Atom-by-atom imaging reveals moire transformations in 2D materials

Atom-by-atom imaging reveals moire transformations in 2D materials
by Clarence Oxford
Los Angeles CA (SPX) Apr 19, 2024

Silicon-based electronics are nearing their physical limits, necessitating the exploration of new materials to meet technological advancements. Two-dimensional (2D) materials, known for their diverse properties such as superconductivity and magnetism, are emerging as viable alternatives for electronic components like transistors. The challenge lies in controlling these properties, which is a complex task.

Researchers at the University of Illinois Urbana-Champaign have devised a technique to observe the thermal rearrangement of 2D materials on an atomic scale. This method allows them to see transitions from twisted to aligned structures via transmission electron microscopy (TEM). They discovered a novel mechanism involving the formation of a new grain within a single layer, which is influenced by the structure of the adjacent layer. This control over the macroscopic twist between layers enhances the overall properties of the system.

The study was spearheaded by materials science professor Pinshane Huang and postdoctoral researcher Yichao Zhang, and their findings were published in Science Advances.

"The alignment and transformation mechanisms of the bilayer interfaces are crucial," Zhang noted. "They dictate the properties of the entire bilayer system, affecting its behavior on both nanoscale and microscopic levels."

2D multilayers are typically heterogeneous in structure and properties, varying across and within samples. Minor variations in the twist between layers can significantly alter device behavior. These materials also tend to restructure in response to external stimuli like heat, which is commonly applied during device fabrication.

Zhang explained, "People often visualize the layers as two sheets of paper twisted at 45 degrees. Our findings reveal a nucleus, or a nanoscale aligned domain, that expands and can potentially encompass the entire bilayer under the right conditions."

Despite the challenges of capturing atomic dynamics due to the limitations of existing imaging technology, the team managed a unique approach. They encapsulated the twisted bilayer in graphene, creating a miniaturized reaction chamber to maintain atomic positioning during heating, thus allowing observation with TEM without lattice destruction.

The encapsulated bilayer was then placed on a chip capable of rapid heating and cooling. By administering half-second heat pulses ranging from 100-1000 C and using TEM to monitor atomic positions after each pulse, the researchers could observe the evolving atomic arrangements.

"This visual observation helps us understand the initial structure and its evolution with heat," said Huang. "The ability to adjust the macroscopic twist is crucial as it directly influences the properties of the entire system."

Research Report:Atom-by-atom imaging of moire transformations in 2D transition metal dichalcogenides