Blueshift of plasmon resonance with decreasing cluster size in Au nanoclusters embedded in silica matrix

Gold nanoclusters are grown by 1.8 MeV Au++ implantation in silica matrix and subsequent air annealing in the temperature range of 873K-1273K. Post-annealed samples show plasmon resonance in the optical region (~ 2.38-2.51 eV) for average cluster radii ~1.04-1.74 nm. A blueshift of the plasmon peak is observed with decreasing cluster size in the annealed samples. Similar trend of blueshift with decreasing cluster size in case of Au nanoclusters embedded in the porous alumina matrix [B. Palpant, et al., Phys. Rev. B 57, 1963 (1998)] has convinced us to assume a possible role of 'rind' like porosity at the Au nanocluster-matrix interface with available open volume defects in the amorphous silica matrix.