28 May 2004 Toward measuring concentration gradients in polymer-dispersed liquid crystals with secondary ion mass spectrometry
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Dynamic secondary ion mass spectrometry (SIMS) is usually applied to measure depth profiles in inorganic multi-layer systems. SIMS on organic multi-layer samples is highly complicated due to the complex fragmentation of the sample which results in fingerprint of masses representing the components in the sample. Using multivariate statistics, we succeeded to interpret the SIMS spectra and were able to identify layers with different compositions in artificially produced two-layer samples. The method is demonstrated for samples of a poly(isobornylmethacrylate) coating on a polymer dispersed liquid crystal consisting of the nematic liquid crystal (E7) and poly(isobornylmethacrylate). Quantification of the E7 concentration is complicated by evaporation in the vacuum system. Infrared spectroscopy proved that the loss of E7 from poly(isobornylmethacrylate) can be prevented by capping the sample with poly(vinyl alcohol). Cooling to cryogenic temperatures will be required to suppress further evaporation during SIMS analysis. The SIMS depth resolution of a two-layered sample was determined by discriminant function analysis to be 130 nm at a depth of one micrometer, which allows the application of SIMS for a typical optical grating.
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B. K. Charlotte Kjellander, Leo J. van IJzendoorn, Arthur M. de Jong, Dirk J. Broer, Wouter J. H. van Gennip, Martien J. A. de Voigt, Hans J. W. Niemantsverdriet, "Toward measuring concentration gradients in polymer-dispersed liquid crystals with secondary ion mass spectrometry", Proc. SPIE 5289, Liquid Crystal Materials, Devices, and Applications X and Projection Displays X, (28 May 2004); doi: 10.1117/12.526549; https://doi.org/10.1117/12.526549

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