Tuning the charge carriers in epitaxial graphene on SiC(0001) from electron to hole via molecular doping with C60F48

Abstract

We demonstrate that the intrinsic electron doping of monolayer epitaxial graphene on SiC(0001) can be tuned in a controlled fashion to holes via molecular doping with the fluorinated fullerene C60F48. In situ angle-resolved photoemission is used to measure an upward shift of (0.6 ± 0.05) eV in the Dirac point from −0.43 eV to +0.17 eV relative to the Fermi level. The carrier density is observed to change from n ∼ (1 × 1013 ± 0.1 × 1013) cm−2 to p ∼ (2 × 1012 ± 1 × 1012) cm−2. We introduce a doping model employing Fermi-Dirac statistics which explicitly takes temperature and the highly correlated nature of molecular orbitals into account. The model describes the observed doping behaviour in our experiment and readily explains why net p-type doping was not achieved in a previous study [Coletti et al., Phys. Rev. B 81, 8 (2010)] which used tetrafluorotetra-cyanoquinodimethane (F4-TCNQ).

Water Affinity to Epitaxial Graphene: The Impact of Layer Thickness

“…Additionally, the buffer layer features (hardly distinguishable on the surface potential image under ambient conditions) have also become visible in vacuum. The work function value of 1LG obtained in vacuum, (4.31 ± 0.02) eV agrees well with the value of 4.34 eV measured by Tadich et al on clean epitaxial graphene …”

Controlling Molecular Doping in Organic Semiconductors

“…3D dopant structures are bulkier than the planar structures, and thus promising for reducing diffusion rates . C 60 F 36 and C 60 F 48 (not shown) are two examples of substituted C 60 molecules that are decorated with electron‐withdrawing fluorine to increase the EA. Both molecules are completely insoluble and can only be processed using vacuum deposition.…”

Surface functionalization of WSe2 by F16CoPc

“…Such two‐dimensional electron systems confined to an interface can exhibit fascinating physical properties and, therefore, are of particular interest to fundamental as well as applied research. Following the concept of interface charge transfer, also graphene and TMD monolayers have been modified by the deposition of electron acceptors or donors with the results of intriguing properties such as superconductivity or magnetism . Recently, it has been demonstrated that doping electrons into the surface of the TMD WSe 2 results in the formation of a two‐dimensional electron gas concomitant with an unusual shift of the chemical potential indicating a negative electron compressibility, and a lifting of the spin degeneracy of the valence bands .…”