UV-photoemission study of barium,europium and ytterbium

Measurements are reported of the photoemission spectra and absolute yield of thin films of Eu, Ba and Yb for the photon energy range 2 to 21 eV. Transitions from the occupied 4f-states in Eu and Yb have been observed and the binding energies deduced. The excitation probability of the 4f electrons is found to be very low and an explanation based on their atomic-like nature is given. Transitions involving valence band states are compared with predictions based on published energy band schemes and the density of states for the unoccupied 5d band in Yb is deduced. The effect of chemisorbed oxygen on Ba and Eu surfaces is reported.