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Plasma Tech Could Replace One of World’s Rarest Materials

Image Credits: University of Sydney, Press Release

A team led by a researcher from the University of Sydney has developed a low-cost, sustainable, and readily available technology that can dim the screens of electronic devices, anti-reflection automobile mirrors, and smart architectural windows at a fraction of the cost of current technology.

It would replace one of the world’s scarcest – yet highly ubiquitous in use – modern materials: indium. A rare chemical element, that it is widely used in devices such as smartphones and computers, windscreen glass and self-dimming windows.

Although small amounts are used to manufacture smart device screens, indium is expensive as it is hard to source; it naturally occurs only in small deposits. Industrial indium is often made as a by-product of zinc mining, which means a shortage could occur if demand for optoelectronic devices – such as LCDs and touch panels – ramps up.

Dr Behnam Akhavan, an ARC DECRA Fellow from the School of Biomedical Engineering, School of Physics and Sydney Nano has developed a plasma-generated, hybrid nanocomposite material that is free of indium, and offers a low-cost, accessible and environmentally sound electrochromic technology that allows glass to be dimmed at the push of a button or touch of a screen.

The research was published in Solar Energy Materials and Solar Cells on 19 July 2021. The plasma-generated material is composed of tungsten oxide and silver and can be applied to coat almost any solid surface, including flexible plastics. Known as the fourth state of matter, plasma is created by adding energy to gas. Plasma is used most commonly in fluorescent light bulbs, neon signs and some television and computer screens.

Dr Akhavan noted that when the transparency of a wearable electronic or a smart window is changed, an electrochromic device is doing the work. Until now, these devices have typically relied on materials like rare indium to do the job. What we have created is a manufacturer’s dream: a technology that removes the need for indium and instead uses a plasma-engineered, three-layered structure that is much cheaper to produce.

Early iterations of the technology were produced for the first time in 2019, using a new method of tungsten oxide deposition known as ‘HiPIMS’ (the plasma technology used to create these materials). Now, instead of a bare tungsten oxide layer, the group has developed a nanocomposite of tungsten oxide and silver. This nanotechnology-enabled approach allows electrochromic devices to efficiently and rapidly change colour upon a user’s request.

The plasma coatings are transparent and also electrically conductive. They are made up of a layer of silver that is approximately 10,000 times thinner than the width of human hair, placed in between two nano-thin layers of tungsten oxide decorated with silver nanoparticles.

It was also noted that these plasma-fabricated coatings can then be applied to electronic papers, smartphones and glass windows and can be dimmed with the application of a small electrical current.

Plasma technology is based on a simple physical principle. Matter changes its state when energy is supplied to it: solids become liquid, and liquids become gaseous. If even more energy is supplied to a gas, it is ionized and goes into the energy-rich plasma state, the fourth state of matter.

Plasma was first discovered by Irving Langmuir in 1928. It is not rare; actually, quite the opposite is true. More than 99% of the visible matter in the universe is in the plasma state. It can be seen in its natural form on earth as lightning or as polar light in the Arctic and Antarctic, for example. During a solar eclipse, plasma can be observed as a bright circle of light (corona) around the sun.

With increasing energy input, the state of matter changes from solid to liquid to gaseous. If additional energy is then fed into a gas by means of electrical discharge, the gas will turn into plasma.

Because it is easy to use and can be integrated inline, plasma treatment has been used for many years in almost all areas of industry, including automobile engineering, transport, electronics manufacturing, packaging technology, consumer goods, life sciences, textiles and new forms of energy.

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