Computational Investigations Of Transproperties Of The Molecular Switch And Crossed Nanotubes

This paper can be divided in to two segments.Quantum chemical study on transport properties and electronic structure of optical molecular switchesAccording to experimental study about reversible, light-controlled conductance switching of molecular devices based on photochromic diarylethene molecules. A systematic investigation of transport properties and electronic structure of two molecular switches we designed in which using first-principles is represented. In our calculation, we demonstrate a two probe system which consist of a segment of diarylethene connected with either two nano-scale CNT(6,0) electrodes or two bulk Au(111)electrodes. Our results reveal that theâ… -â…¤curves of "off" state of two swithes exhibit clear current suppression, no matter what the electrodes are. But as to the "on" state, theâ… -â…¤curve exhibits complete nonlinear behavior and NDR phenomenon was observed when electrodes are CNT(6,0) while exhibits clearly linear behavior when electrodes are bulk Au. The two systems are all exhibiting typical switching effects. To get more insight information, we track the spatial structure from the Frontier molecular orbits of two states of systems when electrodes are CNT(6,0) to make a reasonable guess, and design another system coupled with the gold electrodes to verify our conclusions. That is, electronic structure of molecular is a crucial factor for the transport properties of molecular devices, while the electrode band structures, the molecular orbital energy levels and the coupling conditions between electrodes and system are all playing important roles for the transport properties of molecular devices.Transport properties and mechanism of crossed carbon nanotubes with Haeckelite defect In the second segment we pay our attentions on the longitudinal transport properties of carbon nanotubes and potential influence of the defects. By applying non-equilibrium Green's functions in combination with the density-functional theory, we investigate the electronic transport properties of crossed CNT and crossed CNT with Haeckelite defect (crossed HNT). We focuses on the transport properties of erect carbon nanotubes and the affect the Haeckelite defect may bring. Our results suggest that, the transport properties of four systems under two kinds electrodes are totally different. Furthermore, by comparing the results, we found, crossed HNT'sâ… -â…¤curve shows a linear feature when CNT (6,0) are electrodes, and crossed CNT is showing a completely non-linear characteristics, intermittent NDR phenomenon was observed. Besides, by comparing the transport spectrum and density of state of the equilibrium states at Fermi level of two systems, we found that the transfer of electronics between electrodes and system would introduce metal-induced gap states(MIGS) especially at low bias when electrode are gold. And the origin of NDR is the variation of the transmission spectrum caused by the applied bias.