Sakurai Atsunori, Takahashi Shota, Mochizuki Tatsuto, Sugimoto Toshiki
Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Aichi 444-8585, Japan.
Graduate Institute for Advanced Studies, SOKENDAI, Okazaki, Aichi 444-8585, Japan.
Nano Lett. 2025 Apr 23;25(16):6390-6398. doi: 10.1021/acs.nanolett.4c06065. Epub 2025 Apr 10.
Vibrational sum frequency generation (SFG) is a nonlinear spectroscopic technique widely used to study the molecular structure and dynamics of surface systems. However, the spatial resolution achieved by far-field observations is constrained by the diffraction limit, obscuring molecular details in inhomogeneous structures smaller than the wavelength of light. To overcome this limitation, we developed a system for tip-enhanced SFG (TE-SFG) spectroscopy based on a scanning tunneling microscope. We successfully detected vibrational TE-SFG signals from adsorbed molecules on a gold substrate under ambient conditions. The phase analysis of interferometric SFG spectra provided information on molecular orientation. Furthermore, the observed TE-SFG signal was confirmed to originate from a highly localized region within a gap between the tip apex and the sample substrate. This method offers a novel platform for nonlinear optical nanospectroscopy, paving the way for the investigation of surface molecular systems beyond the diffraction limit.
振动和频产生（SFG）是一种非线性光谱技术，广泛用于研究表面系统的分子结构和动力学。然而，远场观测所实现的空间分辨率受到衍射极限的限制，使得小于光波长的非均匀结构中的分子细节变得模糊不清。为了克服这一限制，我们基于扫描隧道显微镜开发了一种用于针尖增强SFG（TE-SFG）光谱的系统。我们成功地在环境条件下检测到了金基底上吸附分子的振动TE-SFG信号。干涉SFG光谱的相位分析提供了分子取向的信息。此外，观察到的TE-SFG信号被证实源自针尖顶端与样品基底之间间隙内的一个高度局域化区域。该方法为非线性光学纳米光谱提供了一个新的平台，为超越衍射极限研究表面分子系统铺平了道路。
