碲化钨薄膜的红外近场光学成像  

Near-field imaging of WTe

作　　者：代珍兵[1,2] 罗国语 贺言 王冲 晏湖根[3,4] 李志强 DAI Zhen-Bing;LUO Guo-Yu;HE Yan;WANG Chong;YAN Hu-Gen;LI Zhi-Qiang(Department of Physics,Sichuan Normal University,Chengdu 610066;College of Physics,Sichuan University,Chengdu 610065,China;State Key Laboratory of Applied Surface Physics,Fudan University,Shanghai 200438,China;Department of Physics,Fudan University,Shanghai 200438,China)

机构地区：[1]四川师范大学物理与电子工程学院,四川成都610066 [2]四川大学物理学院,四川成都610065 [3]复旦大学应用表面物理国家重点实验室,上海200438 [4]复旦大学物理学系,上海200438

出　　处：《红外与毫米波学报》2022年第2期464-469,共6页Journal of Infrared and Millimeter Waves

基　　金：国家自然科学基金(11874271)。

摘　　要：研究了过渡金属硫族化合物碲化钨的近场光学响应,通过Drude-Lorentz模型拟合得到其块材在室温下的介电常数,并利用有限偶极模型计算出碲化钨样品与金刚石基底的近场散射信号比。当样品边缘未出现散射信号增强时,实验结果与理论模型符合较好;当样品边缘出现信号增强现象时,理论模型与实验观测结果不符,说明这部分样品的光学性质并不能完全由块材所描述,从而推测样品表面具有与块材无耦合作用的碲化钨纳米薄层,同时对在样品边缘很强的近场散射信号给出了可能的解释。这个工作为今后对拓扑材料的光学研究提供了参考。Near-field optical response of WTe;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 WTe;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 WTe;lead to an enhancement of the local optical conductivity. This work provides a reference from the optical research of topological materials in the future.

关 键 词：碲化钨薄膜 近场光学成像 介电常数 拓扑 

分 类 号：O43[机械工程—光学工程]