Surface Raman spectroscopy: Instrumentation and application in surface and corrosion sciences.

摘要

This thesis discusses both instrumentation developments and applications of Raman spectroscopy. In the second chapter of this dissertation, the application of Raman spectroscopy to the study of the migration and corrosion inhibition effect of chromate conversion coatings (CCC) on an aluminum aircraft alloy is discussed. This alloy, designated as AA-2024-T3, is very susceptible to corrosion, therefore is treated with a chromate solution to form a thin film prior to use. The CCC film offers the alloy an outstanding corrosion resistance and self-healing properties. Combined with X-ray photoelectron spectroscopy (XPS) and electrochemical techniques typically exploited in corrosion science, Raman spectroscopy revealed that the self-healing process is based on the chromate release of the CCC film, and corrosion inhibition effect of the chromate adsorbed on the alloy. It is found that the released chromate works like a guided missile to passivate corrosion sites, and prevent pitting corrosion at very low bulk concentrations.;Chapter 3 deals with Raman spectroscopic instrumentation. By combining a Sagnac interferometer and a charge coupled device (CCD), a multichannel Fourier transform (MCFT) Raman spectrometer is developed, which offers the advantages of both multichannel technique and interferometry, and accomplishes the goal of a large sampling area and simultaneous data collection in a solid state device. The principle, characterization, and possible applications of the multichannel Fourier transform Raman spectrometer are discussed.;In chapter 4, a method to determine surface molecular orientations is developed, using polarized Raman spectroscopy. This method expands the utility of a previously developed method, and enables the determination of adsorbate orientation of all planar molecules. Methylene blue (MB) adsorbed on highly ordered pyrolytic graphite (HOPG) is used as an example. It is found that the monolayer MB molecules all adsorb flat on HOPG surface.