Agilent 5991-4601EN Introduction to SECM and Combined AFM-SECM - Application Note c20140725 [5] free download

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Keysight Technologies Introduction to SECM and Combined AFM-SECM Application Note Introduction Scanning electrochemical microscopy (SECM) is a powerful scanning probe technique, which is suitable for investigating surface reactivity, and processes at the solid/liquid as well as liquid/liquid interface. Redox reactions and their kinetics involving active species are of fundamental importance in emerging research and application areas ranging from the analysis of biochemical signaling processes e.g., at live cells and tissues to relevant questions in material sciences including e.g., fuel cell technology, catalysis, sensing, and environmental chemistry. PD Dr. Christine Kranz, Institute of Analytical and Bioanalytical Chemistry, University of Ulm Dr. Shijie Wu, Keysight Technologies, Inc. While electrochemical scanning tunneling microscopy (EC-STM) and electrochemical atomic force microscopy (EC-AFM) are predominantly based on imaging structural/topographical and electronic changes at a biased macroscopic sample surfaces, SECM advantageously combines fundamental microelectrochemical information via the entire palette of electroanalytical techniques with imaging modalities. The scanning electrochemical microscope was introduced by Bard and coworkers with the fundamental principle entailing scanning a biased ultra-microelectrode (UME) as an imaging probe across the sample surface, while recording Faradaic (redox) currents at the UME, and optionally, also at the sample.1 In contrast to EC-AFM and EC- STM, SECM is not limited to conductive or biased samples. In addition, due to thoroughly developed theoretical descriptions and models SECM readily allows the quantification and prediction of experimental data. Since the introduction of SECM, a multitude of imaging modalities have been developed and experimentally demonstrated based on a wide variety of electrochemical analysis techniques including DC voltammetry2 , redox competition mode3, and alternating current (AC)-SECM imaging4. The so-called feedback mode is the most commonly applied imaging mode in SECM5. Here, the probe and the sample are immersed in a solution containing a redox active species (e.g., R providing a reversible redox behavior governed by diffusion). If an appropriate potential is applied at the probe, R is oxidized to O, thereby resulting in a steady state Faradaic current, which is proportional to the radius, r of the UME and the concentration, c of the redox species following I = 4nFDcr (n = number of transferred electrons, F = Faraday constant, D diffusion constant of the redox active species). If now the biased probe (i.e., the UME) is moved t