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Third-order effects in resonant sum-frequency-generation signals at electrified metal/liquid interfaces
Patrick Koelsch1, Mutlu Muglali, Michael Rohwerder
1National ESCA and Surface Analysis Center for Biomedical Problems, Department of Bioengineering, University of Washington, Box 35170, Seattle, Washington 98195-1750, USA.
Journal of the Optical Society of America. B, Optical Physics
|November 16, 2013
Summary
Third-order effects were observed in vibrational sum-frequency-generation (SFG) spectroscopy at electrified interfaces. This finding advances the understanding of resonant SFG signals in self-assembled monolayers (SAMs).
Area of Science:
- Surface Science
- Spectroscopy
- Electrochemistry
Background:
- Vibrational sum-frequency-generation (SFG) spectroscopy is a powerful technique for studying surfaces and interfaces.
- Electrified interfaces, crucial in electrochemistry and materials science, present complex environments for spectroscopic analysis.
- Third-order nonlinear optical effects can arise from the interaction of multiple electromagnetic fields at interfaces.
Purpose of the Study:
- To investigate the presence and significance of third-order effects in resonant SFG signals at electrified interfaces.
- To analyze the contribution of third-order nonlinear optical phenomena in self-assembled monolayers (SAMs) under electrochemical conditions.
- To quantify the ratio of third-order to second-order nonlinear optical susceptibilities.
Main Methods:
- Utilized broadband vibrational sum-frequency-generation (SFG) spectroscopy.
- Employed a thin-layer analysis cell for spectro-electrochemical investigations of a hydrophobic araliphatic SAM on Au(111) in a 100 mM NaOH electrolyte.
- Separated resonant and non-resonant contributions and analyzed data using a fitting function incorporating third-order terms.
Main Results:
- Demonstrated that mixing incident laser fields and the surface electric field can induce third-order effects in resonant SFG signals.
- Observed these effects in well-ordered SAMs with optically nonlinear molecular groups and significant surface potentials.
- Estimated the ratio of third-order to second-order susceptibilities to be on the order of 10-10 m/V.
Conclusions:
- Third-order nonlinear optical effects are significant in SFG spectroscopy at electrified interfaces, particularly for SAMs with high optical nonlinearity.
- The study provides a quantitative estimation of these third-order contributions, enhancing the interpretation of SFG spectra.
- This work offers new insights into the nonlinear optical response of molecules at electrochemical interfaces.
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