Effect of nano-holes and their arrangement for enhanced bendability of metal electrodes
Metallic thin films often exhibit poor mechanical robustness, which makes them unsuitable for use as electrodes in flexible and stretchable electronic devices. This prompted us to investigate the effect of creating a pattern of nano-holes, in an electrode consisting of a metallic thin film, on its mechanical and electrical properties. The adoption of nano-network structures is shown to afford significantly improved bendability to the films, with a change in electrical resistance of only 21% after 10,000 bending cycles, under a bending strain of 6.3%. Contrary to the planar silver (Ag) films in which large cracks are formed, structures that contain nano-holes act as barriers that block crack growth; consequently, because only short cracks are formed in these films, changes in their resistance are much lower. In this paper, we suggest a novel model based on random grain boundaries to simulate the behavior of various nano-pattern arrangements when the film is subjected to mechanical stress. Our modeling studies revealed that nano-holes secure the electrical current pathways by effectively blocking crack propagation, and that optimizing orientation, size, and coverage of these nano-holes can further improve the mechanical properties. While the diamond patterns exhibit superior characteristics to those for rectangular ones, their directional dependence are shown to be reduced by adopting randomly dispersed nanostructures. We additionally verified experimentally that an array of holes (rectangular, diamond-shaped, and randomly patterned) significantly affects crack propagation and resistance change.bstract text goes here.