Filling boron nitride nanotubes with metals

The authors' endeavors over the last few years with respect to boron nitride (BN) nanotube metal filling are reviewed. Mo clusters of 1-2 nm in size and Fe-Ni Invar alloy (Fe similar to60 at. %; Ni similar to40 at. %) or Co nanorods of 20-70 nm in diameter were embedded into BN nanotube channels via a newly developed two-stage process, in which multi-walled C nanotubes served as templates for the BN multi-walled nanotube synthesis. During cluster filling, low-surface-tension and melting-point Mo oxide first filled a C nanotube through the open tube ends, followed by fragmentation of this filling into discrete clusters via O-2 outflow and C --> BN conversion within tubular shells at high temperature. During nanorod filling, C nanotubes containing Fe-Ni or Co nanoparticles at the tube tips were first synthesized by plasma-assisted chemical vapor deposition on Fe-Ni Invar alloy or Co substrates, respectively, and, then, the nanomaterial was heated to the melting points of the corresponding metals in a flow of B2O3 and N-2 gases. During this second stage, simultaneous filling of nanotubes with a Fe-Ni or Co melt through capillarity and chemical modification of C tubular shells to form BN nanotubes occurred. The synthesized nanocomposites were analyzed by scanning y, elec- and high-resolution transmission electron microscopy diffraction, electron-energy-loss spectroscopy and energy-dispersive X-ray spectroscopy. The nanostructures are presumed to function as 'nanocables' having conducting metallic cores (Fe-Ni, Co, Mo) and insulating nanotubular shields (BN) with the additional benefit of excellent environmental stability.