Polymerizable ionic liquids for microstructures fabrication

Due to unique properties such as low vapor pressure and high ionic conductivity, room-temperature ionic liquids (RTILs) are very attractive not only for the chemical industry, but also for nano- and microstructures fabrication. The fabrication process conventionally involves usage of radiation sensitive polymer-based solutions (resists). We propose to replace those resists with eco-friendly solvent-free RTILs, which are polymerized by electron beam or UV light. Ionic liquids are also promising material for passive and active photonics components fabrication since their properties can be tuned in many ways by introducing special functionalities to the chemical structure of ions. In the present study, it is shown that different ionic liquids (with allyl or vinylbenzyl substituent) can be solidified on solid substrates (e.g. silicon or glass) by standard patterning lithography methods such as electron beam lithography in vacuum chamber and optical lithography with UV lamp. The thickness of the layer can be modified with ionic liquids mixture or by modified spin coating technique. By using patterning techniques, microstructures of different geometrical shapes are obtained from polymerizable RTILs containing fluorescein dianions. The shapes of obtained polymerized microstructures are also related to properties of the material including viscosities of selected ionic liquids. Various properties of polymerizable ionic liquids, such as thermal stability, viscosity, refractive index and light absorption can be adapted depending on the final application. Due to good optical properties, the fabricated microstructures can be used as photonic components, such as optical microresonators and waveguides.