Interference surface resistance control

A major advantage of the recently developed interference microscopy technique [74, 75] is that in addition to allowing a direct measurement of sorption/desorption rates on the single crystal scale it provides, from the form of the transient concentration profiles, direct experimental evidence concerning the nature of the rate controlling resistances to mass ffansfer. Recent studies by this technique have shown that the influence of sffuctural defects and surface resistance to mass transfer are far more important than has been generally assumed [76-80]. For some systems it appears that sorption rates are controlled by surface resistance while in other cases the profiles suggest a combination of... 

To prepare ultrathin polymer films on the surface of wafers, especially those of large diameter (6 or 8 inch), uniformity and defect density become important factors in determining the resist quality. The conventional spin coating method has been reported to introduce interference striations (11) and high defect densities (2.31 when used to prepare ultrathin polymer films. As an alternative approach, the LB technique has been proposed as being suited to the preparation of more uniform ultrathin polymer films (2). Using this technique monolayer polymer films can be transferred layer by layer to the surface of a solid substrate from the water surface. An important feature of the LB technique is that the accumulation of monolayer films allows the thickness of the built-up film to be controlled in a precise manner. Consequently, extremely uniform and ultrathin polymer films can be prepared. 

The Faradaic resistance or polarization resistance Rp is inversely proportional to the corrosion rate. It is evident from the Nyquist plot that the solution resistance. Rn, measured at high frequency can be subtracted from the sum of Rp and Rn at low frequency to give the value of Rp corrected for ohmic interferences from solution resistance. For processes controlled by diffusion in the electrolyte (concentration polarization) or in a surface film or coating, an additional resistive element called the Warburg impedance, W, must be included in the circuit. The Warburg impedance appears at low frequencies on the Nyquist plot as a straight line superimposed at 45° (slope = 1) to both axes, as shown in Fig. 31.5. 

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