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Spectral Depth Profiling of Arbitrary Surfaces by Thermal Emission DecayFourier Transform Infrared Spectroscopy

Volume 57, Number 12 (Dec. 2003) Page 1494-1501

Notingher, Ioan; Imhof, Robert E.; Xiao, Peng; Pascut, Flavius C.

We report a new spectroscopic technique that combines step-scanning Fourier transform infrared spectroscopy with opto-thermal transient emission radiometry (OTTER) in order to provide nearsurface depth-resolved spectra in the range 700-1800 cm-1. It works nondestructively, without contact, with samples of arbitrary shape and size, without requiring prior preparation. The depth of surface probed depends on the thermal diffusivity of the sample; for organic materials it is ~10 μm. With homogeneous samples, absolute absorption coefficients can be measured. With two-layered samples, the technique proved able to distinguish between the spectral properties of the top layer and the substrate and to estimate the thickness of the top layer. We present a theoretical analysis with the main design features of the instrumentation and software, together with studies of homogeneous and layered samples, to validate the methods and illustrate the potential of the technique for practical applications.