14. Polarimetric and Other Optical Probes for the Solid–Liquid Interface

The rise of nanoscience and nanotechnology has induced a remarkable change in the science of liquid surfaces and interfaces: from a macroscopic and thermodynamic oriented approach the field is now steadily moving towards a microscopic and atomistic understanding. However, the need to measure, monitor, understand and ultimately control (electro-) chemical and physical processes occurring at liquid interfaces and surfaces cannot been simply fulfilled by transferring the highly successful electron beam or ion beam techniques into the liquid environment due to the limited free path of electrons or ions. Optical techniques, especially polarimetric techniques, have experienced a renaissance in the surface science of the liquid–solid interface and will become even more important in the future. Despite the penetration depth of light is for all materials at least of the order of 100 nm or above, surface sensitive optical probes have been developed, capable of monitoring processes on the nanosecond scale with thickness resolution of less than a monolayer. On the first sight, however, the major disadvantage of optical probes, being of indirect nature compared to electron microscopy or spectroscopy, proves then to be a fascinating feature, because all polarimetric, linear or nonlinear intensity and sum frequency, or scattering optical probes require modeling the full system for understanding the interactions between the liquid and solid at the interface. In the following we will demonstrate, after an introduction to electrochemistry, with a few selected examples the power of polarimetric techniques for understanding the liquid interface and review prior work especially for the electrochemical interface by polarimetric probes. The importance of correlation measurements, mainly current voltage measurements and scanning probe techniques for a thorough understanding is finally highlighted.