  Chemical vapor deposition synthesis of large domain hexagonal boron nitride
(h-BN) with uniform thickness on Cu foils is of great challenge, originating
from the extremely high nucleation densities and the reverse hydrogen etching
competition reaction. We report herein the successful growth of wafer-scale
high-quality h-BN monolayer film with the largest single crystalline domain
sizes up to 72 micrometer in edge length using a folded Cu enclosure approach.
The highly-confined growth space with this facile and unique approach enables
the drastic decrease of nucleation centers together with the effective
suppression of hydrogen etching reaction. It is revealed, for the first time,
that the orientations of as-grown h-BN monolayers are strongly correlated with
the crystalline facets of growth substrates, with the Cu (111) being the best
substrate for growing high-quality single crystalline h-BN monolayer,
consistent with the density functional theory calculations. The present study
offers a practical pathway for growing high-quality h-BN films and deepens the
fundamental understanding of h-BN growth process.
