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Adsorption-Induced Kondo Effect in Metal-Free Phthalocyanine on Ag(111)

Abstract : We report on the formation of a two-dimensional supramolecular Kondo lattice made of organic molecules comprising only C, N, and H atoms, namely metal-free phthalocyanines 2HPc (C 32 H 18 N 8), adsorbed on a Ag(111) surface. Low-temperature scanning tunneling microscopy/spectroscopy (LT-STM/STS), ultraviolet photoemission spectroscopy (UPS), and density functional theory (DFT) are used to investigate the electronic structure of the system for low molecular density and commensurate self-assemblies. Abrikosov− Suhl resonances that are characteristic of the arising of a Kondo effect are observed by using both STS and UPS at low temperature. Whereas freestanding 2HPc is a no-spin-bearing molecule, it acquires an unpaired electron in its πconjugated lowest unoccupied molecular orbital (LUMO) upon adsorption on Ag. As a result, the Kondo effect can be interpreted as originating from the interaction between this unpaired π-spin and the Ag Fermi sea. Extra side resonances are observed in STS spectra that are a manifestation of the coupling between the π electron and molecular vibrational excitations, qualifying the effect as the molecular vibrational Kondo effect. The variation of the Kondo temperature T K of single molecules and upon two-dimensional self-assembly is discussed. This study brings new insights into the Kondo-related physics in correlation with molecular spins and low dimensionality. Moreover, it may open new routes to the synthesis of organic molecular spintronic devices.
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https://hal.archives-ouvertes.fr/hal-03079564
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Submitted on : Wednesday, September 8, 2021 - 12:12:49 PM
Last modification on : Tuesday, October 19, 2021 - 11:17:12 PM

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J. Granet, M. Sicot, I.C. Gerber, G. Kremer, T. Pierron, et al.. Adsorption-Induced Kondo Effect in Metal-Free Phthalocyanine on Ag(111). Journal of Physical Chemistry C, American Chemical Society, 2020, 124 (19), pp.10441 - 10452. ⟨10.1021/acs.jpcc.9b11141⟩. ⟨hal-03079564⟩

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