defining a layer of graphene over photonic crystal waveguide

respected sir,
i have designed a photonic crystal slab and then formed a photonic crystal 
waveguide by removing a row of holes. now i want to place a layer of 
graphene over the waveguide i.e. the portion of the slab from where holes 
have been removed. can u please tell me how to write the code for defining 
such layer over the photonic crystal slab