Importance of lattice contraction in surface plasmon resonance shift for free and embedded silver particles

The size evolution of the surface plasmon resonance was investigated for fr ee and embedded silver particles between about 2 to 10 nm in size. The crys tal lattice of such particles as analyzed by high resolution electron micro scopy show linear contraction with reciprocal particle size. Based on this, a model was presented by combining the lattice contraction of particles an d the free path effect of electrons to predict the size evolution of the re sonance. The results reveal a contribution of the lattice contraction to th e resonance shift according to a roughly linear relation that changes sligh tly with particle radius (> 1.0 nm) and surrounding media. This surface pla smon resonance shift proceeds linearly with reciprocal size for Ag particle s in vacuum and argon, but for Ag particles embedded in glass it appears to be independent of the radius down to nearly 1 nm. All predictions are quan titatively compared to previously reported experimental data and a good agr eement is obtained. An unusual red-shift observed for Ag particles in glass may be attributed to a thermal expansion mismatch induced lattice dilatati on.