Scanning electrochemical microscopy conducting surfaces

A variety of other techniques have been used to investigate ion transport in conducting polymers. The concentrations of ions in the polymer or the solution phase have been monitored by a variety of in situ and ex situ techniques,8 such as radiotracer studies,188 X-ray photoelectron spectroscopy (XPS),189 potentiometry,154 and Rutherford backscatter-ing.190 The probe-beam deflection method, in which changes in the density of the solution close to the polymer surface are monitored, provides valuable data on transient ion transport.191 Rotating-disk voltammetry, using an electroactive probe ion, provides very direct and reliable data, but its utility is very limited.156,19 193 Scanning electrochemical microscopy has also been used.194... 

The scanning tunneling microscope (STM) has led to several other variants (61). Particularly attractive for electrochemical studies is scanning electrochemical microscopy (SECM) (62-65). In SECM, faradaic currents at an ultramicroelectrode tip are measured while the tip is moved (by a piezoelectric controller) in close proximity to the substrate surface that is immersed in a solution containing an electroactive species (Fig. 2.17). These tip currents are a function of the conductivity and chemical nature of the substrate, as well as of the tip-substrate distance. The images thus obtained offer valuable insights into the microdistribution of the electrochemical and chemical activity, as well... 

Scanning electrochemical microscopy (SECM the same abbreviation is also used for the device, i.e., the microscope) is often compared (and sometimes confused) with scanning tunneling microscopy (STM), which was pioneered by Binning and Rohrer in the early 1980s [1]. While both techniques make use of a mobile conductive microprobe, their principles and capabilities are totally different. The most widely used SECM probes are micrometer-sized ampero-metric ultramicroelectrodes (UMEs), which were introduced by Wightman and co-workers 1980 [2]. They are suitable for quantitative electrochemical experiments, and the well-developed theory is available for data analysis. Several groups employed small and mobile electrochemical probes to make measurements within the diffusion layer [3], to examine and modify electrode surfaces [4, 5], However, the SECM technique, as we know it, only became possible after the introduction of the feedback concept [6, 7],... 

Within a regular scanning electrochemical microscopy (SECM) system, the probe microelectrode, called the tip electrode, can be precisely positioned several micrometers away from a substrate under the control of a three-dimensional motorized positioner in the solution containing redox-active species. By scanning the SECM tip within the plane paralleling a substrate surface and simultaneously monitoring tip current (/ [ ), which is sensitive to the presence of conducting and... 

Scanning tunnelling microscopy, scanning electrochemical microscopy, and AFM-surface potential measurements have also been used to investigate Nafion films. Scanning electrochemical microscopy reveals a domain-like structure containing circular features ca. 1-2 nm in diameter made up of a conductive center (presumed to be ion-rich regions) surrounded by a much less conductive zone. " Atomic force microscopy surface potential measurements detect features that were interpreted as ion channels in Nafion membranes. The size of the claimed ion channels was... 

Scanning electrochemical microscopy (SECM), which has an intermediate resolution between that of conventional lithography and AFM/STM, is useful for mapping the electrochemically active areas of electronically conductive patterns of the films [38] it also can be used for the special mode of coating of the surface of metallic electrodes with ECP films by electroless deposition [39]. 

Whitworth, A.L., Mandler, D. and Unwin, P.R. (2005) Theory of scanning electrochemical microscopy (SECM) as a probe of surface conductivity. Physical Chemistry Chemical Physics, 7, 356-365. 

Scanning Electrochemical Microscopy (SECM), Fig. 3 Mechanism of lateral electron transfer that is responsible for a positive feedback current in cases where the conductive surface is unbiased... 

Alternating current scanning electrochemical microscopy (AC-SECM) was recently used to detect precursor sites for localized corrosion on lacquered tinplates (114). AC-SECM utilizes the effect of an increasing (decreasing) solution resistance as the SECM tip approaches an insulator (conductor) for mapping domains of different conductivity/electrochemical activity on surfaces immersed in electrolytes. It was demonstrated that AC-SECM could be used to visualize microscopic cracks and holes in the coating of the lacquered tinplates. 

Fig. 20.31 Basic principles of scanning electrochemical microscopy (SECM). (A) Hemispherical diffusion far from electrode (B) feedback diffusion near a conductive electrode (C) hindered diffusion near an insulating electrode surface. The probe s electroactive area is shaded in the diagrams. (Reproduced with permission from Ref. 157.)...

A main advantage of electrochemical deposition is the ease of manipulation by deposition parameters, such as potential, time, concentration of monomers, and water content in the deposition solution. Many works have shown that the thickness and properties of sol-gel films are strongly dependent on the deposition conditions [2,18,21,36]. Specifically, nanostructured sol-gel films can be electro-deposited using a template as a building block. The templates used include an anodized aluminum oxide (AAO) membrane and a cetyltrimethylammonium bromide (CTAB) surfectant [28,37]. In addition, the electrodeposition of sol-gel films can also be spatially confined to conductive patterns on the electrode surface [38], or localized by a microelectrode using scanning electrochemical microscopy (SECM) [39,40]. 

Azevedo, J., C. BourdUlon, V. Derycke, S. Campidelli, C. Lefrou, and R. Comut. 2013. Contactless surface conductivity mapping of graphene oxide thin films deposited on glass with scanning electrochemical microscopy. Anal. Chem. 85 1812-1818. 

FIGURE 4.12 Typical parallel conductance, Op (a) and parallel capacitance (b) vs. tip displacement curves for a blunt W tip at 100% RH and 25°C for a mica substrate treated with solution A. Tip bias is 3V with respect to the Au counter electrode. The tip approaches the substrate surface at a rate of 3 nm/s. (Reprinted with permission from Fan, F.-R.F. and Bard, A.J., Imaging of biological macromolecules on mica in humid air by scanning electrochemical microscopy, Proc. Natl. Acad. Sci. USA, 96, 14222-14227, 1999. Copyright 1999 National Academy of Science, USA.)... 

Since the pioneering work of Rohrer and Binning,77 scanning tunelling microscopy (STM) has been used to image atomic-scale features of electrically conductive surfaces under ultra-high-vacuum but also at atmospheric pressure and in aqueous electrochemical environments. The ability of STM to image chemisorption and surface reconstruction is well... 

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