Controlled Synthesis of Sub-Millimeter Nonlayered WO₂ Nanoplates via a WSe₂-Assisted Method

2D metal oxides (2DMOs) have stimulated tremendous attention due to their distinct electronic structures and abundant surface chemistry. However, it remains a standing challenge for the synthesis of 2DMOs because of their intrinsic 3D lattice structure and ultrahigh synthesis temperature. Here, a reliable WSe₂-assisted chemical vapor deposition (CVD) strategy to grow nonlayered WO₂ nanoplates with tunable thickness and lateral dimension is reported. Optical microscopy and scanning electron microscopy studies demonstrate that the WO₂ nanoplates exhibit a well-faceted rhombic geometry with a lateral dimension up to the sub-millimeter level (≈135 µm), which is the largest size of 2DMO single crystals obtained by CVD to date. Scanning transmission electron microscopy studies reveal that the nanoplates are high-quality single crystals. Electrical measurements show the nanoplates exhibit metallic behavior with strong anisotropic resistance, outstanding conductivity of 1.1 × 10⁶ S m⁻¹, and breakdown current density of 7.1 × 10⁷ A cm⁻². More interestingly, low-temperature magnetotransport studies demonstrate that the nanoplates show a quantum-interference-induced weak-localization effect. The developed WSe₂-assisted strategy for the growth of WO₂ nanoplates can enrich the library of 2DMO materials and provide a material platform for other property explorations based on 2D WO₂.