Surface states on the LaB₆(100), (110) and (111) clean surfaces studied by angle-resolved UPS

The surface states on the LaB₆(100), (110) and (111) clean surfaces have been studied by means of angle-resolved UV photoelectron spectroscopy with unpolarized light. Surface states on LaB₆(110) and (111) have been observed for the first time, and the energy-band structures have been determined. The surface states on LaB₆(110) are located at ∼1.8 and ∼3.0 eV below E_F. They are associated with the occurrence of the c(2 × 2) surface structure on LaB₆(110). The surface states on LaB₆(111) are located at ∼1.5 and ∼2 eV below E_F. The dispersion of the lower band is relatively large (∼0.9 eV) compared with those on LaB₆(100) and (110). The surface state at ∼2 eV below E_F on LaB₆(111) has a maximum energy at Γ point (k∥ = 0), while that on LaB₆(100) has a minimum energy at Γpoint. The surface state at ∼2 eV below E_Fon LaB₆(100) possesses Δ₁ symmetry at k∥ = 0, and has even parity with respect to the (010) and (011) planes. The surface state at ∼1.8 eV below E_F on LaB₆(110) has even parity with respect to the (11̄0) plane, and odd parity with respect to the (001) plane. The surface state at ∼3.0 eV below E_F has even parity with respect to both the (11̄0) and (001) planes. The low-lying surface state on LaB₆(111) has Δ₁ symmetry at k∥ = 0. All these surface states on the LaB₆ clean surfaces are interpreted in terms of dangling bonds of the surface boron frameworks which are mainly B 2p in character.