SURFACE ELECTRONIC-STRUCTURE OF TM(0001) AND YB(111)

Occupied d-like surface states were observed for the close-packed surf aces of Tm(0001) and Yb(111) metal films grown epitaxially on W(110) a nd Mo(110) substrates, respectively. In the case of Tm metal, the surf ace state exhibits almost no dispersion and is extended over the whole surface Brillouin zone, while in the case of Yb metal, it is restrict ed to a narrow region around the ($$$) over bar Gamma point. The surfa ce shifts of the 4f binding energies on these close-packed surfaces we re determined to be 0.47 +/- 0.05 eV for Tm(0001) and 0.45 +/- 0.03 eV for Yb(111). Both values;are substantially smaller than reported prev iously for polycrystalline surfaces of the two metals. State-of-the-ar t band-structure calculations, based on density-functional theory, pre dict a hat surface state slightly above the Fermi energy. There is no obvious explanation for this inconsistency at the present time.