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1253Re: [nanotech] Y-junction Nanotubes

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  • Bruce Bombere
    Nov 1, 2000
      One thing that occured to me from reading the article was the old
      drum random access memory storage devices where magnetic donuts with
      three wires passing through each, two wires each carrying half charge
      and one sensor wire. This same "donut" arrangement might be contrived
      on a molecular level for random memory storage given the semiconductor
      and metal characteristics of carbon nanotubes.

      Ihsan Hariadi wrote:
      > It is interesting to realize that Carbon Nanotubes could behave
      > as either semiconductor or metal. The article below, among other,
      > reports the possibility of building so-called "Y-junction" Carbon
      > nanotubes to form
      > a Metal-Semiconductor-Metal contact
      > Is there any possibility to dope the Carbon Nanotube semiconductors
      > to form both n-type and and p-type ones, and hence, to realize
      > p-n junction, or more complex devices, ...? Thankyou.
      > << ihsan >>
      > ----------------------------------------------------------
      > From : "Danial Irfachsyad" < d.irfachsyad@... >
      > Date : Thu, 26 Oct 2000 17:40:52 -0000
      > Subject: Nanotechnology: Crossroads in carbon
      > ----------------------------------------------------------
      > Nature 26 Oct 2000:
      > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      > Nanotechnology: Crossroads in carbon
      > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      > Liesbeth Venema
      > The smallest electronic device could be based on just one single
      > molecule. Carbon nanotubes flexible, hollow nanowires with
      > versatile electronic properties have already proven themselves as
      > miniature diodes and transistors. In a paper in Applied Physics
      > Letters (77, 2530-2532, 2000), C. Rao and colleagues from the
      > Jawaharlal Nehru Centre for Advanced Scientific Research in India
      > now demonstrate an efficient method for synthesizing a more
      > advanced structure from carbon nanotubes: Y-junctions. Such
      > structures could be used in new types of molecular devices.
      > Carbon nanotubes are known for their remarkable property to be
      > either a semiconductor or a metal, depending on their diameter
      > and the winding of the carbon sheet from which the nanowire is
      > made. A sharp bend in a nanotube can actually be thought of as a
      > junction between two nanotubes with different electronic
      > behaviour and so provide a transition from semiconductor to metal
      > over a distance of just a few nanometres. Such sharply bent
      > tubes have already been used as molecular diodes. But scientists
      > are always on the lookout for more complex structures based on
      > carbon nanotubes. A Y-junction can be thought of as a connection
      > between three different carbon nanotubes, which could form, for
      > example, a microscopic metal-semiconductor-metal contact.
      > In previous attempts to construct complex junctions, two
      > nanotubes have been crossed or Y-shaped templates have been used
      > to laboriously mould a junction from a single nanotube. A simple
      > method to produce carbon nanotubes is pyrolysis of organic
      > molecules. In this process, carbon-containing molecules are
      > decomposed at high temperatures, using appropriate catalysts.
      > Rao and co-workers have finely tuned this method to create their
      > Y-tubes, with a 70% yield. They decompose nickelocene, an organic
      > molecule containing a nickel atom, along with another organic
      > molecule, thiophene, at a temperature of 1,273 K. An electron
      > microscope image of the product (shown here) reveals that the Y-
      > shaped nanotubes are multi-walled and have an outer diameter of
      > about 40 nanometres. The angle between the upper arms is almost
      > 90°.
      > One of the current objectives in nanotube synthesis is to have
      > control over the electronic properties of the end product.
      > Although the electronic structure of these Y-junctions is not
      > known exactly, initial measurements by Rao and co-workers show
      > that their Y-junctions can behave like diodes. This work is still
      > preliminary, but it will inspire further studies into making
      > three-point nanotube junctions with specific semiconductor-metal
      > transitions. Such molecular junctions will be useful building
      > blocks in the continuing miniaturization of complex electronic
      > devices.
      > --= oOo =--
      > The Nanotechnology Industries mailing list.
      > "Nanotechnology: solutions for the future."

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