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A strongly adhering ZnO crystal layer via a seed/buffer-free, low-temperature direct growth on a polyimide film via a solution process

ZnO is a functional material used as a thin-film device that can have numerous applications in a sustainable society. In general, a seed/buffer layer is considered necessary for the fabrication of ZnO crystal layers on substrates. Herein, we demonstrated the direct growth of a ZnO crystal layer without any such layer. Using a liquid-phase method, randomly oriented, rod-like ZnO crystals were formed directly on a polyimide film. The study confirmed irregularities in nano-order on the surface of the film, where ZnO crystals are fixed. These results suggest that the anchor effect contributes to the direct growth. According to our findings, a seed layer is not required for fabricating a ZnO crystal layer film if polymer substrates are optimally treated. Omitting a seed layer would open new insights into the practical uses of ZnO. The simplification of the mass production process, improvement of functionalities, such as transparency and thickness, as electric devices are potential examples.