| 1. |
- Alijan Farzad Lahiji, Faezeh, et al.
(författare)
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Unusual tilted growth and epitaxial relationship of NaCl B1-structured NiO and CrN on r-plane Al2O3
- 2024
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Ingår i: Journal of Applied Physics. - : American Institute of Physics Inc.. - 0021-8979 .- 1089-7550. ; 135:6
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial NiO and CrN thin films were deposited on a single-crystal Al2O3(11¯02) (r-plane sapphire) using magnetron sputtering. The two materials were intentionally deposited into two different deposition chamber designs and under different conditions (temperature, pressure, gases, and energy of sputtered particles). Despite the differences in the deposition condition and material system, both materials had the same feature with uncommon tilted epitaxial growth. Through an in-depth x-ray diffraction analysis of the NaCl (B1)-structured materials on r-plane sapphire, the full twin domain epitaxial relations were determined and can be described as (110)NaCl(B1)∥(44¯03)Al2O3 and [11¯2]NaCl(B1)∥[1¯1¯20]Al2O3. This relationship differs from the previously observed orientation of (100)NaCl(B1)∥(11¯02)Al2O3 and [100]NaCl(B1)∥[101¯0]Al2O3. These results are of general relevance for the growth of the extended NaCl (B1)-structured cubic material family onto a r-plane sapphire substrate where similar epitaxial growth can be expected.
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| 2. |
- Azina, Clio, et al.
(författare)
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Microstructural and compositional design of Cr2AlC MAX phases and their impact on oxidation resistance
- 2024
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Ingår i: Journal of the European Ceramic Society. - : ELSEVIER SCI LTD. - 0955-2219 .- 1873-619X. ; 44:8, s. 4895-4904
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of MAX phases has largely been investigated, but the effect of secondary phases and microstructure is still unclear. We report on the effect of reactive and non-reactive sintering, and starting powders, on the microstructure, phase formation, and chemical composition of Cr2AlC MAX phases. The grain sizes are shown to be sensitive to both the processing method and the starting powders. Secondary phases were observed mostly in reactively sintered samples as Cr7C3 and AlCr2 were identified, and Al contents varied between 24.4 and 28.0 at %. Finally, the oxidation behavior of the produced MAX phases was evaluated after 60 and 120 min at 1100 degrees C. The Al content, the average grain size of the as-sintered samples, and the presence of secondary phases affected the decomposition of the MAX phase into Cr-carbides in the vicinity of the oxide scale and the composition of the oxide scale, respectively.
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| 3. |
- Gangaprasad Rao, Smita, et al.
(författare)
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Mechanical properties of Xe-ion-irradiated high-entropy-alloy-based multilayers
- 2024
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 124:6
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter, we investigate the mechanical stability of HEA-based multilayers after Xe-ion irradiation. CrFeCoNi/TiNbZrTa metallic and nitride thin films with a bilayer thickness of 30 nm were grown by reactive dc-magnetron sputtering on Al2O3(0001) substrates for irradiation studies and on Si(100) substrates for other characterizations. The films were subjected to 3-MeV Xe-ion irradiation at room temperature (RT) and at 500 degrees C. The crystal structure and mechanical properties of the films before and after irradiation were studied by x-ray diffraction and nanoindentation. Before irradiation, both the metallic and nitride multilayers displayed a lower hardness (7 and 20 GPa, respectively). Annealing at 500 degrees C for 150 min increased the hardness of the multilayer samples, but it also induced intermixing of elements between the sublayers of the metallic multilayer. Irradiation hardening was observed only in the metallic multilayer at room temperature. When comparing the effects of irradiation damage vs the effects of annealing on the mechanical properties, it was observed that annealing the multilayers had a more pronounced effect.
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| 4. |
- Hjort, Victor, et al.
(författare)
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Influence of Ammonia Annealing on Cr-N Thin Films and Their Thermoelectric Properties
- 2024
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Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962.
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Tidskriftsartikel (refereegranskat)abstract
- CrN-based thin films are emerging as thermoelectric materials for energy harvesting. Their thermoelectric properties depend on phase composition and stoichiometry, necessitating control over the nitrogen content and how it affects the phase composition. Here, the effect of high-temperature ammonia annealing on the thermoelectric properties as well as crystal structure of thin films of Cr-N on c-plane sapphire (Al2O3(0001)) was investigated. Single-phase (cubic CrN) and mix-phase (cubic CrN + hexagonal-Cr2N) Cr-N films were annealed in ammonia, converting any secondary phase of hexagonal Cr2N to cubic CrN. The thermoelectric properties of the films that contained a secondary phase of hexagonal (CrN)-N-2 greatly improved upon annealing, with an increase of 900% to 0.5 x 10-3 W m(-1) K-2 for the film annealed at 800 degrees C for 2 h. Annealing of single-phase films of cubic CrN resulted in films with near-insulating electrical properties. For the thermoelectric applications of CrN, ammonia annealing can be beneficial over meticulous deposition control.
