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Abstract

Spin-, angle- and energy-resolved photoemission with circularly polarized synchrotron radiation from BESSY has been applied to deduce information about the electronic structure of silicon in the Λ-direction. We used the highly symmetrical experimental set-up of normal radiation incidence and normal electron emission. This method, which has in the past several times been applied to metals and rare gas crystals with medium and high atomic numbers, has thus been applied now to a semiconductor with a low atomic number (Z = 14). For photon energies between 5.5 and 10 eV we find a peak V in the photoemission spectra which corresponds to a transition from the valence bands in the bulk band structure of silicon in the Λ-direction. The electrons which contribute to the peak are spin polarized due to a spin-orbit splitting ΔE_so smaller than 50 meV. Adsorption of 0.5 ML Ag or Au induces band bendings and work function changes and yields a sharper peak and less secondary electron background than the clean Si(1 1 1)-surface. For both the clean and adsorbate covered surface and k_⊥ away from Γ we determine ΔE_so from a spin analysis of peak V and find values between 20 and 35 meV with typical errors of 10 meV. These values in Λ-direction are smaller than the ΔE_so-value of 44 meV at the Γ-point [1, 2].