(275g) Low-Temperature Synthesis of Molecularly-Capped Nanowires from Liquid Flux of Ions and Nanoparticles[Invited]

This talk will describe two new, simple, scalable, low-temperature (<100 °C) strategies to synthesize nanowires using flux of ions (Bi, Te), or nanoparticles (Au, Ag) in aqueous-solutions. The nanowires are molecularly passivated by either a difunctional coupling agent to the aqueous solution, or a water-immiscible organic phase. The nanowire structure, surface chemistry, and key aspects of the formation mechanisms will be discussed based on electron microscopy, X-ray and electron diffraction, UV- visible spectroscopy, and thermogravimetry analyses. The thermoelectric properties of the Bi2Te3 nanowires will also be briefly described.

First, I will demonstrate a room-temperature method to assemble Au or Ag nanoparticles into nanowire networks by mechanically agitating a biphasic mixture of an aqueous hydrosol containing the nanoparticles, and toluene. The nanowires are passivated with toluene. The diameter of the wires can be adjusted from 5- to 35-nm by controlling the nanoparticle size. We will show that nanowires form by coalescence of the nanoparticles at the toluene-water interface, and the wire morphology is strongly dependent on the type of organic phase used in the biphasic liquid mixture. This approach is attractive for forming micro- and macro-foams of nanowires for possible applications in catalysis or composites.

Second, I will describe the synthesis of 27- to 130-nm-diameter single-crystal nanowires of bismuth telluride with a trigonal crystal structure at ~100 °C. Reduction of orthotelluric acid and bismuth chloride in the presence of thioglycolic acid or L-cysteine results in carboxyl- or amine-terminated nanowires due to thio-ligation of bismuth. High resolution TEM suggest that nanowire growth occurs by atom flux attaching to the growing front of the (101) planes. Dispersed films of nanowires exhibit n-type behavior due to sulfur incorporation, and yield a Seebeck coefficient of -100 µV/K, and a conductivity of 600 m. Preparing such single-crystal nanowires capped with desired functional groups are attractive for redispersing the wires in liquid media for further processing, and assembling on chemically tailored surfaces to realize novel thermoelectric devices.