The surface morphology of the BN films was assessed by scanning electron microscopy (SEM, Gemini). The microscope was operated with conventional and immersion lens (in-lens) secondary electron detectors, and an accelerating voltage of High-resolution TEM (HRTEM) imaging and electron energy loss spectroscopy (EELS) analyses were performed in the double-corrected Linköping FEI Titan 3 60-300, operated at 300 kV. The microscope is equipped with a monochromated X-FEG high-brightness gun, efficient high solid angle Super-X Energy Dispersive X-ray detector and ultrafast Gatan GIF Quantum ERS post-column imaging filter. HRTEM images were recorded under negative spherical aberration imaging (NCSI) conditions with slight positive defocus, both ensuring high-resolution images with bright-atom contrast . EELS spectrum images of 50 x 50 pixels were acquired for 1 min using a 0.25 eV/channel energy dispersion, 0.2 s pixel dwell time and a collection semi-angle of 55 mrad. Elemental B, C and N distribution maps/profiles were extracted from EELS spectrum images by background subtraction, using a power law, and choosing characteristic edges B-K (188-200 eV), C-K (284-310 eV) and (c) N-K (401-430 eV) energy loss integration windows.