#nondestructive testing

Fast, non-destructive test for two-dimensional materials

By now it is well understood that thinning a material down to a single atom thickness can dramatically change that material's physical properties. Graphene, the best known 2D material, has unparalleled strength and electrical conductivity, unlike its bulk form as graphite. Researchers have begun to study hundreds of other 2D materials for the purposes of electronics, sensing, early cancer diagnosis, water desalination and a host of other applications. Now, a team of Penn State researchers in the Department of Physics and the Center for Two-Dimensional and Layered Materials (2DLM) has developed a fast, nondestructive optical method for analyzing defects in two-dimensional materials.

"In the semiconductor industry, for example, defects are important because you can control properties through defects," said Mauricio Terrones, professor of physics, materials science and engineering and chemistry, Penn State. "This is known as defect engineering. Industry knows how to control defects and which types are good for devices."

To really understand what is going on in a 2D material like tungsten disulfide, which has a single atom-thick layer of tungsten sandwiched between two atomic layers of sulfur, would require a high-power electron microscope capable of seeing individual atoms and the holes, called vacancies, where the atoms are missing.

Green laser light probes metals for hidden damage

Imagine being able to check the structural integrity of an airplane, ship or bridge, without having to dismantle it or remove any material for testing, which could further compromise the structure. That's the promise of a new laser-based technique that chemists are developing to reveal hidden damage in metals.

The researchers will present their work today at the 253rd National Meeting & Exposition of the American Chemical Society (ACS).

"Metals are often subjected to mechanical stress or fatigue that can weaken them structurally, but you can't tell that just by looking at them," James E. Patterson, Ph.D., says.

One real-world example is a U.S. Air Force plane that was unintentionally turned upside down in flight, a feat it wasn't designed for. The maneuver exceeded the specifications for the plane's stress tolerance, Patterson says, but there was no way to know if the inversion had actually damaged components enough to cause the plane to crash during a future flight. So the entire multimillion-dollar plane had to be scrapped.

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