Positive and negative nanohole-fabrication on glass surface by femtosecond laser with template of polystyrene particle array

Abstract

We demonstrate a new nano-processing technique using the near- electromagnetic field around a small transparent particle irradiated by an 820 nm femtosecond laser pulse. We fabricate a 2D nanohole array with negative and positive patterns on a soda lime glass surface by irradiating a monolayer of 790 nm diameter polystyrene (PS) particles, arranged in a close-packed hexagonal lattice, with a femtosecond laser pulse. At the lower laser fluence domain, PS particles act as focusing lenses and/or near-field enhancers due to Mie scattering; it enables nanohole processing just under the particle (positive patterning). Nanoholes with diameters ranging from 84 to 170 nm are fabricated in this regime. At the higher fluence domain, the PS particle acts as a mask; while the positive nanohole formation disappears, then it enables nano-patterning of the surface in gap areas corresponding to the region between particles (negative patterning). Nanoholes with diameters ranging from 65 to 110 nm are fabricated in this case. The switching of negative and positive nano-patterning by simply controlling the incident laser fluence is experimentally demonstrated for the first time to our knowledge. A simple theoretical explanation for the switching of the positive and negative patterning is presented by FDTD simulation of the near-field distribution.