The dielectric 35 may be arranged to provide an electrically insulating layer between the graphene and one or more of the electrodes 25 or other components of the apparatus 21. The dielectric 35 may comprise any suitable electrically insulating material. In some examples the dielectric 35 may comprise aluminum oxide which could be deposited using atomic layer deposition or any other suitable process. In some examples the dielectric 35 may comprise a polymer or any other suitable material.

In some examples the dielectric 35 may also be arranged as a barrier to protect the graphene from contamination. For instance the dielectric 35 could comprise a material which is impermeable, or partially impermeable to contaminants such as water or oxygen or anything else which could contaminate or affect the charge carrier characteristics of the graphene.

In some examples the graphene may be activated before the dielectric 35 is deposited. The activation of the graphene may counteract the low surface energy of the graphene and may enable uniform deposition of the dielectric 35 over the graphene. For instance, a seed layer may be evaporated onto the graphene to enable the atomic layer deposition of the dielectric 35.