Nonlinear diffusion in modulated structures and low temperature kinetics at the aluminum-silicon interface

umerical analysis techniques are employed to model diffusion in composition modulated structures (Au-Ag and AlAs-GaAs) and in spinodal alloys (negative diffusion coefficients) using the nonlinear diffusion equation developed by Cahn. This model links the infinitesimal fluctuations of the early stages of spinodal decomposition with the corresponding stationary states. The modelling of the early exponential growth, the nonlinear intermediate stage and the final stationary state, as well as the error analysis and derivation of the stability criteria for convergence with the analog solution, is described in detail.;The diffusion kinetics of the aluminum-silicon system at low temperatures has been characterized by a novel technique. Previously published studies used bulk samples (plates or wires) to determine bulk diffusivities, or thick films of 1 or 2 micrometers Al on a silicon substrate to investigate the diffusion kinetics; whereas the present samples consist of thin films comprised of alternately deposited ultrathin layers of Al and Si. This approach permits the characterization of the diffusion kinetics at the Al-Si interface through the cumulative effects of several hundred interfaces while minimizing the effects of bulk material.;Composition modulated films with wavelengths of 1.3 to 6.0 nanometers were prepared by thermal evaporation of Al and Si. The resistivity of these films was monitored by the "four-point probe" technique during isothermal annealing at temperatures in the range of 75C to 150C. The resistivity was observed to increase initially and later decrease, eventually stabilizing at a value lower than the starting resistivity. The increase in resistivity is attributed to an increase in disorder caused by Si diffusing into the Al layers, and the decrease in resistivity to stress relief in the film.;Analysis of the data has allowed the calculation of diffusion coefficients (D(75C) = 1.9...