Hot-Drawing Process Aligns and Toughens Carbon Nanotube Fibers
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As reported in the November 18, 2005, issue of Angewandte Chemie International Edition (p. 7439; DOI: 10.1002/anie. 200501264), J. Lee and N. Kotov from the University of Michigan and A. Govorov
from Ohio University created a reversible nanothermometer built from two types of NPs connected by a polymer that acts as a molecular spring. The superstructure is based upon a layer of poly(ethylene gly-
Metal–Oxide–Metal Heterojunction Nanowires Formed Oxide nanowires are currently being developed and investigated for a variety of nanoelectronics applications because of their unique properties and potential opportunities for “bottom-up” assembly. Going a step further, if metal–oxide–metal (MOM) heterojunctions could be formed, sandwiching a functional oxide between two noble-metal nanowires, they could have distinct advantages over all-oxide nanowires. The synthesis of MOM nanowires using a template-based method has now been reported by J.S. Tresbeck and A.L. Vasiliev of the University of Connecticut and N.P. Padture of the Ohio State University. As reported in the October 2005 issue of the Journal of Materials Research (p. 2613; DOI: 10.1557/jmr.2005.0347), the researchers examined Au-SnO2-Au systems and Au-NiO-Au systems (see Figure 1 for Au-SnO2-Au nanowires). Au-Sn-Au and AuNi-Au nanowires were formed inside anodic aluminum oxide (AAO) templates with 60-nm and 220-nm diameter nanoholes, respectively. First, one side of the template was sealed using 0.5-μm-thick Ag thin film. A small 0.5-μm Ag segment was electroplated within the nanoholes. Au was then electroplated inside the nanoholes. This was followed by Sn or Ni electroplating. Au was then again electroplated on top of the Sn or Ni. The Ag and the AAO template were then dissolved using nitric acid and NaOH, respectively, yielding Au-Sn-Au or Au-Ni-Au nanowires, which were centrifuged and rinsed. These nanowires were subjected to heat treatment to yield Au-SnO2-Au (through oxidation of Sn to SnO and then SnO to SnO2) or Au-NiO-Au nanowires, through oxidation of Ni to NiO. The nanowires were then dispersed in deionized water or ethanol. These MOM nanowires were examined in both a scanning and a transmission electron microscope. The overall length of Au-SnO2-Au nanowires in one case was more than 2 μm. The Au diameter was ~60 nm, and the SnO2 segment was ~60 nm in diamea ter and ~70 nm in length. Grain size in the SnO 2 ranged from 5–10 nm. Similarly, the overall length of a AuNiO-Au nanowire was more than 7 μm, with a Au diameter of ~270 nm, a b NiO diameter of ~300 nm, and ~200 nm length. These dimensions varied for different templates used. The study has demonstrated the feasibility of synthesizing MOM nanowires in the Au-SnO2-Au and the Au-NiO-Au systems. This synthesis method appears to be applicable to a wide variety of metal-oxide combinations. Also, there are several potential unique advantages of this architecture. The dimensions of the functional oxide segment in the nanowires can be controlled by varying the electroplating conditions. The synthesis metho
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