| 1. |
- Qviller, A. J., et al.
(författare)
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Thermal stability of photovoltaic a-Si:H determined by neutron reflectometry
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:23, s. 231909-
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Tidskriftsartikel (refereegranskat)abstract
- Neutron and X-ray reflectometry were used to determine the layer structure and hydrogen content of thin films of amorphous silicon (a-Si:H) deposited onto crystalline silicon (Si) wafers for surface passivation in solar cells. The combination of these two reflectometry techniques is well suited for non-destructive probing of the structure of a-Si:H due to being able to probe buried interfaces and having sub-nanometer resolution. Neutron reflectometry is also unique in its ability to allow determination of density gradients of light elements such as hydrogen (H). The neutron scattering contrast between Si and H is strong, making it possible to determine the H concentration in the deposited a-Si:H. In order to correlate the surface passivation properties supplied by the a-Si:H thin films, as quantified by obtainable effective minority carrier lifetime, photoconductance measurements were also performed. It is shown that the minority carrier lifetime falls sharply when H has been desorbed from a-Si:H by annealing. (C) 2014 AIP Publishing LLC.
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| 2. |
- Abila, R., et al.
(författare)
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Oil extraction imperils Africa’s Great Lakes
- 2016
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 354:6312, s. 561-562
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- As the world's demands for hydrocarbons increase (1), remote areas previously made inaccessible by technological limitations are now being prospected for oil and gas deposits. Virtually unnoticed by the public, such activities are ongoing in the East African Great Lakes region, threatening these ecosystems famed for their hyper-diverse biota, including the unique adaptive radiations of cichlid fishes (2). Countries in the region see exploitation of hydrocarbon reserves as a vital economic opportunity. In the Lake Albert region of Uganda, for example, the government foresees a $3.6 billion oil profit per year starting in 2018—a sum almost as high as the country's current annual budget (3). However, oil extraction in the East African Great Lakes region poses grave risks to the environment and local communities.
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| 3. |
- Eggert, B. G. F., et al.
(författare)
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Magnetic transitions in V-Fe-Co-Ni-Cu-based high entropy alloys
- 2023
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Ingår i: Materials Today Physics. - : Elsevier. - 2542-5293. ; 35
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Tidskriftsartikel (refereegranskat)abstract
- FeCoNi, V0.85FeCoNi, FeCoNiCu1.15 and V0.85FeCoNiCu1.15 alloys have been synthesized by arc melting and analyzed by powder X-ray diffraction, electron microscopy, magnetic measurements, and density functional theory (DFT). The influence of each alloying element on the magnetic exchange interaction, Curie temperature (TC) and magnetocaloric effect is evaluated. The experimental results show that Cu and V "dilute" the magnetic properties and couple antiferromagnetically to Fe, Co, and Ni. Analysis of the microstructure reveals a lack of solubility between V and Cu with FeCoNi, and between themselves, thus lowering the concentration of V and Cu in the main solid solution of the 5-element alloy V0.85FeCoNiCu1.15. Tc decreases significantly from 997 K in FeCoNi to 245 K in V0.85FeCoNi and 297 K in V0.85FeCoNiCu1.15, respectively. The derivative of magnetization as a function of temperature (dM/dT) in the vicinity of Tc is drastically reduced due to the presence of V which indicates a reduced magnetocaloric effect. DFT calculations confirm antiferromagnetic coupling of V to the ferromagnetic FeCoNi-base and predict a similar behavior for other transition metal elements (e.g., Ti, Cr, Mn). This leads to a lowering of Tc, which is needed to establish the magnetocaloric effect at room temperature. However, it comes at a cost of reduced magnetic moments. Nevertheless, the use of V and Cu has shown possible routes for tuning the magnetocaloric effect in FeCoNi-based high entropy alloys.
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| 4. |
- Qviller, A. J., et al.
(författare)
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Direct observation of magnetic proximity effects in amorphous exchange-spring magnets by neutron reflectometry
- 2020
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Ingår i: Physical Review Materials. - 2475-9953. ; 4:10
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report a direct observation of a magnetic proximity effect in an amorphous thin-film exchange-spring magnet by the use of neutron reflectometry. The exchange-spring magnet is a trilayer consisting of two ferromagnetic layers with high T-c separated by a ferromagnetic layer, which is engineered to have a significantly lower T-c than the embedding layers. This enables us to measure magnetization depth profiles at which the low-T-c material is in a ferromagnetic or paramagnetic state, while the embedding layers are ferromagnetic. A clear proximity effect is observed 7 K above the intrinsic T-c of the embedded layer, with a range extending 50 angstrom.
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| 5. |
- Eggert, Bruno G. F., et al.
(författare)
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Exploring V-Fe-Co-Ni-Al and V-Fe-Co-Ni-Cu high entropy alloys for magnetocaloric applications
- 2022
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 921
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Tidskriftsartikel (refereegranskat)abstract
- A series of V1-x-Fe-Co-Ni-Al1+ x and V1-x-Fe-Co-Ni-Cu1+ x high entropy alloys with varying compositions (0 <= x <= 0.75) has been investigated for magnetocaloric applications. Compositions were selected according to established properties, such as configurational entropy, atomic size difference, and enthalpy of mixing. To study the influence of composition on magnetic ordering temperatures, the V and (Al/Cu) contents were changed while the content of Fe, Co and Ni was retained at 20 at. % each. The crystal structure and microstructure of the as-cast alloys were compared to literature phase guidelines and thermodynamic calculations based on the CALPHAD approach. The V-Fe-Co-Ni-Al compounds are monophasic and crystallize in a disordered body centered cubic structure or its ordered B2 variant, while the V-Fe-Co-Ni-Cu compounds are all multiphasic. Magnetic transitions in the V-Fe-Co-Ni-Al system span over 400 K, with Curie temperature ranging from 155 K in equiatomic VFeCoNiAl, to 456 K in non-equiatomic V0.25FeCoNiAl1.75. The V-Fe-Co-Ni-Cu alloys display magnetic transitions that span about 150 K, with Curie temperature ranging from 230 K for equiatomic VFeCoNiCu to 736 K for non-equiatomic V0.25FeCoNiCu1.75. The magnetic properties of the V-Fe-Co-Ni-Cu compounds were evaluated by means of density functional theory. Individual element-specific moments, magnetic exchange integrals between atomic pairs, and Curie temperatures were calculated. V0.85FeCoNiCu1.15 is selected due to its Curie temperature of 329 K, and its calculated isothermal entropy change of 0.75 J/kg.K for a field change of 5 T is comparable to other 3d metal-based high entropy alloys that form disordered solid solutions. (c) 2022 The Author(s). Published by Elsevier B.V. CC_BY_4.0
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