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| 5. |
- Honnali, Sanath Kumar, 1996-
(författare)
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Energy-efficient physical vapor deposition of transition metal nitride thin films
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on providing insights into energy-efficient ways of growing protective thin films using physical vapor deposition (PVD) by magnetron sputtering, specifically high-power impulse magnetron sputtering (HiPIMS). This technique involves ionizing the material to be deposited to a high degree. The properties of the film for applications such as protective coatings could thus be controlled by modulating the energy and guiding the ions using electric and magnetic fields, respectively. The multiprincipal element TiZrNbTa nitride system is of interest for its corrosion-resistant coating applications. This material system consists of refractory metals that exhibit different ionic charge states with significant mass contrast. Thus, when sputtered with HiPIMS, the properties of the films strongly depend on the mass and energy of the bombarding metal ions. The transport of these ions to the substrate is influenced by the magnetic field distribution in the chamber. To demonstrate the influence of the magnetron arrangement, the deposition is performed without external heating. Two magnetron arrangements were chosen: a tilted closed-field design with four magnetrons and a single magnetron. The films exhibited different properties depending on the magnetron design used. The single magnetron design induces changes in the preferred orientation of the films from 111 to 200 along with film composition and density. A reduction in residual stress was observed with only a ~6 % degradation in the hardness compared to the closed-field design. I also demonstrate epitaxial growth of TiZrNbTaNx films without external heating. The films were grown with a single magnetron design on single crystal sapphire substrate. Applying a pulsed substrate bias with a long pulse width instead of a constant bias, resulted in low argon (~1 at. %) and oxygen (0.5 at. %) content in the films. In addition, the films exhibited a higher optical absorbance in the near-infrared region than the high-temperature grown films. The total energy consumption for film deposition was reduced by approximately 50 % compared to dc magnetron sputtering (DCMS) at 400°C growth temperature. This reduction is without considering the substrate heating and stabilization phase, which is shorter compared to the industry standard where the entire chamber is heated up to ~500-600°C. These findings are beneficial in designing film growth conditions for energy-efficient processes without compromising film quality. This could also address the challenges of growing high-quality films on temperature-sensitive substrates.
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| 6. |
- Li, Youbing, et al.
(författare)
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A-site alloying-guided universal design of noble metal-based MAX phases
- 2024
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Ingår i: Matter. - : Cell Press. - 2590-2393 .- 2590-2385. ; 7:2, s. 523-538
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Tidskriftsartikel (refereegranskat)abstract
- Mn+1AXn (MAX) phases have attracted significant attention due to their structural diversity and potential applications. Designing MAX phases with single-atom-thick A layers featuring 4d/5d-orbital electronic elements is interesting work. Here, we present a comprehensive report on noble metal-based M2(A1-xA′x)C (M = V, Ti, Nb; A = Al, Sn, In, Ga, Ge; A′ = Ru, Rh, Pd, Ir, Pt, Au and combinations thereof; 0 < x ≤ 0.4) phases featuring A sublayers of 4d/5d-orbital electronic elements through an A-site alloying strategy. The chemical composition of MAX phases can be adjusted by selecting different M- and A-site elements, with morphology tailored by distinct C sources. Furthermore, the V2(Sn0.8Pt0.2)C (15.7 wt % Pt) catalyst showed better performance for hydrogen evolution reaction compared to the commercial Pt/C (20 wt % Pt) electrode. This study highlights the prospects of A-site alloying for the design of novel MAX phases with unique properties and promising applications in electrocatalysis and beyond.
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| 7. |
- Linder, Clara, et al.
(författare)
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Effect of Mo content on the corrosion resistance of (CoCrFeNi)1−xMox thin films in sulfuric acid
- 2024
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Ingår i: Thin Solid Films. - : Elsevier B.V.. - 0040-6090 .- 1879-2731. ; 790
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Tidskriftsartikel (refereegranskat)abstract
- (CoCrFeNi)1−xMox thin films with various Mo content (0–10 at.%) were grown by magnetron sputtering on a stainless steel substrate. The films with 0–2 at.% presented two crystal structures: one FCC phase and one sigma phase, while films with higher Mo content only had the FCC structure. All films have a (111) texture and follow the topography of the substrate. The corrosion resistance of the films was evaluated in 0.05 M H2SO4 at room temperature and at 80 °C. It was observed that the corrosion current densities considerably decreased for Mo > 2 at%, and that the current densities were higher at the elevated temperature. Scanning Kelvin Probe Force Microscopy showed a large potential difference between the main FCC phase and sigma phase for the Mo0–2 films. This would suggest that preferential dissolution of the FCC phase occurs over the sigma and reduces the corrosion resistance. Such preferential dissolution does not occur for the higher Mo content films with only the FCC phase. The high corrosion resistance was also attributed to the inhibition of Fe and Cr dissolution by Mo and the stabilisation of the Cr enriched oxide by incorporating Mo oxides into the passive film, identified by X-ray photoelectron spectroscopy. The low corrosion current densities (below 1 µA/cm2) make these thin films possible candidates for protective coatings of bipolar plates in PEM fuel cells.
