Electronic density of state in metal/polyimide Langmuir–Blodgett film interface and its temperature dependence

Abstract

Surface potentials of heat-treated polyimide (PI) Langmuir–Blodgett (LB) films deposited on Au, Cr, and Al electrodes were measured in a dark vacuum vessel at various temperatures as a function of the number of deposited layers. The potential depended on the thickness of PI LB films and the work function of base metal electrode. The spatial charge distribution in PI LB films on various electrodes was determined from the relationship between the surface potential and the number of deposited layers. Based on this result, distribution of the density of electronic state in PI LB films was determined. It was experimentally shown that the electrostatic phenomena in PI LB films at the metal/film interface were explained taking account of surface states which exist within the range of ∼1 nm from the interface and molecular–ion states which exist in the entire range. Further, it was found that distribution of electronic density in states of polyimides was broadened with the increment of temperature.