Atomically Resolved Surface Reconstruction of WO₃ (002)

The rearrangement of surface atoms in oxide nanocrystals, namely surface reconstruction, plays an important role in improving the physical and chemical properties of metal oxides. However, structural information pertaining to reconstructed surfaces is scarce due to the challenges associated with directly imaging surface and sub-surface atoms under reconstruction conditions. Herein, the reconstruction of the nanocrystalline tungsten trioxide (002) surface is directly investigated via scanning transmission electron microscope (STEM). The results reveal that the atoms on the reconstructed WO₃ (002) surface are rearranged into a (1 × 2) structure, and the structural model is determined by density functional theory (DFT) calculation. In addition, after surface reconstruction, the Fermi level shifted toward the conduction band compared to the initial surface, achieving an effect similar to n-type doping. Surprisingly, analogous atomic rearrangements are also observed in cracks, indicating that sub-nanometer fractures in tungsten trioxide can be remedied through surface reconstruction, thus proposing an unconventional mechanism for crack healing. Furthermore, DFT calculations are used to analyze the models and electronic properties of the reconstruction structures. These findings provide insights into the surface reconstruction of WO₃ (002) and the healing of nanoscale cracks in tungsten trioxide.