Characterisation of a Coated Glass Filter

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SIMS depth profile analysis of a non-defect area of the filter by DSIMS (left) clearly shows the alternating layer structure :-

The individual layer thicknesses are ~10nm for silver and yttrium oxide layer and ~30nm for zinc sulphide.

Formation of silver sulphide has occurred through chemical interaction between the adjacent silver and zinc sulphide layers.

Carbon contamination is present at or near to the silver / zinc sulphide interfaces. This is probably a result of poor vacuum quality in a reactor vessel.

OH is found in the zinc sulphide layer and particularly at the zinc sulphide / yttrium oxide interface. Again this may be a reflection of vacuum quality during layer deposition, or moisture ingress post-production.

Progressive SIMS image acquisitions through a defect area (right) show the buckling and displacement of the layer structure and the probable cause of defect formation :-

A silicate-rich particulate is found at the centre of the defect area at the interface between original glass substrate and the coating layer structure.

Localised physical stresses in the coating, caused by the particulate and expansion of any associated moisture, result in the eventual distortion of the coating, radiating outwards from the nucleation site.

SIMS images of defect area showing yttrium oxide (YO2 - top left), zinc sulphide (ZnS - top right), silicate (SiO3 - bottom left) and overlayed (bottom right).