[en] Fine structures appearing in boron nitride (BN) sample bombarded by N₂⁺ ion (60 keV) were examined by JEM-200 cx high-resolution transmission electron microscopy (HRTEM) at 200 kV accelerating voltage. In the curved region of plate-like h-BN crystal sp² sheets (spacing 0.33 nm), it was observed that the t-BN structure with an average inter planer spacing of 0.35 nm was formed. Although the mechanism of formation of the t-BN structure is unclear, it appears that the discussion based on the viewpoint of beam-solid interaction may be critical in understanding the growth process of the t-BN structures