Microreactor‐Assisted Soft Lithography for Rapid and Inexpensive Patterning of Nanostructured ZnO/CuO Heterojunctions

Abstract

A novel, scalable process to deposit nanostructures with multiscale 3D geometric shapes and its application in fabricating p–n heterojunctions with n‐type ZnO and p‐type CuO is demonstrated. The process combines a microreactor‐assisted solution deposition with soft lithography to control and generate a chemical reactive flux that is transported by a patterned microfluidic channel for film printing. The precursor solutions are mixed and heated in a microreactor to generate reactive species controllably. Patterned polydimethylsiloxane (PDMS) channels guides the reacting solution to the substrate surface to form ZnO nanostructures with multiscale 3D geometric shapes. The channel geometry, flow rate, and substrate temperature are found to control the pattern geometry. A thin‐film diode composed of two different layers of a thin film with CuO at the bottom and ZnO at the top is fabricated to demonstrate fabrication of complicated functional nanostructures using low‐cost and facile solution‐based methods on desired substrate regions. The growth of the thin film can be controlled and accelerated compared to the traditional chemical bath deposition process, thanks to the continuous formation of the precursor solution with constant concentrations.