Surface potential sample problem

Fig. 1.25. The s-wave-tip model. The tip was modeled as a spherical potential well of radius R. The distance of nearest approach is d. The center of curvature of tip is To, at a distance (R + d) from the sample surface. Only the 5-wave solution of the spherical-potential-well problem is taken as the tip wavefunction. In the interpretation of the images of the reconstructions on Au(llO), the parameters used are R = 9 A, d = 6 A. The center of curvature of the tip is 15 A from the Au surface. (After Tersoff and Hamann, 1983.)...

Coulometry. If it can be assumed that kinetic nuances in the solution are unimportant and that destmction of the sample is not a problem, then the simplest action may be to apply a potential to a working electrode having a surface area of several cm and wait until the current decays to zero. The potential should be sufficiently removed from the EP of the analyte, ie, about 200 mV, that the electrolysis of an interferent is avoided. The integral under the current vs time curve is a charge equal to nFCl, where n is the number of electrons needed to electrolyze the molecule, C is the concentration of the analyte, 1 is the volume of the solution, and F is the Faraday constant. 

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