Optimizing the near‐field and far‐field properties of tips in tip‐enhanced Raman scattering
Optimizing the near‐field and far‐field properties of tips in tip‐enhanced Raman scattering
复制标题
DOI：
10.1002/jrs.6113
复制
发表时间：
2021-05
影响因子：
2.5
通讯作者：
A. Sifat;E. Potma
中科院分区：
文献类型：
--
作者：
A. Sifat;E. Potma
针尖增强拉曼散射（TERS）的过程主要取决于实验中使用的针尖顶点附近的形态。许多尖端设计都专注于近场电磁增强的优化，这在很大程度上受到纳米级细微细节的控制，这些细节在尖端制造过程中仍然难以重现。聚焦离子束（FIB）的使用允许以可再现的方式修改尖端上的较大特征，但这种方法不能产生对于最佳近场增强重要的亚20 nm结构。尽管如此，FIB铣削为改善尖端天线的远场辐射特性提供了极好的机会，这一特性在TERS研究界受到的关注相对较少。在这项工作中，我们使用时域有限差分（FDTD）模拟来研究几种尖端天线系统的近场和远场辐射效率，这些系统可以以可行的方式用FIB技术构建。从钝的蚀刻尖端开始，我们发现可以用柱状尖端获得TERS信号的出色的整体增强。此外，通过在尖端轴上应用垂直凹槽，可以进一步提高整体效率，产生的TERS信号比从半径为10 nm的理想（未修改）尖锐尖端获得的信号强10倍。所提出的设计构成了一个可行的路线走向尖端制造过程中，不仅产生更多的可重复的提示，但也承诺更强的TERS信号。
The process of tip‐enhanced Raman scattering (TERS) depends critically on the morphology near the apex of the tip used in the experiment. Many tip designs have focused on optimization of electromagnetic enhancement in the near‐field, which is controlled to a large extent by subtle details at the nanoscale that remain difficult to reproduce in the tip fabrication process. The use of focused ion beams (FIB) permit modification of larger features on the tip in a reproducible manner, yet this approach cannot produce sub‐20‐nm structures important for optimum near‐field enhancement. Nonetheless, FIB milling offers excellent opportunities for improving the far‐field radiation properties of the tip‐antenna, a feature that has received relatively little attention in the TERS research community. In this work, we use finite‐difference time‐domain (FDTD) simulations to study both the near‐field and far‐field radiation efficiency of several tip‐antenna systems that can be constructed with FIB techniques in a feasible manner. Starting from blunt etched tips, we find that excellent overall enhancement of the TERS signal can be obtained with pillar‐type tips. Furthermore, by applying vertical grooves on the tip's shaft, the overall efficiency can be improved even more, producing TERS signals that are up to 10‐fold stronger than signals obtained from an ideal (unmodified) sharp tip of 10‐nm radius. The proposed designs constitute a feasible route toward a tip fabrication process that not only yields more reproducible tips but also promises much stronger TERS signals.