Characterization of polyimide Langmuir-Blodgett films on silver using infrared, Raman and x-ray photoelectron spectroscopies

Abstract

Ultrathin films of the dimethylhexadecylamine salt of the polyamic acid of pyromellitic dianhydride (PMDA) and oxydianiline (ODA) were deposited onto silver substrates using the Langmuir–Blodgett (LB) technique. These films were transformed to PMDA/ODA polyimide by both thermal and chemical processes. Reflection–absorption infrared spectroscopy (RAIR), surface-enhanced Raman scattering (SERS) and x-ray photoelectron spectroscopy (XPS) indicated that there was no strong interaction between the tertiary amine salt films and the silver substrates and that imidization of these films was quite complete. Both RAIR and SERS were also used to determine the molecular orientation in as-deposited tertiary amine salt films and in films that were imidized. It was concluded that ODA moieties were parallel to the silver surfaces in the as-deposited films. However, both SERS and RAIR indicated that imide formation induced orientation in which the PMDA moieties became more perpendicular to the silver surface while the ODA moieties were more parallel. © 1998 John Wiley & Sons, Ltd.