π- A isotherms and electrical properties of polyamic acid alkylamine salts (PAAS) Langmuir-Blodgett films

Abstract

Deposition conditions, surface morphology, and electrical properties of polyamic acid alkylamine salts (PAAS) Langmuir-Blodgett (LB) films have been investigated through a study of surface pressure-area π- A isotherms, AFM (atomic force microscopy), and current-voltage characteristics. To obtain the optimum conditions of film deposition, the π- A isotherms were examined by varying temperature, barrier moving speed, dipping speed, spreading amount of solution etc. The Z-type LB films were made at the surface pressure of 5 mN m −1 and 25 mN m −1 for the AFM study; the former surface pressure forms the gas phase and the latter one forms the solid phase. The LB films made in the gas phase show domains with a size of about 200 Å diameter and 70 Å height. However, the LB films made in the solid phase show a very smooth surface with 2 Å surface roughness. In the current-voltage characteristics measured along the perpendicular direction of the films, ohmic conduction has been observed below ≈ 10 5 V cm −1 and the calculated electrical conductivity is about 10 −13 S cm −1. Nonohmic conduction has been observed above ≈ 10 5 V cm −1 and the conduction mechanism can be explained by the Schottky effect.