Blueshift of surface plasmon resonance spectra in anneal-treated silver nanoslit arrays

Silver nanoslit arrays were anneal treated in vacuum, and the effects on the surface morphology of silver and the surface plasmon resonance characteristics were investigated. Optical transmission through nanoslit arrays shows a distinctive change in the spectral profiles after annealing: A clear blueshift of the transmission peaks and dips (20 nm shift for an anneal temperature of 150 degrees C). Scanning electron microscopy reveals a morphological change of silver: Increased grain sizes, and smooth and round surface profiles after the anneal treatment. The observed blueshift of transmission spectra correlates well with the geometrical and dimensional changes of silver islands defined between slits, which are found to alter the surface plasmon resonance conditions involving various mechanisms in different regimes.