Recent experiments have demonstrated the synthesis of non-spherical gold and silver nanoparticles. Particle morphologies that have been synthesised include hemispherically capped cylinders (nanorods), cubes, triangular prisms and hexagonal prisms.1-4 The techniques utilised for these syntheses include various electrochemical reactions, the use of particular surfactant systems, and the addition of trace amounts of other metals. These novel structures have interesting optical properties, with the scattering behaviour in the UV-visible region depending on the orientation of the nanoparticle with respect to the incident light, as well as the polarisation of the incident light; for example, aligned gold nanorods illuminated with polarised white light appear either red or blue depending on the direction of polarisation. While understanding the scattering spectra of these nanoparticles is non-trivial, it is an essential step in the development of optical applications for these materials. The application of numerical approaches such as the Discrete Dipole Approximation5 will be described as a method by which experimental spectra may be understood. It will be seen that the Discrete Dipole Approximation approach readily reproduces the major features of the scattering spectra for a range of particle morphologies at least qualitatively. Approaches for improving the quantitative agreement between experimentally determined and simulated spectra will also be discussed.
  1. Y.Y. Yu, S.S. Chang, C.L. Lee, and C.R.C. Wang, Journal of Physical Chemistry B 101, 6661 (1997).
  2. T.K. Sau and C.J. Murphy, Journal of the American Chemical Society 126, 8648 (2004).
  3. J. Perez-Juste, L.M. Liz-Marzan, S. Carnie, D.Y.C. Chan, and P. Mulvaney, Advanced Functional Materials 14, 571 (2004).
  4. N. Okada, Y. Hamanaka, A. Nakamura, I. Pastoriza-Santos, and L.M. Liz-Marzan, Journal of Physical Chemistry B 108, 8751 (2004).
  5. B.T. Draine and P.J. Flatau, Journal of the Optical Society of America A-Optics Image Science and Vision 11, 1491 (1994).

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