Asymmetrical Spectral Continuum between Anti-Stokes and Stokes Scattering Revealed in Low-Frequency Surface-Enhanced Raman Spectroscopy

Abstract

An asymmetrical spectral continuum is observed in low-frequency surface-enhanced Raman spectroscopy (LF-SERS) in the terahertz (THz) region. This background continuum appears as a flat baseline in the Stokes side and a slope in the anti-Stokes side. Analysis shows this asymmetry originates from the different scaling of anti-Stokes and Stokes scattering with respect to the Bose–Einstein distribution. Such asymmetry is readily visible, under room temperature, in the low-frequency THz spectral range. Accounting for this spectral intensity asymmetry reveals the intrinsic continuum background of electronic origin, differing from local normal modes and collective relaxational motions. We also describe a numerical method, independent of line shape models, to determine sample temperatures while simultaneously accounting for this asymmetrical background continuum. Finally, we show that such asymmetrical spectral continuum is generally observable in low-frequency Raman scattering.

Probing Local Optical Fields via Ultralow Frequency Raman Scattering from a Corrugated Probe

“…Even though the origin of the contrast that we observe in the images is clear, distinct phenomena can lead to ULF Raman scattering from the probe away from and/or in contact with the nanoparticles (see Figure d). The Stokes/anti-Stokes asymmetry observed here can, on one hand, be associated with electronic Raman scattering, as discussed in a recent report . That said, enhanced vibrational Raman scattering from heterogeneous metallic nanostructures sustained near the apex of the sputtered plasmonic probe cannot be excluded .…”

“…The Stokes/anti-Stokes asymmetry observed here can, on one hand, be associated with electronic Raman scattering, as discussed in a recent report. 11 That said, enhanced vibrational Raman scattering from heterogeneous metallic nanostructures sustained near the apex of the sputtered plasmonic probe cannot be excluded. 12 Indeed, seminal works in the area of plasmon-enhanced Raman scattering assigned similar observations to localized acoustic vibrations from nanostructures sustained on rough metal films.…”

Evolution of structural dynamics in cesium lead halide perovskite colloidal nanocrystals from temperature-controlled synthesis

“…Common examples include molecular motions, such as translation, rotation, and libration, in molecular liquids and polymers. 20 These are also the structural dynamic basis of dielectric relaxation. 21 Severely overdamped nuclear motions in solids, including many ferroelectrics, also give rise to such prominent central peaks.…”

“…In the low frequency region, however, it produces a non-negligible multiplier to the overall scattering cross section; this factor has a strong frequency dependence and diverges as the scattering frequency approaches zero. 20 Its divergence at zero frequency renders finite inherent spectral responses into a peak. Thus, to reveal the underlying intrinsic spectral response, we normalize as measured low frequency Raman spectra using the Bose-Einstein factor following previously reported procedures.…”

Nanophotonics for Chemical Imaging and Spectroscopy

“…The above-echoed goal of characterizing increasingly complex interfaces comprises a recurrent theme in modern SERS-based spectroscopy and imaging studies. This VSI therefore includes a variety of SERS studies covering a broad range of fundamental and applied studies. − From work aimed at better understanding the unique optical properties of a single rod on a mirror to the ultrasensitive detection of plant biomarkers and herbicides, and through 3D SERS imaging of nanoporous gold–silver microstructures, the scope of SERS work in this issue is appropriately and exquisitely diverse. An interesting contribution that analyzed SERS hotspot dynamics in dry and aqueous environments is worth singling out .…”