Scanning Tunneling Microscopy Study Of Electronic Structures Of Indium Selenide And Tungsten Selenide

Transition metal chalcogenides(TMDs)have attracted the attention because they are good objects for studying basic physics and their performance in device application by more and more scientists.In this thesis,through the design of related experiments and the introduction of moiréstructures,scanning tunneling microscopy(STM)and scanning tunneling spectroscopy(STS)are used to study the two-dimensional(2D)atomic interlayer coupling of indium selenide and the weak coupling between 2D tungsten selenide that supported by Au film,the results are as follows:(1)According to the characterization of the local morphology and electronic structure of?-InSe with different atomic layer numbers,the evolution of the band gap dependent on the number of atomic layers of?-InSe is clarified.The band gap changes from 2.5 eV in the few layers to 1.2 eV in the bulk phase,and the band gap changes1.3 eV.The mechanism of the band gap change cannot be explained by the quantum confinement effect alone,but also the strong interlayer coupling in?-InSe.Furthermore,the obtained results of?-InSe band gap change with thickness are fitted with a free electron model,a small reduced mass and a large exciton radius are obtained,this experiment result indicate strong interlayer coupling exists in?-InSe.(2)A moiréstructure induced by lattice mismatch and a robust band gap was found on the bulk?-InSe.It is found that the band gap in the moiréstructure region is close to the band gap of the bulk phase?-InSe,and the band gap in the periodic stacking region in the moiréstructure remains unchanged(1.3 e V),indicating that the effect of different stacking structures on the electronic structure is negligible,that is,a strong interlayer coupling between the upper surface layer and the sub surface layer of?-InSe,the modulation of the electronic structure induced by the moirépotential is smeared out.Also,the calculated density of states(DOS)of each region also proves the above results.Meanwhile,in order to quantify the hybridization between the neighboring orbitals from different?-InSe layers,the hopping integral is calculated.The results prove that the interlayer coupling in?-InSe is not of pure van der Waals origin,but demonstrates some degree of strong covalent bonding.(3)The single-layer WSe₂ was transferred to the Au film was studied,and it was found that the p_z orbitals of the Se atoms in the bottom layer of WSe₂ did not interact with the d electrons of Au,showing the characteristic of weak coupling.The atomic arrangement of the single-layer WSe₂ at the edge and on the terrace of the Au film is continuous and the lattice constant does not change,and the moiréperiodic structure is formed due to lattice mismatch.Through the characterization of local morphology and electronic structure,it is found that the change in the contrast of the STM morphology is opposite to the intensity changes of the characteristic states near the valence band maximum(VBM)and the conduction band minimum(CBM)in STS,this may be the regulation of the moiréperiodic potential.The STS results show that the band gap is unchanged and there is no shift of the electronic state,which proved that there is a weak coupling interaction between the transferred monolayer WSe₂ and the substrate Au.In summary,this thesis explores and proves that?-InSe is a strong interlayer coupling material through STM combined with STS,and the monolayer WSe₂ was transferred to the Au film exhibits intrinsic physical properties due to the weak coupling effect with the supported Au film.