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

The low-pressure oxidation of the Co(1610) surface has been studied within the temperature range 25-250-degrees-C using ellipsometry. After the oxidation high-energy ion scattering, in combination with shadowing and blocking, has been performed to obtain values for the absolute oxygen coverage and the stoichiometry of the oxide. At room temperature the oxidation virtually stops at a value of the ellipsometric parameter deltaDELTA = 2.71-degrees +/- 0.04-degrees, corresponding to an oxygen coverage of (4.1 +/- 0.1) x 10(15) oxygen atoms/cm2. At 200 and 250-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) oxygen atoms/cm2 are taken up, the oxidation proceeds with a relatively tow rate. Low-energy electron diffraction measurements show that no structure is present after room-temperature oxidation, but oxidation at 200 and 250-degrees-C results in a partially ordered oxide. The stoichiometry of the oxide is found to be Co1.03+/-0.15O.