AFM-SECM

A Bruker Dimension Icon for AFM with a SECM unit was used to study surfaces in a liquid cell. The SECM measurements were carried out in a PeakForce SECM module, which combines peak force tapping (PFT) imaging mode with the AFM-SECM approach. AFM measurements were performed in PeakForce controlled mode at a force of ~50 nN. PeakForce SECM imaging scans the probe under the main scan first, then lift scan (Supplementary Note ¹) with 100 nm above sample surface. SECM measurements in this paper, here explicitly the recording of the feedback current were performed in the main scan mode, i.e., with the probe in close proximity of the sample⁴². The immersed sample was not externally contacted but charge neutrality was given by ion flow within the liquid cell (so called unbiased sample), which results in the measurable net charge flow occurring at the probe, which is by convention called “feedback”. The setup of the photoelectrochemical cell used in AFM-SECM system is shown in Supplementary Note ⁷.