Charge neutrality and band-gap tuning of epitaxial graphene on SiC by molecular doping
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چکیده
Epitaxial graphene on SiC 0001 suffers from strong intrinsic n-type doping. We demonstrate that the excess negative charge can be fully compensated by noncovalently functionalizing graphene with the strong electronacceptor tetrafluorotetracyanoquinodimethane F4-TCNQ . Charge neutrality can be reached in monolayer graphene as shown in electron-dispersion spectra from angular-resolved photoemission spectroscopy. In bilayer graphene the band-gap that originates from the SiC/graphene interface dipole increases with increasing F4TCNQ deposition and, as a consequence of the molecular doping, the Fermi level is shifted into the band-gap. The reduction in the charge-carrier density upon molecular deposition is quantified using electronic Fermi surfaces and Raman spectroscopy. The structural and electronic characteristics of the graphene/F4-TCNQ charge-transfer complex are investigated by x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The doping effect on graphene is preserved in air and is temperature resistant up to 200 °C. Furthermore, graphene noncovalent functionalization with F4-TCNQ can be implemented not only via evaporation in ultrahigh vacuum but also by wet chemistry.
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تاریخ انتشار 2010