Toward Theorectical Limits of FT-IR Microspectroscopy for Ultra-Thin Organic Layers

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Abstract
In this work the influence of the substrate geometry on FT-IR microspectroscopical transmission measurements is reported with special emphasis on the impact on the lateral resolution. Mid-infrared transparent fibers (chalcogenide glass) and even substrates (zinc selenide ATR crystal) were sprayed with drops (drop size distribution: 15 to 150 μm in diameter) of an organic polymer with specific absorption bands in the mid-infrared range. Quadratic scans along the surface of the fiber and of the even substrate gave information about whether the drops distributed on the surface appear laterally resolved, by maintaining the local information in the resulting contour plot. Several scans with different microscopic apertures accentuate the relation between the diameter of the focused IR beam on the sample surface and the broadening of the drop image in the contour plot.