| In the development of nanoscale semiconductor devices,two-dimensional materials have become the core materials of the next-generation novel devices due to their atomic-level thickness and no dangling bonds on the surface.In two-dimensional materials,metallic MXene exhibits excellent electrical conductivity and mechanical properties,and semiconductor Mo S2displays high carrier mobility.The metal-semiconductor interface formed by the two can effectively alleviate the Fermi pinning effect.Regulating the interfacial properties of metal-semiconductor under strain can optimize the carrier transport characteristics of devices,and promote its application in the field of flexible electronic devices.Ti3X2 is a material system with excellent electrical conductivity in MXene.However,the mechanical and electronic properties of structurally modulated Ti3X2 at the atomic-molecular level are ambiguous.The essential relationship between elemental composition modulation of metal and metal-semiconductor interface properties under strain is incomplete.The regulatory relationship between surface functional modulation MXene and metal-semiconductor interface properties under strain is unclear.The theoretical system of regulating the interfacial properties of the metal-semiconductor under strain by adjusting metal structure has not been established.Therefore,the following research is carried out in this dissertation:（1）The mechanical and electronic properties of Ti3X2（X=B,C,N）were theoretically studied.The result of the stress-strain curves of Ti3X2 show that Ti3B2 has the weakest ideal strength.Ti3B2 and Ti3N2 show anisotropic mechanical properties,whereas Ti3C2 shows better isotropic mechanical properties,that is,the direction of applied strain does not affect the mechanical stability of Ti3C2.Meanwhile,the Ti3B2,Ti3C2 and Ti3N2 all have metallic properties without strain,and the conductivity of Ti3B2,Ti3C2 and Ti3N2 increases in turn.They also maintain metallic properties under critical strain,indicating their potential as metal electrodes under strain.Furthermore,the work function of Ti3X2 decreases as the strain increases.This study elucidates the effect of elemental component modulation on the mechanical and electronic properties of Ti3X2 from the atomic-molecular level,which provides a theoretical basis for regulating the interfacial properties of metal-semiconductor under strain.（2）The configurations for Ti3X2/Mo S2（X=B,C,N）were constructed,and the effect of element composition adjustment Ti3X2 on the interfacial properties under strain was investigated.The interfacial interaction weakens with the increase of out-of-plane tensile strain,and all the interfaces change from ohmic contact to Schottky contact with the emergence and increasing of the tunneling barrier.Owing to the difference in the work function of Ti3X2 and the interface polarization potential of Ti3X2/Mo S2,both the interfaces of Ti3C2/Mo S2 and Ti3B2/Mo S2 are transformed from ohmic contact to n-type Schottky contact,while the Ti3N2/Mo S2 interface shifts from ohmic contact to p-type Schottky contact.The results show that the interfacial properties under strain can be regulated by adjusting the element component X of Ti3X2,where the interface changes from ohmic contact to Schottky contact and the conduction type of Mo S2 varies.It provides theoretical support for the preparation of flexible devices based on Ti3X2/Mo S2.（3）To further broaden the scope of interface regulation,the method of surface functionalized metal can weaken the interface interaction was adopted.The surface functional group was used to modulate the Ti3C2 with high stability,and the mechanical and electronic properties of Ti3C2T2（T=F,O,OH）were studied.The calculations show that Ti3C2T2（T=F,O,OH）exhibits metallic characteristics when no strain is applied.Ti3C2T2 has excellent mechanical properties,and the ideal strength of Ti3C2O2,Ti3C2F2 and Ti3C2（OH）2 decreases successively,but is better than that of Ti3C2.This indicates that the existence of surface functional group improves the ideal strength of Ti3C2.In addition,the projected density of state of Ti3C2T2（T=F,O,OH）under critical strain shows that Ti3C2T2（T=F,O,OH）still has metallic properties under strain.The results of the work function under strain show that when the tensile strain in-plane is increasing,the work function of Ti3C2F2 gradually increases and the work function of Ti3C2O2 gradually decreases,whereas the work function of Ti3C2（OH）2 decreases firstly and then rises.It lays a theoretical foundation for regulating the interfacial performance of metal-semiconductor based on Ti3C2T2（T=F,O,OH）.（4）The configurations of Ti3C2T2/Mo S2（T=F,O,OH）interfaces were built,and the interfacial properties of Ti3C2T2/Mo S2 interface under strain regulating by functionally modulated metal was studied.The Ti3C2（OH）2/Mo S2 interface maintains ohmic contact under both in-plane and out-of-plane strains.Under the tensile strain regulation in-plane,the Ti3C2T2/Mo S2（T=F,O）interface with p-type Schottky contact changes to n-type Schottky contact,and then to n-type ohmic contact.When the interfacial property is regulated by out-of-plane strain,Ti3C2F2/Mo S2 interface can exhibit the transition from p-type Schottky to n-type Schottky under compressed or stretched strain,whereas Ti3C2O2/Mo S2 interface with p-type Schottky contact is transformed into p-type ohmic contact under the increasing strain and n-type Schottky contact under the reducing strain.The result shows that the switching of the Ti3C2T2/Mo S2 interface between p-type Schottky,n-type Schottky and n-type Ohmic contacts under strain is realized by modulating the surface functional group T of Ti3C2T2,which broadens the range of interface regulation.In conclusion,the metallic properties of Ti3X2（X=B,C,N）and Ti3C2T2（T=F,O,OH）under strain are clarified from the atomic-molecular level.Meanwhile,the essential relationship between Ti3X2（X=B,C,N）and Ti3X2/Mo S2 interfaces under strain is revealed.The weaker interfacial interaction of Ti3X2/Mo S2 makes the higher regulation efficiency of interface types under strain.Moreover,the relationship between Ti3C2T2（T=F,O,OH）and the interfacial properties of Ti3C2T2/Mo S2 under strain is illustrated clearly.The Ti3C2F2/Mo S2 interface can switch between p-type Schottky contact,n-type Schottky contact and ohmic contact by adjusting the type of surface functional group.A theoretical system is formed that regulate the interfacial properties of metal-semiconductor under strain by adjusting metal structure of elemental composition or surface functional groups,which provided a theoretical clue for the application of interface in two-dimensional flexible electronic devices. |
