Today and tomorrow, we're reporting on presentations at an important conference on Productive Nanosystems: Launching the Technology Roadmap. Chris Phoenix is providing live blog coverage for us...
Next talk: "Multifunctional Carbon Nanotube-Based Systems: Linking Synthesis and Function"
David B. Geohegan, Distinguished Research Staff Member, Oak Ridge National Laboratory
Link synthesis to structure; structure to functionality
Goal: Measure nanotube growth; understand macro-scale functionality
Nanotubes have two kinds of property they want to develop: electronic (where they're extremely impressive - up to one milliamp per tube!) and structural (where it's still hard to build high-performance composites).
It's hard to build high-quality tubes in high quantity. And previously, it's been common to synthesize tubes and go directly to building stuff, without characterizing them.
Two ways to synthesize nanotubes: High temperature, which makes high-quality tubes, but also lots of other junk (low purity). Low-temperature synthesis grows tubes on substrates, at high purity, but with defects.
There are fundamental questions, such as: What's the difference between high and low temperature growth? Why can you sometimes grow tubes without catalysts? These questions remain after years of research...
(Why would a curved carbon structure grow above a flat metal surface? Computer study says that a curved carbon flake points the dangling bonds at the edges down into the surface, which is happier.) (In high-temperature synthesis, the tubes don't start to grow until the gas cools some... because the metal clusters that catalyze the growth don't condense until then.) (They found that condensed carbon clusters are consumed by newly condensed particles to grow the tubes.)
No standards of purity exist for carbon nanotubes. They're making single-wall nanotube (SWNT) membranes and measuring their optical properties.
Electric field-induced contrast: an imaging method in an electron microscope that shows how electrons are transported through a nanotube network between electrodes. Very cool! Wish I'd thought of it. Useful to investigate the electrical/electronic properties of nanotubes in polymers.
Then there's another layer of questions involving nanotube-polymer interactions...
There's a long discussion of growing nanotubes in a pulsed-laser reactor. Cool videos of plasma plumes. Lots of observations about the conditions in which various nanotubes grow. "This looks complicated, but it's only about six rate equations."
So, this talk was about studying nanotube growth and properties--for nanotubes grown and/or used in bulk. It's important to understand nanotubes, but this work is not about machines or even electronic circuits built of nanotubes. So I'm not sure that it contributes to our understanding of how to build atomically precise structures that don't happen to be nanotubes. For those interested in nanotubes: In response to a question, he said that he could envision a continuous-flow reactor that grew, centrifuged, cleaned, and sorted the nanotubes into bottles.
Chris Phoenix
Tags: nanotechnology nanotech nano science technology ethics weblog blog
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