title: Low frequency Raman scattering from acoustic phonons confined in ZnO nanoparticles.
abstract: We report here the first observation of the low frequency Raman scattering from acoustic phonons in semiconducting zinc oxide (ZnO) nanoparticles without embedding in any solid matrix. ZnO nanoparticles (size 5-10 nm) with nearly spherical shape have been synthesized using a chemical route. A shift in the phonon peaks toward higher frequencies along with broadening was observed with a decrease in particle size. The size dependence of the acoustic phonons in ZnO nanoparticles is explained using Lamb's theory that predicts the vibrational frequencies of a homogeneous elastic body of spherical shape. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar vibrations (l = 2) of the spheroidal mode due to the confinement of acoustic vibrations in ZnO nanoparticles.
authors.affiliation: Department of Physics and Astrophysics, University of Delhi, Delhi-110007, India.
authors.forename: Harish Kumar
authors.initials: HK
authors.lastname: Yadav
authors.forename: Vinay
authors.initials: V
authors.lastname: Gupta
authors.forename: K
authors.initials: K
authors.lastname: Sreenivas
authors.forename: S P
authors.initials: SP
authors.lastname: Singh
authors.forename: B
authors.initials: B
authors.lastname: Sundarakannan
authors.forename: R S
authors.initials: RS
authors.lastname: Katiyar