Faster Is Smoother and So Is Lower Temperature: The Curious Case of Thin Film Growth of Tetracene on SiO₂

We have examined the effect of growth rate on the growth mode of thin films of tetracene on SiO₂ at a substrate temperature of 0 °C. For a preponderance of conditions examined here, only the thin-film phase is formed. From a combination of in situ real-time synchrotron X-ray scattering and ex situ atomic force microscopy, we have observed a transition from 3D growth to 2D layer-by-layer (LbL) growth as the rate of growth is increased, similar to previous results obtained at a substrate temperature of 30 °C. For this lower substrate temperature, however, we find that this transition occurs at a much lower growth rate. We attribute this to the lower temperature significantly diminishing the rate of upward step-edge crossing transport, which competes with the rate of attachment at island edges and results in 2D LbL growth. By examining the effects of both the rate of growth and the substrate temperature, we can assign an activation energy of ∼19 kcal mol^–1 to these upward set-edge crossing events.