Salt - A dash of salt can simplify the creation of two-dimensional materials

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Salt - A dash of salt can simplify the creation of two-dimensional materials

Post by Cr6 on Sat Apr 21, 2018 5:09 am

Found this intriguing in light of Mathis' "Salt" paper. This is the one that made me a "Believer"!  Cool
NEW PAPER, 1/6/2014. Salt is not What We Thought, and molecular bonding isn't, either.
http://milesmathis.com/salt.pdf

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A dash of salt can simplify the creation of two-dimensional materials, and thanks to Rice University scientists, the reason is becoming clear.


https://phys.org/news/2018-04-scientists-salt-lowers-reaction-temperatures.html#nRlv (more at link...)

Boris Yakobson, a Rice professor of materials science and nanoengineering and of chemistry, was the go-to expert when a group of labs in Singapore, China, Japan and Taiwan used salt to make a "library" of 2-D materials that combined transition metals and chalcogens.

These compounds could lead to smaller and faster transistors, photovoltaics, sensors and catalysts, according to the researchers.

Through first-principle molecular dynamics simulations and accurate energy computations, Yakobson and his colleagues determined that salt reduces the temperature at which some elements interact in a chemical vapor deposition (CVD) furnace. That makes it easier to form atom-thick layers similar to graphene but with the potential to customize their chemical composition for specific layer-material and accordingly electrical, optical, catalytic and other useful properties.

The research team including Yakobson and Rice postdoctoral researcher Yu Xie and graduate student Jincheng Lei reported its results this week in Nature.

The team led by Zheng Liu of Nanyang Technological University in Singapore used its seasoned technique with CVD to create 47 compounds of metal chalcogenides (which contain a chalcogenand an electropositive metal). Most of the new compounds had two ingredients, but some were alloys of three, four and even five. Many of the materials had been imagined and even coveted, Yakobson said, but never made.

In the CVD process, atoms excited by temperatures—in this case between 600 and 850 degrees Celsius (1,112 and 1,562 degrees Fahrenheit)—form a gas and ultimately settle on a substrate, linking to atoms of complementary chemistry to form monolayer crystals.
A molecular dynamics simulation by Rice University scientists shows a layer of salt and molybdenum oxide mixing together to form molybdenum oxychloride. The atoms are oxygen (red), sodium (yellow), chlorine (green) and molybdenum (purple). Credit: Yakobson Group

Researchers already suspected salt could facilitate the process, Yakobson said. Liu came to him to request a molecular model analysis to learn why salt made it easier to melt metals with chalcogens and get them to react. That would help them learn if it might work within the broader palette of the periodic table.

"They did impressively broad work to make a lot of new materials and to characterize each of them comprehensively," Yakobson said. "From our theoretical perspective, the novelty in this study is that we now have a better understanding of why adding plain salt lowers the melting point for these metal-oxides and especially reduces the energy barriers of the intermediates on the way to transforming them into chalcogenides."

Whether in the form of common table salt (sodium chloride) or more exotic compounds like potassium iodide, salt was found to allow chemical reactions by lowering the energetic barrier that otherwise prevents molecules from interacting at anything less than ultrahigh temperatures, Yakobson said.

"I call it a 'salt assault,'" he said. "This is important for synthesis. First, when you try to combine solid particles, no matter how small they are, they still have limited contact with each other. But if you melt them, with salt's help, you get a lot of contact on the molecular level.

"Second, salt reduces the sublimation point, where a solid undergoes a phase transformation to gas. It means more of the material's component molecules jump into the gas phase. That's good for general transport and contact issues and helps the reaction overall."

Cr6
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