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'Sodium-scooter' delivers

January 28, 2018

Korean food delivery system is renowned to be fast and efficient. Scooters speed through the city to bring orders timely to your doorstep. Researchers from the Center for Integrated Nanostructure Physics, within the Institute for Basic Science (IBS, South Korea) have developed a low-temperature reaction, where a "chemical scooter delivery" can be used as a metaphor. A "sodium-scooter", namely Na2Te, transports tellurium to molybdenum disulfide (MoS2) and tungsten disulfide (WS2) monolayers. With the help of the scooter, sulfur atoms were replaced with tellurium. The process occurs at 525 °C, about 300 °C lower than previously achievable. This study, published in Nature Communications, is expected to facilitate the exploration of new properties in these 2D materials.

"We call it scooter, because it delivers quickly. MoTe2 molecules decompose to molybdenum and tellurium at high temperatures, but the scooter anchors telluride to MoS2 and acts as a catalyst that lowers the activation temperature of the reaction," explains YUN Seok Joon, the first author of the study.

Using this approach, the research team prepared semiconducting molybdenum ditelluride (2H-MoTe2), metallic 1T'-MoTe2, MoS2xTex and WS2xTex alloys. The conversion which began at the edges and grain boundaries of MoS2, was complete. 2H-MoTe2 formed near the edge and is favored at low temperatures, while 1T'-MoTe2 at high temperatures. In this method, the team could produce a diode with 2H-MoTe2 on the edge and 2H-MoS2 on the inner part. The resulting materials had different bandgap (1.1 eV), and higher degree of valley polarization (~37%) than MoS2.
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Institute for Basic Science

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