碲化钨薄膜的红外近场光学成像

Near-field optical response of WTe₂ thin films was studied by using scanning near-field optical microscopy (SNOM), we have observed bright fringes near the edge of the thin film sample and also a thickness dependence on optical contrast to the sample and substrate. To understand this behavior, first we obtain the dielectric function of WTe₂ at room temperature by Drude-Lorentz model via fitting the infrared radiation (IR) reflectance and conductivity spectra, then the near-field ratio of thin film sample to the diamond substrate is calculated by the Finite-dipole model. The experimental result reveals that the behavior of the sample cannot be fully described by the bulk properties. We assume that a decoupled thin layer exists on the surface of the bulk. There are two possible explanations for the observation of the near-field patterns of bright outside fringes. Firstly, a hot-spot field may be produced between the tip and the sample edge due to the enhancement of the local electric field under the IR illumination, a similar behavior has been revealed in surface-metallic black phosphorus. Another probability is that the topological edge states of top decoupled monolayer WTe₂ lead to an enhancement of the local optical conductivity. This work provides a reference from the optical research of topological materials in the future.