Browsing by master's degree program "Master 's Programme in Materials Research"
Now showing items 41-42 of 42
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(2022)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.
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(2023)X-ray emission spectroscopy (XES) is an elemental characteristic x-ray technique that is used in studying the electronic properties of varied materials. It is based on an x-ray emission process that occurs due to an absorption process. First an x-ray photon is shot at the sample and electron in the inner core absorbs this x-ray photon. The electron gets kicked out of its place, creating an empty electronic state called an electron hole. This leaves the atom to an excited state that then de-excites by emitting an elemental characteristic x-ray photon. One of the main aspects of x-ray emission spectroscopy is to study sensitivity of XES towards different emission lines in different chemical environments and then compare the results. X-ray emission spectroscopy is a relatively easy technique to perform because it does not require a long-range crystal order and experiments can be done in an atmospheric pressure and in room temperature. A series of measurements were performed with non-resonant XES to study chemical properties of different uranium oxides. The experiment was done at the SOLEIL Synchrotron Facility in France. Main goal of the experiment was to study the sensitivity of XES to different uranium L3-emission lines by measuring different uranium oxides with different uranium oxidation states and compare the shape of each emission spectrum. The results showed that there are no visible differences between different samples when using non-resonant XES. However, the experiment also showed that when the resonant part is included in the measurements, then there are visible differences between different samples. This indicates the resonant part is required to collect to see differences in the spectrum when comparing the speciation of different samples.
Now showing items 41-42 of 42