Theoretical Research On Electrical Properties Of Single Molecule Nanometer Devices

Molecular electronic devices have attracted more and more attention. With continuous development in experimental techniques of micro-electronics and improvement of theoretical methods, constructing some functional electronic devices based on single molecules becomes a hot research topic. Last years sees some important theoretical and experimental developments in single molecule science and one of important branches in single molecule science is the investigation on the electrical properties of single molecule devices. The electrical properties of molecular devices is basically determined by the electronic structure of molecules, and influenced by the coupling between the connected electrodes and the central molecules. Molecule devices based on benzene rings has received intensive attention in recent years, due to the existence of highly itinerary -orbital electrons in such structures. In this work we have investigated the electrical properties of some benzene-based molecular structures, as well as the chaotic effects in the I-V characteristics.The thesis consists of six chapters.In the first chapter, we introduce some background knowledge of single-molecular electronic devices, some related experimental techniques and some theoretical methods for the study single-molecular electronic devices. We also explain what we have done and why we did so.In the second chapter, the theory of self-consistent field for many-particle system is presented, which includes Born-Oppenheimer approximation, Hartree-Fock method and the density functional theory.In the third chapter, we introduce Green's function theory after discussing a single level conducting model, and present a general formula to calculate the current within Green's function formalism. We also present some background knowledge for the first-principles simulation software by integrating the non-equilibrium Green's function formalism and the density functional theory.The main body of this paper is in the fourth chapter, in which we conduct some investigations on the electrical properties of single molecule devices sandwiched between two electrodes. We study the influence of the coupling between the molecule and the metal electrode surface on the I-V characteristics of the molecular devices. We find that the electrode spacing, the molecular structure length and molecular configuration have different effects on the electrical properties of molecular devices. We also study two types of organic molecules exhibiting rectifying effect, and discuss five kinds of underlying mechanisms for the rectifying effects. Finally, start by investigating the negative differential resistance effect, we study nonlinearity in I-V characteristic from the chaos. And we investigate the chaotic effects of molecular structures after connecting such structures to a chaotic electric circuit.The main conclusions are given in the last chapter.