For TEM analysis, cross-sectional samples were prepared using a focus ion beam (FIB) lift-out technique, employing a CarlZeiss Cross-Beam 1540 EsB system. The BN thin film polytypes and elemental distribution were explored at the atomic scale using high resolution TEM (HRTEM) imaging and electron energy-loss spectroscopy (EELS) techniques. Characterization was performed using the Linköping double Cs corrected FEI Titan 3 60-300 operated at 300 kV. HRTEM images were recorded under negative spherical aberration imaging (NCSI) conditions with slight positive defocus, both ensuring high-resolution images with bright-atom contrast. Scanning TEM electron energy loss spectroscopy (STEM-EELS) spectrum images of 43x96 pixels were acquired for 1 min using a 0.5eV/channel energy dispersion, 0.2 s pixel dwell time and a collection semi-angle of 55 µrad of the employed Gatan GIF Quantum ERS post-column imaging filter. Elemental B, C, N, and O distribution maps were extracted from EELS spectrum images by background subtraction, using a power law, and choosing characteristic edges B-K (187-216 eV), C-K (285-311 eV), N-K (401-436 eV) and O-K (538-555 eV) energy loss integration windows.