共查询到20条相似文献,搜索用时 15 毫秒
1.
Modulated nanowires have been proposed as candidates for efficient thermoelectric applications. It has been previously shown within the low-temperature ballistic regime of phonon transport that the thermal conductivity can be significantly reduced when the width of the nanowire is modulated. Here, we report on the thermal conductivity of modulated Si nanowires calculated within a kinetic theory model. The size dependence is taken into account through the sampling of k-points in the first Brillouin zone and a frequency-dependent calculation of the boundary scattering length. It has been found that the thermal conductivity of modulated nanowires can be drastically reduced compared with that of nanowires with constant width. Interestingly, the thermal conductivity is even smaller than that of corresponding straight wires with width equal to the smallest width in the modulated nanowires. The dramatic decrease of the thermal conductivity of modulated nanowires is attributed to their small transmissivity. 相似文献
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Russian Microelectronics - The effective thermal conductivity coefficient of a binary semiconductor heterostructure is calculated by an example of the GaAs/AlAs superlattice at different layer... 相似文献
3.
Hossein Karamitaheri Neophytos Neophytou Mohsen Karami Taheri Rahim Faez Hans Kosina 《Journal of Electronic Materials》2013,42(7):2091-2097
We study the effect of confinement on the phonon properties of ultra-narrow silicon nanowires of side sizes of 1 nm to 10 nm. We use the modified valence force field (MVFF) method to compute the phononic dispersion and extract the density of states, the transmission function, the sound velocity, the ballistic thermal conductance, and boundary-scattering-limited diffusive thermal conductivity. We find that the phononic dispersion and the ballistic thermal conductance are functions of the geometrical features of the structures, i.e., the transport orientation and confinement dimension. The phonon group velocity and thermal conductance can vary by a factor of two depending on the geometrical features of the channel. The 〈110#x232A; nanowire has the highest group velocity and thermal conductance, whereas the 〈111#x232A; has the lowest. The 〈111#x232A; channel is thus the most suitable orientation for thermoelectric devices based on Si nanowires since it also has a large power factor. Our findings could be useful in the thermal transport design of silicon-based devices for thermoelectric and thermal management applications. 相似文献
4.
Anisotropic and Ultralow Phonon Thermal Transport in Organic–Inorganic Hybrid Perovskites: Atomistic Insights into Solar Cell Thermal Management and Thermoelectric Energy Conversion Efficiency 下载免费PDF全文
Energy‐related functionality and performance of organic–inorganic hybrid perovskites, such as methylammonium lead iodide (MAPbI3), highly depend on their thermal transport behavior. Using equilibrium molecular dynamics simulations, it is discovered that the thermal conductivities of MAPbI3 under different phases (cubic, tetragonal, and orthorhombic) are less than 1 W m?1 K?1, and as low as 0.31 W m?1 K?1 at room temperature. Such ultralow thermal conductivity can be attributed to the small phonon group velocities due to their low elastic stiffness, in addition to their short phonon lifetimes (<100 ps) and mean‐free‐paths (<10 nm) due to the enhanced phonon–phonon scattering from highly‐overlapped phonon branches. The anisotropy in thermal conductivity at lower temperatures is found to associate with preferential orientations of organic CH3NH3+ cations. Among all atomistic interactions, electrostatic interactions dominate thermal conductivities in ionic MAPbI3 crystals. Furthermore, thermal conductivities of general hybrid perovskites MABX3 (B = Pb, Sn; X = I, Br) have been qualitatively estimated and found that Sn‐ or Br‐based perovskites possess higher thermal conductivities than Pb‐ or I‐based ones due to their much higher elastic stiffness. This study inspires optimal selections and rational designs of ionic components for hybrid perovskites with desired thermal conductivity for thermally‐stable photovoltaic or highly‐efficient thermoelectric energy harvesting/conversion applications. 相似文献
5.
