| Summary: | 碩士 === 中原大學 === 物理研究所 === 100 === 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.
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