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