Single-wall nanotubes of boron nitride (BN) are among the most promising quasi-1D materials with outstanding mechanical strength. However, synthesizing them in a controlled and reproducible way remains challenging. Here the authors show a technique of creating BN tubes by cutting bilayer BN sheets with an electron beam and interconnecting the two layers at an open edge. The in situ experiments in an electron microscope show that the spontaneous interlinking of the two layers leads to flattened tubular structures when a narrow ribbon is created. Below a certain width of the ribbon, van der Waals interaction between the layers is overbalanced by the stress in the layer so that the walls separate and a tube with circular diameter forms. The smallest stable BN tubes with a diameter of 0.45 nm, corresponding to a (3,3) tube, can be produced by this technique. The diameter can only be decreased in discrete steps, showing that all possible BN tubes with a given axis alignment relative to the BN lattice can be made. This is a novel top-down approach that allows the authors to create and study a variety of ultrathin nanotubes from related 2D materials.

中文翻译：

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用双层h-BN制成最小的BN纳米管

氮化硼（BN）的单壁纳米管是最有前途的准一维材料，具有出色的机械强度。然而，以受控和可再现的方式合成它们仍然具有挑战性。在这里，作者展示了一种通过用电子束切割双层BN薄板并在开放边缘将两层互连来创建BN管的技术。电子显微镜下的原位实验表明，当形成窄带时，两层的自发交联导致扁平的管状结构。在碳带的某个宽度以下，层之间的范德华相互作用会由于层中的应力而过分平衡，从而使壁分离并形成具有圆形直径的管。直径为0.45 nm的最小稳定BN管，相当于（3,3）管，可以用这种技术生产。直径只能以不连续的步骤减小，这表明可以制造出所有相对于BN晶格具有给定轴对准的BN管。这是一种新颖的自上而下的方法，使作者可以从相关的2D材料创建和研究各种超薄纳米管。