quantum wires

[dpeilow]

"The electrical conductivity of QW is higher than that of copper at one-sixth the weight, and QW is twice as strong as steel. A grid made up of such transmission wires would have no line losses or resistance, because the electrons would be forced lengthwise through the tube and could not escape out at other angles."

However, in 2006 it was "estimated that at least 5 years will be needed"...

A room temperature superconductor?

 

[Norbert]

A room temperature superconductor?

Good question. It does sound like it would have a similar effect, on the other hand, if that were really the case, I would expect this to be expressed more directly.

 

[doug]

"The electrical conductivity of QW is higher than that of copper at one-sixth the weight, and QW is twice as strong as steel. A grid made up of such transmission wires would have no line losses or resistance, because the electrons would be forced lengthwise through the tube and could not escape out at other angles."

What the heck? Who wrote that? It's kinda of embarrassing coming from Argonne.

 

[doug]

Good question. It does sound like it would have a similar effect, on the other hand, if that were really the case, I would expect this to be expressed more directly.

I can guess that the author is referring to superconducting carbon nanotubes. There was some indirect evidence a while back that they might exhibit room temperature superconductivity (via the Meissner effect and some other stuff I won't go into). Last time I worked on them though, direct superconductivity could only be found around 10 Kelvin or so.

Anyhow, I'm just annoyed that the author clearly doesn't know what she's talking about. In that quote she's confusing superconductivity with quantum confinement, and making broad statements about 1-D systems in general that are inaccurate. They should have had someone qualified go over it.

 

[Norbert]

I can guess that the author is referring to superconducting carbon nanotubes. There was some indirect evidence a while back that they might exhibit room temperature superconductivity (via the Meissner effect and some other stuff I won't go into). Last time I worked on them though, direct superconductivity could only be found around 10 Kelvin or so.

Anyhow, I'm just annoyed that the author clearly doesn't know what she's talking about. In that quote she's confusing superconductivity with quantum confinement, and making broad statements about 1-D systems in general that are inaccurate. They should have had someone qualified go over it.

After reading it several times, I already got the impression it might have been mixing nanotech with superconductivity (about which is written more further down in the same chapter). Might even be simply some kind of copy & paste error. Would you know enough about this topic to tell whether the factor of six, compared to copper, could be correct?

 

[Norbert]

Maybe that sentence also has to do with that the "classical formula" for resistance "is not valid for quantum wires" (Quantum wire - Wikipedia, the free encyclopedia )

This article, "NASA Funds 'Miracle Polymer'", is from 2005, and mentions some of the same information as the Argonne text:

http://www.wired.com/science/space/news/2005/04/67350

"The cable, also known as a quantum wire, would theoretically conduct electricity up to 10 times better than traditional copper wire and weigh one-sixth as much."

Even the information at Rice Universtity (10x Copper Conductivity, 6x lighter) is dated 2003, at the bottom of

The Richard E. Smalley Institute for Nanoscale Science and Technology

--- EDIT ---

It seems Rice University is making progress, this is from 7/29/2009, now at lengths of the order of magnitude of centimeters :

http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=12867&SnID=449111395

In this case, the lines are nanotubes, hollow cylinders of pure carbon. Individually, they're thousands of times smaller than a living cell, but Hauge's new method creates bundles of SWNTs that are sometimes measured in centimeters, and he said the process could eventually yield tubes of unlimited length.

Large-scale production of nanotube threads and cables would be a godsend for engineers in almost every field. They could be used in lightweight, superefficient power-transmission lines for next-generation electrical grids, for example, and in ultra-strong and lightning-resistant versions of carbon-fiber materials found in airplanes. Hauge said the SWNT bundles may also prove useful in batteries, fuel cells and microelectronics.

 

[doug]

Yes, so to me, QW stands for "quantum well" but it can also mean "quantum wire", which is just an electronic system with a 1 dimensional density of states. Thing is you can make them any number of ways. I made them out of silicon back in high school, and silicon quantum wires are neither strong as steel nor superconducting. Quantum wire is a general term and doesn't just refer to carbon nanotubes (CNT).

