尖锐材料边界处的近场边缘条纹
Near-field edge fringes at sharp material boundaries
摘要：
研究了散射型扫描近场光学显微镜（s-SNOM）对材料锐边成像时近场条纹的形成。我们研究的材料包括超导体、金属、近完美导体以及具有各向异性介电常数和双曲色散的材料。对于我们的理论分析，我们使用的技术相结合的全波数值模拟尖端样品近场相互作用和信号解调在更高的订单类似于在典型的S-SNOM实验中所做的。与以前的尖端样品相互作用近场模型不同，我们的先进技术允许模拟现实的尖端和样品结构。我们的分析澄清了最近出现的层状材料，如六方氮化硼和过渡金属二硫属化物（特别是二硫化钼），以及传统的等离子体材料，如金的边缘成像。在几个波长下研究了面元氮化硼，包括它具有声子-极化激元激发和双曲色散的波长。基于我们的结果的s-SNOM成像在不同的解调阶数，我们指定共振和非共振类型的边缘，并描述每种情况下的边缘条纹。我们澄清近场边缘条纹形成材料尖锐的边界，明亮的条纹和边缘的低对比度区域外，并阐述了分离它们的必要性，从传播波的极化激元材料的表面上。
英文摘要：
We have studied the formation of near-field fringes when sharp edges of materials are imaged using scattering-type scanning near-field optical microscope (s-SNOM). Materials we have investigated include dielectrics, metals, near-perfect conductor, and those that possess anisotropic permittivity and hyperbolic dispersion. For our theoretical analysis, we use a technique that combines full-wave numerical simulations of tip-sample near-field interaction and signal demodulation at higher orders akin to what is done in typical s-SNOM experiments. Unlike previous tip-sample interaction near-field models, our advanced technique allows simulation of the realistic tip and sample structure. Our analysis clarifies edge imaging of recently emerged layered materials such as hexagonal boron nitride and transition metal dichalcogenides (in particular, molybdenum disulfide), as well as traditional plasmonic materials such as gold. Hexagonal boron nitride is studied at several wavelengths, including the wavelength where it possesses excitation of phonon-polaritons and hyperbolic dispersion. Based on our results of s-SNOM imaging in different demodulation orders, we specify resonant and non-resonant types of edges and describe the edge fringes for each case. We clarify near-field edge-fringe formation at material sharp boundaries, both outside bright fringes and the low-contrast region at the edge, and elaborate on the necessity of separating them from propagating waves on the surface of polaritonic materials.
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