| The synthesis of noble metal colloids is of importance to a number of technological applications, most often taking advantage of the optical properties of these materials. The size and shape of metal colloids dominate their optical absorbance and non-linear optical properties. Of particular interest for several applications are anisotropic particles such as platelets and rods. These particles have been reported in literature for approximately seventy years using a wide variety of synthesis techniques, although the reproducibility and yield of these schemes are low. Furthermore, the mechanistic explanations for these techniques are inadequate to explain the appearance of similar structure in different reaction environments. In this dissertation, several synthesis techniques from the literature, along with modified and original techniques, were used to synthesize anisotropic colloids of copper, silver and gold. The particles were characterized using scanning and transmission electron microscopy to determine their crystal habit and internal crystallographic structure. It was found that similar structures were observed to be synthesized in different schemes. These similarities were used to make a mechanistic description that did not depend on a unique reaction environment. Two dimensional particles in the shape of triangular or hexagonal prisms were found to have a constant (111) main face and contained one or more twin planes parallel to this face. The anisotropy of these particles was attributed to the formation of reentrant grooves, sites of preferential metal adatom attachment where a twin plane intersects two surface planes. One dimensional particles in the form of rods or wires were also observed in multiple schemes, and had a consistent pentagonal cross-section. The internal structure of these particles was found to consist of five crystal variants bounded by five (111) type twin planes along a [110] direction. It is proposed that this structural arrangement creates a radial stress which restricts the growth of the particle perpendicular to the axis. In order to relieve this stress, edge dislocations form, emerging at the end faces and creating self-perpetuating steps that accelerate axial growth. Other particle types, such as ribbons, tetrahedra and decahedra, were also characterized and their growth was described using the mechanisms developed for the prism and rods. |
