First-principles Study Of Electronic Properties Of Doped Few-layer Graphene

Due to the unique structure with the physical and chemical properties, graphene has been researchfocus of nanomaterials science since its discovery. Especially, because of its superexcellent electronicproperties, graphene may substitute the traditional semiconductor silicon material and carbonnanotube to be new nanoscale electronic device. In order to provide considerable insight intoelectronic properties of graphene and tune its electronic band structure effectively, we study electronicproperties of several different systems of doped few-layer graphene and obtain a number ofinteresting results. We first comment current situation of investigations for graphene, including itsdiscovery and synthesis, microstructure, physical properties and application perspective. Using virtueof suitable theortical methods: the first-principles method based on density functional theory, weinvestigate the effect of doping on electronic properties of graphene by calculating the electronicstructures and charge distribution characteristics, and discuss the essential mechanisms. The thesis isorganized as follows:In Chapter1, the discovery, synthesis, typical structure, electronic properties, applications andthe background of doped graphene are introduced.In Chapter2, we give a brief introduction to the first-prinicples method based on densityfunctional theory and then, investigate its application on doping effect of carbon-based nanostructures.Through injecting a negative charge to the system, a study of charge distribution characteristic ofiodine atom doped carbon nanotubes with different diameters is performed. It is found that charges ofarmchair and zigzag tubes increase with the increasing diamaters except these zigzag tubes whosediamaters are smaller than (10,0). Besides, the average charges of each carbon atom for the two typesof carbon nanotubes exhibit similar variation trends with diamaters, therefore having the samephysical mechanism. We can compare the electronegativity of carbon tubes with iodine atom,according to their ability of attracting negative charges. In addition, we find that it is suitable for usingfirst-principles method to study the doping effect of carbon-based nanostructures and calculate theelectronic properties.In Chapter3, we discuss the possibility of obtaining new graphene-based material, where thehydrogen atoms in the graphane are substituted by halogen atoms. Our calculations show thatgraphane-like carbon-halogen compounds of CF, CCl and CBr are stable. CF and CCl aresemiconductors with smaller band gaps than that of graphane, while CBr is metal. We also performab-initio molecular dynamics simulations to study thermal stability of CF and CCl. It is found thatthey are thermodynamically stable at room temperature, and CF is more stable than CCl with increasing temperature. At last, the effect of a monovacancy defect on the stability and electronicstructures of CF (as an example) is considered.In Chapter4, taking into account the effect of doping atom and substrate on the electronicproperties of graphene, we calculate charge distributions in single-sided and dual-sided dopedfew-layer graphene. It is found that, as the graphene is doped with a dopant on one side, the chargetransfer will take place between the dopant and its nearest carbon layer, which can donate and acceptmost of the transferred charges compare to the interior carbon atom layers. The charge distributioncharacteristic of dual-sided doping depends on the doping-type combination: for n-C-n type, both ofthe doping atom and substrate are charge donors, the two bounding layers will accept transferredcharges from each nearest dopant. For the n-C-p type, the carbon layer adjacent to the acceptor tendsto be charge neutral. Such behavior can be explained by a multi-layer capacitor model, which showselectrostatic effect plays a crucial role in determining charge distribution.In Chapter5, we study the charge distribution characteristics of potassium-doped layeredcombined systems of graphene and hexagonal boron nitride based on their structural similarities. Twoconfigurations of potassium-doped1~5hexagonal boron nitride layers on5graphene layers and thereverse geometry of1~5graphene layers on5hexagonal boron nitride layers are considered. We findthat the charge distribution exhibits different features in these two situations. In the former case, theoutmost hexagonal boron nitride layer cannot screen the external charges offered by potassium atomcompletely and most of transferred charges reside on the two bounding layers. The graphene layerscan accept part of transferred charges due to the preponderant band filling of graphene than that ofhexagonal boron nitride. In contrary, the outmost graphene layer near potassium atom can acceptalmost all of transferred charges and only a few of them stay at interior layers in the latter case, suchbehavior can be explained by classical electrostatic shielding effect. More amazing result is that thecharacteristics of charge transfer are independent of the number of graphene and hexagonal boronnitride layers.In Chapter6, the summary of the thesis and prospect of future works are given.