  The effects of Ga+ ion irradiation and high temperature annealing on behavior
of nanocrystalline graphene directly grown on quartz and sapphire are
presented. It is shown that nanocrystalline graphene stands fairly high doses
of ion irradiation (up to 3e14 cm-2 of 5 to 50 keV Ga+ ions) without
degradation in conductance. At higher doses, nanocrystalline graphene rapidly
loses its conductance and at doses over 2e15 cm-2 becomes actually insulating.
Annealing in vacuum restores conductance of the irradiated nanocrystalline
graphene and, if the irradiation has not exceeded a dose of 3e15 cm-2, this
restoration can be complete. Ion irradiation at high doses approaching 1e16
cm-2 results in complete ion sputtering of a few layer graphene. Along with the
irradiation-induced reduction of conductance and the temperature-induced
restoration of conductance, two other effects of the ion irradiation are the
enhancement of adhesion of graphene to substrate and the increase in the
nucleation capability of substrate for direct deposition of graphene. For 50
keV Ga+ ions, the enhancement of adhesion is observed at irradiation doses over
2e14 cm-2. The promoted graphene nucleation is observed in a broad dose range.
It is shown that the above effects can be used for development of methods of
patterning of graphene on insulating substrates and a method of imprint
lithography of graphene.
