Significant increase of the intensity of the diffusion processes in condensed films is usually connected with the contribution of grain boundary diffusion as such films possess highly dispersed structure with the huge portion of grain boundaries. But at the same time if one investigates the diffusion it is difficult to separate the influence of volume, grain boundary and surface diffusion in materials with a small size structures.
In this work we present the results of studies of diffusion activity in systems with the components that form a phase diagram of simple cigar type, namely the Au-Cu film system prepared by subsequent condensation of components in vacuum. The measurements of electric resistance of multilayer Au-Cu system with 40 layers of Au and 40 layers of Cu with 2 nm thickness of each layer have shown the formation of almost homogeneous solid alloy already after the first heating up to 573K. Estimations of activation energies of processes taking place give the values from 0.43eV to 0.54eV. These values one should probably consider as the activation energy of the formation of homogeneous alloy from the multilayered system that is the activation energy of diffusion in such system.
Electron and X-Ray diffraction, Auger spectroscopy methods were used for investigation studying the diffusion activity in Cu-Au and Au-Cu film systems of variable thickness (20-3nm) with 1:1 ratio of components thicknesses prepared by means of vacuum condensation on the substrate at a room temperature. The formation of variable composition alloy at film thickness below 5nm was found independently from the sequence of the component deposition at a room temperature of the substrate. This result indicates the significant role of the size effect resulting in a great reduction of the vacancy formation energy among the diffusion processes caused by the condensation. Estimations of the effective coefficient of diffusion of Cu in to Au with 2 nm thickness of each component yield the value of ~ 10-15 cm2/c that exceeds the value of the coefficient of surface diffusion by 7 orders of magnitude. Such huge increase in the diffusion activity is probably caused by the determinative role of the vacancies in the grain boundary areas of the contacting layers.