-- -Time flies like the wind. Fruit flies like a banana. Stranger things have - -happened but none stranger than this. Does your driver's license say Organ -Donor?Black holes are where God divided by zero. Listen to me! We are all- -individuals! What if this weren't a hypothetical question? [EMAIL PROTECTED] ---------- Forwarded message ---------- Date: Tue, 28 Aug 2001 14:50:33 -0700 From: Jon Callas <[EMAIL PROTECTED]> To: The Eristocracy <[EMAIL PROTECTED]> Subject: I.B.M. Creates a Tiny Circuit Out of Carbon <http://www.nytimes.com/2001/08/27/technology/27NANO.html?ex=999950012&ei=1&en=11e3faeccbadcc9d> August 27, 2001 I.B.M. Creates a Tiny Circuit Out of Carbon By KENNETH CHANG In another step toward post-silicon computers, I.B.M. (<http://www.nytimes.com/redirect/marketwatch/redirect.ctx?MW=http://custom.marketwatch.com/custom/nyt-com/html-companyprofile.asp&symb=IBM>news/quote) scientists have built a computer circuit out of a single strand of carbon. The I.B.M. circuit performs only a single, simple operation - flipping a "true" to "false" and vice versa - but it marks the first time that a device made of carbon strands known as nanotubes has been able to carry out any sort of logic. It is also the first logic circuit made of a single molecule. At least another year or two of research is needed before I.B.M. can even evaluate whether a practical computer chip can be manufactured from nanotubes, said Dr. Phaedon Avouris, manager of nanoscale science at IBM Research and the lead scientist on the project. But the fact that the researchers were able to build the circuit raises hopes that nanotubes could eventually be used for computer processors that pack up to 10,000 times more transistors in the same amount of space. Dr. Avouris declined to speculate when a chip with nanotube circuitry might appear commercially, but he described nanotubes as "the best candidate from what we've seen" in the emerging field of molecular electronics. "This is yet another test that nanotubes have passed," Dr. Avouris said. "The physics works." The processing power of computer chips has consistently doubled every year or two as the size of transistors continues to shrink. But current chip-making technology, which etches circuits into silicon, is expected to run up against fundamental physics limits in 10 to 15 years. A nanotube, which resembles a rolled-up tube of chicken wire, is about one hundred- thousandth the thickness of a human hair. Its thinness, only about 10 atoms wide, makes it a promising candidate for circuits in future faster and smaller computer chips. It takes its name from nanometer, a unit of measurement one-billionth of a meter long, which is a convenient length for specifying molecular dimensions. Dr. Charles M. Lieber, a professor of chemistry at Harvard and an expert in the field of nanotechnology, called the I.B.M. achievement "quite significant." The effort to incorporate nanotubes in computer chips is a "great strategy and one that could be implemented relatively quickly," he said. The I.B.M. researchers presented their findings yesterday at a meeting of the American Chemical Society in Chicago. An article describing the results will appear in the September issue of the journal Nano Letters. Nanotubes are not the only approach to building ultratiny circuits. Other researchers, like those at Hewlett-Packard (<http://www.nytimes.com/redirect/marketwatch/redirect.ctx?MW=http://custom.marketwatch.com/custom/nyt-com/html-companyprofile.asp&symb=HWP>news/quote), have designed custom molecules that act as on- off switches. However, unlike transistors, the switches do not amplify electric signals, and a computer made of molecular switches would have to employ a different method for performing calculations, one that scientists are still working to devise. "They don't even have a transistor," Dr. Avouris said. "In that sense, we're way ahead in the game. You don't have to worry about finding a different architecture. You use what exists now." In April, the same researchers at I.B.M.'s T. J. Watson Research Center in Yorktown Heights, N.Y., reported that they had constructed vast arrays of transistors made out of carbon nanotubes, but the arrays were not wired up to perform any calculations. In the latest research, the scientists succeeded in hooking up two of these transistors to perform the true-false flipping operation. Even more remarkably, the two transistors exist along sections of the same nanotube. This function - a "not" operator - is one of three fundamental logic operations that underlie all computer calculations. (The other two operations are "and" and "or"; the "and" operator compares whether two statements are both true; the "or" operator determines if at least one statement is true.) In the binary language of 1's and 0's used by computers, a "not" operator converts a "0" (the equivalent of "false") into a "1" ("true"). It also works the other way, changing a "1" into a "0." Computer calculations are all reduced to combinations of "and," "or" and "not" operators. To build the circuit, the researchers draped a single nanotube on a silicon wafer over three parallel gold electrodes, added a layer of polymer between two of the electrodes and then sprinkled some potassium atoms on top. All of the carbon nanotube transistors built previously were positive-type transistors, meaning that they carried current via empty spaces, or "holes," in the sea of electrons that act like positive charges. The sprinkled potassium atoms added enough electrons to the nanotube that its behavior changed to that of a negative-type transistor, where current is carried by electrons. The piece of nanotube sprinkled with potassium atoms acted like a negative-type transistor; the section protected under the polymer layer remained a positive-type transistor. The combination of the two transistors formed a "not" operator, flipping an incoming voltage signal to an opposite output signal. The ability to change positive-type transistors to negative-type is "a very neat trick" said Dr. Uzi Landman, a professor of physics at the Georgia Institute of Technology. "As a demonstration, it is an important step." The logic circuit is about one-15,000th an inch wide - larger than the equivalent silicon structure - but Dr. Avouris said that it could eventually be shrunk so that 10,000 nanotube transistors fit in the space taken up by one current-day silicon transistor. "In principle, it can be small," he said. "It's a matter of just making the connections." The I.B.M. researchers are now trying to build the more complicated "and" and "or" operators and tie them together into more complex circuits. [ To unsubscribe, send email to [EMAIL PROTECTED] with body "unsubscribe man-bytes-dog" (the subject is ignored).]
