16.3 - Single particle deposition on nanometer electrodes

Abstract

This chapter describes the electrochemical deposition of single particles onto electrodes of nanometer dimensions. The chapter mainly focuses on the deposition of material on nanometer-sized electrodes and the uses of such composite systems. There are a number of methods which in principle allow the formation of a nanoelectrode-film/particle composite: (a) direct physical contact of electrode to particle; (b) electrochemical deposition of particle or film; and (c) electrophoretic deposition of particles. Direct physical contact with a particle is made difficult in the nanoscopic regime because of the difficulty in imaging the particle system. For electrodes and particles in the micron-size domain, it is possible to use optical microscopes to see the particles and, using micromanipulators, move the electrode so that it is in contact with the particle. Deposition of particles through electrochemical deposition requires a suitable substrate and electrochemical system which shows a suitable nucleation density. The use of nanoelectrodes of suitable materials will allow a significant growth of understanding of nucleation and growth of a diverse number of systems. Standard electrochemical theory has been applied to the growth of single particles on microelectrodes. The growth of a single particle during single nucleation and growth is commonly preceded by an induction period. The formation of new nuclei is a result of aggregation of small atom clusters due to surface diffusion along the electrode surface. After the induction period, growth of the particle may be measured by following the current transient. The production of single nuclei is somewhat helped by the formation of “nucleation exclusion zones” around the growing particles. In the area surrounding a growing particle, there will be a reduction in the concentration of precursor, and this will reduce the probability of nucleating a new particle.