Combined Surface-Enhanced Raman and Infrared Absorption Spectroscopies for Streamlined Chemical Detection of Polycyclic Aromatic Hydrocarbon-Derived Compounds

Probing the Local Near-Field Intensity of Plasmonic Nanoparticles in the Mid-infrared Spectral Region

“…To materialize this idea, we designed a series of close-packed two-dimensional (2D) NP array substrates composed of gold nanoparticles (AuNPs) with different diameters (marked as R ). Such 2D substrates have been demonstrated to exhibit broadband plasmon near-field enhancements in MIR wavelengths. − And then we used the femtosecond IR pump-SFG probe technique to investigate the ultrafast vibrational dynamics of the NO 2 symmetric stretching mode (ν NO 2 ) of self-assembled 4-NTP monolayers on substrate surfaces and molecular orientation, extracting local near-field intensity by eq . The local field strongly depends on the diameter of the AuNPs and regulates the vibrational anharmonicity of ν NO 2 mode.…”

“…Assuming that the IR near-field intensity at the Au film surface is I 0 , the local field intensity of AuNPs is determined to be 7.80 I 0 , 12.54 I 0 , 14.72 I 0 , and 16.80 I 0 for R = 15, 25, 40, and 55 nm, respectively. It needs to be mentioned that the local near fields of AuNPs are spatially inhomogeneous, and the strong enhancement of local fields occurs at the gap between neighboring AuNPs that can form hotspots. ,,, Accordingly, the near-field intensity determined by our IR pump-SFG probe experiments mainly represents the local field near or at the gap between neighboring AuNPs.…”

“…The 2D AuNP array substrates show broadband absorption in the visible to IR wavelength range, indicating that these substrates can yield an enhanced local near field under excitation of both visible and IR pulses (Figure S3). − Hence, there are two cases in which the local near field of AuNP substrates can be excited in our IR pump-SFG probe experiments: (1) an incident IR-pump pulse and (2) an incident visible- and IR-probe pulse and SFG emission light. Usually, dynamic bleaching originates from the excitation of an IR pump pulse.…”

An Ultra-broadband Metallic Plasmonic Antenna for Ultrasensitive Molecular Fingerprint Identification

“…However, the narrow band of metallic PA (hundreds of wavenumber width) is difficult to match with the wide spectral range in near-field enhanced applied scenarios, such as the molecular fingerprint vibration frequencies in the resonant surface-enhanced infrared absorption (rSEIRA), and the light–matter interaction is sharply off when the mismatch happens, leading to weak or no enhancement (spectral detuning) . Although the metal island films possess a broadband spectroscopic response in the mid-infrared region, it does not satisfy the requirement of materials since it is a far-field effect . Currently, the metal micron-scale structures fabricated by photolithography are their principal materials, , and the combination of metallic PA with different scales and the regulation of dielectric metasurfaces are the main routes to extend the bandwidth. ,, However, the finite increased bandwidth and restricted applied conditions imply that it requires a better strategy to fix this issue. , Hence, spectral detuning is a general and inevitable obstacle in this field.…”