Synthesis of Ultrathin ZnO Sheets Using Physical Vapor Deposition Method*

Ultrathin zinc oxide (ZnO) is a promising material for potential photocatalysis applications, such as producing green hydrogen by splitting water in the presence of sunlight. Synthesizing high-quality ultrathin ZnO is a fundamentally important step in realizing their applications. The physical vapor deposition (PVD) method is a promising method for preparing ultrathin ZnO because it allows tuning the amount of material deposited on a substrate so that ultrathin ZnO with atomic level thickness can be fabricated. Here, we investigated the utilization of a semi-sealed quartz tube to enhance the vapor pressure of ZnO, thereby optimizing its growth. We utilized Al₂O₃ as a substrate to synthesize ZnO sheets. Our study shows that employing a semi-sealed quartz tube facilitates the growth of enlarged and crystalline ultrathin ZnO compared to the absence of the tube. The atomic force microscopy measurements reveal that these ultrathin ZnO islands exhibit thicknesses as low as ~ 1 nm while their lateral size extends up to ~ 6 µm. As more Zn atoms are exposed to the ultrathin ZnO surfaces that provide many active sites for catalytic reactions, these ultrathin ZnO can potentially be useful for photocatalytic applications.