Rapid growth and super air stability of 2D ultrathin superconducting Mo₂C crystals

In the past decade, chemical vapor deposition (CVD)-grown ultrathin Mo₂C crystals have attracted extensive interest for applications in two-dimensional superconductivity, electrocatalysis, and heterojunctions. However, conventional growth methods suffer from low growth rates, limiting large-area fabrication, and the air stability of ultrathin Mo₂C remains poorly understood. Here, rapid growth of ultrathin Mo₂C single crystals is achieved via CVD using a bilayer Cu/MoC_x substrate. The combination of a pre-carburized MoC_x substrate and a reduced CH₄/H₂ ratio is identified as the key factor enabling fast growth by effectively regulating the supply of Mo and C. A lateral growth rate of up to 8.3 μm/min at 1090 °C, exceeding previously reported values by more than fourfold, is achieved, while ultrathin Mo₂C crystals with lateral sizes up to ∼320 μm are obtained at 1086 °C by prolonging the growth time. Despite the rapid growth, the ultrathin Mo₂C crystals exhibit high crystalline quality, smooth surfaces, and robust superconductivity. Moreover, their air stability is systematically investigated, revealing no detectable oxidation or degradation after ∼150 months of air exposure, while their superconductivity remains well preserved. These results demonstrate the exceptional growth efficiency and air stability of ultrathin Mo₂C, highlighting its strong potential for future applications, particularly in nanomechanical resonators.