Two-dimensional nanostructures on optical glass via nanosphere lithography and vapor HF etching

It is desired to have artificial optical materials with controllable optical properties. One approach is to create composite materials with nanomachining and nanostructures. In this research, two-dimensional (2D) nanostructures were created on the surface of optical glass using nanosphere lithography. The effective refractive index of the artificial layer is smaller than the refractive index of the substrate and can be varied by changing the size of the nanoparticles and depth of etching. In comparison with conventional techniques, this approach is more efficient and cost-effective for the creation of large areas of thin surface layers as an artificial material. A uniform monolayer of 200 nm polystyrene nanospheres was deposited on soda-lime glass slides. Deposition was performed via a slide-coating technique to take advantage of capillary forces. The slides were etched with vapor-phase hydrofluoric acid (HF) to create 2D structures. Vapor-phase etching was selected in order to etch the substrate without disturbing the monolayer nanoparticle mask. The etching rate of nanostructures was studied. An atomic force microscope (AFM) was used to monitor the nanosphere monolayers and etching analysis. It was shown that the nanoparticle pattern was successfully transferred to the surface of the substrate. The resultant thin-layer of modified substrate serves as an artificial material with a desired refractive index which modifies the surface reflection and transmission properties. The substrate with the created artificial material layer demonstrated reduced reflectivity in optical wavelengths.