In situ observation of reversible rippling in multi-walled boron nitride nanotubes

Abstract

The recent observation of high flexibility in buckled boron nitride nanotubes (BNNTs)contradicts the pre-existing belief about BN nanotube brittleness due to the partially ioniccharacter of bonding between the B and N atoms. However, the underlying mechanismsand relationships within the nanotube remained unexplored. This study reports for the firsttime the buckling mechanism in multi-walled BNNTs upon severe mechanical deformation.Individual BNNTs were deformed inside a transmission electron microscope (TEM)equipped with an in situ atomic force microscopy holder. High-resolution TEM imagesrevealed that bent BNNTs form multiple rippling upon buckling. The criticalstrain to form the first ripple was measured as 4.1% and the buckling processwas reversible up to 26% strain. As opposed to carbon nanotubes, the BNNTsbuckled into V-shaped ripples rather than smooth wavy shapes. The ripplingwavelength was quantified in terms of the outer diameter and thickness of thenanotubes. The BNNTs showed a larger rippling wavelength compared to thatof CNTs with the same number of walls. This difference was explained by thetendency of BN structures to reduce the number of thermodynamically unfavorableB–B and N–N bonds at the sharp corners in the rippling regions. The BNNTs’structure also exhibited a higher fracture strain compared to their counterpart.