Measuring and modelling the growth of silver nanorods using time-resolved UV/visible extinction spectroscopy : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University, Manawatū, New Zealand

Abstract

Metal nanoparticles are known to have plasmon resonances that are dependent on the size and shape of the particle. As these resonances are easy to observe in situ during the growth of these particles, UV-Visible extinction spectroscopy provides an excellent way to monitor the growth and aid with the understanding of the underlying growth mechanisms. Silver nanorods present an ideal candidate for this, as the longitudinal plasmon peak is known to have a linear relationship with the aspect ratio of the nanorods. This presents an interesting challenge, as any associated growth models would need to explain the growth in term of the aspect ratio rather than an absolute size of the nanorod. The discrete-dipole approximation (DDA) was used to determine the relationship between the plasmon resonance position and the aspect ratio, which was found to be λext = (113 ±10) × A + (277±20). To achieve this, a correction for the error associated the DDA calculations was required to be determined for the capsule geometry that was used for the nanorods. This correction was found to be the same correction the has been reported for spherical particles. A growth model was developed that explains the growth of nanorods in term of the evolution of the aspect ratio. Nanorods were prepared using various reaction condition and the plasmon peaks were observed during the growth. Transmission electron microscopy (TEM) images however, revealed the presence of trigonal platelets and other geometries in the nanorod preparations. Efforts were made to remove these other geometries from the nanorod solution so that the growth model could be applied to the experimental results.