Alloy nanowires: Invar inside carbon nanotubes

Invar (Fe65Ni35), a ‘zero’ thermal expansion alloy consisting of Fe and Ni, has been successfully introduced into carbon nanotubes by pyrolysing, at 800 °C, aerosols of NiCp2/FeCp2 mixtures dissolved in C6H6; scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) studies reveal the presence of flake-like structures (ca. 1–2 mm2) consisting of filled/aligned carbon nanotubes (⩽200 μm in length and ⩽80 nm in diameter) in a carpet pile-like configuration; analysis of the filling material (⩽500 nm in length and ⩽40 nm in diameter) by X-ray powder diffraction and high-resolution electron energy loss spectroscopy (HREELS) line scans, confirmed that Invar was formed; this appears, to the best of our knowledge, to be the first report of mixed metal alloy nanowires forming inside carbon nanotubes.