Christophe Humbert
CNRS, Université Paris-Saclay, Institut de Chimie Physique

“Nonlinear vibrational and electronic spectroscopy at interfaces: a probe traveling from the atom to complex systems”

Surfaces and interfaces play a vital role in Physics and Chemistry because they are the place where fundamentals reactions occur between molecules when two materials differing by their nature and/or their physical phase are in interaction. Vibrational spectroscopies such as IR and Raman are nondestructive analysis tools of in situ chemistry at interfaces but when considering monolayers or less, they may suffer from their lack of sensitivity to discriminate between “bulk” and “surface-adsorbed” molecules. Nonlinear optics and especially Two-Colour Sum-Frequency Generation (2C-SFG) spectroscopy offers a solution to overcome this issue. As showed in this presentation, after establishing the main principles governing this specific technique, we will see that 2C-SFG can be applied to address fundamental questions related to heterogeneous chemistry, interfacial electrochemistry, catalysis and more recently metal and semiconducting nanomaterials [1] within an original theoretical framework based on Feynman loop diagrams unifying Optics and Condensed Matter Physics [2]. In fact, the particular selection rules of this vibro-electronic spectroscopy gives access to unique and complementary information with respect to the traditional optical investigation probes.