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Resonant and Off-Resonant Phonon Properties of Wurtzite ZnS: Effect of Morphology on Fröhlich Coupling and Phonon Lifetime

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journal contribution
posted on 31.07.2018 by Neena Prasad, Balasubramanian Karthikeyan
We report the occurrence of morphology-induced variation in the phonon properties of a poly­(vinylpyrrolidone)-capped ZnS semiconductor. ZnS micro- and nanostructures such as microparticles, nanoparticles, nanorods (NRs), and nanowires (NWs) were synthesized through a single-step hydrothermal method at low temperature. Structural, morphological, and compositional analyses were performed using powder X-ray diffraction, field emission scanning electron microscopy, energy-dispersive spectra (EDS), and high-resolution transmission electron micrographic techniques. Moreover, morphology of the prepared samples was confirmed from off-resonant Raman studies. A strong first and higher orders of longitudinal optical (LO) phonon and weak fundamental and higher orders of transverse optical features were seen from UV Raman scattering. The electron–phonon coupling as a function of morphological changes of the nanostructures was analyzed by studying the differences in LO phonon linewidths among the samples. The dominance of the interaction between the electron and LO phonon (Fröhlich coupling) over the short-range electron–phonon interaction via deformation potential was observed. Exciton–LO phonon coupling was found to be strong in one-dimensional nanostructures (NR and NW) because of the transfer of excitons and phonons in the longitudinal direction and phonon confinement in the transverse direction.