Silk - new opportunities in optics and photonics for an ancient material

Of these multiple possible material conformations, silk films offer particular interest for optics and photonics applications. These silk-based devices are obtained by pouring the water-based fibroin solution (either by spin-coating or casting) onto a substrate. The solution is left to dry in air until it crystallizes into a film whose thickness can be controlled from a few nanometers to hundreds of micrometers. Free-standing films as large as 40 cm have been realized. Optical evaluation of films reveals near-perfect transparency across the visible range while film uniformity as surface roughness can be a few nanometers RMS depending on the drying process. An exciting possibility for the future is the realization of photonics components of increasing sophistication in an entirely organic and biologically active and interactive substrate substrate. In fact, nanopatterning of sub-wavelength features has already by achieved by silk replication of aperiodic structures consisting of an arrangement of 200-nm-diameter holes separated by as little as 30 nm.