MEASUREMENTS OF INTERDIFFUSION IN ELECTRODEPOSITED NICKEL-PHOSPHORUS MULTILAYERS

The interdiffusivity within multilayered electrodeposited thin films of NiP(x)/Nip(y) has been measured using an x-ray technique. The NiP(x), which can be deposited in the range 0 less-than-or-equal-to x less-than-or-equal-to 25 at. %, is crystalline at low phosphorus content but amorphous at high phosphorus content, so that films with a range of crystalline and amorphous structures could be prepared. Measurements on fully amorphous multilayers, where x,y > 18 at. %, give an interdiffusivity of order 10(-22) m2 s-1 at 120-degrees-C, which decreases with time, probably due to structural relaxation. The diffusivity decreases with decreasing repeat length of the films, with a critical repeat length of 40 angstrom. Crystalline/amorphous films show qualitatively different behavior, with the low-phosphorus layer governing the extent of a more limited diffusion phenomenon. This has been interpreted as the diffusion of phosphorus into a limited number of sites within the grain boundaries of the crystalline layers.