Controlled growth of 2D ultrathin GaO crystals on liquid metal.

2D metal oxides (2DMOs) have drawn intensive interest in the past few years owing to their rich surface chemistry and unique electronic structures. Striving for large-scale and high-quality novel 2DMOs is of great significance for developing future nano-enabled technologies. In this work, we demonstrate for the first time controllable growth of highly crystalline 2D ultrathin GaO single crystals on liquid Ga by the chemical vapor deposition approach. With the introduction of oxygen into the growth process, large-area hexagonal α-GaO crystals with a uniform size distribution have been produced. At high temperature, fast diffusion of oxygen atoms onto the liquid surface facilitates reaction with Ga and thus leads to formation of 2D ultrathin crystals. By precisely controlling the amount of oxygen, the vertical growth of the GaO single crystal has been realized. Furthermore, phase engineering can be achieved and thus 2D β-GaO crystals were also prepared by precisely tuning the growth temperature. The controlled growth of 2D GaO crystals offers an applicable avenue for fabrication of other 2D metal oxides and can further open up possibilities for future electronics.