| 1. |
- Aboulfadl, Hisham, 1986, et al.
(författare)
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Alkali Dispersion in (Ag,Cu)(In,Ga)Se2 Thin Film Solar Cells - Insight from Theory and Experiment
- 2021
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 13:6, s. 7188-7199
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Tidskriftsartikel (refereegranskat)abstract
- Silver alloying of Cu(In,Ga)Se2 absorbers for thin film photovoltaics offers improvements in open-circuit voltage, especially when combined with optimal alkali-treatments and certain Ga concentrations. The relationship between alkali distribution in the absorber and Ag alloying is investigated here, combining experimental and theoretical studies. Atom probe tomography analysis is implemented to quantify the local composition in grain interiors and at grain boundaries. The Na concentration in the bulk increases up to ∼60 ppm for [Ag]/([Ag] + [Cu]) = 0.2 compared to ∼20 ppm for films without Ag and up to ∼200 ppm for [Ag]/([Ag] + [Cu]) = 1.0. First-principles calculations were employed to evaluate the formation energies of alkali-on-group-I defects (where group-I refers to Ag and Cu) in (Ag,Cu)(In,Ga)Se2 as a function of the Ag and Ga contents. The computational results demonstrate strong agreement with the nanoscale analysis results, revealing a clear trend of increased alkali bulk solubility with the Ag concentration. The present study, therefore, provides a more nuanced understanding of the role of Ag in the enhanced performance of the respective photovoltaic devices.
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| 2. |
- Aboulfadl, Hisham, 1986, et al.
(författare)
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Atomic-scale characterization of diffusion kinetics in Ru/Al multilayer thin films
- 2019
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Ingår i: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 254, s. 344-347
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure properties of reactive multilayers play a key role in their chemical reactions. Ru/Al multilayers are investigated in as-deposited and annealed conditions using atom probe tomography to probe the interdiffusion and early phase formation. Performing atom probe analysis was accompanied with difficulties stemming from weak adhesion of the bi-layers and reconstruction artifacts. Nonetheless, it was possible to obtain valuable qualitative information concerning diffusion kinetics. Asymmetric interdiffusion during deposition is found. Grain boundary diffusion is shown to have a major contribution on enhancing mass-transport across the layers as well as on the nucleation and growth of the RuAl6 intermetallic phase.
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| 3. |
- Aboulfadl, Hisham, 1986, et al.
(författare)
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Interdiffusion in as-deposited Ni/Ti multilayer thin films analyzed by atom probe tomography
- 2019
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Ingår i: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 236, s. 92-95
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Tidskriftsartikel (refereegranskat)abstract
- The nanoscale design of metallic multilayer thin films is one crucial factor that greatly influences the kinetics, often inducing unusual phase transformations. Metastable or amorphous phases may directly form in as-deposited films of certain thicknesses, which is common for Ni/Ti multilayers. Atom probe tomography and X-ray diffraction analyses are performed here to study the interdiffusion and structural changes as a function of the bilayer thickness in Ni/Ti multilayers. The films are deposited by DC magnetron sputtering with near 50:50 compositions. Multilayers with 5 nm bilayer thickness are found to be highly intermixed, with compositions up to ∼25 at.% for both diffuser metals, inducing amorphization reactions during deposition.
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| 4. |
- Aboulfadl, Hisham, et al.
(författare)
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Microstructural Characterization of Sulfurization Effects in Cu(In,Ga)Se2 Thin Film Solar Cells
- 2019
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Ingår i: Microscopy and Microanalysis. - : CAMBRIDGE UNIV PRESS. - 1435-8115 .- 1431-9276. ; 25:2, s. 532-538
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Tidskriftsartikel (refereegranskat)abstract
- Surface sulfurization of Cu(In,Ga)Se 2 (CIGSe) absorbers is a commonly applied technique to improve the conversion efficiency of the corresponding solar cells, via increasing the bandgap towards the heterojunction. However, the resulting device performance is understood to be highly dependent on the thermodynamic stability of the chalcogenide structure at the upper region of the absorber. The present investigation provides a high-resolution chemical analysis, using energy dispersive X-ray spectrometry and laser-pulsed atom probe tomography, to determine the sulfur incorporation and chemical re-distribution in the absorber material. The post-sulfurization treatment was performed by exposing the CIGSe surface to elemental sulfur vapor for 20 min at 500°C. Two distinct sulfur-rich phases were found at the surface of the absorber exhibiting a layered structure showing In-rich and Ga-rich zones, respectively. Furthermore, sulfur atoms were found to segregate at the absorber grain boundaries showing concentrations up to ∼7 at% with traces of diffusion outwards into the grain interior.
