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Assembly Lines

in any case, before researchers worry about building nanofactories, they need to figure out a practical way to mass-produce any device on the nanoscale. Some hope to make various exotic forms of lithography (optical lithography is the standard technology used to etch patterns on silicon chips) work below 100 nanometers. But how small-and how fast-lithographic methods could ultimately become is anyone’s guess (see “Chips Go Nano,” p. 55). Likewise, pushing molecules around one at a time using an STM is an exceedingly slow-and difficult-way to make anything. What’s more, once you’re done, you still have only one very tiny object. Building a single computer chip one atom at a time using today’s STM technology would take, according to one estimate, 1,000 years.

One solution is to link up the STM or AFM tips in an array that works in parallel-a nanomechanical assembly line that might appeal to Henry Ford. This is the strategy IBM’s Binnig is taking in his information storage device. And while wiring these tiny arrays and turning them into a working device is a chore, the preliminary research at IBM Zurich and several other labs suggests it just might work.

But many believe the longer-term answer lies in a process called self-assembly. Unlike the Drexlerian construction plan that uses self-replicating nanorobots to move atoms around, self-assembly relies on chemistry to position the pieces of a nanoscale structure, taking advantage of certain molecules’ ability to arrange themselves in complex structures. In chemical terms, self-assembly works because molecules seek the thermodynamic minimum of the structure you want. Think of it as a prefab house that builds itself using chemistry.

But so far, chemists and materials scientists have learned to build only the simplest structures. The feat of assembling specific features in the materials and combining different materials remains a daunting challenge.

The solution to that problem could determine which nanodevices are practical-and how long it takes for them to hit the market. For most applications you would need to fabricate and integrate billions of nanoobjects. And to compete in such areas as information technology, you’ll have to do it very cheaply. That, say many scientists, will require the synthesis prowess of chemistry. “Don’t expect anyone to get to the point where you add ingredients in a beaker and out pops an integrated circuit,” says Yale’s Reed. However, the hope is that self-assembly could eventually place nanoelectronic devices “where you want them,” Reed says.
That will take time. But there are encouraging signs that this approach will work. Self-assembly is, in a sense, where chemistry and materials science-the arts of building actual stuff-meet the physics of the nanoscale. Physics has provided scientists with the means to manipulate nanoobjects and understand the workings of the nanoworld, and now researchers are looking to chemistry and materials science for the next advances that will help turn all this work into a practical technology.

No one really knows where those breakthroughs will come from-or even if they’ll come. But, as the science of the nanoworld grows, the shape of the real possibilities are beginning to emerge from the nanofog.

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