Asymmetrical Spectral Continuum between Anti-Stokes and Stokes Scattering Revealed in Low-Frequency Surface-Enhanced Raman Spectroscopy
Shuo Sun, Dhanusha T. N. Rathnayake, Yinsheng Guo
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.