Redox-controlled conductance of polyoxometalate molecular junctions

Cécile Huez (1, 2) , David Guérin (1, 2) , Stéphane Lenfant (1, 2) , Florence Volatron (3) , Michel Calame (4, 5) , Mickael Perrin (4, 6) , Anna Proust (3) , Dominique Vuillaume (1, 2)

1 NCM - IEMN - Nanostructures, nanoComponents & Molecules - IEMN
2 IEMN - Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520
3 IPCM - Institut Parisien de Chimie Moléculaire
4 EMPA - Swiss Federal Laboratories for Materials Science and Technology [Dübendorf]
5 Unibas - Université de Bâle = University of Basel = Basel Universität
6 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]

We demonstrate the reversible in situ photoreduction of molecular junctions of phosphomolybdate [PMo12O40]3- monolayer self-assembled on flat gold electrodes, connected by the tip of a conductive atomic force microscope. The conductance of the one electron reduced [PMo12O40]4- molecular junction is increased by ∼ 10, this open-shell state is stable in the junction in air at room temperature. The analysis of a large current-voltage dataset by unsupervised machine learning and clustering algorithms reveals that the electron transport in the pristine phosphomolybdate junctions leads to symmetric current-voltage curves, controlled by the lowest unoccupied molecular orbital (LUMO) at 0.6-0.7 eV above the Fermi energy with ∼25% of the junctions having a better electronic coupling to the electrodes than the main part of the dataset. This analysis also shows that a small fraction (∼ 18% of the dataset) of the molecules is already reduced. The UV light in situ photoreduced phosphomolybdate junctions are systematically featuring slightly asymmetric current-voltage behaviors, which is ascribed to electron transport mediated by the single occupied molecular orbital (SOMO) nearly at resonance with the Fermi energy of the electrode and by a closely located single unoccupied molecular orbital (SUMO) at ∼0.3 eV above the SOMO with a weak electronic coupling to the electrodes (∼ 50% of the dataset) or at ∼0.4 eV but with a better electrode coupling (∼ 50% of the dataset). These results shed lights to the electronic properties of reversible switchable redox polyoxometalates, a key point for potential applications in nanoelectronic devices.

Mots clés: molecular electronics; conductive AFM; machine learning; polyoxometalate; redox; electron transport

Domaines: Matériaux; Systèmes mésoscopiques et effet Hall quantique [cond-mat.mes-hall]

Cécile Huez, David Guérin, Stéphane Lenfant, Florence Volatron, Michel Calame, et al.. Redox-controlled conductance of polyoxometalate molecular junctions. Nanoscale, 2022, 14 (37), pp.13790-13800. ⟨10.1039/d2nr03457c⟩. ⟨hal-03779937⟩