Theoretical Study of Electron Transport Properties of Fullerene-based Low-dimensional Nanoelectronic Devices
Yakobson, Boris I.
Doctor of Philosophy
Since the discovery of fullerene materials in the early 1990s, such as carbon nanotube, graphene, etc., these new forms of Carbon have been attracted a surge of research interest due to their excellent electrical properties and mechanical strength. In conjunction with more and more low-dimensional materials recently discovered, such as MoS2, Phosphorene, etc., there new materials are considered as the promising candidates for the next generation nanoelectronics. The low dimensionality, however, has raised challenge to theoretical research: size effect, ultra-high aspect-ratio, atomic details, quantum transport, breakdown of Ohm’s law, etc., all of which have been becoming progressively significant and inevitable, as the miniaturization of microelectronics advances to the nano-meter scale. Within the ballistic regime, a couple of theories describing the scattering of Bloch waves at the interface of separate lattice domains have been developed. Among them, the non-equilibrium Green’s function approach (NEGF), combined with the tight-binding method (TB), or localized-basis-function based Kohn-Sham density functional theory (DFT) has been widely employed as a standard way, to study the I-V behaviors for a given open transport system. Other than the plain I-V curves, however, in theory the NEGF is supposed to provide more insight of physics and mechanism regarding the motion and distribution of electron, and further the magnetic properties. Also, the current algorithm for the surface Green’s function only works with electrodes with translational symmetry. Moreover, the NEGF must work with specific atomistic structure, and thus becomes inapplicable for semiconductors whose doping mechanism still remains ambiguous. Unfortunately, in the past literature the relevant research stopped at these fields, which accordingly become where this dissertation starts. In this dissertation, a variety of formalisms and approaches regarding the properties of electron transport, magnetic field and electrostatics in nanoelectronic devices are developed. Under the framework of Landauer picture, the NEGF approach combined with the TB method or the DFT theory , is further advanced, so that we may obtain a deeper vision of physics behind I-V curves, e.g. current distribution, magnetic field, etc. Also we developed the NEGF approach for electrodes with helical symmetry. These approaches are applied to several special nanoscale devices and reveal their novel properties which are never explored. Furthermore, the NEGF approach is combined with classical approximations so that we may compute current transport in heterojunctions with ultra-high aspect-ratio, for which the regular quantum calculation becomes prohibitively expensive. Apparently, these studies may pave the way for the future electronics towards the target of thinner, smaller, and less power loss.
electron transport; nanoelectronics