苯基分子元件導電機制之第一性原理研究

First principle study of electron transport mechanism in phenylene-based molecular devices

李品寰(Ping-Huan Lee)

指導教授 ： 鐘元良

中原大學/理學院/物理研究所/碩士(2012年)

https://doi.org/10.6840/cycu201200992

摘要

本論文主要研究以第一原理計算方法分析分子元件的導電特性。我們使用密度泛涵理論以及非平衡態格林函數方法計算單一苯基分子元件的態密度、分子軌域、電子密度分佈和元件的電流-電壓曲線。從計算結果我們發現苯基分子與電極連接時，分子的費米能階和分子內的能階皆會改變，並且在分子與電極的連接處會產生一本質的位能障影響電子的傳輸，使得通過元件的電流與電壓的關係呈現一非線性曲線。接下來，我們改變分子的結構，讓分子上的某一氫原子被胺基取代成為苯胺分子，並分析其電性。從苯胺元件的計算結果我們發現胺基提高分子的費米能階和分子內的能階，然而胺基的孤對電子影響芳香環上的π電子，造成苯胺分子的π鍵數目比苯環分子少一個，以至於通過苯胺元件的電流些微小於通過苯環元件的電流。由分析的結果我們歸納出取代基會影響分子的電子傳輸，不同的取代基會產生不同導電特性的分子元件。另外，我們進一步模擬由胺基聚合而成的聚苯胺(Polyaniline)分子元件的電性，並比較苯環、苯胺和聚苯胺元件之電流-電壓曲線的不同。

關鍵字

密度泛涵理論 ； 非平衡態格林函數 ； 苯胺單體

並列摘要

The first principle calculation in molecular device is studied for electron transport. Our method is based on density functional theory and non-equilibrium Green’s function method to analyze a single phenylene-based molecular device and calculate its density of states, molecular orbits, electron density distribution and current-voltage (I-V) curves. We find that when the phenylene-based molecular is coupled to electrodes, the Fermi level and energy level of the molecule are modified, and an intrinsic potential barrier is formed at the molecule-electrode interface, which has effect on the electron transport, leading to non-linear I-V curves. Furthermore, we change the structure of the molecule. We have a hydrogen atom of the benzene replaced by a substituent-NH2 to become aniline(C6H5NH2) and analyze its electron transport. From the result of the aniline device, we find that the substituent-NH2 gives rise to the Fermi level and energy level of the molecule but its lone pair of electrons affects the π electrons of the aromatic ring, leading to the number of π-bonding of the aniline is reduced by one compared with the benzene. Thus, the current flowing through the aniline devices is slightly smaller than that of the benzene device. Finally, we conclude that the substituent-NH2 could affect the electron transport of the molecule, creating different electrical transport characteristics. On the other hand, we simulate the electrical property of polyaniline device which is composited of the benzenes and anilines. The different I-V curves of the benzene, aniline and polyaniline are compared with each other.

並列關鍵字

non-equilibrium green's function ； density functional theory ； aniline

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