Profiled microhole

PROFILED MICROHOLE, SPIRAL BEAM, AND ARRAY OF SQUARE COLUMNS... 

The theory has been verified by voltammetric measurements using different hole diameters and by electrochemical simulations [13,15]. The plot of the half-wave potential versus log[(4d/7rr)-I-1] yielded a straight line with a slope of 60 mV (Fig. 3), but the experimental points deviated from the theory for small radii. Equations (3) to (5) show that the half-wave potential depends on the hole radius, the film thickness, the interface position within the hole, and the diffusion coefficient values. When d is rather large or the diffusion coefficient in the organic phase is very low, steady-state diffusion in the organic phase cannot be achieved because of the linear diffusion field within the microcylinder [Fig. 2(c)]. Although no analytical solution has been reported for non-steady-state IT across the microhole, the simulations reported in Ref. 13 showed that the diffusion field is asymmetrical, and concentration profiles are similar to those in micropipettes (see... 

Another important parameter is the electrode polarity. Using an anode compared with a cathode results in very different microhole shapes, as discussed in Section 5.4. The microhole profile is also a function of the tool shape. For cylindrical tools (cathodes), the typical profile is conical but the hole bottom presents in general two bumps. These bumps, due to localisation of the discharges at the tool edges, are more pronounced for ceramic and composite materials than for glass [19]. 

In EMM, microtool surface finish is very important since it directly affects the mechanical strength of the tool [33] as well as machining accuracy. Therefore, precise microtools of micron scale size with a good surface quality are preferred while fabricating microfeatures like microhole, microgrooves, 3D cavities, and complex profiles. Microtools are generally fabricated in situ in an EMM setup or fabricated by other methods and are used in EMM. Machining accuracy improves with a reduction in... 

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