Multichannel scanning probe microscopy and spectroscopy of graphene moiré structures

The graphene moiré structures on 4d and 5d metals, as they demonstrate both long (moiré) and short (atomic) scale ordered structures, are the ideal systems for the application of scanning probe methods. Taking graphene-Ir(111) as an example, we present the complex studies of this graphene-metal moiré-structure system by means of 3D scanning tunnelling and atomic force microscopy/spectroscopy as well as Kelvin-probe force microscopy. The results clearly demonstrate variation of the moiré and atomic scale contrast as a function of the bias voltage as well as the distance between the scanning probe and the sample, allowing one to discriminate between topographic and electronic contributions in the imaging of a graphene layer on metals. The presented results are compared with the state-of-the-art density functional theory calculations demonstrating excellent agreement between theoretical and experimental data.