A method includes depositing a first material layer over a first substrate; and depositing a graphene layer over the first material layer. The method further includes depositing an amorphous silicon layer over the graphene layer and bonding the amorphous silicon layer to a second substrate, thereby forming an assembly. The method further includes annealing the assembly, thereby converting the amorphous silicon layer to a silicon oxide layer. The method further includes removing the first substrate from the assembly and removing the first material layer from the assembly, thereby exposing the graphene layer.