Extended Data Fig. 5 | Comparison of a-BN and nc-BN f ilms. a, Structure of
nc-BN film deposited at 700 °C. b, Low-magnification TEM images of nc-BN.
The selected-area electron diffraction pattern in the inset shows a typical
polycrystalline ring pattern. c, High-resolution TEM images of nc-BN, clearly
showing small crystallites of hBN. The cross-sectional TEM image in the inset
indicates a layered structure. d, Magnification of the area indicated by the blue
box in c. e, Fast Fourier transform image showing the hexagonal superstructure
of multilayer hBN. f, g, XPS profiles of the B 1s (f) and N 1s (g) peaks observed in
3-nm-thick a-BN and nc-BN samples. h, Raman spectra of a-BN, nc-BN and
epitaxially grown trilayer hBN (tri-hBN; 1.2 nm thick; used as reference) samples
transferred onto SiO 2 /Si substrates. i, FTIR spectra for a-BN (red) and nc-BN
(blue) measured using s-polarized radiation at an incident angle of 60°.
The E1u longitudinal optical (LO) mode is related to the amorphous phase of BN;
see ref.^19.