| 1. |
- Keller, Jan, et al.
(författare)
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Effect of KF absorber treatment on the functionality of different transparent conductive oxide layers in CIGSe solar cells
- 2018
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Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 26:1, s. 13-23
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Tidskriftsartikel (refereegranskat)abstract
- This contribution studies the impact of the KF-induced Cu(In,Ga)Se2 (CIGSe) absorber modification on the suitability of different transparent conductive oxide (TCO) layers in solar cells. The TCO material was varied between ZnO:Al (AZO), ZnO:B (BZO), and In2O3:H (IOH). It is shown that the thermal stress needed for optimized TCO properties can establish a transport barrier for charge carriers, which results in severe losses in fill factor (FF) for temperatures >150°C. The FF losses are accompanied by a reduction in open circuit voltage (Voc) that might originate from a decreased apparent doping density (Nd,app) after annealing. Thermally activated redistributions of K and Na in the vicinity of the CdS/(Cu,K)-In-Se interface are suggested to be the reason for the observed degradation in solar cell performance. The highest efficiency was measured for a solar cell where the absorber surface modification was removed and a BZO TCO layer was deposited at a temperature of 165°C. The presented results highlight the importance of well-designed TCO and buffer layer processes for CIGSe solar cells when a KF post deposition treatment (KF-PDT) was applied.
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| 2. |
- Keller, Jan, et al.
(författare)
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On the Paramount Role of Absorber Stoichiometry in (Ag,Cu)(In,Ga)Se2 Wide‐Gap Solar Cells
- 2020
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Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 4:12
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Tidskriftsartikel (refereegranskat)abstract
- This contribution evaluates the effect of absorber off‐stoichiometry in wide‐gap (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells. It is found that ACIGS films show an increased tendency to form ordered vacancy compounds (OVCs) with increasing Ga and Ag contents. Very little tolerance to off‐stoichiometry is detected for absorber compositions giving the desired properties of 1) an optimum bandgap (EG) for a top cell in tandem devices (EG = 1.6–1.7 eV) and at the same time 2) a favorable band alignment with a CdS buffer layer. Herein, massive formation of either In‐ or Ga‐enriched OVC patches is found for group I‐poor ACIGS. As a consequence, carrier transport and charge collection are significantly impeded in corresponding solar cells. The transport barrier appears to be increasing with storage time, questioning the long‐term stability of wide‐gap ACIGS solar cells. Furthermore, the efficiency of samples with very high Ga and Ag contents depends on the voltage sweep direction. It is proposed that the hysteresis behavior is caused by a redistribution of mobile Na ions in the 1:1:2 absorber lattice upon voltage bias. Finally, a broader perspective on OVC formation in the ACIGS system is provided and fundamental limitations for wide‐gap ACIGS solar cells are discussed.
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| 3. |
- Wiedorn, Max O., et al.
(författare)
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Megahertz serial crystallography
- 2018
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The new European X-ray Free-Electron Laser is the first X-ray free-electron laser capable of delivering X-ray pulses with a megahertz inter-pulse spacing, more than four orders of magnitude higher than previously possible. However, to date, it has been unclear whether it would indeed be possible to measure high-quality diffraction data at megahertz pulse repetition rates. Here, we show that high-quality structures can indeed be obtained using currently available operating conditions at the European XFEL. We present two complete data sets, one from the well-known model system lysozyme and the other from a so far unknown complex of a beta-lactamase from K. pneumoniae involved in antibiotic resistance. This result opens up megahertz serial femtosecond crystallography (SFX) as a tool for reliable structure determination, substrate screening and the efficient measurement of the evolution and dynamics of molecular structures using megahertz repetition rate pulses available at this new class of X-ray laser source.
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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. |
- Berastegui, Pedro, et al.
(författare)
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Magnetron Sputtering of Nanolaminated Cr2AlB2
- 2020
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Ingår i: Coatings. - : MDPI. - 2079-6412. ; 10:8
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Tidskriftsartikel (refereegranskat)abstract
- A ternary Cr(2)AlB(2)phase was deposited as a film using magnetron sputtering. Its anisotropic structure displays both structural and chemical similarities with the nanolaminated MAX phases (M(n+1)AX(n)(n = 1-3) where M usually is an early transition metal, A is typically an element in group 13-14 and X is C or N), and can be described as CrB slabs separated by layers of Al. Combinatorial sputtering was used to optimise the sputtering process parameters for films with the Cr(2)AlB(2)composition. The influences of substrate, temperature and composition were studied using X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy. Films deposited at room temperature were X-ray amorphous but crystalline films could be deposited on MgO substrates at 680 degrees C using a composite Al-B, Cr and Al targets. X-ray diffraction analyses showed that the phase composition and texture of the films was strongly dependent on the chemical composition. Films with several phases or with a single Cr(2)AlB(2)phase could be deposited, but an additional Al target was required to compensate for a loss of Al at the high deposition temperatures used in this study. The microstructure evolution during film growth was strongly dependent on composition, with a change in texture in Al-rich films from a preferred [010] orientation to a [100]/[001] orientation. A model based on Al desorption from the surface of the growing grains is proposed to explain the texture variations.
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| 6. |
- Berg, Camilla, et al.
