Fig. 2: Hyperspectral CL and EELS maps and structural analysis of hBN flakes.

a CL spectrum of the hBN flake integrated over the red box, featuring three different emission energies, marked by \({\lambda }_{1}\), \(\,{\lambda }_{2}\), and \({\lambda }_{3}\). The inset depicts an SEM image of the measured hBN flake, which is placed on a holey carbon film by liquid exfoliation. The red area marks the measurement area. b Hyperspectral CL images of the marked area for the three spectral peaks indicated. The purple box shows the position at which the results in Figs. 3 and 4 are acquired. c Low-loss electron energy loss spectra of the flake showing three distinguished phonon peaks. The inset shows the transmission electron microscopy image of the flake. d Scanning EELS images of the inset figure in (c), integrated along the highlighted energy regions E₁, E₂, and E₃, showing the spatial distribution of the phonon resonances. e High-energy EELS measurement of the hBN flake showing peaks at the energies associated with the boron and nitrogen K-edge transitions, but no peak for carbon. The results are obtained from the region shown by a black box in (f) right bottom panel. f (Left) HRTEM image of an hBN flake. The larger image shows the atomic structure of the flake, indicating the presence of some defects in the atomic lattice. The inset shows the Fourier transform of the image. (Right) The transmission electron microscopy image of the measured area and the resulting color-coded image representing the atomic composition of hBN flake on holey carbon. Here, boron and nitride are yellow and green, respectively, while carbon is blue and oxygen is red.