Anatase TiO ₂ (112) Epitaxial Thin Films Grown by Mist Chemical Vapor Deposition

Epitaxial thin films serve as essential platforms for studying the physical and chemical properties of materials. High-index planes, in particular, are expected to exhibit novel functionalities but are often thermodynamically unstable, making their selective growth challenging. Anatase TiO2 has attracted considerable attention for applications in catalysis, sensing, and electronic devices. To date, the fabrication of anatase TiO2(001) and (100) epitaxial thin films has been extensively studied using conventional pulsed laser deposition and sputtering methods. However, there have been few reports on other crystallographic orientations. In this study, we use the mist chemical vapor deposition method to demonstrate the deposition of anatase TiO2(112) epitaxial thin films on Al2O3(0001) substrates. The out-of-plane and in-plane epitaxial relationships are [112]TiO2//[0001]Al2O3 and [110]TiO2//[101̅0]Al2O3, respectively. This crystal orientation differs from those obtained via pulsed laser deposition and sputtering, where rutile TiO2(100) typically grows on Al2O3(0001) substrates. We conclude that surface reactions play a crucial role in determining crystal orientation. The selective growth of such high-index crystal planes is essential for realizing diverse functionalities, including enhanced electronic and catalytic properties.