Study of microscopic level physics at nanoscale using Raman scattering

Abstract

A comparison of experimentally observed Raman scattering data with Raman line-shapes, generated theoretically using phonon confinement model, has been carried out to understand the sensitivity of different Raman spectral parameters on quantum confinement effect. Size dependent variations of full width at half maximum (FWHM), Raman peak position and asymmetry ratio have been analyzed to establish the sensitivity of their corresponding physical counterparts (phonon life time and dispersion) in confined systems. The comparison has been done in three different confinement regimes namely, weakly, moderately and strongly. Proper reasoning has been assigned for such a variation after validation of the theoretical analysis with the experimental observations. A moderately confined system was created by preparing 6 nm sized silicon nanostructures using metal induced etching. An asymmetrically broadened and red shifted Raman line-shape was observed which established that Raman width to be the most sensitive parameter. Raman spectral asymmetries induced by electron phonon interaction (Fano resonance) with quantum confinement effect have also been discussed for Si NSs. The methodology has been validated by studying the effect of similar microscopic perturbations, Fano coupling with quantum size effects on different Raman spectral parameters to know the sensitivity of different Raman spectral parameters which also reveals Raman width to be the most sensitive parameter. Sensitivity of a given Raman spectral parameters has been shown to be used as a tool to understand the role of external perturbations in a material.