to make a suggestion about the electronic character of instabilities observed in PDP.

On the high conductivity of nonconjugated polymers

The mechanism of charge transfer in a metal-electroactive polymer-metal structure has been experimentally studied near the threshold of the uniaxial-pressure-induced transition into a high-conductivity state in the polymer. The dynamics of the I-V curve is investigated as a function of the applied pressure. The data obtained are analyzed in terms of the model of injection currents using the concepts of possible scanning of a quasi-Fermi level near an injection level. Our estimates suggest that a narrow band made of deep trap states located near the Fermi level forms in the polymer film in the pretransition pressure range. In the immediate vicinity of the transition range, a narrow band of coherent charge transfer appears from these states; this band can be responsible for the high metal-type conductivity of thin polymer films, which has been repeatedly observed by many researchers.

New effects in electroactive polymers: new basics for sensors

Abstract Recently, new conjugated polymers of the poly(phthalidylidenarylene)s class have been synthesized. They consist of functional units sensitive to a number of external influences, such as temperature, pressure, electric field, pH-medium, etc. These influences cause an insulator-metal transition in the polymer film. As a result, the film resistance changes by 10–12 orders of magnitude. In addition, the films display electroluminescence. These phenomena open broad prospects for the application of these polymers in a variety of industrial products.

Thermostimulated instabilities in thin PPB films

Abstract The paper presents results of the study of a new kind of instability observed in thin poly (3,3′-phthalidylidene-4,4′-biphenylylene)s (PPB) films, namely, thermostimulated instability. It occurs at about 265 K as a result of heating at a certain rate and in thin polymer films gives rise to the insulator-metal transition. Investigations of the PPB IR spectrum under similar heating conditions show that at this temperature relaxation excitations occur in the C  C double bonds. Possible mechanisms of the phenomenon are discussed.

Bistable electronic switching in poly(arylenephthalides)

Experimental and theoretical data show that the phenomenon of bistable switching in thin films of poly(arylenephthalides) (PAPs), which was reported previously, has an electronic nature and is related to the unique properties of PAP molecules. This phenomenon has been studied in metal-PAP-metal and ITO-PAP-ITO structures (ITO = indium tin oxide) with various thicknesses of the polymer film. First results are reported that demonstrate the principal possibility of using thin PAP films as a basis for resistive nonvolatile electronic memory cells. These data show that the bistable switching is related primarily to the electronic properties of the polymer film and is not influenced by the oxidation of electrodes and/or the growth of metal filaments from the electrodes.

Influence of doping on electronic instabilities in poly(phthalidylidenearylene/S

Summary form only given. Electron instabilities was reported to observe in thin films of pristine polymers of poly(phthalidylidenearylene)s (PPA) class under the action of various external influences such as electric field, pressure, temperature etc. They result in the transition from the insulating to the metal-like state and vice versa. The role of trapping states in these effects was noted. In the present paper we investigated these phenomena in the PPA doped with iodine. Comparative analysis of the instabilities in doped and undoped polymer films was performed. It was shown, that the transitions, similar to those observed in the thin undoped PPA films, occurs in the doped films of these polymers as well. Moreover, the metal-like state was obtained in the films which was much more thicker then undoped ones and the metal-like phase content was greater. The possibility of obtaining of the highly conductive metal- like phase with large dimensions is discussed.

Metal-like state in undoped polymer films: techniques of inducing and properties

Summary form only given. An abnormally high sensitivity of the conductivity of thin polymer films to some external influences, such as uniaxial pressure, electric field, temperature, electron beam has been discovered. A common feature for all these phenomena is that they are shaped as the dielectric-metal phase transition which are initiated by external influences of the abnormally low values. The latter include uniaxial pressure, electric field, electron beam and temperature. The present paper discusses experimental results obtained during the investigations of the phenomena.

Poly(phthalidylidenearylene)s: new effects - new horizons of application

Abstract Recently, new nonconjugated polymers of a poly(phthalidylidenarylene)s class were synthesized. They consist of functional units sensible to a number of external influences, such as temperature, pressure, electric field, PH-medium, etc. These influences cause the insulator-metal transition in the polymer film. As a result, the film resistance changes by 10–12 orders of magnitude. In addition, the films display electroluminescence. These phenomena open broad prospects for the application of these polymers in a variety of industrial products.