  We report about investigations of time-dependent structural modifications in
single crystal graphene due to laser irradiation even at moderate power levels
of 1mW in a diffraction limited spot. The structural modifications have been
characterized by in situ scanning confocal Raman spectroscopy, atomic force
height microscopy and transport studies. The time evolution of the Raman
spectrum reveals two different effects: on a short time scale, dopants,
initially present on the flake, are removed. The longer time scale behavior
points to a laser induced gradual local decomposition of single crystal
graphene into a network of interconnected nano-crystallites with a
characteristic length scale of approximately 10 nm due to bond-breaking. The
broken bonds offer additional docking sites for adsorbates as confirmed in
transport and AFM height studies. These controlled structural modifications may
for instance be valuable for enhancing the local reactivity and trimming
graphene based gas sensors.
