Theoretical Raman line shape functions have been studied to take care of quantum confinement effect and Fano effect individually and jointly. The characteristics of various Raman line shapes have been studied in terms of the broadening and asymmetry of Raman line shapes. It is shown that the asymmetry in the Raman line-shape function caused by these two effects individually does not add linearly to give asymmetry of lineshape generated by considering the combined effect. This indicates existence of interplay between the two effects. The origin of interplay lies in the fact that Fano effect itself depends on quantum confinement effect and in turn provides an asymmetry. This can not be explained by considering the two effects contribution independent of each other. arXiv:1508.00388v1 [cond-mat.mes-hall] 3 Aug 2015

A comparative study of quantum confinement of electrons and phonons in silicon nanocrystals produced by laser-induced etching on a silicon (Si) substrate and continuous wave (cw) laser-induced crystallization in a-Si:H film on a quartz substrate is presented here. Raman line shapes of optical phonons confined in Si nanocrystals were utilized using a phenomenological phonon-confinement model. It is appropriately modified by incorporating a Gaussian distribution of sizes for two-dimensional (columnar) and three-dimensional (spherical) confinement parameters for laser-induced etching and cw laser-induced crystallization processes, respectively. The calculated mean crystallite sizes were in consonance with those calculated from the bond-polarizability model. Confinement effects were found to be more prominent in Si nanocrystals prepared by laser-induced crystallization in comparison to laser-etched Si. Photoluminescence spectra of both the samples were also utilized to study the dimensionality aspect of nanocrystals.

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