The great potential of self-assembled colloidal structures in several technological areas of modern photonics derives from the low cost and relative simplicity with which they are fabricated. The optical properties of this kind of medium are not only determined by the response of its isolated constituents but also by their spatial arrangement. When polystyrene spheres self-assemble in a periodic fashion, the spatially ordered variation of the dielectric function gives rise to photonic bands and thus the colloidal structure becomes a photonic crystal [1,2]. In this study, colloidal thin films were prepared by the spin-coating [3] and vertical deposition method [4]. By varying the spinning velocity, acceleration and duration of rotation, we obtained different number of colloidal crystal layers. Also, we have prepared opals (multilayer films) with the vertical deposition technique and compared the obtained structures with those obtained by the spin-coating method. In both cases, the thin films were fabricated by depositing colloidal dispersions of 300 nm polystyrene spheres onto microscope glass slide substrates. The morphology of samples was studied by atomic force microscopy, while their optical properties were investigated by spectroscopic ellipsometry and UV-VIS-IR spectrophotometry. An appropriate model has been developed for the determination of the optical properties of the colloidal films by ellipsometry. In order to validate the model applied, the parameters obtained have been compared with those determined by means of transmittance measurements. From transmittance measurements, in the case of monolayer films, diffraction peak in the visible range was observed. On the other side, in the case of opal has been verified the presence of a photonic band gap which should be attributed to Bragg diffraction [5].V International School and Conference on Photonics and COST actions: MP1204, BM1205 and MP1205 and the Second international workshop "Control of light and matter waves propagation and localization in photonic lattices" : PHOTONICA2015 : book of abstracts; August 24-28, 2015; Belgrad
