Scanning photoelectrochemical microscopy (SPECM) enables the investigation of photoelectrochemical processes at a substrate by integrating an illumination system into a conventional SECM set-up. The illumination can be integrated below the photoactive substrate, irradiating the substrate from the back (back illumination) or above the substrate, irradiating the substrate from the top by using a glass fiber inserted into a glass capillary (front illumination). Generally, the photocurrent at the substrate is recorded. The illumination from the back allows the detection of e.g. oxygen, which was produced in the photoreaction at a conventional UME. In the case where the illumination is realized via a glass fiber inside a single-barrel capillary, only the photocurrent at the substrate can be detected. Inserting an Ag wire into the capillary allows additional measurements of ion conductance currents. This can be used in a SICM experiment for distance-control of the capillary. In another setup with front illumination, a double-barrel or theta capillary is used. One barrel can be modified to yield a carbon UME whereas the second barrel is used for introducing the glass fiber for illumination. Certainly, other combinations of substrate illumination and recording of photocurrents are possible.

SECM SPECM application
Back illumination and recording of photocurrent at the photoactive substrate and ORR current at the UME.
SECM SPECM application
Front illumination through a glass fiber inside a capillary and recording of the photocurrent.
SECM SPECM application
Front illumination through a glass fiber inside a theta capillary and recording of photocurrent at the photoactive substrate and ORR current at the UME.