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Study On Two-dimensional Lateral Heterostructures And Their Transport Properties

Posted on:2020-09-23Degree:MasterType:Thesis
Country:ChinaCandidate:Z Q LiFull Text:PDF
GTID:2381330596476389Subject:Engineering
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Two-dimensional(2D)materials have become the hotspot in materials study due to their unique electronic and optical properties.At the same time,based on various 2D materials,different heterostructures have been constructed,and many novel structures and electronic properties have been discovered.2D heterostructures can be divided into two types:One type is the vertical 2D heterostructures by stacking a single layer of 2D material layers by mechanical transfer or the like.The other type is the 2D lateral heterostructures of a single atomic plane which is directly synthesized and seamlessly stitched.Vertical heterostructures have been extensively studied due to their relatively simple synthesis process.The lateral heterostructures have received less attention due to the reasons,such as difficulty in experimental synthesis.Although difficult to synthesize experimentally,the lateral heterostructures combine with covalent bonds in the atomic plane and have good planar integration,which also draw interests of people.In this thesis,the first principle calculation is used to study the modulation of the electronic properties of single-layer graphene by different nanohole and different nanohole arrays,and the new formed 2D heterostructures have also been discussed.The transport properties of hexagonal nanohole and hexagonal nanohole array graphene devices were studied by using the non-equilibrium Green’s functions.The thesis content is as follows:Firstly,the currently status of 2D heterostructures experimental synthesis and characterization are summarized,the extensive applications of 2D heterostructures in electronic and optoelectronic devices are also introduced.Moreover,the research significance of 2D lateral heterostructures compared with the 2D vertical heterostructures are illustrated.Then,a method for modulating single-layer graphene by introducing nanohole is studied based on single-layer graphene materials.By comparing with the pure graphene nanoribbons,it is found that the nanohole have a better modulation effect on the electronic properties of the graphene nanoribbons,and different shape of nanohole have different modulation effects on the nanohole electronic properties.Next,the modulation of the electronic properties of graphene nanoribbons by hexagonal nanoholes arrays is discussed.Different nanoholes arrays were found having different modulation effects on the nanoribbons.Unlike traditional graphene nanomesh(GNM),nanoholes arrays(patterns)and nanoribbon widths jointly affect the electronic properties of nanoribbons,and their band gaps remain oscillating.The electronic properties are modulated by changing the nanohole array pattern and nanohole symmetry properties.Based on these modulation methods,the band alignment of different nanohole nanoribbons are calculated.It is found that the type II band alignment can be achieved by introducing different nanohole,and different nanoribbon widths have a clearly influence on the band alignment of the nanohole nanoribbons.Even with the same nanohole and different width nanoribbons,the type of band alignment can also be changed.Nanoribbons modulated by different hexagonal nanoholes arrays have also been discussed.Hexagonal nanoholes arrays nanoribbons are similar to width-modulated graphene nanoribbons and can only achieve type I band alignment.Then,the type III band alignment nanoribbon heterostructures formed by N and B doping are also discussed.Different band alignment nanoribbons heterostructures enrich the tunability of graphene devices and promote the potential use of graphene nanoribbon devices.Finally,based on the non-equilibrium Green’s function,the transport properties of graphene hexagonal nanohole devices are explored.The transport properties of graphene devices with different nanohole arrays(patterns)using graphene as electrodes are discussed.It is found that different nanoholes arrays have certain effects on device transport properties,but even with different nanoholes arrays,the rectification ration of such devices is very small.Next,the transport properties of nanoholes graphene and graphene as electrodes are discussed.It is found that the rectification characteristics of nanoholes graphene as electrode are more obviously.With the length of the intermediate part is increased and the nanoholes array(pattern)are used as electrode,the rectification performance has been greatly improved.The exploration of these transport mechanisms provides a reference for nanoholes modulation and nanoholes devices.
Keywords/Search Tags:Two-dimensional heterostructures, Nanohole, Nanoholes arrays, Graphene heterostructures, Transport properties
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