NANOTUBES AND THEIR IMPLICATIONS FOR COMPUTING Natasha Katsura, Fran Mateycik, and DJ Wagner Quick links: Introduction Nanotube Structure Mechanical Properties   Interconnects/Heat Sinks Memory/Logic NOT Gate   Video Displays The Future References Please Read our Policies for Use of ScIT Materials

Introducing . . . The Carbon Nanotube

In 1965, even before the advent of personal computing, Gordon Moore of Intel predicted that the number of transistors that can be packed onto on a computer chip would double every 18 to 24 months. This was possible because as transistors could be made smaller, signals could be sent through chips faster.  This increase in transit speed would translate directly into faster computers.  Although Moore's pronouncement was initially met by skepticism and even derision, the microelectronics industry has been illustrating the veracity of Moore's Law ever since.  Today, however, the computing industry is facing the physical limits of silicon-based technology.  Without the advent of a substantially new technology, the rate of progress defined by Moore’s Law will start to slow, possibly as soon as 2005. “Even if they can be made smaller, at some point smaller transistors may not perform faster; in fact, their performance could even be worse, if they worked at all”, notes Randy Isaac, vice president for systems, technology and science research at IBM.¹  For example, as barriers between conduction regions get thinner, charges can “tunnel” through barriers and short-circuit the chip.  Unlike previous hurdles of a technological nature that were overcome by devising better production methods, this limit is a physical one that cannot be circumvented with technology alone.  The search is taking place around the globe for new materials and processes to extend the conventional technology.  One of the promising candidates being explored is the carbon nanotube.

Nanotubes have an impressive list of attributes.  They can either exhibit properties of conductors or exhibit semiconductor behavior depending upon their structure, they can conduct electricity better than copper, they can transmit heat better than diamond, and they rank among the strongest materials known – not bad for structures that are just a few nanometers across.    New research continues to discover new applications for them, such as a cancer-targeting laser² and a nano-scale motor.³ Carbon nanotubes have so many beneficial properties, they appear to be the gift of a fairy godmother.  In this story, the fairy godmother is Sumio Iijima of NEC Corp in Japan, who first discovered nanotubes in 1991.⁴ He used a transmission electron microscope (his version of a magic wand) to magnify carbon ash.  In that ash he found tiny cylinders of carbon atoms with diameters on the order of a nanometer - and he called the cylinders nanotubes.

As one might imagine from the list of nanotube properties, nanotubes could profoundly impact many different technologies.  Light-emitting nanotubes can be used in ultra-thin video displays.  The structural properties of nanotubes can be used to reinforce bridges and to build safer cars.  And transistors made with nanotubes could possibly keep Moore's Law valid for a few more years.

back to top
 

Structure of Nanotubes

Nanotubes do indeed deserve the "nano" prefix - they can be as small as ten atoms across, about 1/50,000th the diameter of a human hair.  In case the reader is still having trouble grasping the smallness of nanotubes, two scientists who work with nanotubes have provided a helpful analogy.  “One could take a chip of graphite and after magnifying it a billion times, creating a metal-gray rocky landscape about the size of Texas, we might spot a three-foot-diameter pipeline stretching from horizon to horizon. This is a nanotube.  Actually, a one-nanometer-wide pipeline occupies almost no space even over a substantial length.  Nanotubes sufficient to span the 250,000 miles between the earth to the moon at perigee could be loosely rolled into a ball the size of a poppyseed." ⁵
 

The many structures of carbon
Fullerene and Nanotube figures courtesy of Mitch Mailman, Damian Huising, and Saroj Nayak

(a)  Diamond	(b)  Graphite	(c)  Fullerene	(d)  Nanotube
Colors in (a), (c), and (d) represent depth, with red closest to the viewer, and violet (or blue for (c) and (d)) furthest away.

