Intelligent Machines

Nanotech by the Numbers

It’s virtual reality, writ small: atom-by-atom simulations of new materials could usher in the nanotech future sooner than anybody imagined.

In his cramped cubicle at Nanomix, a nanotechnology company in Emeryville, CA, just across the bay from San Francisco, theoretical physicist Seung-Hoon Jhi peers at a computer model of a hydrogen fuel tank, carefully tracking the movement of individual molecules. As he raises the temperature of a simulated sheet of boron and nitrogen atoms from a frigid 50 Kelvin to a slightly less chilly 80 Kelvin, he watches the reaction of a handful of hydrogen molecules dotting its surface. The boron nitride sheet undulates, yet the hydrogen molecules hold fast. It’s an encouraging sign in a virtual experiment that may have just saved weeks or months of painstaking experimental testing in Nanomix’s effort to develop more efficient hydrogen storage materials for fuel cell cars.

It’s cyberdreaming, of course. But Jhi and his Nanomix colleagues are so confident in the veracity of this computerized modeling, pieced together from precise calculations of the behavior of individual atoms, that they are using the simulations to design and test materials that have never been made before-materials whose ordering at the nanometer scale (a nanometer is a billionth of a meter) can produce properties useful in applications ranging from ultrasensitive sensors to flat-panel displays to stealthy coatings for war planes. Down the hall, less than 15 meters from Jhi’s cubicle, the company’s experimentalists are busy working in the lab to synthesize the most promising results of the modeling.

While Nanomix is just one of several recent startups hoping to exploit nano materials, the company is betting it has an edge: the skill to both virtually design the materials-without so much as stirring a beaker-and then go into the lab and make them. Its cofounders-theoretical physicist Marvin Cohen and experimental physicist Alex Zettl, both from the University of California, Berkeley-have been collaborating on such alchemy for over a decade. Now they are hoping to leverage that expertise as the basis for a nanotech business. “Our goal is to have the first working nano components on the market,” says Nanomix CEO Charles Janac.

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Designing materials on computers has tempted industrial researchers for more than a decade. In theory, at least, the idea is simple enough: using the rules of quantum mechanics it is possible to calculate the behavior of the electrons that swirl around an atom. Given enough computing power, one should be able to use such calculations to design a material atom by atom, building in desirable properties by adjusting the electronic profile. The problem is, the properties of materials result from the interactions of a huge number of atoms. And even today’s most powerful supercomputers struggle with quantum calculations involving more than five or six hundred atoms, severely limiting the ability to design new materials.

But nano materials, which are often isolated molecules-or molecules whose properties arise from limited interactions -make a far easier target for computers. Indeed, in many ways, quantum modeling is turning out to be an ideal way to explore the nano world. The “predictive power” of nano modeling, says James Tour, a chemist and leading nanotech researcher at Rice University in Houston, “is turning out to be tremendous.”

Nanomix believes it is just this predictive power that will allow it to revolutionize the discovery of nano materials. Thanks to a head start from its computer simulations, the company, which started up in 2000, is already engineering tiny gas sensors that use carbon nanotubes-molecules just a few nanometers wide, with walls an atom thick-to detect dangerous gases. By the end of next year, Nanomix plans to begin selling these nanotube-based sensors to detect gasoline vapors-protecting refineries, chemical plants and pipeline stations from leaks. Each sensor should cost 10 times less than a conventional leak detector and operate for a year on a watch battery. Linked to wireless transmitters no bigger than postage stamps, they could be scattered by the tens of thousands, blanketing an industrial facility-or squeezed into leak-prone valves to ferret out failing seals, something not possible with far larger and more expensive conventional sensors.

At the same time, Nanomix is drafting designs for novel nano materials for hydrogen fuel storage-materials with an even greater ability to store hydrogen than the boron nitride sheets on Jhi’s screen. If these materials become reality, they could dramatically increase the performance of fuel cell cars, finally making automobiles that run on hydrogen fuel commercially practical. The company has also begun to ponder how novel nano materials like nanotubes could be used in tiny computing devices.

Nano materials for fuel cells and nano computers will likely take years to develop. But Nanomix believes its plan to begin selling sensors and other early applications of nanotech will make it a viable business long before then. “People keep saying nanotechnology is a long way out, and it is in the sense that it’s a long-term trend that’s going to have a huge impact on the world economy. But some of the early applications are just 18 months away,” predicts Janac.

Sensing Success

Inventing a new material, say a new polymer or metal alloy, has never been easy-and is often more a case of serendipity than theoretical design. Even at leading industrial facilities such as DuPont’s central research lab, which has invented many of today’s most important polymers and high-tech materials, the process is often a hit-or-miss endeavor governed more by the instincts of experimentalists than the calculated predictions of theorists. At the nanoscale, however, the instincts of researchers often begin to fail, as the strange rules of the quantum world take over. “We’re getting into areas where our intuition, which is often based on our prior experiences, is really quite deficient,” says Ed Wasserman, science advisor to DuPont central research and development.

