One-step, subwavelength patterning of plasmonic gratings in metal–polymer composites

Abstract

2D and 3D micro/nano fabrication based on two-photon polymerization (TPP) has emerged as a strong contender for additive manufacturing. Here we present direct patterning of gold nanostructures using a femto-second laser inside a commercially available photoresist matrix without incorporating any dye. The nanostructures are written directly by in situ reduction of gold precursor within the photoresist using femto-second laser irradiation. The photo-initiator triggers the reduction of the gold precursor and induces simultaneous polymerization of the photoresist based on two-photon absorption phenomenon. Diffraction gratings with varied loadings of gold precursor in the photoresist have been fabricated and their diffraction efficiencies have been measured in the infrared region. Further 2D and 3D gold loaded mesh structures with subwavelength linewidths have been fabricated with sturdy features which may find metamaterial and plasmonic applications. The effect of gold precursor loading & laser power on line widths have been studied. A minimum line width of 390 nm has been achieved for 5 wt% gold precursor loaded polymers enabling the fabrication of sub-wavelength 2D and 3D plasmonic nanostructures.