Fabrication of periodic Ag tetrahedral nanopyramids via H2O2-assisted nanosphere lithography for plasmonic applications

Abstract Nanosphere lithography (NSL) has been developed to prepare the monolayered hexagonally close-packed nanospheres in a large area. In our work, polystyrene (PS) sphere array was prepared by air-water interfacial floating method using hydrogen peroxide (H2O2) solution. Compared to the conventionally used H2O in the air-water interfacial floating method, since the viscosity and density of 30% H2O2 solution increase from 1.0 to 1.074 mPa·s and 1.0 to 1.14 g/cm3, respectively, the highly ordered array of PS spheres (with a density of ~1.05 g/cm3) could float and self-assemble on the surface of H2O2 solution without adding the surfactant or surface modification during the NSL process. Also, H2O2 solution could generate the higher surface tension gradient to not only alleviate the presence of second-layer defects induced by the submerged PS nanospheres but also facilitate the self-assembly of PS sphere array due to the Marangoni convection effect. We demonstrated the effects of H2O2-assisted NSL on the second-layer defects formation, single domain size and self-assembly. In addition, the periodic Ag tetrahedral nanopyramids array (PATNA) on glass substrate was fabricated using the PS spheres array as the mask, and the optical properties of transmittance and extinction were investigated experimentally and theoretically. The PATNA prepared using the PS sphere array with H2O2 assistance showed the stronger extinction and narrower FWHM compared to the one without H2O2 assistance. The measured localized surface plasmon resonance peak was in good agreement with simulation results, and the PATNA with a large area on glass substrate had the potential for plasmonic applications.