Phase-controlled synthesis and two-dimensional electronic transport of ultrathin tungsten carbide platelets

The transition metal carbide (TMC) family has been previously studied for various catalytic, mechanical, and electronic applications, and recently TMCs have been isolated into the ultrathin limit. A bottom-up approach has been developed to synthesize non-layered, ultrathin TMCs (UThTMCs). In this work, liquid metal assisted chemical vapor deposition is used to control the growth of different phases of tungsten carbide. In particular, WC and W2C single crystal nanoplates are synthesized when using copper and gallium, respectively, as the tungsten diffusion barrier. First principles calculations confirm the stability found experimentally in the two synthesized carbide phases. We also report the first low temperature measurements of electronic transport in WC below 300 mK and ultrathin W2C down to 1.8 K. We find that WC does not enter a superconducting state, while UThTMCs of W2C enter a quasi-2D superconducting state below 2.8 K. Our results provide new ground on the synthesis of other UThTMCs with controlled crystal phase. Given the richness of phases among metal carbides and the related transition metal nitride family, further research will be motivated by this work to isolate novel carbide and nitride phases in this ultrathin limit. Finally, it is important to note that the electronic transport of UThTMCs follows a quasi-2D regime and further systems should be evaluated and compared, especially the superconducting phases. These UThTMCs and their heterointerfaces could find important applications in electrocatalysis, carbide plasmonics, transparent conducting films, and materials for effective radiation shielding due to their high density and ability to absorb neutrons and gamma rays.