Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

A methodology of correlation of optical-intermediate and functional transparent coatings properties

Thin silicon oxide films (SiOx) were produced using electron-beam evaporation (EBE) technique. Different types of source evaporated materials were used, such as standard silicon monoxide (SiO) and silicon dioxide (SiO2), as well as mixed materials of silicon (Si), SiO2 and SiO, in order to obtain all possible stoichiometries. Depending on the applied deposition conditions and the different evaporation processes, SiOx coatings of different stoichiometry, properties, and thickness, were formed.

A number of SiOx coatings, grown on polymeric membrane substrates, were studied in terms of their optical properties either ex situ or in situ and in real-time during the evaporation processes, using the Spectroscopic Ellipsometry (SE) and the Multi-Wavelength Ellipsometry (MWE) techniques, respectively. For the evaluation and the determination of the specified optical parameters an appropriate modeling and fitting procedure was carried out.

This allowed the calculation of the Penn Gap (the energy where the strong electronic absorption takes place) and of the static dielectric constant or refractive index n. On the basis of the work carried out so far, these two parameters have proved to be the two most important optical parameters correlated to the final functional properties, such as the barrier properties (i.e., oxygen transmission - ORT and water vapour transmission - WVTR) of the SiOx coatings. The latter were determined with the appropriate permeation tests.

In addition, the strong correlation between the SiOx films' thickness and their barrier properties was verified. A precise determination of the thickness of coatings was achieved by analysing SE and MWE data, even in a real-time analysis mode. The latter is very important if we take into account that there is a complexity in the accurate calculation of the thickness of the SiOx films, which are grown onto polymeric membranes. SE and MWE results for thickness were compared with the respective values deduced either theoretically, by means of calibrated deposition rates of the evaporation processes, or experimentally by means of i) XRF, ii) EDX, and iii) SEM techniques, which were applied ex situ.

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Aristotle University of Thessaloniki
54124 Thessaloniki