Sub-wavelength structures can set the absorption, reflection and thermal emission of a surface almost independently of what the surface is made of. Selective absorbers, radiative coolers and structural colour have all been demonstrated this way. The obstacle is manufacturing: the best-performing structures are still written by electron-beam lithography, which does not scale to the areas that solar modules, building surfaces or wafer-level optics need.
We work on nanostructures that can be made without lithography — disordered scattering layers, self-assembled masks, nanowire forests — and on the optics that follow from them. Devices we have built include a single-material near-infrared selective absorber based on a refractive-index-tunable Tamm plasmon structure, a photon sieve on a III-V nanowire forest, double-sided anti-reflection nanostructures on convex lenses, and large-area disordered light-harvesting layers for photovoltaic modules.
The same process variation that makes nanofabrication hard to control also makes each device unique. We read that uniqueness optically and use it for authentication, in silk fibres, liquid crystals and edible materials.