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A non-optical shear-force-based detection scheme for accurately controlling the tip-to-sample distance in scanning electrochemical microscopy (SECM) is presented. With this approach, the detection of the shear force is accomplished by mechanically attaching a set of two piezoelectric plates to the scanning probe. One of the plates is used to excite the SECM tip causing it to resonate, and the other acts as a piezoelectric detector of the amplitude of the tip oscillation. Increasing shear forces in close proximity to the sample surface lead to a damping of the vibration amplitude and a phase shift, effects that are registered by connecting the detecting piezoelectric plate to a dual-phase analogue lock-in amplifier. The shear force and hence distance-dependent signal of the lock-in amplifier is used to establish an efficient, computer-controlled closed feedback loop enabling SECM imaging in a constant-distance mode of operation. The details of the SECM setup with an integrated piezoelectric shear-force distance control are described, and approach curves are shown. The performance of the constant-distance mode SECM with a non-optical detection of shear forces is illustrated by imaging simultaneously the topography and conductivity of an array of Pt-band microelectrodes.

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The potential of needle-type Pt disk nanoelectrodes as extremely miniaturized scanning probes for high resolution scanning electrochemical microscopy (SECM) was investigated. The accuracy of a piezoelectric shear-force based distance control allowed a precise positioning of the Pt nanoelectrodes in close proximity to the surface of interest not only in tip approach experiments but also throughout scanning and SECM imaging. As proof of the advanced quality of SECM imaging, high-resolution current and topography images of a three-dimensional LIGA microstructure will be presented both simultaneously acquired by operating Pt nanoelectrodes in the constant-distance mode of SECM.

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