Single-Electron Charging Features of Larger, Dodecanethiol-Protected Gold Nanoclusters:  Electrochemical and Scanning Tunneling Microscopy Studies

Abstract

In this report, we demonstrate the single-electron charging features of larger-sized (ca. 3.72 nm) Au nanoclusters protected with dodecanethiol [approximate composition, Au1415(RS)328] using combined electrochemical and scanning tunneling microscopic (STM) studies. In particular, these nanoclusters show a highly populated single-electron charging peak in voltammetric experiments, where the calculated capacitance is in good agreement with the experimentally obtained value of 1.6 aF. In comparison to the voltammetric studies, STM measurements over a single Au particle on the highly oriented pyrolytic graphite surface reveal nonlinear current-voltage (I-V) characteristics with a large central gap, signifying single-electron-transfer features. The I-V results demonstrate a clear Coulomb blockade effect with a central gap of around 0.2 eV, which is in good agreement with the orthodox theory for the double barrier tunnel junction system. The standard heterogeneous electron-transfer rate constant estimated from impedance measurements is found to be of 7.97 x 10(-6) cm.s(-1), suggesting that the process is very sluggish. Furthermore, diffusion coefficient (Dc) values calculated from chronoamperometry and impedance measurements are in good agreement with theoretically calculated values using the modified Stokes-Einstein equation. The electron-transfer rate constant estimated from cyclic voltammograms of adsorbed monolayer protected Au nanoclusters is found to be about 2 s(-1), which is slower than that reported for its smaller analogues.

Information Processing Schemes Based on Monolayer Protected Metallic Nanoclusters

“…Figure 2(b) shows that the nanostructures exhibit single electron effects in the I-V curves at different temperatures (the dashed curve is calculated by using the orthodox theory). 6 16 17 The I-V curve has a central region with suppressed conductivity (Coulomb blockade), as expected for SETs. 5 6 12 Also, the current as a function of the gate voltage, measured at fixed bias voltage, clearly shows the current oscillation characteristic of SETs.…”

“…We cite briefly some characteristics of available chemical hardware (type and size of nanoparticle and structure of ligand). [5][6][7][8][9][10][11][12][13][14] The electrical properties of MPCs have been reviewed by Murray, 1 Homberger and Simon, 4 and Feldheim and Keating. 5 The attached ligands act as stabilizers that impart chemical functionality to the nanoparticles immobilized through electrostatic or covalent attachment.…”

“…2 The metallic nanocluster attached to the electrodes by the ligands can be described as a MPC-based SET that could be gated by an external potential. [3][4][5][6] The Coulomb staircase observed experimentally in the current-bias voltage (I-V) curves [3][4][5] is caused by the approximately regular current steps corresponding to successive, one-electron changes in the MPC electronic charge. Single electron tunnelling to and from the metallic core occurs through the junction resistance R T , which is much higher than the quantum resistance R 0 = h/e 2 = 26 k , where h is the Planck constant and e is the unit charge.…”

“…This condition allows the electrons to be localized in the MPC. [4][5][6] In addition, the electrostatic energy required to add an electron to the MPC should be much higher than the thermal energy, e 2 /2C kT, where k is the Boltzmann constant and T is the temperature. This condition assures that the thermal fluctuations cannot modify the MPC charge state (because of the high charging energy) and then a sufficiently high external voltage should be applied to overcome this Coulomb blockade effect.…”

Quantized Double‐Layer Charging of Rhodium2057(Tridecylamine)321 Clusters Using Differential Pulse and Cyclic Voltammetry

“…[1][2][3][4] In addition, earlier reports have demonstrated QDL-charging behavior of larger-core clusters (e.g., Au 1400 , Au 2869 ), where surface adsorption plays an important role. [5][6][7] Also, much of the effort aimed at observing the QDL charging of smaller monolayer-protected clusters (MPCs) (1-2 nm) has involved the use of gold particles, with a few exceptions such as Ag, [8] Pd, [9] and Cu, [10] and semiconducting systems such as Si [11] and CdTe.[12]Most of the reports have discussed the synthesis of smaller metal particles and their electrochemical properties, suggesting a tiny-capacitor model for metal nanoclusters that show multiple peaks in voltammetric experiments, corresponding to QDL charging (a single-electron-transfer phenomenon in this size regime). STM studies under high vacuum at 83 K also reveal a reversible "Coulomb blockade" (CB) phenomenon, with multiple equidistant charging steps with different bias.…”