Spherical indentation and scratch durability studies of transparent conducting layers on polymer substrates

The effect of moderate normal and tangential spherical loading on the durability of brittle ceramic films sputtered on polymer substrates is investigated. Indium tin oxide films with various thicknesses are deposited by sputtering on polyethylene terephthalate substrates and their mechanical durability is assessed using a spherical nanoindenter and scratch tester with built-in optical microscopy capability.It is observed that crack initiation occurs at 40 mN normal applied load. As loading increases, formation of brittle ring cracking and of secondary radial cracks is evident. It is also shown that ring crack spacing is thickness dependent. During scratch testing two main coating failure modes are observed. The first is through thickness cracking and the second is buckling spallation of the coating. Both failure mechanisms exhibit thickness dependence.