Photoinduced, controlled generation of palladium crystallite structures in polyimide films

Structures of Pd crystallites with nanometer dimensions are formed on the surface of and inside polyimide films by a combination of photochemical and thermal processes. Photoinduced transformations of polyamic acid films containing Pd2+ complexes prior to thermal curing affect the subsequent thermal imidization of the polymer and reduction of the remaining palladium ions. The extent of photolysis controls the formation and characteristics of surface and subsurface metallic layers as well as the sizes of Pd particles generated within and below the interlayer region. Interference between waves reflected from the continuous embedded Pd layer and waves reflected from the continuous surface metal layer is the origin of the colors observed in photolyzed and cured films. Multicolored areas are a result of nanometer range variations of the interlayer distance. Optical properties typical of Fabry-Perot filters are observed when the thickness of the surface layer and internal metal layer are similar. The etalon-like films experience significant reversible dimensional changes upon exposure to white light.