The photochemical growth of silver nanoparticles on semiconductor surfaces--initial nucleation stage.
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.
Nanotechnology Centre, Cranfield University, Bedfordshire, UK. s.c.dunn@cranfield.ac.uk
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Burgess