We have exploited STM based methods for making single molecule measurements under electrochemical potential control in aqueous electrolytes and, in particular, recently in ionic liquids. The electrochemical potential can be used to control the redox state of single molecule bridges and switch the electrical conductance from low to higher values. This has been referred to as the “single molecule electrochemical transistor” configuration, with the electrochemical potential “gating” the molecular conductance in the STM nano-gap configuration. Recent results from our group on gating the conductance of single molecules will be discussed including studies of viologens, redox active metal terpyridine molecular wires and pyrrolo-tetrathiafulvalene (pTTF) molecular bridges. In the latter case as the electrochemical potential was swept through the 3 redox states of pTTF an “off−on−off−on− off” conductance switching was observed. The mechanism of charge transport in the STM nano-gap setup is discussed and electrochemical measurements in ionic liquids are presented.
References
(1) Brooke, R. J.; Jin, C.; Szumski, D. S.; Nichols, R. J.; Mao, B.-W.; Thygesen, K. S.; Schwarzacher, W. Single-Molecule Electrochemical Transistor Utilizing a Nickel-Pyridyl Spinterface. Nano Letters 2015, 15, 275-280.
(2) Osorio, H. M.; Catarelli, S.; Cea, P.; Gluyas, J. B. G.; Hartl, F.; Higgins, S. J.; Leary, E.; Low, P. J.; Martín, S.; Nichols, R. J.; Tory, J.; Ulstrup, J.; Vezzoli, A.; Milan, D. C.; Zeng, Q. Electrochemical Single-Molecule Transistors with Optimized Gate Coupling. Journal of the American Chemical Society 2015, 137, 14319-14328.
(3) Catarelli, S. R.; Higgins, S. J.; Schwarzacher, W.; Mao, B.-W.; Yan, J.-W.; Nichols, R. J. Ionic Liquid Based Approach for Single-Molecule Electronics with Cobalt Contacts. Langmuir 2014, 30, 14329-14336.
(4) Kay, N. J.; Higgins, S. J.; Jeppesen, J. O.; Leary, E.; Lycoops, J.; Ulstrup, J.; Nichols, R. J. Single-Molecule Electrochemical Gating in Ionic Liquids. Journal of the American Chemical Society 2012, 134, 16817-16826.
(5) Kay, N. J.; Nichols, R. J.; Higgins, S. J.; Haiss, W.; Sedghi, G.; Schwarzacher, W.; Mao, B.-W. Ionic Liquids As a Medium for STM-Based Single Molecule Conductance Determination: An Exploration Employing Alkanedithiols. Journal of Physical Chemistry C 2011, 115, 21402-21408.
(6) Sedghi, G.; Garcia-Suarez, V. M.; Esdaile, L. J.; Anderson, H. L.; Lambert, C. J.; Martin, S.; Bethell, D.; Higgins, S. J.; Elliott, M.; Bennett, N.; Macdonald, J. E.; Nichols, R. J. Long-range electron tunnelling in oligo-porphyrin molecular wires. Nature Nanotechnology 2011, 6, 517-523.