There’s a limit to how small a piece of chocolate chip cookie you can have. At some point, you’ll either have a piece of chocolate or a piece of cookie, but not a piece of chocolate chip cookie.
You run into the same problem if you’re trying to make smaller silicon processor chips, says Kerry W. Hipps, professor of chemistry and materials science. Eventually the chip gets too small to function as a processor.
The processor is the brain in your computer. It makes the decisions about what data should go where, including how to route input like keyboard strokes, and how to route output to hard drives and modems. It also does all the arithmetic that goes on inside your computer.
Up to now, making faster processors has happened along with a reduction in the size of their smallest building block, the transistor. If current trends continue, that’ll put us in the chocolate chip cookie situation around 2010, when transistors are reduced to near the 50-nanometer-size range, says Hipps.
In order to work as processors, silicon chips contain a small number of variations in the form of atoms that either have fewer electrons than silicon atoms, such as boron, or more electrons, such as arsenic. The area of contact between these electron-rich and electron-poor regions is the transistor, the place where electrons, or electrical current, is routed through the chip or turned on and off.
When the transistors get too small to contain enough of these atoms, we’ll no longer be able to use them as processors, says Hipps. “We’ll have to find another way.” That way is via “nanotechnology,” designing and building from the bottom up, molecule by molecule, even atom by atom.
“One nanometer is really tiny,” says Hipps. One nanometer is the size of an average molecule. One nanometer is to a meter as a BB is to the width of the United States.
Working at the nanometer scale is beyond imagination for most of us, but it’s something Hipps and his lab do every day. One of their main projects solves a very real problem for those working with individual molecules and atoms: how to see what they’re doing and what they’ve done. The answer is that they use electrical energy to make pictures rather than light—in Hipps’s case by using a tunneling electron microscope.
Conventional measuring techniques such as photography or even high-resolution optical microscopy see at the scale of hundreds of billions of atoms. Tunneling electron microscopes can see just one molecule, even its parts, says Hipps. They do so by detecting the flow of electrons and translating it into a picture, just as the intensity of reflected light is translated into a photograph.
By varying the voltage used to drive the current, they can determine which parts of molecules will accept electrons and which will donate them, necessary information if you are designing transistors just one molecule in size.
Building faster processors is not the only reason for nanotechnology, however. Smaller is important, because if parts are smaller, electricity travels a shorter distance, making for increased speed, of course, but also using less power. Smaller processors mean keeping the size of computers down, so that increasingly powerful computers will continue to fit on your desktop.
“Building smaller will allow us to go where no machine has gone before,” says Hipps. He envisions the possibility of nanomachines traveling inside and perhaps cleaning out clogged arteries. It also allows for the creation of materials in an entirely new manner, by designing molecules that assemble themselves into new structures. If we could design a material with different types of molecules in close proximity to each other, we might, for example, create a fabric that detects blood flow, and then both releases antibiotic and constricts to act as a pressure bandage.
Hipps didn’t begin his scientific career looking at parts of molecules and electron movement. The technology he uses and refines wasn’t in existence then. Now that it is, he’s able to fulfill a long-standing wish. “I always wanted to go beyond the shapes of things and know where the electrons were going and how energy was exchanged,” he says.
He also now is able to show his first-year chemistry students what many earlier students didn’t believe in because they couldn’t see it: one molecule.