**3.2. Chemical doping**

As mentioned briefly in the electrostatic doping section, chemical dopants can be utilized to modify the electrical characteristics of graphene, modifying the Fermi energy to create p- or n-type doping as shown in Figure 14. [19, 46] The chemical doping mechanism of graphene works by having the dopant bond either ionically or covalently to the delocalized pz orbital. [46] The covalent bonding of a dopant with graphene occurs through modification of the delocalized pz orbitals to electrostatically hold an adatom onto the surface, which modifies the band structure by binding the electrons in the pz orbitals, thus creating a required energy (a band gap) for conduction. [46] The chemical dopant can be ionically bonded to a single carbon atom by breaking a c–c bond and attaching to that bonding spot, which breaks the graphene symmetry introducing a scattering defect and a band gap opening. [46, 51] The amount of surface adatoms is reliant upon the dopant and the type of bonding with ionic bonding and larger electronegativity being able to obtain a stronger bond, higher dopant concentration, and higher band gap shifting. [46] However, it should be noted that the higher the doping, the more scattering and the lower the mobility, leading chemical doping to be typically done on vertical devices with a small cross section and thus small diffusion length. [19, 46]

**Figure 14.** The functionalization scheme of graphene utilizing a H2 plasma [46].
