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- Böör, Katalin, et al.
(författare)
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On the growth kinetics, texture, microstructure, and mechanical properties of tungsten carbonitride deposited by chemical vapor deposition
- 2022
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 40:5
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten carbonitride [W(C,N)] was deposited on cemented carbide substrates by chemical vapor deposition (CVD) in a hot-wall reactor using tungsten hexafluoride (WF6), acetonitrile (CH3CN), and hydrogen (H-2) as precursors. Tungsten carbides and nitrides with a hexagonal 6-WC type structure are generally difficult to obtain by CVD. Here, it was found that the combination of WF6 and CH3CN precursors enabled the deposition of W(C,N) coatings with a delta-WC type structure and columnar grains. A process window as a function of the deposition temperature and precursor partial pressures was determined to establish the conditions for the deposition of such coatings. Scanning electron microscopy, x-ray diffraction, electron backscatter diffraction, and elastic recoil detection analysis were used for the investigation of the coating thickness, microstructure, texture, and composition. From the investigation of the kinetics, it was concluded that the growth was mainly controlled by surface kinetics with an apparent activation energy of 77 kJ/mol, yielding an excellent step coverage. The partial reaction orders of the reactants together with their influence on the microstructure and coating composition was further used to gain a deeper understanding of the growth mechanism. Within the process window, the microstructure and the texture of the W(C,N) coatings could be tailored by the process parameters, enabling microstructural engineering with tuning of the mechanical properties of the W(C,N) coatings. The nanoindentation hardness (36.6-45.7 GPa) and elastic modulus (564-761 GPa) were found to be closely related to the microstructure.
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- Fang, Hailiang, et al.
(författare)
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Structural, microstructural and magnetic evolution in cryo milled carbon doped MnAl
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- The low cost, rare earth free τ-phase of MnAl has high potential to partially replace bonded Nd2Fe14B rare earth permanent magnets. However, the τ-phase is metastable and it is experimentally difficult to obtain powders suitable for the permanent magnet alignment process, which requires the fine powders to have an appropriate microstructure and high τ-phase purity. In this work, a new method to make high purity τ-phase fne powders is presented. A high purity τ-phase Mn0.55Al0.45C0.02 alloy was synthesized by the drop synthesis method. The drop synthesized material was subjected to cryo milling and followed by a fash heating process. The crystal structure and microstructure of the drop synthesized, cryo milled and flash heated samples were studied by X-ray in situ powder diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy and electron backscatter diffraction. Magnetic properties and magnetic structure of the drop synthesized, cryo milled, flash heated samples were characterized by magnetometry and neutron powder diffraction, respectively. The results reveal that the 2 and 4hours cryo milled and flash heated samples both exhibit high τ-phase purity and micron-sized round particle shapes. Moreover, the fash heated samples display high saturation magnetization as well as increased coercivity.
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- Fondell, Mattis, 1984-, et al.
(författare)
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Phase control of iron oxides grown in nano-scale cauliflower structures: hematite, maghemite and magnetite
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate that iron oxide in the form of hematite, suitable as absorber in photoelectrochemical cells, can be produced by pulsed chemical vapour deposition. By choosing carbon monoxide or nitrogen as carrier gases in the process the phase and granularity of the grown material can be controlled. The choice of carrier gas a ect the decomposition rate of iron pentacarbonyl used as iron precursor. The iron oxide phase is also dependent on the chosen substrate, here fluorine doped tin oxide and crystalline silicon have been used. Regardless of the substrate nitrogen yields hematite, whereas carbon monoxide gives magnetite on Si and maghemite on fluorine doped tin oxide. A combination of Raman spectroscopy, X-ray di raction, and hard X-ray photoelectron spectroscopy were used for characterization of the crystalline phase and chemical composition in the films. Scanning electron microscopy were used to visualise the deposited films’ nano-structure reminiscent of a cauliflower.
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- Fondell, Mattis, et al.