Carbon nanotubes represent just one of the many structures pure carbon can form.  In crystalline form, pure carbon is known as diamond.  Diamond is formed when carbon atoms bond with a tetrahedral structure, such as that shown in Figure (a) above.  Graphite is also pure carbon, created when carbon bonds in a hexagonal structure, shown in Figure (b) above.  The reader may be acquainted with the lubricating properties of graphite found in sprays such as WD-40^®.  Carbon, it seems, is not only necessary for biological life to exist, it also is critical to many amenities carbon-based life forms enjoy.  Perhaps less well-known are carbon fullerenes, with atomic structures similar to geodesic spheres such as the one found at Epcot Center^®. In this form, carbon again forms hexagons, but the hexagons are connected into a spherical shape, as shown in Figure (c) above.  Fullerenes are also known as "buckyballs;" both names pay tribute to F. Buckminister Fuller, who designed the first geodesic dome.  The hexagon structure of graphite is evident in nanotubes as well, but in nanotubes the sheet of hexagons has rolled up into a tube, as shown in Figure (d) above.  This atomic structure is very stable, and no intrinsic limit exists on how long a tube can become.⁶  Theoretically, one could grow a nanotube spanning the distance from earth to the moon!  Lest you think such long spans of nanotube material are merely a hyperbole, consider that some scientists and engineers are seriously working toward building a "space elevator" between Earth and orbiting satellites, using carbon nanotubes. ⁷  Proponants claim such a feat is possible by the year 2020, fewer than 30 years after the initial discovery of nanotubes.

Most nanotubes formed naturally are so-called multi-walled nanotubes.  These can consist either of several concentric nanotubes (Figure (c)) or of a single sheet rolled several times like a roll of wrapping paper (Figure (b)).  A single-layered tube is called a single-walled nanotube (Figure (a) to right and Figure (d) in Structures of Carbon figure above).  Single-walled nanotubes are not produced as readily as multi-walled nanotubes are, but they can exhibit behavior not found in their multi-walled counterparts.  Scientists are looking for practical ways to mass-produce single-walled nanotubes while continuing to explore applications and production techniques of multi-walled tubes.  The process by which the atoms bond to form nanotubes is not completely understood.  One theory (from a source published in 2000) relates the growth to knitting:  "it appears that [nanotubes] may grow by adding atoms to their ends, much as a knitter adds stitches to a sweater sleeve."8  But the study of nanotubes continues to be a cutting-edge field, and new discoveries are being made regularly.  In October, 2005, a group at Stanford led by Hongjie Dai published their successes at mass-producing single-walled nanotubes.9  This discovery could significantly hasten the integration of nanotubes into computer chips and biotechnologies.  (Dai was honored for this work by receiving the American Physical Society's 2006 McGroddy Prize for New Materials.)

(a) (b) (c)

back to top

Mechanical properties

Due to the strength of carbon bonds and the regularity of their atomic structure, nanotubes demonstrate incredible mechanical properties.  Nanotubes are stiff - stronger and tougher than steel - but at the same time elastic.  This means they will bend rather than break when experiencing a significant stress.  And once the stress is removed, the nanotubes will revert to their original shape, showing no effects of their ill-usage.^{6, 10}
   

To see how these properties might be useful, consider this example given by Christian Schönenberger, a nanotube researcher at Universität Basel in Switzerland:  “Imagine owning a BMW car made from carbon nanotubes and being unlucky enough to crash into a wall. Due to the high force of the impact, the nanotubes would bend and then buckle, squeezing your BMW into a shape of something like a Volkswagen Beetle. This would happen over a relatively long distance, which would provide an effective ‘crunch zone’. Moreover, after the crush all the buckles would unfold and your BMW would ‘reappear’ as if nothing had happened!  To be completely safe, however, the nanotubes would have to be combined with energy-absorbing materials, otherwise the collision between the car and the wall would be completely elastic and you would rebound from the wall with the same speed as you hit it!"10  In our cartoon to the right, we have substituted a 1957 Ford station wagon for the BMW and left the details of the transition to the reader's imagination, but the result is the same.  The car absorbs the impact, yet comes out of the collision with no damage.  One can imagine numerous other situations where this elasticity would be very useful.

