Electrochemical gating of single osmium molecules tethered to Au surfaces

SANTIAGO HERRERA; CATHERINE ADAM; ALEJANDRA RICCI; ERNESTO JULIO CALVO

JOURNAL OF SOLID STATE ELECTROCHEMISTRY (PRINT)

SPRINGER

Lugar: Berlin; Año: 2015 vol. 20 p. 957 - 967

1432-8488

The electrochemical study of electron transport betweenAu electrodes and the redox molecule Os[(bpy)2(PyCH2NH2CO-]ClO4 tethered to molecular linkers of different length(1.3 to 2.9 nm) to Au surfaces has shown an exponential decay ofthe rate constant kET0 with a slope β = 0.53 consistent withthrough bond tunneling to the redox center. Electrochemical gatingof single osmium molecules in an asymmetric tunnelingnano-gap between a Au(111) substrate electrode modified withthe redox molecules and a Pt-Ir tip of a scanning tunneling microscopewas achieved by independent control of the referenceelectrode potential in the electrolyte, Eref − Es, and the tipsubstratebias potential, Ebias. Enhanced tunneling current at theosmium complex redox potential was observed as compared tothe off resonance set point tunneling current with a linear dependenceof the overpotential at maximum current vs. the Ebias. Thiscorresponds to a sequential two-step electron transfer with partialvibration relaxation from the substrate Au(111) to the redox moleculein the nano-gap and from this redox state to the Pt-Ir tipaccording to the model of Kuznetsov and Ulstrup (J Phys ChemA 104: 11531, 2000). Comparison of short and long linkers ofthe osmium complex has shown the same two-step ET (electrontransfer) behavior due to the long time scale in the completereduction-oxidation cycle in the electrochemical tunneling spectroscopy (EC-STS) experiment as compared to the timeconstants for electron transfer for all linker distances, kET