Deciphering Near-field response with the Far-field Wavelength-scanned SERS spectra of 4- Mercaptopyridine adsorbed on nanocolloidal gold entrapped in Langmuir Reverse Schaefer film of 5CB liquid crystal molecules
Wavelength-scanned (WS) SERS spectra of 4-Mercaptopyridine molecule (4-MPy) adsorbed on immobilised gold nanoparticles in the Langmuir Reverse Schaefer (L –RSh) film matrix of 5CB molecule have been reported. WS-SERS spectral profile exhibits increment in intensities of the enhanced Raman bands of 4-MPy with increase in wavelength of the exciting laser source. The rationale behind the experimental observations is supported by simulated extinction spectra and the enhancement factor measurements of the modelled systems using T-matrix formalism. SERS intensity fluctuations of 1000 cm-1 band of 4-MPy molecule as collected from three different locations of the L –RSh film substrate are also analyzed. Surprisingly, depending upon the spatial locations of the substrates, the intensity fluctuations of the above referred band exhibit both Poisson and Gaussian distributions albeit maximum number of the probe molecule that can reside in the scattering areas under investigations cannot exceed sixteen. These observations suggest that origin of SERS from single/ few molecules or from ensemble averaged system cannot be inferred from the statistical distributions of the Raman intensity fluctuations. The present experimental observations are also expected to unveil the relation between near-field plasmonic behaviors of the substrate with the corresponding far-field SERS spectra of 4-MPy molecule.