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小木虫论坛-学术科研互动平台 » 材料区 » 微米和纳米 » 前沿热点 » 纳米材料研究动态系列报道专栏
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wshk1980

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[交流] 纳米材料研究动态系列报道专栏

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美化学家发现金纳米棒自发地将自己组装成一种环状超结构
Science Daily — Rice University chemists have discovered that tiny building blocks known as gold nanorods spontaneously assemble themselves into ring-like superstructures.
链接：http://www.SciEI.com/news/science/Chemistry/Index.html
This finding, which will be published the chemistry journal Angewandte Chemie, could potentially lead to the development of novel nanodevices like highly sensitive optical sensors, superlenses, and even invisible objects for use in the military.

“Finding new ways to assemble nano-objects into superstructures is an important task because at the nanoscale, the properties of those objects depend on the arrangement of individual building blocks,” said principal investigator Eugene Zubarev, the Norman Hackerman-Welch Young Investigator and assistant professor of chemistry at Rice.

Although ring-like assemblies have been observed in spherical nanoparticles and other symmetrical molecules, until now such structures had not been documented with rod-shaped nanostructures.

Like many nanoscale objects, gold nanorods are several billionths of a meter, or 1,000 times smaller than a human hair. Zubarev used hybrid nanorods for this research because attached to their surface are thousands of polymer molecules, which are flexible chainlike structures. The central core of the nanorods is an inorganic crystal, but the polymers attached to the outside are organic species. The combination of the inorganic and organic features resulted in a hybrid structure that proved to be critical to the study.

英文全文：http://www.sciencedaily.com/releases/2007/03/070310145606.htm

[ Last edited by popsheng on 2007-4-28 at 18:12 ]
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1楼 2007-03-22 20:49:37
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zhaokelun1975

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Nanoscale 'Coaxial Cables' for Solar Energy Harvesting

Figure 1: A cross-section of a conventional coaxial cableScientists have designed a new type of nanowire – a tiny coaxial cable – that could vastly improve a few key renewable energy technologies, particularly solar cells, and could even impact other cutting-edge, developing technologies, such as quantum computing and nanoelectronics.

The nanowire, developed by researchers from the National Renewable Energy Laboratory (NREL) and Lawrence Berkeley National Laboratory, may solve several problems currently associated with renewable energy applications.

Figure 2: A cross-section of the nanoscale coaxial cable, in which nitrogen, phosphorus, and gallium atoms are shown in blue, yellow, and magenta, respectively. White spheres represent hydrogen atoms, which help render the surface of the wire chemically non-reactive.One overarching problem is that current semiconducting materials with the potential for use in renewable energy devices lack one key characteristic. When electrons in these materials are excited by light and jump to higher energy levels (leaving vacancies, known as “holes,” in the lower levels), both the electrons and the holes typically move around in the same region. Thus, they tend to recombine. This is desirable for certain applications, such as light-emitting devices, where electron-hole recombination produces light, but is not ideal for renewable energy devices. A better scenario is the separation of the excited electrons from the holes such that, in the case of solar cells, for example, the electrons can be drawn off and used for electricity.
“Our nanowires were designed to provide this feature, along with a superior electrical conductivity,” said NREL materials scientist Yong Zhang, the study's corresponding researcher, to PhysOrg.com. “Both of these properties are critical in order for renewable energy devices to reach their ultimate efficiency limits.”
Conventional coaxial cables consist of a central copper wire symmetrically surrounded by a braided copper conductor, with an insulating spacer material between the two. The braid serves as a return route for electrons that have already passed down the core wire; it can equally be viewed as a channel for holes moving in the opposite direction. The insulator separates the charge passing through the wire and braid.
Mimicking this structure, the group designed a nanoscale version consisting of a central wire, the “core,” surrounded by a shell (the shell is not cylindrical like conventional cables, but rather is hexagonal). The researchers used two semiconducting materials: gallium nitride (GaN) and gallium phosphide (GaP). They made two samples, one with a GaN core and GaP shell, and another with a GaP core and GaN shell. Both wires are approximately four nanometers in diameter (according to Zhang, this particular size was chosen by considering the computational effort needed to analyze the wires' properties, because larger wires, while easier to make, require considerably more computing power and time to model. Similar success, he says, could be achieved with nanowires up to 10-15 nanometers in diameter). In neither sample is an insulating spacer required. This phenomenon is the result of the specific semiconducting behaviors of GaN and GaP.

