Linseed oil has been and is used for vast number of applications, such as in food and paint industry, and wood preservation. It is a good environmental choice, as it originates from renewable sources. Linseed oil is mainly a mixture of triglyceride of fatty acids, both saturated and mono- or polyunsaturated, which allows the oil to oxidize. The oxidation occurs via an auto-oxidation mechanism with the carbon-carbon double bonds and oxygen from the air, reacts to form a polymer. Herein, four different linseed oils (three commercial ones and one industrially available) were analyzed to obtain a better understanding of why different oils provide different protection of wooden materials. This was done by a study of the unoxidized oil, followed by an oxidation time-resolved study of oxidized oil films. The analysis was done by nuclear magnetic resonance, gas chromatography - mass spectrometry and/or inductively coupled plasma atomic emission spectroscopy. This study provided the fatty acid profile of the oils, which were similar for all oils. The unoxidized oils contained some metals ions which probably originate from additives. Aluminum, cobalt, iron, manganese, and zinc was detected in some of the oils at concentrations up to 135 mg/L, but only manganese was detected in all oils and its concentration was much higher than all other metals together. The time-resolved oxidation study had some problems with the solubility of the formed polymers. Several solvents were examined, such as dimethylsulfoxide, alkaline alcohol solutions and toluene, before chloroform-d was chosen as solvent. Though, chloroform-d was not a perfect solvent; it was capable to solve a fraction of the sample, but the fraction decreased with oxidation time. After fifteen days of oxidation, only a few percent of the sample could be dissolved, but for short oxidation times (<48 h) the majority of the samples were dissolved. The oils were analyzed after thirteen different oxidation times. Some structural changes appeared, for example loss of unsaturated protons and some oxidation products arose, such as peroxides and aldyhydes. The diffusion coefficient decreased over the first 3-4 days of oxidation, as expected when the polymerization progressed. After a week of oxidation, the diffusion coefficient increased again, this could possibly be explained by the solubility problem for the large polymer formed. Contrary, at shorter oxidation times this method probably could still be used, as the majority of the sample was dissolved. However, the solubility problem made it impossible to conclude anything about the oxidation rate at longer oxidation times and thus prevented any ranking of the oils. / Linolja har använts och används för många olika tillämpningar, till exempel i mat- och färgindustrin, samt för att bevara trä. Det är klimatmässigt ett bra val, då det kommer från en förnyelsebar källa. Linolja innehåller huvudsakligen en blandning av triglycerider av fettsyror, som både kan vara mättade, enkelomättade eller fleromättade, detta gör att linolja kan oxidera och torka. Oxidationen sker via en auto-oxidation mekanism, med kol-kol dubbelbindningarna och syre från luften som producerar till en polymer. I detta projekt undersöktes fyra olika linoljor (tre kommersiella och en industriell), för att ge en bättre förståelse till varför olika oljor ger olika bra skydd för trämaterial. Detta gjordes genom att undersöka de icke-oxiderade oljorna och sedan göra en tidsstudie på oxiderade oljefilmer. Alla dessa prover analyserades med nuclear magnetic resonance, gas chromatography - mass spectrometry and/or inductively coupled plasma atomic emission spectroscopy. Studien gav resultat på sammansättningen av fettsyror i oljorna, vilken var liknande för alla oljorna. De icke-oxiderade oljorna innehöll ett par metaller, som förmodligen kommer från additiv. Aluminium, kobolt, järn, mangan och zink hittades i några av oljorna i koncentrationer upp till 135 mg/L, men bara mangan var detekterad i alla oljorna och dess koncentration var högre än alla andra metaller tillsammans. Tidsstudien hade problem med lösligheten av proverna. Flertalet lösningsmedel undersöktes, exempelvis dimetylsulfoxid, alkaliska alkohollösningar och toluen, innan kloroform-d valdes som lösningsmedel. Däremot var kloroform-d inte ett perfekt lösningsmedel, den hade förmågan att lösa en del av proverna, men den delen minskade med oxidationstid. Efter femton dagar kunde den bara lösa ett par procent, men efter kortare oxideringstider (<48 h) gick majoriteten av proven att lösa. Oljorna analyserades vid tretton olika oxideringstider. Några strukturella förändringar uppmättes, till exempel minskade mängden dubbelbindningar, och ett par biprodukter från oxideringen detekterades, så som peroxider och aldehyder. Diffusionskonstanterna för oljorna minskade under de första 3-4 dagarna av oxidering, precis som förväntat under polymeriseringen. Efter en vecka av oxidering ökade diffusionskonstanterna igen, det kan förmodligen förklaras av löslighetsproblemen, då diffusionskonstanten är beroende av koncentrationen. Å andra sidan, vid kortare oxideringstider kan denna metod fortfarande användas, eftersom vid denna tidpunkt löste sig fortfarande majoriteten av provet. Dock, löslighetsproblemet gjorde det omöjligt att dra slutsatser kring längre oxideringstider och därmed förhindrades rangordning av oljorna.

