Apr 15, 2002
IBM forges ahead with nanoscale computing
IBM scientists in the US have used "molecular-cascade-like computation" to make a circuit that can do a one-time calculation. IBM's Don Eigler revealed the technique in a talk on future computation in nanometre-scale structures at the Institute of Materials Congress 2002 in London, UK, last week.
The logic circuit, which used the movement of 500 carbon monoxide molecules on a copper surface, measured just 12 nm x 17 nm. In comparison, the same device made using next-generation complementary metal-oxide silicon (CMOS) technology measures 7.65 µm x 6.97 µm.
"We're right at the very beginning, the only thing that we can say with any certainty is that [molecular-cascade circuits] are small," said Eigler. "Which is good."
Eigler is famous for using a scanning tunnelling microscope (STM) to spell out IBM with individual xenon atoms back in 1990. Now he and his team have been using an STM to position carbon monoxide molecules on copper surfaces in an ultrahigh vacuum at a temperature of 4K. Depending on how they are arranged, the molecules may or may not reconfigure into a more stable position.
For example, three molecules placed in a line rearranged themselves in less than 10 ms, while molecules positioned in a chevron pattern took about 5 minutes to move. Molecules in the most stable pattern, on the other hand, were stable for at least two weeks.
The researchers also found that they could alter the stability of groups of molecules (and hence the speed with which they move) by adding additional carbon monoxide molecules nearby. Although faster than the STM can measure, Eigler estimates that the quickest reconfigurations took about a nanosecond, or less, per step.
Eigler reckons this cascade-like computation is definitely worthy of future investigation. "We don't know if it's useful or not, it's our job to find out," he said. "As a scientist, I love those challenges. It gives me job security."
The researchers have used these tricks to make a number of logic elements, including gates that could be used for data storage, data retrieval and data inversion. There's still one essential element of a computer missing - a reset mechanism - but Eigler and his group are "working on it".
About the author
Liz Kalaugher is editor of nanotechweb.org.