STM Study Of The Electronic Modulation On H-BN Thin Films And Pseudo Landau Level On SnTe Surface

In this thesis,mainly two systems are studied using scanning tunneling microscope.One system is the high quality hexagonal boron nitride（h-BN）thin films grown on the surface of Cu foils by means of chemical vapor deposition.The other one is the surface geometric and electronic properties of the tin telluride（SnTe）thin films fabricated on the SrTiO₃ substrates by molecular beam epitaxy.The main experimental results are listed below:（1）Scanning tunneling microscope and spectroscope（STM/S）was applied to the study of h-BN thin film grown on Cu foil by means of chemical vapor deposition（CVD）.Large-scale STM images show atomically flat surface of the BN thin film,and STS data indicate the STM images reflect spatial distribution of tunneling barriers between Cu substrate and STM tip.Hexagonal lattice with atomic resolution was revealed in ultra-low sample bias STM images,while electronic modulations in ordered as well as disordered pattern were observed in high sample bias STM images.It is found that the electronic modulations in STM images are not Mori′e pattern due to lattice mismatch,but originate from spatial distribution of tunneling barrier induced by adsorption of H,B and/or N atoms on Cu surface in the CVD process.（2）By means of molecular beam epitaxy,high quality SnTe（001）islands are deposited on the SrTiO₃ substrates.Using scanning tunneling microscope,the lattice mismatch between the topmost of the islands and the substrates is studied as a function of the height of the SnTe islands.We find that there exist a one directional strain on the surface of few-layer SnTe islands.The lattice mismatch becomes smaller when the height of the island increases.For the islands as thick as 6 unit-cell,the surface lattice mismatch is as large as 5.3%,while for the 17 unit-cell islands,the lattice constants are equal to their bulk values,indicating that the lattice mismatch is eliminated.Scanning tunneling spectra are obtained on the surface with large lattice mismatch.We find the dI/dV curves obtained at 77K differ from that obtained at 4.2K.There are extra peaks on the curve measured at 4.2K.While no similar peak is found in the dI/dV curves obtained on the surface without lattice mismatch.We analysis the energy position of the peaks and conclude that the peaks we observed are pseudo laudau levels which is induced by the strain at the interface.There is an energy gap for a few layer SnTe with lattice mismatch.We find that our experimental results for the energy level of the peaks can be well fitted with the massive dirac laudau level equation,revealing that the pseudo laudau levels detected on the surface of the SnTe islands are massive dirac fermions type.