Nanotubes' amazing strength is already being exploited in manufacturing.  For example, the bicycle that helped Floyd Landis win the 2006 Tour de France incorporated nanotubes in its frame, to add strength but keep it light-weight.¹¹  Of course, some are saying it was doping that helped Landis in his amazing come-back; we think the nanotubes had a bigger effect!

back to top

Implications for computing:  Interconnects and Heat Sinks

Nanotubes have unique electrical properties.  The regularity of the atomic lattice minimizes collisions between conduction electrons and atoms, giving nanotubes a very high electrical conductivity similar to that of copper.  Yet the structure of nanotubes is such that they can withstand much higher currents than even copper.  IBM Researchers Collins and Avouris state,⁸ "a bundle of nanotubes one square centimeter (roughly half an inch) in cross section could conduct about one billion amps.  Such high currents would vaporize copper or gold."  On top of this high electrical conductivity is a similarly high thermal conductivity.^8,12  Furthermore, the strength of the carbon bonds in nanotubes makes them able to withstand high temperatures.  This unique combination of electrical and thermal properties has the tremendous implications for computing.
 

One of the difficulties in shrinking electrical components such as transistors is that the electrical operations inside computers produce heat.  If more devices were packed into smaller spaces, the temperature inside the computer could become high enough to start damaging the chips themselves.  Many heat-removing techniques have already been implemented in computer technology.  (The most obvious, but not the only, approach is the fan found in the back of desktop computers.)  Packing transistors more densely requires the development of improved heat-removal methods.  One of the sources of heat in chips is resistance in the interconnects.  Interconnects connect various electrical components to each other on a chip, in the same manner that roads connect driveways and parkinglots (see Figure to the left).  They are currently made of aluminium.  Aluminum is a decent electrical conductor, but not nearly as good as carbon nanotubes.  A related difficulty in shrinking electrical components is that making the aluminum interconnects any thinner results in broken connections, as "the gust of electrons moving through [the interconnects] becomes strong enough to bump the metal atoms around."8

Replacing aluminum interconnects with carbon nanotubes would solve all of the above problems at once, perhaps allowing silicon technology to keep up with Moore's Law for a few more years.  Because the electrical conductivity of nanotubes is greater than that of aluminum, the nanotubes could carry greater amounts of current and power more devices while taking up less space on the chip.  This greater electrical conductivity means a smaller resistivity, so the current would produce less heat when flowing through the nanotubes.   And whatever heat is produced will be conducted away by the nanotubes much more efficiently than by aluminum.  Nanotubes are several times thinner than the current width of aluminum interconnects, and nanotubes' structural integrity prevents the broken connections that can occur when thinner aluminum interconnects are used.

back to top
 

Implications for computing:  Computer Memory and Logic Devices

Nanotubes have amazing conductivity, but the property that promises the biggest impact on computing is their ability to act like a doped semiconductor.  All semiconductor technology relies on the properties semiconductors such as silicon obtain when infused with a small percentage of atoms of another type.  Elements in the column of the periodic table to the right of silicon contribute an extra conduction electron and produce n-type behavior.  Elements in the column to the left of silicon contribute a hole and produce p-type behavior.  (Click here to bring up the content module that describes doped semiconductors in more detail.)  Nanotubes naturally exhibit p-type behavior, with holes providing most of the conduction.  Scientists have discovered,¹³ however, a way to get n-type behavior from nanotubes, as explained in the next section.  Transistors, which not only perform all of the logic in a computer but also play a critical role in electric memory (used in RAM), require both n- and p-type materials.

The ability to achieve both types of behavior from nanotubes opens up profound possibilites.  In 2001, IBM nano-scientists demonstrated an entire logic device constructed out of a single nanotube (plus base and connecting wires).¹⁴  According to one review of this work, “More measurements are needed but the current results show, after taking into account difference in size, nanotube transistors show a performance superior to that state-of-the-art silicon transistors."¹⁵

back to top
 

How can a nanotube act like a transistor?

