Surface deformation of amorphous silicon thin film on elastomeric substrate

Stiff thin layers on compliant substrates can generate various surface structures using equi-biaxial stress caused by large thermal expansion rate differences. We investigated the detailed understanding on the evolution of self-assembled wrinkle patterns of ultra-thin amorphous silicon (a-Si) layers on polydimethylsiloxane substrate. It turns out that the generation of various wrinkle patterns depends on the position of their orientation, film thicknesses, mechanical properties of the a-Si films, and the amount of pre-strain. The various self-assembled patterns include one-dimensional wavy patterns, randomly ordered two-dimensional structured patterns, and herringbone structures. The self-assembled wrinkles can be characterized by the wavelength and amplitude of the distinct structures: the amplitudes of the various patterns increase as the amount of pre-strain increases, while the wavelengths remain constant within our experimental ranges. The experimental results of the wavelengths and amplitudes for the wavy structured patterns of 270-nm-thick a-Si layer are in good agreement with the theoretical solutions of the single crystalline silicon (c-Si) model, which implies that the theoretical modeling of the deformation of c-Si film can be expandable to the case of a-Si film deformations.