Raman Determination of Molecular Structure and Physical Properties of Dielectric Coatings

摘要

Single and multilayer coatings exhibit optical properties controlled by localized chemical bonding and inherent microstructure that result from a particular deposition technique. The application of Raman spectroscopy to characterize such materials is attractive in that it is one of the few available methods that directly probes the chemical bond. Furthermore, optical properties of the coating can advantageously be used to enhance the sensitivity of the Raman probe through interference and resonance phenomena as well as guided wave enhancement techniques. Polycrystallite grain size and extent of grain orientation can also be determined from the spectra. In addition, inherent compressional stress in coatings, manifested in vibrational line shifts, may be quantified; conversely, knowledge of the vibrational frequency dependence on applied pressure will allow an estimate of the coating elastic properties. The capability for real-time in situ analysis represents a major strength of the Raman technique. Examples are discussed detailing real-time microstructural changes in oxidic coatings subjected to temperature fluctuations or high-energy pulsed laser irradiation. (ERA citation 11:036368)