No abstract

Cutting and folding 2D systems is one of the explored paths to tune physical and chemical properties in atomic thick matter. Contrarily to graphene, boron nitride 1 (BN) nanoribbons are difficult to obtain and their folded structures have not been yet reported. Here we show that pressure application in multiwall boron nitride nanotubes leads to different types of tube internal organizations including BN nanoribbon formation and folds. The new observed tube-structures are associated to the breaking of a number of the internal tubes leading either to non-organized structures in the form of internal tube alveoli or in an organized stacking of folded h-BN nanoribbons. Irreversible changes in the morphology of multiwall BN nanotubes (MWBNNTs) take place from ∼7 GPa and morphologically modified tubes could be observed up to pressures of at least 49 GPa. The here used experimental probes included high resolution transmission microscopy, electron tomography and Raman spectroscopy. Atomistic modelling was also performed showing the formation of pinch structures along the tubes which favour pressure induced bond-breaking and hybridization changes and confirming the folded structure. Both experiments and modelling show that tube polygonization is a prominent characteristic of MWBNNTs even at ambient pressure. Overall, the pressure evolution of MWBNNTs strongly differs from their carbon analogues. The high mechanical stability of BN tube geometry is of interest for composite based structural materials. On the other side, the availability of h-BN nanoribbons and folded structures opens new prospects to produce physically modified BN properties.