Pulsed photoconductivity and current oscillations in poly(vinyl chloride)

Abstract

SynopsisTransient photocurrents in poly(viny1 chloride) films are shown to be due to photoinjection of electrons from metallic cathodes. Most of the injected electrons are promptly trapped, but some drift across the sample to the anode under the inhence of an external electric field. The mobility of these electrons, determined by transient photoconductivity techniques, is 4.7 f 0.5 X 10-4 cma/V-sec at 27"C, and rises to 3.4 f 0.5 X 10-8 cma/V-sec at 43"C, the measuring cell having been evacuated to a pressure of 10-torr at both temperatures. Diffusion of helium into the samples appears to decrease the electron mobility. It is suggested that electron transport is correctly described by using an energy-band model for intramolecular motion and an activated hopping model for intermolecular transfer. Oscillations observed in the transient photocurrents in the frequency range 101106 HZ are attributed to electron avalanche formation at the anode, with photosuccesson. EXPEWMENTALPolymer films containing no additives were formed by dissolving a commercial PVC powder (I.C.I. Corvic D55/9) in tetrahydrofuran at room temperature and evaporating the solvent at a reduced pressure of about 40 torr. The films, typically 0.05-mm thick, were subsequently outgassed at torr for several days. Electrodes were not evaporated directly onto the samples, since the heat radiated from the evaporator filament was sufficient to cause deformation and slight dehydrochlorination. A Herasil

Thermoluminescence with pseudo first-order kinetics

“…The time tT for which thermalised electrons will travel before being trapped is ( N m ) " (Bube 1974, p 333), where Nis the density of unoccupied electron traps, a i s the electron trap capture cross-section and U is the thermal velocity of electrons. Taking N = 10" cm-3 (Reiser et a1 1969, Creswell and Perlman 1970, Boustead and Charlesby 1970, a = lo-" cm2 and U = 10' cm S -' , we obtain tT = S. On the other hand, several pulsed radiation-induced-conductivity measurements on amorphous dielectrics show currents falling, due to trapping of electrons and holes, within a few ps of the end of the irradiation pulse (Szymanski and Labes 1969, Tabak 1970. Ranicar and Fleming 1972.…”

Propriétés diélectriques du chlorure de polyvinyle en très basse fréquence

“…[1,2,3] ; la nature des porteurs, le mécanisme de leur déplacement et les effets de surface sont encore mal connus. Le chlorure de polyvinyle [4,5] (PVC) semble un matériau très intéressant pour ce type d'étude, son comportement étant très caractéristique. Le travail que nous exposons ici concerne des échantillons de PVC industriel (Plymouth).…”