Spatially Resolved, Site-Dependent Charge Transfer and Induced Magnetic Moment in TCNQ Adsorbed on Graphene

Abstract

A site-dependent charge transfer to 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) adsorbed on a single layer of periodically rippled graphene grown epitaxially on Ru(0001), identified by X-ray photoemission techniques, can be spatially resolved using Scanning Tunneling Microscopy, which can also detect the formation of magnetic moments. The molecules adsorbed on the lower part of the ripples are charged with electrons donated from the doped graphene overlayer and develop a magnetic moment, while those at the upper part of the ripples are neutral. On the other hand, TCNQ adsorbed on graphene on Ir(111) shows negligible charge transfer and no magnetic moment. These observations explain the spatially dependent longrange magnetic order observed recently for TCNQ on gr/Ru(0001).

Temperature-controlled metal/ligand stoichiometric ratio in Ag-TCNE coordination networks

“…On the other hand, for TCNQ on graphene/Ir(111) of in multilayers, where no charge transfer takes place, the N1s core level appears at 399.3 eV. 30 This confirms that TCNE is charged upon adsorption on Ag(111).…”

“…For TCNE salts, where the TCNE molecules is negatively charged, the C1s and N1s peaks appear around 285.9 and 398.8 eV, respectively, [27][28][29] which are closer to the experimentally found binding energies. The similar TCNQ molecule when adsorbed on Cu(100) 16 and graphene/Ru(0001) 30 is known to become charged by electron transfer from the surface, and XPS experiments show a N1s core level at 398.7 and 398.3 eV, respectively. On the other hand, for TCNQ on graphene/Ir(111) of in multilayers, where no charge transfer takes place, the N1s core level appears at 399.3 eV.…”

Mapping spin distributions in electron acceptor molecules adsorbed on nanostructured graphene by the Kondo effect

“…1a and b). The observation of this orbital below the Fermi level is a clear indication of the effectiveness of the charge transfer from graphene to the isolated molecules which lead to the partial occupation of the LUMO of the neutral molecule [11]. A close inspection of the Fig.…”

“…We illustrate this principle using two related electron-acceptor molecules: namely 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-p-quinodimethane (F 4 -TCNQ) adsorbed on graphene grown on Ru(0001). The molecules are nonmagnetic in the gas phase, but, upon adsorption, they accept charge from graphene, creating an unpaired electron ground state [11] and developing magnetic moments. The decoupling of the molecular orbitals from the electron sea of the metallic substrate facilitated by the graphene monolayer allows us to image the spatial distribution of the Kondo resonance and the corresponding spin distribution with much higher resolution than in the case of direct molecular adsorption on metals [12,13].…”

Surface chemistry of porphyrins and phthalocyanines

“…In addition, on strongly interacting substrates such as Ru(0 0 0 1), the electronic structure of the graphene layers is laterally substantially modulated over the Moiré unit cell. Effects of this modulation including laterally inhomogeneous transfer of electron density have been described for various molecular systems [301]; these effects also play a role in the case of phthalocyanine adsorption on graphene/Ru(0 0 0 1). Another example for a strongly interacting substrate is graphene/Ni(1 1 1).…”