Gas-Flow-Assisted Wrinkle-Free Transfer of a Centimeter-Scale Ultrathin Alumina Membrane onto Arbitrary Substrates.

The transfer of an ultrathin membrane onto arbitrary substrates is important in different practical fields. Conventional wet-transfer methods inevitably induce wrinkle defects as a result of the large contact angle of the trapped droplet between the membrane and the substrate. Here, we demonstrate a gas flow-assisted method (GFAM) to transfer centimeter (cm)-scale ultrathin membranes onto arbitrary substrates (including a curved substrate) without wrinkles. GFAM makes use of contact angle hysteresis to bulge the trapped droplet between the substrate and the ultrathin membrane and simultaneously stretch the ultrathin membrane during rapid dewetting driven by gas flow. Moreover, GFAM can be easily fulfilled by using compressed air for seconds. Compared with conventional hydrophilic treatments or organic liquid wetting, this method has no durability concern and does not change the surface nature of substrates. Taking a widely used ultrathin anodic aluminum oxide (AAO) membrane as an example, we successfully demonstrate the application of a large-area wrinkle-free ultrathin AAO membrane to defect-free ordered nanostructure array fabrication and investigate the micro-scale details of macro-scale wrinkles generated by the conventional ways. In addition, its corresponding superiority over the defective counterpart is further studied in optical sensing. This method is highly valuable for promoting the simplicity of large-area ultrathin membrane transfer in practice.