The Study of Surface Plasmon in Au/Ag Core/Shell Compound Nanoparticles

Au/Ag core/shell nanoparticles are fabricated by laser-ablating Ag plates in Au colloid solution. The absorption band is found to blue shift with increasing ablation time. Mie theory calculations show that the shift is caused by the increase of the Ag shell thickness. The average Ag shell thickness can be determined from the measured absorption peak. Using the plasmon hybridization approach, we show that the absorption band around 510 nm originates from an anti-bonding mode omega (-+) caused by the interaction between a bonding Ag shell mode omega (--) and Au sphere mode omega (S-Au). The blue shift of the omega (-+) mode with the increase of Ag shell thickness is also well predicted by the hybridization theory.