Highlighting the Dynamics of Graphene Protection to Oxidation of Copper under Operando Condition (vol 11, pg 29448, 2019)

We performed spatially-resolved near-ambient-pressure photoemission spectromicroscopy on graphene-coated copper in operando under oxidation conditions in oxygen atmosphere (0.1 mbar). We investigated regions with bare copper and areas covered with mono- and bi-layers graphene flakes, in isobaric and isothermal experiments. The key method in this work is the combination of spatial and chemical resolution of the scanning photoemission microscope operating in near-ambient-pressure environment, thus allowing to overcome both materials and pressure gap typical of standard UHV XPS and to observe in operando the protection mechanism of graphene towards copper oxidation. The ability to perform spatially resolved XPS and imaging at high pressure allows for the first time a unique characterization of the oxidation phenomenon by means of photoelectron spectromicroscopy, pushing the limits of this technique from fundamental studies to real materials in working conditions. While bare Cu oxidizes naturally at room temperature, our results demonstrate that such graphene coating act as an effective barrier to prevent copper oxidation at high temperatures (over 300 °C), until oxygen intercalation beneath graphene starts from boundaries and defects. We also show that bilayers flakes can protect at even higher temperature. The protected metallic substrate, therefore, does not suffer corrosion preserving its metallic character, making this coating appealing for any application in an aggressive atmospheric environment at high temperature.