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H. Mahr, D. Feiertag, C. Eisenmenger-Sittner:
"Automated Determination Of The Thickness Of Transparent Films On Granular Substrates";
Poster: Joint Vacuum Conference 14 (JVC-14), Dubrovnik, Kroatien; 04.06.2012 - 08.06.2012.

Coated granular materials are used in a wide area of applications as e.g. interface modification in composite materials. Determining the film thickness on such granular materials can be a complicated and time consuming task. In the case of transparent substrates like diamonds space resolved optical transmission spectroscopy can be used to determine the film thickness given the film is transparent.
In this work the capability of film thickness measurement with commercially available optical scanners is shown. To calibrate the scanner films with a linear variation in thickness are deposited on glass substrates. Transmission values for various film materials and film thicknesses were calculated from literature and compared to measurements preformed by an optical scanner and by a spectrometer. A good match of results achieved by these three methods was achieved.
For film thickness measurement of granular materials, size and shape of the granulates, which act as substrates, have to be considered. Diamonds have a special form of coplanar facets, are transparent in the optical range and the grain size is within the scanner resolution, therefore they are ideal substrates for the implemented measurement. The scanned data is refined with algorithms for particle detection and removing immeasurable areas within the particles and a brightness histogram is generated. With this method it is possible to determine if the scanned granular material is homogenously coated or still uncoated. A quantitative thickness measurement is possible by extracting maxima in the brightness histogram. Fitting these maxima with a Gaussian function leads to an estimate of the mean film thickness and its distribution. These results are verified on different diamond types with different grain sizes and for different coating materials and film thicknesses.

This work was supported by the Austrian Science Fund (FWF), project "T-scan", grant number TRP-6