Fabrication of two-dimensional periodic relief grating of tethered polystyrene on silicon surface as solvent sensors

In this study we used a novel process, involving advanced lithography and oxygen plasma treatment to generate well-defined 400 nm-resolution hole array. 400 nm pillar array of polystyrene (PS) on silicon surface was successively grafted from the bottom layer of initiator by atom transfer radical polymerization (ATRP) to generate two-dimensional periodic relief grating (2DPRG). The 2DPRG of the tethered PS after immersion in solvents possessing various polarities present solvent-responsive properties in static water contact angles (SWCAs) and effective refractive indices (n_eff) because of transition between stretched and coiled regime of the polymer. The n _eff of the 2DPRG of tethered PS after immersion in water and toluene are 1.46 and 1.39 resulting of red and green color observed along an oblique angle closed to 60°∼ 70°by naked eye, respectively. These reversibly properties created from a reversible conformational change of 2DPRG of tethered PS exhibited switching property in change of solvent polarity which is practical for environment sensor applications.