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基于超声浸水透射技术, 实验研究了有限尺寸二维正方晶格钢/水声子晶体多点缺陷模态性质. 利用COMSOL Multiphysics软件建立该声子晶体有限元计算方法, 求解了9×9超胞多点缺陷声子晶体能带结构, 把缺陷局域模态频率与数值仿真和实验结果进行对比, 结果表明: 实验数据和理论值能够很好符合. 进一步分析发现, 点缺陷数量影响声波局域效应、本征模态和传播特性, 为设计有限尺寸声波器件提供理论依据.
关键词:
声子晶体
多点缺陷
实验研究
有限元 相似文献
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构造了界面具有原子混合的硅锗(Si/Ge)单界面和超晶格结构.采用非平衡分子动力学模拟研究了界面原子混合对于单界面和超晶格结构热导率的影响,重点研究了界面原子混合层数、环境温度、体系总长以及周期长度对不同晶格结构热导率的影响.结果表明:由于声子的“桥接”机制,2层和4层界面原子混合能提高单一界面和少周期数的超晶格的热导率,但是在多周期体系中,具有原子混合时的热导率要低于完美界面时的热导率;界面原子混合会破坏超晶格中声子的相干性输运,一定程度引起热导率降低;完美界面超晶格具有明显的温度效应,而具有原子混合的超晶格热导率对温度的敏感性较低. 相似文献
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通过广义梯度近似的第一原理全电子相对论计算, 研究了不同界面类型InAs/GaSb超晶格的界面结构、电子和光吸收特性. 由于四原子界面的复杂性和低对称性, 通过对InAs/GaSb超晶格进行电子总能量和应力最小化来确定弛豫界面的结构参数. 计算了InSb, GaAs型界面和非特殊界面(二者交替)超晶格的能带结构和光吸收谱, 考察了超晶格界面层原子发生弛豫的影响.为了证实能带结构的计算结果, 用局域密度近似和Hartree-Fock泛函的平面波方法进行了计算. 对不同界面类型InAs/GaSb超晶格的能带结构计算结果进行了比较, 发现界面Sb原子的化学键和离子性对InAs/GaSb超晶格的界面结构、 能带结构和光学特性起着至关重要的作用. 相似文献
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A transfer-matrix formalism is employed to study optical-phonon transport in a macroscopic continuum model for both periodic and Fibonacci polar-semiconductor superlattices. A phonon bandgap with subband structures is obtained for the periodic superlattices. However, in the Fibonacci superlattices, there is a spectrum trifurcation and self-similarity. The LO phonon localization length is calculated from which we confirm the existence of complete exponential localization of LO phonons. 相似文献
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《Comptes Rendus Physique》2016,17(10):1146-1153
Improvements of the thermoelectric properties in bulk materials have very often relied on the reduction of thermal conductivity, which is mostly based on phonon propagation. Reducing further phonon transport has remained a difficult task due to the fact that current thermoelectric materials are already efficient thermal insulators, and also because of the broadness of the Planckian phonon spectrum. Nanostructuring has provided new paths for decreasing thermal conduction, especially by means of scatterers, be them nano-objects, surfaces, or interfaces. In this chapter, the physics of demonstrated nanoscale methodologies for the reduction of thermal conduction will be proposed together with illustrations from direct simulations. 相似文献
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Our observations of the reflection or backscattering of high-frequency phonons (v =280 GHz to 1 THz) at silicon-solid interfaces disagree significantly with predictions from the acoustic mismatch model. Interfaces composed of materials theoretically wellmatched, show high scattering experimentally. In contrast, interfaces theoretically poorly matched, show less phonon scattering than expected. Generally, this is best expressed by the fact that the interface scattering ranges from roughly 30–60% for different phonon modes with little dependence on the material covering the silicon crystal and different techniques of interface preparations. Thus, our experiments indicate that the well-known Kapitza anomaly of the phonon scattering at solid-liquid helium interfaces is not a special case; the same anomaly appears to be present at all tested interfaces. Our experiments are compared with detailed calculations which either assume pure specular or pure diffusive scattering. In these calculations the influence of the crystal anisotropy for the phonon propagation (phonon focussing) is included. This comparison shows, especially for the free silicon surface, that phonons are completely diffuse scattered. Hence, the acoustic mismatched model relying on specular reflection cannot be applied to the real silicon interface. The frequency dependence of phonon scattering at a free silicon interface indicates the existence of at least two different diffusive scattering mechanisms. Within our experimental limits in these two scattering processes the phonons are elastically scattered. 相似文献
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A non-equilibrium molecular dynamics model is developed to investigate how a thin film confined between two dissimilar solids affects the thermal transport across the material interface. For two highly dissimilar (phonon frequency mismatched) solids, it is found that the insertion of a thin film between them can greatly enhance thermal transport across the material interface by a factor of 2.3 if the thin film has one of the following characteristics: (1) a multi-atom-thick thin film of which the phonon density of states (DOS) bridges the two different phonon DOSs for the solid on each side of the thin film; (2) a single-atom-thick film which is weakly bonded to the solid on both sides of the thin film. The enhanced thermal transport in the single-atom-thick film case is found mainly due to the increased inelastic scattering of phonons by the atoms in the film. However, for solid-solid interfaces with a relatively small difference in the phonon DOS, it is found that the insertion of a thin film may decrease the thermal transport. 相似文献
