Research On Interfacial Interaction And Electronic Properties Between Two-dimensional Materials And CeO₂

Two-dimensional(2D)materials possess novel physical and chemical properties,and have a wide applications due to quantum size effect.However,in applications,typically in devices,2D materials are not free-standing and are instead deposited on substrates to form heterostructures.As a result,the physical properties of 2D materials are strongly affected due to thin thickness of few layers materials.Therefore,it is very important to understand the interfacial interaction between 2D materials and substrates and its influence on electronic properties of 2D materials.The metal oxides are not only excellent substate,but also poss ess outstanding synergistic effect in heterostructures.In this thesis,CeO₂as an example,we systematically studied interfacial interactions between four representative 2D materials and CeO ₂,and its effects on electronic properties of 2D materials by first principles.The main contents are as follows:1.We have systematically studied the interfacial interaction between silicene with high chemical activity out of layer and CeO₂(111)and its influence on electronic properties.It is found that the interface between silicene and CeO ₂(111)possesses strong covalent and weak vd Ws interaction,which is related to atomic stacking configurations.When silicene covalently bond to CeO₂(111),the intrinsic?bonding networks of silicene are broken,which leads to appearance of magnetism and annihilation of non-trivial topological state in silicene.When silicene bond CeO ₂(111)by vd Ws interaction,the intrinsic bonding characters of silicene can be preserved,however,the topological properties have also been destroyed due to breaking of inversion symmetry and opened bandgap.In order to preserve quantum spin Hall effect of silicene,we have constructed symmetrical sandwich structure(CeO₂(111)/silicene/CeO₂(111))to exclude the effect of substrate.2.We have systematically studied the interface interaction between monolayer transition metal dichalcogenides(MX₂)with cemical inert out of layer and CeO₂(111)and its influence on electronic properties.Interestingly,the intensity of interaction and interfacial distances depend on chalcogen(X)element.Compared with MSe₂/CeO₂(111),the interaction strength of MS₂/CeO₂(111)is stronger and the interfacial distance is smaller.Althouth the interaction in M X₂/CeO₂ heterostructures is weak vd Ws interaction,the electroic band edge states of MX₂ can be changed:from direct band gap to indirect band gap,which also depend on the X elements.In addition,X elements also affect the charge transfer and optical pro perties of MX₂/CeO₂(111)heterostructures.For heterostructures with same X element,their charge transfer and optical absorption are very similar.3.In order to further determine the influence of chalcogen(X)elements on the interaction and electronic properties,we systematically studied the interface interaction and electronic properties of Janus-MoSSe and CeO₂(111).When the S atom contacts CeO₂(111)(Janus-Se MoS/CeO₂(111)),the interfacial binding energy and the charge transfer are much greater than th ese of heterostructure with Se contacting CeO₂(111)(Janus-SMoSe/CeO₂(111)).In addition,the X elements at interface also determine type of band-alignment of these heterojunctions.For Janus-SMoSe/CeO₂(111),the band-alignment is type II;however,for Janus-Se Me S/CeO₂(111),the band-alignment become to type I.The difference of X element at interface and type of band-alignment of heterostructures also lead various characters of photo-induced carrier transfer.In Janus-SMoSe/CeO₂(111),photo-induced holes can rapidly transfer to Janus-MoSSe from CeO₂;however,in Janus-Se MoS/CeO₂(111),photo-induced electrons can transfer to CeO₂ from Janus-MoSSe quickly.Interestingly,although the photocarriers transfer is different,the intrinsic physical mechanism of the photo-induced carriers transfer in such vd Ws based heterojunctions just owes to non-adiabatic coupling.4.In order to further determine the internal physical mechanism of the dominant carrier transfer in vd Ws heterojunction based on 2D materials and metal oxides,we systematically studied the interface interaction and electronic properties of monolayer g-C₃N₄/CeO₂(111)heterostructure,which is widely focued by experiments.The monolayer g-C₃N₄ is also combined to CeO₂(111)by vd Ws interaction,which can effectively form type II band-alignment.For both of separation and recombination of photo-induced carriers,the key factors leading to the carrier transfer are non-adiabatic coupling effect,rather than interfacial electric field.In addition,compared with the recombination,the separation of photo-induced carriers is more rapid,which means that g-C₃N₄/CeO₂ is a type II heterojunction,which is consistent with most of the experimental results.