APL Photon. 4, 056107 (2019)

A flexible, low-loss metamaterial with an epilson near zero (ENZ) response has been made by scientists from the University of St Andrews University in Scotland and CNR-SPIN institute in Italy. The structure consists of thin stacked layers of silver, germanium and SU-8 polymer with a total thickness of 100 nm and a 15:85 metal-to-dielectric ratio. The layers are deposited on a sacrificial substrate that allows the metamaterial membrane to be removed following fabrication. The result is a free-standing thin coating that is flexible and conformable and can be applied to non-flat devices. Tests indicate that the coating retains its optical properties after 10,000 bending cycles and can be bent to fit surfaces with a radius of curvature of a few micrometres. ENZ materials are of interest as they provide spectral regimes where the refractive index approaches zero, stretching the wavelength within the material so the electromagnetic field remains near constant over an extended area. They are useful for applications including wavefront engineering, sub-diffraction-limit imaging and the enhancement of optical activity.