Low-dimensional forest-like and desert-like fractal patterns formed in a DDAN molecular system

Two kinds of forest-like and desert-like patterns are formed by thermal evaporation of 4-dicyanovinyl-N, N-dimethylamino-1-naphthalene (DDAN) onto SiO₂ substrates. Based on thermal kinetics of the molecules on the substrate the transformation between the forest and desert patterns is due to two factors. The first one is the diffusion length, which is related to the deposition rate, the diffusion potential energy barrier and the substrate temperature. The second one is the strong interaction between the two polarity chemical groups of the molecules, which is beneficial to the formation of branches. Totally different patterns are also found on mica substrates, and are attributed to the anisotropic diffusion and the stronger interaction between DDAN molecules and the mica surface.