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Development of a HBr-Based ICP-RIE Process for Smooth and Anisotropic Etching of III–V Semiconductors
(2026) Nyström, Emil
This thesis presents the development of a dry etching recipe using hydrogen bromide (HBr) for the fabrication of InP/InGaAs-based heterostructures. The recipe aims to replace a methane-based process to avoid chamber contamination while maintaining a highly directional etch profiles and smooth surfaces. HBr in particular was selected as an alternative etching chemistry due to its potential to achieve desired result, while also offering reduced plasma-induced damage compared to conventional processes. Though systematic research and optimization of process parameters such as, pressure, temperature, ICPpower, RF-power, and flowrate, a recipe was developed that produces sidewall-angles up to 88.9 degrees and smooth surfaces. A hard mask material combination of Ni and Cr was found to be optimal which yields a selectivity up to 22:1, and a Si carrier should be used to add a passivation mechanism to the etching recipe. The developed recipe has successfully been applied to Fermi-level managed barrier diodes (FMBD), resonant-tunnelling diodes (RTD), and heterostructure barrier varactors (HBV), demonstrating consistent etch-performance across different InP/InGaAs-layer stacks. Electrical measurements confirmed functionality of devices fabricated using the new process, validating the suitability as a replacement for the methane-based dry etch process recipe.
Investigation into the efficiency of a PLM system
(2025) Kåreby, Markus
This thesis explores time-related data recorded within a Product lifecyle management (PLM) system, with a focus on Engineering Change Requests (ECRs). A total of 166 ECRs were collected, categorized into four distinct cases, and analyzed to understand process times, task distribution, outlier occurrences, and iterative work. Data was manually gathered and visualized using box plots. The analysis showed that cases handling Product Change Requests (PCRs) had significantly longer and more variable processing times, often due to inactive time being recorded as active work in the data. Furthermore, a noticeable proportion of outliers and iterative work were found in certain data sets generally belived to be caused by the requirement of PCRs. Limitations in the data included lack of clear project identifiers, inconsistencies in how time was recorded, and the inability to differentiate between rework and multi-article tasks. Despite these constraints, inefficiencies were identified such as idle time, undocumented steps, and inconsistent timestamping. The thesis finds that the PLM data is not fully representative of actual work, but inefficacies are and were still possible to be identified from the data. Recommendations for improving data quality include automation of data collection, better categorization of ECRs, and improving data tracking. These measures would support better process understanding and lead to potential efficiency increase in the product change workflows
A microstructural investigation of Fe-oxides for developing high-temperature corrosion lifetime prediction models
(2026) Flora Alto, Alexandra
The aim of this study was to investigate the microstructure of oxide scales formed in environments relevant to biomass- and waste boilers used for superheater appli cations. It also investigated how KCl can a!ect both the corrosion kinetics and mi crostructure, specifically the characteristics of oxide grain boundaries. The obtained data provides insights into high-temperature corrosion and ultimately help improve high-temperature corrosion lifetime prediction models for superheater tubes. The study starts with a literature review about corrosion and analytical methods. To simulate the environment that exists for the superheater tubes of biomass- and waste power plants, the furnace’s environment was prepared to attain constant levels of the following: 20 % water vapor, 5 % O2 and 75 % N2 at 400 °C. Each exposure of the sample groups was performed according to four phases, namely sample prepara tion, exposure to simulation of the environment, preparation before SEM analysis, and SEM analysis. Results showed that pure Fe samples exposed longer to the simulated environment experienced the corrosion process to a greater extent, which results in a thicker ox ide scale on the Fe sample surface. In addition, KCl appears to have increased the corrosion rate, as demonstrated by the greater oxide scale thickness, the higher mass gain of the samples, and the observability of oxide grains after both exposure times. The combined use of SEM-EDS (EDX) made it possible to perform EDX mapping and EDX point analysis of the exposed samples. This facilitated the identification of the Fe sample surface, the Fe-rich oxide scales, and the KCl layer located on top of the oxide scales. The flat BIB milling technology implemented during sample preparation prior to SEM imaging enabled the identification and di!erentiation of oxide grains, BIB milling marks, and mechanical polishing scratches. This indicates that there is a need for improvement in the flat BIB milling technique, which could be achieved by testing variations in the accelerating voltage, the angle of incidence of the ion beam, and the flat BIB milling exposure time. In conclusion, the flat BIB milling method, when combined with SEM, has the potential to reveal oxide grains at the nanoscale, making the observation of these oxide grains in the oxide scale more accessible than with widely utilized conventional technologies. Nevertheless, this study also shows that the method requires further development. Therefore, future work should focus on optimizing the BIB parameters to achieve the best possible Fe surface finish. Lastly, exposure time and the presence of KCl appears to have a positive e!ect on the detection of oxide grains and the growth of the oxide scale on pure Fe samples.