The function of a transistor is to act like a switch, or to allow a large change in output for a small input.  (Click here to bring up the content module that describes the operation of transistors in more detail.)The switch is not creating something out of nothing, but rather using a small signal to unleash a large store of energy.  (Think of a light switch.  A gentle touch will unleash a current that can provide appliances with much more energy than was exerted with the touch.)  A related feature, also important, is that combining transistors to produce sophisticated processors requires that the output be at least as large as the input.  (If this were not so, the signal would die out as it moved from transistor to transistor, limiting the number of operations that can be combined.)  Nanotubes, as it turns out, can provide the semiconductor behaviors necessary for producing a transistor. ^{8, 16, 17}

The IBM group built a NOT gate out of one nanotube (plus 3 electrodes and other backing) by making two transistors out of the same nanotube.  Since "natural" nanotubes exhibit p-type behavior, it should be no surprise that transistors made out of natural nanotubes are p-type transistors.  A p-type transistor is turned on by a negative voltage.  A positive input does nothing to a p-type transistor.  In order to effectively create logic devices, it is useful to have both p- and n-type transistors.  The IBM group was able not only to produce nanotubes that can be used in n-type transistors, but they were able to produce both a p-type transistor and an n-type transistor on different regions of the same nanotube! ¹⁷

By subjecting the nanotube to a process called “vacuum annealing,” the researchers were able to produce n-type transistor behavior.  This behavior disappears when the nanotube is exposed to air, but it can be preserved by “sealing” the tube and thereby preventing oxidation.  By sealing only a portion of the tube and exposing the rest to air, one obtains n-type behavior from the sealed portion, and p-type behavior from the exposed portion.  A NOT gate is then produced by connecting the nanotube between a positive voltage source (connected to the p-portion) and a negative voltage drain (connected to the n-portion), as shown in the animation below.  The center region of the nanotube,  encompassing parts of both the p- and the n-portions, is connected to a common output terminal.  The entire contraption, about one micron long, is then insulated from a fourth terminal called the gate.  When the gate voltage is positive, current will flow from the negative drain, through the n-type transistor, to the output.  When the gate voltage is negative, current will flow from the positive source through the p-type transistor, to the output.  Thus the output is always opposite the sign of the input, producing NOT behavior.  The animation below illustrates the key features of this nanotube NOT gate.

back to top

Video Displays

Out of all of the potential applications of nanotubes, the first to make it into your house will probably involve nanotubes as sources of light.  Prototypes of nanotube devices are being tested in everything from full-color flat-panel TV screens to ultra bright outdoor lighting.  One "recent" article summarizing these nanotube applications is found in the January, 2006, edition of Nanotubes Monthly. ²¹

Conventional televisions and computer monitors rely upon cathode ray tubes (CRTs) to shoot beams of electrons at a phosphorescent screen.  The screen lights up where the electrons hit it.  CRTs, however, are bulky and heavy, and consumers are turning to flat-panel screens reliant on other technologies.  But current flat-panel screens, such as those on laptops, have their own problems.  In general, flat panels are more expensive than CRT screens, and they often do not provide as high quality a picture.  (For example, most laptop screens are more difficult to see from the side than from head-on.  TVs need to be easily viewed from a variety of angles.)  Nanotubes could provide a compromise, combining the easily-viewed phosphorescent screen of traditional displays with the sleek thinness and lightness of flat screens.

