Technologies are generally described for method and systems effective to at least partially alter a defect in a layer including graphene. In some examples, the methods may include receiving the layer on a substrate where the layer includes at least some graphene and at least some defect areas in the graphene. The defect areas may reveal exposed areas of the substrate. The methods may also include reacting the substrate under sufficient reaction conditions to produce at least one cationic area in at least one of the exposed areas. The methods may further include adhering graphene oxide to the at least one cationic area to produce a graphene oxide layer. The methods may further include reducing the graphene oxide layer to produce at least one altered defect area in the layer.