Questions surrounding the nucleation mechanism for nanostructures that are grown on semiconductors, such as lead zirconate titanate, using photochemical techniques have ranged from 'What is the nucleation process?' to 'Is it possible to produce homogeneous nanoscale patterns?' Here we demonstrate that nucleation occurs at discrete locations on the surface of the substrate that are indicative of a disruption of the local Stern layer due to a local defect or electric field in the substrate. The band diagram for the system is such that when a cluster forms it is possible for electrons to migrate into the silver metal and so replace the surface positive charge, associated with the positive domain of the ferroelectric, with a local negative charge. Once the initial cluster starts to form, the rate of growth of an individual cluster increases due to a restructuring of the Stern layer and increased probability of reaction of an electron with the cations in solution. We show that the nucleation density does not change significantly from the initial nucleation density, and that approximately 15% of the particles that form on the surface are 50% larger than the other particles. The reasons for no significant change in nucleation density stem from the concentration of available disrupted locations in the Stern layer, and variations in the growth rate are discussed in terms of the local electric field and defect influences.

The reaction of aqueous solutions of Na 2 PdCl 4 and K 3 Co(CN) 6 results in gelatinous polymeric materials, characterized by bridging cyanides between the central metals of the adducts. Such materials are referred to as cyanogels. A mechanical perturbation method, three-point beam-bending, was used to measure the viscoelastic relaxation behavior and permeability of a series of Pd/Co cyanogels of differing concentrations. The shear and Young's modulii of the cyanogel network was found to increase with an increase in concentration. Permeability was found to decrease with an increase in concentration, and was found to range from 239 to 3.67 nm 2 over the concentration range 0.175-0.600 M. This suggests that the Pd/Co cyanogel contains an average pore structure size with the radii ranging from 40 to 5 nm over the concentration range investigated.

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The reaction of aqueous solutions of SnCl 4 ‚5H 2 O and K 4 Fe(CN) 6 in a 2/1 Sn/Fe atomic ratio results in a hydrogelled polymeric material, characterized by bridging cyanides between the central metals of the adducts. Materials of this type have previously been noted upon reaction of PdCl 4 2with cyanometalates in aqueous solution and have been referred to as cyanogels. Dehydration of Sn/Fe cyanogels results in xerogels that maintain the initial polymeric structure of the hydrogel. Thermal processing of such gels under an air atmosphere at 900 °C produces a solid homogeneous mixture of microcrystalline SnO 2 and Fe 2 O 3 .

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