Silicon-based electronics are reaching their physical limits, leading researchers to explore new materials to meet modern technological demands. Two-dimensional (2D) materials offer unique properties like superconductivity and magnetism that make them promising for use in electronic systems like transistors. However, controlling these materials is challenging, prompting researchers at the University of Illinois Urbana-Champaign to develop a method to visualize the rearrangement of 2D materials atom-by-atom using transmission electron microscopy (TEM). They observed a new mechanism where a new grain was seeded in one monolayer, guided by the adjacent layer, allowing for more control over the properties of the entire system.
Led by professor Pinshane Huang and postdoctoral researcher Yichao Zhang, the research was published in Science Advances and focused on understanding how 2D interfaces align and transform within bilayers. The structure and properties of 2D multilayers can vary widely even within the same sample, affecting the behavior of devices. By heating the 2D materials, the researchers found that aligned regions could form at relatively low temperatures, around 200°C, similar to typical processing temperatures for electronic devices. This visualization at the atomic scale provides critical insights into the behavior of these materials under external stimuli like heat.
To visualize the atomic movement, the researchers encapsulated the twisted bilayer in graphene to create a reaction chamber around it, allowing for observation at atomic resolution during heating. This unique approach holds the atoms in place, preventing them from being destroyed by high-energy electrons from the TEM. By subjecting the encapsulated bilayer to quick heat pulses and observing atom positions after each pulse, the team could track the movement of individual atoms as they rearranged into energetically favorable configurations. This understanding of rearrangement mechanisms can lead to better control over interfacial alignment at the nanoscale.
The ability to control the macroscopic twist between layers of 2D materials is crucial for tuning their properties. Huang emphasizes the excitement surrounding the tuneability of these materials, as rotating one layer on the other can significantly alter the system’s properties. For example, specific angles of rotation in 2D material graphene can induce superconductivity, while changing the bandgap can alter the color of light absorbed or emitted. By manipulating the orientation of atoms between layers, researchers can fine-tune the properties of 2D materials for various applications in electronics and beyond.
Overall, this research provides valuable insights into the behavior of 2D materials at the atomic level, shedding light on the mechanisms behind their rearrangement under heat. The ability to visualize and track individual atoms during this process opens up new possibilities for controlling the properties of electronic systems based on 2D materials. This work highlights the importance of understanding and manipulating interfaces in bilayer systems to optimize their performance for future technological advancements.
