Physicists at the National Institute of Standards and Technology are using light to fabricate some of the smallest manmade metallic structures on Earth. Their techniques eventually may be used to build ultrasmall computer chips and other advanced microcircuits.
Using light to focus atoms has allowed scientists to surpass the size limitations of conventional lithography, the method by which many commercial electronic chips are currently made. The new method, which uses what NIST scientists call "atom optics," is able to produce a large number of repeating structures simultaneously. Also, the structures are very uniformly sized and spaced.
In conventional optics, lenses made of matter are used to focus light waves; while in atom optics, lenses formed from light are used to focus matter waves. Because of its quantum mechanical properties, matter can be focused more finely than light.
"The ability to manipulate atoms with light is really an enabling discovery," said NIST physicist Jabez McClelland. "There are potential applications for electronics and magnetics, as well as other microscopic technologies. For example, manufacturers might one day use the technique to draw electronic wires only a few atoms wide."
Using the atom optics method, NIST physicists Rajeev Gupta, Jabez McClelland and Robert Celotta have fabricated repeating lines and dots of chromium atoms on a silicon surface. They first demonstrated this method by making chromium lines in 1993. They created a more complex pattern of dots in 1995. The NIST team was the first to successfully create durable metal structures with atom optics.
The NIST researchers use a laser wave to act as a lens and focus a stream of atoms as they deposit on a surface. The atoms are guided into tiny parallel rows by the peaks and valleys in the laser lightwave. In this manner, NIST scientists have formed arrays of thousands of parallel chromium lines. Each line is about 38 nanometers (billionths of a meter) wide, or less than one one-thousandth the diameter of a human hair. The lines are very accurately spaced, 212.78 nanometers apart. These structures are essentially "contact prints" of a light wave. As such, they are the most accurate "rulers" available on the nanometer length scale.
Of greater challenge than drawing such tiny straight lines is the ability to manipulate the atoms into more complex patterns. In a recent step toward this goal, NIST scientists made arrays of chromium "nanodots" on a silicon surface. The nanodots were created by using two perpendicular laser waves to guide the chromium atoms onto the surface.
The next step is to create more complex patterns of dots or curved lines. This may be possible by gently moving the silicon surface as the atoms are focused through the laser waves.
These projects represent several that NIST researchers are pursuing with the Consortium on Light Force Dynamics, a collaboration of six research groups at four different institutions, sponsored by the National Science Foundation. Research teams from NIST, Harvard, AT&T; Bell Labs and Colorado State University make up the consortium.
As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.
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