Atomic Imaging of Molybdenum Oxide Nanowires with Unique and Complex Periodicity by Advanced Electron Microscopy

Crystalline Mo₅O₁₄ exhibits distinctive structural features such as tunnel structure and pseudolamellar arrangement according to the ideal model. However, the spatial resolution of the conventional technique of transmission electron microscopy (TEM) is insufficient to distinguish the actual positions of atoms. In this work, we aimed to systematically analyze and identify the Mo₅O₁₄ nanowires fabricated by the chemical vapor deposition (CVD) process. Utilizing high-angle annular dark-field (HAADF), annular bright-field (ABF), and enhanced annular bright-field (E-ABF) within the scanning transmission electron microscope (STEM) mode reveals the structural features at the atomic scale. In addition, the ultrahigh resolution images have confirmed the crystallographic insights in [001] growth direction for the Mo₅O₁₄ nanowires with a tunnel structure throughout the nanowire. The cross-sectional images show the unique close-packed plane and atomic arrangement with a network of MoO₆ octahedra and MoO₇ pentagonal bipyramids. These results are consistent with the theoretical atomic arrangement, supporting the realization of Mo₅O₁₄-type catalysts used in the selective oxidation process and battery applications.