Patterning of gold nanoparticles in large-area periodic polymer structures by two-beam interference technique

Abstract In this work, we demonstrate a simple and efficient one-step method for fabricating large-area gold nanoparticle (Au NP) gratings within a polymer thin film using a two-beam interference technique. The hybrid metallic/polymer structures were obtained by first mixing a gold precursor with a SU-8 photoresist, followed by exposures to a two-beam interference pattern. The interference lithography induces spatially controlled optical-thermal reactions that reduces metallic ions, resulting in the formation of Au NPs in polymerized SU-8 photoresist, which faithfully follows the interference pattern. By using one exposure, 1D periodic SU-8 structures containing Au NPs were demonstrated, with a periodicity as small as 300 nm. The spatial distribution of Au NPs was thoroughly characterized using optical microscopy, atomic force microscopy and transmission electron microscopy, providing their sizes and uniformity, and their spatial arrangement in polymer thin films. Our results demonstrate that gold precursor concentration and irradiation time are critical factors influencing the spatial size distribution of the Au NPs and the modulation depth of the polymeric structures. Furthermore, by applying multiple exposures with varying rotation angles of the sample, diverse 2D periodic and quasi-periodic patterns were also achieved. This interference-based technique thus enables a rapid and scalable fabrication of Au NP gratings, which exhibit both plasmonic and diffractive properties, making them highly promising for applications in plasmonic and photonic devices.