Tuning the Electronic Structure of Graphene by Molecular Dopants: Impact of the Substrate.
A combination of ultraviolet and X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and first principle calculations was used to study the electronic structure at the interface between the strong molecular acceptor 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (F6TCNNQ) and a graphene layer supported on either a quartz or a copper substrate. We find evidence for fundamentally different charge redistribution mechanisms in the two ternary systems, as a consequence of the insulating versus metallic character of the substrates. While electron transfer occurs exclusively from graphene to F6TCNNQ on the quartz support (p-doping of graphene), the Cu substrate electron reservoir induces an additional electron density flow to graphene decorated with the acceptor monolayer. Remarkably, graphene on Cu is n-doped and remains n-doped upon F6TCNNQ deposition. On both substrates, the work function of graphene increases substantially with a F6TCNNQ monolayer atop, the effect being more pronounced (∼1.3 eV) on Cu compared to quartz (∼1.0 eV) because of the larger electrostatic potential drop associated with the long-distance graphene-mediated Cu-F6TCNNQ electron transfer. We thus provide a means to realize high work function surfaces for both p- and n-type doped graphene.
Humboldt-Universität zu Berlin , Institut für Physik, Brook-Taylor-Straße 6, 12489 Berlin, Germany.
Christos
C
Christodoulou
Laboratory for Chemistry of Novel Materials, University of Mons , Place du Parc 20, 7000, Mons, Belgium.
Angelos
A
Giannakopoulos
Humboldt-Universität zu Berlin , Institut für Physik, Brook-Taylor-Straße 6, 12489 Berlin, Germany.
Giovanni
G
Ligorio
Humboldt-Universität zu Berlin , Institut für Physik, Brook-Taylor-Straße 6, 12489 Berlin, Germany.|Helmholtz-Zentrum Berlin für Materialen und Energie GmbH , Albert Einstein Strasse 16, 12489, Berlin, Germany.
Martin
M
Oehzelt
Humboldt-Universität zu Berlin , Institut für Physik, Brook-Taylor-Straße 6, 12489 Berlin, Germany.
Melanie
M
Timpel
Humboldt-Universität zu Berlin , Institut für Physik, Brook-Taylor-Straße 6, 12489 Berlin, Germany.
Jens
J
Niederhausen
University of Modena e Reggio Emilia , Engineering Department, "E. Ferrari", Via Vigolese 905, 41125, Modena, Italy.|IOM-CNR , Area Science Park, SS 14 Km, 163.5, 34149, Basovizza, Trieste, Italy.|Department of Physics, University of Johannesburg , PO Box 524, Auckland Park, 2006, South Africa.
Luca
L
Pasquali
IOM-CNR , Area Science Park, SS 14 Km, 163.5, 34149, Basovizza, Trieste, Italy.
Angelo
A
Giglia
Max Planck Institute für Polymerforschung , Ackermanweg 10, 55128, Mainz, Germany.
Khaled
K
Parvez
Max Planck Institute für Polymerforschung , Ackermanweg 10, 55128, Mainz, Germany.
Klaus
K
Müllen
Laboratory for Chemistry of Novel Materials, University of Mons , Place du Parc 20, 7000, Mons, Belgium.
David
D
Beljonne
Humboldt-Universität zu Berlin , Institut für Physik, Brook-Taylor-Straße 6, 12489 Berlin, Germany.
Norbert
N
Koch
Humboldt-Universität zu Berlin , Institut für Physik, Brook-Taylor-Straße 6, 12489 Berlin, Germany.
Marco V
MV
Nardi
doping; electrode; graphene; molecular acceptor; photoelectron spectroscopy