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Scanning electrochemical microscope (SECM) is used to investigate the electronic properties of Langmuir monolayers of alkane thiol protected gold nanocrystals. Factors influencing the conductivity of the monolayer nanocrystals array are discussed.

The use of monolayer-protected clusters as redox mediators in scanning electrochemical microscopy experiments is demonstrated. The use of scanning electrochemical microscopy(SECM) in both amperometric and potentiometric modes presents a versatile tool for probing the local concentration and flux of the electroactive species.

The study demonstrates how the differences in ion solvation in the film versus the elctrolyte phase can control the apparent redox properties of the model electroactive nanoparticle thin films. The absence of rectification when the film is immersed in organic solvents with identical anions show that the film behavior is ion limited rather than ion rectified.

The ion permeability of self-assembled monolayers (SAMS) formed on the surface of charged alkanethiol-protected gold nanoparticles, so-called monolayer-protected clusters (MPCs), is reported. It is shown that mo o-MPCS in spite of their large size and different nature of the electron transfer process can be treated to redox molecules analogously.

The amperometric detection of single carboxylated micro- and nanospheres adsorbing on electrodes as well-resolved, discrete steps in the current-time response is reported. The detection technique can be scaled down to detect individual molecules preferentially binding at nanometer electrodes.

Thiol-protected gold nanoparticles, which are called monolayer protected clusters (MPC), are unique and can be repeatedly isolated and dispersed without irreversible aggregation. The core charges between the limits of thiolate and AU(I) SR desorptions constitute the bounds of the MPC electrochemical window.

The novel use of the scanning electrochemical microscope to follow the compression of a monolayer of monodisperse silver thiol-capped nanoparticles on a Langmuir trough is presented. The result reveals that the transition from an insulating to conductive behavior with compression can be followed.

An investigation on the kinetics of heterogeneous electron transfer (ET) as a function of driving force at the interface between two immiscible electrolyte solutions using scanning electrochemical microscopy (SECM) is presented. The study concluded that at high driving force, experimental rate constants decreased with increasing overpotential, deviating from predictions based on Butler-Volmer kinetics.

A monolayer of alkanethiolate protected gold nanocrystals (NCs) is used as a model system to investigate electron transfer (ET) kinetics between a solution redox mediator and the NC core. The findings indicate a profound difference in the rate of ET depending on the redox couple used (FeMeOH versus Fe(CN)6(super 4-)), illustrating the importance of molecule specific properties, such as the effect of their relative hydrophilicities.

A study was conducted to demonstrate that noble metals could be deposited on single-walled carbon nanotubes (SWNT) sidewalls under direct potential control, where the nanotube acts as a nonsacrificial template for the deposition clusters. The main observations were that the metal clusters could be deposited on the SWNT sidewalls under potential control and the particle size and surface coverage could be tuned with potential, deposition time and metal salt concentration.

A detailed study of association between monolayer protected clusters (MPCs) and base electrolyte ions is presented. MPC redox properties are investigated using electro analytical techniques and it is found that the results are consistent with electrostatic charging of a metallic core.

Research developing new methods of electrochemical processes of cadmium sulphides in semiconductor nanoparticles is presented. Particular attention is given to reactions pertaining to the correlations between electrochemical and optical band gaps.

A novel method to readily determine the lipophilicity of electrogenerated charged species is reported. This is achieved by local electrolysis at a Pt coated micropipette and, subsequently, driving the electrogenerated species to transfer across the liquid–liquid interface supported at the tip of the micropipette under potential control. The formal potential of ion transfer can then be used to give a measure of its relative lipophilicity. The method proposed is facile and enables the study of potentially unstable charged products of electron transfer reactions. [Copyright &y& Elsevier]

A synthesis strategy to obtain monodisperse hexanethiolate-protected Au38 clusters based on their resistance to etching upon exposure to a hyperexcess of thiol is reported. The reduction time in the standard Brust-Schiffrin two-phase synthesis was optimized such that Au38 were the only clusters that were fully passivated by the thiol monolayer which leaves larger particles vulnerable to etching by excess thiol. The isolated Au38 was characterized by mass spectrometry, thermogravimetric analysis, optical spectroscopy, and electrochemical techniques giving Au38(SC6)22 as the molecular formula for the cluster. These ultrasmall Au clusters behave analogously to molecules with a wide energy gap between occupied (HOMO) and unoccupied levels (LUMO) and undergo single-electron charging at room temperature in electrochemical experiments. Electrochemistry provides an elegant means to study the electronic structure and the chemical stability of the clusters at different charge states. We used cyclic voltammetry and scanning electrochemical microscopy to unequivocally demonstrate that Au38 can be reversibly oxidized to charge states z = +1 or +2; however, reduction to z = -1 leads to desorption of the protecting thiolate monolayer. Although this reductive desorption of thiol from the cluster surface is superficially analogous to electrochemical desorption of planar self-assembled monolayers (SAMs) from macroscopic electrodes, the molecular details of the process are likely to be complicated based on the current view that the thiolate monolayer in clusters is in fact composed of polymeric Au-S complexes. [ABSTRACT FROM AUTHOR]

This article reports the use of the scanning electrochemical microscope (SECM) to investigate the electronic properties of Langmuir monolayers of alkane thiol protected gold nanocrystals (NCs). A substantial increase in monolayer conductivity upon mechanical compression of the Au NC monolayer is reported for the first time. This may be the room temperature signature of the insulator to metal transition previously reported for comparable silver NC monolayers. Factors influencing the conductivity of the monolayer NC array are discussed. [ABSTRACT FROM AUTHOR]

Metal nanoparticles coated with an organic monolayer, so-called monolayer protected clusters (MPCs), can show quantised charging at room temperature due to their sub-attofarad capacitance arising from the core size and the nature of the protecting monolayer. In this tutorial review, we examine the factors affecting the energetics of MPC charging. In the first section, the underlying physics of quantised charging is outlined and we give an overview of the various methods that can be used to measure single electron transfer to nanoparticles. In the subsequent sections, we discuss how electrochemical measurements can be used to give information on the quantised charging of freely diffusing and films of immobilised MPCs. The predictions of models used to determine MPC capacitance are compared with experimental data from the literature.

Nanometer-sized electrodes are used to probe the transport of ions in liquid by monitoring heterogeneous electrochemical reactions. We observe pronounced nonlinearities of ion flux versus concentration when transport is localized within a region smaller than 10 nm. We show that these observations cannot be explained using conventional continuum, mean-field descriptions of ionic transport. The data indicate that these deviations are caused by the high flux of charged species that is achieved at nanometer-sized electrodes.