Electron Transport Properties Of Low-dimensional Carbon And Silicon Nanomaterials

Since the invention of large scale integrated circuits, people have been continuously promoting their performance by improving the integration level, which is to decrease the dimensions of their elementary components, such as diodes and field-effect transistors (FETs). Due to the unique properties of nano-electronics, they have attracted much attention in recent years and been considered as the key of future electronics. According to the different materials used in nano-electronics, they can mainly be divided into nanowire electronics, molecule electronics and graphene (graphene-like) electronics. Although remarkable achievements have been made in nano-electronics, there are still many critical problems remained unsolved, which severely constraining their development and application.In this thesis, molecular dynamics and non-equilibrium green function combined with quantum theories (extended Huckel theory and density functional theory) are employed to systematically investigate several problems in nano-electronic studies, aiming to obtaining the electron transport properties of ultra-thin Si nanowires and the effect of doping, revealing the reason for the discrepancy between theoretically calculated and experimentally measured conductance of molecule electronics, exploring new FET models constructed by hexagonal CBN hybrid nano-structures and systematically investigating their electron transport properties and potential applications. The primary coverage and results of this thesis are given as follows:(1) The electron transport properties of ultra-thin Si nanowire FETs are studied. The effect of doping in Si nanowires on these FETs is revealed. Current amplification effect and controllable negative differential resistance (NDR) with robust on-off ratios are observed in these devices. In addition, it is found that both nanowire structure and applied bias can change the mechanism of NDR. Moreover, doping position significantly affects the electron transport properties of these ultra-thin Si nanowires.(2) We systematically investigate the effect of coupling pattern between graphene molecule and electrodes on the electron transport properties of graphene molecule FETs. Besides, the effect of chemical decoration of graphene molecule is also explored. The results show that the coupling pattern between graphene molecule and electrodes plays a dominant role in the electron transport mechanism of graphene molecule FETs. Different coupling patterns chosen in calculation can lead to consistent or inconsistent results with experimental values. Therefore, we proposed that the discrepancy between previous theoretical calculations and experiments is induced by different molecule-electrode coupling patterns in these studies. In addition, chemical decoration is found to be an effective method of tuning the performance of graphene molecule FETs.(3) According to the fact that graphene and hexagonal boron nitride (BN) sheet have the same crystal structure and similar lattice constants but rather different electronic properties, we propose a new kind of FET model constructed by graphene-BN hybrid nanoribbons. Their electron transport properties and the effect of vacancy, chirality and width of nanoribbons are investigated. These FETs do not need metal electrods to act as source and drain, which significantly improves their performance stability. Outstanding switching performance is observed in these FETs. Moreover, it is found that these FETs can exhibit100%spin polarization if the hydrogen atoms at the N edge of the BN nanoribbon are removed, suggesting their promising applications in spintronics.This study provides a deep understanding on the electron transport properties of low dimensional carbon and silicon nano-materials. It is also of practical significance for developing ultra-thin Si nanowire FETs, designing high-performance molecule electronics and exploring monoatomic layer electronics and spintronics.