  The electronic properties of graphene can be modified by the local
interaction with a selected metal substrate. To probe this effect, Scanning
Tunneling Microscopy is widely employed, particularly by means of local
measurement via lock-in amplifier of the differential conductance and of the
field emission resonance. In this article we propose an alternative, reliable
method of probing the graphene/substrate interaction that is readily available
to any STM apparatus. By testing the tunneling current as function of the
tip/sample distance on nanostructured graphene on Ni(100), we demonstrate that
I(z) spectroscopy can be quantitatively compared with Density Functional Theory
calculations and can be used to assess the nature of the interaction between
graphene and substrate. This method can expand the capabilities of standard STM
systems to study graphene/substrate complexes, complementing standard
topographic probing with spectroscopic information.
