CVD Monolayer Graphene Mid-IR Thermal Emitter - NUDT, 2025

Meng, Q. et al. (2025). Electrically driven mid-infrared thermal emission from a graphene metamaterial with near unity emissivity. *Optics & Laser Technology*. https://doi.org/10.1016/j.optlastec.2025.112562

Optics & Laser Technology · 2025

NUDT integrated ACS Material monolayer graphene into a MIM metamaterial to build an electrically driven mid-infrared emitter with ~98% emissivity at 7 µm.

About this research

Researchers at the National University of Defense Technology used monolayer CVD graphene purchased from ACS Material to demonstrate an electrically driven mid-infrared thermal emitter with near-unity emissivity, reaching about 98% absorptivity/emissivity at a wavelength of 7 µm. The team combined the graphene with a metal-insulator-metal (MIM) metamaterial perfect absorber, using the graphene as a Joule-heating emission layer driven by an applied bias voltage. Calibrated against a carbon-black blackbody reference, the device delivered narrowband, spectrally selective emission whose intensity scaled with applied voltage while the peak position stayed fixed near 7 µm. The work establishes a practical route to integrated, dynamic, spectrally selective infrared light sources.

Active infrared thermal emitters with spectrally selective emission are highly desirable yet rarely demonstrated. Most MIM metamaterial emitters are passive, requiring an external hot stage or high-temperature background to radiate, which limits their use in infrared communications, thermal image generation, gas sensing and active camouflage. Graphene is attractive for thermal emitters because of its excellent electrical properties, high-temperature stability and broadband emission, but its intrinsically low emissivity has historically capped efficiency. By coupling electrically driven graphene with a resonant MIM absorber, this paper addresses the dual challenge of achieving both active (electrically modulated) emission and high, spectrally selective emissivity in a single compact device. This is directly relevant to long-tail research interests such as narrowband mid-infrared sources, non-dispersive infrared (NDIR) gas sensing and dynamic thermal management.

The ACS Material monolayer graphene was the central active layer of the device. Fabrication followed a top-down process: a 150 nm gold film was deposited on the substrate by electron-beam evaporation as a perfect infrared reflector, then a 75 nm Al2O3 film was grown by atomic layer deposition (ALD). The monolayer graphene was then transferred and etched into the desired shape, with the paper stating it was "purchased from ACS Material." Gold electrodes were patterned to ensure electrical contact, and a second 75 nm Al2O3 film was deposited to protect the graphene from oxidation. The top micro-disc resonator layer (period P ≈ 4 µm, disc radius r ≈ 1.15 µm, 50 nm Au) was then defined by ultraviolet lithography and lift-off. Raman spectroscopy after fabrication confirmed the layer was monolayer graphene, supporting its capability for high-speed modulation. The graphene functioned as the conductive two-dimensional ohmic Joule-heating layer, modeled with intraband and interband conductivity terms (Fermi level ~0.1 eV, τ = 10⁻¹⁴ s, T = 300 K) in COMSOL finite-element simulations.

The quantitative results are strong. COMSOL simulations predicted a magnetic-resonance absorption peak at 7 µm reaching 98% for TM-polarized normal-incidence light, with rotational symmetry allowing TE excitation as well. Measured absorption spectra peaked at 7 µm with 97% absorptivity, the small redshift and reduction attributed to fabrication tolerances. SEM confirmed near-target geometry (period P = 3.996 µm, diameter d = 2.304 µm, radius r = 1.152 µm versus the design r = 1.15 µm). Using Kirchhoff's law and a carbon-black blackbody reference heated on a hot stage to 600 K, the emissivity was calibrated and matched the measured absorptivity. For electrically driven operation, an AC source with a 1 kHz square waveform (50% duty cycle) drove the graphene to avoid room-temperature background interference. Radiation intensity increased monotonically with applied voltage (measured at 12 V, 14 V and 16 V), while the emission peak stayed fixed at 7 µm because it is governed by the metamaterial resonance. Normalized emission spectra at different voltages shared nearly identical line shapes and agreed well with measured absorption, confirming efficient conversion of broadband thermal emission into narrowband spectrally selective emission.

The device enables integrated, dynamic, spectrally selective mid-infrared light sources. The authors highlight applications in infrared spectroscopy, infrared communications, gas sensing, thermal imaging and active thermal camouflage. Because the emission wavelength is set by the MIM geometry rather than the graphene itself, the approach is universal: simulations show that varying the micro-disc period or insulator thickness preserves perfect absorption/emission while tuning the resonant wavelength. This geometric tunability, combined with electrical modulation through Joule heating, points toward emitters tailored to specific molecular absorption bands, for example in mechanical-chopper-free NDIR sensors. The insensitivity of the magnetic resonance to incidence angle over a useful range further supports practical optical integration.

For researchers working on graphene optoelectronics, mid-infrared photonics and metamaterial emitters, this study illustrates that monolayer CVD graphene can serve effectively as an electrically driven emission layer when paired with a resonant absorber. The monolayer graphene used here was sourced from ACS Material, whose CVD graphene product line is available to groups pursuing similar 2D-material device fabrication. The paper's measured results—97% absorptivity and voltage-tunable narrowband emission at 7 µm—reflect the performance achievable with high-quality monolayer material in a carefully fabricated device, providing a credible benchmark for follow-up work.

How ACS Material products were used

• Monolayer CVD Graphene (CVD Graphene)  — “followed by the transfer and etching of the monolayer graphene to obtain the desired shape (purchased from ACS Material)”

Product Performance in this Study

The monolayer graphene served as the electrically driven Joule-heating emission layer integrated into the MIM metamaterial; Raman confirmed monolayer quality and the device achieved near-unity emissivity (~98%) at 7 µm.

Related product categories

• CVD Graphene

Frequently asked questions

How does monolayer graphene improve a mid-infrared thermal emitter?

Monolayer graphene acts as an electrically driven Joule-heating layer. On its own graphene has low emissivity, but when integrated into a metal-insulator-metal metamaterial resonator it heats efficiently under applied voltage and feeds the resonance. In this study the combination produced narrowband emission at 7 µm with near-unity emissivity around 98%, far exceeding bare graphene emitters.

What grade of graphene is suitable for metamaterial thermal emitters?

Monolayer CVD graphene is preferred because it offers high temperature stability, good electrical conductivity for Joule heating, and supports high-speed modulation. In this work the monolayer graphene was purchased from ACS Material, transferred onto an Al2O3-coated gold structure, and confirmed to be single layer by Raman spectroscopy before serving as the active emission layer.

Why is spectrally selective emission important for infrared sources?

Spectrally selective emission concentrates radiated energy into a narrow band, which is essential for applications like gas sensing where the source must match a molecular absorption line. The metamaterial sets the peak wavelength (7 µm here) independent of drive voltage, so increasing voltage raises intensity without shifting the peak, enabling efficient narrowband infrared sources.