In-Situ and Time-Resolved Ellipsometry for Probing Surface Terminations and Reaction Kinetics via Exciton Resonances

Description

Surface band-bending in semiconductors, commonly used in catalytic reactions or as sensors, serves as a direct indicator of
surface dipoles and can therefore be employed to monitor surface terminations and their kinetics. Using in-situ spectroscopic
ellipsometry [1, 2], we measured surface band-bending in-situ within an electrochemical environment. Remarkable sensitivity
was achieved when excitonic resonances were present in the accessible spectral range. Surface charge-induced electric fields
caused measurable changes in the dielectric function, even at very low potentials, due to screening effects on the excitonic
resonances (Fig. 1). We demonstrated these effects on crystalline ZnO surfaces, a material used, for instance, in CO2 reduction
catalysis with metal adsorbates [?]. The theoretical basis for the influence of electric fields on excitonic resonances has been
described already by Blossy [3].
We determined the flat-band potential and the undisturbed excitonic dielectric function with high precision, enabling
comparisons with intrinsic electric fields unavoidable present at most semiconductor surfaces. Finally, we utilized this
approach to study the charge transfer and reaction kinetics under anodic potentials in an aqueous solution of 0.1 M NaClO4
using pump-probe ellipsometry. This methodology provides a powerful tool for understanding semiconductor surface processes
in electrochemical environments.

Period	12 Jun 2025
Event title	10th International Conference on Spectroscopic Ellipsometry
Event type	Conference
Location	Boulder, United States, ColoradoShow on map
Degree of Recognition	International