222 | Nature | Vol 579 | 12 March 2020
Article
the B 6 N 7 seed to the 0° (or 60°) orientation when docking to the A (or
B) steps (Fig. 3a). In Fig. 3a, b the distance between the Cu step edge
and the B 6 N 7 zigzag edge for each configuration has been determined
by energy minimization (Extended Data Fig. 8). The resulting binding
energy for each configuration changes in a subtle yet very important
way with the presence of Cu step edges (Fig. 3b): the two configurations
NIBII (60°) and NIBIII (0°), which were nearly degenerate when consider-
ing only plane-to-plane epitaxy, are now separated by δE values of
approximately 0.23 eV, this value raising in proportion with the
docking length, rapidly amplifying the Boltzmann selectivity factor
–9.5
–9.0
–8.5
–8.0
–7.5
–7.0
–6.5
Binding energy (eV)
Astep
Bstep
NIIBI NIIIBII NIBIII
NIIIBI NIIBIII NIBII
ab
0°
60°
Top-layer Cu
First-layer Cu
Second-layer Cu
Third-layer Cu
NIIIBI NIIBIII NIBII NIBIII NIIIBII NIIBI
60° 0°
Plane only
Edge-to-step
N
B
Bottom Cu
Fig. 3 | DFT calculations of epitaxy at nucleation, with and without
considering step-edge docking. a, Lowest-energy atomic arrangements for
six B 6 N 7 –Cu (111) configurations, considering the edge docking to two typical
step-edge terminations (A and B) of top-layer Cu (111). b, Calculated binding
energies for the six B 6 N 7 –Cu (111) configurations, with and without including
the edge-to-step epitaxy effect. The bottom image is a three-dimensional view
of the NIBII–Cu (111) configuration.
hBN
Two-inch hBN/Cu/sapphire
Two-inch hBN lm
Four-inch SiO 2 /Si
ab c
hBN
2cm
TRT/PMMA/hBN
Fig. 4 | Schematic and photographs illustrating the wafer-scale hBN transfer
processes. a, As-grown two-inch hBN film on a Cu (111)/sapphire wafer. Top,
schematic; bottom, photograph. b, Electrochemical delamination, using an
aqueous solution of NaOH (1 M) as the electrolyte, the Cu layer in the TRT/
PMMA/ hBN/Cu (111)/sapphire stack as the cathode, and a platinum (Pt) foil as
the anode, with an applied DC voltage of 4 V. During this process, the TRT/
PMMA/hBN stacked film is detached from the Cu (111)/sapphire through the
generation of hydrogen bubbles at the hBN/Cu interface. PMMA, poly(methyl
methacrylate); TRT, thermal release tape. c, Two-inch monolayer hBN film
transferred onto a four-inch SiO 2 / S i w a fe r.