Theoretical Calculations Of Two-dimensional Structures And Doping Properties Of Diamond

Diamond has wide band gap,high thermal conductivity,hardness,chemical inertness,inherent biocompatibility and other unique properties,which make it widely used in many fields.In addition to conventional bulk diamond,diamond-related nanostructures have also attracted a significant amount of interest.Designing new diamond nanostructures and found new properties become an important frontier scientific issue.Since the successfully stripped from graphite of graphene in 2004,people have become more and more interest in the study of two-dimensional?2D?materials.Following our group research on the structure and properties of 2D?111?diamond films,based on the relative stability of?110?diamond surface,we systematically studied the effects of the layer number n and surface modification of2D?110?diamond nanofilms on their structural stability and electrical properties.In addition,it caused great interest in research due to the significant impact that defects have on the physical properties of diamond.The structure and related properties of defects is the key to the development and application of new materials.Silicon-related defects usually presence in synthetic diamond,silicon-vacancy attracts much attention due to their potential use as a single photon source for quantum information processing devices.Hence,this thesis will also focus on the structure and related properties of silicon-related defects in bulk and 2D diamond.The following results are obtained:1.For the first time,we propose by first-principles calculations to study the layer number?n?dependent structural evolution and electronic properties of bare and hydrogenated 2D?110?oriented diamond nanofilms.It is found that for the original diamond nanofilms with n?2,the cubic structures are not stable and will be reconstructed to few layer graphene.Interestingly,when n?3,the original cubic phases can be mainly maintained,which are significantly different to that previously reported evolution process of?111?diamond nanofilms.Further more,the semi-hydrogenation?SH?and full-hydrogenation?FH?are performed on the outmost sides of 2D film,which are helpful to stabilize the cubic diamond phase with very slight relaxations.Importantly,the bare?n?3?and SH structures show metallic behaviors,while the FH structures are semiconductor with a n-dependent band gap.It thus means that the 2D?110?diamond nanofilms,modulating by n and surface functionalization,appear as a unique member in the carbon family.2.The spin and charge states related electrical and magnetic properties of the substitutional silicon?Si_C?,vacancy?V_C?,the complexes of silicon-vacancy?SiV?,and silicon-divacancy?SiV₂?in diamond are theoretically investigated by first-principles calculations.Interestingly,The Si_C reflects a slight impact in the vicinity of the band gap without a spin-splitting state.While the band structures of the charged?negative and neutral?V_C,SiV,and SiV₂ show flat midgap levels in the band gap,which stems from the dangling bonds surrounding the vacancies.The vacancies play crucial role in producing varying magnetic moments by the spin-splitting.Gaining or losing different spin orientated electrons has impact on the energy separation of spin-splitting and the magnetism of the material.3.We propose by first-principles calculations to study the structural,electrical and optical properties of 2D hydrogenated bilayer diamond films?2D-HBDF?with silicon dopant as well as the complex of silicon-vacancy?SiV?.It is found that the two different positions of substitutional silicon?named as Si_C-I and Si_C-II?are energetically favorable and present semiconductor characteristics with similar direct band gap.For the cases of Si_C-I and Si_C-II combined with vacancy,named as Si_CV_C-I and Si_CV_C-II,the flat intermediate bands appear in band gap.Especially,the ground state is paramagnetic?nonmagnetic?for the case of Si_CV_C-I?Si_CV_C-II?dependent on the distributions of Si dopant and vacancy.The optical absorptions relating to the cases of SiV extend a high intensity in the visible light region.It reveals that the introducing vacancy in substituted silicon and their positions related to the carbon and hydrogen play an important role in modulating the electronic and optical properties of the 2D-HBDF.For the diamond-related materials,it is of great significance to explore the new structures and find novel optoelectronic properties.It is believed that the novel 2D?110?nanofilms theoretically predicted in this work are potentially favorable for realizing high performance diamond-based optoelectronic and electronic nanodevices.It is of great significance to explore novel properties of 2D diamond and find its potential applications in wide variety fields.Doped diamond with an altered gap or midgap states can effectively affect the electrical and magnetic properties.The substituted silicon and vacancy in diamond provide a way to modulate the defect levels and magnetism,while the spin and charge states play important roles.These results are helpful for constructing high performance SiV based optoelectronic and magnetic novel diamond devices applied in wild fields.It is of great significance to explore the new properties of 2D diamond and find its potential applications in various fields.It is believed that an exciting prospect of using such 2D-HBDF will be helpful to construct novel low dimensional diamond based optoelectronic devices.