The authors describe a method, which uses CMOS compatible materials and processes, to fabricate such narrowband mid-infrared emitters. The basic platform is the well-known metal-insulator-metal (MIM) structure, which generates a high field enhancement in the few-nanometres-thin insulator layer and a narrow-tuneable resonance as a function of its geometrical dimensions. The authors present simulations and experiments showing that a periodic arrangement of MIM structures (period = 1.5 μm, widths from 800 to 653 nm) possesses narrow resonances varying between 2000 cm¯¹ and 3000 cm¯¹ as a function of the width of each MIM patch. It is also possible to combine structures of different dimensions in the same chip, yielding separate spectral lines, which are useful in a reference-probe experiment. Furthermore, the devices are polarization- and angle-insensitive, which enormously simplifies the design and the fabrication of this kind of emitters.
Finally, the authors demonstrate, as proof of principle, how these emitters perform when directly excited by a heat source. Although the emissivity data are still noisy, they clearly show promise for the use of this platform in future, highly sensitive, cost-effective and compact gas sensors.
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