Tuning the Electronic Structure of Graphene by Molecular Dopants: Impact of the Substrate

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• 作者：Christos Christodoulou ; Angelos Giannakopoulos ; Giovanni Ligorio ; Martin Oehzelt ; Melanie Timpel ; Jens Niederhausen ; Luca Pasquali ; Angelo Giglia ; Khaled Parvez ; Klaus M眉llen ; David Beljonne ; Norbert Koch ; Marco V. Nardi
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：September 2, 2015
• 年：2015
• 卷：7
• 期：34
• 页码：19134-19144
• 全文大小：714K
• ISSN：1944-8252

文摘

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 (鈭?.3 eV) on Cu compared to quartz (鈭?.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.