Surface-enhanced Raman scattering of SnO_2 bulk material and colloidal solutions

Surface-enhanced Raman scattering (SERS) effects on tin dioxide in the form of bulk material, nanostructured thin films, and colloidal solutions were investigated. Raman spectra are characterized by the three Raman scattering peaks at 478, 633, and 776 cm(-1), assigned to the E-g, A(1g), and B-2g modes, typical of rutile SnO2. In the presence of the silver nanoparticles, in addition to the enhancement intensity of some of the fundamental tin dioxide rutile Raman features, the appearance of a new Raman scattering peak at about 600 cm(-1) is observed. These spectral features are observed, in the presence of silver nanoparticles, also in other SnO2-based systems such as pulsed laser deposited thin films, with different stoichiometry, and in water colloidal solutions. The observed SERS effects are explained in terms of electric field gradient mechanism that are generated near a metal surface. In particular, the appearance of a peak near 600 cm(-1) is attributed to the Raman activation of the infrared E-u transverse optical mode.