Browsing by master's degree program "Materiaalitutkimuksen maisteriohjelma (Materials Research)"

In this project, poly(2-methyl-2-oxazoline)-block-poly(2-n-butyl-2-oxazine)-block-poly(2-methyl-2- oxazoline) (PMeOx-b-PnBuOzi-b-PMeOx) and poly(2-methyl-2-oxazoline)-block-poly(2-n-propyl-2- oxazine) (PMeOx-b-PnPrOzi) with block lengths of 35-20-35 and 100-100, respectively, were synthesized. When dispersed in water these thermoresponsive polymers aggregate into micellar aggregates or form hydrogels. Polymers were characterized with 1H-NMR, GPC, and DLS. Age-related macular edema and diabetic macular edema are the most common reasons for blindness in industrialized countries. The triamcinolone acetonide, a corticosteroid used to treat both of these macular edemas, was loaded into the polymeric micelles or hydrogel of synthesized polymers using the thin film method. The loading efficiency for a triblock copolymer ((PMeOx35-b-PnBuOzi20- b-PMeOx35) polymeric micelles was 4 % at the polymer/drug ratio of 10/4 and for a hydrogel (PMeOx100-b-PnPrOzi100) it was 48 % with the same polymer/drug ratio. The properties of the PMeOx100-b-PnPrOzi100 hydrogel formulations with the drug were studied with rheological measurements, DSC, DLS, and GPC of formulations. The formulation showed storage modulus of 3 kPa and the gelation temperature at 16 °C. From the DSC two glass transition temperatures were obtained, Tg1 at around 12 °C and Tg2 at around 74 °C. The particle size distribution of the formulation obtained with DLS showed that there were assumingly micelles or vesicles with a hydrodynamic radius between 20 and 80 nm. The drug release from the hydrogel formulation was studied with the dialysis membrane method and all the drug was released within 24 hours. Both copolymers formed quite unstable formulations with the drug. The results from this study gives information how polyoxazoline- and polyoxazine-based materials can be used to encapsulate and release corticosteroids, such as triamcinolone acetonide. To increase the drug loading capacity and to stabilize formulations, some surfactants for the drug could be tested in the future.

In this master's thesis, polyzwitterionic copolymers were synthesized and analyzed with various methods. In the literature part, the theory behind the reactions and results is covered in order to explain the phenomena. In the literature part of the thesis, articles were used to describe the theory as extensively as possible. The theory elaborates on the most important topics considering the research part. The main topics are reversible addition-fragmentation polymerization (RAFT), polymerization-induced self-assembly (PISA), and polyzwitterions. In the reversible addition-fragmentation polymerization chapter the kinetics and possible monomers and RAFT agents are gone through also considering the pros and cons. Different disadvantages are dealt with as well when talking about RAFT polymerization. In the PISA chapter different possible morphologies and different types of PISA polymerizations are covered, concentrating still on RAFT polymerization. In this chapter also core blocks of PISA were discussed covering the core forming block used in the research, diacetone acrylamide. lastly, polyzwitterions were discussed explaining the theory, possible applications, polyelectrolyte complexes, and thermoresponsivity of polyzwitterions. Also, in this part polysulfobetaines were covered since it is the zwitterionic block in the copolymer synthesis. In the experimental part, PSBMA-PDAAM diblock copolymers were synthesized and studied with different methods. Different lengths of block copolymer were synthesized and they were studied with the most common characterization methods. Thermoresponsivity, morphology, and also the effect of the solids content of different block lengths were studied. Measurements turned out to be a success since many different morphologies were witnessed and the thermoresponsive behavior of this copolymer showed interesting results.

Positron Annihilation Spectroscopy is a powerful tool for defect characterisation, especially vacancies. Various defect properties can be studied, including defect behaviour at low and high temperatures. Despite the technique having its roots in the mid-20th century, there is little research on fundamental positron behaviour at ultralow temperatures. In this thesis, Positron Annihilation Lifetime Spectroscopy and Doppler Broadening Spectroscopy, two sub-methods of the spectroscopy technique, were used to measure positron trap-free Ge in the temperature range of 14 mK-300 K. Since a positron trap-free sample was used, the purpose was not to study defect processes. Instead, the aim of the thesis was to investigate whether any interesting positron processes could be seen at ultralow temperatures in the annihilation data. Previous research in Al has shown no change in either lifetime or Doppler broadening below 77 K. Measuring the positron lifetime in the sample located in a cryostat required designing a special detector setup, as the count rate was greatly reduced due to geometry. To tackle this, lifetime detectors consisting of BaF2 scintillators and quartz-windowed photomultiplier tubes were used. In addition, both analogue and digital signal processing techniques were tested for the lifetime setup, with the digital method proving to be preferable. Doppler Broadening was measured with a high-purity germanium detector connected to a digital gamma spectrometer. The results show a decrease in S-parameter and an increase in W-parameter with decresing temprature, with the rate of change being greatest at ultralow temperatures. This behaviour is concluded to be due to incomplete positron thermalization. The positron lifetime results are more difficult to interpret, as setup challenges resulted in results of questionable accuracy. Still, the trend suggests no change in lifetime over the whole temperature interval, which is in accordance with previous research.

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.

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.

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.

