Microelectrode microband

In the case of microcyclinders and microbands, fG,micro is time dependent (Table 2.3) and only a pseudo-stationary response can be achieved. This is because all the microelectrode dimensions have to fall in the range of the microns to attain a true steady state. The expressions for the pseudo-stationary current-potential responses when the diffusion coefficients of species O and R fulfills Dq = Dr are ... 

Nevertheless, it is possible to obtain a constant relationship between the current at both microelectrodes for certain geometrical conditions. Thus, for microbands and microhemicylinders fulfilling rc = w/4, a constant ratio is obtained, but in this case it is necessary to use the same experimental timescale [10] ... 

For microelectrodes like microbands or microcylinders for which /g,micro is not constant, only pseudo-stationary behavior can be achieved. 

The UMDE evinces strong edge effects or very uneven current densities along the radius of the disk. It shares this problem with all the other flat microelectrodes such as microbands or rings. The exception of course are the hemispherical or hemicylindrical microelectrodes, which have no effective edges and behave as half of a sphere or cylinder, and also deeply recessed disks or bands, which approach the shrouded types. 

Miniaturization of electrodes and of electrochemical cells has had considerable Impact on electrochemical sensor design as well as on fundamental electrochemical studies (9,29). Microelectrodes In particular have opened up new avenues for designing electrochemical sensors. Microelectrodes are physically small electrodes (microdisks have radii of 1-3 microns, microbands have widths down to ca 5 nm). Such... 

R. G. Compton, A. C. Fisher, R. G. Wellington, P. J. Dobson, and P. A. Leigh. Hydrodynamic voltammetry with microelectrodes Channel microband electrodes - Theory and experiment, J. Phys. Chem. 97, 10410-10415 (1993). 

A number of methods exist for fabricating microelectrode arrays [6] and a variety of array geometries are encountered with the most common being arrays of microdiscs and arrays of microbands. Microdiscs are most frequently arranged as a regularly distributed (i.e., a square or... 

The diamond growth can also be patterned to produce microelectrode array structures [18,19]. Several possible microstructures are possible, such as microbands, microdiscs, and microcolumns. Micropyramids are another microstructure that can be produced, and an image of such an array is shown in Fig. 5. The SEM image reveals a monolithic diamond-tip array. The tips are ca. 2 pm in base diameter and are equally positioned over the surface with a spacing of ca. 5 pm. 

In the last decade special attention has been paid to this type of electrode arrangement. Two eventualities appeared in electroanalytical practice. The first one is represented by assemblies of casually or regularly arranged micro- or ultramicroelectrodes. The second eventuality is realized by a set of microbands that have the length of macroscopic dimension (usually several mm of magnitude, cf. Fig. 10). These types are not microelectrodes in the proper sense of this term. They are fabricated usually by microlithographic techniques. 

One of the characteristics of microelectrodes is an enhanced rate of mass transport of reactants and products to and from the electrode surface. Nonlinear diffusion prevails at microelectrodes two-dimensional diffusion at microcylinder or microband electrodes and three-dimensional diffusion at microspherical and microdisk electrodes. The enhanced mass transport at microelectrodes, which is often called the edge effect, causes increased current density and results in steady-state current responses at sufficiently slow potential sweep rates in potential sweep voltammetry, as will be illustrated in section 3. 

Microelectrode suuctures have been created that mimic aspects of brain function. Amatore and coworkers have described assemblies of paired microband electrodes that behave like a neuronal synapse (26). The generator electrode in these devices mimics a synaptic terminal, and the collector electrode functions as a postsynaptic membrane. These artificial synapses can be designed in several configurations to perform Boolean logical operations, such as AND or OR operations. 

Since at short times, a microelectrode behaves as a conventional electrode, all the theories developed for potential steps and potential sweeps at large electrodes are applicable. Conversely, at long times, the theories developed for steady-state techniques are applicable. However, the geometry of the electrode determines the expression for the limiting current. The most important ones are given in Table 11.3. For microbands and microcylinders, the current reaches a quasi-steady state. This is a consequence of the infinite length of the electrode relative to its characteristic dimension. 

Harriman K, Gavaghan DJ, Houston P, Kay D, Siili E (2000) Adaptive finite element simulation of currents at microelectrodes to a guaranteed accuracy. ECE and EC2E mechanisms at channel microband electrodes. Electrochem Commun 2 576-585... 

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