It was interesting to observe the island features of ~1–2 mmon the
IPGE surface (i.e., “white” areas in Fig. 1d). SEM characterization
indicated that there were almost no graphene present in the “black”
boundaries. The island formation occurred right after inkjet printing
and was not caused by the reduction step. The island formation was
also observed to be much less pronounced on more hydrophilic
substrates and appeared to be dependent on the hydrophobicity of the
initial surface. Within each island, graphene appeared to be densely
stacked with the appearance of secondary boundaries (i.e., “white”
lines in the SEM image of Fig. 1e) that were continuously networked
over an average distance of ~20–30 μm. At high magnification
(Fig. 1f), the graphene sheets appear to be more wrinkled and
stacked less uniformly at these boundaries than in the areas within
the boundaries. This morphological development was observed on
other substrate materials.