Water-assisted controllable growth of atomically thin WTe 2 nanoflakes by chemical vapor deposition based on precursor design and substrate engineering strategies.

WTe 2 nanostructures have intrigued much attention due to their unique properties, such as large non-saturating magnetoresistance, quantum spin Hall effect and topological surface state. However, the controllable growth of large-area atomically thin WTe 2 nanostructures remains a significant challenge. In the present work, we demonstrate the controllable synthesis of 1T' atomically thin WTe 2 nanoflakes (NFs) by water-assisted ambient pressure chemical vapor deposition method based on precursor design and substrate engineering strategies. The introduction of water during the growth process can generate a new synthesized route by reacting with WO 3 to form intermediate volatile metal oxyhydroxide. Using WO 3 foil as the growth precursor can drastically enhance the uniformity of as-prepared large-area 1T' WTe 2 NFs compared to WO 3 powders. Moreover, highly oriented WTe 2 NFs with distinct orientations can be obtained by using a-plane and c-plane sapphire substrates, respectively. Corresponding precursor design and substrate engineering strategies are expected to be applicable to other low dimensional transition metal dichalcogenides, which are crucial for the design of novel electronic and optoelectronic devices.