Browsing by master's degree program "Magisterprogrammet i materialforskning"

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.

Molecular hydrogen is considered as the primary alternative to replace fossil fuels for future energy supply. Hydrogen can be produced sustainably through electrocatalytic hydrogen evolution reaction which is a vital step in water electrolysis. So far, the efficiencies of electrochemical and photoelectrochemical water electrolysis systems are too low to satisfy the demands for hydrogen on a commercial scale. Plasmonic nanostructures containing a plasmonic and a catalytic component hold great promise for enhancing the performance of typical water electrolysis systems through plasmonic photocatalysis utilizing localized surface plasmon resonance excitation. Here, a novel plasmonic-catalytic u@AgPd nanorattle is synthesized, characterized, and investigated for plasmon-enhanced hydrogen evolution reaction to provide new insights into the design of light-assisted water electrolysis systems. The nanorattle exhibited significant improvements of performance towards hydrogen evolution reaction under 427 nm illumination, displaying a near 2-fold current increase and a decreased overpotential of 58 mV at a current density of 10 mAcm-2. The material is evidenced to plasmon-enhance the electrocatalytic performance through a combination of charge transfer and local heating mechanisms.

4D printing is becoming increasingly investigated as it is emerging as a pioneering method for biofabrication. By implementing programmable shape changing thermoresponsive hydrogels in bioink formulations, a 4D response can be achieved, which can be manipulated to print artificial organs and tissues. The limited selection of biocompatible thermoresponsive hydrogels, accompanied by the mechanical weakness of hydrogels have restricted the mainstream application of this technology in the field of bioprinting. The most commonly studied thermoresponsive polymer is poly(N-isopropylacrylamide), but it is understood that the monomer N-isopropylacrylamide exhibits cytotoxicity at low concentrations. The primary goal of this study is to investigate poly(2-substituted-2-oxazoline) macromonomers as potential alternatives to poly(N-isopropylacrylamide), and the secondary goal is to investigate microgels as an additive in crosslinked networks to enhance hydrogel mechanical strength. The results in this work indicate that poly(2-n-propyl-2-oxazoline-co-2-ethyl-2-oxazoline) is a promising candidate for 4D printing, because it’s LCST can be fine-tuned by altering the monomer ratio. However, it still requires further investigation as it requires an acrylamide comonomer to crosslink, and it also has compatibility issues with commercial printing additives like Pluronic F127. The addition of 2 wt.% microgel also showed promise as it enhanced the hydrogels mechanical strength over threefold.

Radiation therapy is one of the key treatments for cancer, utilizing ionizing radiation to destroy cancer cells. Proton therapy uses high-energy proton beams since protons have a favorable depth-dose curve. Clinical proton beams must meet strict quality standards in order to maximise the efficacy of the treatment while ensuring the patient safety. Real-time knowledge of the beam’s intensity profile is essential for an accurate beam delivery. While gas-filled ionization chambers have traditionally been used as the standard beam monitor, the swift development of the beam delivery techniques demands for more accurate beam monitors. Semiconductor detectors potentially offer more accurate and efficient alternative for ionization chambers. In this study, the feasibility of using a silicon pixel detector in proton beams was investigated. The detector was originally designed for tracking minimum ionizing particles at the CMS experiment at CERN. Two experiments — one with an alpha source and one in a proton beam — were carried out to characterize the detector. The response to protons with different intensities and energies was investigated more closely in the proton beam. The results show that the detector response to different proton energies agrees with theoretical expectations. The saturation of the pixels limits measuring the full energy of the protons, however measuring the full energy is not essential in beam profile measurements. The detector also has a linear response to the beam intensity, although, the counting efficiency of the detector should be improved with new readout electronics. With different readout electronics, the detector might be a viable option for the beam profile measurements in clinical proton beams.

Lipid-based solid-fat substitutes (such as oleogels) structurally modified using ultrasonic standing waves (USW), have recently been shown to potentially increase oleogel storage-stability. To enable their potential application in food products, pharmaceuticals, and cosmetics, practical and economical production methods are needed compared to previous work, where USW treated oleogel production was limited to 50-500 µL. The purpose of this work is to improve upon the previous procedure of producing structurally modified oleogels via the use of USW by developing a scaled up and convenient approach. To this aim, three different USW chamber prototypes were designed and developed, with common features in mind to: (i) increase process volumes to 10-100 mL, (ii) make the sample extractable from the treatment chamber, (iii) avoid contact between the sample and the ultrasonic transducer. Imaging of the internal structure of USW treated oleogels was used as the determining factor of successful chamber design. The best design was subsequently used to produce USW treated oleogels, of which the bulk mechanical properties were studied using uniaxial compression tests, along with local mechanical properties, investigated using scanning acoustic microscopy. Results elucidated the mechanical behaviour of oleogels as foam-like. Finally, the stability of treated oleogels was compared to control samples using an automated image analysis oil release test. This work enables the effective mechanical-structural manipulation of oleogels in volumes of 10-100 mL, paving the way to possible large-scale lipid-based materials USW treatments.