When a voltage is applied to nanotubes, they emit electrons from their tips.  Most materials used in electronics will emit electrons when a sufficiently high voltage is applied, but nanotubes do this at much lower voltages than other materials.  And their tiny tips provide a sharply focused beam.  This beam of electrons can be directed at a phosphorescent screen, just like the electron beam in traditional CRT monitors.  The signal to be shown is converted into electrical voltages which are sent to the appropriate nanotubes.  Those desired nanotubes emit electrons, which cause the phosphorescent particles on the screen to emit light and produce the picture.  ISE Electronics Corp (affiliated with Noritake) was the first (in 1998) to build a (small) prototype video monitor consisting of nanotubes aligned behind a phosphorescent screen.  This early breakthrough fostered hopes that commercialization of nanotube displays would quickly follow.  Producing nanotube screens, however, has proven more difficult than expected.  At the original time of this writing (2002), Samsung was projected to start marketing a 32-inch nanotube television in late 2003 or early 2004 ^8,22,23 Applied Nanotech Inc. (ANI) also predicted October, 2004 for a debut of nanotube displays.²⁴  But nanotube displays have not yet (August, 2006) been brought to the market.  Multiple hurdles have impeded the creation of commercial displays:  the lack of a method to mass-producing nanotubes, the related difficulty of making the displays affordable in a market already occupied by competing technologies (flat panel LCDs and plasma displays), and the challenge of designing a technology robust enough to meet the needs of consumers.  According to Kazuo Konuma, a member of a panel that advises the Japanese government on future technologies, nanotube displays "tend to short and destroy themselves quickly and they degrade far faster than the tens of thousands of hours of reliable operation needed for commercial acceptability.  [Carbon nanotube display] commercialization has been greatly expected, but if [such displays] do not completely conquer the problem of electric discharge destruction completely, it must be said that commercialization remains difficult."²⁴  Still, progress is being made.  Motorola and ANI seem to have overcome many of the obstacles facing nanotube screens. In early 2005, Motorola produced a 4.7" prototype nanotube display, having found a way to grow regularly-spaced nanotubes on glass.^25,26   Applied Nanotech (ANI) produced a 25-inch display later that year.²⁷   Motorola predicts that, if the industry embraces the new technology, full-size nanotube TVs could be rolling off the production line in 2007. 

back to top

The Future Is . . . Still the Future

The possibilities for nanotubes are exciting, but production difficulties stand in the way of mass-production of nanotube devices.  Devices and prototypes created to date have been manufactured individually, at a cost prohibitive to the typical consumer.  Researchers in both industry and academia are devoting much effort to developing an automated manner of growing nanotubes with uniform, predictable, properties.  One goal of many groups is to find a way of getting nanotubes to self-assemble.  Northwestern University's nanoelectronics group described the goal thusly:  "If you want to build just one patio, you can take the time to lay bricks one by one.  But if you want to build a trillion identical patios, you need to get the bricks to somehow do the job themselves, to self-assemble into patios.  We don’t know how to get the bricks to self-assemble, because there are no natural forces between the bricks that are strong enough compared to the size and weight of the bricks to have an effect. The situation is different for nanometer scale objects."¹  In the microscopic world, self-assembly occurs all the time, such as when proteins fold into complicated structures.  The rub is that scientists still don't understand how such biological systems achieve self-assembly, so they have no blueprint to use in their quest for nanotube self-assembly.  Until they develop a method of mass-production of nanotubes, most applications of nanotubes will remain in the research laboratory, and silicon will continue to dominate computing technologies.

back to top
 

References:
 

