Metallocene-based molecule junctions: Electron transport across Au||Au and Au||graphene electrodes

Metallocenes are a wide family of organometallic compounds, in which two cyclopentadienyl ligands ‘sandwich’ a metal ion, M(η⁵-C₅R₅)₂, and have considerable potential for use as components in molecular electronics applications. Here we have studied the electronic transport properties of the matallocenes MCp₂ (M = V, Cr, Mn, Fe, Co, Ni, Ru; Cp = η⁵-C₅H₅) and MCp*₂ (M = Mn, Fe, Co; Cp* = η⁵-C₅Me₅). Molecular junctions have been fabricated using either two gold, or one gold and one graphene electrode(s), giving rise to single-molecule conductance values of the order of -4 to -3 log(G/G₀)) depending on both the nature of the metallocene and the electrode materials. Calculations on model junctions at the density functional theory level of theory reveal significant charge transfer from the metallocene to the junction electrodes and changes in the nature of the primary charge transport pathways in response to the nature of the metal, supporting ligands, molecular oxidation state and electrode composition.