Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Diffusion scanning electrochemical microscopy

As described in the introduction, submicrometer disk electrodes are extremely useful to probe local chemical events at the surface of a variety of substrates. However, when an electrode is placed close to a surface, the diffusion layer may extend from the microelectrode to the surface. Under these conditions, the equations developed for semi-infinite linear diffusion are no longer appropriate because the boundary conditions are no longer correct [97]. If the substrate is an insulator, the measured current will be lower than under conditions of semi-infinite linear diffusion, because the microelectrode and substrate both block free diffusion to the electrode. This phenomena is referred to as shielding. On the other hand, if the substrate is a conductor, the current will be enhanced if the couple examined is chemically stable. For example, a species that is reduced at the microelectrode can be oxidized at the conductor and then return to the microelectrode, a process referred to as feedback. This will occur even if the conductor is not electrically connected to a potentiostat, because the potential of the conductor will be the same as that of the solution. Both shielding and feedback are sensitive to the diameter of the insulating material surrounding the microelectrode surface, because this will affect the size and shape of the diffusion layer. When these concepts are taken into account, the use of scanning electrochemical microscopy can provide quantitative results. For example, with the use of a 30-nm conical electrode, diffusion coefficients have been measured inside a polymer film that is itself only 200 nm thick [98]. [Pg.398]

Bath, D.B., et al. 2000. Scanning electrochemical microscopy of iontophoretic transport in hairless mouse skin. Analysis of the relative contribution of diffusion, migration, and electroosmosis to transport in hair follicles. J Pharm Sci 89 1537. [Pg.298]

Zhang, J., C.J. Slevin, C. Morton, P. Scott, D.J. Walton, and P.J. Unwin. 2001. New approach for measuring lateral diffusion in Langmuir monolayers by scanning electrochemical microscopy (SECM) Theory and application. J. Phys. Chem, B 105 11120-11130. [Pg.180]

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],... [Pg.178]

Formation or consumption of reacting species at the electrode surface causes concentration distribution of electroactive species in the solution phase during electrolysis. Equi-concentration contours stand for a concentration profile. A concentration profile can be measured by detecting current or potential by use of a small probe electrode at various locations near a target large electrode. A typical method is scanning electrochemical microscopy. See also diffusion layer, - scanning electrochemical microscope. [Pg.153]

The scanning electrochemical microscopy (SECM) technique introduced in recent years by Allen Bard is another area where the smallness of the electrode is essential [38]. The principle in SECM is a mobile UME inserted in an electrolyte solution. The UME is normally operated in a potentiostatic manner in an unstirred solution so that the current recorded is controlled solely by the spherical diffusion of the probed substance to the UME. The current can be quantified from Eqs. 48, 49, or 89 as long as the electrode is positioned far from other interfaces. However, if a solid body is present in the electrolyte solution, the diffusion of the substance to the UME is altered. For instance, when the position of the UME is lowered in the z direction, that is, towards the surface of the object, the diffusion will be partially blocked and the current decreases. By monitoring of the current while the electrode is moved in the x-y plane, the topology of the object can be graphed. The spatial resolution is about 0.25 pm. In one investigation carried out by Bard et al, the... [Pg.543]

FIG. 3 Basic principles of scanning electrochemical microscopy (SECM) (A) far from the substrate, diffusion leads to a steady-state current, iT (B) near a conductive substrate, feedback diffusion leads to iT > iT 0O (C) near an insulating substrate, hindered diffusion leads to iT < iT 0O. (Reprinted with permission from A. J. Bard, G. Denuault, C. Lee, D. Mandler, and D. O. Wipf, Acc. Chem. Res. 23, 357 (1990). Copyright 1990 American Chemical Society.)... [Pg.5]

A.L. Barker, J.V. Macpherson, C.J. Slevin, and P.R. Unwin (1998). Scanning electrochemical microscopy (Seem) as a probe of transfer processes in 2-phase systems— theory and experimental applications of secm-induced transfer with arbitrary partition-coefficients, diffusion-coefficients, and interfacial kinetics. J. Phys. Chem. B 102, 1586-1598. [Pg.570]

Fig. 3.25a-c Basic principles of scanning electrochemical microscopy a the small tip is far from the substrate, lU-tramicroelectrode behavior, steady state current, b near a conductive substrate, feedback diffusion leads to It > It, ==>, c near an insulating substrate, hindered difiusion leads to Ij < It,o -If,CO = 4nFDca, where n is the charge number of the electrode reaction, F is the Faraday constant, D is the difiusion coefficient, c is the concentration and a is the radius of the microdisk electrode, which is usually less than 20 Xm [15], (Reproduced with the permission of the American Chemical Society)... [Pg.107]

Leonhardt, K., Avdic, A., Lugstein, A. et al. (2013) Scanning electrochemical microscopy diffusion controlled approach curves for conical AFM-SECM tips. Electrochemistry Communications, 27, 29-33. [Pg.243]

Uitto OD, White HS, Aoki K (2002) Diffusive-convective transport into a porous membrane. A comparison of theory and experiment using scanning electrochemical microscopy operated in reverse imaging mode. Anal Chem 74(17) 4577-4582. doi 10.1021/ac0256538... [Pg.1834]

Unwin PR, Bard AJ (1992) Scanning electrochemical microscopy. 14. Scanning electrochemical microscope induced desorption - a new technique for the measurement of adsorption desorption-kinetics and surface-diffusion rates at the solid liquid interface. J Phys Chem 96(12) 5035-5045... [Pg.1835]


See other pages where Diffusion scanning electrochemical microscopy is mentioned: [Pg.295]    [Pg.108]    [Pg.195]    [Pg.139]    [Pg.145]    [Pg.122]    [Pg.125]    [Pg.180]    [Pg.428]    [Pg.447]    [Pg.639]    [Pg.145]    [Pg.184]    [Pg.220]    [Pg.628]    [Pg.804]    [Pg.1933]    [Pg.444]    [Pg.104]    [Pg.13]    [Pg.234]    [Pg.365]    [Pg.444]    [Pg.1380]    [Pg.1451]    [Pg.471]    [Pg.844]    [Pg.846]    [Pg.920]    [Pg.103]    [Pg.40]   


SEARCH



Electrochemical microscopy

Microscopy diffusion

Scanning electrochemical microscopy

© 2024 chempedia.info