Electronic Structure And Transport Properties Of Quasi-one-dimensional Graphene-like Nanomaterials

With the rapid development of nanoelectronics and molecular electronics,nanoscale circuits composed of nanoscale devices have also been developing in the direction of smaller size,higher integration and higher efficiency.Therefore,the properties of two-dimensional nanomaterials have been highly required.Because traditional silicon materials can not break through the physical limit,silicon materials are no longer meeting the higher requirements of electronic devices.Graphene was successfully prepared in 2004.With its unique physical and chemical properties,graphene has attracted a great deal of attention in condensed matter physics and computational chemistry.Graphene was once considered to be the first choice to replace traditional silicon materials in the future.However,due to the zero band gap of intrinsic graphene,the application of graphene in the preparation of electronic devices is greatly limited.In recent years,more and more two-dimensional nanomaterials have been found,and have been successfully prepared,such as phosphorene.Firstly,We demonstrate theoretically how local strains can be tailored to control quantum transport of carriers on monolayer armchair and zigzag phosphorene nanoribbon.We find that the electron tunneling is forbidden when the in-plane strain exceeds a critical value.The critical strain is different for different crystal orientation of the ribbons,widths,and incident energies.By tuning the Fermi energy and strain,the channels can be transited from opaque to transparent.Moreover,for the zigzag-phosphorene nanoribbon,the two-fold degenerate quasiflat edge band splits completely under certain strain.These properties provide us an efficient way to control the transport of monolayer phosphorene-based microstructure.Secondly,we found a new kind of graphene-like nanoribbons that can be periodically embedded in four-eighth-membered rings into graphene nanoribbons.This structure has been prepared experimentally and can be observed under the scanning tunneling microscope to obtain an apparent atomic structure.This material consists of the original six-membered ring and the added four-eighth-membered ring,so that we cut along different directions will get a lot of different boundaries of the band structure.We mainly explored the band structure of three different edges,mainly using the first-principles calculations based on the density functional theory.We found that the ferromagnetic state is their ground state and will exhibit different electromagnetic properties due to the different edge trimming,and spin metal and spin semiconductors will appear.By investigating the projected density of states of the boundary carbon atoms in different orbits of different meta-rings,we have found an interesting thing.The unsaturated marginal carbon atoms of the six-membered ring are the main source of the entire band magnetism,and the eight-membered ring is unsaturated.The carbon atom is the main factor determining the electronic state at the Fermi level,which is the main cause of metals and semiconductors,and it also determines the optional split at the Fermi level.In order to further explore its generality,we explored the effects of the scale effect and the quantum confinement effect on nanoribbons.We calculated the spin polarizability of the three bands at different widths,and emphatically explored the band structure changes of the semiconductor band structure with the width.We found that when the band width is increasing,the band energy structure will produce a semiconductor-to-metal transition,which allows us to trim different edges and different widths.We can get the semiconductor or metal and the band structure with different spin polarizability,which greatly provides us with reference and convenience for exploring carbon-based materials.