Yadav Harish Kumar, Gupta Vinay, Sreenivas K, Singh S P, Sundarakannan B, Katiyar R S
Department of Physics and Astrophysics, University of Delhi, Delhi-110007, India.
Phys Rev Lett. 2006 Aug 25;97(8):085502. doi: 10.1103/PhysRevLett.97.085502.
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.
我们在此报告首次观察到未嵌入任何固体基质的半导体氧化锌（ZnO）纳米颗粒中声子的低频拉曼散射。使用化学方法合成了形状近乎球形的ZnO纳米颗粒（尺寸为5 - 10纳米）。随着颗粒尺寸减小，观察到声子峰向更高频率移动并展宽。利用预测球形均匀弹性体振动频率的兰姆理论解释了ZnO纳米颗粒中声子的尺寸依赖性。我们的结果表明，观察到的低频拉曼散射源于ZnO纳米颗粒中声振动的限制导致的球型模式的球形（l = 0）和四极振动（l = 2）。
