Extended Data Fig. 6 | Optical micrograph of hBN grown on Cu (111)/
c-sapphire at different temperatures. All as-grown hBN/Cu (111) was slowly
oxidized at 150 °C in air in order to enhance the contrast between hBN and Cu.
Black dashed lines indicate Cu twin grain boundaries. Regions with a red
dashed outline are magnified in lower images. a, hBN grown at 995 °C, with hBN
triangles aligned in the same Cu grain. b, hBN grown at 1,010 °C. Note that the
hBN f lakes grown at 995 °C and 1,010 °C are easily damaged after oxidation at
150 °C in air. c, d, All hBN triangles point in the same direction in the same
Cu (111) grain after growth at 1,025 °C and 1,055 °C, and triangles seem
unchanged after oxidation. e, After growth at high temperature (1,070 °C), all
hBN f lakes align in the same direction, but show different (stretched) shapes.