Kinetics of chemical compound growth by surface interdiffusion

The kinetics of lateral spreading and thickening of a layer of the intermetallic compound A(m)B(n) along the free surface of a substrate B caused by surface interdiffusion in a binary system A-B have been analyzed and studied experimentally in the Cd-Ni and Zn-Cu systems in the temperature ranges 200-280 degrees C and 160-280 degrees C, respectively, under compressive Ar pressures from 0.05 to 0.9 GPa. Over the Ni and Cu substrates the intermetallic compounds Cd21Ni5 and Cu5Zn8 were observed by scanning electron microscopy, atomic force microscopy and optical microscopy methods. By comparison of the experimental data on the growth kinetics with the proposed theory, the Cd and Zn diffusion coefficients over the Cd21Ni5 and Cu5Zn8, surfaces, respectively, have been calculated. Arrhenius equations have been obtained for pressures of 0.05 and 0.9 GPa, and the surface diffusion activation volumes have been determined for both systems. The surface diffusion mechanism has been discussed. (C) 2000 Elsevier Science B.V. All rights reserved.