Ultrathin and Electrically Tunable Metamaterial with Nearly Perfect Absorption in Mid-Infrared

Ultrathin and Electrically Tunable Metamaterial with Nearly Perfect Absorption in Mid-InfraredUltrathin and Electrically Tunable Metamaterial with Nearly Perfect Absorption in Mid-Infrared.

( a ) The schematic of the graphene metamaterial perfect absorber and the unit cell of the metamaterial arrays. The tunable reflectance can be achieved by back-gating of graphene between the Si 3 N 4 membrane and the metasurface. ( b ) The SEM image of the metamaterial structure topping the absorber, with L = 1.25 μm and W = 0.3 μm. ( c ) Reflectance spectra for the absorbers in ( a ) with different metamaterial structures. ( d ) Simulated results for the same structures in ( c ).

( a ) The ratio between Q a and Q r , with different W and tanδ. ( b ) Q a and Q r change when L = 1.25 μm and tanδ = 0.08. ( c ) Black dashed lines indicate the quality factor (Q a and Q r ) of the simulated results with fixed W, while red square dots show the experimentally tunable regime of graphene modulated by electricity. ( d ) Q a /Q r of the simulated and experimental results. 2D polarization images depict | E Z | distribution at V G = −8 V and V G = 26 V.

( a ) Raman spectra of the graphene we used coating on SiO 2 substrate and the graphene integrated in the absorber with cross arrays of L = 1.25 μm and W = 0.3 μm (inset figure). The wavelength of the applied laser is 633 nm. ( b ) The source–drain current is controlled by back-gating. Dirac point is achieved at around the bias of 17 V. The reflectance spectra of the absorbers with different cross-shaped metamaterials. ( c ) Modulation of reflectance achieved by back-gating of graphene with cross-shaped metamaterial of L = 1.25 μm and W = 0.3 μm. ( d ) The change in reflectance and frequencies at different back-gate bias.

Abstract.

5 dB change in absorption near the perfect absorption region. Our work provides a general guideline for designing and realizing tunable infrared devices and may expand the applications of perfect absorbers for mid-infrared sensors, absorbers, and detectors in extreme spatial-limited circumstances.

1. Introduction.

270 nm (thickness λ 0 / 15 ). The MIM tri-layer structure forms an agile platform to engineer the infrared optical properties of the structure. The bottom metal layer of the MIM structure provides two-fold functions: a mirror to form resonant cavity and an effective gate to adjust the Fermi level in the graphene layer, and hence the absorption. This tunable absorption provides a compact, flexible, and post-fabrication fine adjustment freedom to the hybrid metamaterials.

2. Materials and Methods.

3. Results and Discussion.

17 V) and, with increasing the carrier density (no matter electron or hole), the reflection value decreases, which indicates additional absorption. In the meantime, with decreasing V G , the resonant frequency increases slightly (

1%), which may be ascribed to a smaller effective mode volume. The rather limited tunability of the present device is associated with the quality of the graphene layer, which consisted of impurities and defects due to CVD growth and device fabrication processing. The tunability can be further improved with better sample quality or using BN/graphene/BN sandwiched structures.