  Chemical vapor deposited graphene is nanopatterned by a spherical
block-copolymer etch mask. The use of spherical rather than cylindrical block
copolymers allows homogeneous patterning of cm-scale areas without any
substrate surface treatment. Raman spectroscopy was used to study the
controlled generation of point defects in the graphene lattice with increasing
etching time, confirming that alongside the nanomesh patterning, the
nanopatterned CVD graphene presents a high defect density between the mesh
holes. The nanopatterned samples showed sensitivities for NO2 of more than one
order of magnitude higher than for non-patterned graphene. NO2 concentrations
as low as 300 ppt were detected with an ultimate detection limit of tens of
ppt. This is so far the smallest value reported for not UV illuminated graphene
chemiresistive NO2 gas sensors. The drastic improvement in the gas sensitivity
is believed to be due to the high adsorption site density, thanks to the
combination of edge sites and point defect sites. This work opens the
possibility of large area fabrication of nanopatterned graphene with extreme
density of adsorption sites for sensing applications.