So with appropriate doping, CNTs can be insulating, semiconducting, or metallic. Yes "10x Copper Conductivity, 6x lighter" is possible. (Smalley was actually a collaborator before he sadly passed away.) The issue has always been manufacturing. It's hard to make them long enough to be useful.

Anyhow, my problem with that quote from the Argonne paper (which I didn't read, so perhaps it's out of context) is that it simplifies things to the point of being inaccurate.
"...electrons would be forced lengthwise through the tube and could not escape out at other angles" is a cringe inducing over simplified statement of 1-D quantum confinement which is a separate issue from the formation of Cooper pairs (required for superconductivity) which is implied by the statement "no line losses or resistance."

 

[edo]

I think it isn't really a super conductor. A superconductor would be infinitely conductive, not just 10x. Quantum wires can have extremely high conductivities, if the coupling losses don't get in the way.

I think I've seen somewhere that graphine produces a 2D quantum confinement on it's surfaces; so nanotubes, being a tube of graphine, can act like quantum wire.

 

[doug]

I think it isn't really a super conductor. A superconductor would be infinitely conductive, not just 10x. Quantum wires can have extremely high conductivities, if the coupling losses don't get in the way.

I think I've seen somewhere that graphine produces a 2D quantum confinement on it's surfaces; so nanotubes, being a tube of graphine, can act like quantum wire.

This is all correct. As I pointed out above, a CNT is just an example of a quantum wire. A quantum wire doesn't even have to be a conductor.

I didn't mean to sound so negative. (My issue was with the wording of that Argonne quote. I have to assume the author is not a scientist.) Carbon nanotubes provide a lot of interesting physics for those who study solid state. The fact that they can be superconducting (perhaps even above room temperature) is exciting stuff. But it's still very much "in the lab" as they say.

 

[Norbert]

It seems Rice University is making progress, this is from 7/29/2009, now at lengths of the order of magnitude of centimeters :

Rice University | News & Media

Since this thread is now in the "Off Topic" category, I might as well add a direct link to this article, which has two beautiful photos of growing SWNTs (single-walled carbon nanotubes), and a graphic illustrating how it works:

http://www.springerlink.com/content/k3171447366x7101/?p=ef1000b71add4582b65ed4ebc3ae7e5c&pi=1

And a different one:

http://ceramics.org/ceramictechtoday/tag/robert-hauge/

 

[Norbert]

It seems Rice University is making progress, this is from 7/29/2009, now at lengths of the order of magnitude of centimeters

And now, as of this month, at "hundreds of meters" :

The Rice group has used acid processing methods to assemble carbon nanotubes into fibers 50 micrometers thick and hundreds of meters long. "There are no limitations on the fiber length," says Pasquali. The Rice group demonstrated its assembly method with high-quality, single-walled carbon nanotubes.

However, one remaining miracle is necessary:

One important hurdle for large-scale manufacturing of carbon nanotubes remains: Today, there aren't any good methods for making the nanotubes themselves in large, pure batches. In order to make nanotube transmission lines, for example, the Rice group would need to start with a large batch of nanotubes containing all metallic nanotubes and no semiconducting ones. Last month, chemists at the Honda Research Institute published a paper in Science describing a method for making large amounts of metallic nanotubes that Pasquali says is promising. "For transmission lines you need to make tons, and there are no methods now to do that," he says. "We are one miracle away."

Technology Review: Making Carbon Nanotubes into Long Fibers

 

[johnr]

One important hurdle for large-scale manufacturing of carbon nanotubes remains: Today, there aren't any good methods for making the nanotubes themselves in large, pure batches.

Star Trek-like Replicator? Electron Beam Device Makes Metal Parts, One Layer At A Time

I wonder if this electron beam technique would be up to the task. It sounds like it's capable of high precision on the microscopic level at very low cost, and works with most all metals.

