Scientists can sometimes get away with approximations. What's a few million years when you're calculating the age of the cosmos? But engineers need precision.
They cannot reliably make what they cannot measure. And in the world of nanotechnology, where a billionth of a meter can make a huge difference, they've had a tough time. Now they're beginning to get some help.
Three recently reported achievements show how researchers finally are mastering the exquisite precision needed when devices are built atom by atom.
For example, MIT scientists have come up with a tool to make what they call "the world's most precise rulers - with 'ticks' only a few hundred billionths of a meter apart." It can lay out a grate of lines and spaces across a large semiconductor wafer with unprecedented speed.
Tracing such patterns with precise control over areas 12 inches or more across "has bedeviled labs around the world," says Mark Schattenburg, whose team at the MIT Space Nanotechnology Laboratory in Cambridge, Mass., developed the tool. He expects this new level of precision to help chipmakers do a much better job of laying down the tiny circuitry that could lead to even smaller and more powerful computer chips.
Equally important, it should boost the ability of astronomical gratings to reveal cosmic secrets, such as the temperatures and chemical compositions of far-away stars and planets. That's because Dr. Schattenburg's Nanoruler can measure with an accuracy of less than one nanometer - one billionth of a meter - while the wavelengths of light are several hundred nanometers long. So the spaces between lines on one of his grids can easily be set to light wavelengths. When they are, the grating spreads that light into a spectrum of colors that reflects the composition and temperature of the light source.
Meanwhile, David Pritchard at the MIT-Harvard Center for Ultracold Atoms has given students of the very small a leg up on an important, century-old quest: the precise mass of atoms.
Scientists have pursued this by carefully measuring how an electrically charged atom or molecule - called an ion - orbits in a magnetic field. Its motions under the magnetic force reveal its mass. Researchers have pushed the precision of such measurement from 1 part in 1,000 to a few parts in 100 million during the past century. Dr. Pritchard and his co-workers now have raised that precision to a few parts per trillion.
They have done it by learning to work with two ions at a time. In previous attempts, interactions between two ions were difficult to test because they interfered with each other. Pritchard's team learned how to place the ions so they balanced - rather than interfered - with each other.
Nanotechnologists also need better ways to observe what they are doing, for instance, when they grow and study tiny fibers of carbon. The fibers grow with help from a catalyst that allows carbon to precipitate from a hydrocarbon such as methane. Though nanotechnologists have been able to grow the fibers, they didn't know what was going on until a Danish team used a new microscope and published tiny, play-by-play images in a recent issue of Nature.
Stig Helveg at the Haldor Topsøe company and colleagues at the Technical University of Denmark in Lyngby employed a microscope that uses electrons rather than light to form the images. These show how the catalyst for the reaction - nickel crystals 5 to 20 nanometers in diameter - grew the fiber.
The unsuspected key to the fiber growth was the ability of the crystal to rapidly change shape from spherical to elongated and back to spherical. Technologists need to know such things if they are to grow carbon nanofibers on an industrial scale.
As nanotechnology evolves from lab curiosity to industrial process, engineers will need even more instruments that can measure the scale of tiny phenomena.