The fabrication of large area nanoscale periodic structures on material surfaces for hydrophobicity engineering has been difficult due to the complex processes. Here we propose a two-step fabrication method for periodic nanostructures by combining laser interference lithography (LIL) and reactive ion etching (RIE). Sub-micron periodic nanotip patterns are fabricated in the photoresist by LIL, and then transferred into the silicon substrate using RIE. By measuring the contact angle (CA) of a water droplet on the substrate surface, the wettability of the surface with nanotip structures of various periods is studied. Our experiments show that the nanotip structures fabricated by the combined LIL and RIE process deliver satisfactory hydrophobic tendencies when the periods fall into the submicron scale. When the period of the structure is small enough, the hydrophilicity of the surface can be altered into hydrophobicity. The hydrophobicity achieved by this method is reusable and sustainable with low cost and no composition alteration comparing to chemical methods. The process developed in this work provides potential applications in biosensingand digital fluidics.
Modeling and process design for laser interference lithography used in fabricating two-dimensional periodic structures
