Electrical properties of C-22-quinolinium(TCNQ) and polyamic acid alkylamine salts Langmuir-Blodgett films

Abstract

Electrical properties of C-22-quinolinium (TCNQ) and polyamic acid alkylamine salts Langmuir-Blodgett (LB) films have been investigated through a study of surface pressure (pi)-area (A) isotherms, current-voltage(I-V) characteristics, frequency-dependent dielectric responses, and thermal iv-stimulated currents (TSC). Through-plane I-V characteristics of C-22-quinolinium(TCNQ) LB films show an anomalous behavior of breakdown near the electric-field strength of 10(6) V/cm. Frequency-dependent dielectric constants of the thermally annealed C-22-quinolinium(TCNQ) LB films show that there are two characteristic dispersions in a frequency range of 10-13 Hz; one is a dispersion occurring near 1 MHz coming from the orientational polarization of the molecules and the other is probably due to an interfacial polarization below 1 kHz when the annealing temperature is above 80 degrees C. The annealing temperature-dependent dielectric constants of the C-22-quinolinium(TCNQ) LB films show that there are two maximum: one at near 80 degrees C and the other at near 180 degrees C. The first peak seems to be related to a disorder of allyl chains. In the I-V characteristics of Z-type polyamic acid alkylamine salts (PAAS) LB films measured along the through-plane at room temperature, ohmic conduction has been observed below around 10(5) V/cm, which is: similar to that of C-22-quinolinium(TCNQ) LB films. Non-ohmic conduction has been observed above around 105 V/cm and the conduction mechanism can be explained by Schottky effect. Frequency-dependent dielectric responses of the PAAS LB film show that there is a dispersion at 10(4) Hz when the annealing temperature reaches about 100 degrees C. Measurements of thermally-stimulated currents of those LB films were performed from room temperature to about 250 degrees C and the temperature was increased at a rare of 0.2 degrees C/s linearly. TSC peaks are observed at about 70 degrees C in the arachidic acid LB films, and at about 70 and 160 degrees C in thr PAAS LB films. They indicate that the peak at 70 degrees C is resulted from die alkyl group, and the other peak at 160 degrees C is probably due to C-O group in PAAS molecules. (C) 1998 Elsevier Science S.A. All rights reserved.