A Comparative Study of Visible Raman Scattering of Ceria Prepared by Sol-gel and Hydrothermal Techniques with Gold Nanoparticles

Nano-structured ceria was synthesized by using sol-gel and hydrothermal techniques. Prior to measurements by Raman spectroscopy, the prepared ceria was dispersed onto glass substrates by spin-coating, and this was followed by the deposition of gold nano-particles onto the surface of the ceria by direct current magnetron sputtering. The F_2g Raman peak, oxygen vacancy and longitudinal optical modes of ceria were successfully observed with visible Raman laser excitation wavelength of 532 nm at non-resonance Raman conditions. The surface oxygen adsorption on ceria surface was also detected. The F_2g Raman peaks of ceria for all of the samples were red-shifted because of the nano-crystalline structure and strain effect on the samples. In the case of the hydrothermally processed gold coated ceria, the F_2g Raman peak was further red-shifted to 451 cm^-1 because of temperature effect and anharmonicity, and the peak intensity was also found to be enhanced by at least one order of magnitude (x13). This increase in peak intensity was attributed to the electrical field enhancement via localized surface plasmon resonance of the gold nano-particles. (paper)