REACTIVE WETTING-INDUCED AND DEWETTING-INDUCED DIFFUSION-LIMITED AGGREGATION

Diffusion-limited-aggregation-like fractals, formed by the wetting of an eutectic SnPb alloy ball on an Au/Cu/Cr multilayered thin film and the dewetting of SnPb from the Cr surface after the Au/Cu thin film un derneath the wetting cap was consumed, have been observed experimental ly. The wetting-formed fractal is inside the precursor of the SnPb wet ting cap, while the dewetting-formed fractal sits around the center of the SnPb cap. A unique characteristic of the former is that its growt h direction is opposite to the wetting direction of the SnPb. More int erestingly, the latter seems to be a reverse process of the regular fr actal formation, and it ends up with a diffusion-limited-aggregation-l ike pattern. The dimensions of the two fractal patterns are measured t o be 1.83 +/- 0.07 and 1.79 +/- 0.06. Their formation mechanisms are d iscussed in terms of diffusion-limited aggregation and its reverse pro cess, respectively.