Production and Characterization of Single-Crystal FeCo Nanowires Inside Carbon Nanotubes

Abstract

We describe the synthesis of novel monocrystalline FeCo nanowires encapsulated inside multiwalled carbon nanotubes (MWNTs). These FeCo nanowires exhibit homogeneous Fe and Co concentrations and do not contain an external oxide layer due to the presence of insulating nanotube layers. The method involves the aerosol thermolysis of toluene-ferrocene-cobaltocene solutions in inert atmospheres. The materials have been carefully characterized using state-of-the-art high-resolution transmission electron microscopy (HRTEM), electron-energy-loss spectroscopy (EELS), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), electron diffraction, HREELS-STM elemental mapping, X-ray powder diffraction, and SQUID magnetometry. We noted that the formation of FeCo alloys occurs at relatively low pyrolytic temperatures (e.g., 650-750 degrees C). These single-crystal nanowires, which have not been reported hitherto, always exhibit the FeCo (110) plane parallel to the carbon nanotube axis. The FeCo nanomaterials have shown large coercive fields at room temperature (e.g., 900 Oe). We envisage that these aligned ferromagnetic nanowires could be used in the fabrication of high-density magnetic storage devices and magnetic composites.

Heterojunctions between metals and carbon nanotubes as ultimate nanocontacts

“…Specimens of Fe-, Co-, Ni-and FeCo-filled MWNTs were synthesized (18,19) as described in the materials and methods section below. Electron irradiation experiments were carried out in an electron microscope by focusing an electron beam with a diameter in the range 2-20 nm, resulting in current densities of 10 3 Ϫ 10 5 A/cm 2 , onto metal-filled nanotubes.…”

“…Metal-filled MWNTs were synthesized by aerosol pyrolysis (18,19). For producing Fe-, Co-, Ni-and FeCo-filled MWNTs, solutions (3 wt % solute-tosolvent) of ferrocene, Co acetylacetonate II, nickelocene, or a mixture of ferrocene and cobaltocene dissolved in toluene or ethanol were used, respectively.…”

Encapsulation, Compensation, and Substitution of Catalyst Particles during Continuous Growth of Carbon Nanotubes

“…[11,16,17] As carbon nanotubes are capable of drawing materials inside, [3][4][5][6][7] we have explored this basic idea to track the distribution of catalyst particles by sequentially feeding two different catalyst sources (e.g. Ni and Fe).…”

“…[2] Metal particles enclosed inside CNTs were frequently observed in samples made by CVD methods, [3,4] and nanowires with various compositions (Fe, Fe-Ni and Fe-Co alloy) have been made by choosing and combining catalyst sources, with hollow CNTs as templates. [5][6][7] Continuous feeding of carbon source and catalyst precursor (e.g. ferrocene dissolved in xylene) is a widely used approach to produce long aligned CNTs with length up to millimeter scale.…”

Fabrication of Ion-Induced Carbon Nanocomposite Fibres and their Application to Magnetic Force Microscope Probes

“…Thus, the synthesis of CNTs encapsulating ferromagnetic metals has been attempted by CVD methods (Bao et al, 2002;Leonhardt et al, 2003;Alexandrou et al, 2004;Schneider et al, 2004;Tyagi et al, 2005;Elías et al, 2005). For their synthesis, however, besides the high growth temperatures required, the metals which could be encapsulated in CNTs are mainly limited to the catalyst used for the CNT growth.…”