Graphene/Substrate Charge Transfer Characterized by Inverse Photoelectron Spectroscopy

Wave vector-resolved inverse photoelectron spectroscopy (IPES) measurements demonstrate that there is a large variation of interfacial charge transfer for graphene grown by chemical vapor deposition (CVD) on a range of dielectric or metallic substrates. Monolayer graphene grown by CVD on monolayer BN(0001)/ Ru(0001) exhibits strong charge transfer from the substrate to graphene of 0.07(1) e(-) per carbon atom, as manifested by filling of the pi* band and displacement of the Fermi level. IPES measurements of CVD single layer graphene on Ru indicate a substrate-to-graphene charge transfer from the substrate of 0.06(1) e(-) per carbon atom, in agreement with reported angle-resolved photoemission results. The IPES spectra of CVD single layer graphene on Ni(poly) and on Cu(poly) indicate 0.03(1) e- per carbon atom charge transfer from Ni and Cu substrates. Single layer graphene has also been grown by free radical-assisted CVD on MgO(111), resulting in a layer of graphene and an oxidized carbon interfacial layer between the graphene and the substrate. IPES measurements indicate that 0.02(1) e(-) per carbon atom charge is transferred from graphene to the MgO substrate. Additionally, IPES and photoemission data indicate that single layer graphene/MgO(111) exhibits a band gap. These data demonstrate that IPES is an effective method for precise measurement of substrate/ graphene charge transfer and related electronic interactions, in part because of the extreme surface sensitivity of the technique, and suggest new strategies for extrinsic doping of graphene for controlled mobilities for device applications.