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| 5. |
- Broering Chaar, Ana Beatriz, et al.
(författare)
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Microstructural influence of the thermal behavior of arc deposited TiAlN coatings with high aluminum content
- 2021
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 854
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the microstructure on the thermal behavior of cathodic arc deposited TiAlN coatings was studied as a function of isothermal annealing. Two compositionally similar but structurally different coatings were compared, a Ti0·34Al0·66N0.96 coating with a fine-grain structure consisting of a mixture of cubic (c) and hexagonal (h) phases, and a Ti0·40Al0·60N0.94 coating with a coarse-grain structure of cubic phase. By in situ wide-angle synchrotron x-ray scattering, spinodal decomposition was confirmed in both coatings. The increased amount of internal interfaces lowered the decomposition temperature by 50 °C for the dual-phase coating. During the subsequent isothermal anneal at 1000 °C, a transformation from c-AlN to h-AlN took place in both coatings. After 50 min of isothermal annealing, atom probe tomography detected small amounts of Al (∼2 at.%) in the c-TiN rich domains and small amounts of Ti (∼1 at.%) in the h-AlN rich domains of the coarse-grained single-phase Ti0·40Al0·60N0.94 coating. Similarly, at the same conditions, the fine-grained dual-phase Ti0·34Al0·66N0.96 coating exhibits a higher Al content (∼5 at.%) in the c-TiN rich domains and higher Ti content (∼15 at.%) in the h-AlN rich domains. The study shows that the thermal stability of TiAlN is affected by the microstructure and that it can be used to tune the reaction pathway of decomposition favorably.
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| 6. |
- Bushlya, Volodymyr, et al.
(författare)
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Tool wear mechanisms of PcBN in machining Inconel 718: Analysis across multiple length scale
- 2021
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Ingår i: CIRP Annals - Manufacturing Technology. - : Elsevier BV. - 1726-0604 .- 0007-8506. ; 70:1, s. 73-78
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Tidskriftsartikel (refereegranskat)abstract
- Recently, PcBN tooling have been successfully introduced in machining Ni-based superalloys, yet our knowledge of involved wear mechanisms remains limited. In this study, an in-depth investigation of PcBN tool degradation and related wear mechanisms when machining Inconel 718 was performed. Diffusional dissolution of cBN is an active wear mechanism. At high cutting speed oxidation of cBN becomes equally important. Apart from degradation, tool protection phenomena were also discovered. Oxidation of Inconel 718 resulted in formation of γ-Al2O3 and (Al,Cr,Ti)3O4 spinel that were deposited on the tool rake. Also on the rake, formation of (Ti,Nb,Cr)N takes place due to cBN-workpiece interaction. This creates a sandwich tool protection layer forming continuously as tool wear progresses. Such in operando protection enabled counterbalancing tool wear mechanisms and achieved high performance of PcBN in machining.
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| 7. |
- Cengiz, Sezgin, 1984, et al.
(författare)
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Effect of Ce addition on microstructure, thermal and mechanical properties of Al-Si alloys
- 2023
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Ingår i: Materials Today Communications. - : Elsevier BV. - 2352-4928. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- In this study, commercial Al–12Si and Al-12Si-xCe (x = 0.5, 1, 2, 4, 8 and 12 wt% Ce) alloys were synthesized and the effect of cerium (Ce) content on the microstructure and on thermal and mechanical properties of the alloys was systematically investigated. The coefficient of thermal expansion decreased from 25.9 × 10−6 K−1 to 23.3 × 10−6 K−1 (50–493 °C) with increasing amount of Ce in the alloys. XRD analyses revealed that α-Al, Si, and CuZn5 were present in all of the alloys. The addition of Ce resulted in the formation of Al9FeSi3, Al0.85CeSi1.15 and AlCeSi2. The chemical composition of the alloy and the existing phases was investigated with energy dispersive spectroscopy in a scanning electron microscope at micrometer scale and with atom probe tomography at nanometer scale in three dimensions. Ce was found to be exist within eutectic Si and Ce-rich intermetallic phases. The addition of 2 wt% Ce into the Al-12Si alloy improved the ultimate tensile strength of the alloy by 25–30%. Further Ce addition (4–12 wt%) resulted in a dramatic drop in the strength of the alloy. The low ductility of the Al-12Si alloy was remarkably improved for the alloys containing Ce up to 2 wt%.