Encapsulation of carbonic anhydrase in metal-organic frameworks to facilitate CO2 capture
(2026) Sjöstrand, Ellen
Reducing carbon emissions is crucial to stop global warming. The current methods to capture and store carbon dioxide are expensive and energy demanding. Therefore, a new technique using the enzyme carbonic anhydrase was evaluated in this project. Five protocols were tested to encapsulate SazCA, which is a carbonic anhydrase from the thermophilic bacterium Sulfurihydrogenibium azorense, in metal-organic frameworks (MOFs) called zeolitic imidazolate framework-8 (ZIF-8). Encapsulating enzymes in metal-organic frameworks has previously been shown to increase their reusability and thermostability. The enzyme was first produced through heterologous expression from Escherichia coli and purified with affinity chromatography. The MOF was then synthesized together with SazCA. It was confirmed through X-ray diffraction that two of the protocols were successful in producing pure SazCA@ZIF-8. The structure was then identified with scanning electron microscopy, which showed that the protocol with a ratio of 70:1 of the precursors 2-methylimidazole and zinc nitrate hexahydrate had particles with the most desirable cubical shape and were also mostly uniform in size. However, evaluation of the enzymatic activity with Wilbur-Anderson units assay after the encapsulation showed that it only reached about 2-5 % of the activity in free SazCA. This was shown to most likely partly be because the free zinc ions were inhibiting the enzyme. However, it was also shown that the activity improved with 122.41 % by introducing sonication, which increases the diffusion rate. Finally the thermostability was tested and compared to that of free SazCA at the temperatures 75, 85 and 95 ◦C for 1 and 4 hours. At 85 ◦C it was observed that the thermostability in the encapsulated SazCA was higher than in the free SazCA. After 1 h at this temperature the relative activity compared to the free SazCA was 11.85 ± 0.72 %, compared to 1.97 ± 0.30 %, which it was initially. In conclusion, even though the SazCA encapsulated in ZIF-8 lost most of its original activity, important design principles were identified, which could benefit future research within the field.
Evaluating the Performance of Transfer Function Models for Identifying Groundwater Disturbances in Infrastructure Projects
(2026) Alfredsson, Viktor; Blomquist, Ella
Hydrogeology is inherently challenged by the difficulty of making direct observa tions. To address this, numerical groundwater models are commonly developed to simulate hydrogeological conditions at specific study sites. However, such models require extensive input data and are often time- and resource-intensive. As a result, alternative, data-driven modeling techniques are of growing interest. This study evaluates the performance of a data-driven Transfer Function model in identifying and analyzing groundwater head disturbances caused by underground excavation activities. The transfer function model used for this project is the open-source Python package Pastas. Focusing on the Haga Station site within the Västlänken infrastructure project in Gothenburg, Sweden, the research compares transfer function models with a numerical benchmark model developed using MOD FLOW. Synthetic and constructed disturbance scenarios in the form of excavation shafts were modeled in the benchmark model to generate time series of groundwater head, leakage and infiltration. These time series were then used to test the transfer function model’s ability to detect controlled disturbances. To validate the results, a qualitative assessment was also performed using observed field data. The findings demonstrate that transfer function models developed using Pastas can replicate general groundwater trends and detect some disturbance signals. However, the models showed significant variation between different well simulations, with in consistencies in how disturbances were interpreted. Additional limitations include the overestimation of recharge and the underestimation of leakage into shafts fol lowing transfer function model calibration. Despite these challenges, the transfer function approach shows promise due to its low data requirements and its ability to model complex hydrogeologic study sites. This work contributes to a better under standing of transfer function model capabilities and their potential application in hydrogeological assessments of infrastructure projects.