Physicists Use Laser Light to Focus Atoms on Surfaces

Physicists at the National Institute of Standards and Technology have successfully demonstrated a rapid new process for fabricating infinitesimally small metallic structures.

The new process, known as "atom optics," manipulates chromium atoms into precise locations on a silicon surface using laser light.

This technique of focusing chromium atoms with a laser opens new avenues for creating smaller and faster electronic devices. The physicists report on this discovery in the Nov. 5 issue of Science.

Producers of microelectronic devices are pushing the limits of miniaturization with currently available technologies. In order to push beyond these limits, many research efforts are aimed at new fabrication techniques for still smaller electronic components.

NIST physicists have patterned structures by channeling chromium atoms between the peaks in a light wave. As focused by laser light waves, the chromium atoms form tiny parallel rows on a silicon surface.

Each row is approximately 65 nanometers (or 65 billionths of a meter) wide, about one-thousandth of the diameter of a human hair. These rows, visible with a scanning electron microscope, are about 34 nanometers high and 213 nanometers apart.

Although other scientists have used light to focus sodium atoms, the NIST experiment marks the first time this technique has been used to create durable metallic structures.

"It's 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, he says manufacturers might one day use the technique to draw electronic wires only a few atoms wide.

McClelland co-authored the Science paper with Robert Scholten and Robert Celotta, all of NIST's Electron Physics Group, and Eric Palm, now with Florida State University.

Scientists in the Electron Physics Group use a variety of high-powered microscopes to create images of single atoms or clusters of atoms in different shapes and sizes on surfaces. Specially adapted microscopes also allow the scientists to measure these structures' electrical properties.

A goal of this research is to determine the physical laws operating on nanometer-scale objects, explains Celotta, leader of the Electron Physics Group. Such information gives U.S. industry an edge in the quest to create smaller and faster electronic components.

McClelland and colleagues created the chromium nanostructures on a silicon surface using the waves in a laser as channels for the chromium atoms. Lasers, as all forms of light, have characteristic wave oscillations that repeat at regular distances, or wavelengths.

The physicists selected a laser with a wavelength of 425 nanometers and grazed it across a silicon surface in a vacuum chamber. They then released a stream of chromium atoms to flow through the laser beam toward the surface. The atoms tumble down the peaks in the laser wave and stick onto the silicon surface. In this way, it is possible to rapidly make a well-ordered array of lines covering a relatively large area.

The next stage in this research will be to attempt to make arbitrary patterns, such as dots, curves or more complex shapes, that would be of practical use in microelectronic devices. This could potentially be done by using two perpendicular lasers to funnel the atoms onto spots rather than in lines.

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.