LeHigh Research Yields Hardest, Thinnest Coatings

Lehigh University researchers Dr. Nicholas Strandwitz and Dr. Brandon Krick, who are on the faculty of Lehigh’s P.C. Rossin College of Engineering and Applied Science and affiliated with the university’s Institute for Functional Materials and Devices (I-FMD), believe they’ve discovered the hardest, thinnest, most wear-resistant coatings yet — plasma-enhanced atomic layer-deposited titanium and vanadium nitrides.

“This new material beats commercial coatings by orders of magnitude in wear performance,” says Krick.

In 2018, the National Science Foundation (NSF) granted Strandwitz, an assistant professor of materials science and engineering, and Krick, an assistant professor of mechanical engineering and mechanics, a Grant Opportunities for Academic Liaison with Industry (GOALI) award to work with an industry partner to study what exactly makes these nitride films so good.

A GOALI award supports shared research interests between academic and industrial partners. It’s meant to further knowledge that could lead to breakthroughs in critical industrial needs. The award lasts three years and totals over $500,000. Funding for the nitrides project began Jan. 1, 2019.

Titanium and vanadium nitride films are already known to be extremely hard and wear-resistant. Traditionally, they’re grown by sputtering, pulsed laser deposition or chemical vapor deposition methods. In a first, the group’s collaborators at Veeco/CNT grew their nitride films using plasma-enhanced atomic layer deposition (PE-ALD). Veeco/CNT is a supplier of ALD systems based in Waltham, Massachusetts.

“In atomic layer deposition, you’re building one layer of atoms at a time,” says Strandwitz. “It’s a technique that’s already used in microelectronics, like on those in your phone, where you might need a film that is exactly three nanometers thick. If the film is four or two nanometers thick, your transistor switch won’t work. And you have a few billion transistors in your phone.”

The technique involves a vapor process that uses two or more self-limiting chemical reactions to grow one layer of film at a time. In this case, a titanium precursor enters the system’s chamber as a gas, reacts with the substrate and forms a monolayer. Excess titanium gets sucked out, then the second gas (nitrogen plasma) gets pumped in. It bonds with the titanium and forms a second monolayer. This two-step process is repeated until the film reaches the desired thickness.

The technique is enhanced by a plasma generator, hence the PE in the PE-ALD.

“For growing nitrides, you need a lot of thermal energy, like 800 Celsius,” says Strandwitz. “Or, you need a plasma to make the nitrogen more reactive. Generating plasma means we’re knocking electrons off the nitrogen molecules as they’re flying around in the gas, making the nitrogen more reactive so it will bond to the surface and become part of the film. If you just float nitrogen gas through there, nothing would happen because the N2 molecule is super stable. So with plasma, we can grow these films at 50°C, just slightly above room temperature.”

To read the full article, visit https://engineering.lehigh.edu/news/article/interdisciplinary-collaboration-yields-hardest-thinnest-coatings-yet-discovered

Story by Christine Fennessy, staff writer, P.C. Rossin College of Engineering and Applied Science.