Imaging and tuning molecular levels at the surface of a gated graphene device

A. Riss, S, Wickenburg, L. Z. Tan, H.-Z. Tsai, Y. Kim, J. Lu, A. J. Bradley, M. M. Ugeda, K. L. Meaker, K. Watanabe, T. Taniguchi , A. Zettl, F. R. Fischer, S. G. Louie, M. F. Crommie

Department of Physics, Department of Chemical and Biomolecular Engineering, Department of Chemistry, University of California, Berkeley, CA 94720, U. S. A.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U. S. A.
Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
Kavli Energy NanoSciences Institute, University of California and the Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U. S. A.
Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
Department of Chemistry, National University of Singapore, Singapore 117543, Singapore
Institut für Angewandte Physik, Technische Universität Wien, 1040 Wien, Austria

ACS Nano 8 (2014) 5395-5401

Gate-controlled tuning of the charge carrier density in graphene devices provides new opportunities to control the behavior of molecular adsorbates. We have used scanning tunneling microscopy (STM) and spectroscopy (STS) to show how the vibronic electronic levels of 1,3,5-tris(2,2-dicyanovinyl)benzene molecules adsorbed onto a graphene/BN/SiO₂ device can be tuned via application of a backgate voltage. The molecules are observed to electronically decouple from the graphene layer, giving rise to well-resolved vibronic states in dI/dV spectroscopy at the single-molecule level. Density functional theory (DFT) and many-body spectral function calculations show that these states arise from molecular orbitals coupled strongly to carbon-hydrogen rocking modes. Application of a back-gate voltage allows switching between different electronic states of the molecules for fixed sample bias.

Corresponding authors: Alexander Riss and Michael F. Crommie

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