The integration of shear force sensing into SECM enables experiments in constant-distance mode (in comparison to conventional constant-height mode) with simultaneous acquisition of topography information. This is of special interest since the current response at the microelectrode is strongly distance-dependent. The microelectrode is equipped with two piezo crystals. By applying an AC voltage at the dither piezo, the microelectrode is set in vibration. The amplitude and phase of the vibration is recorded at both the dither and the receiver piezo. Close to the surface, shear forces occur and a change of amplitude and/or phase shift can be detected at the receiver piezo at certain frequencies. This sensing of shear forces enables a distance control within several nanometers of the surface without disturbance of electrochemical experiments.
