Fig. 1

Hexagonal boron nitride (h-BN) crystals Raman and microstructural characterizations. a Raman spectra of the E_2g mode, obtained using 532 nm excitation, of the 99% ¹⁰B (monoisotopic ¹⁰B), 48% ¹¹B (isotopically disordered), 78% ¹¹B (near-natural), and 99% ¹¹B (monoisotopic ¹¹B) h-BN samples at room temperature. b Selected area electron diffraction (SAED) image, showing a hexagonal diffraction pattern consistent with diffraction into (hki0) reflections and a [0001] surface normal of the specimen. c Scanning electron microscopy (SEM) micrograph, steps are marked with yellow arrows; scale bar, 100 μm. d, e Electron back-scattered diffraction (EBSD) color map obtained by scanning a selected (60 µm × 90 µm) area with 1 µm step size: d inverse pole figure, illustrating the top surface of the sample being the (0001) plane of the hexagonal structure of h-BN. e Orientation deviation mapping, showing misorientation (tilt) up to ~ 2° between grains; scale bar is 30 μm. f Bright-field and g dark-field transmission electron microscopy (TEM) images under two beam diffracting conditions with \(g = 11\bar 20\), in-plane (near-screw) dislocations were observed (indicated by purple arrows) in (f), which dissociated into closely spaced partial dislocations (indicated by yellow arrows) in (g); scale bar is 1 μm. h Bright-field TEM image, sub-grain boundary, visible as fringes indicated by purple arrows; scale bar is 1 μm. Note that using TEM, the crystal was found to have areas a few tens of microns across which were free of defects. Images (f–h) were taken at selected area of h-BN where defects were observed