Redox-controlled conductance of polyoxometalate molecular junctions

Abstract

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...

Experimental observation of the role of countercations in modulating the electrical conductance of Preyssler-type polyoxometalate nanodevices

“…32 In our hands, the acido-basic titration of H 1b and also see Section 2 in the ESI †). 17,28 The thicknesses (systematically measured by ellipsometry, see Section 3 in the ESI †) are summarized in Table 1.…”

“…Self-assembled monolayers. The SAMs on TS Au were fabricated following a protocol developed and optimized in our previous works for the electrostatic immobilization of POMs on amine-terminated SAMs 17,28 (Section 2 in the ESI †).…”

“…We formed, by electrostatic deposition, monolayers of these POMs on an ultraflat Au surface prefunctionalized with a positively charged self-assembled monolayer (SAM) of amine-terminated alkylthiol chains following the protocol already developed and reported in our previous work for other POMs. 17,28 The electron transport (ET) properties of these POMs were measured by conductive-AFM (atomic force microscopy) and the current vs. voltage curves of these MJs were statistically analyzed (hundreds of I – V traces) to determine the energy position of the molecular orbitals involved in the ET and the electronic coupling between the molecules and the electrodes. We demonstrate that the energy position of the LUMO of P 5 W 30 with respect to the Fermi energy of the electrodes increases from ∼0.4 eV to ∼0.7 eV and that the electrode coupling energy evolves from ∼0.05 to 1 meV depending on the nature of the counterion in the order of K + , NH 4 + , H + and TBA + .…”

“…[3][4][5][6][7] Not only the conductance of the MJs, but also the shape of the current-voltage (I-V) behavior can be in situ switched between a linear (symmetric) and a rectifying (asymmetric) behavior by inserting/removing the ions or moving the precise position (electrical field driven) of the ions in the MJs, [8][9][10][11] opening the way toward molecular-scale programmable functional devices and synaptic (neuro-inspired) behavior. 12,13 Polyoxometalates (POMs) are candidates of choice owing to their remarkable reversible multi-redox states 14,15 and photo-stimulable redox properties, 16,17 and they have attracted growing interest with several recent demonstrations of proof-of-principles such as silicon-integrated POM-based memory devices 18 and unconventional (in-memory and neuromorphic) computing devices. [19][20][21] In solution, it is well known that the nature of counterions has a strong impact on the redox potentials for the POMs, and hence on the electron transfer rates.…”

Increasing the redox switching capacity of Lindqvist-type hexavanadates by organogold post-functionalisation

“…2–5 However, the stabilisation and switching of POM anions at the level of solution-processed single molecules or thin films on metallic and non-metallic surfaces is a challenging task, requiring along with intimate deposition conditions a careful control over the electrode surface interactions as well as the molecular attributes (counter cations, 6–8 ligands 9–11 ) and the redox properties of the POM. 12–16…”