Recently, the Dai Ning 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 optical technology, and successfully measured the dielectric tensor of boron nitride and molybdenum disulfide. New purchase large size laser grade MgF2 optics anisotropy characterization methods have been developed.
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 base 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 sale of custom optical prism assemblies 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. Dielectric constant correlation; subsequently, the TE and TM waveguide modes were excited in van der Waals nanosheets using a scattering-type scanning near-field optical microscope (s-SNOM), and real-field near-field optical imaging was 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 purchasing laser grade optical prism. 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.