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首页> 外文期刊>Physica, B. Condensed Matter >Effect of point defects on the decay of the longitudinal optical mode
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Effect of point defects on the decay of the longitudinal optical mode

机译：点缺陷对纵向光学模式衰减的影响

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The longitudinal optical mode at the zone center often has the highest frequency in the phonon spectrum, so that its phonons cannot be scattered elastically into other modes. Their decay rate Gamma is enhanced by defects above the intrinsic anharmonic rate Gamma(ah) by the combined action of anharmonic processes and defects such as point defects. This can occur by a second-order process. The phonon is scattered first into a neighboring mode. This intermediate state is followed by anharmonic decay. The intrinsic anharmonic decay rate Gamma(ah) is almost independent of the intermediate state mode, so that Gamma(ah) can be factored out of the second-order decay rate. An expression of the overall decay rate is obtained. A different result can be obtained by convoluting the point defect scattering over the anharmonic line width. This procedure was used numerically for isotopic mixtures of Ge and Si. An algebraic expression for the convolution is given here. These different approaches are compared to each other and compared to the observed line broadening in the isotopic mixtures. The second-order theory is also applied to line broadening due to Si solutes and their associated Al vacancies in aluminum nitride. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 8]
机译：在区域中心的纵向光学模式通常在声子频谱中具有最高频率，因此其声子不能弹性地散射为其他模式。通过非调和过程与缺陷（例如点缺陷）的联合作用，高于固有非调和率Gamma（ah）的缺陷会提高其衰减率Gamma。这可以通过二阶过程发生。声子首先被散射到邻近模式。该中间状态之后是非谐波衰减。本征非谐衰减率Gamma（ah）几乎与中间状态模式无关，因此可以将Gamma（ah）排除在二阶衰减率之外。获得总衰减率的表达式。通过在非调和线宽上对点缺陷散射进行卷积可以获得不同的结果。该程序在数值上用于Ge和Si的同位素混合物。这里给出卷积的代数表达式。将这些不同的方法相互比较，并与在同位素混合物中观察到的谱线加宽相比较。由于氮化硅中的Si溶质及其相关的Al空位，二阶理论也适用于线拓宽。 （C）2002 Elsevier Science B.V.保留所有权利。 [参考：8]

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