Graphene-based electromechanically tunable subwavelength mid-IR perfect absorber

In this article, we propose and numerically investigate a graphene-based electromechanically tunable perfect absorber design. The fundamental motivation is to demonstrate the electromechanically tunable feature in graphene metasurface at the mid-infrared regime, which otherwise exploited only the chemical potential feature in the literature. The structure consists of a gold grating on a gold substrate separated by an oxide spacer with an overlay of monolayer graphene with free-standing segments. By applying external DC voltages, the free-standing region of the graphene layer deflects, owing to the electrostatic force it experiences. This shifts the resonance absorption wavelength. In the mid-infrared region of 5-10 mu m, a very low actuation voltage of 1.6 V displaces the graphene membrane by 1 nm, resulting in a wide shift of 60 nm in resonance wavelength. A continuous tunability with near-perfect absorption over a wavelength range of 200 nm for an applied voltage of only 7 V is demonstrated. At a voltage greater than 7 V, a mode hopping phenomenon is observed, hampering the perfect absorber operations with a shift in wavelengths. It is shown that the perfect absorption is again retained at some higher voltage. Such implementations hold promising applications in nanophotonics sensors, detectors, real-time beam steering, etc.