The future of LEDs in a super-thin bilayer material

Ultra-thin light emitting devices are one step closer with bilayer material, with each layer measuring less than one nanometer in thickness.

Tom Page

A material combining atomically thin layers of molybdenum disulfide and rhenium disulphide has been created that promises ultra thin and flexible light sources.

“Both absorb light very well as semiconductors, and they’re both very flexible – can be stretched or compressed,” said Hui Zhao, associate professor of physics and astronomy at the Ultrafast Laser Lab at the University of Kansas.

“The goal of this whole direction of research is to produce light-emitting devices, such as LEDs that are ultra-thin (just a few nanometers thick) and flexible enough that you can bend it. We showed through this bilayer material, it can be achieved.”

Earlier attempts have produced various bilayer materials by stacking different types of atomic sheets, but in those cases the electrons and their “seats” exist in different atomic layers.

What is a seat?

“One can think of a material as a classroom full of students, which are the electrons, one on each seat,” Zhao explained.

“Sitting on a seat, a student, or electron, can’t move freely to conduct electricity. Light can provide enough energy to stand up some of the students, who can now move freely and, as electrons, to conduct electricity. This process is the foundation for photovoltaic devices, where the energy of sunlight is captured and converted to electricity.”

He went on to explain that emission of light involves the inverse process, in which a standing electron sits down in a seat, releasing its kinetic energy in the form of light.

The new material was created using the low-tech “Scotch tape” method pioneered in creating graphene.

The atomically thin sheets were connected by the van der Waals force, which the team explained is the force which enables a gecko lizard to scale a smooth window pane.

“The van der Waals force isn’t very sensitive to the atomic arrangement,” said Zhao. “So, one can use these atomic sheets to form multilayer materials, in a fashion like atomic Lego.

“We’d someday like to see LEDs that are thinner, more energy efficient and bendable,” Zhao remarked. “Think about a computer or phone screen if you could fold it a few times or and put it in your pocket.”

Zhao co-authored a paper on the subject in the journal Nanoscale Horizons.