Abstract
The morphological analysis of the end of boron nitride nanotubes (BNNTs) using high-resolution transmission electron microscopy (HR-TEM) can provide valuable insight into the growth mechanism in high temperature pressure (HTP) laser ablation where the best quality of BNNT materials can be obtained so far. Two growth modes of BNNT coexisting during the synthesis process have been proposed based on HR-TEM observation and length analysis. One is the root growth mode, in which boron nitride (BN) species formed via the surface interaction between surrounding N2 molecules and boron nanodroplets incorporate into the tubular structure. Another mode called open-end growth mode means the prolongation of tube growth from the exposed BN edge surrounding the surface of boron nanodroplets which is constructed by the heterogeneous nucleation of absorbed BN radicals from the gas plume. The statistical data, the proportions of end structures and the length of BNNTs, could be fitted to two growth modes, and the open-end growth mode is found to be especially effective in producing longer nanotubes with a higher growth rate. The scientific understanding of the growth mechanism is believed to provide the control for optimized production of BNNTs.
Highlights
The morphological analysis of the end of boron nitride nanotubes (BNNTs) using high-resolution transmission electron microscopy (HR-TEM) can provide valuable insight into the growth mechanism in high temperature pressure (HTP) laser ablation where the best quality of BNNT materials can be obtained so far
In the root growth mechanism, BN radicals created from the dissociation of nitrogen molecules in the subsurface of condensed boron nanodroplets contribute substantially to the formation of BNNTs at the interface between the BN cap and the boron nanodroplets
The difference in measured proportions of end structures of BNNTs collected at different positions in the vertical gas plume suggests that the open-end growth occurs only in the area close to the boron ball’s surface, approximately 1 cm above, whereas root growth can be sustained at higher positions
Summary
The morphological analysis of the end of boron nitride nanotubes (BNNTs) using high-resolution transmission electron microscopy (HR-TEM) can provide valuable insight into the growth mechanism in high temperature pressure (HTP) laser ablation where the best quality of BNNT materials can be obtained so far. The www.nature.com/scientificreports dynamics of nitrogen atoms and the formation of a tubular structure from a BN cap on the surface of boron droplets was demonstrated in a way that genuinely supported the root growth mechanism.
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