2D materials tailored to improve optical and electronic devices

Researchers have found that altering 2D materials could improve the capabilities of optical and electronic devices.

 The research, led by Shengxi Huang, assistant professor of electrical engineering and biomedical engineering at Penn State University, found that altering the material in two different ways – atomically and physically – could enhance light emission and increase signal strength in many devices that rely on these materials.

In the first method of their study, the researchers modified the atomic make-up of the materials. In commonly used 2D materials, researchers rely on the interaction between the thin layers, known as van der Waals interlayer coupling, to create charge transfer that is then used in devices. However, this interlayer coupling is limited because the charges are traditionally distributed evenly on the two sides of each layer.

In order to strengthen the coupling, the researchers created a new type of 2D material, known as Janus transition metal dichalcogenides, by replacing atoms on one side of the layer with a different type of atoms, creating an uneven distribution of the charge.

“This [atomic change] means the charge can be distributed unevenly,” Huang explained. “That creates an electric field within the plane and can attract different molecules because of that, which can enhance light emission.”

The researchers added if van der Waals interlayer coupling can be tuned to the right level by twisting layers with a certain angle, it can induce superconductivity, carrying implications for advances in electronic and optical devices.

In the second method of altering 2D materials to improve their capabilities, the researchers strengthened the signal that resulted from an energy up-conversion process by taking a layer of MoS2, a common 2D material that is usually flat and thin, and rolling it into a roughly cylindrical shape.

The energy conversion process that takes place with the MoS2 material is part of a non-linear optical effect where, if a light is shone into an object, the frequency is doubled, which is where the energy conversion comes in, the researcher said.

“We always want to double the frequency in this process,” Huang said. “But the signal is usually very weak, so enhancing the signal is very important.” But by rolling the material, the researchers said they achieved a more than 95 times signal improvement.

As of late, Huang intends to put these two advances together. “The next step for our research is answering how we can combine atomic engineering and shape engineering to create better optical devices,” she said.

A paper on the research of the atomic structure, ‘Enhancement of van der Waals Interlayer Coupling through Polar Janus MoSSe’, was published in the Journal of the American Chemical Society (ACS).