[show abstract][hide abstract] ABSTRACT: Single-crystalline free-standing hexagonal Fe(1.3)Ge nanowires (NWs) are synthesized for the first time using a chemical vapor transport process without using any catalyst. Interestingly, Fe(1.3)Ge NWs are found to be ferromagnetic at room temperature, while bulk Fe(1.3)Ge has the lower critical temperature of 200 K. We perform first-principles density functional calculations and suggest that the observed strong ferromagnetism is attributed to the reduced distances between Fe atoms, increased number of Fe-Fe bonds, and the enhanced Fe magnetic moments. Both experimental and theoretical studies show that the magnetic moments are enhanced in the NWs, as compared to bulk Fe(1.3)Ge. We also modulate the composition ratio of as-grown iron germanide NWs by adjusting experimental conditions. It is shown that uniaxial strain on the hexagonal plane also enhances the ferromagnetic stability.
Journal of the American Chemical Society 11/2010; · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report fabrication of Heusler alloy Fe(3)Si nanowires by a diffusion-driven crystal structure transformation method from paramagnetic FeSi nanowires. Magnetic measurements of the Fe(3)Si nanowire ensemble show high-temperature ferromagnetic properties with T(c) > 370 K. This methodology is also successfully applied to Co(2)Si nanowires in order to obtain metal-rich nanowires (Co) as another evidence of the structural transformation process. Our newly developed nanowire crystal transformation method would be valuable as a general method to fabricate metal-rich silicide nanowires that are otherwise difficult to synthesize.
[show abstract][hide abstract] ABSTRACT: We report synthesis of vertical Ni3Co nanowires on a c-plane sapphire substrate by chemical vapor transport method. A vapor−solid−solid mechanism was proposed for Ni3Co nanowire growth, which was catalyzed by Ni3Co2 nanoparticle at the tip. As-synthesized vertically aligned single-crystalline Ni3Co nanowires exhibit strongly ferromagnetic properties. Such single-crystalline ferromagnetic alloy nanowires could be important in the application of spintronics such as nonvolatile memory devices. We could also control the composition of the nanowire by adjusting experimental conditions, producing Ni, Ni3Co, and NiCo nanowires.
Chemistry of Materials - CHEM MATER. 01/2010; 22(5).
[show abstract][hide abstract] ABSTRACT: We have successfully synthesized vertically aligned single-crystalline Co5Ge7 NWs on a curved thin graphite layer as well as on a very thin graphite layer. Vertical Co5Ge7 nanobelts are also synthesized on a graphite substrate. The vertical Co5Ge7 nanobelt arrays or Co5Ge7 NW arrays have been selectively grown on a graphite substrate depending on the experimental conditions. As grown Co5Ge7 NW arrays satisfy most requirements for the ideal emitters of FEDs, such as sharp tips, superb electrical conductivity, thermal and chemical stability, and vertical alignment to the substrate. The vertical Co5Ge7 NW arrays showed very efficient FE properties comparable to those of CNTs because of their optimum morphology. The NW emitter arrays on the curved graphite layer could be used for future flexible FEDs. Since the crystal structure of thin HOPG is close to that of graphene layers, our results could be extended to the epitaxial growth of Co5Ge7 NWs and nanobelts on graphene.