准一维纳米结构热电转换机理及其性能调控

发布时间：2018-04-10 01:08

本文选题：纳米线　切入点：纳米带　出处：《湖南大学》2015年博士论文

【摘要】：随着能源短缺、环境污染问题日益严重,开发高性能热电材料和高效热电转换技术引起了世界各国的高度重视。准一维纳米结构材料一方面可以利用强烈的声子-边界散射来降低晶格热导率,另一方面可以利用量子限制效应提高功率因子,从而提高其热电性能。本论文运用第一性原理结合玻尔兹曼输运方程和非平衡格林函数方法,以及分子动力学方法系统研究了准一维纳米体系(纳米带,纳米管和纳米线)中的热输运和热电性质,并得到一些有意义的结果。首先,我们利用非平衡分子动力学方法研究了不同尺寸和不同生长方向的砷化铟纳米线的声子热输运性质。计算结果表明砷化铟纳米线的热导率具有显著的各向异性特征。并且发现其沿着[110]方向生长的纳米线热导率要比沿着[100]和[111]方向生长的纳米线热导率大三倍左右。随着温度的升高,沿着[110]方向生长的纳米线热导率会迅速下降。然而,其他两个方向上的热导率对温度变化不太敏感。另外,我们还发现随着砷化铟纳米线长度的增加,会出现从弹道热输运到弹道-扩散混合热输运的转变,并且对这些结果给出了简要的物理分析。我们还推测出具有闪锌矿结构纳米线的热导率都有各向异性特征。其次,运用非平衡格林函数方法,我们研究了砷化铟纳米管的热电性质。研究结果表明,由于量子限制效应的增强而导致功率因子的增加,使得具有某一特定内径的砷化铟纳米管比砷化铟纳米线具有更高的热电优值。砷化铟纳米管的热电优值可以达到1.74,这一数值相当于砷化铟纳米线热电优值的三倍左右。另外,我们还发现砷化铟纳米管的热电优值随着内径的增加而急剧减少,这是由于低频率光学声子模的“红移”导致声子热导急剧增加而造成的。接着,运用非平衡格林函数方法和分子动力学模拟方法,我们研究了多重核壳纳米线的热电性能。结果表明:与单一成分的纳米线比较,多重核壳纳米线的热电性能随着壳层数的增加而显著提高,这是因为其声子热导能够明显减小。在室温下,Ga Sb/In As多重核壳纳米线的热电优值是单一成分的Ga Sb纳米线的三倍。另外,我们还发现核壳纳米线和单一成分纳米线的热电优值都随着温度升高而增大,但是核壳纳米线热电优值的增加速度要比单一成分纳米线的热电优值增大的缓慢。这些结果表明单一成分纳米线更适合做高温度下的热电材料,而多重核壳纳米线更合适做室温下的热电材料。然后,运用非平衡格林函数方法,我们系统地研究了四种典型的石墨炔纳米带的热电性质。结果表明:由于高的功率因子和低的声子热导,β-,γ-和(6,6,12)-石墨炔纳米带表现出优异的热电性能,他们的热电优值可以达到石墨烯纳米带热电优值的10倍。另外,我们也研究了引入缺陷对β-型石墨炔热电性质的影响。我们发现含有缺陷的β-型石墨炔纳米带具有比理想β-型石墨炔更高的热电优值。含有缺陷的β-型石墨炔的热电优值可达1.64,是理想β-型石墨炔纳米带热电优值的六倍左右,这是由于缺陷所产生的声子局域态对声子产生强烈的散射,导致声子热导急剧减少,而与此同时时功率因子并没有恶化引起的。最后,运用第一性原理计算结合声子玻尔兹曼输运方程,我们系统地研究了单层WSe_2的声子输运。跟其他二维材料比较,发现单层WSe_2具有超低热导率,这是由于超低的德拜频率和重的原子质量导致的。在室温下,1μm典型样本的热导率是3.98W/m K,比Mo S2要低一个数量级,10nm大小样本的热导率可以进一步降低大约95%。并且,我们发现ZA声子模对热导率起主导作用,在室温下的相对贡献几乎达到80%,明显比单层Mo S2要高。这是因为在单层WSe_2中,ZA声子模比LA声子模和TA声子模具有更长的声子寿命。
[Abstract]:With the energy shortage and environmental pollution problems have become increasingly serious, the development of high performance thermoelectric materials and high thermoelectric conversion technology has attracted great attention around the world. A quasi one dimensional nanostructure materials can reduce lattice thermal conductivity using strong phonon boundary scattering, on the other hand can improve the power factor of the quantum confinement effect, so as to improve the thermoelectric properties. This paper using the first principle combined with the Boltzmann transport equation and non-equilibrium Green function method, and the molecular dynamics method of quasi one dimensional nano system (nanobelts, nanotubes and nanowires) in the heat transport and thermoelectric properties, and get some meaningful results. Firstly, the phonon thermal indium arsenic we use non-equilibrium molecular dynamics method to study the different dimensions and the growth direction of the nanowires. The calculation results show that the transport properties of indium arsenide The thermal conductivity of nanowires has obvious anisotropic characteristics. And the growth along the [110] direction of the nanowires thermal conductivity than the growth along the [100] direction and [111] direction of the nanowire thermal conductivity is about 3 times. With the increase of temperature, the growth along the [110] direction of the nanowires thermal conductivity decreased rapidly. However, the thermal conductivity of other the two direction of the rate is not too sensitive to temperature change. In addition, we also found that with the increase of InAs nanowire length, will shift from ballistic thermal transport to ballistic diffusion heat transport, and the results are given a brief analysis of the physics. We also speculate that thermal conductivity of sphalerite the structure of the nanowire rate are anisotropic characteristics. Secondly, using the non-equilibrium Green's function method, we study the thermoelectric properties