Reversible Oxygen-Driven Nickel Oxide Structural Transition on the Nickel(111) Surface at Near-Ambient Pressure

NiO cluster formation with strictly controlled O-2 exposure on a Ni(111) surface has been investigated extensively for decades under ultra-high vacuum (UHV) conditions. The classical model of three-stage Ni oxidation refers to the relationship between NiO cluster evolution and the kinetics of O-2 exposure; however, this information has a critical inherent limitation because of the pressure gap between UHV and real reaction conditions. Here, we report reversible NiO phase transitions on the Ni(111) surface at near-ambient pressure by using scanning tunneling microscopy at room temperature. The restricted kinetic growth of NiO cluster evolution expands unexpectedly to oxide multi-layer formation at 100mTorr of O-2. Furthermore, metastable NiO islands can be manipulated by varying the partial CO pressure of the gas mixture. The interplay between the CO and O-2 molecules on the Ni(111) is correlated definitely to either surface oxide formation or competitive CO adsorption on the defect-laden multi-layered NiO interface. c. 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei