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Spectroscopic Ellipsometry Study of Liquid Crystal and Polymeric Thin Films in Visible and Near Infrared

Volodymyr Tkachenko ,Antigone Marino ,Francesco Vita ,Franco D\\\\\\\'Amore ²,Luca De Stefano ³,Mario Malinconico ⁴,Massino Rippa ⁵,Giancarlo Abbate
INFM Unit of Naples (Italy) INFM Unit of Naples and Department of Physical Sciences - University of Naples Federico II ²CoreCom, Milan, Italy ³CNR-IMM, Naples, Italy ⁴CNR-ICTP, Pozzuoli (NA), Italy ⁵Department of Physical Sciences - University of Naples Federico II
In order to be applied in photonic devices for telecom applications, soft materials, polymers and in particular liquid crystals, need to be optically characterised at the working wavelengths, typically in the Near IR region (NIR). Unfortunately, for most of these materials very few data are available in literature, especially in the NIR range. Moreover, because of the nature of these media, it is often necessary to make measurements on samples consisting of complicated multilayer stacks, including anisotropic, inhomogeneous, absorbing, and/or depolarising films. Recently, different ellipsometric techniques have been proposed to fulfil this task. However, in the case of such complicated sample structures, despite showing strong potentialities, ellipsometry seems to be very sensitive to the choice of a proper physical model and a good initial guess in the fitting procedure. In this work, we show the results of ellipsometric measurements, in the range from visible to NIR, for some liquid crystal and polymeric samples. We point out limits and potentialities of the technique and compare the obtained results with another experimental method, the m-lines spectroscopy, and/or with existing data in literature. The characterisation results of the analysed materials (the nematic liquid crystal 5CB, one commercial and one lab made optical polymer, and an Indium Tin Oxide film) are useful and interesting by themselves. However, more than in the provided data, we put the interest of the present analysis in the warnings about spectroscopic ellipsometry utilisation and eventually the necessity of complementary information.

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