The recent development of ambient pressure XPS makes accessible operando investigation of many phenomena otherwise impossible [1]. The prevention of metal corrosion is of extreme technological importance; therefore, the investigation of the protective action of 2D materials must be carefully assessed [2]. 

We performed ambient pressure XPS in situ experiments on copper coated by graphene and hexagonal boron nitride, in oxidation conditions (O2 atmosphere). To understand the evolution of copper oxidation and the role of graphene, we investigated regions with bare copper, mono- and multi-layers graphene flakes, by using the near ambient pressure scanning photoemission microscope available at ESCAMICROSCOPY beamline (ELETTRA) [3]. Three temperature regimes were identified: (i) up to 300 °C, the amorphous carbon desorbs and the Cu under graphene remains metallic, while the bare Cu regions readily oxidized; (ii) in a short temperature range up to 360 °C, the oxygen starts to intercalate from graphene edges or defects and slightly oxidized the Cu underneath (Figure 1); (iii) at T higher than 360 °C the carbon is etched away.

At HIPPIE beamline (MAX IV), we compared Cu, graphene and hBN through AP-XPS up to 5 mbar in O2 atmosphere. We identified different protection thresholds, with graphene being able to protect the copper up to higher temperature with respect to hBN.  

These in situ experiments clearly highlight the role of 2D materials as protecting layers of copper from oxidation.