Taming the Blackbody with Infrared Metamaterials as Selective Thermal Emitters

In this Letter we demonstrate, for the first time, selective thermal emitters based on metamaterial perfect absorbers. We experimentally realize a narrow band midinfrared (MIR) thermal emitter. Multiple metamaterial sublattices further permit construction of a dual-band MIR emitter. By performing both emissivity and absorptivity measurements, we find that emissivity and absorptivity agree very well as predicted by Kirchhoff’s law of thermal radiation. Our results directly demonstrate the great flexibility of metamaterials for tailoring blackbody emission.

Figure 1

Design of the infrared metamaterial absorber. (a) Top view of a single band metamaterial absorber unit cell with dimensions of: $a=3.2$, $l=1.7$, $w_1=0.5$, in microns. (b) Schematic of a dual-band metamaterial absorber with dimensions, (in microns): $a_2=7$, $l_1=3.2$, $l_2=2.0$, $w_2=0.4$. (c)–(d) Perspective view for single and dual-band metamaterial absorbers. Thickness of dielectric spacer is: $t_1=0.2\mu \mathrm{m}$, $t_2=0.3\mu \mathrm{m}$.

Figure 2

(a) Experimental absoprptivity of the single band metamaterial absorber. (b) Experimental absoprptivity of the dual-band metamaterial absorber. Inset displays SEM images of one unit cell for the fabricated single and dual-band absorbers.

Figure 3

Experimental emittance and normalized emissivity. (a) Emittance of the single band metamaterial emitter at five different temperatures and Emittance of the blackbody reference at $300°\mathrm{C}$. (b) Emittance of the dual-band metamaterial emitter at five different temperatures and Emittance of the blackbody reference at $300°\mathrm{C}$. (c) Normalized emissivity of single band metamaterial emitter. (d) Normalized emissivity of dual-band metamaterial emitter.

Figure 4

Comparison between the experimental absorptivity and emissivity. (a) absorptivity and emissivity for the single band absorber (emitter). (b), absorptivity and emissivity for the dual-band absorber (emitter).

Figure 5

Designed metamaterial emissivity (blue curve) and EQE (red curve) of GaSb. Inset shows a schematic of the metamaterial design with 16 sublattices. Dimensions of the design are $a=1080\mathrm{nm}$, $l_1=173\mathrm{nm}$, $l_2=127\mathrm{nm}$, $l_3=221.5\mathrm{nm}$, $l_4=190\mathrm{nm}$. Each cross sublattice has a line width of 20 nm and thickness of 50 nm. The thickness of the dielectric spacer is 78.8 nm and the ground plane is 200 nm. The unit cell also possesses two mirror planes, one horizontal and one vertical, as noted.