It is, however, a place where theoretical quantum physicists feel right at home-a realm where they can play god, creating new materials by simply shuffling around atoms. One of those gods is Nanomix cofounder Cohen, a pioneer in quantum modeling. In the 1960s, Cohen had the insight that since it is only an atom’s outermost electrons that interact to give a material its properties, it is possible to greatly simplify the calculations needed for simulations by dealing only with those electrons. This mathematical shortcut revolutionized quantum-mechanical modeling. “If you do an all-electron calculation, it’s almost like trying to find the weight of the captain of a ship by weighing the ship and then weighing the captain with the ship,” explains Berkeley physicist Steven Louie, an advisor to Nanomix. By in essence weighing the captain directly, Cohen’s software now makes it practical to use a PC to quickly crank out predictions on nano materials with novel combina-tions of electronic, magnetic and light-handling properties.

But Cohen also realized that such simulations are only as real as the skills of the experimentalists down the hall. So in the early 1990s, he began collaborating with Berkeley colleagues, like Alex Zettl, who were experienced in synthesizing novel materials. The discovery-and actual synthesis-of boron nitride nanotubes in 1994 was one early success. Cohen, pondering the atomic structure of boron nitride sheets, realized that it should be possible to roll up the sheets to form cylindrical molecules. Other researchers had recently made similar molecular tubes from carbon, but no one had extended the technique to boron and nitrogen. Cohen and his students booted up their models and calculated that boron nitride nanotubes would not only be stable but would exhibit interesting electrical properties. Within a year, experimentalist Zettl had found a way to make the novel nanotubes and affirmed the predicted properties.

A neat scientific trick, for sure, but how do you turn that type of physics wizardry into a business?

The immediate challenge for researchers at Nanomix is to perfect the sensors that Janac has promised to begin selling next year. So far, Nanomix’s theorists have identified the specific types of nanotubes that would react most sensitively to the hydrocarbons that can permeate refineries, chemical plants and pipelines. They’ve also predicted how each gas would alter conductance through the tubes, providing a voltage “footprint” that would identify it. Now the experimentalists must figure out how to mass-produce the nanotube-based devices. And they must deliver a product reliable enough to safeguard the lives of plant operators.

That type of development of a new material can easily take a decade. But if Nanomix-using its modeling and theoretical expertise to shortcut the process-can pull off the trick in the next year or so, it will validate its strategy for nano invention. It will also open the door to a whole world of sensors. For starters, Nanomix should be able to tailor nanotube sensors to sniff out just about any gas, from carbon monoxide to the compounds used in chemical weapons. And the company is sponsoring academic research aimed at tuning nanotubes to sense the biochemical whiffs of disease, measuring insulin levels in diabetics or detecting antigens that indicate infection. Nanotubes are the ultimate sensing platform, asserts Janac. “You don’t need more than single-molecule sensitivity, your power consumption is going to be nanowatts, and in terms of size you can’t get smaller-at least in the foreseeable future-than a nanotube. We think we’re going to revolutionize the sensor business with this architecture.”

Nano Dollars

But technical challenges are not the only pressures facing Nanomix. Not only is the company racing to get a nano product to market, it must beat the competition to the relatively small pool of venture capital funding available for nanotech startups. Among many experts, excitement over the prospects of nanotechnology may be growing, but the willingness of investors to sink money into highly speculative technologies is not growing nearly as fast. Which means that Nanomix-like a number of other young nanotech companies-must struggle not only to answer daunting scientific questions but simply to survive.

San Francisco-based Alta Partners gave Nanomix seed funding in 2000, and as of last year Nanomix had raised $4.5 million. But since then, additional funds have been hard to find, as venture capitalists have grown cautious following last year’s economic crash. “It’s been a long slog getting other people to invest,” says Alta partner Peter Schwartz.

Ironically, it is exactly the strengths of Nanomix-a strong academic pedigree and theoretical expertise-that can handicap the company in front of potential investors wary of a field where results often sound more like basic research than viable products. And Nanomix’s bevy of theorists makes it especially easy to mistake the firm for a basic-research lab.

The pressure has led Nanomix to put a short-term emphasis on product development at the expense of the company’s efforts in theoretical physics. But while Cohen may accept the immediate necessity of getting a product out the door in order to win financial backing, he remains committed to his dream: a company that invents and commercializes nano materials by coupling quantum modeling and theory with deft experimentation. It’s a dream filled with exotic materials, limited only by the rules of physics and the cleverness of its practitioners.

Like many nanotech researchers, Cohen and his scientific colleagues at Nanomix are convinced that nano materials will have applications not only in sensing and hydrogen storage, but in electronic devices a thousand times smaller than today’s silicon transistors-making possible ultrafast, ultrasmall computers. Lilliputian circuits with billions of nano components may still be years in the future, but Nanomix researchers are already thinking of the nano materials that could make them happen.

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