Tracking interfacial changes of graphene/Ge(1 1 0) during in-vacuum annealing

Graphene quality indicators obtained by Raman spectroscopy have been correlated to the structural changes of the graphene/germanium interface as a function of in-vacuum thermal annealing. Specifically, it was found that graphene becomes markedly defective at 650 °C. By combining scanning tunneling microscopy, X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy, we concluded that these defects are due to the release of H gas trapped at the graphene/germanium interface. The H gas was produced following the transition from the as-grown hydrogen-termination of the Ge(1 1 0) surface to the emergence of surface reconstructions in the substrate. Interestingly, a complete self-healing process was observed in graphene upon annealing at 800 °C. The identified subtle interplay between the microscopic changes occurring at the graphene/germanium interface and graphene's defect density is integral to advancing the understanding of graphene growth directly on semiconductor substrates, controlled 2D-3D heterogeneous materials interfacing and integrated fabrication technology.