Electronic Structure of Self-Assembled Monolayers on Au(111) Surfaces: The Impact of Backbone Polarizability

Authors

  • LinJun Wang,

    1. Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences 100190 Beijing (P.R. China)
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  • Gerold M. Rangger,

    1. Institute of Solid State Physics, Graz University of Technology Petersgasse 16, A-8010 Graz (Austria)
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  • Lorenz Romaner,

    1. Institute of Solid State Physics, Graz University of Technology Petersgasse 16, A-8010 Graz (Austria)
    2. Department of Material Physics, University of Leoben Franz-Josef Str. 18/II, A-8700 Leoben (Austria)
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  • Georg Heimel,

    1. Insitut für Physik, Humboldt-Universität zu Berlin Newtonstr. 15, 12489 Berlin (Germany)
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  • Tomas Bučko,

    1. Fakultät für Physik and Center for Computational Materials Science, Universität Wien Sensengasse, 1090 Wien (Austria)
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  • ZhongYun Ma,

    1. Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences 100190 Beijing (P.R. China)
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  • QiKai Li,

    1. Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences 100190 Beijing (P.R. China)
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  • Zhigang Shuai,

    Corresponding author
    1. Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences 100190 Beijing (P.R. China)
    2. Department of Chemistry Tsinghua University 100084 Beijing (P.R. China)
    • Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences 100190 Beijing (P.R. China).
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  • Egbert Zojer

    Corresponding author
    1. Institute of Solid State Physics, Graz University of Technology Petersgasse 16, A-8010 Graz (Austria)
    • Institute of Solid State Physics, Graz University of Technology Petersgasse 16, A-8010 Graz (Austria).
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Abstract

Modifying metal electrodes with self-assembled monolayers (SAMs) has promising applications in organic and molecular electronics. The two key electronic parameters are the modification of the electrode work function because of SAM adsorption and the alignment of the SAM conducting states relative to the metal Fermi level. Through a comprehensive density-functional-theory study on a series of organic thiols self-assembled on Au(111), relationships between the electronic structure of the individual molecules (especially the backbone polarizability and its response to donor/acceptor substitutions) and the properties of the corresponding SAMs are described. The molecular backbone is found to significantly impacts the level alignment; for molecules with small ionization potentials, even Fermi-level pinning is observed. Nevertheless, independent of the backbone, polar head-group substitutions have no effect on the level alignment. For the work-function modification, the larger molecular dipole moments achieved when attaching donor/acceptor substituents to more polarizable backbones are largely compensated by increased depolarization in the SAMs. The main impact of the backbone on the work-function modification thus arises from its influence on the molecular orientation on the surface. This study provides a solid theoretical basis for the fundamental understanding of SAMs and significantly advances the understanding of structure–property relationships needed for the future development of functional organic interfaces.

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