Bimetallic core-shell catalysts represent a new pathway to create highly selective and highly active catalysts. This can be done by using a relatively inactive metal as the core material and a more active metal as the shell material. The composition of both the core and shell structure can then be altered in order to tune the selectivity of the nanocatalyst. The synergistic effects of using bimetallic core-shell catalysts arise in part from the misfit strain that is encountered as a result of the difference in lattice spacings between the core and shell materials. The catalysts investigated here consist of an Au core and a Pd shell. Particles with four different Pd shell thicknesses were synthesized and the corresponding strain was measured. There is a 5.07% difference in the lattice spacings between Au and Pd, we therefore expect strain values to be near this amount. In this work, we directly measured the displacement fields that arise due to lattice mismatch in Au-Pd nanorods using High Resolution Scanning Transmission Electron Microscopy (HRSTEM) and 4D Scanning Transmission Electron Microscopy (4D-STEM). The strain was then calculated using three different analytical methods: Geometric Phase Analysis (GPA), Gaussian Peak Fitting, and nanodiffraction. These methods all measure the variations in local lattice parameters and plot these values for every pixel in the original STEM image, this results in a 2D strain map. These maps were then compared to see which produced the highest quality strain quantification.

A polyoxazine based reversibly crosslinking hydrogel material developed for MEW was modified to increase its resistance to thermal degradation and impart control over its swelling properties. A portion of side chain functionalized Diels-Alder crosslinking moieties was replaced by hydrophobic octyl groups to induce the formation of a dual network hydrogel of equal crosslink density upon swelling. This modification was found to have no negative effects on the processing behavior of the material and was able to produce MEW printed scaffolds with equal stacking accuracy and fiber shape fidelity at processing temperatures 20˚C lower than a fully chemically crosslinked material. The thermal degradation of this dual network crosslinked material was significantly reduced, showing minuscule increases in viscosity when held at processing temperatures for several hours. The swelling of the dual network hydrogel was found to be similar to that of fully chemically crosslinked hydrogels despite consisting of significantly fewer chemical crosslinks, demonstrating another potential avenue of control over this material property. Finally, promising alterations in mechanical properties were observed in the dual-network hydrogel versus chemically crosslinked hydrogels, along with observations of water induced crystallization attributed to the octyl chains.

One of the main goals of materials research is to find the link between the properties of materials and their fundamental structures. The distinct properties of thin films, categorized as materials from a few single layers of atoms to some hundreds of nanometers, have enjoyed an unparalleled demand in modern device manufacturing, and thus the investigation of factors which determine thin film structure and morphology is a vital area of research. In the case of thin films, their final structures can often be connected back to the initial film formation stages, such as in the crystallographic growth competition during island growth and coalescence. In this thesis, thin film growth stages are studied from the perspective of how they are affected by impurities. From the initial diffusion of adatoms on a bare substrate; to the formation of islands, their growth and coalescence; to the mobility of grain boundaries and bulk diffusion leading to the formation of a fully continuous layer; impurities influence each of these thin film growth processes in a multifaceted way, either acting as growth inhibitors, promoters or potentially neutral agents. To this end, Ag and Cu thin films were synthesized by magnetron sputtering onto SiO_2/Si substrates, with thicknesses ranging from 3 nm to 30 nm using varied deposition conditions, with the addition of a 3 nm amorphous carbon layer to limit further restructuring and oxidation. Impurities were let into the deposition atmosphere via a controlled opening of a leak valve, corresponding to a step-wise increase of base pressure from 10^(-8) Torr to 10^(-6) Torr and finally 10^(-5) Torr. The full range of thin films was deposited with each base pressure (except for 10^(-5) Torr for Cu) using two deposition rates, around 0.1 Ås^(-1) and 2 Ås^(-1). Each film was characterized ex situ with ellipsometry, 4PP, XRD and AFM to map the morphological and microstructural evolution during film growth. It is found that impurities tend to inhibit island coalescence and initial grain growth, resulting in a reduction of continuous film formation thickness and average grain size, leading to the formation of flatter films with, in most cases, less surface roughness. In later stages, it is found that impurities may allow for more grain growth by their incorporation into the growing facets. In terms of crystal structure, it is shown that impurities have a more pronounced effect on (111) oriented grains, inhibiting their growth, thus altering the preferred growth orientations of Ag and Cu by allowing (200) grains to grow larger. Grain radii and equivalent ellipse distributions showed the different responses of Ag and Cu to impurities. Ag films showed more prominent effects when a lower deposition rate was used, highlighting the impact of impurities on diffusive processes, while Cu films exhibited more effects with the use of higher deposition rates, indicating that the role of impurities, in this case, was more significant after the formation of a continuous layer.

Aluminium nitride is a piezoelectric material commonly used in piezoelectric microelectromechanical systems (MEMS) in the form of thin films deposited by sputtering. AlN-based devices are found in wireless electronics in the form of acoustic filters, but they also have prospective applications in a wide variety of sensor systems. To enhance the piezoelectric properties of AlN, some of the Al can be replaced with scandium, which is required for next-generation devices. However, addition of Sc makes both the deposition and patterning of the film more difficult. This work focuses on patterning of AlN and Sc0.2Al0.8N thin films with wet etching. Both materials are etched anisotropically, which in theory enables etching the materials with little deviation from the mask dimensions. However, in practise, undercutting at the mask edges occurs easily making the structures narrower compared to the etch mask. This work investigates and compares the mechanisms and etch rates of AlN and Sc0.2Al0.8N. Tetramethyl ammonium hydroxide was mostly used for etching, but also H3PO4 and H2SO4 were tested. Addition of 20 atom-% Sc lowered the etch rate of the material and resulted in more undercutting. The causes behind mask undercutting were examined by using 11 differently deposited etch masks, and the undercutting was minimized by optimizing the mask deposition, using thermal annealing, and optimizing the etching temperature. Finally, the work identifies and discusses the relevant factors in depositing and patterning the AlN, ScxAl1-xN and mask films.