2D Material May Be Too Brittle for Flexible Electronics, Optical Use


A


team of researchers at Rice University (Houston) has found that an atom-thick material under consideration for use in flexible electronics and optical devices may be more brittle than previously believed.


The team led by Rice materials scientist Jun Lou tested the


tensile strength of 2D semiconducting molybdenum diselenide and discovered that flaws as small as one missing atom can initiate catastrophic cracking under strain. A link to the report in the journal Advanced Materials is available at http://onlineli- brary.wiley.com/doi/10.1002/adma.201604201/abstract. “It turns out not all 2D crystals are equal,” said Lou, a


Rice professor of materials science and nanoengineering. “Graphene is a lot more robust compared with some of the others we’re dealing with right now, like this molybdenum diselenide. We think it has something to do with defects inherent to these materials.”


The finding may cause industry to look more carefully at


the properties of 2D materials before incorporating them in new technologies, he said.


These defects could be as small as a single atom that leaves a vacancy in the crystalline structure, he said. “It’s very hard to detect them,” he said. “Even if a cluster of vacancies makes a bigger hole, it’s difficult to find using any technique. It might be possible to see them with a transmission electron microscope, but that would be so labor-intensive that it wouldn’t be useful.” Molybdenum diselenide is a dichalcogenide, a 2D semiconducting material that appears as a graphene-like hexagonal array from above but is actually a sandwich of metallic atoms between two layers of chalcogen atoms, in this case, selenium. Molybdenum diselenide is being con- sidered for use as transistors and in next-generation solar cells, photodetectors and catalysts as well as electronic and optical devices.


Lou and colleagues measured the material’s elastic modu- lus, the amount of stretching a material can handle and still


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