Fractal Formation in Sputtered Films of Bi₂Sr₂CaCU₂O_7-x on Si Substrates

Fractal regions appearing in BSCCO films after annealing have been investigated by atomic force microscopy and transmission electron microscope. The fractal dimensions and fractal density (number of fractals per unit area) are temperature dependent. At lower annealing temperature (450°C) both the morphologies and fractal dimensions closely resemble those arising in two dimensional diffusion-limited-aggregation (DLA) simulations. The observation results show that after annealing at 600°C or higher temperature, the fractal regions changed, even disappeared, which means the growth mechanism is very different from that of traditional DLA. A random diffusion and successive nucleation model has been proposed to explain the results.