Quantitative depth profile analysis of micrometer-thick multilayered thin coatings using step-scan FT-IR photoacoustic spectroscopy

This paper demonstrates the results of the comparison of step-scan FT-IR photoacoustic spectroscopy with other established spectroscopic and microscopic techniques in the quantitative depth profile determination of micrometer- and submicrometer-thick multilayered thin coatings. The power of the phase rotation and phase spectrum analytical methods to clearly distinguish the infrared signature of submicrometer-thick coatings is demonstrated. The thickness determined by the step-scan FT-IR photoacoustic method is in very reasonable agreement with optical microtomy/microscopy measurements performed at-line during the coating process. The former technique described in detailed here offers substantial benefits in terms of measurement time and operator dependency, while not sacrificing the accuracy of the measurement. The problem of saturation and its effect on "real-life" samples is also discussed.