Surface Preparation And Characterization Of Antimony And Tin Based Two-dimensional Materials

When the scale of layered material changes from three-dimension(3D)to two-dimension(2D)or even lower dimensions,it usually shows extensive symmetry breaking and size-related quantum confinement effects,and many of its properties will also change accordingly.The 2D material family and its derived materials have a wide variety and rich characteristic attributes.They have excellent performance in physical,chemical,optical,and electronic properties,providing the potential for their application in multiple fields.Their small size and high maneuverability also provide a broader application prospect.Herein we use molecular beam epitaxy to grow antimony and tin based two-dimensional materials which there are few research results about but are important for new materials,new properties and new device exploration in 2D material study,and use low-temperature scanning tunneling microscope/spectroscopy(STM/STS),angle-resolved photoelectron spectroscopy(ARPES)and other technologies to characterize the topological and electrical properties.We have successfully prepared antimonene with high epitaxial stress,discovered the interface superconductivity and interface polarons phenomenon of SnSe2 films,and the quantum confinement effect caused by the substrate in Sn films.Our work provides important reference value for exploring the novel properties and practical applications of two-dimensional materials.In Chapter Ⅰ,we the mainly introduce the classification,main properties,growth methods and characterization methods of two-dimensional materials,and then summarize the research work of this paper.In Chapter Ⅱ,the growth of antimony atoms on Ag(111),Ag(100),Cu(111)and Au(111)metal single crystal substrates is studied,and the combination of STM and Density functional theory(DFT)calculations proves that We have successfully prepared antimonene on Ag(111)single crystal.In Chapter Ⅲ,1T-SnSe2 films were prepared on HOPG substrates.A V-shaped band gap near the Fermi level was observed in the STS spectra of both single-layer(ML)and double-layer(BL)films.For BL films,the energy gap is within 32meV-44meV,and the conductivity loss at 5K is as high as 90%.With the temperature gradually increased to 77K,and the V-shaped band gap gradually evolved into a shallow dip.This band gap exhibits the characteristics of a pseudgap.At the same time,many defects were observed on the film surface,mainly classified as point,line and surface defects,and due to the pinning of the defects and the effect of the HOPG substrate,these defects were accompanied by charge density waves with a period of(2 × 2).The appearance of charge density waves in point defects and line defects have about 3 cycle lengths.In Chapter Ⅳ,through the combination of STM and ARPES technology,the appearance of interfacial polarons was observed in ML SnSe2 films epitaxially grown on a niobium-doped strontium titanate(STO)substrate.The ARPES energy spectra show that the energy band structure has a nearly flat energy band,and this in-gap band is obviously related to the charge modulation in real space phenomenon observed by STM.Based on this,we proposed an interface polaron model,which attributed the in-gap band to the charge accumulation at the SnSe2 and STO interface and the electron-phonon coupling effect causing the formation of self-trapped small polarons.In Chapter Ⅴ,ML and BL stanene films were prepared on the oxidized Cu(110)surface,and their surface topological and electronic structures were characterized by STM.It was found that the dl/dV spectrum of a specific region of the film surface has obvious oscillation peaks,and the intensity of the oscillation peaks increase in the positive direction of the bias voltage increases,and the interval between the peak positions also gradually increases.Through dl/dV map analysis,a rectangular quantum corral pattern caused by the quantum confinement effects was observed on the surface of ML stanene stanene films.The quantum corrals come from the effect of the closed rectangular boundary formed by the(2 × 1)reconstruction phase of the CuO surface of the Sn within the closed rectangular boundary.So the quantum confinement effects occur on ML stanene films.