What the Press has to say about Carbon Nanotubes

Carbon nanotubes are a very significant discovery for nanotechnology. Since the Carbon Nanotubes have so many great features, including the electric conductivity, thermal conductivity, and strength, there have been predictions that these nanotubes would serve much better in computer chips than silicon. The problem with Carbon nanotubes right now is its price, and the lack of knowledge concerning its toxicity. Here is what the New York Times paper has to say about this ground-breaking technology.

New York Times:

Nanotubes only a few atoms in diameter, which spontaneously form from hexagonal arrays of carbon atoms, were discovered in 1991 by Dr. Sumio Iijima of NEC Fundamental Research Laboratories in Tsukuba, Japan. These tubes, actually elongated molecules, form in furnaces from vapor generated by carbon arcs and lasers. They take their name from the nanometer, a unit of measurement one-billionth of a meter long — a convenient length for specifying molecular dimensions.

As ever smaller electronic devices are needed to improve the speed and power of computers, ”the silicon industry is coming up against a brick wall,” Dr. Zettl said. The solution may be to replace the silicon-based devices used today with minuscule carbon molecules, which would have another advantage: they conduct heat much faster than silicon, and therefore would be more suitable for microelectronics.

Research reported last October by Dr. Zettl and his colleagues produced evidence that a single nanotube molecule could contain many tiny devices: transistors and other essential components of electronic systems.

”Nanotube fibers are uniquely tough,” Dr. Lieber of Harvard said. ”It’s certain that they will be an ingredient in a new family of composite materials that will be much stronger than existing fiber-reinforced composites.

To see the full article go to this URL- http://query.nytimes.com/gst/fullpage.html?res=9900E0DB163FF934A25751C0A96E958260&sec=&spon=&pagewanted=2

Here are some YOU TUBE videos of Carbon Nano tubes and explanations for what they are and can do.

Carbon Nanotubes

Carbon nantubes are 1nanometer in diameter and can be thousands of nanometers long. They are more than 50 times stronger than steele and great thermal and electic conductors. There is some hope that these tubes can be used for computers because they are much smaller than silicon. Here is an article from IBM about the potential use of these nanotubes:

http://www.pa.msu.edu/cmp/csc/nanotube.html

Yorktown Heights, N.Y., April 27, 2001 … IBM scientists developed a breakthrough transistor technology that could preview how computer chips can be made smaller and faster than what is currently possible with silicon.

As reported in the April 27 issue of the journal Science, IBM researchers have built the world’s first array of transistors out of carbon nanotubes — tiny cylinders of carbon atoms that measure about 10 atoms across, are 500 times smaller than today’s silicon-based transistors and are 1,000 times stronger than steel. The breakthrough bypasses the slow process of manipulating individual nanotubes one-by-one, and is more suitable for a future manufacturing process.

This achievement is an important step in finding materials that can be used to build computer chips when silicon-based chips cannot be made any smaller — a problem chip makers are expected to face in about 10-20 years.

“This is a major step forward in our pursuit to build molecular scale electronic devices,” said Phaedon Avouris, lead researcher on the project and manager of IBM’s Nanoscale Science Research Department. “Our studies prove that carbon nanotubes can compete with silicon in terms of performance, and since they may allow transistors to be made much smaller, they are promising candidates for a future nanoelectronic technology.”

Using Carbon Nanotubes as Transistors in Chips

Depending on their size and shape, the electronic properties of carbon nanotubes can be metallic or semiconducting. The problem scientists had faced in using carbon nanotubes as transistors was that all synthetic methods of production yield a mixture of metallic and semiconducting nanotubes which “stick together” to form ropes or bundles. This compromises their usefulness because only semiconducting nanotubes can be used as transistors; and when they are stuck together, the metallic nanotubes overpower the semiconducting nanotubes.

Beyond manipulating them individually, a slow and tedious process, there has been no practical way to separate the metallic and semiconducting nanotubes — a roadblock in using carbon nanotubes to build transistors. The IBM team overcame this problem with “constructive destruction”, a technique that allows the scientists to produce only semiconducting carbon nanotubes where desired and with the electrical properties required to build computer chips.

New Technique: “CONSTRUCTIVE DESTRUCTION”

The basic premise of “constructive destruction” is that in order to construct a dense-array of semiconducting nanotubes, the metallic nanotubes must be destroyed. This is accomplished with an electric shockwave that destroys the metallic nanotubes, leaving only the semiconducting nanotubes needed to build transistors.

Here is how it works:

  1. The scientists deposit ropes of “stuck together” metallic and semiconducting nanotubes on a silicon-oxide wafer,
  2. Then a lithographic mask is projected onto the wafer to form electrodes (metal pads) over the nanotubes. These electrodes act as a switch to turn the semiconducting nanotubes on and off,
  3. Using the silicon wafer itself as an electrode, the scientists “switch-off” the semiconducting nanotubes, which essentially blocks any current from traveling through them,
  4. The metal nanotubes are left unprotected and an appropriate voltage is applied to the wafer, destroying only the metallic nanotubes, since the semiconducting nanotubes are now insulated,
  5. The result: a dense array of unharmed, working semiconducting nanotube transistors that can be used to build logic circuits like those found in computer chips.

Moore’s Law states that the number of transistors that can be packed on a chip doubles every 18 months, but many scientists expect that within 10-20 years silicon will reach its physical limits, halting the ability to pack more transistors on a chip. Today, chip makers are constantly battling to make the channel length in transistors smaller and smaller. The channel is the path where data travels from one place to another inside chips. The IBM team has successfully used carbon nanotubes as the channel in the transistors they have built.

Transistors are a key building block of electronic systems — they act as bridges that carry data from one place to another inside computer chips. The more transistors on a chip, the faster the processing speed, indicating why this advance by IBM scientists could have a profound impact on the future of chip performance.

Related Carbon Nanotube Work at IBM

In the same report, the IBM scientists show how electrical breakdown can be used to remove individual carbon shells of a multi-walled nanotube one-by-one, allowing the scientists to fabricate carbon nanotubes with the precise electrical properties desired. The report also shows how the scientists fabricate field-effect transistors from carbon nanotubes with any variable band-gap desired.

In parallel studies of carbon nanotubes, IBM researchers have been working to improve the electrical characteristics of individual nanotube transistors. The unpublished data from these studies show that if the carbon nanotubes are scaled up to the size of today’s silicon-based transistors, the performance would be the same. This proves that the smaller carbon nanotube transistors should allow for Moore’s Law to continue on its path when silicon cannot be made any smaller.

The report on this work is published in Science, Vol. 292, Issue 5517, April 27, 2001. The authors of the report “Engineering Carbon Nanotubes and Nanotube Circuits Using Electrical Breakdown” are Phaedon Avouris, of IBM’s T.J. Watson Research Laboratory in Yorktown Heights, N.Y., Philip G. Collins, formerly of IBM, now with Covalent Materials in Emeryville, California, and Michael S. Arnold, an IBM intern from the University of Illinois.