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Softening behavior of acoustic phonon mode in ZnO nanoparticles: the effect of impurities and particle size variation with temperature
Author(s) -
Yadav Harish Kumar,
Sreenivas K.,
Katiyar R. S.,
Gupta Vinay
Publication year - 2011
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.2901
Subject(s) - phonon , anharmonicity , softening , impurity , particle size , materials science , coalescence (physics) , nanoparticle , rayleigh scattering , condensed matter physics , particle (ecology) , raman spectroscopy , chemical physics , chemistry , nanotechnology , composite material , optics , physics , organic chemistry , oceanography , astrobiology , geology
Decay dynamics of the acoustic phonon mode in ZnO nanoparticles, synthesized using the wet chemical technique, is investigated. It is well established that optic phonon modes in a semiconductor favor an anharmonic decay dynamics; in contrast, acoustic modes evidence a rather complex decay behavior, manifesting their dependence on other parameters such as particle size, impurity species, etc. At lower temperatures ( T < 500 K), the anharmonic decay process, caused by the weakening of the bond strength, is responsible for the observed decrease in the acoustic mode wavenumbers. However, particle growth due to the coalescence sintering process is prominent at higher temperatures (>600 K) and governs the softening behavior of the acoustic phonon mode towards the Rayleigh line. On the other hand, the precursor species and reaction byproducts on the surface of ZnO nanoparticles induce an anomalous softening behavior in the decay dynamics at specific temperatures by damping the acoustic phonon mode. Copyright © 2011 John Wiley & Sons, Ltd.