Transition mechanism from semimetallic to semiconductor behavior in a graphene film at the formation of a multiply connected structure

Recently, it has been found that “closed” nanopores with connected edges lying in neighboring layers can be formed in films consisting of one-to-five-layer graphene flakes irradiated by electrons or heavy ions. In the latter case, a significant change in the transport properties of such modified films from the semimetallic to semiconductor behavior is observed. However, the complete understanding of the mechanism of this transition has not been achieved. A mechanism of such behavior proposed in this work is based on the formation of several graphene layers topologically connected by several nearly located closed nanopores. In this case, the pronounced curvature of graphene layers disturbs the semimetallic character of the spectrum in this system.