Alumina nanowire arrays standing on the surface of a porous anodic alumina membrane have been achieved by first forming a porous anodic alumina membrane with parallel Y-branched nanochannels by reducing the applied anodizing voltage by a factor of 1/ √ 2 in the anodization process of high-purity Al foil, and then chemically etching the Y-branched nanochannel alumina membrane in an aqueous phosphoric acid solution. The novel nanostructures may be used for two-dimensional photonic bandgap structural materials.
We present simple, self-assembled, and robust fabrication of ultrahigh density cobalt nanowire arrays. The binary Co-Al and Co-Si systems phase-separate during physical vapor deposition, resulting in Co nanowire arrays with average diameter as small as 4.9 nm and nanowire density on the order of 10(16)/m(2). The nanowire diameters were controlled by moderating the surface diffusivity, which affected the lateral diffusion lengths. High resolution transmission electron microscopy reveals that the Co nanowires formed in the face-centered cubic structure. Elemental mapping showed that in both systems the nanowires consisted of Co with undetectable Al or Si and that the matrix consisted of Al with no distinguishable Co in the Co-Al system and a mixture of Si and Co in the Co-Si system. Magnetic measurements clearly indicate anisotropic behavior consistent with shape anisotropy. The dynamics of nanowire growth, simulated using an Ising model, is consistent with the experimental phase and geometry of the nanowires.
Development of a rational synthetic method of flexible nanomaterials may enable exciting avenues in both fundamental research and novel device applications. In this paper, flexible boron nanowires have been successfully synthesized on both Si (111) and scanning tunneling microscope (STM) tungsten (W) tips via thermoreduction of boronoxygen compounds with active metal (magnesium). These as-prepared nanowires, which are structurally uniform and single crystalline, represent good semiconductor at high temperature. Electrical conductivity of these intrinsic nanowires can be improved two orders by introducing doping atoms. Tensile stress measurements demonstrate excellent mechanical property of as-synthesized boron nanowires as well as resistance to mechanical fracture even under a strain of 3%. Importantly, simultaneous electrical measurement reveals that the corresponding electrical conductance is very robust and remains constant under mechanical strain. Our results can be briefly explained by Mott's variable range hopping (VRH) model. A stable field emission current was also observed from a single boron nanowire. Boron nanostructures with excellent controllability, remarkable mechanical flexibility and field emission characteristics represent promising candidates for flexible nanoelectronic circuits as well as electron emission nanodevices.
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