Periodic pattern of iron oxide using 2D microgel colloidal crystal as template

Abstract

High-throughput and low-cost methods for the fabrication of 2D patterned structures are highly desirable. Herein we proposed a new colloidal lithography method using 2D microgel colloidal crystal (CC) as template. Unlike the previously developed methods in which the microgel spheres act as lithography mask, herein they act as nanoreactors to convert a precursor into the target product. As an example, highly ordered 2D CC of poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-AA)) microgel was prepared on charge-reversible silicon wafer. The template was first treated with trimethylchlorosilane (TMCS) and then loaded with Fe(NO3)3. Finally the polymer was removed and Fe(NO3)3 was converted in situ to Fe2O3 by calcination, and an ordered Fe2O3 array was obtained. The composition left after calcination was confirmed to be Fe2O3 by XPS. TMCS treatment was demonstrated to be necessary to obtain arrays of discrete patches, instead of continuous film. 0.2 mM Fe(NO3)3 solution was found to be optimal for Fe(NO3)3 loading. A calcination temperature of 600 °C was high enough to remove the polymeric materials and convert Fe(NO3)3 to Fe2O3. The method not only allows constructing ordered structures in a simple and cost-efficient way, but also adjusting the parameters of the pattern by adjusting the parameters of the template.