 

[Norbert]

Thanks for the link. I wouldn't know, however, I have read somewhere that they think there is good chance this last hurdle might be taken in the near future.

 

[Norbert]

For those interested in anything carbon nanotube:

Technology Review: Complex Integrated Circuits Made of Carbon Nanotubes

BTW, here my idea for separating metallic carbon nanotubes from semiconducting ones: One applies an electrostatic charge so that the metallic ones all move away from each other. That leaves the semiconducting ones in place.

 

[Norbert]

Sounds like progress on (one of) the remaining hurdles, separating the various kinds of nanowires:

http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=14248&SnID=367172411

 

[Norbert]

I'm not to sure what to make of this:

http://www.udri.udayton.edu/News/2010/Pages/FuzzyFiber.aspx

I must be missing something, as to me it seems to either overstate the scientific achievement, or otherwise limiting the application to aerospace and expecting to create only 70 high-tech jobs doesn't make any sense to me.

 

[Norbert]

Another (possible) step towards being able to select the type of nanotube to grow (hopefully highly conductive, low weight, nanowires):

http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=15147&SnID=1242125265

It may be worth chemists' efforts to look more closely at the energy between the catalyst and carbon structure. "This has some promise," he said. "If you can tweak this preference, if you can change energy from the catalyst side, you change the preference of the chirality. And then you can tell these self-assembling carbons, 'Please dance this way; don't dance that way.'"

 

[Norbert]

Some progress on producing metallic nanowires:

Pure Nanotubes by the Kilo - Technology Review

An improved process for making large amounts of pure metallic carbon nanotubes could hold the key to overhauling the electrical power grid with more efficient transmission lines.

Researchers at Rice University plan to generate a large quantity of this material by the end of summer. They'll use these nanotubes to make long and highly conductive fibers that could be woven into more efficient electrical transmission lines.

Some express caution:

Aaron Franklin, a researcher at IBM's Watson Research Center, says the new study probably doesn't "reveal the golden ticket for achieving high volumes of metallic-only tubes." The amplification process is still not producing very large quantities of the material, Franklin notes.

Alternative methods being developed:

While the Rice group continues to work on amplification, other researchers are exploring alternative ways of making pure nanotubes in quantity. Mark Hersam, a professor of chemistry at Northwestern University, developed what is now one of the most commonly used separation methods. He founded a company called NanoIntegris to sell pure nanotubes. He says ramping up production "is now essentially an industrial optimization exercise."

 

[Norbert]

It's real!

Nanotube Cables Hit a Milestone: As Good as Copper - Technology Review

For the first time, researchers have made carbon-nanotube electrical cables that can carry as much current as copper wires. These nanotube cables could help carry more renewable power farther in the electrical grid, provide lightweight wiring for more-fuel-efficient vehicles and planes, and make connections in low-power computer chips. Researchers at Rice University have now demonstrated carbon-nanotube cables in a practical system and are designing a manufacturing line for commercial production.

They carry about 100,000 amps of current per square centimeter of material, about the same amount as copper wires, but weigh one-sixth as much. They outperform copper on a metric called current density, which means they should be able to carry more electricity over longer distances without losing energy to heat—a problem with today's electrical grid, and with computer chips. And because they're made of carbon, not metal, they don't corrode.

"It is a testament to how mature these materials are becoming that they are able to measure conductivities that now exceed common metals," says Michael Strano, a professor of chemical engineering at MIT who was not involved with the work. Surpassing metals, he says, "represents a milestone."

"This is very exciting, especially considering the enormous importance of decreasing the weight of [electrical] cables in airplanes and cars" to improve fuel efficiency, says Ray Baughman, director of the NanoTech Institute and professor of chemistry at the University of Texas at Dallas. Baughman was not involved with the work.

 

[Norbert]

Rice University | News & Media