A Surface Spectroscopy Study of U Overlayers on Graphite.

X-ray and ultra violet photoelectron spectroscopies have been used to study U overlayers deposited on graphite by magnetron and straight diode sputtering. We investigated the mode of growth, the electronic structure of the U phase and overleyer-substrate reactions after deposition and annealing. At submonolayer coverage U deposits as clusters pointing to a low overlayer-substrate interaction. With increasing dosage, U clusters agglomerate forming eventually a continuous U overlayer. At low U dosage, U4f and valence band spectra exhibit correlation satellites which are attributed to the narrowing of the 5f bands and eventual 5f localization, because of the decreased coordination of U atoms. In thicker overlayers these satellites are missing showing U to have the same electronic structure as in bulk U metal. Even immediately after deposition some of the surface carbon loses its graphite character and becomes carbidic, which is mainly attributed to a weak interaction between surface U and the graphite substrate. Annealing at 600*C results in further reaction between U and graphite and leads to the formation of UC.

GOUDER Thomas;  COLMENARES C.A.;  NAEGELE Jochen Rainier; 

1995-12-04

JRC11907