Geometrical study of the sequence of development of interfaces in a carbon-metal thin multilayer structure

Abstract

The sheet conductance and the thickness are both recorded during the successive condensations of amorphous carbon (a-C) and of a metal (Ag or Au). These recordings showed that a new a-C film is set up after filling the intergranular spaces of each metallic condensate. During the metal condensations, a computation program expresses the pair of recorded measurements in terms of granulometric quantities (concentration of grains, mean diameter, intergranular separation.), During the carbon evaporation, this program indicates a possible coalescence between grains of metal deposit at the beginning of a-C covering. After fixation of the deposit geometry, the same program gives us the value of a-C thickness for which the grains are entirely buried. If the metallic condensate is correctly modelled, this thickness should be in good agreement with the abscissa of the change of slope in the curve of sheet conductance versus condensed carbon thickness. By comparing these evolutions as the stacking sequence progresses, it is shown, that, for the same thickness of metal condensates, the concentration of grains and fractional area of substrate which is covered, are increasing whereas both their diameter and their separation are decreasing. This result is explained by an increasing concentration of the preferred nucleation sites as the number of bilayers is raised.