Abstract
Pristine carbon nanotubes (CNTs) and nickel-filled CNTs (Ni-filled CNTs) were synthesized by chemical vapor deposition using lanthanum nickel alloy (LaNi5) particles as a both catalyst and source for the Ni-filling. Pristine CNTs and Ni-filled CNTs were formed without and with catalyst oxidation of LaNi5 alloy, respectively. Transmission electron microscopy analysis clearly illustrated that the formation of Ni-filling during the growth of CNTs was due to the catalyst oxidation. X-ray diffraction and selected area electron diffraction analysis demonstrated that the encapsulated Ni exists as a single crystal face centered cubic structure. Compared with the pristine CNTs, the first order and second order Raman spectra of Ni-filled CNTs showed a disorder induced D band, an increased ID/IG ratio, and a decreased IG′/IG ratio. The magnetic properties of the Ni-filled CNTs were studied by vibrating sample magnetometer at room temperature. Coercivity value of Ni-filled CNTs reached the maximum at 445.87 Oe, which is significantly larger than that of the bulk Ni at room temperature. The Ni-filling process through the catalyst oxidation is explained using the “surface segregation” mechanism. In addition, we have suggested the possible growth model involved in their formation.
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