Graphene as the anti-oxidation protective layer: How good or bad can it be?

Abstract

This study investigates the conditional anti-oxidation layer of graphene on Cu and its variation of morphology and strain state, demonstrating that the oxidation process could be divided into two stages. The chemical vapor deposition (CVD) growth and a high-humidity environment were exploited to observe the Cu foil oxidizing with the protection layer of graphene. The observation of optical microscopy (OM) and scanning electron microscopy (SEM) reveals the sequence process of the anti-oxidation layer of graphene on the diverse Cu orientations. Except for the wrinkles on graphene and orientations of Cu, the vacancies in the graphene play a crucial role in anti-oxidation. Furthermore, the oxidation of underlying Cu deteriorates the quality of graphene and reduces the strength of interaction at the graphene/Cu interface. The oxidation of graphene-capped Cu is divided into two stages: (i) The attenuated graphene/Cu interaction due to the Cu oxidation beneath, and (ii) the generation and enlargement of CuO particles damage the adjacent graphene, as clearly observed in the OM and SEM images. The time evolution analysis using angular-resolved photoelectron spectroscopy (ARPES) offers robust evidence to support the worse quality of graphene and the decoupling between graphene and Cu foil after the oxidation process. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy express that the defects are created by the degradation of graphene rather than the generation of external functional groups. Thus, the Cu oxidation simultaneously influences both the substrate (Cu) and the protective layer (graphene), substantially weakening the graphene/Cu interaction.