The crystal structure of magnetite (Fe3O4) involves Fe2+ ions in sites with octahedral (Oh) symmetry and Fe2+ and Fe3+ ions in sites with tetrahedral (Td) symmetry. Magnetite exhibits several interesting physical phenomena, such as the Verwey transition, in which the roles of the different Fe sites are an active subject of research. In the X-ray standing wave (XSW) technique, incoming and diffracted X-ray beams interfere inside a crystal, creating a standing wave with the periodicity of the diffracting atomic lattice. The phase of the wave, i.e. whether the nodes are located on the lattice planes or between them, can be adjusted by finely tuning the diffraction angle. Changing the phase in this way makes it possible to selectively vary the contributions of different atoms and absorption types (dipole versus quadrupole) to the measured total absorption spectrum. Iron K-edge absorption spectra in magnetite were studied in the presence of an XSW in an experiment conducted at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. This thesis presents an analysis of the data gathered during the experiment, with the goal of decomposing the experimentally measured pre-edge peak into its constituent components. The methods used in the analysis include principal component analysis and fitting predicted absorption peaks calculated with the Quanty software to the experimental data. The results show the dipole and quadrupole contributions of the tetrahedral sites responding to changes in the phase of the XSW in opposite ways in a manner consistent with theoretical predictions.

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.

This thesis contributes to the ongoing development of a novel, environmentally friendly e-waste recycling technology. We utilize high-intensity focused ultrasound to locally extract gold from the surface of printed circuit boards via cavitation erosion. Acoustic cavitation erosion is the phenomenon in which the acoustically driven violent collapse of gas bubbles in liquid cause damage to nearby solids. Bubble collapse is preceded by its dramatic growth, which is driven by the rarefactive phase of the acoustic wave. In this work, I investigate the effect of ultrasound frequency on the efficiency of gold extraction. Gold extraction experiments were conducted with three custom-built transducers, with different resonant frequencies [4.2, 7.3, 11.8] MHz. The geometries of the transducers are identical, as were the electrical driving parameters. With each transducer, a sequence of gold extraction experiments was conducted with an increasing number of acoustic bursts (ranging from 100k to 1.9M). The results demonstrate that the lowest frequency (4.2 MHz) is 3.8 and 4.5 times more efficient at extracting gold compared to [7.3, 11.8] MHz, respectively. This dramatic improvement is likely due to larger cavitation bubbles associated with lower frequencies. Larger bubbles in the cavitating zone would be expected to undergo more bubble coalescence due to a higher gas volume ratio. Since the energy of bubble collapse increases with bubble size, increased bubble coalescence should augment the energy of bubble collapse. These results provide valuable insights relating to cavitation research and will guide the ongoing development of our novel e-waste recycling technology.

Polysiloxanes are silicon-based polymers consisting of R2SiO repeating units. They are commonly used in many commercial applications, for example, as adhesives, additives, or waterproof coatings. This thesis concentrates on polysiloxanes used as optically clear adhesives, which are needed in display applications to, for instance, bond cover lenses to touch panel sensors. This kind of a material needs to have a high refractive index to match glass or plastic, and it has to be transparent and thermally stable. In addition, it must resist degradation and yellowing from UV exposure and humidity. Anionic ring-opening polymerization was used to synthesize optically transparent polysiloxanes with varying side-groups. These polymers exhibited high refractive index values, which were adjusted by changing the amount of phenyl group -containing monomers or with chain terminating agents. End-functionalization reactions were performed for the synthesized polymers to introduce methacrylate groups to the chain ends, which could later be used in crosslinking trials involving a photoinitiator. The results present an effective synthetic route for the ring-opening polymerization for transparent, high refractive index poly(dimethylsiloxane-co-diphenylsiloxane) and poly(methylphenylsiloxane) that could be used as adhesives after selective chain end functionalization and crosslinking reactions. The properties of the synthesized polysiloxanes were characterized with several different methods, such as size exclusion chromatography, rheology, and NMR spectroscopy. End functionalization reactions were performed for some of the synthesized polymers. These were then further characterized to verify the suitability of the reaction.

In nuclear medicine, radiopharmaceuticals are administered to the patient to diagnose or treat various diseases. The radioactive activity of these radiopharmaceuticals is measured using a radionuclide calibrator. In this study, the response of a radionuclide calibrator in different measurement conditions was studied. Code system PENELOPE (2018) that applies Monte Carlo methods in electron and photon transport simulation was used to investigate the response as a function of photon energy emitted by the source, source location, source volume and source container type. These calculated results were compared to corresponding experimental results. Overall, the computational results conformed well with the experimental results. The computational energy-response followed a similar trend to the efficiency curve extracted from the manual of Capintec CRC-25R radionuclide calibrator. The response of the calibrator to a Tc-99m source as a function of both vertical and horizontal displacement was inspected, and the results indicated a cubic and exponential trend, respectively. In both cases, results present that there is an agreeing optimal depth range (14 - 23 cm) at which the source should be located. Within this range, the variation in response remains below 2 %. Furthermore, the central axis of the chamber was deemed horizontally optimal for measurements. In the radius range 0 - 2.1 cm, experimental results showed an increase of 4 % relative to the centre position. Corresponding calculated results presented an increase of about 3 %. The response as a function of volume and container type was calculated for Tc-99m and I-123 source, respectively. In the case of volume-response, computational results presented a decrease of around 0.5 % for volumes between 2 to 5 ml in a plastic syringe. Experimental methods showed a corresponding decrease no greater than 0.8 %. Measuring response in a 15C transparent glass vial instead of a 3 ml plastic syringe, showcased that the response is only 81 % and 75 % of that in the syringe in simulated and experimental results, respectively.