Surface-Enhanced Raman Scattering from Surface Layers of Gas-Evaporated Silver Small Particles

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Abstract
Silver small particles prepared by the gas-evaporation technique with four different heater materials, i.e. Mo, W, C and Ta, have been studied by Raman and X-ray photoemission spectroscopy. Raman spectra of the particles prepared with the Mo and W heaters exhibit a strong and asymmetric band at about 900 cm-1 and a few weak bands below 350 cm-1. These Raman bands are absent in the spectra of particles prepared by C and Ta heaters. Results of XPS suggest the formation of oxides of Mo and W at the particle surfaces. The observed Raman bands can thus be attributed to surface-enhanced bands originating from the oxide coatings. We identify the coatings with amorphous Ag2MoO4 and Ag2WO4.