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Science snapshots: New nitrides, artificial photosynthesis, and TMDC semiconductors

DOE/Lawrence Berkeley National Laboratory

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IMAGE: A study led by Wenhao Sun of Berkeley Lab features a large, interactive stability map of the ternary nitrides, highlighting nitride compositions where experimental discovery is promising in blue. view more 

Credit: Wenhao Sun/Berkeley Lab

Groundbreaking Study Maps Out Paths to New Nitride Materials

Formed by elements combining with nitrogen, nitrides can possess unique properties with potential applications from semiconductors to industrial coatings. But before nitrides can be put to use, they first must be discovered - and the odds of finding them in nature are slim.

Now, your chances of discovering new nitrides just got better with a groundbreaking Nature Materials study led by Berkeley Lab in close collaboration with the National Renewable Energy Laboratory (NREL) and a number of other institutions.

The study features a large, interactive stability map of the ternary nitrides, highlighting nitride compositions where experimental discovery is promising in blue. So far, the map has yielded the prediction of 244 new stable ternary nitride compounds.

"For ancient explorers, sailing into the unknown was a very risky endeavor, and in the same way, exploration of new chemical spaces can also be risky," explained Wenhao Sun, lead author of the paper and staff scientist at Berkeley Lab. "If you don't find a new material where you are looking, it can be a big waste of time and effort. Our chemical map can help to guide the exploratory synthesis of nitrides, just as maps helped to guide explorers, allowing them to navigate better."

Read the full release from NREL here .

Here Comes the Sun: A New Framework for Artificial Photosynthesis
By THERESA DUQUE

Scientists have long sought to mimic the process by which plants make their own fuel using sunlight, carbon dioxide, and water through artificial photosynthesis devices, but how exactly substances called catalysts work to generate renewable fuel remains a mystery.

Now, a PNAS study led by Berkeley Lab - and supported by state-of-the-art materials characterization at the Joint Center for Artificial Photosynthesis, powerful X-ray spectroscopy techniques at the Advanced Light Source, and superfast calculations performed at the National Energy Research Scientific Computing Center - has uncovered new insight into how to better control cobalt oxide, one of the most promising catalysts for artificial photosynthesis.

When molecules of cobalt oxide cubane, so named for its eight atoms forming a cube, are in solution, the catalytic units eventually collide into one another and react, and thus deactivate.

To hold the catalysts in place, and prevent these collisions, the researchers used a metal-organic framework as a scaffold. The technique is similar to how tetramanganese, a metal-oxygen catalyst in natural photosynthesis, protects itself from self-destruction by hiding in a protein pocket.

"Our study provides a clear, conceptual blueprint for engineering the next generation of energy-converting catalysts," said Don Tilley, senior faculty scientist in Berkeley Lab's Chemical Sciences Division (and a co-corresponding author of the study.

You Don't Have to Be Perfect for TMDCs to Shine Bright
By Theresa Duque

Atomically thin semiconductors known as TMDCs (transition metal dichalcogenides) could lead to devices that operate more efficiently than conventional semiconductors in light-emitting diodes, lasers, and solar cells. But these materials are hard to make without defects that dampen their performance.

Now, a study led by senior faculty scientist Ali Javey of Berkeley Lab - and published in the journal Science - has revealed that TMDCs' efficiency is diminished not by defects, but by the extra free electrons.

In a previous study, the researchers used chemical treatments to improve TMDCs' photoluminescence quantum yield, a ratio describing the amount of light generated by the material versus the amount of light absorbed. "But that's not ideal because the treatments are unstable in subsequent processing," said co-first author and graduate student researcher Shiekh Zia Uddin.

For the current study, the researchers discovered that when they applied an electrical voltage instead of a chemical treatment to TMDCs made of molybdenum disulfide and tungsten disulfide, the extra free electrons are removed from the material, resulting in a quantum yield of 100%.

"A quantum yield of 100% is unprecedented in inorganic TMDCs, said Der-Hsien Lien, postdoctoral researcher and co-first author. "This is an exciting result that shows it might be much easier and cheaper than previously thought to make useful optoelectronic devices from these materials."

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Media contact: Theresa Duque, tnduque@lbl.gov, 510-495-2418

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