Browsing by Author "Tiznado, Hugo"

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    Optical Properties of TiO2 Grown by Atomic Layer Deposition Using Various Oxidizing Agents: The Ellipsometry Analysis of Absorption Properties
    (Weinheim : Wiley-VCH, 2024) Vazquez‐Arce, Jorge Luis; Suta, Tibor; Fodor, Bálint; Makai, László; Contreras, Oscar; Bahrami, Amin; Nielsch, Kornelius; Tiznado, Hugo
    This study analyzes the optical properties of TiO2 films grown via atomic layer deposition (ALD) using Tetrakis(dimethylamino)titanium with oxidizing agents such as H2O, H2O2, O3, and O2-plasma. TiO2-H2O exhibited Ti3+ states and oxygen vacancies characteristic of black TiO2, enhancing visible-NIR light absorption. This effect increased with more ALD cycles due to the surface memory effect, leading to a decreased growth rate. In contrast, films grown with H2O2, O3, and O2-plasma are more stoichiometric, has fewer defects, and show no visible-NIR absorption due to the absence of Ti3+. TiO2 films deposited with H2O also show increased surface roughness and hydrophobicity, while films grown with other oxidizing agents exhibited higher roughness but decreased hydrophobicity. Ellipsometry and UV–vis spectroscopy confirmed that TiO2 films grown with H2O has an increased refractive index and extinction coefficient in the visible range, along with a bandgap widening due to the Moss-Burstein effect. Conversely, films grown with other oxidizing agents showed a decreased bandgap with increasing thickness and an increased refractive index but a zero extinction coefficient below the bandgap. Mid-IR ellipsometry measurements revealed the dielectric response, highlighting the critical role of the oxidizing agent in tailoring the properties of TiO2 films for energy and environmental applications.
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    Structural, optical, and electrical characterization of TiO2-doped yttria-stabilized zirconia electrolytes grown by atomic layer deposition
    (Melville, NY : AIP, 2024) Vazquez, Jorge Luis; Bahrami, Amin; Bohórquez, Carolina; Blanco, Eduardo; Dominguez, Manuel; Soto, Gerardo; Nielsch, Kornelius; Tiznado, Hugo
    Electrolyte material optimization is crucial for electrochemical energy storage devices. The specific composition and structure have an impact on conductivity and stability, both of which are essential for efficient device performance. The effects of controlled incorporation of TiO2 into a Yttria-Stabilized Zirconia (YSZ) electrolyte using the atomic layer deposition (ALD) technique are investigated in this study. The surface chemical composition analysis reveals variations in the Ti oxidation state and a decrease in the O/(Zr + Y + Ti) ratio as TiO2 concentration increases. The formation of acceptor states near the valence band is proposed to reduce the bandgap with the Fermi level. The structural properties indicate that as TiO2 concentration increases, surface homogeneity and crystallite size increase. The contact angle with water indicates a hydrophobic behavior influenced by surface morphology and potential oxygen vacancies. Finally, electrical properties, measured in Ru/TiO2-doped YSZ/Au capacitors operated at temperatures between 100 and 170 °C, showed that the TiO2 incorporation improved the ionic conductivity, decreased the activation energy for conductivity, and improved the capacitance of the cells. This study highlights the importance of the ALD technique in solid-state electrolyte engineering for specific applications, such as energy storage devices.