ONSET OF ELECTRICAL-CONDUCTION IN PT AND NI FILMS

The resistance R(f) of Pt and Ni films has been measured during deposition (by ion-beam sputtering) for different deposition rates r and substrate temperatures T(S) (300 less-than-or-equal-to T(S) less-than-or-equal-to 575 K). At the onset of deposition (the nucleation stage) R(f) varies only slowly with deposition time T and oscillations occur in R(f) vs T which are damped at the larger values of r, T(S). Over the second stage, during which the metallic nuclei grow in size, R(f) decreases over many orders of magnitude and the R(f) versus fractional coverage x behavior is described by percolation-type equations around a critical thickness t(c). The film thickness t(min) (=rT(min)) at which the film becomes continuous (x = 1) is identified with the minimum in the Rt2 vs t graph. For t > t(min) the R(f) vs t behavior is described by surface and grain-boundary scattering equations, the derived values of grain size are related to T(S), r, and compared with transmission electron microscope observations. Postdeposition temperature cycling measurements on films deposited at T(S) = 300 K show predominantly thermally activated conduction for t < t0 (t(c) < t0 < t(min)). Rf is decreased by annealing, except in the case of Pt (t < 1 nm) and Ni (t less-than-or-equal-to 1.5 nm), due to agglomeration and the formation of conducting links which also change the temperature coefficient of resistance.