Supplemental material to the article "Sub-nm precise measurement of adhesive gaps by imaging interferometry"

The measurements are performed using PTB's Precision Interferometer on a standard material (ULE®) together with a common adhesive (3MTM Scotch-WeldTM DP-460EG), gap thickness approx. 100 µm. Measurements on the sample without adhesive reveal that the length changes without adhesive are within approx. 0.1 nm under comparable conditions.

On the adhesive sample, on the other hand, drying in a vacuum and water vapor treatment lead to shrinkage and swelling. These long-term process processes can be described very well by simple but empirical fitting functions. The measurement uncertainty budget results in typical values of approx. 0.3 nm for changes of the adhesive gap thickness.