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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.

Reversible electrochemical injection of discrete numbers of electrons into sterically stabilized silicon nanocrystals (NCs) (~2 to 4 nanometers in diameter) was observed by differential pulse voltammetry (DPV) in N,N'-dimethylformamide and acetonitrile. The electrochemical gap between the onset of electron injection and hole injection-related to the highest occupied and lowest unoccupied molecular orbitals--grew with decreasing nanocrystal size, and the DPV peak potentials above the onset for electron injection roughly correspond to expected Coulomb blockade or quantized double-layer charging energies. Electron transfer reactions between positively and negatively charged nanocrystals (or between charged nanocrystals and molecular redox-active coreactants) occurred that led to electron and hole annihilation, producing visible Light. The electrogenerated chemiluminescence spectra exhibited a peak maximum at 640 nanometers, a significant red shift from the photoluminescence maximum (420 nanometers) of the same silicon NC solution. These results demonstrate that the chemical stability of silicon NCs could enable their use as redox-active macromolecular species with the combined optical and charging properties of semiconductor quantum dots., In a bulk semiconductor, electrons and holes move freely throughout the crystal. However, in a nanocrystal, confinement of the electrons and holes leads to a variety of optical and electronic [...]

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.