Edge controlled growth of hexagonal boron nitride crystals on copper foil by atmospheric pressure chemical vapor deposition

Most of the chemical vapor deposition (CVD) systems used for hexagonal boron nitride (h-BN) growth employ pyrolytic decomposition of a precursor molecule, such as ammonia borane (AB), at a temperature close to its melting point. So the control of its partial pressure is essential for high quality crystal growth. Here, we report on the edge controlled growth of a h-BN single crystal larger than 25 mu m in edge length on purchased Cu foils. The key was the controlled supply of borazine gas generated by the decomposition of AB, and the stepwise decomposition of AB was found to be essential for the growth of regular h-BN crystals. The h-BN growth was mostly governed by the position of the nucleation point rather than Cu orientation as confirmed by electron back-scattered diffraction (EBSD) analysis. It was also demonstrated that the variation in temperature during the growth and cooling processes induced wrinkles larger than 20 nm due to the thermal straining of the Cu surface and a negative expansion coefficient of h-BN. These results provide a detailed understanding of h-BN growth, which will be applicable to other 2D materials.