Tracer self-diffusion and electromigration in thin tin films

A nondestructive tracer-scanning technique was devised to study lateral self-diffusion and electromigration in evaporated thin Sn films. The diffusional spreading and migration of tracer distributions of Sn119m in thin Sn film matrices was recorded over a temperature range 142–213 °C. Determination of the profile shape enabled the diffusivity D to be unfolded, while the profile shift provided values of the migration velocity V. The temperature-dependent results may be summarized as follows: (1) D= (1.8+1.9−0.9) ×10−5 exp(−10 700±700/RT) cm2/sec; (2) V= (1.07+1.10−0.54) ×10−4/T exp(−9800 ±650/RT) cm/sec at a current density of 1×104 A/cm2; and (3) the direction of self-electrotransport is toward the anode at all temperatures. From these data, values of the effective valence Z* and defect resistivity were derived from the Nernst-Einstein and Huntington formulas describing electrotransport. The results are consistent with a bulk-assisted grain-boundary transport mechanism involving a vacancy defect.