Rubrene polycrystalline films growth from vacuum deposition at various substrate temperatures

Rubrene polycrystalline films growth from vacuum deposition (with a fixed source temperature of 300 °C) were characterized with respect to various substrate temperatures (Tsub=103-221 °C). First, the growth behavior of these as-deposited polycrystalline films is confirmed to follow an activated surface-adsorption process with an activation energy EA=0.69±0.01 eV. A comparison of EA for the growth of some other small organic molecular solid films is given. Then, the surface morphology and the temporal evolution of the grain size in these polycrystalline films with respect to Tsub are described and discussed. Furthermore, by X-ray diffraction, these rubrene crystalline grains are confirmed to have an orthorhombic structure, and the average coherent length and lattice microstrain of the crystallites deposited at high Tsub (189-221 °C) are estimated and compared. This experimental work reveals that Tsub has a strong influence on the growth rate, the surface morphology, and the structural properties of the as-deposited rubrene polycrystalline films.