XPS studies of the valence band and of the 4f and 3d levels of Ce hydrides

We have analyzed the valence band region and the 3d core levels of Ce, CeH2.1 and CeH2.9 by means of X-ray photoelectron spectroscopy. Hydrogen induced states appear about 5 eV below EF. The density of states at EF is about 4 times smaller in CeH2.1 than in Ce and vanishes completely in CeH2.9 in agreement with the metal to semiconductor transition which was observed in resistivity measurements. The 4f level is well split off the hydrogen induced band at 2 eV for both hydrides. The 3d core levels are shifted by 1.9 and 2.1 eV from Ce to CeH2.1 and CeH2.9, resp., and exhibit intense satellites on the low BE side. A simple method to prepare large, compact samples of rare earth hydrides is described.