Diamond is the hardest material known, because its carbon atoms form very short covalent bonds, according to co-author Richard B. Kaner, UCLA professor of inorganic chemistry and materials science and engineering. Most of the diamond used in the world is actually synthetic and very expensive. Diamond powder is used for oil drills and machines that build roads and cut holes in mountains. Diamond cannot be used, however, to cut steel without ruining the diamond blade.

Cubic boron nitride is a diamond substitute used to cut steel; it is made synthetically under very high-temperature, high-pressure conditions, and is even more expensive than diamond, Kaner said.

There are two ways to make super-hard materials that are "ultra-incompressible,” meaning they are resistant to shape deformation, which is a necessary condition for hardness: One is to imitate diamond by using carbon and combining it with boron or nitrogen to maintain short bonds; the other is to look for metals that are already incompressible and try to make them hard, said Kaner. He and his colleagues are developing the second approach.