Browsing by Subject "atomic layer deposition"
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(2022)Ensuring adequate air quality is integral to healthy living. Since in modern societies the majority of time is spent indoors, understanding indoor air pollution and the means of air purification are of great importance. Adverse health effects are induced by volatile organic compounds (VOC) that originate from everyday activities and our surroundings. Photocatalysis is a radiation-activated chemical transformation that can be used to decompose organic pollutants into harmless constituents. However, existing air purification solutions employing photocatalysis often rely on UV light limiting the use of solar radiation. Titanium dioxide is a popular photocatalyst material, but it requires modification to its electronic properties to respond to visible light. An established approach is to introduce atoms of other dopant elements into the titania lattice. Atomic layer deposition (ALD) is a thin film deposition technique widely studied especially in metal and metal oxide research. Following from the principle of sequential saturation of the surface, control over the size and composition of the film may reach atomic level. Since the chemical configuration of a doped TiO2 film is of utmost importance to successful modification, ALD is an excellent tool to examine suitable photocatalytic TiO2 chemistries. Furthermore, thin solid films of catalytically active material would have a distinguished advantage for deployment in real-life settings over their powderous counterparts. The literature review of this thesis explores the semiconductor photocatalysis with an eye on its suitability to indoor air purification. The motivation is to give the reader a view on the air quality issue, the existing technological solutions and how a thin film photocatalyst could supplement the field. Titanium dioxide doping concepts are introduced to elucidate the rationale behind the experimental efforts. The experimental part describes a development project to deposit visible-light responding photocatalysts. Titanium dioxide thin films co-doped with nitrogen and zinc/fluorine were grown on steel plates. An in-house built reactor system was used to study acetaldehyde degradation under irradiation. Unfortunately, the reactor experienced a malfunction, rendering a large part of the results futile. Moreover, months of valuable time were lost in chasing a mirage of fallacious data. In the end an ALD grown photocatalyst responding to visible light could not be materialized.
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(2024)Rare earth trifluorides are a group of 17 compounds which have intriguing optical, electrical, and luminescence properties. However, realizing these properties in the form of thin films has had its challenges. Overall, research on the subject has been scarce. On the other hand, some rare earth fluoride thin films have found usage in for example optical filters in ultraviolet and infrared wavelengths.In this thesis a review of rare earth fluoride thin films and their deposition methods is made. Potential of the rare earth fluoride thin films is explored starting from the bulk properties of the rare earth fluorides which are compared to the published results for thin films. Additionally, the current status, challenges, and potential of rare earth fluoride thin films is discussed in the light of different deposition methods and their differences. In the experimental part of the thesis, deposition of holmium fluoride thin film by atomic layer deposition (ALD) is studied alongside its properties. In the HoF3 deposition, Ho(thd)3 (thd = 2,2,6,6- tetramethyl-3,5-heptanedionato) and niobium pentafluoride were used as precursors, latter of which was used as an ALD fluoride precursor for the first time.
Now showing items 1-2 of 2