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| 3. |
- Gharavi, Mohammad Amin, et al.
(författare)
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Microstructure and thermoelectric properties of CrN and CrN/Cr2N thin films
- 2018
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Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 51:35
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Tidskriftsartikel (refereegranskat)abstract
- CrN thin films with an N/Cr ratio of 95% were deposited by reactive magnetron sputtering onto (0 0 0 1) sapphire substrates. X-ray diffraction and pole figure texture analysis show CrN (1 1 1) epitaxial growth in a twin domain fashion. By changing the nitrogen versus argon gas flow mixture and the deposition temperature, thin films with different surface morphologies ranging from grainy rough textures to flat and smooth films were prepared. These parameters can also affect the CrNx system, with the film compound changing between semiconducting CrN and metallic Cr2N through the regulation of the nitrogen content of the gas flow and the deposition temperature at a constant deposition pressure. Thermoelectric measurements (electrical resistivity and Seebeck coefficient), scanning electron microscopy, and transmission electron microscopy imaging confirm the changing electrical resistivity between 0.75 and 300 , the changing Seebeck coefficient values between 140 and 230 , and the differences in surface morphology and microstructure as higher temperatures result in lower electrical resistivity while gas flow mixtures with higher nitrogen content result in single phase cubic CrN.
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| 4. |
- Hänninen, Tuomas, 1988-, et al.
(författare)
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Silicon carbonitride thin films deposited by reactive high power impulse magnetron sputtering
- 2018
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 335, s. 248-256
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous silicon carbonitride thin films for biomedical applications were deposited in an industrial coating unit from a silicon target in different argon/nitrogen/acetylene mixtures by reactive high power impulse magnetron sputtering (rHiPIMS). The effects of acetylene (C2H2) flow rate, substrate temperature, substrate bias voltage, and HiPIMS pulse frequency on the film properties were investigated. Low C2H2 flow rates (<10 sccm) resulted in silicon nitride-like film properties, seen from a dense morphology when viewed in cross-sectional scanning electron microscopy, a hardness up to ∼22 GPa as measured by nanoindentation, and Si-N bonds dominating over Si-C bonds in X-ray photoelectron spectroscopy core-level spectra. Higher C2H2 flows resulted in increasingly amorphous carbon-like film properties, with a granular appearance of the film morphology, mass densities below 2 g/cm3 as measured by X-ray reflectivity, and a hardness down to 4.5 GPa. Increasing substrate temperatures and bias voltages resulted in slightly higher film hardnesses and higher compressive residual stresses. The film H/E ratio showed a maximum at film carbon contents ranging between 15 and 30 at.% and at elevated substrate temperatures from 340 °C to 520 °C.
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| 5. |
- Hänninen, Tuomas, 1988-
(författare)
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Silicon Nitride Based Coatings Grown by Reactive Magnetron Sputtering
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon nitride and silicon nitride-based ceramics have several favorable material properties, such as high hardness and good wear resistance, which makes them important materials for the coating industry. This thesis focuses the synthesis of silicon nitride, silicon oxynitride, and silicon carbonitride thin films by reactive magnetron sputtering. The films were characterized based on their chemical composition, chemical bonding structure, and mechanical properties to link the growth conditions to the film properties. Silicon nitride films were synthesized by reactive high power impulse magnetron sputtering (HiPIMS) from a Si target in Ar/N2 atmospheres, whereas silicon oxynitride films were grown by using nitrous oxide as the reactive gas. Silicon carbonitride was synthesized by two different methods. The first method was using acetylene (C2H2) in addition to N2 in a Si HiPIMS process and the other was co-sputtering of Si and C, using HiPIMS for Si and direct current magnetron sputtering (DCMS) for graphite targets in an Ar/N2 atmosphere. Langmuir probe measurements were carried out for the silicon nitride and silicon oxynitride processes and positive ion mass spectrometry for the silicon nitride processes to gain further understanding on the plasma conditions during film growth. The target current and voltage waveforms of the reactive HiPIMS processes were evaluated.The main deposition parameter affecting the nitrogen concentration of silicon nitride films was found to be the nitrogen content in the plasma. Films with nitrogen contents of 50 at.