1	Lerner, Eric J., "The end of the road for Moore’s Law?", think research by IBM, 1999, vol. 4.  http://domino.research.ibm.com/comm/wwwr_thinkresearch.nsf/pages/moore499.html.
2	Mark Shwartz, "Nanotech-laser kills cancer, preserves healthy cells," Stanford Report, August 2, 2005.  http://news-service.stanford.edu/news/2005/august10/nanotube-081005.html.  Original publication of results:  Nadine Wong Shi Kam, Michael O’Connell, Jeffrey A. Wisdom, and Hongjie Dai, "Carbon nanotubes as multifunctional biological transporters and near-infrared agents for selective cancer cell destruction," Proceedings of the National Academy of Sciences, 102 (33) 11600–11605 (2005). Available at http://www.stanford.edu/dept/chemistry/faculty/dai/group/Reprint/96.pdf.
3	Robert Sanders, "Physicists build world's smallest motor using nanotubes and etched silicon," University of California at Berkeley press release, July 23, 2003. http://www.berkeley.edu/news/media/releases/2003/07/23_motor.shtml.  Original publication of results:  A. M. Fennimore, et. al., "Rotational actuators based on carbon nanotubes," Nature 424, 408-410, (July 24 2003).  Available at http://physics.berkeley.edu/research/zettl/pdf/285.Nat424fennimore.pdf.
4	"Ultrasmall Structures Bring Big Future", on NEC Global website, Special Feature from March, 2002. http://www.nec.com/global/features/index7/index.html.
5	Yakobson, Boris and Smalley, Richard E., "Fullerene Nanotubes and Beyond," American Scientist, July-August 1997.
6	Lerner, Erick J., "Putting Nanotubes to Work", The Industrial Physicist, December 1999. Available at http://www.aip.org/tip/INPHFA/vol-5/iss-6/p22.pdf.
7	Lurie, Karen, "Space Elevator", ScienCentral News, 2004.  http://www.sciencentral.com/articles/view.php3?article_id=218392162&language=english. Also see the Instutute for Scientific Research page at http://www.isr.us/research_es_se.asp.
8	Collins, Philip G. and Avouris, Phaedon, "Nanotubes for Electronics," Scientific American, December, 2000. Available at http://researchweb.watson.ibm.com/nanoscience/NTs_SciAm_2000.pdf.
9	Strehlow, Anne, "Scientists find new method for creating high-yield single-walled carbon nanotubes," Stanford Report, October 26, 2005. http://news-service.stanford.edu/news/2005/october26/dai-102605.html. Original publication of results: Guangyu Zhang, et. al, "Ultra-high-yield growth of vertical single-walled carbon nanotubes: Hidden roles of hydrogen and oxygen," Proceedings of the National Academy of Sciences, 102 (45) 16141–16145 (2005). Available at http://www.stanford.edu/dept/chemistry/faculty/dai/group/Reprint/102.pdf.
10	Schönenberger, Christian, "Multiwall Carbon Nanotubes," Physics World, June, 2000.  http://physicsweb.org/article/world/13/6/8/1.
11	Michael Kanellos, "Carbon nanotubes enter Tour de France," CNET News.com, July 7, 2006. http://news.com.com/Carbon+nanotubes+enter+Tour+de+France/2100-11395_3-6091347.html?tag=fd_carsl.
12	Berber, Savas, Kwon, Young-Kyun, and Tománek, David, "Unusually High Thermal Conductivity of Carbon Nanotubes," Physical Review Letters, 84 (20) 4613-4616 (2000). Available at http://www.pa.msu.edu/cmp/csc/eprint/trm/prlxtrm.pdf.
13	Gore, Park, Fuhrere, and McEuen, "Electrolyte gating of single-walled carbon nanotubes", talk given by Gore at March, 2001 APS meeting. Sami Rosenblatt, Yubal Yaish, Jiwoong Park, Jeff Gore, Vera Sazonova, and Paul McEuen.  "High Performance Electrolyte Gated Carbon NanotubeTransistors". Nano Letters. 2, 8 (2002).  Available at http://www.jeffgore.homestead.com/files/ElectrolyteGating.pdf.
14	"First Single-Molecule Computer Circuit," IBM Research News, August 26, 2001. http://domino.research.ibm.com/comm/pr.nsf/pages/news.20010827_logiccircuit.html.
