Theoretical Studies On The Rectification Of Molecular Devices Based On Doped Graphene Electrodes

Since1947, the first transistor invented by Shockley et al has emerged. The development ofsilicon-based semiconductors is so amazing that it reaches to a large integrated scale now. Withthe further development of devices’ miniaturization, nanoelectronic devices are considered toreplace traditional silicon-based devices, thus they get widespread attention. Molecular device isone of the main candidates for nanoelectronics devices. Among them, the molecular rectifiers asa kind of basic function molecular devices become the scientists’ hotspot. Currently there are alot of rectified mechanism types of the molecular rectifiers. Generally people considered thepresence of asymmetry in molecular devices can cause rectification from the point of view ofstructure. During the40years from the proposed molecular rectification idea to now, althoughresearch work has yielded a lot of results, there is still a distance from practical applications. Inthe preparation of molecular rectifiers and the research of rectifying mechanisms, there are stillmany problems to be solved, such as stability and reliability of the rectifying molecules,rectifying properties, the rectifiers’ repeatability as well as the dependence on external conditionsand so on.Additionally, graphene as a new carbon-based material has been found since2004, due toits unique geometry and distinctive electrical properties, researchers consider that it is an idealcandidate material to be hopeful to replace the traditional silicon-based devices, which is givenwidespread attention by a large number of researchers. Especially graphene nanoribbons areformed by cutting graphene in a particular way. They have become an ideal choice for integratedcircuit interconnected material because of their excellent characteristics with high conductivity,low noise etc.In this paper, based on non-equilibrium Green’s function method combining densityfunctional theory, our work is the theoretical study of the electronic transport properties of OPEmolecule attached zigzag graphene nanoribbons electrodes. We don’t find rectifying behaviorwhen molecular devices use pure graphene electrodes. Through the middle or the edge of theright graphene electrodes doped with boron atom or nitrogen atom periodically, we detected theI-V curve showed significant asymmetry, and observed obvious rectifying phenomenon. Theresults show that the rectified direction is the same by doping, while the edge side of the rightgraphene nanoribbons electrodes is doped, we are able to get the greater rectification ratio. Forthe two different doping atoms, the rectifying characteristics of the boron atom compared with the nitrogen atom are more prominent. While we calculate the molecular devices with doublenitrogen-doped graphene electrodes, the current shows a significant oscillation behavior inaddition. Our results provide guidance information for the design of functional molecular devicesbased on graphene nanoribbons.This thesis is divided into four chapters as follows. The first chapter is introduction part. Itis a brief introduction to the rectifying types of molecular rectifiers and the research advances ofcarbon-based molecular rectifiers, as well as the research on graphene and graphene nanoribbons.The second chapter is the theoretical part that introduces the first-principles calculation methods,adiabatic approximation, Hartree-Fock method and the density functional theory, a commonlyused tool to study the electronic structure, and the non-equilibrium Green’s function method,which is usually used to solve the electron transport properties in nanoscale. In addition, we alsopresent the combination of the density functional theory and nonequilibrium Green’s functionmethod to get molecular devices electron transport properties through self-consistent solutionprocess. The third chapter describes my calculations and the corresponding results by using theabove method. We study mainly the transport properties of OPE molecule attached zigzaggraphene nanoribbons electrode. We focus on the impact of rectifying properties of moleculardevices with boron-or nitrogen-doped graphene electrodes, and explain their rectificationmechanisms. The fourth chapter is a brief summary and outlook for our work.