标题: 原子级分子线与金属线奈米接面的热导、电导与热电性质比较
Comparison of electron, thermal transport and thermoelectric properties between molecular
作者: 郭孟学
陈煜璋
Kuo. Meng-Hsueh
Chen,Yu-Chang
电子物理系所
关键字: 第一原理;分子动力学;电导;热导;热电性质;First Principles;molecular dynamics;conductance;thermal conductance;thermoelectric
公开日期: 2017
摘要: 我们利用密度泛函理论(Density Function Theory)结合非平衡格林函数(Non-Equilibrium Green's Function)的理论,并透过第一原理的计算方法来研究不同长度与结构的苯环(BDT)分子线接面与不同长度与粗细的金奈米线接面系统的电子的电导、电子与声子热导、与Seebeck系数,也透过古典非平衡态分子动力学模拟计算的方法来研究奈米系统的声子热导性质,同时也考虑了其在低温时,基于Bose-Einstein distributions的量子修正,并综合比较分线与分子线与金属线接面的热电转换效率[热电优值(ZT)]。首先,我们计算双苯环的最佳化结构,并发现双苯环单分子接面中苯环间夹角增加会导致电导上升。单苯环至五苯环不同长度苯环单分子线接面的电导会随着苯环分子数增加而下降,而在金属线的电导则不会因为长度增加而下降。而在分子线与金属的接面热导研究中发现温度在低于得拜温度下,原子线与金属线的声子声子热导与温度呈现正比关系,而在高于得拜温度时,因为声子的振频已经完全被激发,所以声子热导与温度无明显关系,而在分子线与金属线的热导比较中可以发现在分子线热导是由声子所主导,而在金属线的热导是由电子所主导,而在分子线与金属线的热电优值研究发现,奈米系统的热电优值(ZT)的趋势会与Power Factor一致。
Density Function Theory coupled to Non-Equilibrium Green's Function (NEGF-DFT) has been applied to study the electrical conductance, electron thermal conductance, and the Seebeck coefficient for various lengths and different structures of benzene ring (BDT) single-molecule junctions and gold nanowires systems. Classical non-equilibrium molecular dynamics simulation (NEMD) has been applied to investigate the phonon thermal conductivity of these two nanometer scale system, whereas quantum correction based on Bose-Einstein distributions at low temperature has also been considered to correct the phonon thermal conductance in low-temperature regime. We further investigate and compare their thermoelectric figure of merit (ZT).Firstly, we optimize the structure of the di-benzenedithiol(DBDT), and investigate the dependence of the conductance on the angle between two benzene rings. It was found that the conductance of the DBDT increase with the rising of the angle. We find that the thermal conductance of DBDT single-molecule junctions and gold nanowires junction systems are proportional to temperature in the low-temperature regime. The phonon has been completely excited at temperatures larger than the Debye temperature, so the phonon thermal conductivity and temperature no significant relationship. In contrast to the fact that the phonon’s thermal conductance increases as the temperature increases in low-temperature regime. We observe that the phonon’s thermal current dominates the thermal current in the DBDT single-molecule junctions, while the electron’s thermal current dominates the thermal current in the gold nanowires. The trends of thermoelectric figure of merit (ZT) and the Power Factor with respective to temperature are similar in both the DBDT single-molecule junctions and gold nanowires.
URI: http://etd.lib.nctu.edu.tw/cdrfb3/record/nctu/#GT070352030
http://hdl.handle.net/11536/141119
显示于类别:Thesis