Field enhancement of semiconductors is highly dependent on the wavelength of light. The wavelength dependence is particularly promising for light–matter interaction applications, such as sensors, photocatalysts, and solar cells, as well as to achieve an understanding of plasmon-free field enhancement. However, there are few reports on the field enhancement of two-dimensional (2D) semiconductors and no reports on the wavelength dependence to date. Here, we present the field enhancement of tungsten disulfide (WS₂) for a 2D layered semiconductor. The enhancement factor (EF) of a single WS₂ flake was evaluated by using confocal fluorescence microspectroscopy. The wavelength dependence was investigated both by experiment and with theoretical calculations for the range from the visible to the near-infrared (NIR) region (400–2000 nm). As a result, the EFs for a single WS₂ flake were visualized as maps upon six different excitation wavelengths. The maps were compared with maps of electric fields from finite-difference time-domain calculations, based on the x–y–z position of a single WS₂ flake at the same position measured by using atomic force microscopy. The EF in the NIR region showed the largest enhancement, and the maximum EF was demonstrated at a specific number of layers (150 layers) as EF = 100.

中文翻译：

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二维分层WS ₂中近红外增强的光谱可视化

半导体的场增强高度依赖于光的波长。波长相关性对于光-质相互作用应用（例如传感器，光催化剂和太阳能电池）以及对无等离子体激元场增强的理解特别有希望。但是，迄今为止，关于二维（2D）半导体的场增强的报道很少，也没有关于波长依赖性的报道。在这里，我们介绍了用于二维层状半导体的二硫化钨（WS ₂）的场增强。单个WS ₂的增强因子（EF）通过使用共聚焦荧光光谱法评价薄片。通过实验和理论计算研究了从可见光到近红外（NIR）区域（400–2000 nm）的波长依赖性。结果，单个WS ₂薄片的EF可视化为六个不同激发波长上的图。根据单个WS ₂薄片在相同位置通过原子力显微镜测得的x–y–z位置，将这些图与来自有限差分时域计算的电场图进行比较。NIR区域中的EF表现出最大的增强，并且在EF = 100的特定层数（150层）下显示出最大EF。