  We study the stability of various kinds of graphene samples under soft X-ray
irradiation. Our results show that in single layer exfoliated graphene (a
closer analogue to two dimensional material), the in-plane carbon-carbon bonds
are unstable under X-ray irradiation, resulting in nanocrystalline structures.
As the interaction along the third dimension increases by increasing the number
of graphene layers or through the interaction with the substrate (epitaxial
graphene), the effect of X-ray irradiation decreases and eventually becomes
negligible for graphite and epitaxial graphene. Our results demonstrate the
importance of the interaction along the third dimension in stabilizing the long
range in-plane carbon-carbon bonding, and suggest the possibility of using
X-ray to pattern graphene nanostructures in exfoliated graphene.
