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Abstract:
Using the Langmuir-Blodgett (LB) technique, ultrathin films of the dimethyldodecyl ammonium salt of PMDA-ODA polyamic acid (PACS) were deposited as 1-, 3- and 5-layer films on gold and silver surfaces. These films were imidized to polyimide in the UHV system by heating to temperatures of 523 K. The layer-by-layer deposition method allows one to study the interaction of the individual layers of the polymer precursor and the polymer with the substrate surfaces with X-ray photoelectron spectroscopy (XPS). Our results show an initial chemical interaction between the PACS films with the gold and silver surfaces. Heating in vacuum leads to desorption of the dimethyldodecyl ammonium chain and imidization of the films. A weak interaction of the first polyimide layer with the gold substrate is detected in the C 1s and O 1s spectra. For the thicker layers, our data indicate the formation of stoichiometric polyimide. On silver, the interaction with the substrate is substantially stronger, leading to inhibition of imidization in the first polymer layer. For the thicker layers, also complete imidization is indicated. The deficit in carbonyl C 1s and O 1s photoemission intensity in the Langmuir-Blodgett deposited films cannot be explained by chemical deviations from the expected polyimide stoichiometry. It is suggested, that the deviation from stoichiometry in the C 1s and O 1s spectra is caused by different intensity distributions into shake satellites for the different carbon and oxygen species.
