Lanthanum, Cerium, Praseodymium, and Neodymium Metals and Their Interaction with Oxygen Studied by Photoelectron Spectroscopy

摘要

Clean films of La, Ce, Pr, and Nd, prepared by in situ evaporation have been investigated by photoelectron spectroscopy. Different light sources He I (hv = 21.2 eV), He II (hv = 40.8 eV) and Mg K alpha (hv = 1253.6 eV) have been used for the electron excitation in order to characterize the metals. Measurements have been performed after exposing the clean metals to various amounts of oxygen. From the vanishing of the emission from the sd conduction band upon exposure the conclusion is drawn that an oxide layer thicker than the probing depth (20 A) is formed on all four metals and that the oxide (at room temperature) has the form: Me sub 2 O sub 3 , Me=La, Ce, Pr, Nd. The tetravalent cerium oxide is obtained when the film is heated to about 600 exp 0 C during oxygen exposure. The interaction with oxygen is also characterized by recording the oxygen 1s level and some metal core levels (Me 3d, 4d and 4p). The results from the pure metals and from the metal oxides give further experimental evidence for a 4f level binding energy of 1.9 eV in gamma -cerium. (Atomindex citation 13:694995)