Synthesis of disilicide single crystal thin films with a new silicon network and study on its electronic structure

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Evaporation of alkali earth metals and rare earth metals such as Ca, Sr and La on Si substrates forms MSi_2 (M = Ca, Sr, La) epitaxial film with a new various Si network, different from the diamond-type network. Although, carbon, which locates just above Si in the periodic table, forms a various network such as graphite, C_<60> and carbon nanotube, only diamond-type network has been known for Si. The purpose of the present study is to grow MSi_2 (M = Ca, Sr, La) epitaxial films and to study its electronic band structure depending on the Si network and the M ion located between the Si networks.First, we have attempted to grow CaSi_2/Si(111) epitaxial films by evaporating Ca onto the Si(111) substrates. We have found the growth condition by using RHEED (Reflection High Energy Electron Diffraction) and AES (Auger Electron Spectroscopy) and succeeded in the growth of CaSi_2/Si(111) epitaxial films with a substrate temperature of 600 ℃ and the evaporation rate of 0.06-0.08 Å/s. We have carr … More ied out on angle-resolved photoemission spectroscopy (ARPES) for the grown epitaxial films on beamlines BL7 and BL9 at HiSOR of Hiroshima Synchrotron Radiation Center, Hiroshima University. With increasing the thickness of the evaporated Ca ion, θ, the hybridization band between the Ca 3d and Si 3p states, crossing the Fermi level (E_F), is observed. The experimental results roughly correspond to the band dispersion derived from the band-structure calculation based on LPAW [1]. We have found that with increasing 0, the Fermi wave number increases. In addition, we have succeeded in the observation of the Fermi surface with a six-fold symmetry, reflecting the surface of CaSi_2/Si(111).After the experiments for CaSi_2/Si(111), we moved to study for SrSi_2/Si(111). Now, we have detected the band dispersion of SrSi_2/Si(111) films grown at the substrate temperature of 700 ℃. Continuously, we plan to investigate systematically the electronic structure of MSi_2/Si by changing M and orientations of the substrate Si.[1] S. Fahy and D. R. Hamann, Phys. Rev. B 41, 7587 (1990). Less