Fabrication of optical metasurfaces in iridium for high-temperature applications

Optical metasurfaces are gaining attention as a new technology because they can perform the tasks of several traditional optical elements simultaneously, while at a fraction of the size and weight. Their performance is dictated by the subwavelength structured surface, which also makes them extremely sensitive to morphology changes after fabrication. Oxidation and plastic deformation (edge rounding) are two dominant types of surface changes that occur in high-temperature environments, which limit optical metasurfaces from being a useful technology for those applications. Iridium is a refractory metal that is stable in these types of environments. The lack of reactivity, extremely high melting temperature, and high hardness are what makes iridium an ideal choice for the application. However, these features also present major challenges for lithographic pattern transfer at the nanoscale. We present several techniques for etching nanoscale patterns into iridium films, demonstrating the potential for use of optical metasurfaces in high-temperature environments.