Advancing the Understanding of Surface Science through Nonlinear Optics and Electrochemistry

Surface characterization is essential for understanding chemical and electrochemical transformations occurring on surfaces or at interfaces. Battery electrode aging processes, biofilm growth, crystallization, and transport/signaling across cellular membranes are only a few examples of such phenomena. This special issue delves into applied electrochemistry and nonlinear optical techniques applicable to surface characterization.

Near-field techniques usually require specialized instrumentation. However, although much improvement has been made over recent years, many surface-characterization tools are still limited to samples in a vacuum; therefore, in-situ and in-operando experiments are impractical. On the other hand, optical techniques are more flexible and less demanding regarding sample handling. Still, they usually need more surface specificity and sensitivity, and in principle, they have a lower resolution compared to electron beam-based techniques.

On the other hand, optical techniques also offer different contrast modalities. For example, Second-harmonic generation (SHG) or surface-enhanced Raman spectroscopy (SERS) are versatile optical tools for probing surfaces. From symmetry considerations, SHG responses are forbidden from the bulk of metallic electrodes and observed only from the surface where the symmetry is broken. Thus, high sensitivity can be attained using SHG, and when both SHG and SERS are combined, selectivity and sensitivity can be achieved. In addition, nanofabrication of metallic surfaces can further improve the sensitivity of SHG and SERS by orders of magnitude due to local field enhancement.

In recent years, much improvement has been made in super-resolution microscopy and imaging, enabling fast yet high-resolution imaging over areas as large as half-by-half-millimeter squares. For the field of electrochemistry, such development is very important since it may open the door for real-time optical characterization of solid-liquid interfaces during charging/discharging cycles, which can potentially lead to significant improvements in the performance and durability of the electrode. These contributions not only expand the horizons of applied electrochemical science but also underline its influence on our daily lives and its pivotal role in addressing global challenges related to climate and energy.