OXIDATION OF THE CO(10(1)OVER-BAR0) SURFACE

The low-pressure oxidation of the Co(1610) surface has been studied wi thin the temperature range 25-250-degrees-C using ellipsometry. After the oxidation high-energy ion scattering, in combination with shadowin g and blocking, has been performed to obtain values for the absolute o xygen coverage and the stoichiometry of the oxide. At room temperature the oxidation virtually stops at a value of the ellipsometric paramet er deltaDELTA = 2.71-degrees +/- 0.04-degrees, corresponding to an oxy gen coverage of (4.1 +/- 0.1) x 10(15) oxygen atoms/cm2. At 200 and 25 0-degrees-C the initial oxidation rate appears lower but no saturation is observed: after a fast initial stage, in which about 7 x 10(15) ox ygen atoms/cm2 are taken up, the oxidation proceeds with a relatively tow rate. Low-energy electron diffraction measurements show that no st ructure is present after room-temperature oxidation, but oxidation at 200 and 250-degrees-C results in a partially ordered oxide. The stoich iometry of the oxide is found to be Co1.03+/-0.15O.