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| 8. |
- Ma, Hairui, et al.
(författare)
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Synthesis and characterization of c-TiAlN/h-Cr2N multilayer films deposited by magnetron sputtering on Si (100) substrates
- 2024
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Ingår i: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 976
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Tidskriftsartikel (refereegranskat)abstract
- A series of c-TiAlN/ h-Cr2N multilayer films with modulation periods Lambda of 10, 20 and 30 nm and thickness ratios (Cr2N thickness /Lambda) of 25%, 50% and 75% were prepared by dc magnetron sputtering on the Si substrate. The microstructures were characterized by scanning electron microscopy, x-ray diffraction, and the mechanical properties were measured by curvature measurement method and nanoindentation. With the Cr2N ratio increasing from 25% to 75%, the orientation of Cr2N layers changed from a randomly orientation to a 0001 preferential orientation, while inversely, the c-TiAlN layer changed from a 001 preferential orientation to a 111 preferential orientation or a randomly orientation. In the meantime, and regardless of the modulation period, the lattice parameter of c-TiAlN decreased from 4.16 angstrom to 4.12 angstrom and was explained by an increase of tensile stress between + 0.2 and + 1.3 GPa when the increase of Cr2N% in the modulation. With the increase of Cr2N ratio, the morphology of the film changed and led to surface with apparent porosity and large grain sizes of 100 x 300 nm. The film with 25% Cr2N ratio and modulation period of 20 nm exhibited the highest hardness reaching 22 +/- 1.3 GPa and reduced Young's modulus of 253 +/- 6 GPa.
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| 9. |
- Naumovska, Elena, et al.
(författare)
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Local structure of hydrated nanocrystalline films of the proton conductor BaZr 1-x Sc x O 3-x/2 studied by infrared spectroscopy
- 2024
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Ingår i: Vibrational Spectroscopy. - 0924-2031. ; 130
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Tidskriftsartikel (refereegranskat)abstract
- We report results from a study of the local structure of hydrated nanocrystalline 2 μm films of the well known proton conductor BaZr1-xScxO3-x/2 with x = 0.45, 0.54 and 0.64, using infrared (IR) spectroscopy. The films were prepared by magnetron sputtering. Analysis of the IR spectra focused on the O–H stretching region (2000—3700 cm-1), which reveals the presence of several distinct O–H stretching bands for which the intensity and frequency of each band vary in an unsystematic manner with Sc concentration. The spectra for the two higher Sc concentrations, x = 0.54 and 0.64, exhibit a distinct, highly intense O–H stretching band centered at around 3400–3500 cm-1, which is assigned to relatively symmetric, weakly hydrogen-bonding, proton configurations. The spectrum for the lower Sc concentration, x = 0.45, does not feature such a band but a broader, weaker, O–H stretching band between approximately 2500 and 3700 cm-1, suggesting that the protons are more homogeneously distributed over a range of different local proton coordinations in this relatively weakly doped material. A comparison to the IR spectra of powder samples of similar compositions suggests that for x = 0.45, the spectra and proton coordination of films and powder samples are similar, whereas for x = 0.54 and 0.64, a larger fraction of protons seems to be located in weakly hydrogen-bonding proton configurations in the films compared to the respective powder samples.
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| 10. |
- Naumovska, Elena, et al.
(författare)
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Local structure of hydrated nanocrystalline films of the proton conductor BaZr1-xScxO3-x/2 studied by infrared spectroscopy
- 2024
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Ingår i: Vibrational Spectroscopy. - : Elsevier. - 0924-2031 .- 1873-3697. ; 130
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Tidskriftsartikel (refereegranskat)abstract
- We report results from a study of the local structure of hydrated nanocrystalline 2 m films of the well known proton conductor BaZr1-xScxO3-x/2 with x = 0.45, 0.54 and 0.64, using infrared (IR) spectroscopy. The films were prepared by magnetron sputtering. Analysis of the IR spectra focused on the O–H stretching region (2000—3700 cm-1), which reveals the presence of several distinct O–H stretching bands for which the intensity and frequency of each band vary in an unsystematic manner with Sc concentration. The spectra for the two higher Sc concentrations, x = 0.54 and 0.64, exhibit a distinct, highly intense O–H stretching band centered at around 3400–3500 cm-1, which is assigned to relatively symmetric, weakly hydrogen-bonding, proton configurations. The spectrum for the lower Sc concentration, x = 0.45, does not feature such a band but a broader, weaker, O–H stretching band between approximately 2500 and 3700 cm-1, suggesting that the protons are more homogeneously distributed over a range of different local proton coordinations in this relatively weakly doped material. A comparison to the IR spectra of powder samples of similar compositions suggests that for x = 0.45, the spectra and proton coordination of films and powder samples are similar, whereas for x = 0.54 and 0.64, a larger fraction of protons seems to be located in weakly hydrogen-bonding proton configurations in the films compared to the respective powder samples.
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