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| 8. |
- Fazi, Andrea, 1992, et al.
(författare)
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Characterization of as-deposited cold sprayed Cr-coating on Optimized ZIRLO™ claddings
- 2021
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 549
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Tidskriftsartikel (refereegranskat)abstract
- As-produced Cr-coated Optimized ZIRLO™ cladding material fabricated with the cold-spray (CS) deposition process is studied. Cross-sectional electron microscopy, nano-hardness profiling, transmission electron microscopy, transmission Kikuchi diffraction, and atom probe tomography (APT) were performed to investigate the nature of the CS Cr-coating/Optimized ZIRLO™ interface, the microstructure of the coating, and the effects of the deposition on the Zr-substrate microstructure. The former surface of the Zr-substrate was found to have a highly deformed nano-crystalline microstructure, the formation of which was attributed to dynamic recrystallization occurring during coating deposition. This microstructural change, evaluated with electron backscattered diffraction and nano-hardness profiling, appeared to be confined to a depth of a few microns. Through APT analysis, a 10–20 nm thick intermixed bonding region was observed at the interface between coating and substrate. The chemical composition of this region suggests that this layer originated from a highly localized shearing and heating of a thin volume of the outermost former surface of the substrate. The study of the intermixed bonding region's crystalline structure was performed with high resolution transmission electron microscopy and revealed a distorted hexagonal close-packed structure.
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| 9. |
- Fritze, Stefan, et al.
(författare)
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Elemental distribution and fracture properties of magnetron sputtered carbon supersaturated tungsten films
- 2024
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 477
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Tidskriftsartikel (refereegranskat)abstract
- The combination of strength and toughness is a major driving force for alloy design of protective coatings, and nanocrystalline tungsten (W)-alloys have shown to be promising candidates for combining strength and toughness. Here we investigate the elemental distribution and the fracture toughness of carbon (C) alloyed W thin films prepared by non-reactive magnetron sputtering. W:C films with up to ~4 at.% C crystallize in a body-centered-cubic structure with a strong 〈hh0〉texture, and no additional carbide phases are observed in the diffraction pattern. Atom probe tomography and X-ray photoelectron spectroscopy confirmed the formation of such a supersaturated solid solution. The pure W film has a hardness ~13 GPa and the W:C films exhibit a peak hardness of ~24 GPa. In-situ micromechanical cantilever bending tests show that the fracture toughness decreases from ~4.5 MPa·m1/2 for the W film to ~3.1 MPa·m1/2 for W:C films. The results show that C can significantly enhance the hardness of W thin films while retaining a high fracture toughness.
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| 10. |
- Grini, S., et al.
(författare)
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Dynamic Impurity Redistributions in Kesterite Absorbers
- 2020
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951.
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Tidskriftsartikel (refereegranskat)abstract
- Cu2ZnSn(S,Se)4 is a promising nontoxic earth-abundant solar cell absorber. To optimize the thin films for solar cell device performance, postdeposition treatments at temperatures below the crystallization temperature are normally performed, which alter the surface and bulk properties. The polycrystalline thin films contain relatively high concentrations of impurities, such as sodium, oxygen and hydrogen. During the treatments, these impurities migrate and likely agglomerate at lattice defects or interfaces. Herein, impurity redistribution after air annealing for temperatures up to 200 °C and short heavy water treatments are studied. In addition, nonuniformities of the sodium distribution on a nanometer and micrometer scale are characterized by atom probe tomography and secondary ion mass spectrometry, respectively. Sodium and oxygen correlate to a greater extent after heat treatments, supporting strong binding between the two impurities. Redistributions of these impurities occur even at room temperature over longer time periods. Heavy water treatments confirm out-diffusion of sodium with more incorporation of oxygen and hydrogen. It is observed that the increased hydrogen content does not originate from the heavy water. The existence of an “ice-like” layer on top of the Cu2ZnSnS4 layer is proposed.
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