Two-dimensional Semiconductor Directed Exfoliating And Research On Interlayer Coupling Characteristics

Two-dimensional(2D)van der Waals(vd W)semiconductor materials,such as transition metal dichalcogenides(TMDs)MX₂(where M=Mo,W;X=S,Se)have emerged as promising low-dimensional quantum materials and significant possibilities for the post-Moore era in recent years.Its single-atom layers feature traits that distinguish them from bulk-phase materials,including direct bandgap,high exciton binding energy,and strong light-matter interactions.More importantly,the 2D vd W heterostructures created by varying the type of material between the layers,the stacking direction,and the twisted angle reveal completely new properties not found in the components,making them an important research platform for investigating novel quantum phenomena.For starters,unlike graphene,the artificial bilayer MX₂ has two different stacking order:parallel stacking(Rhombohedral,R-type)and antiparallel(Hexagonal,H-type);it has different interlayer coupling and energy band topology features.For example,because of the broken inversion symmetry and interlayer charge transfer of parallel stacks,it exhibits novel physical properties such as interfacial ferroelectricity.However,to date,exfoliating methods have primarily focused on the exfoliating sample's mass,size,and yield,with little information on the sample's lattice orientation.And we only determine crystallographic phase information after stacking is complete,such as polarization second harmonic generation spectrum,which reduces the research's efficiency significantly.And moirésuperlattices are formed as a result of twisted angles and differences in lattice constants between layers.Moirépotential wells are formed when the intra-face atomic site shape and extra periodic modulation cause the potential energy level to fluctuate at specified high symmetry sites.Free excitons can be trapped in such a network of potential wells,resulting in quantum photoemission and bosonic many-body effects.Hexagonal boron nitride(h BN)is projected to create deeper moirépotential wells than MX₂ because to its wide band gap and low dielectric constant,which make it ideal for researching moiréexciton behavior at higher temperature.Finally,the existence of moirésuperlattice atomic reconstruction and lattice relaxation in the small twisted angle homogenous bilayer system would allow for a deeper physical content of the interlayer coupling control.According to the above problems,we have done the following research and have achieved certain research results,the key elements of which are as follows:1.Exfoliation of monolayer 2D semiconductor materials and crystallographic phase identification are the basis for studying their physical properties.We report a new large area and directed exfoliating method,which solves the difficulties in the hetero-stacking direction of TMDs materials that could not be pre-controlled.By gold(Au)atoms favor epitaxy along the specific atomic step edges of TMDs,we obtain high-quality,large-size(sub-millimeter scale),and high-yield of monolayers via Au-assisted mechanical exfoliation method.H-type and R-type stacking configurations of bilayer TMDs are built directly at once result of foreseeing the lattice orientation.The experimental results,which were characterized by spectroscopy,electronic diffraction,and angle-resolved photoemission spectroscopy,support the exfoliating process of the unique edge lock we propose.This technique for directed exfoliating gives a broad technical approach to the stacking of multilayer 2D materials and the construction of twisted angle electronics.2.To investigate the information of the 2D semiconductor materials interlayer exciton and moiréexciton.We tested the interlayer exciton peaks by photoluminescence spectrum in Mo S₂/WS₂ type II energy band structure,which based on the directional large-area exfoliating technique of TMDs materials.And we used Au surface in plan nanocavity to enhance the interlayer exciton luminescence.We used reflectance difference spectrum to investigate the stark effect of interlayer excitons in R-type Mo S₂/Mo S₂ stacking,revealing that interlayer excitons in TMDs materials are strongly modulated by plasma fields or external electric fields.Finally,we discovered the moirépotential wells in twisted-angle h BN at a depth of 807 me V by using cathodoluminescence spectrum.It is expected to further research into bosonic-type strong correlated physics based on depth-trapped moiréexcitons.3.Finally,using the splitting characteristics of Mo S₂~1₂₂2))mode under Raman spectrum,we investigated the atomic reconstruction and lattice relaxation process of the Mo S₂ moirésuperlattice at small twisted angles,and determined the angular range where the atomic reconstruction and lattice relaxation occur.Moreover,we inserted monolayer h BN in the middle of bilayer Mo S₂ to eliminate the atomic reconstruction and lattice relaxation with the goal of guaranteeing interlayer coupling.This introduces a new interlayer and moiréexciton regulation parameter.Based on the interfacial ferroelectricity effect of Mo S₂ moirésuperlattices,we also built R-type Mo S₂/Mo S₂stacking ferroelectric tunneling junctions.It has a switching ratio of 10~4 and memory properties,which is expected to future research into ferroelectric memristor arrays based on TMDs materials.