Amorphous to Crystalline Polymorphic Behaviors of TiO$_{2}$ Thin Films Deposited Under Various Oxygen Pressures by Pulsed Laser Deposition

TiO$_{2}$ is a versatile wide bandgap transparent semiconducting oxide with three well known polymorphs: Anatase, rutile and brookite. The crystalline polymorphs of TiO$_{2}$ require high temperature annealing processes to form from an amorphous precursor. Our research aims to understand the formation behaviour of these metastable polymorphs of TiO$_{2}$ as related to amorphous precursor properties. In this study, TiO$_{2}$ thin films deposited at room temperature on a-SiO$_{2}$ substrates by PLD under different oxygen pressures and then annealed with same annealing process. Changing the oxygen pressure for each deposition resulted in different phase structures after the annealing processes. We found that lower pressure favors rutile, middle pressure favors brookite, and higher pressure favors anatase formation. Microstructural properties of TiO$_{2}$ thin films are investigated by XRD, Raman spectroscopy, SEM, XPS, and optical transmission and reflection spectroscopy.