% were deposited at N2/Ar flow ratios of 0.3 and above. These films showed Si-N as the dominating component in Si 2p X-ray photoelectron spectroscopy (XPS) core level spectra and Si–Si bonds were absent. The substrate temperature and target power were found to affect the nitrogen content to a lower extent. The residual stress and hardness of the films were found to increase with the film nitrogen content. Another factors influencing the coating stress were the process pressure, negative substrate bias, substrate temperature, and HiPIMS pulse energy. Silicon nitride coatings with good adhesion and low levels of compressive residual stress were grown by using a pressure of 600 mPa, a substrate temperature below 200 °C, pulse energies below 2.5 Ws, and negative bias voltages up to 100 V.The elemental composition of silicon oxynitride films was shown to depend on the target power settings as well as on the nitrous oxide flow rate. Silicon oxide-like films were synthesized under poisoned target surface conditions, whereas films deposited in the transition regime between poisoned and metallic conditions showed higher nitrogen concentrations. The nitrogen content of the films deposited in the transition region was controlled by the applied gas flow rate. The applied target power did not affect the nitrogen concentration in the transition regime, while the oxygen content increased at decreasing target powers. The chemical composition of the films was shown to range from silicon-rich to effectively stoichiometric silicon oxynitrides, where no Si–Si contributions were found in the XPS Si 2p core level spectra. The film optical properties, namely the refractive index and extinction coefficient, were shown to depend on the film chemical bonding, with the stoichiometric films displaying optical properties falling between those of silicon oxide and silicon nitride.The properties of silicon carbonitride films were greatly influenced by the synthesis method. The films deposited by HiPIMS using acetylene as the carbon source showed silicon nitride-like mechanical properties, such as a hardness of ~ 20 GPa and compressive residual stresses of 1.7 – 1.9 GPa, up to film carbon contents of 30 at.%. At larger film carbon contents the films had increasingly amorphous carbon-like properties, such as densities below 2 g/cm3 and hardnesses below 10 GPa. The films with more than 30 at.% carbon also showed columnar morphologies in cross-sectional scanning electron microscopy, whereas films with lower carbon content showed dense morphologies. Due to the use of acetylene the carbonitride films contained hydrogen, up to ~ 15 at.%. The co-sputtered silicon carbonitride films showed a layered SiNx/CNx structure. The hardness of these films increased with the film carbon content, reaching a maximum of 18 GPa at a film carbon content of 12 at.%. Comparatively hard and low stressed films were grown by co-sputtering using a C target power of 1200 W for a C content around 12 at.%, a negative substrate bias less than 100 V, and a substrate temperature up to 340 °C.
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| 6. |
- Imam, Mewlude, et al.
(författare)
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Plasma CVD of hydrogenated boron-carbon thin films from triethylboron
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:3
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature chemical vapor deposition (CVD) of B - C thin films is of importance for neutron voltaics and semiconductor technology. The highly reactive trialkylboranes, with alkyl groups of 1-4 carbon atoms, are a class of precursors that have been less explored for low-temperature CVD of B - C films. Herein, we demonstrate plasma CVD of B - C thin films using triethylboron (TEB) as a single source precursor in an Ar plasma. We show that the film density and B/C ratio increases with increasing plasma power, reaching a density of 2.20 g/cm3 and B/C = 1.7. This is attributed to a more intense energetic bombardment during deposition and more complete dissociation of the TEB molecule in the plasma at higher plasma power. The hydrogen content in the films ranges between 14 and 20 at. %. Optical emission spectroscopy of the plasma shows that BH, CH, C2, and H are the optically active plasma species from TEB. We suggest a plasma chemical model based on β-hydrogen elimination of C2H4 to form BH3, in which BH3 and C2H4 are then dehydrogenated to form BH and C2H2. Furthermore, C2H2 decomposes in the plasma to produce C2 and CH, which together with BH and possibly BH3-x(C2H5)x are the film forming species.
