Interaction of Oxygen with Thin Cobalt Films

The interaction of oxygen with thin cobalt films supported on oxidized Si(100) substrates was studied using Auger electron spectroscopy (AES) and work function changes (Δφ) at 130 and 300 K. Oxygen uptake curves were derived from the ratio changes of the O KLL and Co LMM Auger signals at 513 and 778 eV, respectively. They showed a constant sticking coefficient ( s o ) up to ≈15 langmuirs, especially at 130 K, possibly indicating adsorption through a molecular precursor that diffuses over the chemisorbed layer. At 300 K, s o = 0.2, while at 130 K, 0.5 ≥ s o ≥ 0.3, depending on the dosing pressure. Up to ≈10 langmuirs O 2 at 300 K, the work function increased 0.20 eV. At that coverage, the Co MVV Auger transitions indicated an oxide formation. From this coverage onward, the work function decreased, saturating at ≈80 langmuirs with a value ≈−1.2 eV below the clean Co surface, pointing to oxygen diffusion into the bulk.