Partially Metal-Coated Tips for Near-Field Nanospectroscopy
Partially Metal-Coated Tips for Near-Field Nanospectroscopy
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DOI：
10.1103/physrevapplied.15.014048
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发表时间：
2021-01
影响因子：
4.6
通讯作者：
Yujia Zhang;Xinzhong Chen;Derek Chen;Z. Yao;Suheng Xu;P. McArdle;M. M. Qazilbash-M.;Mengkun Liu
中科院分区：
文献类型：
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作者：
Yujia Zhang;Xinzhong Chen;Derek Chen;Z. Yao;Suheng Xu;P. McArdle;M. M. Qazilbash-M.;Mengkun Liu
具有功能性光学响应的扫描探针是扫描近场光学显微镜的关键组件。对于在红外和太赫兹 (THz) 频率下进行的纳米光谱，一大挑战是常用的金属涂层硅尖端在整个光谱范围内产生不可调节的耦合效率，这极大地限制了信噪比。在这里，我们通过有限元数值建模测试了波长选择性尖端增强的通用设计方案的可能性。我们采用基于 $\mathrm{Si}$ 的尖端，顶部具有不同的金涂层长度，从而在尖端顶点产生可定制的近场场强。计算显示，由于几何天线谐振，金属涂层尖端具有与波长相关的增强因子，通过调整金属涂层的长度，可以在从可见光到太赫兹频率的宽光谱范围内精确调谐。通过将涂层图案改变为非手性尖端上的手性螺旋结构，我们还证明了涂层长度效应在设计高性能对映体近场扫描中的有用性。我们的方法和发现为开发近场光学探针、推动尖端增强近场检测（例如荧光、拉曼、红外和太赫兹纳米光谱）的检测和分辨率极限提供了有趣的视角。
Scanning probes with functional optical responses are key components of scanning near-field optical microscopes. For nanospectroscopy performed at IR and terahertz (THz) frequencies, one major challenge is that the commonly used metal-coated silicon tips yield nonadjustable coupling efficiency across the spectrum, which greatly limits the signal-to-noise ratio. Here, we test the possibility of a generic design scheme for wavelength-selective tip enhancement via finite-element numerical modeling. We employ a $\mathrm{Si}$-based tip with various gold-coating lengths on the top, yielding a customizable near-field field strength at the tip apex. Calculations show a wavelength-dependent enhancement factor of the metal-coated tip due to the geometrical antenna resonances, which can be precisely tuned throughout a broad spectral range from visible to terahertz frequencies by adjusting the length of the metal coating. By changing the coating pattern into a chiral helical structure on an achiral tip, we also demonstrate the usefulness of coating-length effect in designing high-performance enantiomeric near-field scanning. Our methods and findings offer interesting perspectives for developing near-field optical probes, pushing the detection and resolution limits of tip-enhanced near-field detections, such as fluorescence, Raman, IR, and THz nanospectroscopies.