Abstract:

A transition from metal-like double-layer capacitive charging to redox-like charging was observed in electrochemical ensemble Coulomb staircase experiments on solutions of gold nanoparticles of varied core size. The monodisperse gold nanoparticles are stabilized by short-chain alkanethiolate monolayers and have 8 to 38 kilodaltons core mass (1.1 to 1.9 nanometers in diameter). Larger cores display Coulomb staircase responses consistent with double-layer charging of metal-electrolyte interfaces, whereas smaller core nanoparticles exhibit redox chemical character, including a large central gap.
The change in behavior is consistent with new near-infrared spectroscopic data showing an emerging gap between the highest occupied and lowest unoccupied orbitals of 0.4 to 0.9 electron volt.

S. Chen, R. S. Ingram, M. J. Hostetler, J. J. Pietron, R. W. Murray, Department of Chemistry, Kenan Laboratories, University of North Carolina, Chapel Hill, NC 27599-3290, USA.
T. G. Schaaff, J. T. Khoury, M. M. Alvarez, R. L. Whetten, Schools of Chemistry and Physics, Georgia Institute of Technology, Atlanta, GA 30332-0430, USA. * To whom correspondence should be addressed. E-mail: rwm@email.unc.edu (R.W.M.) or robert.whetten@physics.gatech.edu (R.L.W.)

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