15	Rotman, David,  "The Nanotube Computer," Technology Review, March 2002. Available at http://www.technologyreview.com/read_article.aspx?id=12774&ch=infotech
16	"Chip Evolution: IBM Scientists Develop Breakthrough Transistor Technology with Carbon Nanotubes," IBM Research News, April 30, 2001. http://domino.research.ibm.com/comm/pr.nsf/pages/news.20010425_Carbon_Nanotubes.html. Original publication of results: Philip G. Collins, Michael S. Arnold, Phaedon Avouris, "Engineering Carbon Nanotubes and Nanotube Circuits Using Electrical Breakdown," Science 292(5517), 706-709 (April 27, 2001). Available at http://www.research.ibm.com/nanoscience/Science-2001.pdf.
17	V. Derycke, R. Martel, J. Appenzeller, and Ph. Avouris, "Carbon Nanotube Inter- and Intramolecular Logic Gates," in Nano Letters, 1(9), 453-456 (2001) Available at http://pubs.acs.org/cgi-bin/sample.cgi/nalefd/2001/1/i09/html/nl015606f.html or http://www.research.ibm.com/nanoscience/nl015606f.pdf and
18	Z. Chen, et. al.,  "An Integrated Logic Circuit Assembled on a Single Carbon Nanotube," Science 311, 1735-1735 (2006).  The abstract can be found at http://www.sciencemag.org/cgi/content/abstract/311/5768/1735.
19	Chhavi Sachdev, "Nanotube kinks control current," Technology Research News, September 12, 2001. http://www.trnmag.com/Stories/2001/091201/Nanotube_kinks_control_current_091201.html. Original publication of results: Postma, et al., "Carbon Nanotube Single-Electron Transistors at Room Temperature," Science 293, 76-79 (July 6, 2001).  The abstract can be found at http://www.sciencemag.org/cgi/content/abstract/293/5527/76.
20	A. Bachtold, P. Hadley, T. Nakanishi, C. Dekker, "Logic circuits with carbon nanotube transistors," Science, 294, 1317-1320 (2001).  The abstract can be found at http://www.sciencemag.org/cgi/content/abstract/sci;294/5545/1317.
21	"APPLICATION OF THE MONTH: Carbon nanotubes as electron sources in field emission," Carbon Nanotubes Monthly, January, 2006. http://www.nanosprint.com/nanotubes/newsletter/monthly_0106/application.html.
22	For a photo of the prototype nanotube display, go to this "Nanopicture of the Day": http://www.nanopicoftheday.org/2003Pics/CNT Display.htm.
23	László Forró and Christian Schönenberger, "Carbon nanotubes, materials for the future," Europhysics News 32 (3), (2001). Available at http://www.europhysicsnews.com/full/09/article3/article3.html.
24	Paul Kallender, "A Full-Color Prototype May Finally Deliver on Nanotube TV Promises," Small Times:  Big News in Small Tech, Oct. 2, 2003.  http://www.smalltimes.com/document_display.cfm?section_id=46&document_id=6746.
25	Stephen Shankland, "Motorola builds nanotube-based display," CNET News.com, May 8, 2005. http://news.com.com/Motorola+builds+nanotube-based+display/2100-1008_3-5698503.html?tag=st.bp.story.
26	Elle Cayabyab, "More than meets the eye: Motorola announces nanotube displays," Ars Technica, May 10, 2005. http://arstechnica.com/news.ars/post/20050510-4887.html.
27	Michael Kanellos, 'Texas company demos carbon nanotube TV," CNET News.com, September 7, 2005. http://news.com.com/Texas+company+demos+carbon+nanotube+TV/2100-1041_3-5853193.html?tag=st.bp.story

Other Interesting Links:

• IBM Research page about nanotubes:  http://www.research.ibm.com/nanoscience/nanotubes.html.
• NEC page with links to press releases about nanotubes: http://www.nec.com/global/features/archive.html.
• Samsung research, at http://www.sait.samsung.co.kr/eng/main.jsp - roll over "Research," click on "Research Areas," then either "Opto" or  "Nano" area.
• UCLA nanotech (not nanotubes but, hey, it's cool and has "nano" in it) art exhibit: http://news.nationalgeographic.com/news/2003/12/1223_031223_nanotechnology.html and http://notime.arts.ucla.edu/zerowave/zerowave.html
• Carbon Nanotubes Monthly Newsletter:  http://www.nanosprint.com/nanotubes/newsletter/.