Transfer Printing of Solution-Processed 3D ZnO Nanostructures with Ultra-High Yield for Flexible Metasurface Color Filter

This work describes a facile thermal transfer printing process for solution-processed high-quality ZnO nanostructures. Nanostructures are synthesized through patterned solution growth and transfer-printed onto a polymer substrate with an inverted configuration. Thus, the shape of the solution-processed ZnO nanostructures can be regulated to have diversified forms, clearly defined edges, and improved surface profiles. To further demonstrate the scalability of such transfer printing process, a metasurface color filter with 300 mu m x 500 mu m "windmill" pattern is designed and more than 300 000 nanorod units included. After the structures are transferred, the color filter can be gradually tuned by O-2 plasma treatment. Moreover, the uneven height of as-synthesized nanorods with different diameters can be evenly rescaled, implying a precise control over the vertical dimension. Lastly, an ultra-high transfer accuracy is validated with a lateral displacement of less than 7 nm. The presented work demonstrates a facile and low-cost transfer printing route toward ZnO-based metasurfaces on flexible substrates.