ICMCTF2019 Session F4-1-WeM: Functional Oxide and Oxynitride Coatings I

The TaON material is a promising candidate for application as a visible-light-driven photocatalyst splitting water into H₂ and O₂ and thus converting solar energy into chemical energy. The photo-generated electron-hole pairs act here as the active water splitting species. In order to work as a water splitting photocatalyst, the material must satisfy certain conditions: (i) band gap of proper width (preferably corresponding to visible light absorption ) and (ii) suitable alignment of the band gap with respect to the water splitting redox potentials. The subsequent transport of the charge carriers through the material (particularly across the films thickness) plays an important role in the effectivity of the process.

In this work we first demonstrate that using reactive high-power impulse magnetron sputtering (HiPIMS) as the deposition technique followed by post-annealing of the amorphous as-deposited film at 900°C in a vacuum furnace allows us to prepare a polycrystalline film exhibiting a pure TaON phase. Such film satisfies the above mentioned conditions for a water splitting photocatalyst (band gap of ~2.6 eV). However, as it is desirable to prepare the TaON phase in situ, we investigate the possibilities of substrate heating and biasing during deposition while focusing on fine-tuning of the elemental composition. Additionally, as the monoclinic TaON phase exhibits anisotropic charge carrier conductivity, tailoring of the texture of the film can further improve the charge carrier transport in a desired direction. In this work, we therefore also investigate the possibilities of deposition at high power densities in a pulse (up to 4 kW/cm²) and/or deposition onto suitable substrates providing proper seeding layers (e.g., Pt, ZrO₂) to prepare textured TaON film allowing enhanced charge carrier mobility across the film thickness.

Indium tantalum oxide thin film was deposited by sputtering using three different designs: 5-7 and 10-14 nm alternative layers of Ta₂O₅ and In₂O₃, and co-sputtering of In₂O₃ and Ta₂O₅. Then as-deposited films were rapid annealed at different temperatures to assess the thermal effects on microstructures and photocatalytic functions. Results from XRD and EDS indicates that crystalline InTaO₄ emerges in 5-7 and 10-14 nm stacks of films but absent in the co-sputtered films. Since crystalline InTaO₄ is capable of photocatalysis under both ultraviolet and visible light, we particularly tested the annealed films in water to degrade methylene blue under visible light. The photo-induced degradation on methylene blue by 5-7 and 10-14 nm stacks can reach 45% after 6-hour continuous exposure. Using UV-Visible-NIR spectroscopy, we can estimate the optical band gaps in these annealed films and from these estimations, a mechanism for the photocatalysis is discussed following. This mechanism is similar to other electron-hole separation and transfer across the heterogeneous junctions in semiconductors.

Nosocomial infections are microbial infectious diseases that are acquired in healthcare settings, and are a worldwide health problem. The surfaces are involved in the spread of these infections, thus there is an urgent need to eliminate this route of transmission. Nanotechnology allows the production of materials with improved properties and effective action against pathogens. Zinc oxide (ZnO) is frequently used due to its excellent antimicrobial properties.

This work focused on the evaluation of the antimicrobial activity of ZnO thin films. All the samples were produced by reactive DC magnetron sputtering and tested against the fungus Candida albicans. A first set of thin films were produced with different O₂ flows, which affected the thin films’ chemical composition and morphology. Additionally, some of the thin films were subjected to an annealing treatment, which promoted the crystallization of the ZnO matrix. A second set of thin films was produced modifying the deposition angle, using the Glancing Angle Deposition technique, GLAD, with a fixed O₂ flow. These changes were performed to increase the porosity and roughness of the thin films, which may allow the tailoring of the film’s biological response. To evaluate the ZnO thin films surface antimicrobial properties, a direct contact assay was performed, and the results revealed no significant cell growth after five hours of incubation. Analysing possible molecular mechanisms responsible for the antimicrobial activity, it was observed that the loss of membrane integrity and the increase of Reactive Oxygen Species (ROS) within C.albicans cells was correlated with the incapacity of the cells to grow.

As a general conclusion, one may claim that all the thin films showed a significant antifungal activity, and the observed differences among them can be correlated with the evolution of the (micro)structural features.

Combinatorial methodology has been proven its validity in such an application. This approach allows the Zn/Sn ratio continuously to change across a single sample area and a feasible intimate mix of Zn and Sn. Therefore, a single ZTO composition spread sample essentially includes a full spectrum of properties to be investigated. A Zn-Sn-O (ZTO) composition spread, consisting of thickness wedges of SnO and ZnO, was prepared using a state-of-the-art combinatorial sputtering system, equipped with a moving shutter and two RF guns for the targets of Zn and Sn, respectively. The thickness gradient was determined using SEM, α-step and SIMS. It was found a smooth thickness variation across the sample area for both ZnO and SnO with the coefficient of determination (R2) ≅ 0.99, indicating a good control of the ZTO composition spread. Structure evolution was characterized using XRD. We found in-situ 500 ºC annealing resulted in crystallization of the samples, where ZnO, Zn₂SnO₄, ZnSnO₃, and SnO₂ phases were observed, depending upon the ZnO/SnO ratios on the ZTO composition spread. The resistivity was characterized using a four-point probe on different substrates, which revealed lower resistivity near ZnO-rich. Morphology and optical characteristics were studied as well using AFM, SEM and UV-Vis spectrometry. A clear variation trend of both properties was observed. A systematic study of physical properties of ZTO has been successfully demonstrated.

After it became clear that quantum computers are more powerful than originally thought [1], we were asked by the industry to find the most fundamental form of a Turing machine based on Quantum Theory. Do this job in a very comprehensive manner, we found that the deepest layer for the Quantum Computer was not to be found inside the theoretical apparatus of Quantum Theory. Surprising as this may be, it is the General Theory of Relativity which “contained it all”. We found that an extremely simple solution of the Einstein-Field-Equations, using pairwise dimensional entanglement, sports the principle structural elements of computers [2]. We will derive these structural elements and show that the classical computer technology of today and even the quantum computers are just degenerated derivatives of this general solution. In the talk we will discuss thin-film technology- and smart material-options potentially helping us to one day realize the general computer concept.

[1] J. Aron, “Quantum computers are weirder and more powerful than we thought”, www.newscientist.com/article/2170746

[2] N. Schwarzer, “Einstein had it, but he did not see it – Part XXXIX: EQ or The Einstein Quantum Computer”, www.amzon.com, ASIN: B07D9MBRS3