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Tuning Intermolecular Charge Transfer in Donor–Acceptor Two-Dimensional Crystals on Metal Surfaces
journal contribution
posted on 2017-09-25, 00:00 authored by Jonathan Rodríguez-Fernández, Maitreyi Robledo, Koen Lauwaet, Alberto Martín-Jiménez, Borja Cirera, Fabián Calleja, Sergio Díaz-Tendero, Manuel Alcamí, Luca Floreano, Marcos Domínguez-Rivera, Amadeo L. Vázquez de Parga, David Écija, José M. Gallego, Rodolfo Miranda, Fernando Martín, Roberto OteroOrganic charge transfer
(CT) compounds display a wide range of
exotic electronic properties (charge-density wave stabilization, Peierls
transitions, etc.) depending on the amount of charge transferred from
the donor (D) to the acceptor (A) species. A complete exploration
of the complex electronic phase diagrams for such compounds would
thus require methods to systematically tune the amount of charge exchanged
in the CT process. This has proven however challenging in the past:
chemical functionalization of the constituent molecules can also affect
the packing of the molecular units in the crystal, whereas changing
D:A stoichiometry is often not possible in the bulk. Interestingly,
it was recently found that multiple stoichiometries can actually be
achieved by codeposition of different amounts of D and A molecules
on metal surfaces. The question, however, of whether CT processes
between D and A molecules can be tuned with the D:A ratio in such
mixtures has not yet been studied, and it is no trivial matter, since
competing CT processes between the metal surface and the organic adsorbates
might hinder interadsorbate charge transfer. Here we demonstrate that
the CT process from the organic donor tetrathiafulvalene (TTF) to
the acceptor tetracyanoquino-p-dimethane (TCNQ) can
be tuned with exquisite accuracy (∼0.1 e–) by controlling the stoichiometry of D:A cocrystals deposited on
Ag(111). This control opens new avenues to explore the complex phase
diagrams of organic CT compounds and to tailor their electronic properties.