Investigation of defects in polyimide Langmuir-Blodgett film using potentiostat

Abstract

The Langmuir-Blodgett(LB) method has been of interest as a powerful technique for fabricating ultrathin organic films of useful insulating layers of electronic devices, and recently liquid crystal display has been proposed as a possible example of molecular electronics. The conventional alignment method is to rub the surface of polyimide coated ITO glass. But, this process can induce some shorthands in a thin film transistor LCD by static electricity. Therefore, as a nonrubbing method, we used the LB technique to make the alignment in the LCD. In this study, investigations were carried out on the monolayers of poly(amic acid) alkylamine salt which can be imidized by thermal curing and the deposition of the molecules onto ITO glass. Two kinds of PAAS formed apparently stable monolayers at the air-water interface, and the isotherm depended on the pH of the subphase. The monolayer of SE150 PAAS could be deposited in nearly perfect Y-type onto ITO-coated glass. The FTIR spectroscopy data indicate that the film was transferred on the substrate and was imidized by heat treatment. An lectrochemical redox reaction carried out on the surface of the films was adopted to detect defects in LB films by monitoring the cyclic voltammetry. A 5-layered LB film of polyimide was found to be sufficiently effective in restricting the redox peak current via the defects in the LB film. Thus, cylic voltammetry is a convenient method to detect the defects in polyimide LB films.