Recently, the Daiqing team of the National Nanoscience Center and Liu Mengkun, a professor at Stony Brook University in the United States, collaborated to overcome the characterization difficulties caused by the limited size of van der Waals crystals by using near-field optics technology, and successfully measured the dielectric tensor of boron nitride and molybdenum disulfide. A new crystal optical anisotropy characterization method has been developed. National Nano Centers and others have made progress in the study of crystal optical anisotropy Lithium Battery,Lithium Batteries,Lithium Polymer Battery,Lithium Iron Phosphate Battery Power X (Qingdao) Energy Technology Co., Ltd. , https://www.solarpowerxx.com
New two-dimensional materials such as graphene, boron nitride and transition metal chalcogenide belong to van der Waals crystals, each of which has excellent mechanical, electrical and optical properties. It is the basic unit for constructing functionally controlled van der Waals heterojunctions and is also the next generation. The basic material for high performance optoelectronic devices. Van der Waals crystals have a layered structure, which is bonded by strong covalent bond interactions within the layer and combined by weak van der Waals forces between the layers. This layered structure determines the natural anisotropy of various physical properties of van der Waals crystals, where optical anisotropy is critical for the design and optimization of new optoelectronic devices. Due to the current problem of preparing high-quality van der Waals single crystals, traditional optical anisotropy characterization methods based on far-field beam reflection (such as end-reflection and ellipsometry) are difficult to accurately measure the optical anisotropy of van der Waals microcrystals.
The Dai Qing team first demonstrated the existence of ordinary (TE) and extraordinary waveguide (TM) modes in anisotropic van der Waals nanosheets, and the in-plane wavevectors of these two modes are in-plane and out-of-plane with van der Waals crystals, respectively. The dielectric constant is correlated; subsequently, the TE and TM waveguide modes are excited in van der Waals nanosheets using a scattering-type scanning near-field optical microscope (s-SNOM), and real-field near-field optical imaging is performed; finally, by the real space near The Fourier analysis of the field optical image was used to obtain the optical anisotropy of the measured van der Waals crystal. The above method overcomes the limitation of the sample size by the traditional characterization means, and can accurately characterize the optical anisotropy of the uniaxial and biaxial van der Waals crystal materials. The method is equally applicable to the direct characterization of the optical anisotropy of a few layers or even a single layer of van der Waals crystals by optimizing the design of the substrate material.
Relevant research results were published online in Nature-Communication, and their characterization methods have applied for invention patents. The research was funded by the National Natural Science Foundation of China and the Ministry of Science and Technology's key research and development programs.
