In the bustling world of materials science, a team of researchers led by Hitesh Agarwal at ICFO—Institut de Ciències Fotòniques, part of The Barcelona Institute of Science and Technology, has made a significant stride in the engineering of van der Waals heterostructures. Their work, published in the Journal of Physics Materials (JPhys Materials), opens new avenues for the energy sector and beyond, offering a precise method to tailor these intricate materials with atomic-scale accuracy.
Van der Waals heterostructures are like molecular LEGO, allowing scientists to stack and combine different two-dimensional (2D) materials to create structures with unique properties. Hexagonal boron nitride (hBN), often referred to as “white graphene,” is a critical player in this field, acting as a protective encapsulation for active 2D materials like graphene. However, not all applications require full encapsulation. Sometimes, exposing specific surfaces or patterning hBN layers is essential for device functionality.
Agarwal and his team have developed a technique to selectively etch top hBN layers while preserving the underlying active layers. “Our method allows us to create pristine surfaces with atomic-scale flatness, which is crucial for maintaining the electronic quality of the active layers,” Agarwal explains. The process involves a soft selective sulfur hexafluoride (SF6) etching combined with pre- and post-etching treatments, ensuring the integrity of the active layers beneath.
The team demonstrated the effectiveness of their technique using graphene/hBN Hall bar devices. Through Raman spectroscopy and quantum transport measurements, they showed that the etched regions maintained high carrier mobilities, with values exceeding 200,000 cm² V⁻¹ s⁻¹ at low temperatures. They also observed ballistic transport and intrinsic room temperature phonon-limited mobilities, indicating the preservation of electronic quality.
Key to their success were pre-etching steps involving atomic force microscopy brooming and O₂ plasma cleaning. These steps ensured that the exposed surfaces were pristine, ready for further experimentation or application. “This technique provides a clean method for opening windows into mesoscopic van der Waals devices,” Agarwal notes. “It can be used for local probe experiments, patterning top hBN in-situ, and exposing 2D layers to their environment for sensing applications.”
The implications for the energy sector are substantial. Graphene and other 2D materials are at the forefront of research into next-generation energy technologies, from advanced batteries to high-efficiency solar cells. The ability to precisely engineer van der Waals heterostructures could lead to more efficient energy storage and conversion devices, as well as innovative sensors for monitoring energy systems.
Moreover, the technique could revolutionize the field of nanofabrication, enabling the creation of complex, multi-functional devices with atomic precision. “This is a significant step forward in our ability to control and manipulate 2D materials,” Agarwal says. “It opens up new possibilities for the design and fabrication of advanced materials and devices.”
As the world continues to seek sustainable and efficient energy solutions, the work of Agarwal and his team provides a promising path forward. By offering a precise and controlled method for engineering van der Waals heterostructures, they are paving the way for the next generation of energy technologies. The research, published in JPhys Materials, is a testament to the power of interdisciplinary collaboration and the potential of 2D materials to transform our world.