Release Summary
Vibrational sum-frequency generation (VSFG) is a nonlinear spectroscopic method widely used to investigate the molecular structure and dynamics of surface systems. However, in far-field observations, the spatial resolution of this method is constrained by the diffraction limit, which restricts its ability to resolve molecular details in inhomogeneous structures smaller than the wavelength of light. To address this limitation, we developed a tip-enhanced VSFG (TE-SFG) spectroscopy system based on scanning tunneling microscopy (STM). Using this system, we detected VSFG signals from molecules adsorbed on a gold substrate under ambient conditions. Phase analysis of the interferometric VSFG spectra provided insights into the molecular orientation. Furthermore, the observed VSFG signals were confirmed to originate from a highly localized region within the gap between the STM tip apex and sample substrate. Thus, this method offers an innovative platform for nonlinear optical nanospectroscopy, enabling the investigation of surface molecular systems beyond the diffraction limit.
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