Study Of The Electronic Properties And Modulation For The Novel Two-dimensional Materials

Graphene,being with characteristics of high carrier mobility,good thermal conductivity and optical properties,has been successfully synthesized with mechanical exfoliation method by Geim and Novoselov et al in 2004.Due to these excellent physicochemical properties,it has drawn public attention for past decades.Subsequently,other two-dimensional materials such as hexagonal boron nitride,transition-metal dichalcogenides,metal oxide,MXenes,phosphorene and germanene have been experimentallysynthesized as well.In addition,a variety of strategies have been developed to enrich electronic properties of two-dimensional materials such as constructing heterojunctions,surface modification and doping.Based on good quantum effect,excellent mechanical strength and transparency,high specific surface area,extremely high percentage of exposed active sites and easy to modify and so on,two-dimensional nanomaterials have great potential in the applications of photocatalysis,supercapacitor,sensor and so on,which deserves further research.In the aspect of photocatalysis,high specific surface area and band dangling of two-dimensional materials of two-dimensional nanomaterials provide more active sites,thus improving the photocatalytic efficiency.However,carriers recombination is commonly considered as an primary obstacle to the enhancement of photocatalytic performance.In this case,decreasing the recombination rate of photogenerated electrons and holes become a hot topic..Meanwhile,spintronic devices has attached people attention,due to its low energy consuming,high response and miniaturization.Obviously,it could not satisfy the fast-developing requirement for traditional bulk magnetic materials.Therefore,it is a urgent task to explore for novel two-dimensional applied in spintronic fields.Considering metioned above,we systematically investigate the electronic properties of 2D g-C3N4/CdS heterojunctions and MoSSe with vacancy defects based on first-principles calculations.The research contents and conclusions are as follows:Chapter 1:Introduction to the background and research status of two-dimensional nanomaterials.Chapter 2:Introduction of the theoretical basis and software of first-principles calculations.Chapter 3:We have systematically investigated the stability,electronic structures and band alignment of g-C3N4/CdS heterojunctions.It is of interest that a standard type-II band alignment forms between g-C3N4 and CdS monolayers,and g-C3N4/CdS heterojunctions satisfy the condition for photocatalytic water splitting.In addition,an internal electric field arises from g-C3N4 pointing to CdS,which will restrain the recombination of photogenerated carriers.As a result,the photogenerated electrons will shift from CdS to g-C3N4,while the photogenerated holes will transfer from g-C3N4 layer to CdS during the photocatalytic process.Thus improving the ability of water splitting of g-C3N4.Chapter 4:We studied the electronic properties of unstrained and strained Janus MoSSe with vacancy defects.It is found that the formation energy of single atomic point vacancy can be lower than other structures,and thus it is easier to form in experiments.At the same time,based on the analysis of their electronic properties,we found thatunstrained MoSSe with VMoS3Se3 defects has a spin polarization and magnetic moment due to the formation of the localized nonbonding 4d electrons,while the magnetic moment of the remaining ten structures are almost to 0 ?B.In addition,after applying 9%stress on these ten structures,we found that only MoSSe with VMo defect produced magnetic moments,and which has been generated under 5%stress.Chapter 5:The research contents of the paper are summarized,and prospects for the photocatalytic performance of g-C3N4 and the magnetic properties of MoSSe.