We employ a fast Monte Carlo solver, which takes advantage of the geometric symmetry existent in the system to reduce the
computational effort, to investigate the phonon transport phenomena in the cross-plane and in-plane directions of Si/Ge superlattice
thin films. The simulation results show that the heterogeneous interfaces perpendicular to the heat flow direction create
a much stronger thermal resistance than the parallel ones. The cross-plane and in-plane thermal conductivities of a Si/Ge
superlattice thin film increase monotonically with the smoothness of the interfaces and the superlattice period. Most of all,
a minimum of the in-plane thermal conductivity is observed as the ratio of the layer thicknesses is varied for fixed period.
This is due to the effective layer thermal conductivities being determined not only by the phonon intrinsic properties but
also by the strong interface scattering. A detailed examination shows that the minimum appears when the effective layer thermal
conductivities of the Si and Ge layers are about the same. 相似文献
6.
Mallory E. DeCoster Xin Chen Kai Zhang Christina M. Rost Eric R. Hoglund James M. Howe Thomas E. Beechem Helmut Baumgart Patrick E. Hopkins 《Advanced functional materials》2019,29(46)
This work studies the thermal conductivity and phonon scattering processes in a series of n‐type lead telluride‐lead selenide (PbTe–PbSe) nanostructured thin films grown by atomic layer deposition (ALD). The ALD growth of the PbTe–PbSe samples in this work results in nonepitaxial films grown directly on native oxide/Si substrates, where the Volmer–Weber mode of growth promotes grains with a preferred columnar orientation. The ALD growth of these lead‐rich PbTe, PbSe, and PbTe–PbSe thin films results in secondary oxide phases, along with an increase microstructural quality with increased film thickness. The compositional variation and resulting point and planar defects in the PbTe–PbSe nanostructures give rise to additional phonon scattering events that reduce the thermal conductivity below that of the corresponding ALD‐grown control PbTe and PbSe films. Temperature‐dependent thermal conductivity measurements show that the phonon scattering in these ALD‐grown PbTe–PbSe nanostructured materials, along with ALD‐grown PbTe and PbSe thin films, are driven by extrinsic defect scattering processes as opposed to phonon–phonon scattering processes intrinsic to the PbTe or PbSe phonon spectra. The implication of this work is that polycrystalline, nanostructured ALD composites of thermoelectric PbTe–PbSe films are effective in reducing the phonon thermal conductivity, and represent a pathway for further improvement of the figure of merit (ZT), enhancing their thermoelectric application potential. 相似文献
7.
Hsin Wang Wallace D. Porter Harald Böttner Jan König Lidong Chen Shengqiang Bai Terry M. Tritt Alex Mayolet Jayantha Senawiratne Charlene Smith Fred Harris Patricia Gilbert Jeff Sharp Jason Lo Holger Kleinke Laszlo Kiss 《Journal of Electronic Materials》2013,42(6):1073-1084
For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current values of 1.0 to 1.5 would enhance their competitiveness with alternative technologies. In recent years, the most significant improvements in ZT have mainly been due to successful reduction of thermal conductivity. However, thermal conductivity is difficult to measure directly at high temperatures. Combined measurements of thermal diffusivity, specific heat, and mass density are a widely used alternative to direct measurement of thermal conductivity. In this work, thermal conductivity is shown to be the factor in the calculation of ZT with the greatest measurement uncertainty. The International Energy Agency (IEA) group, under the implementing agreement for Advanced Materials for Transportation (AMT), has conducted two international round-robins since 2009. This paper, part II of our report on the international round-robin testing of transport properties of bulk bismuth telluride, focuses on thermal diffusivity, specific heat, and thermal conductivity measurements. 相似文献
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《Electron Devices, IEEE Transactions on》2008,55(11):2886-2897
10.
