A spectroscopic investigation of the shape dependency of gold nanoparticles grown on roughened surfaces

We present an investigation of the optical excitation of surface plasmons on Au films deposited on roughened surfaces by using a glancing angle deposition technique. By adjusting the deposition parameters of calcium fluoride and Au thin films, the spectral position of the surface plasmon resonances can be shifted through the green and into the near infrared region. In particular, we find that a rougher surface with obliquely deposited Au produces distinct spheroid-shaped nanoparticles (NPs). This results in stronger resonances with narrower linewidths, whereas smoother films result in broad red-shifted absorption. Imaging with an atomic force microscope and a scanning electron microscope provides information of NP geometry which are used as inputs for theoretical simulations of the observed spectra. The consequence of geometry distributions and inter-particle interactions are discussed. The ability to control the shape, therefore the optical response, of Au NPs over an arbitrarily large active area is of paramount importance in nano-science, especially in biological sensing applications and surface enhanced Raman scattering.