Custom Medical Cable Assemblies Custom Medical Cable Assemblies,Medical Instrument Sensor Adapter Cable,Ems/Tens Rj45 Snap Ecg Lead Wire,Medical Instrument Cable Dongguan City Yuanyue Electronics Co.Ltd , https://www.yyeconn.com
National Nano Centers and others have made progress in the study of crystal optical anisotropy
Recently, a research team from the National Center for Nanoscience and Technology, led by Dai Qing, collaborated with Professor Liu Mengkun from Stony Brook University in the U.S. to overcome challenges in characterizing van der Waals crystals due to their small size. By employing near-field optical techniques, they successfully measured the dielectric tensor of boron nitride and molybdenum disulfide, developing a novel method for analyzing crystal optical anisotropy.
Two-dimensional materials such as graphene, hexagonal boron nitride, and transition metal dichalcogenides are all classified as van der Waals crystals. These materials exhibit remarkable mechanical, electrical, and optical properties, making them essential building blocks for constructing functional van der Waals heterostructures. They are also key candidates for next-generation high-performance optoelectronic devices. The unique layered structure of these materials—held together by strong covalent bonds within each layer and weak van der Waals forces between layers—leads to natural anisotropy in their physical properties, especially in optical behavior. This optical anisotropy plays a crucial role in the design and optimization of advanced optoelectronic systems.
However, traditional methods like far-field ellipsometry or end-reflection techniques struggle to accurately measure the optical anisotropy of van der Waals microcrystals, particularly when high-quality single crystals are difficult to obtain. To address this challenge, the Dai Qing team introduced a new approach using near-field optics. They first demonstrated the existence of both transverse electric (TE) and transverse magnetic (TM) waveguide modes in anisotropic van der Waals nanosheets. These modes have in-plane and out-of-plane wavevectors, respectively, and their properties are closely related to the material's dielectric constant.
Using a scattering-type scanning near-field optical microscope (s-SNOM), the researchers excited TE and TM modes in van der Waals nanosheets and captured real-space near-field optical images. Through Fourier analysis of these images, they were able to determine the optical anisotropy of the material. This method overcomes the limitations of conventional techniques that are constrained by sample size, allowing precise characterization of both uniaxial and biaxial van der Waals crystals. It is also applicable to few-layer or even monolayer materials, provided the substrate is appropriately optimized.
The findings were published online in *Nature Communications*, and the team has filed for invention patents. The research was supported by the National Natural Science Foundation of China and the Ministry of Science and Technology’s key R&D programs. This breakthrough opens new possibilities for studying and utilizing van der Waals crystals in advanced optoelectronic applications.