(författare)
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Phase control of iron oxides grown in nano-scale structures on FTO and Si(100) : Hematite, maghemite and magnetite
- 2015
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Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 117, s. 85-90
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that iron oxide in the form of hematite, suitable as absorption material in photo-electrochemical cells, can be produced by pulsed chemical vapour deposition. By choosing carbon monoxide or nitrogen as carrier gases in the process the phase and granularity of the grown material can be controlled. The choice of carrier gas affect the decomposition rate of iron pentacarbonyl used as iron precursor. The iron oxide phase is also dependent on the chosen substrate, here fluorine doped tin oxide and crystalline silicon have been used. Regardless of the substrate nitrogen yields hematite, whereas carbon monoxide gives, magnetite on Si and maghemite on fluorine doped tin oxide. A combination of Raman spectroscopy, X-ray diffraction, and hard X-ray photoelectron spectroscopy were used for characterization of the crystalline phase and chemical composition in the films. Scanning electron microscopy were used to visualise the deposited films' nano-structure.
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- Fondell, Mattis, 1984-, et al.
(författare)
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Temperature Induced Diffusion of Sn and Si in Hematite and Implications for Photocatalytic Water Splitting Applications
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The performance of Hematite (α-Fe2O3) for the water oxidation step in solar hydrogen production is dependent upon annealing of the material. In this study, these effects are investigated in terms of temperature induced diffusion of Sn and Si from the substrate into thin films of hematite by using hard X-ray photoelectron spectroscopy (HAXPES). Here, HAXPES is used for the first time to characterize a buried interface between a conducting substrate and a nanostructured thin film overlayer by diffusion upon annealing. This process is prototypical for the large class of photoelectrochemical devices that uses indium and fluorine doped tin oxide as substrates where the device is subsequently annealed. Indeed, we observe that: diffusion of Sn and Si is significant, already at 550 °C; the photocatalytic efficiency of the hematite films increased, from low values to 0.23 mA/cm2; annealing in air preserves the hematite phase, while annealing in vacuum induces a phase transition into magnetite, which impairs the photocatalytic performance. The increase in efficiency is explained in terms of an improvement of the quantum efficiency of the oxygen evolution reaction accompanied by a slight improvement in charge carrier transport.
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- Fritze, Stefan, et al.
(författare)
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Hard and crack resistant carbon supersaturated refractory nanostructured multicomponent coatings
- 2018
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The combination of ceramic hardness with high crack resistance is a major challenge in the design of protective thin films. High entropy alloys have shown in earlier studies promising mechanical properties with a potential use as thin film materials. In this study, we show that small amounts of carbon in magnetron-sputtered multicomponent CrNbTaTiW films can lead to a significant increase in hardness. The film properties were strongly dependent on the metal composition and the most promising results were observed for TaW-rich films. They crystallised in a bcc structure with a strong (110) texture and coherent grain boundaries. It was possible to deposit films with 8 at.% C in a supersaturated solid-solution into the bcc structure without carbide formation. A major effect of carbon was a significant grain refinement, reducing the column diameter from approximately 35 to 10 nm. This resulted in an increase in hardness from 14.7 to 19.1 GPa while the reduced E-modulus stayed constant at 322 GPa. The carbon-containing films exhibited extremely little plastic deformation around the indent and no cracks were observed. These results show that supersaturation of carbon into high entropy films can be a promising concept to combine superior hardness with high crack resistance.
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- Fritze, Stefan, et al.
(författare)
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Influence of Deposition Temperature on the Phase Evolution of HfNbTiVZr High-Entropy Thin Films
- 2019
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 12:4
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we show that the phase formation of HfNbTiVZr high-entropy thin films is strongly influenced by the substrate temperature. Films deposited at room temperature exhibit an amorphous microstructure and are 6.5 GPa hard. With increasing substrate temperature (room temperature to 275 degrees C), a transition from an amorphous to a single-phased body-centred cubic (bcc) solid solution occurs, resulting in a hardness increase to 7.9 GPa. A higher deposition temperature (450 degrees C) leads to the formation of C14 or C15 Laves phase precipitates in the bcc matrix and a further enhancement of mechanical properties with a peak hardness value of 9.2 GPa. These results also show that thin films follow different phase formation pathways compared to HfNbTiVZr bulk alloys.
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