We report the synthesis, structural identification, and electrical properties of the first one-dimensional (1-D) nanomaterials of a semiconducting higher manganese silicide (MnSi(2-x)) with widths down to 10 nm via chemical vapor deposition of the single-source precursor Mn(CO)(5)SiCl(3). The complex Nowotny chimney ladder structure of these homologous higher manganese silicides, also referred to as Mn(n)Si(2n-m), MnSi(1.75), or MnSi(1.8), contributes to the excellent thermoelectric performance of the bulk materials, which would be enhanced by phonon scattering due to 1-D nanoscale geometry. The morphology, structure, and composition of MnSi(2-x) nanowires and nanoribbons are examined using electron microscopy and X-ray spectroscopy. Elaborate select area electron diffraction analysis on single-crystal nanowires reveals the phase to be Mn(19)Si(33), one of a series of crystallographically distinct higher manganese silicides that have a Nowotny chimney ladder structure. Electrical transport study of single nanowires shows that they are degenerately doped with a low resistivity (17 mohms x cm) similar to the bulk.
We report the synthesis, structural characterization, and magnetotransport of single-crystalline nanowires of manganese monosilicide, MnSi. Bulk MnSi has unusual magnetic orderings, helimagnetism, and skyrmions at ambient pressure, and high pressure studies have revealed partial magnetic ordering and non-Fermi liquid behavior. MnSi nanowires were synthesized using chemical vapor deposition of MnCl(2) onto silicon substrates. The morphology, structure, and composition of these nanowires were analyzed using electron microscopy and X-ray spectroscopy. The low-temperature magnetoresistance characteristics of MnSi nanowires reveal the first signature of helimagnetism in one-dimensional nanomaterials.
We report single-crystal nanowires of magnetic semiconducting Fe1-xCoxSi alloys synthesized using a two-component single source precursor approach. Extending our previous syntheses of FeSi and CoSi nanowires from Fe(SiCl3)2(CO)4 and Co(SiCl3)(CO)4 precursors, we found that a homogeneous solution formed upon mixing these two precursors due to melting point suppression. This liquid constitutes the single-source precursor suitable for delivery through chemical vapor deposition, which enables the chemical synthesis of Fe1-xCoxSi alloy nanowires on silicon substrates covered with a thin (1-2 nm) SiO2 layer. Using scanning and transmission electron microscopy and energy dispersive X-ray spectroscopy and mapping, we demonstrate two homogenously mixed alloy nanowire samples with very different Co substitution concentrations (x): 6+/-5%, the ferromagnetic semiconductor regime, and 44+/-5%, the helical magnetic regime. The magnetotransport properties of these alloy nanowires are pronouncedly different from that of the host structures FeSi and CoSi, as well as from one another, and consistent with the physical properties as expected for their corresponding compositions. These novel magnetic semiconducting silicide nanowires will be important building blocks for silicon-based spintronic nanodevices.
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