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A research team led by Professor Changgu Lee of the School of Mechanical Engineering and Dr. Kyuyoun Won of the IBS Center for Two-Dimensional Quantum Heterostructures, in collaboration with Professor Jong-Hoon Lee of UNIST, has devised a breakthrough optical technique that allows the convenient evaluation of the properties of two-dimensional (2D) materials with almost no long-range crystallinity.

Discovered in 2004, graphene—which earned its discoverers a Nobel Prize—sparked intense research into 2D materials, all of which were found and studied in crystalline forms with well-ordered atomic lattices. The better the crystallinity, the superior the mechanical strength, electrical conductivity, and thermal conductivity. For this reason, various 2D materials such as boron nitride and molybdenum disulfide have been explored since graphene’s discovery, while amorphous (non-crystalline) 2D materials have received almost no attention.

Recently, however, a 2D amorphous carbon material, the non-crystalline counterpart of graphene, has been synthesized, and fundamental research has begun in earnest. Although amorphous 2D materials generally exhibit inferior properties compared with their crystalline counterparts, they can reveal entirely unexpected phenomena and provide decisive clues to structural issues in existing three-dimensional amorphous materials, opening diverse avenues for application. For example, traditional amorphous insulators such as silicon oxide—used in semiconductor processes—face physical limits as memory and CPU circuits continue to shrink, because device-to-device interference grows severe at high operating speeds. Amorphous 2D materials, however, have been shown to combine mechanical stability with an ultralow dielectric constant, drastically reducing interference and making them strong candidates for next-generation semiconductor fabrication. Yet their dielectric and physical properties vary with synthesis conditions, posing challenges for commercial production. Precise characterization has required expensive instrumentation such as transmission electron microscopy (TEM) and advanced analysis skills, inevitably slowing research and development.

Professor Lee’s team has developed an easy optical method to analyze the lattice structure and properties of 2D amorphous carbon. Previously, such films were grown on metallic substrates like copper foil, but spectroscopic analysis was practically impossible because of noise from the metal. Transferring the films onto non-metallic substrates introduced contamination that hindered accurate measurements. Consequently, studies relied almost exclusively on costly TEM, creating a high barrier to entry. The team solved this by inventing a direct-growth technique on non-metallic substrates and by comparing Raman and X-ray spectroscopy with TEM results, proving that inexpensive, user-friendly Raman spectroscopy alone can reliably characterize these materials. Because Raman tools are readily accessible to materials researchers and cost one-tenth to one-hundredth of TEM analysis, the team’s method dramatically lowers the hurdle for studying 2D amorphous materials.

Looking ahead, this analytical approach is expected to be applicable to 2D-material-based memory, logic, and AI devices. As silicon miniaturization reaches its limits around 2030, the method could become a key technique for the emerging 2D-material semiconductor industry, which is anticipated to replace silicon.

Authors: Dr. Kyuyoun Won, Professor Jong-Hoon Lee, Jongchan Yoon (co-first author), Dohyun Jeon, Jinhwan Hong, Hyunggu Yoo, Yeji Bang Pawan Kumar Srivastava, Budhi Singh, Professor Jong-Hoon Lee, Professor Changgu Lee

Journal: Spectroscopic signatures of ultra-thin amorphous carbon with the tuned disorder directly grown on a dielectric substrate (Advanced Materials; IF=27.4, December 2024)