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quantum wires

Discussion in 'Off Topic' started by dpeilow, Oct 15, 2009.

  1. dpeilow

    dpeilow Moderator

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    A room temperature superconductor?
     
  2. Norbert

    Norbert TSLA will win

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    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.
     
  3. doug

    doug Administrator / Head Moderator

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

    doug Administrator / Head Moderator

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    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.
     
  5. Norbert

    Norbert TSLA will win

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    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?
     
  6. Norbert

    Norbert TSLA will win

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    #6 Norbert, Oct 17, 2009
    Last edited: Oct 17, 2009
    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

     
  7. doug

    doug Administrator / Head Moderator

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    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."
     
  8. edo

    edo Member

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    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.
     
  9. doug

    doug Administrator / Head Moderator

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    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.
     
  10. Norbert

    Norbert TSLA will win

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    #10 Norbert, Oct 18, 2009
    Last edited: Oct 18, 2009
    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/
     
  11. Norbert

    Norbert TSLA will win

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

    However, one remaining miracle is necessary:

    Technology Review: Making Carbon Nanotubes into Long Fibers
     
  12. johnr

    johnr Member

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    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.
     
  13. Norbert

    Norbert TSLA will win

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    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.
     
  14. Norbert

    Norbert TSLA will win

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  15. Norbert

    Norbert TSLA will win

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  16. Norbert

    Norbert TSLA will win

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    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.
     
  17. Norbert

    Norbert TSLA will win

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    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

     
  18. Norbert

    Norbert TSLA will win

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    Some progress on producing metallic nanowires:

    Pure Nanotubes by the Kilo - Technology Review

    Some express caution:

    Alternative methods being developed:

     
  19. Norbert

    Norbert TSLA will win

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    #19 Norbert, Sep 20, 2011
    Last edited: Sep 20, 2011
    It's real! :)

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


    fiber_x616.jpg


     

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  20. Norbert

    Norbert TSLA will win

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    #20 Norbert, Sep 20, 2011
    Last edited by a moderator: Mar 13, 2016

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