ETRI Develops Nanosheets by Using Sodium Instead of Lithium

Jan 10, 2018

A technology that is able to mass-produce thin nanosheets for 2D semiconductors has been developed. It is expected that this technolog will greatly improve production yield of 2D semiconductors and next-generation electronic devices.
Electronics and Telecommunications Research Institute (ETRI, Director Lee Sang-hoon) made an announcement that a research team led by Yoon Sun-jin, Ph.D., of ICT Materials Research Group developed a technology that is able to manufacture low-cost and eco-friendly nanosheets that do not change its properties by using sodium and water.
Nanosheet is a transparent thin film that is used for manufacturing semiconductors and it is used to materialize next-generation electronic devices that are needed to reduce thickness of semiconductors.
Nanosheet is manufactured by utilizing solution process. Current solution process adds raw material of nanosheet into organic solvent that has lithium ions and apply ultrasonic wave. Once lithium ions weaken binding force of each layer of this raw material of nanosheet by permeating through it, vibration caused by ultrasonic wave causes separation.
However this process creates various elements that may pollute environment. Fact that properties of nanosheets change due to oxidation is another weakness. It is extremely difficult to recover properties of 2D materials such as nanosheets once they change their properties. Although many researches took place in order to develop solution process using water, it was difficult to do so since lithium reacts violently with water.

Yoon Sun-jin (middle), Ph.D., along with researchers from ETRI are observing 2D nanosheet film coated on top of polymer film <Yoon Sun-jin (middle), Ph.D., along with researchers from ETRI are observing 2D nanosheet film coated on top of polymer film>

Research team solved such problem by using sodium instead of lithium. Just like lithium, sodium weakens binding force of this raw material of nanosheet. As a result, sodium makes use of water possible which then prevents high cost, environment pollution, and changes in properties of nanosheets that are caused by using organic solvent.
Semiconductor layers for memory devices can be made with this technology. By coating mixture of polymer with ‘water dispersion, which has nanosheets floating on water, on top of substrate, it is easy to make semiconductor layers. With this method, research team succeeded in creating memory devices based on tungsten disulfide and molybdenum disulfide nanosheets and confirming their operations.
It is expected that this technology will be used in various fields such as flexible and transparent electronic devices, high-capacity storage batteries for electric vehicles, and secondary batteries.
“We have developed this technology in order to create 2D nanosheets safer and cheaper.” said Yoon Sun-jin, Ph.D. “We are planning to use this technology for developing various memory devices and researching properties of 2D semiconductor materials.”
Staff Reporter Kim, Youngjoon |

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