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Published on November 15th, 2016 | By: April Gocha, PhD

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Gallium nitride has wear resistance that approaches that of diamond

Published on November 15th, 2016 | By: April Gocha, PhD

[Image above] Credit: Christa Neu; Lehigh University

 

 

Last year I reported on how wonder-material gallium nitride was attempting to get into a scuffle with the long-reigning champion of electronic materials, silicon.

 

At that time, MIT spinout company Cambridge Electronics had just announced some new gallium nitride offerings to its power-saving product line, which includes gallium nitride transistors and power electronic circuits. The company was developing gallium power electronics—like the boxy power pack on your laptop charging cord—that save energy along with space.

 

Although it looks like Cambridge Electronics still isn’t commercially selling gallium nitride power packs, which are one-third the size of conventional power packs, gallium nitride is still going places in the electronics world.

 

That’s because the material has electronic and optoelectronic properties that make it a contending semiconductor for a host of electronic applications, including LEDs, high-temperature transistors, sensors, and biocompatible electronic implants.

 

But how well does gallium nitride stand up to wear?

 

Researchers at Lehigh University have now filled that surprisingly void knowledge gap when it comes to gallium nitride’s tribological properties. The researchers report that, in addition to gallium nitride’s checklist of other useful properties, the material has a wear rate that approaches that of diamonds—which could open the material’s foray into even more diverse applications.

 

“Our group is the first to investigate the wear performance of GaN,” Guosong Zeng, a Ph.D. candidate in mechanical engineering at Lehigh and first author of the new paper describing the work, says in a Lehigh news release. “We have found that its wear rate approaches that of diamonds, the hardest material known.”

 

Using a custom microtribometer, Zeng and a group of Lehigh scientists performed dry sliding wear experiments on gallium nitride and measured a wear rate of 10-7–10-9 cubic millimeters per Newton–meters (mm3/Nm). Diamond has a wear rate of 10-9–10-10 mm3/Nm.

 

According to the scientists, although similar wear experiments usually measure results after ~1,000 sliding cycles, they had to increase testing to 30,000 cycles to generate measureable wear on gallium nitride.

 

But such wear rates were not uniform, the authors report—gallium nitride has a wear rate that ranges depending on a host of variables, including environmental conditions, crystallographic properties, and humidity.

 

“The first time we observed the ultralow wear rate of GaN was in winter,” Zeng says in the release. “These results could not be replicated in summer, when the material’s wear rate increased by two orders of magnitude.”

 

In a controlled environment in the laboratory, the team measured similar fluctuations in wear rate depending on humidity—increasing humidity during testing also increased the material’s wear rate.

 

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A profilometric scan shows the wear scar left on a GaN coating by a custom microtribometer. Credit: Guosong Zeng; Lehigh University

 

Even despite the variation, however, the surprisingly high wear rate of this already useful material opens up even further avenues of applications for gallium nitride.

 

“The wear resistance of GaN gives us the opportunity to replace the multiple layers in a typical semiconductor device with one layer made of a material that has excellent optical and electrical properties and is wear-resistant as well,” Nelson Tansu, one of the paper’s authors and the Daniel E. and Patricia M. Smith Endowed Chair Professor in the electrical and computer engineering department and director of the Center for Photonics and Nanoelectronics at Lehigh, says in the release.

 

“Using GaN, you can build an entire device in one platform without multiple layers of technologies,” Tansu continues. “You can integrate electronics, light sensors, and light emitters and still have a mechanically robust device. This will open up a new paradigm for designing devices. And because GaN can be made very thin and still strong, it will accelerate the move to flexible electronics.”

 

Plus, gallium nitride’s radiation hardness also means that it could be particularly useful in space applications, for example.

 

According to the release, the team is next exploring gallium nitride’s wear evolution by varying slide distance and cycle number of the wear tests, and then measuring the elemental composition and atomic arrangement of worn versus unworn surfaces of the material.

 

“This is a very new experiment,” Zeng says in the release. “It will enable us to see dynamic surface chemistry by watching the chemical reaction that results when you apply shear, tensile, or compressive pressure to the surface of GaN.”

 

The paper, published in Applied Physics Letters, is “Ultralow wear of gallium nitride” (DOI: 10.1063/1.4960375).

 


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