GaN and GaP, like all semiconductors, are classified by “band gap” – how much energy is required for electrons in the material to jump from the top of the “valence band,” a range of energies for which they don't participate in conduction, to the bottom of the “conduction band,” a range for which they do participate. When GaN and GaP are combined into a wire, the structure as a whole assumes its own band gap, which is very different from that of either component but much more appropriate for solar energy applications.

Besides providing efficient charge separation, the design may be able to remedy several shortcomings of solar-energy applications. For example, they could help widen the coverage of the solar spectrum and minimize energy loss associated with electron-hole recombination.

“We can tailor the properties of these cables to address the specific problems associated with each application,” said Zhang. “Beyond renewable energy applications, they could have exciting uses ranging from quantum computing to nanoelectronics.”

This research is described in detail in the April 5, 2007, online edition of Nano Letters.

Citation: Yong Zhang, Lin-Wang Wang, and Angelo Mascarenhas, “'Quantum Coaxial Cables' for Solar Energy Harvesting.” Nano Lett. ASAP Article, DOI: 10.1021/nl070066t

Copyright 2007 PhysOrg.com.
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12楼2007-04-28 17:48:16
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wshk1980

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Aberration-Corrected Imaging of Active Sites on Industrial Catalyst
Nanoparticle

Lionel Cervera Gontard, Lan-Yun Chang, Crispin J. D. Hetherington, Angus I. Kirkland,
Dogan Ozkaya, and Rafal E. Dunin-Borkowski

Angew. Chem. Int. Ed. 2007, 46, 1 – 4

http://www3.interscience.wiley.c ... /114199478/PDFSTART
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2楼2007-03-24 14:00:24
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wshk1980

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评价一下啊！！！！！！！！！！！！！
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3楼2007-03-29 16:27:40
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zhaokelun1975

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IBM将摩尔定律推进到三维时代


赛迪网2007年4月27日讯    日前，IBM宣布在制造环境中实现了一种突破性的芯片堆叠技术，此举为制造三维芯片扫清了障碍，摩尔定律也将因此而突破原来预期的极限。这种被称为“穿透硅通道（through-silicon vias）”的技术可以大大缩小不同芯片组件之间的距离，从而设计出速度更快、体积更小和能耗更低的系统。

    IBM的这项突破实现了从二维芯片设计到三维芯片堆叠的转变，将传统上并排安装在硅圆片上的芯片和内存设备以堆叠的方式相互叠加在一起，最终实现了一种紧凑的组件层状结构，大大减小了芯片的体积，并提高了数据在芯片上各个功能区之间的传输速度。

    IBM半导体研发中心副总裁Lisa Su表示：“这一突破性的进展是IBM开展十多年探索研究的成果。我们可以将三维芯片从实验室走向制造生产环节，来支持各种各样的应用。”

    这种IBM新方法是依靠新的穿透硅通道技术而非长金属电线来连接目前的二维芯片，这实际上是在硅圆片上蚀刻出来的垂直连接通道，并在其中注满金属。这些通道可以使多个芯片堆叠在一起，同时支持芯片之间更大信息量的传输。

    这项工艺将信息在芯片上传输的距离缩短了1000倍，与二维芯片相比可以增加最多100倍的信息通道或路径。

    IBM已经在自己的生产线上运行使用这种穿透硅通道技术的芯片，并将在2007年下半年开始为客户提供使用这种方法制造的芯片样本，同时在2008年投入生产。这种穿透硅通道技术最早将被用于无线通信芯片领域，这些芯片将被安装在无线LAN和蜂窝应用所使用的功率放大器之中。另外，三维技术也将应用于更广泛的芯片应用领域，包括目前那些运行在IBM高性能服务器和超级计算机中的芯片，这些服务器和超级计算机支持着全球的商业活动、政府和科学研究工作。
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5楼2007-04-28 17:06:23
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