Nanofabrication of negative refractive index metasurfaces

Abstract

We designed and fabricated planar metamaterial ‘particles’ (metasurfaces) intended to achieve negative effective refractive index in mid-infrared. We considered double split ring resonators (negative permeability particles) with additional capacitive gaps to compensate for the inertial inductance, as well as complementary double split rings (negative permittivity). We calculated dispersion relations and considered scaling conditions for our structures. For the fabrication of our experimental samples we used scanning probe nanolithography with z-scanner movement in 20 nm thin silver layers sputtered on positive photoresist or on polycarbonate. The morphology of our structures was characterized by atomic force microscope. We utilized a line width of 80–120 nm and the nanolithographic groove depth in different samples ranged from 4 to 80 nm. We believe our approach could be useful as a simple and low-cost tool for fabrication, assessment and optimization of different metamaterial geometries before larger arrays of particles are fabricated using other, more sophisticated and complex methods.