LANGMUIR-BLODGETT-FILMS OF RIGID ROD OLIGOIMIDES ON GOLD - AN X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY

Angular-resolved x-ray photoelectron spectroscopy (ARXPS) was used to study mono- and multilayer films of rigid oligoimides prepared on gold-coated glass slides by the Langmuir-Blodgett (LB) horizontal lifting technique. The experimentally obtained total atomic ratios were in a good agreement with molecular formulae. The attenuation of the substrate Au 4f photoemission intensities was recorded as a function of both the number of LB dips and the take-off angles. The ratio of the thickness to the attenuation length was determined for three different oligoimides from the slopes of the linear attenuation regions. Interpretation of the thickness/attenuation length ratio was based on the models for the oligoimide LB films of oriented structures. The average tilt angle and the area/molecule used in modeling the oligoimide film structures were determined in independent experiments involving grazing angle infrared (GIR) spectroscopy, electrochemistry and LB pressure-area isotherms. The thicknesses of the oligoimide films were calculated from the models and used to derive the value of the attenuation length from the ARXPS slopes. The attenuation length value for Au 4f core-level photoelectrons (E(k) = 1169.6 eV) was estimated to be 66-70 angstrom in the LB films of all three different oligoimides.