Direct nanoimprinting of metal oxides by in situ thermal co-polymerization of their methacrylates

The use of polymerization to solidify, strengthen and imprint liquid organic materials is the basis of ultraviolet (UV) nanoimprint lithography. In spite of these advantages, the use of polymerization to pattern materials in thermal nanoimprint lithography is almost non-existent. In this study, we demonstrate a facile and general method to directly imprint a host of unary metal oxides (Fe2O3, ZrO2, TiO2, Nb2O5 and Ta2O5) at a very high resolution via in situ thermal free radical co-polymerization of various metal methacrylates in the presence of cross-linker ethylene glycol dimethacrylate using a silicon mold. Polymerization during nanoimprinting rigidly shapes the patterns, traps the metal atoms, reduces the surface energy and strengthens the structures, thereby giving similar to 100% yield after demolding. It was found that the higher oxidation state of metal resulted in excessive cracking of imprinted structures. This could be due to a higher degree of cross-linking of the precursor leading to shrinkage-related stress. Optimization of the resin composition by partially replacing ethylene glycol dimethacrylate with methyl methacrylate alleviated this problem. Heat-treatment of the imprinted structures resulted in the loss of organics, their subsequent shrinkage and converted the patterns to their corresponding metal oxides with line-widths as small as 25 nm.