Abstract
Fast infrared mapping with sub-millimeter lateral resolution as well as time-resolved infrared studies of kinetic processes of functional organic thin films require a new generation of infrared ellipsometers. We present a novel laboratory-based infrared (IR) laser mapping ellipsometer, in which a laser is coupled to a variable-angle rotating analyzer ellipsometer. Compared to conventional Fourier-transform infrared (FT-IR) ellipsometers, the IR laser ellipsometer provides ten- to hundredfold shorter measurement times down to 80 ms per measured spot, as well as about tenfold increased lateral resolution of 120 μm, thus enabling mapping of small sample areas with thin-film sensitivity. The ellipsometer, equipped with a HeNe laser emitting at about 2949 cm(-1), was applied for the optical characterization of inhomogeneous poly(3-hexylthiophene) [P3HT] and poly(N-isopropylacrylamide) [PNIPAAm] organic thin films used for opto-electronics and bioapplications. With the constant development of tunable IR laser sources, laser-based infrared ellipsometry is a promising technique for fast in-depth mapping characterization of thin films and blends.
Highlights
Thin organic films or hybrid films and related interfaces are playing important roles in optical devices, solar cells, as well as biomedical and sensor applications.[1,2,3,4,5,6] In order to characterize thin films, film properties like inhomogeneity, chemical composition, crystallinity, surface morphology, and optical properties must be analyzed, the knowledge of which is required for the successful design and improvement of the respective device or surface.In our thin-film sensitive laboratory-based far-field IR ellipsometers, the size of the probed spot on the sample surface is typically a few ten mm[2] at 65° incidence angle
For materials with known refractive indices, our results show that the singlewavelength IR laser mapping ellipsometer is able to characterize inhomogeneities in thickness and/or chemical composition in small spatial domains with diameters as small as 120 μm in very short time scales
In order to determine the lateral resolution of the IR laser ellipsometer, we performed linescans without and with micro
Summary
Thin organic films or hybrid films and related interfaces are playing important roles in optical devices, solar cells, as well as biomedical and sensor applications.[1,2,3,4,5,6] In order to characterize thin films, film properties like inhomogeneity, chemical composition, crystallinity, surface morphology, and optical properties must be analyzed, the knowledge of which is required for the successful design and improvement of the respective device or surface. We applied the IR laser ellipsometer for the optical characterization of spin-coated polymer films, namely P3HT, a conducting polymer in opto-electronic devices,[3] and PNIPAAm, a temperature-sensitive polymer with potential applications in the fields of biosensors[6] and biomedicine.[5,25,26] For materials with known refractive indices, our results show that the singlewavelength IR laser mapping ellipsometer is able to characterize inhomogeneities in thickness and/or chemical composition in small spatial domains with diameters as small as 120 μm in very short time scales
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