Scanning electron microscopy for various diamond materials. Source: Materials 10, no. 11: 1305How do you surpass the hardness and resiliency of nature’s hardest substance? Look to materials that don’t exist in nature.

That’s the approach taken by physicists at the University of Alabama at Birmingham (UAB), who have turned to the “fourth state” of matter: plasma. An ionized gaseous state, plasma doesn’t exist naturally on Earth — but it can be created by heating neutral gases. By performing the plasma-creation process via microwave heating in the ultra-low-pressure environment of a vacuum chamber — equivalent to the atmosphere 14 miles above the Earth’s surface — a team led by UAB Prof. Yogesh Vohra has made the vapor deposit a thin film of nature’s hardest substance: diamond.

Diamond films have numerous applications, including coatings for extending the durability of artificial joints or the sharpness of cutting tools, sensors for extreme environments (diamonds can survive heat up to 1,100 degrees Fahrenheit before starting to burn) and the creation of new, super-hard materials.

The researchers also discovered that adding minute amounts of boron during the process would change the material properties of the diamond — forcing an abrupt increase from the nanometer scale (60 nanometers for hydrogen/methane/nitrogen) to the microcrystalline scale (800 nanometers with the addition of boron). This allows control over diamond grain film size.

The added boron, additionally, has the power to change the diamond film from a nonconductor to a semiconductor — allowing a new control for electrical properties.

The findings represent the first step in a five-year effort to create novel compounds surpassing diamonds in heat resistance and nearly rivaling them in hardness.

Over the next five years, Vohra and colleagues plan to probe the same principles for making thin films of boron carbides, boron nitrides and carbon-boron-nitrogen compounds. The group is supported by a five-year, $20 million National Science Foundation (NSF) award to create new materials and improve technologies.