The sol-gel chemistry combined with NIL processing
Sol-gel chemistry is based on hydrolysis and condensation of molecular metal oxide precursors in solution. The intermediate products of these chemical reactions are polycondensed oxo-hydroxo nano-building blocks suspended in a volatile solvent. Shaping the final sol-gel material from such intermediate nano-building blocks consists in processing the solution so that the evaporation of the solvent leads to spatial gathering of the blocks into the final morphology. It just requires a final annealing for stabilization into a robust solid material. This approach is conventionally used to prepare thin coatings by liquid deposition.
Obtaining a metasurface by MOx-NIL requires imprinting the sol-gel coatings before stabilization enabling the faithful replication of the 3D structures. Large surfaces can be processed with various oxides compositions and multiple feature morphologies, dimensions and high aspect ratio.