Anisotropic DC Electrical Conductivity and AC Response in C22-Quinolium (TCNQ) LB Films at Room Temperature

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Abstract
Ultra-thin organic films of C22-Quinolium (TCNQ) were deposited onto ordinary microscope slide-glass substrates with a Langmuir-Blodgett technique. Surface pressure(π) - area(A) isotherms were studied to find optimum conditions of deposition by varying the environments. Several tools were employed to confirm the deposition such as the electrical capacitance and the direct thickness measurement. Electrical conductivities were studied in two different directions of the film. It has turned out that this film is highly anisotropic. The obtained conductivities are ∼ 1 × 10−7 S/cm along the film surface direction, and ∼ 1 ∼ 10−14 S/cm in the perpendicular direction. We have also studied ac response by applying a step voltage (1 Hz. 1 V) to the film. From this study, we were able to correlate the electrical capacitance to the number of film layers.