This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Many chemical processes that sustain modern society depend on molecules binding to metal surfaces. The production of synthetic fertilizer, for example, relies on heterogeneous catalysis, in which gases react on the surface of a solid catalyst.
Yet, until now, an important question has remained unresolved: How much of the metal surface actually participates in determining the strength of a chemical bond on the surface? A research team from the Max Planck Institute for Multidisciplinary Sciences (MPI-NAT) in Göttingen, Germany, and the Center for Quantum Nanoscience (QNS) within the Institute for Basic Science (IBS) in Seoul, South Korea, has shown that bonding at metal surfaces extends beyond the atoms immediately surrounding the binding molecule. Using precisely structured platinum surfaces, the researchers found that the strength of a molecule's bond at an atomic step, a site where molecules often bind particularly strongly, can change when another step is moved as far as approximately 10 nanometers (that is, 0.00001 millimeters) away.
The effect depended on the type of molecule and altered adsorption energies, a common indicator of the strength of binding, by up to 0.2 electron volts. The findings were published in Science. "Chemical bonding is often pictured as a local interaction," says Dmitriy Borodin, research group leader at QNS.
He earned his Ph.D. at the MPI-NAT in Alec Wodtke's Department of Dynamics at Surfaces, where he co-developed the measurement methods needed for this study. "A molecule lands on a surface and forms a bond with one or a few nearby atoms. For many purposes, this local picture works well." Bonding to a metal, however, is fundamentally different from bonding between isolated atoms or molecules.
The electrons in a metal occupy electronic states that extend throughout the solid. When a localized molecular orbital interacts with these delocalized metal states, the electronic structure involved in the bond can extend far beyond the adsorption site. Borodin explains, "An analogy is the difference between pressing a finger into sand and pressing it against a stretched drum skin.
In sand, the disturbance remains largely confined to the grains being touched. On a drum skin, the deformation spreads over a much larger area because the surface is mechanically connected. In a metal, it is the delocalized electronic structure that provides this connection." Long-range electronic disturbances around atoms and molecules on metal surfaces have been observed before, particularly in low-temperature studies.
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