Determination of the Tb A_4- critical point energy from angle-resolved UV photoemission of Tb(0001)

The authors report an angle-resolved UV photoemission study of the clean (0001) surface of the rare-earth metal terbium. Normal emission spectra were recorded in the photon energy range 12-50 eV using synchrotron radiation. A number of well-defined features were observed which showed negligible dispersion with photon energy. Close similarity is found between these spectra and those from the (0001) surfaces of Y, Gd and Ho. The binding energy of the Gamma _4- critical point is determined to be 1.5(+or-0.1) eV. They suggest that the apparent shift of the Tb Delta ₁ band to higher binding energy reported by previous workers was a result of the significant Fe contamination of their sample.