For 2D boron, it?s all about the base

Posted by sanny111 on November 18th, 2015

(Img Source:5052 aluminum sheet)
Rice University scientists have theoretically determined that the properties of atom-thick sheets of boron depend on where those atoms are deposited. Calculation of the atom-by-atom energies involved in creating a sheet of boron revealed that the metal substrate - the surface upon which two-dimensional (2D) materials are grown in a chemical vapor deposition (CVD) furnace - makes all the difference.

Theoretical physicist Boris Yakobson and his Rice colleagues found in previous work that CVD is probably the best way to make highly conductive 2D boron and that gold or silver might be the best substrates. But their new calculations show it may be possible to guide the formation of 2D boron by tailoring boron-metal interactions. They discovered that whereas copper, a common substrate in graphene growth, might be best for obtaining flat boron, other metals would produce alternate forms of 2D boron. The Rice team's results appear in Angewandte Chemie.

"If you make 2D boron on copper, you get something different than if you made it on gold or silver or nickel," said Zhuhua Zhang, a Rice postdoctoral researcher and lead author of the paper. "In fact, you'd get a different material with each of those substrates."

In CVD, heated gases deposit atoms on a substrate, where they ideally form a desired lattice. When using CVD to fabricate graphene and boron nitride, the atoms settle into flat hexagonal arrays regardless of the substrate. But 2D boron, the researchers found, is the first known material that could vary its structure based on interactions with the substrate.

Perfectly flat boron would be a grid of triangles with occasional hexagons where atoms are missing. The researchers ran calculations on more than 300 boron-metal combinations, finding that the pattern of atoms on a copper surface and the strength of their interactions would help keep the boron flat. A nickel substrate would work nearly as well, they found.

On gold and silver, however, they determined that weak atomic interactions would lead the boron to buckle. In an extension, they theorized that naturally-forming, 12-atom icosahedrons of boron would assemble into interconnected sheets on copper and nickel, if the boron supply were high enough.

One remaining downside to 2D boron is that, unlike graphene, it will remain difficult to separate from its substrate, which is necessary for its use in applications. But that strong adhesion may have a side benefit. Further calculations suggested boron on gold or nickel may rival platinum as a catalyst for hydrogen evolution reactions in applications like fuel cells.

"In 2007 we predicted the possibility of pure boron fullerenes," Yakobson said. "Seven years later, the first one was observed in a laboratory. This time, with the enormous attention researchers are giving to 2D materials, I'd hope some lab around the world will make 2D boron much sooner."

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