Studying Edge Defects of Hexagonal Boron Nitride Using High-Resolution Electron Energy Loss Spectroscopy

Studying the phonons of hexagonal boron nitride (h-BN) is important for understanding its thermal, electronic, and imaging applications. Herein, we applied high-resolution electron energy loss spectroscopy (HREELS) to monitor the presence of edge defects in h-BN films. We observed an edge phonon at 90.5 meV with the initial formation of island-like domains on Ru(0001), which subsequently weakens with respect to the bulk phonon as the islands congregate into a film. The presence of a weak edge phonon peak even at full surface coverage of the h-BN film indicates the sensitivity of HREELS in detecting line defects. A shoulder peak at similar to 160 meV assignable to sp(3) bonded modes was attributed to grain boundaries arising from misaligned domains. In addition, the strengths of substrate interaction and the rippling of the h-BN film can be judged from the shift in the phonon energy of the out-of-plane TQ(perpendicular to) mode.