Instantaneous Granulometry of a Discontinuous Metal Condensate Deduced by Measuring Its Conductance and Thickness

During the formation of granular metal condensates on dielectric substrates, the measurements both of their sheet conductance C sub c and their mass thickness w make possible the calculation of the mean values of the edge-to-edge distance s between the grains and of their diameter a. This method allows the determination of granulometric quantities under ultra high vacuum (UHV) without disturbing the growth of the condensate. Analytic calculations cannot be done directly. They must be performed by successive approximations. Previous papers used a gradient optimization method which computed the derivate of the function C sub c (s, a). Using this derivate in order to determine the granulometric quantities of a condensate during the deposition process generates noise and singularities which can give wrong (or no) solutions. The present computation is achieved by another method of optimization which does not use the derivate and thereby allows a more consistent solution to be found. For each pair of experimental values C sub c and w, a defect function is defined by weighing the difference between their theoretical and experimental values. All the optimization methods need a starting value of a and s in order to evaluate the first defect function. The choice of these starting values is essential. After the first measurement, the continuity of these quantities (s and a) during the deposition is utilized. For this reason one can use the preceding determination of a and s during the growth of the condensate under UHV. The rapidity and the reliability of the computation are essential for the use of the granulometric computation in monitoring the formation of such condensates. Results are shown for Au on amorphous carbon or on MgO. Graphs. 8 ref.--AA