First-principles Study Of The Endoping Effect On Electron Transport Properties Of The CNT-C₆₀-CNT Junction

Based on a recently developed ab initio non-equilibrium Green's function (NEGF) formalism, we have performed first-principles calculations on the electron transport properties of the doping effect in the center of the C60 with Si, Li or Au atoms of the CNT-C60-CNT junction, and the electron transport properties of the endohedral fullerene Li@C60 is also investigated .In chapter one, following the introduction of the development of the electronic devices, we describe the research background of molecular conductor and the experimental method. Summarized the applications of fullerene molecules in nano-devices. In the last part of this chapter, the main contents of this thesis are listed. In chapter two, we introduce some of first-principles calculation methods, i.e., the Density-Function method and the non-equilibrium Green's function, Ab initio NEGF formalism is presented in detail at the end of this chapter.In chapter three, the effect of doping in the center of the C60 with Si, Li or Au atoms on electron transport properties of the CNT-C60-CNT junction is investigated based on the First-principles study. Variations of transport properties under different contact distances are also discussed. The results show that the doping of Li atom increases the equilibrium conductance greatly under equilibrium contact distance, while it is complex for the doping of Si and Au atom. Characteristics of Current-Voltage properties for different systems are also compared.In chapter four, We present an ab-initio study of electron transport through an endohedral fullerene Li@C60 molecule sandwiched between two (4,4) carbon nanotubes electrodes. The equilibrium conductance will be greatly affected by the doping of Li atom, which is related to the contact distance between the electrodes and the central molecule. At large separation, the doping of Li atom switches the conductance from 0.02G0 to 0.80G0 compared with that of bare C60 device. At the same time, the non-equilibrium transport properties are also investigated.