Fig. 1. Schematic diagram of polaritons in two-dimensional materials

Fig. 2. Schematic diagrams of coupled harmonic oscillator model. (a) The oscillator model of polariton; (b) the coupled oscillator model of the polariton and molecular

Fig. 3. Graphene plasmonic sensors. (a) Tunable graphene plasmonic biosensor^[26]; (b) infrared absorption spectra of devices with varying voltages^[26]; (c) graphene plasmonic biosensor based on CaF₂ substrate^[70]; (d) PEO molecular vibrational mode^[70]; (e) graphene plasmonic gas sensor^[29]; (f) infrared absorption spectra of graphene plasmon after adsorbing gas molecules^[29]

Fig. 4. Cavity enhanced graphene plasmonic devices.(a) Principle diagram and SEM image of cavity enhanced graphene plasmon infrared spectroscopy device^[72]; (b) infrared absorption spectra of 8 nm PEO molecular^[72]; (c) metal/graphene surface plasmon hybrid structure^[73]; (d) schematic diagram of the working principle of the graphene plasmonic device for enhancing Raman and infrared spectroscopy^[73]

Fig. 5. Transmission-type graphene plasmonic device. (a) Transmission-type graphene plasmonic infrared modulator^[76]; (b) infrared spectra of devices with varying gate voltages^[76]

Fig. 6. BP-based anisotropic plasmonic devices. (a) Schematic diagram of BP nanoribbon array device^[85]; (b) the loss function of resonant peaks of BP plasmon at various incident angles^[85]; (c) the intensity of resonance peaks of BP plasmon at various incident angles^[85]; (d) the schematic diagram of graphene-black phosphorus heterostructure sensor^[89]; (e) (f) absorption spectra of the device covered with (dashed lines) and without (solid lines) PEO molecular along the x- and y- direction^[89]

Fig. 7. Boron nitride phonon polariton devices. (a) Schematic diagram of boron nitride nanoribbon resonator^[97]; (b) infrared spectra of CBP molecules with different thicknesses^[97]

Fig. 8. α-MoO₃ phonon polariton devices. (a) Schematic diagram of the α-MoO₃ pyramid arrays based perfect absorber^[104]; (b) the real part of the dielectric constant of α-MoO₃ along different crystalline axes^[104]; (c) absorption responses of the α-MoO₃ pyramid arrays under the illuminations of normally incident x and y polarized waves^[104]; (d) dispersion of α-MoO₃/Si structure in q_x and q_ycross sections^[104]

Fig. 9. Graphene plasmon near-field infrared nano-imaging. (a) Schematic diagram of near-field imaging detection using single-layer graphene covering gold micron holes and its mode distribution^[127]; (b) enhanced evanescent field intensity of single-layer graphene covering gold gratings^[127]