Synthesis of multiwall boron nitride nanotubes dependent on crystallographic structure of boron

► Structure of B is a key factor for BNNT synthesis for milling-annealing method. ► Amorphous boron is coated on the seed during milling of crystalline boron. ► Amorphous BN nanoclusters are crystallized during annealing. ► Growing of bamboo BNNTs is not to the round head-side but to the tail-side.