Epitaxial Growth And Characterization Of Electronic Structure Of AlSe/Al(111)

In recent years,two-dimensional sulfur-based layered compounds formed by direct selenization or tellurization of metal substrates,such as Pt Se₂,as the second type of Dirac semimetal,has high research value in the fields of optics and electricity.In this paper,high-quality aluminum selenide materials were grown on single-crystal Al(111)substrates by molecular beam epitaxy.X-ray photoelectron spectroscopy,angle-resolved photoelectron spectroscopy and other experimental characterization methods,combined with first-principles calculations to explore its structure and electronic properties,the main conclusions are as follows:(1)Using molecular beam epitaxy,chalcogenide selenium with different coverages was deposited on Al(111)substrate.XPS shows that the d-orbital binding energy of Se becomes larger when 0.75ML is deposited,indicating that charge transfer occurs in the combination of selenium and aluminum.Clear high-energy electron diffraction fringes indicate that Se and Al form very fine single crystals at the substrate surface.And we use scanning tunneling microscopy to find that the atoms on the surface of aluminum selenide alloy are arranged in a hexagonal honeycomb shape.The lattice constant is a=3.8?,and its atomic structure is similar to indium selenide and gallium selenide.Combined with theoretical calculations,it is determined that the matching of aluminum selenide and Al(111)substrates is Al Se(3x3)/Al(111)(4x4),and the atomic structure is consistent with the experimental results.These indicate that we have successfully grown large-area single-crystal Al Se alloys.(2)The electronic structures of single crystal Al(111)substrate and Al Se were characterized by angle-resolved photoelectron spectroscopy(ARPES).Before growth,the surface state band of the Al substrate appears at-4.6e V.A clear energy band appeared when 0.75ML was deposited,and with the increase of the deposition amount,the energy band gradually became blurred,and no new energy band appeared.The surface state energy band of the aluminum substrate still existed and was not affected by selenium element.However,due to the strong hybridization of selenium and aluminum,in the high symmetry directions?-K and?-M,two hole-like energy bands appear at the Fermi surface at-4e V.Combined with theoretical calculations,it is found that the two hole-type energy bands are mainly derived from thep_x andp_y orbitals of selenium,while thep_z orbitals have little contribution to the energy bands due to the strong bonding with the substrate.And the two hole-like energy bands are split by 0.2e V due to spin-orbit coupling.In this thesis,Al Se alloy structure was grown directly on Al substrate by molecular beam epitaxy method for the first time.The atomic structure and electronic properties of Al Se alloy were clearly studied.The research on the physical properties and application prospects of aluminum selenide has laid a foundation.