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Free keywords:
polyimide, polyamide acid, NEXAFS, XPS, Langmuir-Blodgett films, monolayers, interphase structure, interfacial chemical bond, molecular orientation, PMDA, ODA, silicon, gold, silver, weak boundary layer, second harmonic generation
Abstract:
In this short review we present recent experiments which can be used to infer the structural parameters of ultrathin polyimide and polyamide acid films as a function of distance from the substrate surface. The polyimide films are prepared by the Langmuir-Blodgett technique in a layer-by-layer fashion, and the orientation of the pyromellitic imide unit in the polyimide macromolecules is determined as a function of film thickness by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. Subsequent delamination experiments on these Langmuir-Blodgett (LG) deposited polyimide films reveal that the locus of failure does not occur in a “weak boundary-layer” adjacent to the silicon substrate as expected from delamination experiments with macroscopically thick films.
As a non-destructive method to study the orientation of polymer molecules during film growth, second harmonic generation (SHG) experiments on the deposition of polyamide acid (PAA) on gold and silver surfaces will be briefly described. In this particular case, the experiments reveal an influence on the interfacial chemical bond on the film structure up to a total thickness of 60-100 mm.
