Graphene as an Ideal Buffer Layer for the Growth of High-Quality Ultrathin Cr₂O₃ Layers on Ni(111)

Metal-oxide nanostructures play a fundamental role in a large number of technological applications, ranging from chemical sensors to data storage devices. As the size of the devices shrinks down to the nanoscale, it is mandatory to obtain sharp and good quality interfaces. Here, it is shown that a two-dimensional material, namely, graphene, can be exploited as an ideal buffer layer to tailor the properties of the interface between a metallic substrate and an ultrathin oxide. This is proven at the interface between an ultrathin film of the magnetoelectric antiferromagnetic oxide Cr₂O₃ and a Ni(111) single crystal substrate. The chemical composition of the samples has been studied by means of X-ray photoemission spectroscopy, showing that the insertion of graphene, which remains buried at the interface, is able to prevent the oxidation of the substrate. This protective action leads to an ordered and layer-by-layer growth, as revealed by scanning tunneling microscopy data. The structural analysis performed by low-energy electron diffraction indicates that the oxide layer grown on graphene experiences a significant compressive strain, which strongly influences the surface electronic structure observed by scanning tunneling spectroscopy.