Scanning Tunneling Microscopy of Mixed Valence Dinuclear Organometallic Cations and Counterions on Au(111)
Song Guo, S. Alex Kandel · The Journal of Physical Chemistry Letters · 2009
Single-molecule electronic components are potential building blocks for next-generation electronic devices. One architecture for such devices is quantum dot cellular automata (QCA), in which binary information is encoded in the charge configuration of a single cell and transferred by electric coupling between neighboring cells. A single mixed-valence molecule with two oxidation−reduction centers can serve as a QCA cell, and ensemble measurements have shown that such molecules may have the desired electronic properties. Scanning tunneling microscopy (STM) is used to image dinuclear metal complexes, trans -[Cl(dppe) 2 Ru(C≡C) 6 Ru(dppe) 2 Cl] ( Ru2 ) on Au(111) at 77 K. Oxidation to Ru2 + [PF 6 ] − creates an unbalanced charge that localizes on one end group of the otherwise symmetric Ru2 molecule. This electronic asymmetry appears in STM images, which also resolve the associated [PF 6 ] − counterions. Comparison of Ru2 and Ru2 + monolayers show that Coulomb interactions create long-range ordering of Ru2 + electronic charge. This is a requirement for functionality in a QCA device.