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| 7. |
- López, Alejandro, 1983-, et al.
(författare)
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Morphology and adhesion of silicon nitride coatings upon soaking in fetal bovine serum
- 2018
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Ingår i: 15th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering and 3rd Conference on Imaging and Visualization, Lisbon, March 26-29, 2018.
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Konferensbidrag (refereegranskat)abstract
- Total hip joint replacements are considered successful in providing patients with close- to-normal lives; however, revision surgeries still represent an individual and socioeconomic burden due to wear and failure of the implants, which occurs at a rate of 3-10% at 10 years. Therefore, eorts are being made to increase the lifespan of articial prostheses. Because of the impossibility to avoid wear debris, functional silicon nitride coatings are being developed due their low wearing, particle solubility and good biological response. However, a compromise needs to be found between coating reactivity and durability.A HIPIMS process was used to sputter a CrN interlayer followed by a SiNx top layer using 1- and 3-fold rotation in an industrial deposition system (CemeCon AG, Würselen, Germany). In order to measure the adhesion of the coatings to the cobalt-chromium-molybdenum substrates a scratch test was used, consisting of generating a scratch with a Rockwell C diamond stylus, at an increasing load from 0 to 100 N, at a displacement rate of 6mm/min. The samples were immersed in 25% fetal bovine serum solution to mimic synovial joint uid and scratched aer 0, 1, 3, 6 weeks periods in this solution. The cross-section of the coatings was assessed through Focused Ion Beam at 30kV for milling and 5kV for secondary electron imaging of the surface.The coatings demonstrated a high nitrogen content, previously shown to be benecial in terms of low dissolution rates. The deposition conditions and coating morphology were found to have an eect on the dissolution rate and thereby also the spallation failure of the coatings. These results are informative for the further development of these coatings into parts of functional 3D implants.
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| 9. |
- Mauri, G., et al.
(författare)
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Neutron reflectometry with the Multi-Blade B-10-based detector
- 2018
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Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 474:2216
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Tidskriftsartikel (refereegranskat)abstract
- The Multi-Blade is a boron-10-based gaseous detector developed for neutron reflectometry instruments at the European Spallation Source in Sweden. The main challenges for neutron reflectometry detectors are the instantaneous counting rate and spatial resolution. The Multi-Blade has been tested on the CRISP reflectometer at the ISIS Neutron and Muon Source in the UK. A campaign of scientific measurements has been performed to study the Multi-Blade response in real instrumental conditions. The results of these tests are discussed in this paper.
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| 10. |
- Moshontz, Hannah, et al.
(författare)
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The Psychological Science Accelerator: Advancing Psychology Through a Distributed Collaborative Network
- 2018
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Ingår i: Advances in Methods and Practices in Psychological Science. - : SAGE Publications. - 2515-2459 .- 2515-2467. ; 1:4, s. 501-515
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Tidskriftsartikel (refereegranskat)abstract
- Concerns about the veracity of psychological research have been growing. Many findings in psychological science are based on studies with insufficient statistical power and nonrepresentative samples, or may otherwise be limited to specific, ungeneralizable settings or populations. Crowdsourced research, a type of large-scale collaboration in which one or more research projects are conducted across multiple lab sites, offers a pragmatic solution to these and other current methodological challenges. The Psychological Science Accelerator (PSA) is a distributed network of laboratories designed to enable and support crowdsourced research projects. These projects can focus on novel research questions or replicate prior research in large, diverse samples. The PSA’s mission is to accelerate the accumulation of reliable and generalizable evidence in psychological science. Here, we describe the background, structure, principles, procedures, benefits, and challenges of the PSA. In contrast to other crowdsourced research networks, the PSA is ongoing (as opposed to time limited), efficient (in that structures and principles are reused for different projects), decentralized, diverse (in both subjects and researchers), and inclusive (of proposals, contributions, and other relevant input from anyone inside or outside the network). The PSA and other approaches to crowdsourced psychological science will advance understanding of mental processes and behaviors by enabling rigorous research and systematic examination of its generalizability.
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