Synthesis of nano-plates of Cr2GaC MAX-phase under capillarity spreading Ga on Cr surface assisted by H2–CH4 microwave plasma

Abstract

Synthesis of the MAX phase is most often conducted at high temperatures, and the synthesized mixture contains many contaminant phases that require removal. The discovery of efficient low-temperature methods for the synthesis of MAX phases and MXenes is the key to their mass application. This work reports a method for obtaining pure MAX-phase with composition of Cr2GaC using a microwave reactor without additional heating. Synthesis was performed under 2 torr vacuum in hydrogen and methane flows of 80 and 20 sccm, respectively. The power of the microwave generator was 500 W at a frequency of 4.5 GHz. The synthesis process consists of creating conditions for capillary interaction (contact angle much lower than 90°, tends to zero), dissolution of chromium substrate in liquid gallium and dissolution of carbon directly from the gas phase (H2–CH4 plasma). The synthesized MAX phase does not contain any phase contaminations and has a thickness of several atomic layers and submicron lateral dimensions. Characterization of the phases was carried out using the transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM), atomic-force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy methods. Diffraction methods show high purity of Cr2GaC phase synthesized by this method, which can be a good precursor for MXenes production.