Symmetry breaking induced optical properties of gold open shell nanostructures.

We use the finite difference time domain method to predict how optical plasmon properties are modified if the symmetrical geometry of gold shell nanostructures is broken. The simulations include three kinds of gold open shell nanostructures of nanobowls, open nanocages, and open eggshells. For all structures, the optical extinction spectra commonly display a distinct red shift when the full shell geometry is broken and a hyperbola-like dipolar plasmonic shift when the fractional height continuously decreases. The optical transitions of gold open shell nanostructures are explained by the plasmon hybridization theory combined with numerical calculations. Furthermore, the calculations exhibit that the local electric fields are strongly enhanced at the edges of the open nanoapertures on those symmetry-broken structures, which suggests a potential application in surface-enhanced Raman spectroscopy.