SECM
AC-SECM in constant distance
This instrument is a high resolution scanning electrochemical microscope with a positioning unit consisting of 3 stepper motors (OWIS, Staufen, 0,625 µm/halfstep) and a piezo electric positioning unit ("nanocube"). Hence, the lateral resolution excels the probe diameter by at least two orders of magnitude. Experiments can be performed in constant tip-to-sample distance using a piezo-piezo shear-force height control. The two piezo ceramics needed are obtained from Piezomechanik Pickelmann, München, and the phase sensitive detection of the tip's resonance frequency is done using the Lock-In amplifier 7280 by Perkin Elmer. Shear force distance control guarantees the mapping of electrochemical activity to be unimpaired by topographic features of the substrate. Topography and local electrochemical properties of the surface are imaged simultaneously. A second Lock-In amplifier (EG & G, Model 5210) allows to carry out alternating current measurements. Similar to impedance measurements the AC-mode of this instrument delivers information about the surface conductivity, just that the data of the scanning electrochemical microscope is obtained locally with good lateral resolution.