TEMPERATURE-DEPENDENT I-V CHARACTERISTICS AND THERMAL ANNEALING EFFECTS OF C-22-QUINOLIUM(TCNQ) LANGMUIR-BLODGETT-FILMS

Abstract

Electrical properties and thermal annealing effects of C-22-quinolium(TCNQ) Langmuir-Blodgett(LB) films were studied. Typical current-voltage(I-V) characteristics along the perpendicular direction show an anomalous behavior of breakdown near the electric-field strength of 10(delta) V/cm. From the study of I-V characteristics in the high-electric field region, it is found that there is a contribution of joule heating in addition to the electrical effect. To see the thermal influence of the specimen, current was measured as a function of temperature(20 similar to 180 degrees C). It shows that the current increases about 4 orders of magnitude near 60 similar to 70 degrees C, and remains constant for a while up to similar to 150 degrees C and then suddenly drops. Such increase of current near 60 similar to 70 degrees C seems to be related to a softness of alkyl chains. Besides the electrical measurements, UV/visible absorption(300 similar to 800nm) of the thermally annealed sample was measured to see the internal-structure change. It is found there are four characteristic peaks. At 494nm, the optical absorption of the thermally annealed specimen at 60 degrees C starts to increase and stays almost constant upto similar to 140 degrees C. And eventually it disappears above 180 degrees C.