Growth of ultrathin cobalt oxide films on Pt(111)

International audienceCobalt surface oxides grown on Pt(111) by depositing Co and dosing with molecular oxygen at temperatures ranging between 300 and 740 K were studied by STM. Oxidation of 1 monolayer (ML) Co results in a 2D moiré structure interpreted as a polar CoO(111) atomic bilayer. It is expanded by 2.7 ± 0.6% in the surface plane with respect to bulk CoO. Insufficient oxidation leads to defects in the moiré pattern, consisting of triangular dislocation loops of different sizes; the smaller ones occupy half of the moiré cell. Low-temperature annealing (450 K) can be used to create a zigzag phase, which is mainly observed in 1-ML-thick areas after several cycles of 1 ML Co deposition and oxidation. The CoO films obtained by deposition/oxidation cycles exhibit Stranski-Krastanov growth; the structure of the 2D layer between the islands depends on the thermal treatment. It exhibits the moiré pattern after annealing at 740 K, whereas the zigzag phase was observed after low-temperature annealing. We have also studied oxidation of surface alloys obtained by depositing Co and annealing. On these surfaces, we found a quasi-(3 × 3) reconstruction. Structure models are presented for all phases observed, and we argue that some of the moiré like structures might be useful as templates for metal cluster growth