Investigations On Strontium Titanate Surface Reconstructure And Two-dimensional Boron Material

The creation and development of surface science is one of the major achievements of modern science.Two-dimensional structures or materials prepared on the surface have become important research objects.Studying these surface structures can reveal the various behaviors of molecules,atoms,and electrons in a two-dimensional state,and greatly promote the development of related disciplines such as optics,electromagnetics,mechanics,and catalysis.Meanwhile,the two-dimensional materials with novel properties have great application prospects.In this thesis,the surface reconstructions,surface molecular self-assembly films and surface 2D material were studied by surface preparation and detection technologies.Furthermore,the first-dimensional calculation method was used to predict a new two-dimensional boron material.First,various types of reconstructed surfaces were prepared on the surface of SrTiO₃（110）processed with different argon ion sputtering conditions and annealing parameters.These reconstructions were studied by scanning tunneling microscopy combined with low-energy electron diffraction to investigate the structural details.This study found that a single detect method is usually limited,and only a combination of multiple surface characterization techniques can accurately calibrate the surface structures.For the O-layer reconstructed surface,it was inferred that there are some structures associated TiO₂ polyhedron by analyzing the scanning tunneling microscope image and combining with previous studies.The suitable surface of SrTiO₃（110）was selected as the substrate,and the C₆₀molecules deposited on the surface of the substrate by molecular beam epitaxy system to obtain various self-assembled structures of C₆₀0 molecules.The surface imaged were obtained by scanning tunneling microscope,and the interaction between the substrate and C₆₀ molecules was analyzed.The subtle difference of C₆₀ structures on these reconstructions helps to reveal the controlling effects on C₆₀ selfassembly process,such as the structure parameter of substrate,intermolecular and adsorbate-substrate interactions.Detailed image analysis also showed that the C₆₀ molecule was not completely fixed on the reconstituted surface of SrTiO₃（110）,but was continuously rotated at a specific adsorption site.The research has provided experience for achieving controlled molecular self-assembly processes.In addition,using the first-principles calculation method,a new two-dimensional antiferromagnetic boron structure named M-B₂₈ was predicted.The structure is thermodynamics and kinetics stability and is a direct bandgap semiconductor.Correlation calculations show that the ground state of the M-B₂₈ structure is antiferromagnetic.By analyzing the energy band and charge density distribution,the origin of M-B₂₈ magnetism was understund and explaining why the material exhibits antiferromagnetic properties.The material also has a high Young’s modulus and good resistance to strain.The prediction of this structure provides guidance for the preparation of 2D boron materials in the future.Thereafter,boron atoms are deposited on the surfaces of Ag（111）and Pb（110）using molecular beam epitaxy.Structural analysis shows that boron atoms form clusters of different sizes on the surface.The experiments have provided experience in the preparation of two-dimensional boron materials.The Cu（111）surface was selected as the substrate,and the molecular beam epitaxy system was used to further explore the effective way to prepare two-dimensional boron materials.A novel layered copper boride material was successfully prepared.The structural parameters of the material were determined by means of scanning tunneling microscopy combined with low-energy electron diffraction.The two-dimensional crystal structure of Cu₈B₁₄ was determined by first-principles calculation combined with experimental observation.In addition,the study found that boron atoms have another cluster structure on the surface of Cu（111）.The clusters are inferred to be B₇ nanodots by scanning tunneling microscopy and combined with previous calculations.