Abstract
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.
Highlights
Combining organic molecules with graphene creates new opportunities for fabricating hybrid devices with tailored properties
We have used scanning tunneling microscopy (STM) and spectroscopy (STS) to show how the vibronic electronic levels of 1,3,5-tris(2,2dicyanovinyl)benzene molecules adsorbed onto a graphene/BN/SiO2 device can be tuned via application of a backgate voltage
We describe a single-moleculeresolved STM study of a molecular monolayer adsorbed onto a back-gated graphene device (Figure 1a) that allows both characterization and gate-induced modification of molecular electronic properties. 1,3,5-Tris(2,2-dicyanovinyl)benzene (CVB) molecules were adsorbed onto a graphene device in ultrahigh vacuum (UHV) and studied via STM spectroscopy at cryogenic temperatures
Summary
Combining organic molecules with graphene creates new opportunities for fabricating hybrid devices with tailored properties. Previous experiments have shown that electronic,1À18 magnetic,[6,19,20] and optical21À23 characteristics as well as chemical reactivity[22,24,25] of graphene devices can be tuned through molecular adsorption Such measurements have been performed primarily using electrical conductivity and optical spectroscopy techniques. Identification of the experimentally observed molecular orbitals was facilitated via density functional theory (DFT) based spectral function simulations which accurately reproduce the orbital structure imaged by STM These simulations allow identification of the vibronic satellites through calculation of the CVB electronÀ phonon coupling. The energy of these modes is in good agreement with the energy spacing of vibronic satellites observed experimentally for CVB on graphene
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