| Molecular electronics is a research whic h aimed at the electronic transport characteristics on the molecular level or molecular scale. The goal of the molecular electronics is to assembling a molecular computer completely by using the single molecule, super molecule or molecular cluster instead of silicon semiconductor transistor solid-state electronics components such as the assembly logic circuit in our daily life in the future, and to further promote the industrialized production. In this paper, we investigate the spin transport properties of a molecule consisting of two phenyl-rings connected by N and transition metal atoms by nonequilibrium Green's function method combined with density function theory. The molecule is coupled to two zigzag graphene nanoribbon electrodes. The main research of this article is to use the benzene molecule which is such simple and common. And the system can be use modulated and controlled easily to let it have some perfect electron transport properties such as switch effect, rectification effect, spin filtering eff ect, magnetoresistance effect and negative differential resistance effect. So a multi-functional molecular device contains such electronic transport properties can be designed, and the main results were as follows:First, the electron transport properties of different transition metal atoms(including Co, Fe, Mn and Cr atoms) were compared in the benzene rings systems, and we can found in the results of calculation that the system can have magnetic resistance effect, negative differential resistance effec t, spin filtering effect and other excellent properties. Parts of the transport phenomenon have been explained by the transmission spectrum under different bias. By the comparison of different transition metal atoms, the comprehensive properties of Co atom s in the system can be more suitable for designing a molecular device. At the same time, we also considered the influence of the width of the graphene electrode and select ed the appropriate width of graphene electrodes, thus a more in-depth study were conducted in the next work.A multifunctional molecular device has been designed on the basis of the calculation we have just seen. The value of the current can be changed by rotating the orientation of the phenyl ring from coplanar site to perpendicular site. The reason is the changing of the coupling between the overlapping degree of the carbon chain and benzene ? orbitals can change the value of the current. And the total current decreases a lot, on order of 100, when the orientation of the phenyl ring chang es from coplanar site to perpendicular site. So our molecular device can be used as a controllable molecular current switch. The methods of rotating the benzene molecule can be the method of laser pulse, the electric field, the microscopic mechanical opera tion, methods of thermal drive, and so on.The value of the current at low bias(-0.1 V to 0.1 V) can change sharply by manipulating the magnetic field direction of the graphene electrode, which meanings the giant magnetoresistance effect exist in both the coplanar and the perpendicular conformations at low biases. The calculated magnetic resistance ratio(MR) can be more than 3000. In addition, obvious phenomenon of spin filtering, rectifying effect and the negative differential resistance effect have been shown in the calculation of the transport properties of the spin current. In the condition of magnetic field direction for AP comformation, the value of rectification ratio for the spin up current reaches its maximum 35000. Transport transmission spectrum and explanations via distribution of MPSH of the molecular orbitals in the bias window are used to explain some phenomenon we have just seen. So the switch effect, magnetic resistance effect, spin filtering effect, rectifying effect and the negative diffe rential resistance effect can be set in a molecular device as a multi-functional molecular device. |
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