| As the rapid development of information technology (IT), the quantum effect was playing a more and more important role in the inorganic semiconductor based integrated circuit, which would have been a dominating effect on the charge transport. Therefore, there were heavily increasing numbers of difficulties in designing and manufacturing new applications with higher levels of integration and performance, which lead to the whole IT industry slow down its steps. The new route to the new generation electronics must be found to continue the trend of the advancements, the Moore’s Law. The molecular electronics was one of the most popular reasonable routine to solving the embarrassment, which meant a "bottom-up" self-assembly construction of molecular circuits with functional organic groups.During the nearly30years, molecular electronics developed quickly, with the inventions of technologies of STM, MCBJ, AFM, SAM, C60, CNT, Grphene and etc. The molecular electronics now had been an interdisciplinary research area, blending concepts and technologies from physics, chemistry, material and biological science. In large number of the research points, the issue on molecular rectification and rectifier were the hottest one and kept attracting eyes of researchers intensively.In this thesis, after reviewing the progress of the IT industry and the molecular electronics, we depicted three models for molecular rectification. And then, we described the theoretical models and methods, such as the SSH Hamiltonian, Green’s Function method, SSH+NEGF method, First Principle Calculation method and DFT+NEGF method. In the next part, we focused and discussed on some excellent experimental results reported by several groups.Firstly, according to the experiments of Yu et al., we employed an extended SSH type tight-binding Hamiltonian coupled with the NEGF method to simulate the2Ph2Py based molecular rectifier successfully. We explained the rectifying mechanism in this conjugated molecule. Then we found that the inner molecular electric dipole moment could be modulated by electron-lattice coupling, which was a key factor for the charge transport. The dipole moment decreased linearly with the e-1coupling increasing, while the positive threshold bias voltage increased contrarily.Secondly, according to the Whitesides’AFM experiments on SAM of HSC11Fc molecule, we performed a DFT+NEGF calculation to simulate the junctions. The rectification in the HSC11Fc based junction was confirmed as its inner molecular property by study a series of junctions with two symmetric electrodes (Au(111)/HSCnFc/Au(111), n=11,9,7). Corresponding to the experimental results, the rectifying ratio (RR) of HSC11Fc was larger than100, however, the RR of HSC11Fc was less than10. According to the analysis on its mechanism, we believed that this was a π-σ type rectifier. By revising the Whitesides’explanation, we interpreted the great difference of RRs between the cases of n=9and n=7. Meanwhile, it was pointed out that the giant RR did not work unless the molecule was long enough. On the other hand, because of the saturated alkyl chain in the junction, the conductance was pretty low, therefore, the current was rather poor. This was not good for the future application. As a result, we designed a gate modulating1,4-(phenyl)4based transistor, which could work as an excellent direction reversible rectifier with sufficient conducting ability.Thirdly, a deeper study of the2Ph2Py molecular junction was performed by taking a DFT+NEGF calculation. The interaction between e-1coupling and charge transfer in this π conjugated molecular rectifier was exhibited. Especially, the lattice distortion was represented concretely by the relative torsions between the phenyl rings, which severely affected the charge transportation. Finally, it could be seen the distortion was of the essence in the rectifying progress.Finally, we summarized our work and gave an outlook of this field. |
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