Undergraduate Thesis Or Project

Anti-Reflective Films: Spectroscopy and Ellipsometry of Porous Films

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  • The relationship between the index of refraction and the porosity of a material is that the index decreases with respect to the porosity. This property can be used to change the index of refraction of films which allows control of the reflection of the material. This is important because being able to control the reflection and thereby the transmission allows you to create anti-reflective or reflective films. There are two studies of porous films done in this thesis. First is the study of the relationship between the index of refraction and porosity of titanium oxide (titania) films using an ellipsometer. Second is examining aluminum phosphate (ALPO) films and determining the thickness and ALPO fraction of the film. The titania films I created did not show the index of refraction to change with the porosity. The ALPO films were determined to be good anti-reflective films with percent reflectance less than ten percent over the visible spectrum. Each of the films showed reflectance of 4 percent or less at a constant wavelength of 550 nm. The three ALPO films studied differed by their thickness and their configuration of the films. A thick single sided film, a thin single sided film, and a double-sided thin film were the three configurations. The reflectance and thickness are determined using Scout, a modeling software made by Wolfgang Theiss, and used to fit the data using the Bruggeman model of effective medium approximation. The ALPO fraction is the percentage of ALPO to air bubbles in the films, while the thickness is the width of the film on a glass substrate. The thickness of the films is determined to be around 320 nm for the thick film, and around 120 nm for the thin films with fraction percentages around 70% as measured on the fiber optic spectrometer.
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