Effect of Nanopores on the Phonon Conductivity of Crystalline CoSb3: A Molecular Dynamics Study 总被引:1,自引:0,他引:1
Xu-qiu Yang Peng-cheng Zhai Li-sheng Liu Gang Chen Qing-jie Zhang 《Journal of Electronic Materials》2014,43(6):1842-1846
Molecular dynamics simulations have been performed to investigate the effect of nanometer-size pores on the phonon conductivity of single-crystal bulk CoSb3. The cylindrical pores are uniformly distributed along two vertical principal crystallographic directions of a square lattice. Because pore diameter and porosity are two key factors that could affect the performance of the materials, they were varied individually in the ranges a 0–6a 0 and 0.1–5%, respectively, where a 0 is the lattice constant of CoSb3. The simulation results indicate that the phonon conductivity of nanoporous CoSb3 is significantly lower than that of no-pore CoSb3. The reduction of phonon conductivity in this simulation was consistent with the ballistic–diffusive microscopic effective medium model, demonstrating the ballistic character of phonon transport when the phonon mean-free-path is comparable with or larger than the pore size. Reducing pore diameter or increasing porosity are alternative means of effective reduction of the thermal conductivity of CoSb3. These results are expected to provide a useful basis for the design of high-performance skutterudites. 相似文献
11.
Cynthia Rodenkirchen Matteo Cagnoni Stefan Jakobs Yudong Cheng Jens Keutgen Yuan Yu Matthias Wuttig Oana Cojocaru‐Mirdin 《Advanced functional materials》2020,30(17)
The thermoelectric compound (GeTe)x(AgSbTe2)1?x, in short (TAGS‐x), is investigated with a focus on two stoichiometries, i.e., TAGS‐50 and TAGS‐85. TAGS‐85 is currently one of the most studied thermoelectric materials with great potential for thermoelectric applications. Yet, surprisingly, the lowest thermal conductivity is measured for TAGS‐50, instead of TAGS‐85. To explain this unexpected observation, atom probe tomography (APT) measurements are conducted on both samples, revealing clusters of various compositions and sizes. The most important role is attributed to Ag2Te nanoprecipitates (NPs) found in TAGS‐50. In contrast to the Ag2Te NPs, the matrix reveals an unconventional bond breaking mechanism. More specifically, a high probability of multiple events (PME) of ≈60% is observed for the matrix by APT. Surprisingly, the PME value decreases abruptly to ≈20–30% for the Ag2Te NPs. These differences can be attributed to differences in chemical bonding. The precipitates' PME value is indicative of normal bonding, i.e., covalent bonding with normal optical modes, while materials with this unconventional bond breaking found in the matrix are characterized by metavalent bonding. This implies that the interface between the metavalently bonded matrix and covalently bonded Ag2Te NP is partly responsible for the reduced thermal conductivity in TAGS‐50. 相似文献
12.
显微拉曼光谱法对多孔硅热导率的研究 总被引:1,自引:0,他引:1
多孔硅优良的热学性能使其成为MEMS领域新兴的热绝缘材料。文中采用一种简便且无损的多孔硅热导率测量技术——显微拉曼光谱技术对电化学腐蚀法制备的不同孔隙率和厚度的多孔硅试样热导率进行了测量,结果表明在多孔硅的拉曼谱峰位置与其温度间存在线性对应关系。在所有样品中,厚度为110μm空隙率为65%的多孔硅显示出最好的绝热性能,其热导率为0.624W/mK。且随多孔硅孔隙率和厚度的减小,其热导率有迅速增加的趋势(厚度和孔隙率为9μm和40%时,其热导率升至25.32W/mK)。 相似文献
13.
S. Yu. Davydov 《Semiconductors》2018,52(7):921-925
In the context of the cluster model of epitaxial graphene, the condition for a stepwise change in the charge of carbon atoms under the action of graphene–substrate electron–phonon interaction and an external electric field is derived. Such charge transfer brings about corresponding steps of the static conductivity and work function of epitaxial graphene. Numerical estimates for the case of weak coupling of quasi-free graphene with metal and semiconductor substrates are given. 相似文献
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采用热分解ZnO粉末法,以Au为催化剂,在Si(100)衬底上外延生长了ZnO纳米线阵列。用扫描电子显微镜(SEM)分析表明:ZnO纳米线的直径在100nm左右,长度约3μm,与衬底表面的夹角约为70.5°,纳米线具有四个特定的倾斜方向A,B,C,D。X射线衍射(XRD)图谱上只有ZnO(0002)衍射峰,说明ZnO纳米线沿C轴择优生长。结合Si与ZnO的晶格结构特征,理论研究得出ZnO纳米线与Si基片的晶格匹配关系为:[0001]_(ZnO)∥[114]_(Si),[0001]_(ZnO)∥[■■4]_(Si),[0001]_(ZnO)∥[1■4]_(Si),[0001]_(ZnO)∥[■14]_(Si),失配度为1.54%。得出了Si(100)衬底对ZnO纳米线生长方向具有控制作用的结论。 相似文献
16.
