  Superperiodic patterns were observed by STM on two kinds of finite-sized
graphene sheets. One is nanographene sheets inclined from a highly oriented
pyrolitic graphite (HOPG) substrate and the other is several-layer-thick
graphene sheets with dislocation-network structures against a HOPG substrate.
As for the former, the in-plane periodicity increased gradually in the
direction of inclination, and it is easily changed by attachment of a
nanographite flake on the nanographene sheets. The oscillation pattern can be
explained by the interference of electron waves confined in the inclined
nanographene sheets. As for the latter, patterns and their corrugation
amplitudes depended on the bias voltage and on the terrace height from the HOPG
substrate. The interference effect by the perturbed and unperturbed waves in
the overlayer is responsible for the patterns whose local density of states
varies in space.
