ARPES And SARPES Study On Two Dimensional Transition Metal Dichalcogenides And Nb₃SiTe₆

Recent years,two dimentional materials receive considerable attention for their unusual properties.Particular focus has been on transition metal dichalcogenides for the abnormal physical properties at monolayer limit.Such properties constitute a promising materials platform for electronics,optoelectronics,spintronics and valleytronics.We study electronic and spin structure of TMDCs by SARPES and ARPES.My thesis includes five aspects:1. We systematically investigate the electronic structure of bulk MX₂after alkali metal deposition.We verify the abnormal band shift caused by negative electron compressibility?NEC?.Besides,we observe the band gap of bulk MX₂after doping.Such experiments give a good reference for more study on alkali metal deposition of monolayer MX₂discussed in other chapters.2. The gap size of MoTe₂is smallest in all TMDCs and most close to Si.Besides,an electrostatic-doping-driven structural phase transition happens in monolayer MoTe₂.We systematically investigate the electronic structure of monolayer,bilayer and multilayer MoTe₂by ARPES.As a result,we first get the electronic structure of monolayer and bilayer MoTe₂.And we get the evidence of direct band gap in monolayer MoTe₂by Rb deposition with a band gap of 0.924e V.The band structure measured by ARPES is in excellent agreement with our PBE calculation.Beside this,we compared the band splitting at K of different layered MoTe₂with a result that splitting size increase with layer stacking.3. We study electronic structure of monolayer WSe₂by ARPES.We show not only high quality band structure but also doping result by Rb deposition.By doping,we get a direct band gap of 1.2e V as well as a parabola band centered at?38?near Fermi level which we suppose it as a feature of quantum well state.What's more,we also find the enlarging splitting size with increasing layers consistent with MoTe₂.4. We systematically study the electronic structure of bulk Nb₃Si Te₆.Our result is consistent with calculation.By comparing the measured band structure of both He I and He II condition and calculated ones with different Kz,we find there's only weak band dispersion along vertical axis and rich bands crossing Fermi level,which are good evidences of the two dimensional material and good conductivity of Nb₃Si Te₆.However,the lack of band measurement along Kz direction lead to the lack of topological structure measurement.5. As the existence of twin domain,it is hardly to observe the 100%spin polarization of monolayer MX₂.Our exfoliated samples can avoid twin domain so that we did SARPES to study the electron spin polarization at K.As a result,we observed 100%spin polarization at K with an opposite spin polarization at K'.What's more,we find spin polarization can be modified by photon energy and polarization.But we did not find spin flip by changing incident photon polarization which is reported by other papers.