Volume 109, Number 2, 2012
|Page(s)||81 - 91|
|Published online||10 May 2012|
Lubricant homogeneity of industrial rough metallic substrates: a multivariate statistical analysis of spectroscopic ellipsometry data
Physique des Matériaux & Optique, Université de
Mons, 20 Place du
Accepted: 18 January 2012
In this paper, a non-destructive method is proposed for measuring the density of a very thin lubricant layer (weight and spatial) on an industrial surface. We considered spectroscopic ellipsometry measurements on rough tinplated steel substrates protected by a lubrication layer. The thickness of the coating was less than the roughness parameter characterizing the metallic surface. As the optical properties of the substrates could not be modelled in a conventional way due to the roughness and the complex structure of the metal, the variations of one of the ellipsometric angle (Δ) were evaluated as a function of the lubricant film surface density. After identification of the potential outliers using a multivariate analysis technique based on the Mahalanobis distance, we interpreted the data using the Drude’s approximation for thin dielectric films. The values of Δ linearly decrease with the lubricant surface density, allowing us to evaluate locally the lubricant surface density and its point-to-point variations.
Key words: Spectroscopic ellipsometry / outliers detection / multivariate analysis / lubricant / tinplated steel (TPS)
© EDP Sciences 2012
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