Making Stuff with Molecular Precision
For more than a decade, scientists have been touting the promise of nanomaterials as a source of new and better products, from stronger structural materials to speedy but power-efficient computers to drugs that target and kill diseased cells. But making commercial products from nanomaterials is tricky.
In these materials, tiny structural changes lead to very different properties, and precision manufacturing is critical. For example, making a structural material from slightly larger or smaller nanoparticles can dramatically affect its strength or toughness. In a nanotube integrated circuit, a single misaligned tube can cause a short, and a nanotube slightly too big or small in diameter can change the operating voltage. “You have to tune your dimensions very carefully to get the desired behavior,” says Placid Ferreira, associate director of the Center for Nanoscale Chemical-Electrical-Mechanical Manufacturing Systems at the University of Illinois at Urbana-Champaign. “In order to exploit nanoscale phenomena in products, you need to have manufacturing tools that give you precision, in quantity, and cheaply.”
The semiconductor industry has been tremendously successful at making chips by laying down thin films on the surface of silicon wafers. But chip makers are continually scaling down transistors to pack more computing power in each chip; chips in the generation that will hit the market in the coming months have transistors that measure just 22 nanometers. At such small sizes, defects at the molecular and even atomic scale become more problematic, so semiconductor equipment makers such as ASM and Applied Materials keep providing ever more precise and expensive tools. In one manufacturing technique, parts of the transistor structure are laid down one atomic layer at a time. When manufacturing layered structures this thin, contamination by just a few atoms can significantly degrade a chip’s speed and energy efficiency.
Ferreira says it’s necessary to develop manufacturing processes and tools that can operate at high levels of precision over much larger areas and on a broader set of materials than those used by the semiconductor industry. For example, scientists have designed a myriad of nanostructured coatings that can make solar cells much more efficient by enabling them to absorb or trap more light. But to get these coatings into commercial products, manufacturers need to make them from inexpensive materials, and they need to be able to turn them out by the meter, not the inch.
Though maintaining atomic precision over large areas is incredibly difficult, some companies are getting there. GE Research started its nanotechnology program about 10 years ago. At that time, says principal scientist Jim Ruud, the company was focused on developing new materials with new properties. Now, he says, several of the company’s nanomaterials are ready for commercialization, and GE is focusing on manufacturing and processing. Incorporating some nanomaterials into products requires new processes; others can be integrated, with care, into existing processes.
“Ideally, you just tweak the existing system to make it better,” says Ruud. This worked for one of the nanotechnologies in the company’s portfolio, a superhydrophobic coating that sheds water very well and will improve the efficiency of steam-turbine blades. When investigating ways of making these coatings over large areas, the GE researchers found that they could use the same high-temperature spray process they use to make other coatings, just by making a few relatively simple changes.
In other cases, working with nanomaterials is not quite so simple. Take the case of a transparent ceramic armor that GE hopes will replace the heavy, thick glass-and-polymer armor currently used on the windows of military vehicles. The new material’s strength derives from the structure of the nanoparticles it’s made from. Ceramics have traditionally been made by sintering together microscale particles through a multistep process. The company had to adapt every step of this process to work with nanoscale powders, and it had to work with the powder manufacturer to redesign the starting material to fit the manufacturing constraints. “You have to start with a product in mind and develop the manufacturing process for that product,” Ruud says.
Nanotechnology also has the potential to improve today’s manufacturing systems by making prototyping and screening technologies less expensive, says Chad Mirkin, director of the International Institute for Nanotechnology and a professor of chemistry at Northwestern University. Mirkin developed a technology called dip-pen nanolithography, which uses arrays of nanoscale tips to “paint” large numbers of nanoscale structures in parallel using molecular inks. One of the earliest uses of this method, which is being commercialized by the company NanoInk, is to quickly prototype devices that usually have to be made through expensive processes in off-site fabs. For example, the technology offers a speedy way to pattern the photolithography masks needed to make novel circuit designs. That makes it easier and less expensive to test more designs so that the best one can be identified faster.
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