Razors edge

Researchers at Rensselaer Polytechnic Institute have created a razor-like material that is truly on the “cutting edge” of nanotechnology.

The sharp nanometre-scale surface of the magnesium nanomaterial they have produced is vastly different from any other nanomaterial that has been created before using oblique angle deposition, according to lead researcher Gwo-Ching Wang, professor and head of physics, applied physics and astronomy at Rensselaer.

The nearly two-dimensional structure of the material also challenges the traditional idea that oblique angle deposition always creates cylindrical structures like nanorods or nanosprings.

Unlike three-dimensional springs and rods, the so-called "nanoblades" that the researchers have created are extremely thin with very large surface areas. They also are surprisingly spread out for a uniform nanomaterial, with one to two microns between each blade, according to Wang.

The material could be extremely useful for energy storage, particularly hydrogen storage, Wang said. The vast surface area of each nanoblade, coupled with the spaces between each blade, could make them ideal for this application.

The widely used oblique angle vapour deposition fabrication technique builds nanostructures by first vapourising a material - magnesium in this case - and then allowing the vapourised atoms to deposit on a surface at an angle. As the deposition angle changes, the structure of the material deposited on the surface also changes.

When the researchers deposited the magnesium straight onto a surface at zero degrees, the blades resembled a handful of cornflakes - flat, flakey structures overlapping one another. It wasn’t until the deposition angle was increased that the blade-like nature of these new nanomaterials became apparent.

As the magnesium deposition angle was increased, the researchers were surprised that the structures first tilted away from the magnesium vapour source instead of the expected inclination toward the source. The blades then quickly curved upward to form nearly vertical structures resembling nano-scale razorblades.

The blades also become ultra thin. From the side, the nanoblades resemble an overgrown lawn with thin, blade-like spires. At a 75 degree angle, the nanoblades had a thickness of as little as 15 nanometres and a width of a few hundred nanometres.

Researchers at Rensselaer are now looking at ways to coat the magnesium nanoblades with metallic catalysts to trap and store hydrogen.

The researchers monitored the blades as they were growing using a reflection high-energy electron diffraction (RHEED) technique to create a surface pole figure or image. The new technique, created at Rensselaer, is different from other diffraction techniques such as X-rays because it monitors the surface structure of the material as it grows. X-rays and other technologies measure the entire material, from the tip of the new growth straight through the substrate that the material is growing on.