Patterning of periodic nano-cavities on PEDOT-PSS using nanosphere-assisted near-field optical enhancement and laser interference lithography

A simple approach for creating periodic nano-cavities and periodic stripes of nano-cavity arrays on poly (3,4-ethylene dioxythiophene)- poly(styrenesulfonate) (PEDOT-PSS) thin films using a combination of optical near-field enhancement through self-assembled silica nanospheres and laser interference lithography is presented. Monolayers of close-packed silica nanospheres (800, 600, and 430nm in diameter) are self-assembled on 2µm thick PEDOT-PSS electropolymerized films and are subsequently irradiated with 10ns pulses of 355nm wavelength laser light. Over areas spanning 2cm2, circular nano-cavities with central holes of size 50-200nm and surrounding craters of size 100-400nm are formed in the PEDOT-PSS films directly underneath the nanospheres due to strong enhancement (11-18 fold) of the incident light in the near-field, which is confirmed through Mie scattering theory. Predictions from theoretical simulations examining the combined effects of near-field enhancement and interference are in good agreement with the experimental results. The results illustrate the versatility of the described technique for creating nano-cavity arrays or nano-pores in PEDOT-PSS over large areas with designed periodicity and hole size.