Lithography-free transmission filters at ultraviolet frequencies using ultra-thin aluminum films

Aluminum allows for significant plasmon responses in ultraviolet (UV) regime of spectrum, where conventional plasmonic materials such as silver and gold lack plasmonic behavior due to their inherent dissipative limitation from lower plasmon frequency and inter-band transition. Such UV plasmonic resonance based on aluminum nanostructures could be challenging due to the smaller feature size of nanoscale resonator and remarkable sensitivity to oxidization. Here we theoretically and experimentally demonstrate lithography-free transmission filters using triple layers of continuous ultra-thin Al and dielectric films. Our proposed transmission filter is a triple-layer Fabry–Perot cavity and operates from 2.5 to 5.5 eV with bandwidth down to 0.5 eV and transmission amplitude up to 50%. Such flat Al ultra-thin film coatings suggest the use of aluminum as low-cost UV filters and UV optoelectronics as well as structural coloring applications. (paper)