Figure 4. Metamaterial-enhanced IR absorption.

(a) FT-IR reflection spectra of the 16-MHDA SAM on a bare Au surface at θ = 80° (top) and on the metamaterial absorber at θ = 30° to 70° (bottom). SAM of 16-MHDA [the inset of (a)] exhibited two absorption dips in the shaded region, corresponding to the symmetric/asymmetric C-H stretching vibrational modes at ~2855/2920 cm⁻¹. Fano-like anti-resonant peaks, indicated by the black arrows, arose from the resonant coupling between the plasmonic mode of the metamaterial and the molecular vibrational modes. (b) Vibrational signal at θ = 40° extracted by the baseline correction (top) and the corresponding Fano fitting curves with the frequency detuning, ω_pl/ω_vib, damping constant, γ (cm⁻¹), and Fano parameter, F, used in Eq. (1) (bottom).