Photoemission study of formation and oxidation of a cerium-copper interface

Deposition of Ce on a polycrystalline Cu film has been studied by x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy with use of synchrotron radiation. The formation of a relatively thick interface, >100 A, is observed at room temperature. The interface is found to contain about 80 at. % Ce and cannot be accounted for in terms of formation of an intermetallic compound based on the Ce-Cu phase diagram. A conversion from trivalent to tetravalent Ce ions is observed for a thin Ce-Cu interface when exposed to oxygen. The Cu substrate is not oxidized appreciably for oxygen exposures up to 1000 langmuir