Spontaneous growth and phase transformation of highly conductive nickel germanide nanowires.
ABSTRACT We report the synthesis, phase transformation, and electrical property measurement of single-crystal NiGe and ε-Ni(5)Ge(3) nanowires (NWs). NiGe NWs were spontaneously synthesized by chemical vapor deposition of GeH(4) onto a porous Ni substrate without the use of intentional catalysts. The as-grown NWs of the orthorhombic NiGe phase were transformed to the hexagonal ε-Ni(5)Ge(3) phase by thermal annealing induced Ni enrichment. This controllable conversion of germanide phases is desirable for phase-dependent property study and applications, and the observation of novel metastable ε-Ni(5)Ge(3) phase suggests the importance of kinetic factors in such nanophase transformations. Electrical studies reveal that NiGe NWs are highly conductive, with an average resistivity of 35 ± 15 μΩ·cm, while the resistivity of ε-Ni(5)Ge(3) NWs is more than 4 times that of the NiGe phase. NWs of nickel germanides, particularly NiGe, would be useful building blocks for germanium-based nanoelectronic devices.
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ABSTRACT: Hierarchical nanostructures of lead sulfide nanowires resembling pine trees were synthesized by chemical vapor deposition. Structural characterization revealed a screwlike dislocation in the nanowire trunks with helically rotating epitaxial branch nanowires. It is suggested that the screw component of an axial dislocation provides the self-perpetuating steps to enable one-dimensional crystal growth, in contrast to mechanisms that require metal catalysts. The rotating trunks and branches are the consequence of the Eshelby twist of screw dislocations with a dislocation Burgers vector along the 110 directions having an estimated magnitude of 6 +/- 2 angstroms for the screw component. The results confirm the Eshelby theory of dislocations, and the proposed nanowire growth mechanism could be general to many materials.Science 06/2008; 320(5879):1060-3. · 31.20 Impact Factor