Web Content Display
Plasma-enhanced titanium and vanadium nitrides form hardest thin films ever
March 12, 2019
Source: ASM International
Lehigh University, Pa., announces that its researchers have developed plasma-enhanced atomic layer deposited titanium and vanadium nitrides that are said to be harder than commercial coatings “by orders of magnitude.”
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 Lehigh group's collaborators at Veeco/CNT grew their nitride films via plasma-enhanced atomic layer deposition, or PE-ALD. Veeco/CNT is a leading supplier of ALD systems based in Waltham, Massachusetts.
The technique involves a vapor process in which two or more self-limiting chemical reactions 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 is pumped out, then the second gas, nitrogen plasma, is pumped in. It bonds with the titanium, and forms a second monolayer. This two-step process is repeated until the film reaches the specified 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°C," says Dr. Nicholas 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 nitrogen molecule is super stable. So with plasma, we can grow these films at 50°C, just slightly above room temperature."
The ability to grow films at that temperature is key. Too-high temps can melt sensitive materials like plastic and aluminum and make even fairly stable metals more brittle. "Having the capability to deposit at low temperatures opens up more materials that you can deposit on," says Dr. Strandwitz.
Materials Processing and Treatment | Coating
Materials Processing and Treatment | Surface Engineering
Materials Processing and Treatment | Thermal Spray Technology
Metals and Alloys | Aluminum
Nonmetallic Engineering Materials | Ceramics