We demonstrate electrical control over coherent optical absorption in a graphene-based Salisbury screen consisting of a single layer of graphene placed in close proximity to a gold back reflector. The screen was designed to enhance light absorption at a target wavelength of 3.2 μm by using a 600 nm-thick, nonabsorbing silica spacer layer. An ionic gel layer placed on top of the screen was used to electrically gate the charge density in the graphene layer. Spectroscopic reflectance measurements were performed in situ as a function of gate bias. The changes in the reflectance spectra were analyzed using a Fresnel based transfer matrix model in which graphene was treated as an infinitesimally thin sheet with a conductivity given by the Kubo formula. The analysis reveals that a careful choice of the ionic gel layer thickness can lead to optical absorption enhancements of up to 5.5 times for the Salisbury screen compared to a suspended sheet of graphene. In addition to these absorption enhancements, we demonstrate very large electrically induced changes in the optical absorption of graphene of ∼3.3% per volt, the highest attained so far in a device that features an atomically thick active layer. This is attributable in part to the more effective gating achieved with the ion gel over the conventional dielectric back gates and partially by achieving a desirable coherent absorption effect linked to the presence of the thin ion gel that boosts the absorption by 40%.

The reflection of light from metallic mirrors results in a near-zero electric field at their surface. This precludes strong light−matter interaction between such mirrors and two-dimensional (2D) materials placed in direct contact with them. Patterning of the metal surfaces with subwavelength grooves can produce anisotropic metasurfaces that offer robust enhancements in the magnitude and control over the direction of the surface fields. Here, we use this control to analyze the Raman tensor for vibrational modes of atomically thin graphene. The anisotropic nature of the grooves leads to different Raman signal enhancement for the G (25 times) and 2D (50 times) Raman peaks of graphene for optimized groove dimensions. A notable suppression of these peaks by 40% for specific groove dimensions is also achieved. These findings suggest the use of metasurfaces as tunable surface-enhanced Raman scattering substrates to study the vibrational modes of 2D materials with reduced background signals.