Spontaneous growth and phase transformation of highly conductive nickel germanide nanowires

We report the synthesis, phase transformation, and electrical property measurement of single-crystal NiGe and ℰ-Ni₅Ge₃ nanowires (NWs). NiGe NWs were spontaneously synthesized by chemical vapor deposition of GeH₄ 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 ℰ-Ni₅Ge₃ 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 ℰ-Ni ₅Ge₃ 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 μγcm, while the resistivity of ℰ-Ni₅Ge₃ 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.