Surface Analysis by Raman-Ellipsometry Spectroscopy

Abstract

We have developed a Laser Raman-Ellipsometry combined system to analyze solid surfaces in situ under chemical reactions. Reaction products in gas phase are analyzed by a mass spectrometer, a surface layer formed by the reaction is analyzed by an Ellipsometer, and surface species by a Raman spectrometer. The system is applied to study the dissociative reaction of CO gas on an iron surface under 1 atm. pressure. C and O atoms from CO gas diffuse into the interior of the Fe to form a diffusion layer, whose thickness and dielectric constant are determined. After formation of the diffusion layer of 11 nm an Fe₃O₄ oxide formation occurs from the surface. We have found that the Fe₃O₄ layer of 16 nm generates the A_1g phonon mode at 672cm^-1 compared with 675cm^-1 from a bulk Fe₃O₄. Two kinds of surface Raman bands induced from CO adsorbed on the Fe₃O₄ are observed at 1121cm^-1 and 1812cm^-1, respectively, which seem to be surface-enhanced. It is concluded that the system is a very powerful tool to study solid surfaces under chemical reaction conditions.