Study On Electron Transport Properties Of Silicon And Carbon Nanomaterials

Due to the unique physical properties of low dimensional nano electronic devices,they have attracted much attention in recent years.A major development of electronic devices is miniaturization of electronic devices,low energy consumption,high speed and sensitivity.With the ordered structures and advantages to the directional transmission of carriers,one dimensional nanostructures(nanowire,nanorod,nanoribbon)and one dimensional semiconductor nano array can improve the separation and transmission of electrons and holes,and are considered as the basic materials of next generation nano optoelectronic devices.So far remarkable achievements have been made in nanowire electronics,But there are still many important problems remained unsolved.These problems severely constrain development and application of nanowire electronics.In our study,non-equilibrium green function(extended Huckel theory)and molecular dynamics are employed to systematically investigate the stable Si nanowires encapsulated into CNTs of different chiralities(Armchair and Zigzag)and effect of doped Si nanowres.We studied the structure changes of ultra-thin Si nanowires encapsulated into CNTs,and the electron transport properties of Si nanowires,strongly confirmed unidirectional continuity and the nature of the field effect transistor of doped Si nanowires,revealed the impact of dopant atoms,and studied the regulation of the gate electrode voltage.The results provide a theoretical support for the future development of ultra-fine nanowire electronics,and have important theoretical significance in-depth understanding electron transport mechanisms of low-dimensional Si materials.At last,we discussed graphene conductance of water molecules adsorbed on grapheme.We investigate the possibility of detecting the ordering of adsorbed molecules on graphene sheet.The results have important theoretical significance for the design of graphene sensor.In this thesis,the primary results are given as follows:(1)We studied six structure and electrical transport property of Si nano wire encapsulated into CNTs of different chiralities(armchair and zigzag),calculated current-voltage(?-?)characteristics,conductance spectra(G-V)with external bias and the density of states of the Si nanowires,analyzed transmission functions and conductance spectra of of Ag,Cu,Au Al doped Si nanowires.We found that the structures transformed from a monoatomic chain to helical and multishell coaxial cylinders as the radii of CNTs increased,however,did not change when the chirality transferred from armchair to zigzag.Our studies showed that the structures played an important role in the transport properties of the optimized Si nanowires and the nanowire formed in(11,11)CNT had better conductance than the others.We calculated the conductance spectra and transmission function of the Si—Ag,Si-Cu,Si-Au and Si-Al alloy nanowires.What's worth noting was that,comparing with the pure Si nanowires,the conductance of the alloy nanowires was lower.In other words,doping metal atoms did not improve the electrical conductance of the semiconductor nanowires.(2)The electron properties and electron transport properties of Ge,Cl and N doped ultrathin Si nanowires theoretically studied.Our studies showed that pronounced negative differential resistance is observed in current-voltage curves of these doped Si nanowires,and negative differential resistance is more pronounced when the doped atoms are aggregated in the center of the Si nanowires.Current peaks of Si nanowires are affected by substitutional atoms.There exists a close correlation between the symmetry of current-voltage curves and the position of substitutional atoms of these nanowires.Gate voltages can regulate the open and close states of devices by changing the energy levels of Si nanowires.By analyzing the transmission spectra,we find that gate voltages change the position of energy levels of nanowires,and thereby modulate the current of nanowire devices.The regulatory characteristics are different from the traditional electronic devices.(3)We studied water molecules adsorbed on graphene,and gap of graphene,conductivity and electron transport properties with distribution of water molecules on graphene.we have demonstrated that a linear dependence of the electron transport properties on the molecular ordering of water on the graphene.Our theoretical results indicate that the graphene allows the ultimate sensitivity such that the ordered water molecules could be detected.The graphene sheet with ordered water molecules exhibits the lowest conductivity.In contrast the clean graphene exhibits the highest conductivity.We believe that our findings are of crucial importance for designing graphene based sensors.This may open the way to detection of molecular ordering.The research results of this thesis have important theoretical guiding significance for the further understanding of the electron transport properties of low dimensional silicon nano materials,and provide the theoretical guidance for the development of ultrafine silicon nanowire field effect transistors,and for the design of the high performance molecular electronic devices and the development of single layer nano electronic devices and spin electronic devices.