Sum-Frequency Generation Spectroscopy
Sum-frequency generation (SFG) spectroscopy is used to assess the vibrational properties of surfaces and interfaces with a monolayer sensitivity. Unlike Raman spectroscopy that is sensitive to the bulk properties, SFG spectroscopy is exquisitely sensitive to the physical and chemical properties of molecular layers at surfaces and interfaces where inversion symmetry is broken.
In SFG spectroscopy, a mid-IR beam is sent onto the surface or interface where it is overlapped with a visible beam. The specific properties of the resulting sum-frequency signal, such as polarization and intensity, provide information on dipole orientation and vibrational spectra at the surface. SFG is a second-order nonlinear process and is allowed only when inversion symmetry is broken, making it a specifically surface-sensitive method. In this type of spectroscopy, one of the pulses is required to have a sufficiently narrow spectral bandwidth in order to obtain a high spectral resolution and, subsequently, distinguish the vibrational fingerprints of the investigated molecules.
One of the main scientific targets of SFG spectroscopy is studying the dynamics of interfacial water, which is done by observing the OH stretching vibrations of normal water and OD stretching vibrations of heavy water at 2.6 – 3.5 μm and 3.5 – 4.5 μm, respectively. Other spectral ranges of interest are 4.5 – 5.5 μm, where the vibrations of metal carbonyls and nitriles occur, and 5.5 – 6.5 μm, where molecular vibrations of interfacial biomolecules take place. Moreover, going further into the mid-IR is also of high interest due to lower frequency biomolecular vibrations.
Broadband mid-IR source such as ORPHEUS-MIR, pumped by PHAROS or CARBIDE laser, covers the spectral ranges of interest and addresses many vibrational levels at once, while SHBC is used to double the laser frequency and narrow down the spectral bandwidth to match the aforementioned requirements. In this configuration, the SFG signal is generated in the visible spectral range, eliminating the need for complex infrared detection.
- Up to 800 cm-1 spectral bandwidth
- 2500 – 15 000 nm tuning range
- < 100 fs pulse duration
- Up to 400 kHz repetition rate
- CEP-stable option
- 515 nm output
- < 10 cm-1 spectral bandwidth
- 2 – 4 ps pulse duration
- > 30% conversion efficiency
- Compact footprint
- High conversion efficiency in MIR
- 1350 – 16000 nm tuning range
- Single-shot – 2 MHz repetition rate
- Up to 80 W pump power
- Up to 2 mJ pump pulse energy
- 189 nm – 20 μm tuning range
- Up to 5 mJ pump pulse energy
- > 25% conversion efficiency
- CEP stabilization of Idler
- 100 fs – 20 ps tunable pulse duration
- 4 mJ maximum pulse energy
- 20 W maximum output power
- Single-shot – 1 MHz repetition rate
- Automated harmonic generators (up to 5th harmonic)
Direct imaging of electric field behavior in 2,7-diphenylbenzothieno[3,2-b]benzothiophene organic field-effect transistors by sum-frequency generation imaging microscopy
C. Katagiri, T. Miyamae, H. Li, F. Yang, and S. Baldelli, Physical Chemistry Chemical Physics 8 (23), 4944-4950 (2021).
Influence of Microcrystallinity on the CO/Pt(poly) Electrode Surface Using Sum Frequency Generation Microscopy Combined With Electrochemistry
H. Li, and S. Baldelli, The Journal of Physical Chemistry C (2021).
In Situ Spectroscopic Probing of Polarity and Molecular Configuration at Aerosol Particle Surfaces
Y. Qian, G. Deng, and Y. Rao, The Journal of Physical Chemistry Letters 16 (11), 6763-6771 (2020).
Robust Binding of Disulfide-Substituted Rhenium Bipyridyl Complexes for CO2 Reduction on Gold Electrodes
M. Cattaneo, F. Guo, H. R. Kelly, P. E. Videla, L. Kiefer, S. Gebre, A. Ge, Q. Liu, S. Wu, T. Lian et al., Frontiers in Chemistry 8 (2020).
High-resolution and high-repetition-rate vibrational sum-frequency generation spectroscopy of one- and two-component phosphatidylcholine monolayers
F. Yesudas, M. Mero, J. Kneipp, and Z. Heiner, Analytical and Bioanalytical Chemistry 19 (411), 4861-4871 (2019).
Plasmonic Effects of Au Nanoparticles on the Vibrational Sum Frequency Spectrum of 4-Nitrothiophenol
M. Linke, M. Hille, M. Lackner, L. Schumacher, S. Schlücker, and E. Hasselbrink, The Journal of Physical Chemistry C 39 (123), 24234-24242 (2019).
Vibrational Energy Redistribution between CH Stretching Modes in Alkyl Chain Monolayers Revealed by Time-Resolved Two-Color Pump–Probe Sum Frequency Spectroscopy
M. Lackner, M. Hille, and E. Hasselbrink, The Journal of Physical Chemistry Letters 1 (11), 108-112 (2019).
Vibrational sum-frequency generation spectroscopy of lipid bilayers at repetition rates up to 100 kHz
F. Yesudas, M. Mero, J. Kneipp, and Z. Heiner, The Journal of Chemical Physics 10 (148), 104702 (2018).
Chemical Imaging of Self-Assembled Monolayers on Copper Using Compressive Hyperspectral Sum Frequency Generation Microscopy
D. Zheng, L. Lu, K. F. Kelly, and S. Baldelli, The Journal of Physical Chemistry B 2 (122), 464-471 (2017).
Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy
H. Wang, T. Gao, and W. Xiong, ACS Photonics 7 (4), 1839-1845 (2017).