Large-area fabrication of TiN nanoantenna arrays for refractory plasmonics in the mid-infrared by femtosecond direct laser writing and interference lithography [Invited]
Optical antennas might be used to efficiently harvest solar energy, if we can manage to fabricate them. Just like radio antennas do with radio waves, optical antennas convert propagating radiation (visible or infrared light) into localized excitations (electical charge to be stored). But choosing an appropriate material to make them is challenging, since traditional metals like gold and aluminum don't stand up to the high temperatures required for photovoltaic devices. In addition, the small features of these antennas force us to use slow, precise fabrication techniques that might not work for every material.
In this paper, Bagheri et al. present a combination of a suitable material and an efficient fabrication technique for making mid-infrared antenna arrays. They use Titanium Nitride (TiN), which belongs to a group of materials called "refractories"—heat-resistant substances used in furnaces and the space shuttle—but TiN also happens to interact efficiently with mid-IR light. The fabrication technique is a combination of chemical etching and laser lithography, and it allows the production of antenna arrays on the scale of tens of microns in a few minutes or faster. The authors point out that their technique can be modified for other antenna materials and geometries, and expect it to "open the door to large-area and low-cost refractory plasmonics in the mid-infrared."