Ultrafast Growth of Thin Hexagonal and Pyramidal Molybdenum Nitride Crystals and Films

Two-dimensional (2D) ultrathin transition-metal carbides, nitrides, and carbonitrides are considered to be a family of important functional materials for various applications; however, it is challenging to realize their fast and efficient growth from gas phase. Herein, we demonstrate a one-step direct and rapid synthesis of ultrathin molybdenum nitride (MoN) crystals with controlled thickness and morphology on liquid copper by controlling diffusion of the Mo source through a liquid copper film method. The growth of a few individual crystals with thickness down to 1 nm and continuous large-area films takes only 3 and 5 min, respectively, which is at least 20 times faster than previously reported. More importantly, a series of morphologies of MoN, including pyramidal crystals, were obtained by adjusting the synthesis time and the amount of hydrogen in nitrogen gas from 15% to 5%. The mechanism of this morphology evolution is explained through the molecular diffusion kinetic growth process. Furthermore, the MoN films present enhanced catalytic activity in the hydrogen evolution reaction due to the exposed catalytically active surface and fast electron transport in highly conductive hexagonal MoN (h-MoN).