Researchers at Northwestern University and the University of Oxford say that relatively simple methods of explaining chemical bond mechanisms typically taught at undergraduate levels turns out to be an accurate way to understand the arrangement of atoms on a oxide’s surface.
“For a long time we have not understood oxide surfaces,” said Laurence Marks, professor of materials science and engineering in the McCormick School of Engineering and Applied Science at Northwestern. “We only have had relatively simple models constructed from crystal planes of the bulk structure, and these have not enabled us to predict where the atoms should be on a surface.
“Now we have something that seems to work,” Marks said. “It’s the bond-valence-sum method, which has been used for many years to understand bulk materials. The way to understand oxide surfaces turns out to be to look at the bonding patterns and how the atoms are arranged and then to follow this method.”
These findings are published in Nature Materials.
According to a news release, NU graduate student James Enterkin matched the electron diffraction patterns from a strontium titanate surface with the patterns with scanning-tunneling microscopy images obtained by Bruce Russell at Oxford. Enterkin then combined these with density functional calculations and bond-valence sums, showing that those that had bonding similar to that found in bulk oxides were those with the lowest energy.
Ulrike Diebold, an expert in the investigation of metal oxide surfaces at the Institute of Applied Physics in Vienna, Austria, commented on the significance of this research in a separate article in Nature Materials. She writes, “This simple and intuitive, yet powerful concept [the bond-valence-sum method] is widely used to analyze and predict structures in inorganic chemistry. Its successful description of the surface reconstruction of SrTiO3 (110) shows that this approach could be relevant for similar phenomena in other materials.”
NU provides a fun 3D model of the surface of SrTiO3 (110) here. (Be sure to try to manipulated the model with your mouse.)