F. Völklein H. Reith M. C. Schmitt M. Huth M. Rauber R. Neumann 《Journal of Electronic Materials》2010,39(9):1950-1956
This paper focuses on the determination of thermal and electrical properties of individual thermoelectric nanowires, primarily
bismuth and bismuth compound nanowires, as functions of their crystallinity, diameter, and composition. For measurements of
the Seebeck coefficient and the electrical and thermal conductivity, specially designed microchips have been developed and
employed. Finite-element simulations demonstrate that the temperature profiles of the microchips provide suitable temperature
gradients for Seebeck-effect measurements and heat-sink conditions for thermal conductivity investigations. First measurements
of thermal conductivity of metallic nanowires and of Seebeck coefficients of granular nanowires prepared by focused electron-beam-induced
deposition are presented. Some of these results are discussed in the framework of finite-size-effect theory. 相似文献
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The temperature dependence of the thermal conductivity κ(T), electrical resistivity ρ(T), and Seebeck coefficient S(T) of Mg2Sn:Ag crystals with 0 at.% to 1 at.% Ag content were measured at T = 2 K to 400 K. The crystals were cut from ingots that were prepared by the vertical Bridgman method. Undoped samples show
a dramatic κ ∝ T
3 rise at low temperatures to a peak value κ
15K = 477 W m−1 K−1. This leads to exceptionally large phonon drag effects causing giant thermopower with S rising sharply to a peak value S
20K = 3000 μV K−1. At higher temperatures S decreases and changes sign to intrinsic values S ≈ −60 μV K−1. The addition of Ag changes the transport properties as follows: (a) κ decreases systematically, the peak shifts to 30 K and falls to 7 W m−1 K−1; (b) ρ changes from high to low values; (c) S(T) changes to a linear dependence with S
300K ≈ 150 μV K−1 to 200 μV K−1. 相似文献
19.
Si1-xGex/Si应变材料的生长及热稳定性研究 总被引:1,自引:1,他引:1
利用分子束外延(MBE)技术生长了Ge组份为0.1-0.46的Si1-xGex外延层。X射线衍射线测试表明,SiGe/Si异质结材料具有良好的结晶质量和陡峭界面,其它参数与可准确控制。通过X射线双晶衍射摆曲线方法,研究了经700℃、800℃和900℃退火后应变SiGe/Si异质结材料的热稳定性。结果表明,随着退火温度的提高,应变层垂直应变逐渐减小,并发生了应变弛豫,导致晶体质量退化;且Ge组分越小,Si1-xGex应变结构的热稳定性越好;室温下长时间存放的应变材料性能稳定。 相似文献
20.
Shunsuke Nishino Mikio Koyano Koichiro Suekuni Keisuke Ohdaira 《Journal of Electronic Materials》2014,43(6):2151-2156
For this study, we developed a thermal conductivity, κ, measurement system using 3ω method. We checked the system accuracy by measuring κ for a glass substrate (1737; Corning). Conventional evaporated aluminum wire and ink-jet printed silver wire were used as sensor wires. The system realized a κ measurement of glass within 10 % error. We estimated κ of aggregated p-type (Bi1?x Sb x )2Te3 particles using a two heat flow model. The estimated thermal conductivity of the sample κ sample are 0.06–0.27 WK?1 m?1, which is smaller than the bulk value. 相似文献