Computers have been getting smaller and smaller from the time they were first constructed. A calculator that would have once filled an entire room can now easily fit in an engineer’s pocket. But there is a limit to how small a computer’s components can get — the size of a single molecule.

Now a team of Northwestern scientists might have broached that limit. The group measured a type of electrical flow through a single molecule mounted on silicon, a finding which would make the molecule useful as a semiconductor, the essential component of a computer chip. That’s a long way from a laptop, but the research suggests it is possible to build a computer on a molecular scale.

Electric flow has been measured in a single molecule before, but this lab was the first to observe the effect at room temperature with silicon components. As a result, a device based on these findings would be compatible with conventional electronics, said material sciences and engineering Prof. Mark Hersam, who leads the lab.

“We limited ourselves to placing these molecules on silicon, just like your traditional Pentium,” Hersam said. “You can’t go and replace a multibillion dollar industry overnight. If you have a new technology, it has to be compatible with the old technology so there’s some transition time.”

The team used a powerful microscope to measure the electrical effects on such a small level. They discovered that a certain kind of organic molecule conducted voltage in a peculiar way.

When the team increased voltage applied to the molecule, the current flowing through the molecule sometimes would decrease, which is atypical. Normally, voltage and current increase proportionately. This effect could enable engineers to use the molecule as a semiconductor.

Hersam lab’s findings were published in the online science journal Nano Letters in October and also will appear in a 2004 print version of that publication.

Hersam estimated that it will take 20 to 30 years to construct computer circuits using single molecules. The time frame is based on the predictions of Gordon Moore, a co-founder of the microchip producer Intel.

According to “Moore’s Law,” the number of transistors on a computer chip doubles every 18 months. Hersam said that if his group and other researchers work hard enough, they could beat Moore’s efficiency standards that have lasted for 30 years.

“If we’re really clever, we could beat it,” he said.

NU was particularly well-equipped to make this sort of discovery because its research departments cooperate so well, Hersam said.

“People like myself, an engineer, talk all the time with chemists and physicists,” Hersam said. “Each of the problems in the respective fields were not all that complicated. Putting it all together was the critical element.”

Hersam added that although he leads the lab, students do most of the important work.

“Undergraduate and graduate students really made it happen,” Hersam said. “I’m just a professor — it was their work and they deserve the credit.”

Andrew Baluch, now a graduate student in material sciences and engineering, helped Hersam build the new microscope when he was an undergraduate. The microscope was essential to the experiment and has the capability to see individual atoms.

One of the lab researchers was so persistent that he even worked on holidays.

Nathan Guisinger, one of Hersam’s graduate students, delivered the crucial data on the experiment to his colleagues as a holiday gift. Guisinger was the only one missing at the lab’s Christmas party. When he finally showed up late that night, Hersam said, he was carrying a printout and looked excited.

“It was pretty dramatic as these things go,” Hersam said. “When I saw him I knew he had gotten it.”

Guisinger had been working so hard because Supriyo Datta, a professor of electrical engineering at Purdue University, had recently visited NU and predicted that this type of electrical flow might be possible.

Datta said he was surprised that Hersam’s lab could turn theory into practice so quickly.

“The only reason he was able to do it so quickly once we discussed it is that he had really done his homework,” Datta said.