Morphology of molybdena fractal clusters grown by vapour-phase deposition

Molybdena fractal clusters of various shapes were obtained experimentally in an evaporation-deposition system. The open ramified deposits grew after heating MoO3 powder at 750–900 °C for 0.5–2 h. They demonstrate two structural forms: the stack-like formation and the net-like one. Scanning electron microscopy observations revealed that the clusters consist of one of three different microstructures: needle-like whiskers, ribbon-like crystals, and fascicular crystals. Each pattern displays the microscopical anisotropy although they are of macroscopical self-similar feature. A nucleation-aggregation model is suggested to explain the non-equilibrium growth processes.