Doctoral defence: Kristel Möls "Metastable TiO2-II in atomic layer deposited thin and ultrathin films: stabilization, properties and impact on film growth"

On 28 August at 14:00 Kristel Möls will defend her doctoral thesis "Metastable TiO2-II in atomic layer deposited thin and ultrathin films: stabilization, properties and impact on film growth" for obtaining the degree of Doctor of Philosophy (in Material Sciences).

Supervisors: 
Professor Jaan Aarik, University of Tartu
Hugo Mändar, University of Tartu

Oponents:
Sandra Stanionytė (Center for Physical Sciences and Technology, Vilnius, Lithuania)
Tomáš Roch (Faculty of Mathematics, Physics and Informatics, Comenius University Bratislava, Slovakia)

Summary: 
This study explores titanium dioxide (TiO₂) thin films, focusing on the structural properties of those, and particularly, on the deposition and characterization of films containing the metastable high-pressure TiO₂-II phase. TiO₂ is a material of great importance due to its unique properties. TiO₂ is used in the paint, paper, pharmaceutical, and cosmetics industries, and has attracted great interest in micro- and nanoelectronics because of its high permittivity and in optical applications because of high refractive index and transparency in the visible spectral range. TiO₂ has also been applied in self-cleaning and antibacterial coatings, photocatalysts, gas sensors, and anti-corrosion coatings.
The TiO₂-II phase is one of the less explored but attractive modifications of TiO₂ that has garnered interest in various areas due to its unique properties. For instance, theoretical studies have predicted superior mechanical and photocatalytic properties of this phase compared with those of anatase and rutile phases of TiO₂. However, as the formation and stabilization of TiO₂-II is unlikely in the majority of conventional material synthesis processes, there is insufficient data on its properties (for instance, refractive index, hardness, and bandgap energy) and formation in thin films. Hence, one of the key contributions of this work is the successful stabilization of TiO₂-II in a form that allowed characterization of its optical and mechanical properties. For this purpose, atomic layer deposition processes allowing formation of TiO₂-II in thin films were investigated and the influence of the deposition process parameters on the material properties was thoroughly studied. As a result, this work provides insights into the effect of TiO₂-II content on optical and mechanical properties of TiO₂ thin films, offering a basis for further exploration and potential for applications, for instance, in photocatalysis and functional coatings with enhanced hardness.