We note a negative slop of the sum from the surface to the maximal
exchange depth. As with copper, we assume that NPs are formed
into the Tin region, as a consequence we can estimate a maximal
average fill factor fav=0.005 for l=8 μm. An estimate of the diffusion
coefficient D for silver and copper is given by the typical evolution
law of the concentration C(x,t) [21]: