Extension of two-dimensional global phase difference correlation analysis to step-scan FT-IR photoacoustic spectral depth profiling of layered systems

This paper first extends two-dimensional global phase difference correlation (2D-GPDC) theory and concept to step-scan FT-IR photoacoustic spectroscopy (PAS), and demonstrates applications of 2D-GPDC in PAS depth-profiling analysis of layered samples with micrometer or sub-micrometer thick surface layers. Simplified rules of 2D-GPDC for FT-IR PAS depth-profiling analysis have been established under typical assumptions. 2D-GPDC provides significant enhancements in both spatial and spectral resolution for PAS depth-profiling studies. The 2D-GPDC method is highlighted with the use of the recently developed advanced software package SpectraCorr™ for two-dimensional correlation spectroscopy (2D-COS). This package is featured with all-quadrant global phase difference coverage, and one-dimensional spectral profile extraction for both magnitude and phase. It also opened a door to new possibilities of both qualitative and quantitative 2D-COS analyses with its versatile display modes and built-in advanced algorithms.