Steamy new synthesis method leads to electronic MOFs

A new process that uses vapor, rather than liquid, to grow a type of highly porous crystal material known as metal-organic frameworks (MOFs) could lead to a new breed of faster, more powerful electronic devices. The method, invented by an international team of scientists from the University of Leuven in Belgium, the National University of Singapore and CSIRO in Australia, has been published in Nature Materials.

For the first time, the researchers have shown how MOFs can be grown using a vapor method that is similar to steam hovering over a pot of hot water. MOFs consist of metal oxide groups surrounded by organic molecules that form a highly porous three-dimensional crystal framework.

MOFs are mainly being developed for gas storage and catalysis applications, but could also significantly boost the processing power of microelectronic devices. However, according to CSIRO researcher Mark Styles, up until now these crystals could only be grown and applied using a liquid solvent, making them unsuitable for electronics applications.

"Just like your smart phone doesn't like being dropped in water, electronic devices don't like the liquid solvent that's used to grow MOF crystals," Styles explained. "It can corrode and damage the delicate circuitry.

"Our new vapor method for growing and applying MOF crystals overcomes this barrier and has the potential to disrupt the microelectronics industry. On the atomic scale, MOF crystals look like bird cages that can be tailor-made to be different shapes and sizes. They have an extremely large surface area, meaning they can be up to 80% empty inside.

"The net result is a structure where almost every atom is exposed to empty space: one gram of MOF crystals has a surface area of over 5000m² – that's the size of a football field. Crucially, we can use this vast space to trap other molecules, which can change the properties of a material. In the case of electronics, this means we can fit a lot more transistors on a microchip, making it faster and far more powerful."

The international team, which was led by Ivo Stassen and Rob Ameloot from the University of Leuven in Belgium, drew on specialist X-ray analysis techniques from CSIRO and the Australian Synchrotron to understand how the vapor process works, and how it can be used to grow the MOF crystals.

"Vapor-phase deposition is already a common method to produce high-tech devices, " says Stassen. "We are the first to use this method for the production of these highly porous materials. We first deposit layers of zinc and let them react with the vapor of the organic material. The organic material permeates the zinc, the volume of the whole expands, and it is fully converted into a material with a regular structure and nanopores."

"This alternative production method opens up new possibilities for MOFs in terms of applications and industries," he adds. "Chemical vapor deposition is a common technique in nanofabrication. Therefore, new MOF applications can be developed relatively quickly: gas sensors, nanochip components and improved batteries."

This story is adapted from material from CSIRO and the University of Leuven, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.