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chl5063木虫 (著名写手)
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Nanowalls contain tiny domains
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The carbon nanowall (CNW) - a promising new form of two-dimensional carbon discovered in 2002 - is made up of tiny nanographite domains, according to new work by researchers in Japan. The result confirms that the material is highly "graphitized", which means that it should have unique physical properties not present in other graphite-based materials. Because of their large surface area, CNWs, discovered in 2002 by Yihong Wu of the National University of Singapore, are good candidate materials for a wide range of applications. These include gas sensors, energy storage devices, catalysts, electrodes for fuel cells and field emission displays. The materials are very thin films about 10–50 nm wide made up of several graphite sheets stacked on top of each other. CNWs differ from other graphite-based materials, such as carbon nanotubes, because they show a higher degree of "graphitization" (or fewer defects) despite the small average size of the graphite regions themselves. This discovery was made by Masaru Tachibana and colleagues at Yokohama City University. To understand this phenomenon, Ken-ichi Kobayashi and colleague of Nissan Arc Ltd, together with Tachibana's group, analysed the nanostructure of CNWs using transmission electron microscopy. By detailed analysis of the electron diffraction patterns and diffraction contrast, they discovered that the material was made up of numerous nanographite domains measuring just 20 nm across on average. According to the team, these domains are the basic units making up the CNWs and are solid evidence that the materials are highly graphitized within these small regions. The researchers believe that the domains originate from the introduction of a few lattice defects in the material, such as dislocations, and the slight rotation of the graphite sheets during their growth or stacking. Kobayashi told nanotechweb.org that being able to control the domain size of a CNW during fabrication could be used to improve its physical properties for various applications. Indeed, the team now plans to study how domain size can be controlled by varying the fabrication conditions in the lab. The researchers reported their work in http://scitation.aip.org/journal ... iss_9/094306_1.html Secondary electron images of the CNWs grown on a quartz substrate as seen in (a) a cross-sectional view and (b) a top view. (Credit: Appl. Phys. Lett.) A schematic diagram of the nanostructure of one CNW film. For simplicity, two amorphous regions are ignored. Small nanographite domains are the constitutional units of the CNW film. Characteristics of the domains include the fluctuation of the [0001] normal direction and the rotation of the ab basal plane of the graphite structure. (Credit: Appl. Phys. Lett.) [ Last edited by chl5063 on 2007-6-1 at 11:51 ] |
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