KEYWORDS: Thin films, Refractive index, Solar cells, Silicon, Photovoltaics, Water, Solar energy, Ellipsometry, Thin film solar cells, Titanium dioxide
Crystalline TiO2 (Anatase configuration) thin films is widely used in the photocatalysis and photovoltaic industries ((self cleaning surface and renewable energies for example). The synthesis of these films is obtained from a dispersed solution of molecular poorly condensed species using Sol-Gel and liquid deposition processes. It allows the introduction of organic molecules (porogenes) inside inorganic network to create what is called hybrid materials.
Spectroscopic ellipsometry is the technique of choice to characterize thickness and refractive indices of such thin layers. The adsorption of water at atmospheric pressure within the pores, modifies the refractive index of the layer. The change in refractive index induced by the introduction of water is measured by ellipsometry. A Lorentz Lorenz effective medium model is used to calculate the volume of water adsorbed by the material. Atmospheric Ellipsometric porosimetry (EPA) measurements become an effective method for characterization of porosity, pore size distribution (PSD), average pore size, Cumulative surface area and Young's modulus of porous films. EP is also suitable to evaluate the sealing of a porous layer.. EP evaluates the change in refractive index due to the penetration of the solvent through the sealing layer into the porous layer. In this paper, the instrument as well as some examples will be presented the abstract two lines below author names and addresses.
Spectroscopic Ellipsometry is the technique of choice to characterize thickness and refractive indices of thin layers.
Atmospheric Ellipsometry Porosimetry (EPA) measures the change of the optical properties and thickness of the
materials during adsorption and desorption of wet air at atmospheric pressure. Concentration of humidity changes at
each step of measurement from dry air to saturated air. This non contact and non destructive technique is an effective
and unique method to characterize porosity, pore size distribution (PSD) and Young modulus of thin porous films. It
does not require to scratch the film, does not need low temperature or low pressure.Detailed description of the technique
will be exposed in the paper and several meso-porous films (with pore size larger than 1nm) using the Kelvin formalism
will be presented. The porosity of the layer ranges from few percent up to 40%. As it is an optical method, it is non
contact, non destructive, fast (down to 15 minutes) and room temperature method. It does require low pressure or any
preparation of sample.
Solid oxide fuel cell is an electrochemical device that converts the chemical energy in fuels into electrical energy by
exploiting the natural tendency of oxygen and hydrogen to react. The cell is constructed with two porous electrodes,
which sandwich an electrolyte. Selection of materials for the individual components presents the most significant
challenges in this technology. Each material must possess the correct chemical, electrical and structural properties to
perform its function in the cell.
Yttria stabilized Zirconia, (YSZ) is a suitable material for two of the components in this system: the anode and the
electrolyte, where its morphology is notably different for each component. Using EPA technique, it becomes possible to
characterize in term of porosity and pore size distribution the morphology of both components made by YSZ. We will
show the characterization of material in thin film with different porosity and pore size distribution. Graded porosity
versus depth could be also demonstrated and will be shown for the first time on such material.
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