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1252Y-junction Nanotubes

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  • Ihsan Hariadi
    Nov 1, 2000
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      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 =--
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