of indium arsenide nanotubes. The results show that, due to the enhancement of quantum confinement To increase the power factor, the indium arsenide nanotubes with a specific diameter has a higher value than thermoelectric InAs nanowires. Thermoelectric InAs nanotubes could reach a value of 1.74, about three times the equivalent of InAs nanowires. Another figure of merit we also found that thermoelectric indium arsenide nanotubes with diameter value increased sharply, which is caused by the low frequency optical phonon mode "red shift" led to a sharp increase in phonon thermal conductivity. Then, using the Green function method and non equilibrium molecular dynamics simulation method, we study the thermoelectric properties of multiple core shell nanoparticles line. The results showed that: compared with the single component of the thermoelectric properties of nanowires, multiple core-shell nanowires increased with the increase of layers of shell, this is because the phonon thermal conductivity can obviously decrease. At room temperature, Ga Sb/In A Thermoelectric s multiple core-shell nanowires is three times the value of Ga Sb nanowires with single component. In addition, we also found that the thermoelectric core-shell nanowires and nanowire single component values are increased with the increase of temperature, but CSNWs ZT value increased faster than a single figure of merit divided into nanowires increases slowly. These results indicate that single component nanowires are more suitable for high temperature thermoelectric materials, and multiple core-shell nanowires more suitable as thermoelectric material at room temperature. Then, using the non-equilibrium Green's function method, we systematically studied the four kinds of typical nano thermoelectric properties of graphdiyne belt. The results showed that: the high power factor and low phonon thermal conductivity, beta, and gamma (6,6,12) - graphdiyne nanoribbons exhibited excellent thermoelectric properties, their ZT value of 10 times can reach graphenenanoribbon ZT value. On the other Outside, we also studied the effect of introducing defects on beta type graphdiyne thermoelectric properties. We found defective beta type graphdiyne nanoribbons with thermoelectric higher than ideal beta type graphdiyne value. ZT defective beta type Shi Moque is 1.64 and the value is about six times the ideal beta type graphite alkyne nanobelts figure of merit, which is due to phonon localized states defects generated by strong scattering of phonon, phonon thermal conductivity leads to decreased rapidly, while at the same time when the power factor is not caused. Finally, combined with the calculation of phonon Boltzmann transport equation using the first principle, our system study of phonon transport of WSe_2 monolayer. Compared with the other two materials, found that the single WSe_2 with ultra low thermal conductivity, which is due to the Debye frequency ultra low and heavy atom quality result. At room temperature, the thermal conductivity of 1 m typical sample The rate is 3.98W/m K, an order of magnitude lower than that of Mo S2, 10nm thermal conductivity of sample size rate can be further reduced about 95%. and ZA, we found that the leading role of phonon thermal conductivity at room temperature, the relative contribution of almost 80%, significantly higher than single Mo S2 to high. This is because in the single 2 WSe_, the ZA phonon phonon lifetime is longer than the LA phonon and TA phonon modes.

【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.1

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