Surface diffusion strategies for chemical vapor deposition of 2D Nb2C MXene films

Chemical vapor deposition (CVD) is a thriving bottom-up synthesis technique that serves as an alternative to the conventional methods involving the etching of layered MAX phases. CVD is particularly advantageous in terms of large-scale synthesis and atomic economy, time and energy savings, as well as the capability to produce bare MXenes without surface terminations. However, its widespread employment remains limited as the growth generally only occurs in specific immiscible alloy systems consisting of transition metals (such as Mo) and low melting point catalytic metals (such as Cu). Here, we propose a surface diffusion liquid metal CVD (SDLM-CVD) method for synthesizing bare few-layer 2D Nb 2 C MXenes. Controlling the Nb/C ratio and its distribution on the Cu liquid surface is the key factor. Single crystalline bare Nb 2 C flakes with a trigonal structure were obtained in a specific region where the appropriate Nb/C ratio is satisfied. Additionally, a continuous 2D Nb 2 C film is formed by leveraging the self-assembling process that observed during the growth. The growth mechanism and the self-assembling mechanism were further elucidated through density functional theory calculations. The SDLM-CVD method provides a novel approach for the direct and large-scale synthesis of materials in the MXenes family.