Structure Evolution And Electrical Transport Properties Of Silicon Nanowires

In recent years, one-dimensional nanomaterials received more and more attention in the academic field due to their excellent characteristics in physics, chemistry, optical and electrical aspects. Because of the specific fluorescence, UV optical properties, field emission, electron transport electrical properties, high surface activity, quantum confinement effect and the Coulomb blocking effects, silicon nanowire is likely to become one of the most ideal materials for manufacturing nanoelectronic devices. It has recently been demonstrated that individual silicon nanowires can be used to fabricate nanoelectronic devices such as nanoscale field effect transistors (FET), nanosensors etc. Therefore, the detailed investigations on the structures and electronic transport properties of silicon nanowires provide significant contribution to the design of nanometer-sized electronic devices.This thesis mainly simulates the structure evolution of the silicon nanowires confined in CNTs using the DISCOVER module of the MATERIALS STUDIO molecular modeling software packages.We also calculate the physical properties, such as density of states, transmission functions, current-voltage (I-V) characteristics, and conductance spectra (G-V) of optimized nanowires sandwiched between two gold contacts. We find that the structures of nanowires are related to the size of the CNTs, rather than the chirality of the CNTs. With the radii of the CNTs increasing continuously, the formed nanowires are composed of coaxial cylindrical shells, and each shell is formed by helical atomic rows. The conductivity of the silicon nanowires are strongly influenced by the geometric structure and the size, especially the former. Electrons transmits more easily in the linear nanowires than in spiral nanowires. As the increase of the length, the electrical properties of the single-chain nanowire vary little, but drop down by leaps and bounds when the nanowire is formed by three helical chains.This thesis also investigates the influence on the electrical properties of silicon nanowires when doping metal atoms into them or adsorbing different molecules on the surface. Our results indicate that after doping metal atoms, the structure of the silicon nanowire transform from order to disorder, while, the current-voltage (I-V) characteristics and conductance spectra (G-V) decrease. Furthermore, with the increase of the number of impurity atom, electrical properties gradually reduced. Because the surface adsorption content will enhance the surface electronic scattering of the silicon nanowires, different molecular adsorption can make the electrical properties reduce. The sensitive degree of silicon nanowires adsorption is:metal atoms> polarity molecules> neutral molecules. In addition, the current-voltage (I-V) characteristics and conductance spectra (G-V) decrease as the number of the adsorption increases.