Reversible Oxygen‐Driven Nickel Oxide Structural Transition on the Nickel(1 1 1) Surface at Near‐Ambient Pressure

Myung Cheol Noh; Jeongjin Kim; Won Hui Doh; Ki‐Jeong Kim; Jeong Young Park

Index: 10.1002/cctc.201702002

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Abstract

NiO cluster formation with strictly controlled O2 exposure on a Ni(1 1 1) 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 O2 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(1 1 1) 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 100 mTorr of O2. Furthermore, metastable NiO islands can be manipulated by varying the partial CO pressure of the gas mixture. The interplay between the CO and O2 molecules on the Ni(1 1 1) is correlated definitely to either surface oxide formation or competitive CO adsorption on the defect‐laden multi‐layered NiO interface.