| As a new type of nano-electrical devices, molecular devices are important using valve in electrical field due to its ascendant electrical properties. By adopting the first-principles calculation based on the density function theory (DFT), we study the electron transport properties of molecular devices and mainly discuss the effect of dopant atoms, distance between molecule and electrode, electrode construction, molecular configuration and adsorption of side group on the electron transport properties of molecular devices. The main contents of this paper are as follows:(1)The effect of Boron and Nitrogen doping alone, Boron/Nitrogen co-doping, and the distance between molecule and electrode on the electronic transport properties of C6o molecular devices is investigated. The results show that the ideal C6o molecular device shows obvious metal properties and the negative differential resistance (NDR). However, the introducing of impurities directly suppresses the electron transport ability of molecular devices. The molecular devices show no NDR with the doping of Boron or Nitrogen individually, while show NDR with the co-doping of Boron and Nitrogen. Variation of the distance between C6o molecule and electrode has great effect on the system’s electron transport properties. As the distance between molecule and electrode increases, electron transport ability becomes weaken significantly due to the couple of molecule and electrode decreasing, and the peak to valley ratio in NDR decreases till disappeared completely.(2) The effect of carbon chain and electrode construction on the electronic transport properties of carbon chain molecular devices is investigated. The results show that the conductivity of carbon chain present obviously odd-even oscillation effect and the electron transport properties of odd carbon chain are stronger than it of even carbon chain. The main cause of the odd-even oscillation effect is that the bond structure of odd carbon chain is double bond which forms a π conjugate structure and is more advantageous to the electron transportation. The C7molecular device shows obvious NDR but no NDR in Cg molecular device. When the electrode construction is not symmetry, the carbon chain molecular device shows rectification due to the symmetry of electrode construction breaking and mismatching between the electrode and the central scattering region. We find that the rectification of C7molecular device is more evident than it of C8molecular device.(3)The electronic transport characters of carbon chain molecular device adsorbing a chemic group (NH2or OH) have been studied. We find that the obvious feature of C7device absorbing a chemic group is the position effect. When the odd serial number of caborn atom is the absorbed site, the ablity of electronic transport of carbon molecular device is markedly weakened. And if the absorbing site is the even serial number, this kind of restrain is getting small. The position effect also exists in C8device, but it is not obvious. After absorbing chemic group, there is negative differential resistance effect in C7device, but not in Cg device. When the chemic group absorbs on the first carbon atom of C8device, the ability of electronic transport is getting strong evidently due to the intrinsic electronic structure broken.(4)The electronic transport characters of double chemic groups adsorbing on carbon chains have been investigated. Firstly, we investigate the double adsorbing on C7molecular device. The results prove that:(a) when an amino group fixes on the first carbon atom and a hydroxy group adsorbs on the even site, there is obvious negative differential resistance effect. If the hydroxy group adsorbs on the odd site, the negative differential resistance effect can not be observed,(b) Since the symmetry of struct is broken, the rectifying effect can be found in all double adsorbing carbon chain devices. Secondly, we investigate the electronic transport of double-group adsorbing on Cg molecular device. We find that:when an amino group fixes on the first carbon atom, the current is very small under low bias. The negative differential resistance effect can be observed when a hydroxy group just adsorbs on the even site. These research conclusions maybe provide theory supports and research basises for designing the molecular devices in experiment. |
