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Estimation of the composition of coelectron-beam-evaporated thin-mixture films by making use of the Wiener bounds

: Franke, Christian; Stenzel, Olaf; Wilbrandt, S.; Wolf, Josephine; Kaiser, Norbert; Tünnermann, A.


Applied optics 54 (2015), Nr.9, S.2362-2370
ISSN: 0003-6935
ISSN: 1539-4522
ISSN: 1559-128X
Fraunhofer IOF ()

Material mixtures offer prospective possibilities for synthesizing coating materials with tailored optical constants. We present experimental results for mixture coatings of alumina/aluminum fluoride and alumina/hafnia deposited by electron beam evaporation. Thereby, the volume filling factors of the components are commonly estimated on the basis of deposition rates measured by quartz crystal microbalance. The interplay between the vapor fluxes from the two evaporation sources, the crosstalk between quartz crystal microbalances, and the influence of the plasma source on the tooling factors limit the accuracy of this estimation, and this has motivated us to develop an alternative approach. The general idea of our approach is based on the commonly high accuracy in thin-film optical constant determination using spectrophotometry. Therefore, these optical constants serve as a reliable input for a rather simple but robust evaluation procedure based on the concept of Wiener bounds. The consistency of the obtained results is illustrated by opposing the data to the elementary film composition estimated from energy-dispersive x-ray spectroscopy.