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Updated: May 25, 2025
Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy
Published on: May 27, 2018
Single-molecule-level detection of interfacial molecular structures and ultrafast dynamics
Xiaoxuan Zheng1,2, Junjun Tan2, Quanbing Pei1
1Hefei National Research Center for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China Hefei Anhui 230026 China shujiye@ustc.edu.cn yiluo@ustc.edu.cn.
Researchers developed a new technique combining femtosecond sum frequency generation vibrational spectroscopy (SFG-VS) with nanoparticle-on-mirror (NPoM) nanocavities to detect ultrafast molecular dynamics at the single-molecule level. This NPoM-SFG-VS method achieves unprecedented sensitivity for studying interfacial molecular behavior.
Area of Science:
- Surface Science and Spectroscopy
- Physical Chemistry
- Nanotechnology
Background:
- Understanding ultrafast dynamics of interfacial molecules is crucial for chemical and biological processes.
- Existing techniques often lack the sensitivity to probe dynamics at the single-molecule level.
- Interfacial molecular behavior dictates surface properties and reactivity.
Purpose of the Study:
- To develop a novel technique for detecting ultrafast vibrational dynamics at the single-molecule level.
- To demonstrate the capability of nanoparticle-on-mirror (NPoM) integrated with femtosecond sum frequency generation vibrational spectroscopy (SFG-VS) for single-molecule sensitivity.
- To investigate the vibrational dynamics and concentration-dependent behavior of interfacial molecules.
Main Methods:
- Integration of femtosecond sum frequency generation vibrational spectroscopy (SFG-VS) with nanoparticle-on-mirror (NPoM) nanocavities (NPoM-SFG-VS).
- Utilized the symmetric stretching vibrational mode (νNO) of para-nitrothiophenol as a probe.
- Prepared self-assembled monolayers (SAMs) with controlled solution concentrations (C) to assess sensitivity and correlation.
Main Results:
- Achieved single-molecule-level sensitivity, detecting signals from approximately 60 molecules using NPoM-SFG-VS.
- Determined the dephasing time (0.33 ± 0.01 ps) and vibrational relaxation time (2.2 ± 0.2 ps) for νNO at the single-molecule level.
- Established a correlation between the peak frequency of νNO and SAM preparation concentration (C), with single-molecule detection achieved at C ≤ 10⁻¹⁰ M.
Conclusions:
- The NPoM-SFG-VS technique provides unprecedented insights into the structures and ultrafast vibrational dynamics of individual interfacial molecules.
- This method enables mapping of microregion distribution of interfacial molecule numbers, advancing surface characterization.
- The findings facilitate precise engineering of surface properties and reactivity through a deeper understanding of single interfacial molecules.
