The structure of PMDA-PDA polyimide monolayers adsorbed on gold surfaces

Monolayers of the rod-like PMDA-PDA polyimide adsorbed on flame-annealed polycrystalline gold films have been studied with scanning tunnelling microscopy (STM) and X-ray absorption spectroscopy. The polyimide layer was deposited using the Langmuir-Blodgett preparation technique of Imai and Kakimoto. STM measurements in air showed that the polyimide chains were aligned along the 〈211〉 directions of the {111}-oriented single crystal regions of the surface. Although {111}-oriented areas were barely identifiable in the corresponding UHV experiments, aligned polymer chains were also observed over large areas of the surface. X-ray absorption measurements on the latter samples at the nitrogen K-edge showed a preferential orientation of the aromatic ring planes.