Fabrication of oxide nanoparticles using oxidation of magnetic alloys in polyimide

Abstract

Oxide nanoparticles embedded in a polyimide (PI) matrix was fabricated by oxidizing a layer of Ni80Fe20 (Co80Fe20) metal film sandwiched between two PI precursor layers. Oxide nanoparticles nucleated in the PI matrix as a by-product of the imidization process. The 3.5 nm-thick Ni80Fe20 film was converted into a mono-layer of NiO oxide particles whose average size was 4.5 nm in diameter. When the metal film thickness was above 3.5 nm, a continuous layer of the metal film was found with selectively oxidized regions along the grain boundary. Similar observation was previously made when the γ-Fe2O3 particles were produced using the same reaction [1]. In case of the Co80Fe20 thin film, the oxide particles were composed of Co3O4 with spinel structure. These Co3O4 particles were, however, rather irregularly shaped with a wide size distribution whereas the NiO nanoparticles had spherical shapes with much narrower size distribution. X-ray photoelectron spectroscopy of oxide nanoparticles showed that the particles had a varying degree of metallic residue, suggesting that these nanoparticles could have metallic cores, surrounded by an oxide layer. Comparing with the γ-Fe2O3 particles produced using the same procedure, relatively larger amount of metallic residue was detected from the NiO and Co3O4 particles, which explains the higher magnetic moment measured from the NiO and Co3O4 particles