Vibrational Frequency of MgO Nanoparticles in a polymer matrix
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Vibrational Frequency of MgO Nanoparticles in a polymer matrix Prafulla K. Jha and Mina Talati Department of Physics, Faculty of Science, The M.S.University of Baroda, Vadodara -390 002 ABSTRACT By using elastic continuum model for a spherical body along with the appropriate boundary conditions at the surface of the body, vibrational frequencies of MgO nanoparticles are calculated in the present paper. It is found that the vibrational frequencies corresponding to these eigen values depend strongly on the size of the nano particles and the peaks in the Raman spectra shift to the higher frequencies side as size of the nano particles decreases. We have also investigated the effect of a polymer matrix on the frequencies and Raman shift of MgO nanoparticles. The damping constant is found to vary linearly with the size of nano particles which shows that the mechanical damping is the prominent mechanism in the damping of the acoustic phonon modes.
INTRODUTION Nano particles due to their interesting and important electronic and optical properties have attracted world wide scientific attention on account of the quantum confinement effect in electrons and phonons in zero dimensions [1-5]. As building blocks for the next generation of electronic and opto-electronic devices ranging from ultra fast switching devices to ultra dense memory devices, nano particles offer potential applications. They exhibit very different behaviour from their bulk counterparts due to the strong spatial confinement. Exciton- phonon interaction is a crucial issue in the nano particle systems and this has motivated much of the previous work on the vibrational modes of these systems as it is certain that carrier- phonon interactions in the nanostructures are modified by the phonon confinement. For acoustic modes, the low frequency phonon spectrum is first altered with the appearance of discrete vibrations. Their frequency and damping reflect not only the size and shape of the nano objects but also the properties of their environment. Particularly, in the case of quantum dots in the matrix the damping takes place due to acoustic energy transfer at the interface and spherical acoustic wave expansion in the surrounding medium. The quantized mode properties thus contain information on the material characteristics, such as coupling between the particle-matrix, interface quality useful for understanding the local environment and its acoustic properties. Nano particles have found their potential utility in the medication as well as in the fabrication of devices. Recently, MgO nano particles are found to be very useful as a biocide. To the best of our knowledge despite its important applications, the vibrational properties of nano particles have not been investigated so far. In this paper, we report the results of our investigation on the vibrational frequencies and Raman scattering of the confined acoustic phonon modes in MgO nano particles using a simple approach based on the elastic body continuum model [6, 7].This approximation considers the equat
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