Surface structures and work functions of the LaB₆ (100), (110) and (111) clean surfaces

The structures of the LaB₆ (110) and (111) clean surfaces have been studied by angleresolved XPS, ISS and LEED. The LaB₆ (110) clean surface has the relaxed and reconstructed c(2 × 2) structure where the surface lanthanum atoms are displaced toward the surface and a c(2 × 2) overlayer structure is caused by a displacement of the surface lanthanum atoms. The LaB₆ (111) clean surface has the relaxed (1 × 1) structure where the surface lanthanum atoms are displaced toward the surface. The work functions of the (100), (110) and (111) surfaces have been measured from the width of UPS spectra and are ~2.3, ~2.5 and ~3.3 eV, respectively. The anisotropy of the work functions has been correlated with the surface structures. The origin of the unusually low work functions of the LaB₆ (100) and (110) clean surfaces in refractory materials is interpreted by electric dipole moments produced by positive charges of surface lanthanum ions.