SERS activity of gas-evaporated silver particles

We have produced silver particles by the gas-evaporation technique and investigated their SERS activity. The enhancement factor is determined quantitatively by measuring the Raman intensity of copper phthalocyanine molecules deposited onto the particle layer. It is shown that the particle layer is a good SERS enhancer, which yields an enhancement of ～ 4 × 10³. It is also shown that a five-fold increase in the enhancement factor is obtained, when the particle layer is coated with a 30 nm silver film. The enhancement presently observed seems to arise from the electromagnetic effects, namely, the excitation of localized surface plasmons for the bare particle layer and that of extended surface plasmons for the silver-coated particle layer.