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Transient vehicle thermal management simulations have the potential to be an important tool to ensure long component lifetimes in heavy-duty vehicles, as well as save development costs by reducing development time. Time-resolved computational fluid dynamics simulations of complete vehicles are however typically very computationally expensive, and approximation methods must be employed to keep computational costs and turn-around times at a reasonable level. In this thesis, two transient methods are used to simulate two important time-dependent scenarios for complete vehicles; hot shutdowns and long dynamic drive cycles. An approach using a time scaling between fluid solver and thermal solver is evaluated for a short drive cycle and heat soak. A quasi-transient method, utilizing limited steady-state computational fluid dynamics data repeatedly, is used for a long drive cycle. The simulation results are validated and compared with measurements from a climatic wind tunnel. The results indicate that the time-scaling approach is appropriate when boundary conditions are not changing rapidly. Heat-soak simulations show reasonable agreement between three cases with different thermal scale factors. The quasi-transient simulations suggest that complete vehicle simulations for durations of more than one hour are feasible. The quasi-transient results partly agree with measurements, although more component temperature measurements are required to fully validate the method.

Recombination mechanisms in gallium arsenide have been studied using temperature-dependent time-resolved photoluminescence-decay. New analytical methods are presented to improve the accuracy in bulk lifetime measurement, and these have been used to resolve the temperature-dependent lifetime. Fits to temperature-dependent lifetime yield measurement of the radiative-efficiency, revealing that samples grown by the Czochralski and molecular-beam-epitaxy methods are limited by radiative-recombination at 77K, with defect-mediated nonradiative-recombination becoming competitive at 300K and above. In samples grown with both doping types using molecular-beam-epitaxy, a common exponential increase in capture cross-section characterized by a high value of E_infinity=(258 +/- 1)meV was observed from the high-level injection lifetime over a wide temperature range (300-700K). This common signature was also observed from 500-600K in the hole-lifetime observed in n-type Czochralski GaAs where E_infinity=(261 +/- 7)meV was measured, which indicates that this signature parametrizes the exponential increase in hole-capture cross-section. The high E_infinity value rules out all candidate defects except for EL2, by comparison with hole-capture cross-section data previously measured by others using deep-level transient spectroscopy. / Thesis / Doctor of Philosophy (PhD)

<p dir="ltr">In the realm of two-dimensional (2D) materials, monolayer (ML) transition metal dichalcogenides (TMDCs) have gained significant interest due to their direct bandgap transition, high carrier mobility, strong light-matter interaction, and robust spin and valley degrees of freedom, starkly contrasting their bulk counterparts. Owing to their large surface-to-volume ratio, the integration of ML TMDCs with other various 2D semiconductors and microcavities offers opportunities to study fundamental photo-physics processes at the heterointerfaces, paving the way for implementation of next-generation devices.</p><p dir="ltr">Chapter 1 provides a concise introduction to 2D materials, particularly TMDCs, and their fascinating optical and electronic properties. It examines the role of excitons in 2D materials, and the impact of energy transfer (ET) and charge transfer (CT) on exciton’s properties in TMDC through the construction of 2D van der Waals (vdW) heterostructures and coupling with optical microcavities. This chapter also delves into the potential enhancement of TMDCs’ optical properties by integrating 2D hybrid lead halide perovskites and ultra-thin three-dimensional (3D) halide perovskites with TMDCs. Furthermore, it sets the general context for light-matter interaction, another form of ET, considering both weak and strong coupling regimes.</p><p dir="ltr">Chapter 2 outlines the optical techniques employed to gather data for this work. A focus is placed on ultrafast optical techniques like transient absorption spectroscopy, which allow for direct probing and analysis of ET and CT dynamics at the heterointerface.</p><p dir="ltr">Photoinduced interfacial CT plays a critical role in the field of energy conversion involving vdW heterostructures constructed by inorganic nanostructures and organic materials. However, the control of atomic-scale stacking configurations to modulate charge separation at interfaces remains challenging. Chapter 3 aims to illustrate tunability of interfacial charge separation in a Type-II heterojunction between ML-WS₂ and an organic semiconducting molecule by rational design of relative stacking configurations using 2D perovskites as scaffoldings. This chapter investigates how different molecular stacking, face-to-face versus face-to-edge, affects CT at the heterointerface. Our findings reveal that the CT process heavily depends on the relative stacking configurations at the organic-TMDCs heterointerface, with charge separation being notably slowed down for face-to-edge configuration compared to face-to-face configuration. These investigations open new opportunities for designing efficient charge separation processes in energy conversion applications by judiciously engineering interfaces between organic and inorganic semiconductors, using 2D perovskites as scaffolds.