Date of Graduation

Fall 2014

Degree

Master of Science in Materials Science

Department

Physics, Astronomy and Materials Science

Committee Chair

Saibal Mitra

Keywords

Tungsten trioxide, molybdenum trioxide, pulsed laser deposition, hotwire chemical vapor deposition, electrochromic device, super ionic conductor, HCl

Subject Categories

Materials Science and Engineering

Abstract

My aim was to see how differently the structure of the films behave during insertion and extraction of ions and electrons. Tungsten trioxide (WO3) has emerged as one of the most widely used transition metal oxides in fabrication of electrochromic devices. Another material that was studied extensively in this context is MoO3. Previous studies have shown limitations in the number of repeated cycles that can be obtained using WO3 and MoO3 films. To further improve on this, I used lesser concentrations of hydrochloric acid (HCl) as the electrolyte in the device fabrication. HCl (0.02 N and 0.05N) were used on amorphous and crystalline WO3, MoO3, and hybrid samples having layers of both compounds. The WO3 and MoO3 thin films deposited at 450oC were characterized using both XRD and Raman spectroscopy and found to be monoclinic and orthorhombic in structure. Cyclic voltammetry experiments were performed on all samples and their bleaching and coloration cycles observed. It was determined that the bias potential required to cause ion insertion depended on the concentration of the HCl, so also does the optical properties of the sample. A potential range of -1.5 V to -3.0 V was used during cyclic voltammetry experiment. The coloration in WO3 and MoO3 is a structure-sensitive phenomenon, and excess electrons can be either localized or delocalized. A UV-visible technique was then used to measure the transmittance and intensity of the films before and at different stages of applied potentials during the course of the experiments. The performances of WO3 deposited using pulsed laser deposition (PLD) showed better coloration and bleaching cycle than those made from hotwire chemical vapor deposition (HWCVD) technique.

Copyright

© Oladeji Taiwo Fadayomi

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