Vertically Aligned Single-Crystalline Ferromagnetic Ni3Co Nanowires

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 of 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 N-i, Ni3Co, and NiCo nanowiresclose7

Compositional ordering and stability in nanostructured, bulk thermoelectric alloys.

Thermoelectric materials have many applications in the conversion of thermal energy to electrical power and in solid-state cooling. One route to improving thermoelectric energy conversion efficiency in bulk material is to embed nanoscale inclusions. This report summarize key results from a recently completed LDRD project exploring the science underpinning the formation and stability of nanostructures in bulk thermoelectric and the quantitative relationships between such structures and thermoelectric properties

Electrodeposition and characterization of nano-crystalline antimony telluride thin films

Electrodeposition is a promising low-cost method to fabricate nanostructured thermoelectric thin films such as Sb 2 Te 3 . However, electrodeposition of crystalline Sb 2 Te 3 without the need for additional processing and with good compositional control has presented a challenge. Here we report on the electrodeposition of crystalline Sb 2 Te 3 thin films at room temperature from a tartaric-nitric acid electrolyte using a pulsed, potentiostatic process. The effects of synthesis conditions on the resulting microstructure and compositional homogeneity are investigated using x-ray diffraction, electron diffraction, electron microscopy, and energy dispersive x-ray spectroscopy. The composition of the Sb-Te films was found to be dependent on the interval between pulses, a result that is likely due to the slow kinetics associated with Sb 2 Te 3 formation at the surface. We also observed a change in texture and microstructure with varied applied pulse duration: for short pulse durations a lamellar microstructure with a {000'} texture forms, whereas for longer pulse durations a more equiaxed and randomly oriented microstructure forms. The thermal conductivities of the pulsed electrodeposited films are surprisingly low at less than 2 W/K·m and are found to systematically decrease with reduced pulse time

Black Ge Based on Crystalline/Amorphous Core/Shell Nanoneedle Arrays

Direct growth of black Ge on low-temperature substrates, including plastics and rubber is reported. The material is based on highly dense, crystalline/amorphous core/shell Ge nanoneedle arrays with ultrasharp tips (&#771;4 nm) enabled by the Ni catalyzed vapor-solid-solid growth process. Ge nanoneedle arrays exhibit remarkable optical properties. Specifically, minimal optical reflectance (< 1 %) is observed, even for high angles of incidence (&#771;75??) and for relatively short nanoneedle lengths (&#771;1 ??m). Furthermore, the material exhibits high optical absorption efficiency with an effective band gap of &#771;1 eV. The reported black Ge could potentially have important practical implications for efficient photovoltaic and photodetector applications on nonconventional substrates.close424