</p><p dir="ltr">Though TMDCs’ large surface-to-volume ratios make them excellent platforms for studying interfacial properties, the presence of bulky ligands on the surface of 2D perovskite poses a challenge, impeding direct interfacial coupling in their heterostructures. Chapter 4 details the fabrication of ML-WS₂ and ultra-thin CH₃NH₃PbX₃ (MAPbX₃, X=Br, I) heterostructures with tunable energy levels, to study the dynamics of CT and ET at these hybrid interfaces. Notably, heterojunctions of WS₂ with pure MAPbBr₃ and MAPbI₃ were elucidated as Type-I and Type-II respectively, using photoluminescence (PL) and time-resolved photoluminescence (TR-PL) measurements. Transit absorption (TA) spectroscopy investigations unambiguously revealed a rapid ET facilitated by CT in the WS₂/MAPbBr₃ heterostructure, with a time constant of ~20 ps, and a predominantly CT in the WS₂/MAPbI₃ heterostructure with a time constant of ~50 femtosecond (fs). The successful interfacing of low-dimensional perovskites with an extensive array of traditional 2D materials such as TMDCs opens up possibilities for novel optoelectronic properties and applications within the field of 2D material systems. Furthermore, the ultrafast and efficient ET and CT processes hold promise for the creation of advanced energy conversion devices.</p><p dir="ltr">In the last chapter, we successfully fabricated a ML-WS₂ in conjunction with a silver (Ag) nanoparticle (NP) array. Our findings affirmed a weak light-matter coupling between ML-WS₂ and the Ag NP array, as evidenced by angle-resolved photoluminescence spectroscopy. Furthermore, an enhancement in the bright exciton emission from ML-WS₂ was observed at reduced temperatures. The analysis of PL enhancement factor at varying temperatures suggested that an upper bound of the enhancement factor for the bright exciton could reach ~51 or even higher at 7 K, given the imperfect uniformity of the electric filed generated around the NPs. This discovery carries significant implications for the manipulation of excitons in TMDCs and expands their potential applications in the field of optoelectronics.</p>

The United Nations have set a number of sustainability goals, Agenda 2030, in order to combat the worlds largest challenges and injustices. The energy market is one of these urgent issues which must be solved. Solar energy is expected to be the fastest growing energy source in the future energy mix. It can be a great way to provide zero emission energy and also become a key part in equality as it can provide energy to people who live off the grid today and raise quality of life all over the world. The aim of this study is to compare different ligands in a copper halide complex to conclude what structural properties of the ligand might be better suited for photoluminescent applications, and especially in solar cells. Eight ligands were chosen for the complexes depending on their level of conjugation: 4,4’-bipyridine, tri(o-tolyl)phosphine, 3,6-di-2-pyridyl-1,2,4,5-tetrazine, pyridine, pyrimidine, pyrazine, phenanthroline, and 2,2’-bipyridine. A series of analytical methods were used to compare the complexes properties; X-Ray diffraction, emission and excitation spectroscopy, time-resolved photoluminescence spectroscopy, microscopy and thermochromism. From these measurements, pyridine and pyrimidine proved to have the greatest potential for working in a solar cell. This was deduced because of the detected crystallinity, having luminescence under UV-light, forming distinct wavelength peaks during excitation and emission in the flourometer, having the longest excited state lifetime and and finally, emitting distinctive colours during thermochromism. When creating the solar cell, pyridine was chosen as ligand due to higher availability than pyrimidine. The method used in this project for making the solar cell is directly applied form a previously tested method, but which was designed for another type of electron donor. This project compared the different ways of applying the copper halide complex on to the cell. The methods used were spin-coating and SILAR for creating the copper iodide thin film and vapour diffusion and immersion to introduce the ligand. These four methods were combined systematically for all combinations. The solar cells were then put in a solar simulator where voltage, current, efficiency and fill factor was measured. The best results came form the solar cell where spin coating and immersion was used, though the overall efficiency of the created cells were low. Copper halide complexes in previous studies have been proven to be reactive with oxygen and the experiments in this project were not carried out in an inert environment. This could have had significant impact on the measurements, as reactions between the complexes and oxygen may have resulted in oxidation and thus inactivation of the complexes. Therefore, it would be interesting to conduct the syntheses again but instead in an inert environment to determine whether oxygen made a major impact on the measurements. In further studies, it would also be worthwhile to investigate how the different layers of the solar cell would have to be adapted for this particular complex to obtain higher efficiency and voltage. Also, making thin film of pyrimidine to be used in a solar cell as it showed the attributes required for a solar cell. Furthermore, it would be interesting to use derivatives of pyrimidine, such as uracil and cytosine which are abundant in nature, as they might be more sustainable choices. This is due to their inherent biodegradability and not posing a threat to either health or environment when handled.

