Oxidation Mechanism And Collaboration Of Oxidation And Defects In Low-Dimensional Materials

In recent years,low-dimensional materials with diverse nano-structures have been drawn extensively attention owing to their unique dimensional features and excellent physical properties.Graphene,as a typical two-dimensional material,has remarkably potential application in the future field of nano-electronic devices because of the massless Dirac fermion near Fermi level.Motivated with the promising application of graphene,other two-dimensional materials such as silene,phosphorene,group?-?compounds,group?-?compounds,Transition metal dichalcogenides layered materials etc.,have also been theoretical prediction and successful synthesis in experiments.In recent years,lots of researches on the structure stabilities,mechanical properties,electrical properties,magnetic properties and optical properties of low-dimensional materials have been studied,thus further developing in-deep understanding of low-dimensional materials.Meanwhile,these studies provide theoretical basis for the practical application of low dimensional materials.Comparing with three-dimensional materials,the carrier mobility of low-dimensional materials is confined in two-dimensional plane.As a results of quantum restriction induced by dimensional feature,low-dimensional materials usually demonstrate kinds of amazing performances.For example,the ultrahigh specific surface area of low-dimensional materials provides high density of active center sites,thus easy to be oxidized or generate defects.Study of surface stabilities is in favour of comprehensive understanding for the nature of active center and reaction mechanism etc.the structure-activity relationship.On the one hand,owing to the strong electronegativity of oxygen,rearrangement of electron on surface after surface oxidation leading to changes of electronic property;on the other hand,defects format defect bands near Fermi level,thereby inducing hybridization of oxidized states and defect states.Therefore,low-dimensional materials provide an effective method to regulate the electronic structures in chemistry and defects.Furthermore,the topological electronic properties of low-dimensional materials,such as quantum spin Hall states,quantum anomalous Hall states,and topological semi-metal states,mayonara zero energy module etc.,have also attraced public attention.Non-trivial edge state is the distinguishing feature of topological quantum state,these trivial edge states are topologically protected.However,once the materials are out of the laboratory environment,the factors of oxidation,defect,or even their synergistic interaction can induce the changes of topological properties,and may lead to a series of novel physical phenomena.In recent years,although there are some conclusions for oxidation behaviors of low-dimensional materials,the researches of topological transformation,defect caused by oxidation,and collaborative interaction are rarely reported,the micro-mechanisms of these problems are still unclear.Hence,systematic studies of oxidation mechanism and collaborative interaction between oxidation and defects for low-dimensional materials are of great significance.The main research contents in this article are as follows:1.Investigated oxidation mechanism and topological transformation induced by oxidation of ML 1T'-WTe₂ which is the quantum spin hall insulator.Combining with First principles calculation,we calculated oxidation reaction pathway and energy berries.The calculation results show that co-existence of O₂ and H₂O in air is the key factor of fast surface oxidation on WTe₂.H₂O can lower the energy barrier of O₂ dissociation and significantly promotes the surface oxidation of ML 1T'-WTe₂.It is worth noting that ML1T'-WTe₂ shows different topological properties under different oxygen coverage.In the case of low oxygen coverage,oxidation make ML 1T'-WTe₂ transfer into a trivial insulator.With the increase of oxidation coverage,fully oxidized ML 1T'-WTe₂—2D WTe₂O convert back into QSH insulator.This work develops deep understanding on the topological transformation induced by oxidation,and provides new idea of chemical regulation of topological property for layered transition metal disulfide compound materials.2.Systematically investigated the effects of surface oxidation in topological insulator Bi₂Se₃.Using first-principles calculations,we comprehensively calculated various oxidized structures and their topological properties,found an energetically favorable oxidation structure,thus further elaborating in-depth analysis of surface degradation of topological surface sates in Bi₂Se₃.Our calculation show that O atoms prefer to migrate from surface layer into subsurface of Bi₂Se₃,and then bond with Se atom and Bi atom to reach the energetically favorable oxidation structure.The results explain the experimental phenomena.By analysis band decomposed charge densities of topological surface states,we found the topological surface sates of Bi₂Se₃ still maintain intact at the interface Se atomic layers between non-oxidized and oxidized layers.For the stable oxidized structure,the O atoms hybridized with substrate Se(or Bi)atoms and hybridized states locate at deep band region,which keep far away from the Fermi level.Magnetic calculations indicate that Bi₂Se₃ film still show time reversal symmetry and band inversion after oxidation.Topological surface states of Bi₂Se₃ film behave robustness against surface oxidization and still maintain intact in the gap after oxidation.We further investigated structure stability of surface oxidation under O₂-rich and O₂-poor conditions,verifying the rapid surface oxidation mechanism of Bi₂Se₃ in air.These research results have significant influence for the future application of Bi₂Se₃with nano-structures.3.Investigated the formations,stabilities,and electronic properties of monolayer arsenene with SW-defect and C-substitution.We also simulated the kinetics of the formation for SW-defect in arsenene.We found the energetically favorable C-doping site by calculating the different sites of C-substitutions in SW-defected area.The electronic structures calculations show that SW-defect and C-substitution induce defect levels in gap which are in favour of formation of defected charge states.Therefore,wecalculated the charge states of monolayer arsenene with SW-defect and C-substitution.The results indicate that defected charge states significantly change the electronic structures.The magnetic properties of C-substitutions are vanished after introducing charge states.Based on the calculations of formation energies,we found that the negative charge states are more stable than positive charge states.Besides,we studied the oxidation mechanism of SW-defected arsenene.The calculations reveal that SW-defect further lowers the energy barrier of O₂ dissociation.Obviously,the formation of SW-defect accelerates surface oxidation on arsenene.4.Studied the stabilities and electronic properties of edge-passivated arsenene nanoribbons.By First-principles calculations,we systematically investigated the edge-passivations of H-,O-,and OH-edge-terminated As NRs.The results indicate that different kinds of edge-passivations significantly affect the band structures of the nanoribbons.The formation energies demonstrated that the edge-passivation can further stabilize the edge-structures of arsenene nanoribbons.Comparing with hydrogen and oxygen cases,hydroxyl group adsorption on edge is most energetically favorable edge-passivation.By analyzing the electronic band structures,the oxidized edge-passivated arsenene nanoribbons behave metallic edge states,while edge-passivation with hydrogen and hydroxyl group process semiconducting gap states.Furthermore,we also calculated the magnetic properties of metallic edge states.The results show that metallic edge-passivations exhibit outstanding ferromagnetic and anti-ferromagnetic properties.Our research provides theoretical basis in design of nanoelectronic devices with arsenene nanoribbons.