The influence of the metal grain size on polymer/metal bilayer wrinkling

We report on the observation of wrinkling processes in very thin polymer/metal bilayer structures prepared spin casting and sputter preparation, respectively. The study utilizes a viscoelastic conjugated polymer typically used in optoelectronic devices with a film thickness of 100 nm. After careful thermal annealing of the polymer films thin gold layers were deposited ranging from 20 nm to 45 nm which induces a slow wrinkling process without the influence of an external stimulus. The resulting wrinkling patterns were characterized by means of atomic force microscopy and compared to calculations based on a novel model for such bilayer systems recently proposed in literature. In particular, the experiments could confirm experimentally the predicted decoupling of the characteristic wrinkling wavelength and amplitude. Moreover, it is found that the grain size of the metal layer plays an essential role in the final appearance of wrinkling patterns for the lower range of metal thickness.