Scanning electrochemical

SECM Scanning electrochemical microscopy [40] An STM serves as microelectrode to reduce electroactive species Electrochemical reactions on surfaces... 

Fulian Q, Fisher A C and Denuault G 1999 Applications of the boundary element method in electrochemistry scanning electrochemical microscopy, part 2 J. Phys. Chem. B 103 4393... 

Selzer Y and Manler D 2000 Scanning electrochemical microscopy. Theory of the feedback mode for hemispherical ultramicroelectrodes steady-state and transient behavior Anal. Chem. 72 2383... 

Zhou F and Bard A J 1994 Detection of the electrohydrodimerization intermediate acrylonitrile radical-anion by scanning electrochemical microscopy J. Am. Chem. See. 116 393... 

Barker A L, Gonsalves M, Maepherson J V, Slevin C J and Unwin P R 1999 Scanning electrochemical microscopy beyond the solid/liquid interface Anal. Chim. Acta 385 223... 

Kranz C, Wittstock G, Wohlschlager FI and Schumann W 1997 Imaging of microstructured biochemically active surfaces by means of scanning electrochemical microscope Electrochim. Acta 42 3105... 

FIGURE 2-16 Design of a scanning electrochemical microscope. (Reproduced with... 

Scanning electrochemical microscopy can also be applied to study localized biological activity, as desired, for example, for in-situ characterization of biosensors (59,60). In this mode, the tip is used to probe the biological generation or consumption of electroactive species, for example, the product of an enzymatic surface reaction. The utility of potentiometric (pH-selective) tips has also been... 

Such approximation is valid when the thickness of the polymeric layer is small compared to die thickness of die crystal, and the measured frequency change is small with respect to the resonant frequency of the unloaded crystal. Mass changes up to 0.05% of die crystal mass commonly meet this approximation. In die absence of molecular specificity, EQCM cannot be used for molecular-level characterization of surfaces. Electrochemical quartz crystal microbalance devices also hold promise for the task of affinity-based chemical sensing, as they allow simultaneous measurements of both tile mass and die current. The principles and capabilities of EQCM have been reviewed (67,68). The combination of EQCM widi scanning electrochemical microscopy has also been reported recently for studying die dissolution and etching of various thin films (69). The recent development of a multichannel quartz crystal microbalance (70), based on arrays of resonators, should further enhance die scope and power of EQCM. 

Salicylate, 182 Sauebrey equation, 53 Scanning electrochemical microscopy, 49, 163... 

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 physical methods mostly require ultra high vacuum conditions having the disadvantage of not being applicable directly to solvent swollen films, but recent developments of in situ measurements in SIMS X-ray diffraction surface enhanced Raman spectroscopy (SERS) and scanning electrochemical tunneling microscopy... 

FIGURE 36.6 Typical configuration of a scanning electrochemical microscope. In this case the solution contains Ox species (mediators) that are reduced on the active part of the micro-electrode, yielding the reduced Red species. A possible reaction of the Red species with the substrate, with the reaction rate. illustrated. 

Bard AJ, Fan FRF, Pierce DT, Unwin PR, Wipf DO, Zhou FM. 1991. Chemical imaging of surfaces with the scanning electrochemical microscope. Science 254 68-74. 

Fernandez JL, Walsh DA, Bard AJ. 2005b. Thermodynamic guidelines for the design of bimetallic catalysts for oxygen electroreduction and rapid screening by scanning electrochemical microscopy. M-Co (M Pd, Ag, Au). J Am Chem Soc 127 357-365. 

Fernandez JL, White JM, Sun YM, Tang WJ, Henkelman G, Bard AJ. 2006. Characterization and theory of electrocatalysts based on scanning electrochemical microscopy screening methods. Langmuir 22 10426-10431. 

Scanning Electrochemical Microscopy as a Local Probe of Chemical Processes at Liquid Interfaces... 

Alternatively, a higher rate of mass transport in steady-state measurements with a larger UME can be obtained by using it as a tip in the scanning electrochemical microscope (SECM). The SECM has typically been employed for probing interfacial ET reactions [29]. Recently, micropipettes have been used as SECM probes (see Section IV.B below) [8b,30]. Although the possibility of probing simple and assisted IT at ITIES by this technique was demonstrated, no actual kinetic measurements have yet been reported. 

In scanning electrochemical microscopy (SECM) a microelectrode probe (tip) is used to examine solid-liquid and liquid-liquid interfaces. SECM can provide information about the chemical nature, reactivity, and topography of phase boundaries. The earlier SECM experiments employed microdisk metal electrodes as amperometric probes [29]. This limited the applicability of the SECM to studies of processes involving electroactive (i.e., either oxidizable or reducible) species. One can apply SECM to studies of processes involving electroinactive species by using potentiometric tips [36]. However, potentio-metric tips are suitable only for collection mode measurements, whereas the amperometric feedback mode has been used for most quantitative SECM applications. 

Perhaps the most important experimental progress made recently in electrochemistry was the introduction of a scanning electrochemical microscope (SECM). Tsionsky et al. have used SECM to study also the rate of ET across a lipid monolayer at the water-benzene interface [48,49]. The presence of the monolayer decreased the rate of ET, being the decrease more significant for longer hydrocarbon chains and larger lipid concentration in solution. It was thus concluded that the ET reaction does not occur at defect sites in the lipid monolayer. 

Bard, A.J. and Mirkin, M.V. (eds) (2001) Scanning Electrochemical Microscopy, Marcel Dekker, New York. 

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