Direct observation of early stage fragmentation of nanosized SiO_x coating deposited by PECVD onpoly(ethylene terephthalate) (PET) film substrates is investigated by means of micro tensile device coupled with atomic force microscope (AFM). This arrangement allows fast measurement of fragmentation patterns of SiOx coatings with thickness below 30 nm. Nanometer thick SiO_x coatings are deposited on three grades of PET films containing predetermined anti-blocking particle density ranging from 0 to 1800 mm~(-2). Crack onset strain and fragment densities of SiO_x coatings are compared with previously obtained data from SEM observations. The results confirm the negative influence of anti-blocking particles on mechanical properties of coatings. The cohesion strength and the interfacial adhesion are modeled using a constant interfacial strength approach with a Weibull-type probability of fracture.
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