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Exziton-Polaritonen in Mikrokavitäten sind Quasi-Teilchen, die unter bestimmten physikalischen Konditionen kondensieren und damit in einen energetisch gleichen, gemeinsamen makroskopischen Quantenzustand (MQZ) übergehen können. Exziton-Polariton-Kondensate können mithilfe von akustischen Oberflächenwellen moduliert werden, um ihre Eigenschaften zu verändern. Dies ist insbesondere von großer Relevanz für zukünftige Anwendungen. In dieser Arbeit wurden die Struktur sowie die Dynamik der Exziton-Polariton-Kondensate in den durch die akustischen Oberflächenwellen erzeugten quadratischen Gittern untersucht. Es wurde dazu die Wellenfunktion der Exziton-Polariton-Kondensate im Rahmen der spektroskopischen und zeitaufgelösten Messungen im Orts- und Impulsraum abgebildet. Die MQZ wurden in einer optisch-parametrischen Oszillatorkonfiguration resonant angeregt. Die spektroskopischen Messungen zeigten, dass Exziton-Polariton-Kondensate in akustischen quadratischen Gittern aus unterschiedlichen MQZ, nämlich aus einem zwei-dimensionalen Gap-Soliton (2D GS) umgeben von mehreren ein-dimensionalen MQZ, und einem inkohärenten Strahlungshintergrund zusammengesetzt sind. Im Rahmen der zeitaufgelösten Experimente wurde die Dynamik der Wellenfunktion des 2D GS untersucht. Die zeitaufgelösten Ergebnisse zeigten, dass sowohl die Intensität der von dem 2D GS emittierten Photolumineszenz (PL) als auch die Kohärenzlänge des 2D GS zeitlich oszillieren. Die Intensität der PL und die Kohärenzlänge hängen von der Anregungsleistung, der Größe des Laserspots sowie von der relativen Position des akustischen Gitters und dem Laserspot ab. Im Ausblick dieser Arbeit wurde theoretisch die Anregung von Tamm-Plasmon/Exziton- Polaritonen (TPEP) sowie deren Modulation mithilfe von akustischen Oberflächenwellen diskutiert. TPEP entstehen durch die Superposition der in der Grenzschicht zwischen Mikrokavität und Metall angeregten Tamm-Plasmonen und den in der Mikrokavität erzeugten Exziton-Polaritonen. / Microcavity (MC) exciton-polaritons can form condensates, i.e. macroscopic quantum states (MQSs), as well under a periodic potential modulation. The modulation by a surface acoustic wave (SAW) provides a powerful tool for the formation of tunable lattices of MQSs in semiconductor MC. In this work, fundamental aspects of the structure and dynamics of exciton-polariton condensate in acoustic square lattices were investigated by probing its wavefunction in real- and momentum space using spectral- and time-resolved studies. The MQSs were resonantly excited in an optical parametric oscillator configuration. The tomographic study revealed that the exciton-polariton condensate structure self-organises in a concentric structure, which consists of a single, two-dimensional gap soliton (2D GS) surrounded by one-dimensional MQSs and an incoherent background. 2D GS size tends to saturate with increasing particle density. The experimental results are supported by a theoretical model based on the variational solution of the Gross-Pitaevskii equation. Time-resolved studies showed the evolution of the 2D GS wavefunction at the acoustic velocity. Interestingly, the photoluminescence (PL) intensity emitted by the 2D GS as well as its coherence length oscillate with time. The PL oscillation amplitude depends on the intensity and the size of the exciting laser spot, and increases considerably for excitation intensities close to the optical threshold power for the formation of the MQS. In the outlook, the formation of Tamm-Plasmon/Exciton-Polariton (TPEP) hybrid states and their modulation by SAWs was theoretically discussed. Here, the upper DBR is partly replaced by a thin metal layer placed on top of the MC. In this case, TPEP form by the superposition of Tamm plasmons at the metal-semiconductor interface and the exciton-polaritons in the MC.