  We show that patterned defects can be used to disrupt the sub-lattice
symmetry of graphene so as to open up a band gap. This way of modifying
graphene's electronic structure does not rely on external agencies, the
addition of new elements or special boundaries. The method is used to predict a
planar, low energy, graphene allotrope with a band gap of 1.2 eV. This defect
engineering also allows semiconducting ribbons of carbon to be fabricated
within graphene. Linear arrangements of defects lead to naturally embedded
ribbons of the semiconducting material in graphene, offering the prospect of
two-dimensional circuit logic composed entirely of carbon.
