Graphene has captured the attention of scientists since its discovery over a decade ago. This one-atom-thick carbon material boasts remarkable electronic properties, incredible strength, and an ultra-lightweight structure. Its potential applications continue to grow, but one major challenge remains: how to introduce a band gap into graphene so that it can function as a semiconductor or insulator, which is essential for building transistors and other electronic devices.
Recently, researchers at the Massachusetts Institute of Technology (MIT) have made significant progress in this area, potentially reshaping some long-held theories about graphene’s behavior. They combined graphene with another single-layer material—hexagonal boron nitride—which shares a similar hexagonal structure and is known for its insulating properties. By placing a graphene layer on top of this insulator, they created a hybrid material that retains graphene’s excellent conductivity while introducing the necessary energy gap for semiconductor applications.
Pablo Jarillo-Herrero, an assistant professor at MIT’s Department of Physics, explained, “By combining these two materials, we’ve achieved a unique set of properties that neither material alone possesses. Graphene is an excellent conductor, and hexagonal boron nitride is a good insulator. When combined, they produce high-quality semiconductors.â€
However, the process isn’t straightforward. The atomic structures of both materials must be nearly perfectly aligned. While both have a hexagonal lattice and similar sizes, boron nitride is about 1.8% larger, making perfect alignment extremely challenging. Even small misalignments can significantly affect the material’s performance.
Currently, there is no flawless method for achieving perfect alignment. Researchers rely on angular matching, but there's still about a 1 in 15 chance of error. Despite this, the resulting semiconductor shows great promise.
Ray Ashoori, a professor at MIT’s Department of Physics, noted, “What’s most exciting is that by adjusting the angle between the layers, we can fine-tune the electronic properties of the final material. This opens up possibilities for creating a wide range of semiconductor materials with tailored characteristics.â€
Previously, scientists tried to make graphene into a semiconductor by cutting it into narrow ribbons, but this approach weakened its electrical performance. The new technique avoids this issue, although the current band gap is still not sufficient for practical use. Researchers believe further improvements could lead to a breakthrough in transistor manufacturing.
Additionally, the MIT team observed a fascinating physical phenomenon in their new material: when exposed to a magnetic field, it displayed a fractal-like pattern known as the "Hofstadter Butterfly Spectrum." This effect, predicted theoretically over a decade ago, was once thought to be unachievable in real materials. Now, it has been experimentally confirmed, marking a significant step forward in understanding graphene-based systems.
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