The STM Studies Of Charge Density Wave In 2H-MoTe₂ Films And Edge State On Bilayer Stanene Films

In this thesis,we report scanning tunneling spectroscopy?STM?studies of MoTe₂ films and stanene films grown by molecular beam epitaxy?MBE?.The research results mainly includes the following two parts:?1?The 2H-and 1T?-phase monolayer MoTe₂ films on highly oriented pyrolytic graphite?HOPG?are studied by STM and scanning tunneling spectroscopy?STS?.The phase transition of MoTe₂ could be controlled by a post-growth annealing process,and the intermediate state during the phase transition is directly observed by STM.For 2H-MoTe₂,inversion domain boundaries are presented as bright lines at high sample bias,but as dark lines at lower sample bias.The dI/dV mappings reveal the distinct distributions of electronic states between boundaries and interiors of domains,which may be resulted from different orbit textures.It should be noted that a 2×2 periodic structure is clearly discernable inside the domains,where the STS measurement shows a small dip of¹50 meV at the vicinity of the Fermi level,indicating that the 2×2 periodic structure may be an incommensurate charge density wave?CDW?.Moreover,a 4×4 periodic structure appears in 2H-MoTe₂ grown at a higher substrate temperature.?2?We have successfully grown stanene films on the Indium antimonide InSb?111?substrate,which is confirmed by reflection high energy electron diffraction?RHEED?and STM.Moreover,the buffer layer is observed and any reconstruction of surface is not found on the stanene films.Using STS,a universal bulk gap³5 meV is observed both at the first and the second layer stanene.Besides,the density of states?DOS?within the bulk gap approaches to zero and the surface becomes more flat on the nanometer scale with increasing the temperature of substrate during growth,which may be attributed to the reduce of surface strain.Our STS measurements reveal that edge state is only located at the edge of the second layer stanene.