It is absolutely clear that on graphite surfaces, electrochemical metal deposition occurs via a Volmer-Weber mode (see for example our recent data on silver and platinum). This means that during the deposition of metal, 3-dimensional metal clusters promptly form even when the total amount of deposited metal is less than one atomic layer. Volmer-Weber growth is brought about by the low surface free energy of the coordinatively saturated graphite basal plane surface (the actual vaue is: = 35 dynes cm^-2). The (100) face of silicon also possesses a low surface free energy provided each dangling bond present at the surface is bonded to a hydrogen atom. On such a hydrogen-terminated Si(100) surface, one might expect to see V-W growth of metals which mimics that seen on graphite.

In fact, this IS what is seen: Shown above are silver nanoparticles which were deposited for various plating durations on the hydrogen-terminated n⁺⁺-Si(100) surfaces. The deposition of silver was carried out potentiostatically from dilute ([Ag⁺] = 1 mM), acetonitrile-based solutions using a large overpotential, E_appl = -800 mV vs. Ag⁺/Ag^o , and a voltage pulse duration ranging from 2 to 25 msec. Under these conditions, less than 0.20 of a silver monolayer was deposited and this silver was present on the surface as silver nanoparticles.

The metallic nature of these nanoparticles was confirmed using selected area electron diffraction. The evolution of the areal density of nanoparticles, and the nanoparticle height, were both tracked as a function of the plating pulse duration ex-situ using non-contact atomic force microscopy. As the pulse duration was increased from 2 to 25 msec, the mean nanoparticle height increased from 2 to 20 nm while the areal density of nanoparticles concurrently increased from 1-3 x 10⁸ cm^-2 to 2-2.5 x 10⁹ cm^-2, as shown below:

This result shows conclusively that the nucleation of silver on Si(100) is progressive in this time domain, and this is one aspect of the deposition which differs from what we have reported at graphite. Progressive nucleation provides a mechanism for the development of size dispersion for growing silver clusters on the surface - something which we view as bad!