THE REACTION OF CLEAN LI SURFACES WITH SMALL MOLECULES IN ULTRAHIGH-VACUUM .1. DIOXYGEN

The creation of clean Li surfaces by vapor deposition and their subseq uent interaction with oxygen have been studied by a combination of ell ipsometry and Auger electron spectroscopy in ultrahigh vacuum. The ell ipsometric parameters Delta and Psi for Li thin films vapor-deposited on a Ni substrate were monotonic functions of the film thickness, and in reasonable agreement with theoretical values calculated for dense ( nonporous) films. The clean Li surface is very reactive sticking coeff icient of unity at the initial stage of oxidation at 5 x 10(-8) Torr O -2. Oxidation of the entire film (75 Angstrom maximum) into Li2O proce eded with an approximately unit reaction probability. A model of oxida tion with in-plane contraction of the oxide film (continuously exposin g fresh Li) is proposed to explain both the high rate of reaction and the observed variation of Delta and Psi with time of exposure to O-2.