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Item type:Publication, Access status: without files , Field-induced conductance switching by charge-state alternation in organometallic single-molecule junctionsCharge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These intrinsic properties are usually manipulated by varying the molecule's electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high-to-low current ratios exceeding 1,000 at bias voltages of less than 1.0â €...V. Density functional theory calculations identify a localized, redox-active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarized ground state unique to the Mo centre. This situation provides an additional slow and incoherent hopping channel for transport, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios.Publicationtype: Journal Article19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Organometallic single-molecule electronics : tuning electron transport through X(diphosphine)₂FeC₄Fe(diphosphine)₂X building blocks by varying the Fe-X-Au anchoring scheme from coordinative to covalent(2014-10-15); ; ; ; A series of X(depe)2FeC≡C-C≡CFe(depe)2X complexes (depe =1,2-bis(diethylphosphino)ethane; X = I 1, NCMe 2, N2 3, C2H 4, C2SnMe3 5, C4SnMe3 6, NCSe 7, NCS 8, CN 9, SH 10, and NO2 11) was designed to study the influence of the anchor group on organometallic molecular transport junctions to achieve high-conductive molecular wires. The FeC4Fe core is electronically functional due to the redox-active Fe centers and sp-bridging ligands allowing a strong electronic delocalization. 1-11 were characterized by elemental analyses, X-ray diffraction, cyclic voltammetry, NMR, IR, and Raman spectroscopy. DFT calculations on model compounds gave the HOMO/LUMO energies. 5-9 were investigated in mechanically controllable break-junctions. For 9, unincisive features at 8.1 × 10-7 G0 indicate that sterical reasons prevent stable junctions to form or that the coordinative binding motif prohibits electron injection. 7 and 8 with the hitherto unexploited coordinatively binding end groups NCSe and NCS yielded currents of 1.3 × 10-9 A (7) and 1.8 × 10-10 A (8) at ±1.0 V. The SnMe3 in 5 and 6 splits off, yielding junctions with covalent C-Au bonds and currents of 6.5 × 10-7 A (Au-5′-Au) or 2.1 × 10-7 A (Au-6′-Au). Despite of a length of almost 2 nm, the Au-5′-Au junction reaches 1% of the maximum current assuming one conductance channel in quantum point contacts. Additionally, the current noise in the transport data is considerably reduced for the covalent C-Au coupling compared to the coordinative anchoring of 7-9, endorsing C-Au coupled organometallic complexes as excellent candidates for low-ohmic molecular wires.Publicationtype: Journal Article28 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , High-conductive organometallic molecular wires with delocalized electron systems strongly coupled to metal electrodes(2014-10-08); ; ; ; Besides active, functional molecular building blocks such as diodes or switches, passive components, for example, molecular wires, are required to realize molecular-scale electronics. Incorporating metal centers in the molecular backbone enables the molecular energy levels to be tuned in respect to the Fermi energy of the electrodes. Furthermore, by using more than one metal center and sp-bridging ligands, a strongly delocalized electron system is formed between these metallic "dopants", facilitating transport along the molecular backbone. Here, we study the influence of molecule-metal coupling on charge transport of dinuclear X(PP)2FeC4Fe(PP)2X molecular wires (PP = Et2PCH2CH2PEt2); X = CN (1), NCS (2), NCSe (3), C4SnMe3 (4), and C2SnMe3 (5) under ultrahigh vacuum and variable temperature conditions. In contrast to 1, which showed unstable junctions at very low conductance (8.1 × 10-7 G0), 4 formed a Au-C4FeC4FeC4-Au junction 4′ after SnMe3 extrusion, which revealed a conductance of 8.9 × 10-3 G0, 3 orders of magnitude higher than for 2 (7.9 × 10-6 G0) and 2 orders of magnitude higher than for 3 (3.8 × 10-4 G0). Density functional theory (DFT) confirmed the experimental trend in the conductance for the various anchoring motifs. The strong hybridization of molecular and metal states found in the C-Au coupling case enables the delocalized electronic system of the organometallic Fe2 backbone to be extended over the molecule-metal interfaces to the metal electrodes to establish high-conductive molecular wires.Publicationtype: Journal Article19