Synthesis of nano-sized ZnO and Fe2O3 particles embedded in a polymeric matrix

Abstract

We studied oxide nanoparticles embedded in a polyimide (PI) film. Polyamic acid (PAA) was spin-coated onto Zn or Fe metal films and PAA / metal films were cured at 400℃ for 1 hour. Transmission electron microscopy was used to characterize oxide nanoparticles in the polyimide film. We found spherical ZnO particles in the size range of 5-20 nm that were dispersed in the PI layer. γ-Fe2O3 phase was verified using selected area diffraction analysis. Average particle size of γ-Fe2O3 was below 10 nm and at the same time much coarser particles were also observed. By using the UV-Vis spectrometer, the optical properties were measured to estimate the quantum size effects. The exciton absorption peak of ZnO particles was observed at about 370 nm, closely corresponding to the value of bulk ZnO. As the result of PAA reacting with the metal films, PAA-metal complexes were formed in the PAA matrix and metal oxide particles were subsequently generated inside the PI film through the reaction between the oxygen from the imidization and the metal that was rejected from the imidization reaction. During curing, the imidization of PAA into PI led to the formation of Zn or Fe oxide particles. This proposed mechanism has been generally accepted for the previously reported PAA / Cu films and we have demonstrated that this process can be extended to different metal oxide systems.