Early stage of growth of a perylene diimide derivative thin film growth on various si(001) substrates

This study deals with the growth mode of N,N '-dipenthyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-5C) thin films from less than 1 monolayer to 23 monolayers thick. The effects of growth temperature and the thickness and nature of the substratesSiO(2) on Si(001) or octadecyltrichlorosilane (OTS) self-assembled monolayer terminated Si(001) surfacesare discussed. Thin films were deposited from a homemade Knudsen cell by using a hot-wall deposition technique. Films were analyzed by atomic force microscopy, X-ray diffraction, and X-ray reflectivity. Films exhibited a (001) orientation with a 1.63 nm d spacing, and a metastable thin film phase was observed without any distinction of the nature of the substrate. However, differences were noticed in the early stages of growth: PTCDI-5C/SiO2 first monolayers presented a Stransky-Krastanov growth mode, whereas PTCDI-5C/OTS first monolayers showed a more complex mode with incomplete wetting of the substrate surface. Differences between the two morphologies softened as the film thickness increased.