High-flux current effects in interfacial reactions in Au-Al multilayers

The influence of high dc currents (up to 1019 A cm(-2)) on the interaction between thin Au-Al layers was investigated over the temperature range 400-500degreesC. In contrast with earlier diffusion couple results, only four of the five intermetallic compounds in this system were observed, in both the absence and the presence of a current at all levels. The intermetallics Au5Al2 and Au2Al were the dominant products while AuAl and AuAl2 were relatively insignificant. The latter showed little change, growing only to a total thickness of a few micrometres, regardless of the magnitude of the current density and time of annealing. While the sequence of formation of the different intermetallics was not affected by the current, the incubation time and rate of growth of the layers were strongly influenced. The incubation time for the appearance of a measurable product layer was markedly reduced by the current, by nearly two orders of magnitude in some cases. The effect of the current on the nucleation of the product phases was investigated through the use of 'pre-nucleated' samples. The results are discussed in light of the effect of the current on atomic flux (electromigration) and on the formation of defects and compared with recent observations on field effects in multilayer systems.