Vibrational Spectroscopy at Surfaces and Interfaces Using Synchrotron Sources and Free Electron Lasers

4. Conclusion and Outlook

In this chapter, we have addressed the issues of an IR beam extracted from a synchrotron ring, and reported on its potentiality for the investigation of the vibrational properties of interfaces, especially in the far IR spectral range, where conventional sources are too low in brightness. Several FTIR instruments are operating or being developed on several synchrotron rings and are expected to bring valuable quantitative information on the adsorbate-substrate bonding, as well as their vibrational dynamics. Accessing this information should be a critical step towards a better understanding of the energetics and the kinetics of interfacial processes, especially in electrochemical interfaces, where adsorption is always a competitive process between the ionic species and the solvent dipoles, which is controlled by the electrode potential.

The development of optical non-linear techniques benefits directly from the progress of the laser technology. In this respect, the Free electron laser offers a great advantage of producing a high power pulsed beam, tunable within a wide IR spectral range, allowing the simultaneous probe of several vibrational modes of the adsorbate. Combining the unique properties of the FEL with the high sensitivity and interface selectivity of SFG between centro-symmetric media allows the investigation of the vibrational properties of adsorbate species, with no interference from a signal of bulk species, which is forbidden in the electric dipole approximation. The recent experimental examples discussed in this lecture show clearly the advantage of this technique. The use of SFG, as well as various related second order optical processes, is increasing rapidly in various surface and interface research fields such as catalysis, corrosion, electrocatalysis, thanks to its versatility, its capability to probe any interface.