Salt holds key to making several new materials: NTU team

Assistant Professor Liu Zheng (left) and Dr Zhou Jiadong insert a ceramic boat, containing salt mixed with other components used to make transition-metal chalcogenides, into a furnace.
Assistant Professor Liu Zheng (left) and Dr Zhou Jiadong insert a ceramic boat, containing salt mixed with other components used to make transition-metal chalcogenides, into a furnace.PHOTO: NTU

Using salt, researchers from Nanyang Technological University (NTU) have created a new group of materials which can be used in smartphones, semiconductors and hydrogen cars, among other things.

In a study published in Nature Journal on April 19, the authors said that using a more purified and concentrated version of table salt can expedite the production process for transition-metal chalcogenides (TMCs).

They are part of a family of more than 1,000 materials, each with the thickness of a single atom or a few atoms. One of the materials, graphene, has been in the spotlight in recent years.

The semi-metal's flexibility and high electrical conductivity allow it to be used in a wide range of applications, from body armour to solar cells. It has also been used to make smartphones that can bend.

But TMCs can be used in a wider range of applications compared with graphene, said Assistant Professor Liu Zheng of the NTU School of Materials Science and Engineering, and principal investigator of the study.

"TMCs can surpass graphene, due to the varying nature of their conductivity," he said.

The challenge that confronted the researchers was how to make them. TMCs are produced by combining certain metals with elements like sulphur, selenium or tellurium. The metals' high melting points meant that only small quantities of fewer than 10 TMCs could be made after a lengthy and costly production process.

It proved insufficient for mass usage beyond the lab.

But research fellow Zhou Jiadong, who is also co-author of the study, eyed an unconventional solution, having studied how salt lowers the melting point of materials used to make ceramics.

With the addition of salts such as sodium chloride or potassium iodide, the melting point of metals are lowered by up to 1,000 deg C.

This allowed the researchers to produce 35 TMCs new to science.

Prof Liu then reached out to collaborators around the world to expedite different aspects of the research needed to analyse each material, from running computer simulations to testing their practical applications. The process usually takes one to two years to complete for just one material.

The researchers are working with industrial partners such as GlobalFoundries and Aixtron to build prototype semiconductor wafers using these materials. Prof Liu is confident of producing them commercially in the next three to five years.

Tests of the materials' use in infrared sensing technology and hydrogen fuel cell technology have also proved promising.

"This work is a milestone in nanomaterials. These materials will become game changers in many areas such as electronics, energy and catalysis,"said Dr Zhou.

A version of this article appeared in the print edition of The Straits Times on May 31, 2018, with the headline 'Salt holds key to making several new materials: NTU team'. Print Edition | Subscribe