In situ observation of reversible rippling in multi-walled boron nitride nanotubes
In situ observation of reversible rippling in multi-walled boron nitride nanotubes
复制标题
多壁氮化硼纳米管中可逆波纹的原位观察
作者：
H. Ghassemi;C. Lee;Y. Yap;R. Yassar
最近观察到的弯曲氮化硼纳米管(BNNTs)具有很高的柔韧性，这与人们先前关于BN纳米管脆性的看法相矛盾，这是由于B原子和N原子之间的部分离子性质造成的。然而，纳米管中的潜在机制和关系仍未被探索。本研究首次报道了多壁BNNTs在严重机械变形时的屈曲机制。单个BNNTs在配备有原位原子力显微镜支架的透射电子显微镜(TEM)中变形。高分辨率的电子显微镜图像显示，弯曲的BNNTs在屈曲时会形成多重波纹。测得形成第一波纹的临界应变为4.1%，屈曲过程在26%应变范围内是可逆的。与碳纳米管不同，BNNTs呈V形波纹，而不是光滑的波浪形。根据纳米管的外径和厚度量化了波纹波长。与具有相同壁数的碳纳米管相比，BNNTs具有更大的波纹波长。这种差异是由于BN结构倾向于减少波纹区尖角处热力学上不利的B-B键和N-N键的数目。BNNTs的结构也表现出比其对应的更高的断裂应变。
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 ionic character of bonding between the B and N atoms. However, the underlying mechanisms and relationships within the nanotube remained unexplored. This study reports for the first time 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 images revealed that bent BNNTs form multiple rippling upon buckling. The critical strain to form the first ripple was measured as 4.1% and the buckling process was reversible up to 26% strain. As opposed to carbon nanotubes, the BNNTs buckled into V-shaped ripples rather than smooth wavy shapes. The rippling wavelength was quantified in terms of the outer diameter and thickness of the nanotubes. The BNNTs showed a larger rippling wavelength compared to that of CNTs with the same number of walls. This difference was explained by the tendency of BN structures to reduce the number of thermodynamically unfavorable B–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.