For the first time in the long and vaunted history of scanning electron microscopy, the unique atomic structure at the surface of a material has been resolved. This landmark in scientific imaging was made possible by a new analytic technique developed by a multi-institutional team of researchers, including scientists from the Molecular Foundry.
“We’ve developed a reasonably direct method for determining the atomic structure of a surface that also addresses the very challenging problem of buried interfaces,” says Jim Ciston, a staff scientist at the Foundry's National Center for Electron Microscopy (NCEM). “Although surface atoms represent a minuscule fraction of the total number of atoms in a material, these atoms drive a large portion of the material’s chemical interactions with its environment.”
Scanning electron microscopy (SEM) is an excellent technique for studying surfaces but typically provides information only about topology at nanoscale resolution. A highly promising new version of scanning electron microscopy, called “high-resolution scanning electron microscopy,” or HRSEM, extends this resolution to the atomic scale and provides information on both surface and bulk atoms simultaneously, retaining much of the surface sensitivity of traditional SEM through secondary electrons.
“Even though powerful instruments have been available for several years, progress in materials science applications has been slow due to an inability to directly interpret the surface and bulk components of HRSEM images independently,” Ciston says. “This difficulty stemmed from the lack of a fully-developed theoretical framework to understand SEM image formation at the atomic scale.” But now, theoretical and modeling aspects of the new imaging technique have now added a sophisticated understanding of what the images mean.