The evolution of island formation during submonolayer growth of poly(chloro-p-xylylene) films on naturally grown silicon oxide substrates is investigated using atomic force microscopy (AFM), and analyzed within the framework of dynamic scaling theory. A transition of film growth mechanism from diffusion-limited aggregation to reaction-limited aggregation is dramatically displayed in an unprecedented progression of the island density distribution functions. As surface coverage increases, a conventional bell-shaped monomodal distribution in early growth regime (θ = 0.07) gradually changes to a monotonically decreasing function, approximately following a power-law. The marginal power-law scaling behavior of the island distribution functions, reminiscent of the behavior of colloid aggregation, strongly suggests that film growth by vapor deposition polymerization is a new type of surface growth governed by reaction-limited aggregation process in which the competition between diffusion and deposition does not define the typical time scale of film growth.

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