Temperature-Dependent I-V Characteristics and Thermal Annealing Effects of C₂₂-Quinolium(TCNQ) Langmuir-Blodgett Films

Abstract

Electrical properties and thermal annealing effects of C₂₂-quinoliuni(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 10⁶ 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 ∼ 180°C). It shows that the current increases about 4 orders of magnitude near 60 ∼ 70°C, and remains constant for a while up to ∼ 150 °C and then suddenly drops. Such increase of current near 60 ∼ 70 °Cseems to be related to a softness of alkyl chains. Besides the electrical measurements, UV/visible absorption(300 ∼ 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°C starts to increase and stays almost constant upto ∼ 140°C. And eventually it disappears above 180°C.