Physical vapor-deposited thin hard films on polymers: sample preparation for SEM analysis

Different methods for visualizing the coating structure and the interfaces of thin films on thermoplastic polymers are compared. Specimens of thin films of titanium, titanium nitride (TiN), titanium carbide (TiC), and Ti/TiN multilayers on the polymers poly(butylene terephthalate), poly(amide) 6,6, poly(propylene), poly(styrene) and acrylonitrile-butadiene-styrene were prepared by grinding and polishing, cutting, and fracture. The results of the various sample preparation techniques were compared with regard to suitability for visualizing the morphology of the hard coatings on the polymeric substrates and the coating/polymer interface region. The samples were investigated using scanning electron microscopy (SEM). The best way to prepare the samples, independent of the nature of the substrate, was found to be freezing in liquid nitrogen followed by fracture of the specimens. This method displays the interface region and the coating morphology rapidly and very clearly.