  We study local electronic properties of graphene oxide (GO) and reduced
graphene oxide (RGO) on metallic (Pt) and insulating (Si3N4) substrates in
controlled humidity environment. We demonstrate that the supporting substrate
plays a crucial role in interaction of these materials with water, with Pt
making both GO and RGO insensitive to humidity variations and change in
environment. On the other hand, in the case of Si3N4 substrate a significant
difference between GO and RGO with respect to humidity variations is
demonstrated, indicating complete water coverage at ~60% R.H for RGO and ~30%
R.H. for GO. Irrespective of the substrate, both GO and RGO demonstrate
relative independence of their electronic properties on the material thickness,
with similar trends observed for 1, 2 and 3 layers when subject to humidity
variations. This indicates a relatively minor role of material thickness in
GO-based humidity sensors.
