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Researchers measure carbon nanotube interaction

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K!~_bY [b]【纳米科技世界快讯】Carbon nanotubes have been employed for a variety of uses including composite materials, biosensors, nano-electronic circuits and membranes.
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;_'d&RQ!\N_I4Gr-d [i]An artist's representation of an amine functional group attached to an AFM tip approaching a carbon nanotube surface in toluene solution. Translucent blue shape on the nanotube represents the polarization charge forming on the nanotube as the result of the interaction with the approaching molecule. Chemical force microscopy measures the tiny forces generated by this single functional group interaction. (Illustration by Scott Dougherty, LLNL)[/i]
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Fn V~'?*K While they have proven useful for these purposes, no one really knows much about what’s going on at the molecular level. For example, how do nanotubes and chemical functional groups interact with each other on the atomic scale? Answering this question could lead to improvements in future nano devices. 3h$`$P9h yZ'^*SuG1?
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In a quest to find the answer, researchers for the first time have been able to measure a specific interaction for a single functional group with carbon nanotubes using chemical force microscopy – a nanoscale technique that measures interaction forces using tiny spring-like sensors. Functional groups are the smallest specific group of atoms within a molecule that determine the characteristic chemical reactions of that molecule.i#X/m g
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0i)s7@JnGof A recent report by a team of Lawrence Livermore National Laboratory researchers and colleagues found that the interaction strength does not follow conventional trends of increasing polarity or repelling water. Instead, it depends on the intricate electronic interactions between the nanotube and the functional group.'MfX@Z4}c5R9W&S
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“This work pushes chemical force microscopy into a new territory,” said Aleksandr Noy, lead author of the paper that appears in the Oct. 14 online issue of the journal, [i][b]Nature Nanotechnology.[/b][/i]a;V s{-q"j6iL1A

9[3~%Uf p,b Understanding the interactions between carbon nanotubes (CNTs) and individual chemical functional groups is necessary for the engineering of future generations of sensors and nano devices that will rely on single-molecule coupling between components. Carbon nanotubes are extremely small, which makes it particularly difficult to measure the adhesion force of an individual molecule at the carbon nanotube surface. In the past, researchers had to rely on modeling, indirect measurements and large microscale tests.
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But the Livermore team went a step further and smaller to get a more exact measurement. The scientists were able to achieve a true single function group interaction by reducing the probe-nanotube contact area to about 1.3 nanometers (one million nanometers equals one millimeter).&?5Z({O!h2o^ F4y8{
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Adhesion force graphs showed that the interaction forces vary significantly from one functionality to the next. To understand these measurements, researchers collaborated with a team of computational chemists who performed ab initio simulations of the interactions of functional groups with the sidewall of a zig-zag carbon nanotube. Calculations showed that there was a strong dependence of the interaction strength on the electronic structure of the interacting molecule/CNT system. To the researchers delight, the calculated interaction forces provided an exact match to the experimental results.
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*F6Wx4X%~+_W “This is the first time we were able to make a direct comparison between an experimental measurement of an interaction and an ab initio calculation for a real-world materials system,” Noy said. “In the past, there has always been a gap between what we could measure in an experiment and what the computational methods could do. It is exciting to be able to bridge that gap.” L^|q{ztj pg
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This research opens up a new capability for nanoscale materials science. The ability to measure interactions on a single functional group level could eliminate much of the guess work that goes into the design of new nanocomposite materials, nanosensors, or molecular assemblies, which in turn could help in building better and stronger materials, and more sensitive devices and sensors in the future.;[ e&Izc
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Source: Lawrence Livermore National Laboratory
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?'VCY [$e [[i] 本帖最后由 nanoquebec 于 2007-10-17 20:34 编辑 [/i]]

纳米级材料科学研究有了“非常手段”  _
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美科学家找到化学官能团与碳纳米管间相互作用的测定方法  
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   本报华盛顿10月17日电 目前，碳纳米管已用于复合材料、生物传感器和纳米电路等技术领域。然而，在其被多方面应用的同时，人们却并不清楚分子级纳米管最终到底会出现什么样的状况。例如，碳纳米管和化学官能团间如何相互作用。对此问题的解答将帮助人们改进未来的纳米装置。 　　
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h'S[~7lX4M 为寻求问题的答案，美国劳伦斯•利弗莫尔国家实验室的研究小组采用化学力显微镜方法，首次掌握了测定单一官能团和碳纳米管间发生特殊相关作用的能力。化学力显微镜方法是一种利用微小弹簧状传感器测量微小作用力的纳米级技术；官能团为某个分子内最小的特殊原子团，它们决定了该分子化学反应的特性。 　　/Z.J^iS)kl

2G\;U;Q6j 从未来新型传感器和纳米装置工程的发展角度出发，人们必须认识碳纳米管和各个化学官能团相互间的作用。碳纳米管十分微小，这导致人们很难测定单一分子在碳纳米管表面的附着力。过去研究人员只能依赖模型、间接测量和较大微尺度实验。美研究小组新成果让该研究向前迈进了一步：他们将纳米管探针的接触区域减少到1.3纳米，从而能够准确地测定出单一官能团与碳纳米管的附着力，了解它们之间的相互作用。 　　
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在最新发表的报告中，研究人员表示，他们发现碳纳米管和官能团之间的相互作用力并不遵循常规极化增强的趋势，而是依赖于它们两者间复杂的电子相互作用。研究报告主要作者阿勒克森德•诺伊表示，他们的研究工作将化学力显微镜方法引入了新的研究领域。 　　
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新研究为纳米级材料科学研究开创了新局面。测定官能团和碳纳米管间相互作用的能力可帮助人们在今后设计纳米复合材料、纳米传感器或分子组装时，消除人为的猜想，从而制造出更好更强的材料以及更灵敏的装置和传感器。 3F/j-t#Z&T

1r"w+Dva From 科技日报