Laser-Induced Graphene Shows Promise in the Development of Flexible ElectronicsFebruary 19, 2020 by Luke James
Scientists at Rice University have made laser-induced graphene using a low-power laser mounted in a scanning electron microscope.
The team at Rice University, in conjunction with Philip Rack, a Tennessee/ORNL materials scientist, have pioneered a process to create laser-induced graphene (LIG). LIG has features that are 60% smaller than the macro version of the material and almost 10 times smaller than what can be typically achieved using an infrared laser.
A graphic showcasing the variety of materials that the Rice University researchers combined with laser-induced graphene to create composites for applications. Image used courtesy of the Tour Group via Rice University
The LIG Process
LIG is a multifunctional graphene foam that is direct-written with an infrared laser into a carbon-based precursor material. In the Rice team’s research, this was achieved using a visible 405 nm laser that directly converts polyimide into LIG, enabling the formation of LIG with a spatial resolution of 12 µm and a thickness of < 5 µm. This spatial resolution, enabled by the smaller-focused spot size of the 405 nm laser, represents a 60% reduction in previously reported LIG feature sizes.
These smaller 405 nm lasers use light in the blue-violet part of the spectrum. They are much less powerful than the industrial lasers that are currently being used to burn graphene into materials.
“A key for electronics applications is to make smaller structures so that one could have a higher density, or more devices per unit area,” James Tour of Rice University said in a statement. “This method allows us to make structures that are 10 times denser than we formerly made.”
A scanning electron microscope shows two tracers of LIG on a polyimide film. Image used courtesy of James Tour of Rice University
A New Path Toward Writing Electronic Circuits
To prove the viability of their concept, the researchers made tiny flexible humidity sensors directly fabricated on polyimide. These devices were then able to sense human breath in 250 milliseconds.
“This is much faster than the sampling rate for most commercial humidity sensors and enables the monitoring of rapid local humidity changes that can be caused by breathing,” said Rice postdoctoral researcher Michael Stanford, lead author of the research team’s paper.
The 405 nm laser is mounted on a scanning electron microscope (SEM) and burns the top five microns of the polymer. This writes graphene features as small as 12 microns.
The Rice team believes that this new LIG process could offer a new path toward writing electronic circuits into flexible materials such as clothing.
“The LIG process will allow graphene to be directly synthesized for precise electronics applications on surfaces,” added Stanford. With growing interest in the LIG process for use in flexible electronics and sensors, further refinement of this process will expand its utility and potentially see it being used in a range of flexible electronics across all industries.
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