Every other week, Ricardo Raudales, a Ph.D. candidate at Stony Brook University’s Department of Neurobiology and Behavior, will take a look at Stony Brook-related science and research news.
Science, like much of Stony Brook’s campus these days, seems to always be under construction. Yet this month, old gray buildings are not the only things being dismantled.
In a recent study in Physical Review Letters, professor Artem Oganov and his colleagues found that the published surface structure for α-boron was flawed. The study was led by Dr. Xiang-Feng Zhou, who works in the Oganov lab at Stony Brook. The incorrect model had come from a Swiss group and indicated that boron, a light element, could display behavior similar to topological insulators, which are compounds of heavy elements.
Topological insulators are a recently discovered class of materials that on their interior act as insulators, but have a surface that can conduct electrons.
“On the surface of materials, very unexpected things happen,” Oganov said. “The rules of chemistry were formulated under normal conditions, and when you create unusual conditions you need to alter the rules to understand
what is happening.”
“When you take a crystal surface, for example, the atoms near the surface have many of their bonds cut off,” Oganov said. “To compensate for the lost bonds, atoms invent very unusual solutions, and you end up with extraordinary chemistry.”
Although the element boron is much lighter than elements making up topological insulators, this fact alone was not enough to exclude it. In order to show boron could not readily conduct electrons, the team had to figure out the surface structure, which was no trivial task.
To model the surface of α-boron the team relied on USPEX (Universal Structure Predictor: Evolutionary Xtallography). The method, developed by the Oganov lab in 2005, is capable of efficiently predicting structures of crystals, surfaces, polymers and nanoparticles and is used by over 2,000 researchers worldwide.
“What is most exciting is to see that the same basic underlying code can be applied to a diverse set of very complex structures,” Oganov said. “This shows the power of the method.”
And while α-boron does not seem to behave like a topological insulator, several interesting aspects clue in how it might have other uses.
“Interestingly, the surface of boron has strong resemblance to its high-pressure phases,” Oganov said. “It may be possible to grow this denser phase on the surface of boron, although we don’t yet now how to do it. These phases could have applications in electronics, and as superhard materials.”
The team will continue to use USPEX to look at a host of different surfaces, many with unusual chemistry and a wide range of applications.
“We could try to understand why nickel irritates human skin, which we think has something to do with the surface of nickel,” Oganov said. “No one really understands how it works.”
“Another interesting problem is why iron rusts but aluminum does not,” Oganov said. “By studying these surfaces we think we will understand rusting better and maybe learn how to prevent it.”
By better understanding surfaces at their atomic level, it might be possible to begin understanding questions that have stumped scientists in different fields.
Ultimately, the group is attempting to answer a very basic problem, which has so far yielded quite unexpected results.
In the meantime, Oganov had some advice for budding Stony Brook scientists.
“Whatever field you become interested in, work hard to read and learn everything you can about it,” Oganov said. “If for a second you ever think you have become an expert, you will soon realize how little it is you actually understand. This is a very stimulating feeling that should keep you moving forward.”