Researchers at UC Berkeley have found a way to expand on technological advancements using optical capabilities, which are crucial for commonly used devices.
By taking two single-atom-thick sheets of graphene, which is a tightly bound single layer of carbon atoms, and layering and twisting them on top of each other, campus researchers were able to convert a common linear material into a more advanced, nonlinear one with a wide range of optical capabilities, according to Fuyi Yang, a campus doctoral student and the study’s lead author.
This research is essential to the field of optoelectronics, which includes technologies such as the enhanced performance of laptops, tablets and phones, according to Yang.
“Just by introducing this twisting mechanism, electrons in the graphene layers have very different behaviors,” said Jie Yao, campus associate professor of materials science and engineering and the study’s senior author. “The results are better than we thought. The nonlinear capability generated by twisting graphene layers is surprisingly strong.”
Nonlinear materials, unlike linear ones, can combine multiple photons into one and therefore hold twice as much energy output, making those materials more capable of powering more complex technologies, according to Yang.
The ability of nonlinear materials, which are scarce, to convert photons can often not be tampered with, Yang added. However, with this research, it is possible to manipulate nonlinear materials’ ability to combine photons, leading to a vast array of technological capabilities not previously available to scientists.
When the sheets of graphene are pulled in opposite directions, the symmetry of their atomic arrangement is transformed, causing the graphene’s physical properties to evolve and to be able to react with more materials, according to Yang.
“This is the first demonstration of an elemental material with intrinsically tunable nonlinearity which not only helps to better understand the symmetry and electronic structure of twisted bilayer graphene, but also provide an out-of-plane nonlinear polarization tensor for more on-chip integration configurations,” Yang said in an email.
By the end of the trials, the team was able to produce 30 samples of bilateral graphene, which entails layering multiple sheets of graphene at an angle to allow them to twist. With each increased twist, the team was able to achieve higher-energy photons in each sample, according to Yang.
While this research has proved to be groundbreaking by showing that transforming graphene into a nonlinear material is possible, it is only a step toward the ultimate goal of being able to make two layers of graphene twist on command, according to Yao.
“That’s one potential direction for future exploration,” Yao said. “If we can change the twisting angle between two graphene sheets in real time, then changing the nonlinear property of that bilayered graphene would be as simple as tuning a radio.”