Growth dynamics of quaterthiophene thin films

The study of the growth of organic semiconductor thin films is a fundamental issue that must be addressed to control and understand the electrical and optical properties of these materials. Here, the growth process of quaterthiophene thin films in almost the full range of coverage, deposited by organic molecular beam deposition, has been studied using ex-situ atomic force microscopy. Initial multilayer growth was observed which gives rise to tridimensional islands with a characteristic mean height. Growth then proceeds increasing only the lateral size of the islands until their aggregation. Finally, a percolation lattice is formed and vertical growth starts again. In order to provide insights into the microscopic growth mechanism, the dynamic behaviour and scaling properties of physical quantities directly related to the film morphology have been analysed. The results suggest that, even if interlayer mass transport is rather effective in these systems and is responsible for the formation of tridimensional islands, the anisotropic interactions among the molecules allow the description of the growth of each film layer individually, with the possibility to quantitatively analyse each stage of growth by applying suitably modified models of the growth of actual bidimensional clusters.