Approaching the Ni percolation threshold by thin-film irradiation

We have reproduced a percolating structure in thin Ni films by an inhomogeneous sputtering process. The morphological disorder has been studied using TEM and 'in situ' transport measurements during ion irradiation. The fluence dependence of the resistance shows a singularity following a 2D percolation law. The formation of the hole structure is consistent with a Poisson mechanism. A computer simulation developed using a code based on a Poisson statistics allows us to account for the experimental values of the percolation threshold (pc=0.37) and the overall shape of the infinite cluster. (author)