Umakoshi Takayuki, Kawashima Koji, Moriyama Toki, Kato Ryo, Verma Prabhat
Department of Applied Physics, Osaka University, Suita, Osaka, 565-0871, Japan.
Institute for Advanced Co-creation Studies, Osaka University, Suita, Osaka, 565-0871, Japan.
Sci Rep. 2022 Jul 27;12(1):12776. doi: 10.1038/s41598-022-17170-7.
Tip-enhanced Raman spectroscopy (TERS) is a powerful tool for analyzing chemical compositions at the nanoscale owing to near-field light localized at a metallic tip. In TERS, atomic force microscopy (AFM) is commonly used for tip position control. AFM is often controlled under the contact mode for TERS, whereas the tapping mode, which is another major operation mode, has not often been employed despite several advantages, such as low sample damage. One of the reasons is the low TERS signal intensity because the tip is mostly away from the sample during the tapping motion. In this study, we quantitatively investigated the effect of the tapping amplitude on the TERS signal. We numerically evaluated the dependence of the TERS signal on tapping amplitude. We found that the tapping amplitude had a significant effect on the TERS signal, and an acceptable level of TERS signal was obtained by reducing the amplitude to a few nanometers. We further demonstrated amplitude-controlled tapping-mode TERS measurement. We observed a strong dependence of the TERS intensity on the tapping amplitude, which is in agreement with our numerical calculations. This practical but essential study encourages the use of the tapping mode for further advancing TERS and related optical techniques.
针尖增强拉曼光谱（TERS）是一种用于在纳米尺度分析化学成分的强大工具，这得益于局域在金属针尖处的近场光。在TERS中，原子力显微镜（AFM）通常用于控制针尖位置。在TERS中，AFM常采用接触模式进行控制，而轻敲模式作为另一种主要操作模式，尽管具有诸如低样品损伤等诸多优点，却并不常被采用。其中一个原因是TERS信号强度较低，因为在轻敲运动过程中针尖大多远离样品。在本研究中，我们定量研究了轻敲幅度对TERS信号的影响。我们通过数值计算评估了TERS信号对轻敲幅度的依赖性。我们发现轻敲幅度对TERS信号有显著影响，将幅度减小到几纳米可获得可接受水平的TERS信号。我们进一步展示了幅度控制的轻敲模式TERS测量。我们观察到TERS强度对轻敲幅度有强烈依赖性，这与我们的数值计算结果一致。这项实用且重要的研究鼓励在进一步推进TERS及相关光学技术中使用轻敲模式。
