Facile nanopatterning of zirconium dioxide films via direct ultraviolet-assisted nanoimprint lithography

A novel ultraviolet (UV)-assisted imprinting procedure that employs photosensitive zirconyl 2-ethylhexanoate is presented for the fabrication of both amorphous and crystalline zirconium dioxide (ZrO2) nanostructures. Upon annealing at 400 degrees C for 1 h, the lateral shrinkage and thickness shrinkage of ZrO2 nanostructures were 69.8 and 66.7%, respectively, indicating an isotropic volume loss. During UV irradiation and annealing treatment, the refractive index of UV-irradiated ZrO2 film is gradually increased by improvement in the packing density and crystallinity of the film. With increasing UV exposure time and annealing temperature, the optical band gap (E-g) of the UV-irradiated ZrO2 film is red-shifted from 5.745 to 5.265 eV, due to the removal of organic groups and the resultant densification of the film during the photochemical reaction and the heat-induced increase in the crystallinity of the film. These results suggest that the refractive index and optical Eg of ZrO2 nanostructures could be controlled by tuning the conditions of UV exposure time and annealing treatment. Nanopatterns of ZrO2, fabricated by direct UV-assisted nanoimprint lithography, are potential candidates for protective coatings for optical mirrors and filters, e.g. high-reflectivity mirrors and broadband interference filters, as well as active electro-optical devices where ordered surface nanostructures are necessary.