- Jaglarz1, K. Marszalek2 B. Jarzabek3, R. Duraj4 and I. Noor5 AK Arof5 N. Wolska6 and B. Sahraoui7
1,6Cracow University of Technology, Faculty of Mechanics M2, Al. Jana Pawła I37,31-864 Cracow, Poland
2AGH University of Science and Technology, Mickiewicza av.30, 30-059 Cracow, Poland
3Institute of Physics, Cracow University of Technology, ul. Podchorazych 1, 30‑084 Cracow, Poland
4Centre of Polimer Material PAN 41-819 Zabrze ul. M. Curie-Skłodowskiej 34 Poland
5University of Malaya, Ionic center, Dept Phys, Dept Phys, Kuala Lumpur 50603, Malaysia
6Elkom Trade S. A. Targowa 21 street, 27-400 Ostrowiec Świętokrzyski
7LUNAM Université, Université d’Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 2 bd Lavoisier, 49045 Angers cedex, France
Thin polymer films are currently under intensive investigation owing to their promising optical and electrical properties. The roughness and refractive index variation in a film, and also presence of unwanted molecular inclusions in bulk created during film formation may lead to incoherent light scattering. Therefore the analysis of thin film optical spectra becomes more complicated. The aim of this work is presentation of light scattering phenomena occurring in polymer layer. They can be described by the Fresnel model for specular reflectance and as well Rayleigh, Debye and scalar theories of light scattering for non-directional reflection from a diffusive film. Furthermore, the optical methods based on combined spectro-goniometric measurements have been presented.
These investigations allow determining many important parameters as: optical constants, films thickness and their surface roughness and also optical scattering coefficients diffusive layers.
Keywords: elastic light scattering, spectroscopic ellipsometry diffusive reflectance and transmittance
The description of optical phenomena in most thin film in general is commonly limited to presentation of interference effect occurring in layers [1,2]. Using Fresnel theory we are able to determine film thickness and as well their optical constants. In these studies one utilizes specular parts of reflected from or transmitted by film. The complex refractive index and film thickness of thin films may be effectively determined by the use of ellipsometric method . Ellipsometry uses the light of known polarization incident on the studied film and detects the polarization state of the reflected light. Incident light is usually linearly polarized and the reflected light has elliptical polarization. Spectroscopic ellipsometry directly determines two angles Ψ and Δ, with:
where Ψ represents the angle determined from the amplitude ratio between p- and s- polarizations and Δ is the phase shift between the polarized waves. rp and rs are the complex Fresnel reflection coefficients for p- and s- polarizations, respectively. Knowledge of ellipsometric angles allows us to determine dispersion of the refractive index n and the extinction coefficient k of the films.
The ellipsometry may be applied when most of reflected and transmitted radiation is coherent. Such condition is done in broad variety of homogenous flat layers, typical in inorganic coatings. In polymer films one may appear other phenomena related to non-coherent and non-specular light scattering. They result mostly from variation of refractive index in bulk material. It may result from non-regular distribution of polymer chains in films [4, 5]. As well in the layer may occur small scattering centers responsible for Rayleigh scattering. As representative samples in order to demonstrate light scattering phenomena the polyazomethine (PPI) thin films have been chosen. The PPI layers are important materials to obtain organic LED’s devices .