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An X-ray peek into electrochemistry.

An X-ray peek into electrochemistry

Most techniques for studying surfaces require that experiments be conducted in a vacuum. But the electrochemical deposition of one metal onto the surface of another metal is a wet process, in which the layer of liquid covering the solid electrode is an integral part of the system. To provide a way of studying such immersed surfaces, Owen R. Melroy and his colleagues at the IBM Almaden Research Center in San Jose, Calif., use high-intensity X-rays, generated by accelerated electrons, to penetrate the liquid and provide information about the underlying surface.

In their first experiments, Melroy and his team looked at the structure of metal layers, only one atom thick, electrochemically deposited on well-defined surfaces. In the case of lead deposited on silver, the researchers discovered that the larger lead atoms do not line up with the silver atoms below. But as the applied voltage increases, the lead atoms are squeezed together about 2.4 percent -- an effect never before seen in a two-dimensional metal layer. As a result, the spacing between rows of lead atoms in a two-dimensional "monolayer" is quite different from that found in bulk lead, which probably influences the way in which electrochemically deposited lead grows into the bulk material.

The researchers have also found that atoms of silver deposited on gold enter specific sites, filling the deep depressions formed by groups of three neighboring gold atoms. Moreover, negative ions found in the surrounding liquid, or electrolyte, end up occupying well-defined sites on the silver monolayer. Such ordered structures in the electrolyte were quite unexpected, Melroy says. "The first layer is better defined than people had thought."
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Author:Peterson, Ivars
Publication:Science News
Date:Feb 4, 1989
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