Oxygen adsorption on thin cobalt films supported on silica

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 K and 300 K. The oxygen uptake curves showed a constant sticking coefficient (s0) up to ≊15 L, indicating adsorption through a molecular precursor. At 300 K, s0=0.2, while at 130 K, 0.5≥s0≥0.3, depending on the dosing pressure. Up to ≊10 L O2 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 onwards, the work function decreased, saturating at ≊80 L with a value ≊−1.2 eV below the clean Co surface, pointing to oxidation.