Etching behavior of α-MoO₃ thin films: Application to single-crystal substrate recycling and post-transfer residue removal

Fabrication of high-performance and durable flexible devices based on epitaxial thin films using the transfer technique has garnered significant attention. Expensive single-crystal substrates, which are essential for epitaxial film growth, are discarded after film transfer. This study demonstrates a substrate recycling strategy through complete removal of α-MoO₃ epitaxial layers in heated water, enabling subsequent redeposition of films with equivalent crystalline quality. Notably, ultrasonic treatment facilitated α-MoO₃ removal without any heating, offering a mild approach. The study extended to investigating the etching behaviors in acetone, ethanol, and NaOH solutions, thereby providing valuable insights for potential lithographic applications. Highly crystallized CoFe₂O₄ films grown on α-MoO₃ layers were successfully transferred onto flexible substrates via mechanical exfoliation, along with the co-transfer of some α-MoO₃ clusters. The subsequent etching in heated water effectively removed residual α-MoO₃ from the CoFe₂O₄ surface, affording smooth, impurity-free films. This approach demonstrates the feasibility of recycling expensive single-crystal substrates and fabricating clean, high-quality, flexible electronic devices.