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Mir Mohammad Sadeghi Michael Thompson Pettes Li Shi 《Solid State Communications》2012,152(15):1321-1330
The recent advances in graphene isolation and synthesis methods have enabled potential applications of graphene in nanoelectronics and thermal management, and have offered a unique opportunity for investigation of phonon transport in two-dimensional materials. In this review, current understanding of phonon transport in graphene is discussed along with associated experimental and theoretical investigation techniques. Several theories and experiments have suggested that the absence of interlayer phonon scattering in suspended monolayer graphene can result in higher intrinsic basal plane thermal conductivity than that for graphite. However, accurate experimental thermal conductivity data of clean suspended graphene at different temperatures are still lacking. It is now known that contact of graphene with an amorphous solid or organic matrix can suppress phonon transport in graphene, although further efforts are needed to better quantify the relative roles of interface roughness scattering and phonon leakage across the interface and to examine the effects of other support materials. Moreover, opportunities remain to verify competing theories regarding mode specific scattering mechanisms and contributions to the total thermal conductivity of suspended and supported graphene, especially regarding the contribution from the flexural phonons. Several measurements have yielded consistent interface thermal conductance values between graphene and different dielectrics and metals. A challenge has remained in establishing a comprehensive theoretical model of coupled phonon and electron transport across the highly anisotropic and dissimilar interface. 相似文献
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由于纳米结构具有极高的表体比,声子-表面散射机制对声子的热输运性质起到关键作用.提出了表面低配位原子对声子的散射机制,并且结合量子微扰理论与键序理论推导出该机制的散射率.由于散射率正比于材料的表体比,这种散射机制对声子输运的重要性随着纳米结构尺寸的减小而增大.散射率正比于声子频率的4次方,所以这种散射机制对高频声子的作用远远强于对低频声子的作用.基于声子玻尔兹曼输运方程,计算了硅纳米薄膜和硅纳米线的热导率,发现本文模型比传统的声子-边界散射模型更接近实验值.此发现不仅有助于理解声子-表面散射的物理机制,也有助于应用声子表面工程调控纳米结构的热输运性质. 相似文献
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利用非平衡格林函数方法研究了石墨纳米带中三空穴错位分布对热输运性质的影响.研究结果发现:三空穴竖直并排结构对低频声子的散射较小,导致低温区域三空穴竖直并排时热导最大,而在高频区域,三空穴竖直并排结构对高频声子的散射较大,导致较高温度区域三空穴竖直并排时热导最小;三空穴的相对错位分布仅能较大幅度地调节面内声学模高频声子的透射概率,而三空穴的相对错位分布能较大幅度地调节垂直振动膜高频声子和低频声子的透射概率,导致三空穴的相对错位分布不仅能大幅调节面内声学模和垂直振动模的高温热导,也能大幅调节垂直振动模的低温热导.研究结果阐明了空穴位置不同的石墨纳米带的热导特性,为设计基于石墨纳米带的热输运量子器件提供了有效的理论依据. 相似文献
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Superlattices are used in modern light-emitting diodes to modify intentionally electron, phonon and/or photon transport within their volumes, which leads to their expected performance characteristics. In particular, superlattices may have a dramatic impact on device thermal properties. Superlattice thermal resistance is anisotropic and usually distinctly higher than its values in constituent bulk materials, which results from phonon reflections and/or phonon scatterings at numerous layer interfaces. In the present paper, thermal resistance of a typical superlattice of layer thicknesses neither much higher nor much lower than the phonon free path is discussed. Besides, as an important example, thermal resistance of the typical GaAs/AlAs superlattice is determined theoretically and compared with its measured values known from literature. 相似文献
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Ke-Min Li Ling-Ling Wang Wei-Qing Huang An-Lian Pan Qing Wan 《Physica E: Low-dimensional Systems and Nanostructures》2009,41(10):1864-1871
By using scattering matrix method, we investigate the acoustic phonons transport in a quantum waveguide embedded double defects at low temperatures. When acoustic phonons propagate through the waveguide, the total transmission coefficient versus the reduced phonon frequency exhibits a series of resonant peaks and dips, and acoustic waves interfere with each other in the waveguide to form standing wave with particular wavelengths. In the waveguide with void defects, acoustic phonons whose frequencies approach zero can transport without scattering. The acoustic phonons propagating in the waveguide with clamped material defects, the phonons frequencies must be larger than a threshold frequency. It is also found that the thermal conductance versus temperature is qualitatively different for different types of defects. At low temperatures, when the double defects are void, the universal quantum thermal conductance and a thermal conductance plateau can be clearly observed. However, when the double defects consist of clamped material, the quantized thermal conductance disappears but a threshold temperature where mode 0 can be excited emerges. The results can provide some references in controlling thermal conductance artificially and the design of phonon devices. 相似文献