Scanning tunneling microscopy gives Salmeron an atom-by-atom view of materials.

Not many people can see individual atoms. And even fewer people get to manipulate them using state of the art tools. Miquel Salmeron is one of these lucky few.

“My research focuses on trying to understand matter atom by atom, as well as how to manipulate matter one atom at a time,” says Salmeron, of Berkeley Lab’s Materials Sciences Division. “It’s materials science, only on a scale that involves a very small number of atoms.”

His quest to learn how atoms behave on metal surfaces and other materials began years ago. “As a kid, I always liked science,” Salmeron says. Born in Spain, Salmeron received an undergraduate degree in physics from the University of Barcelona, and a doctorate in physics from the Universidad Autónoma de Madrid. He then came to Berkeley Lab in 1984 to use a new kind of microscope that gives scientists a ringside seat to the secret world of atoms.

Called a scanning tunneling microscope, the device detects individual atoms using a probe that tapers down to a point only a single atom across. This atom-tipped probe skims across a conductive surface, always maintaining the same current between it and the surface atoms. If the probe moves over an atom with an electron cloud that facilitates electronic conduction, it rises up. If it moves over an atom with an electron cloud that does not favor conduction, the probe drops down. These irregularities are fed into a computer that produces an atom-by-atom contour map of the surface.

Under the scanning tunneling microscope, vacancies appear as red bumps in the image of a palladium surface. The two three-vacancy clusters, one located near the top and one on the right, can facilitate hydrogen adsorption.

Back in 1984, the microscope was so new that scientists were only beginning to learn how it could help them explore materials at the atomic level.

“When I came to Berkeley Lab, my proposed research topic was the application of scanning tunneling microscopes to the study of surface phenomena. I came here with the idea of developing the instrumentation required to conduct this research,” Salmeron says. “And the more I pursued the research, the more manipulating matter at the atomic scale caught my imagination.”

For Salmeron, manipulation means just that: using the tiny tip of the microscope almost like a pool cue. He can move atoms from one place to another, make them rotate or spin, and even break molecules into their constituent atoms like the opening shot of a pool game.

“Sometimes we watch atoms move, sometimes we do the moving ourselves,” Salmeron says.

In addition to manipulating matter at the atomic scale, Salmeron’s research group studies friction and adhesion in nanometer dimensions, which is one billionth of a meter, or thousands of times thinner than a human hair. He also studies the nanometer-scale structure of liquid films during wetting and corrosion, and the catalytic and chemical properties of surfaces.