(författare)
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Electron microscopy evaluation of mineralization on peritubular dentin with amorphous calcium magnesium phosphate microspheres
- 2020
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 46:11, s. 19469-19475
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Tidskriftsartikel (refereegranskat)abstract
- Dentin hypersensitivity can be reduced by the use of a remineralization agent to hinder movement of fluids within the dentin tubules. Penetration of particles into the tubules and a continuous release of Ca2+ and phosphate ions can induce the mineralization of a material mimicking the mineral component of dentin, sealing the tubules. In this work, we have used complementary electron microscopy techniques to investigate the ultrastructure of dentin and crystallization and occlusion effects when using amorphous calcium magnesium phosphate (ACMP) microspheres on extracted human molars. Application of the particles in a gel intended for athome use resulted in intra-tubular mineralization of a carbonate substituted hydroxyapatite (HA). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that crystallization was initiated on the peritubular dentin (PTD) with undirected crystal growth leading to the formation of a porous material. We additionally investigated the effects from using a fluoride toothpaste to potentially improve the remineralization and anti-cariogenic properties of the ACMP microspheres. Energy dispersive x-ray spectroscopy (EDX) using TEM in scanning mode (STEM) showed that fluoride incorporation resulted in an increase in aspect ratio of the crystals, crystal growth directed towards the center of the tubule lumen and densification of the mineralized material. Thus, ACMP microspheres are promising alternatives as occluding agents and the efficacy of the particles could be further improved with the complementary use of a fluoride toothpaste.
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| 7. |
- Comparotto, Corrado, et al.
(författare)
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Chalcogenide Perovskite BaZrS3 : Thin Film Growth by Sputtering and Rapid Thermal Processing
- 2020
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Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:3, s. 2762-2770
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Tidskriftsartikel (refereegranskat)abstract
- Tandem solar cells based on hybrid organic-inorganic metal halide perovskites have reached efficiencies up to 28%, but major concerns for long-term stability and the presence of Pb have raised interest in searching for fully earth-abundant, intrinsic chemically stable, and nontoxic alternatives. With a direct band gap around 1.8 eV and stability in air up to at least 500 degrees C, BaZrS3 is a promising candidate. This work presents the first approach of synthesizing a thin film of such compound by sputtering at ambient temperature with a subsequent rapid thermal process. Despite the short fabrication time, the width of the XRD diffraction peaks and the energy and distribution of the photoluminescence response show comparable crystalline quality to that from bulk synthesis methods. Good crystallization required around 900 degrees C. Such a high temperature could be incompatible with fabrication of tandem solar cells.
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| 8. |
- 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
-
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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| 9. |
- Fritze, Stefan, et al.
(författare)
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Influence of Carbon on Microstructure and Mechanical Properties of Magnetron Sputtered TaW Coatings
- 2020
-
Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 196
-
Tidskriftsartikel (refereegranskat)abstract
- (Ta,W) and (Ta,W):C films with-5 at.% C were deposited by non-reactive magnetron sputtering. They crystallised in a bcc structure with a columnar microstructure. The solid solubility of C in (Ta,W) alloys is very low, which suggests that the (Ta,W):C films are supersaturated with respect to carbon. This was confirmed by diffraction and atom probe tomography (APT) showing that carbon is in the as-deposited (Ta,W):C films homogeneously distributed in the structure without carbide formation or carbon segregation. Annealing at 900 degrees C for 2 h showed no significant column coarsening but an increased defect density at the column boundaries in the (Ta,W):C films. The films were still supersaturated with respect to carbon but APT showed a partial segregation of carbon presumably to defect-rich column boundaries after annealing. The (Ta,W) films exhibited a hardness of-12-13 GPa. Alloying with carbon increased the hardness to-17 GPa. The hardness increased to-19 GPa for the annealed (Ta,W):C films. This annealing-induced hardness increase was explained by C segregation to the more defect-rich column boundaries, which restricts dislocation movements. (Ta,W):C coatings may be a potential alternative to ceramic coatings, worth exploring further by small scale mechanical testing to investigate if these materials are ductile.
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| 10. |
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| 11. |
- Fritze, Stefan, et al.
(författare)
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Magnetron sputtering of carbon supersaturated tungsten films-A chemical approach to increase strength
- 2021
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 208
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten (W)-based materials attract significant attention due to their superior mechanical properties. Here, we present a chemical approach based on the addition of carbon (C) for increased strength via the combination of three strengthening mechanisms in W thin films. W:C thin films with C concentrations up to-4 at.% were deposited by magnetron sputtering. All films exhibit a body-centred-cubic structure with strong texture and columnar growth behaviour. X-ray and electron diffraction measurements suggest the formation of supersaturated W:C solid solution phases. The addition of C reduced the average column width from-133 nm for W to-20 nm for the film containing-4 at.% C. The column refinement is explained by a mechanism where C acts as re-nucleation sites. The W film is-13 GPa hard, while the W:C films achieve a peak hardness of-24 GPa. The W:C films are-11 GPa harder than the W film, which is explained by a combination of grain refinement strengthening, solid solution strengthening and increased dislocation density. Additional micropillar compression tests showed that the flow stress increased upon C addition, from-3.8 to-8.3 GPa and no brittle fracture was observed.
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| 12. |
- Fu, Le, et al.
(författare)
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Observation of yttrium oxide segregation in a ZrO2-SiO2 glass-ceramic at nanometer dimensions
- 2020
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Ingår i: Journal of The American Ceramic Society. - : WILEY. - 0002-7820 .- 1551-2916. ; 103:12, s. 7147-7158
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Tidskriftsartikel (refereegranskat)abstract
- Dopant segregation at grain boundaries (GBs) in ceramics has been widely reported, while whether similar segregation behavior occurs in glass-ceramics remains unknown. The distribution of dopant in glass-ceramics may be totally different due to the existence of glass phase. This study examines the distribution of Y3+ ions in a ZrO2-SiO2 glass-ceramic. Two samples were prepared by hot pressing, yttrium oxide-doped, and undoped 65 mol% ZrO2-35 mol% SiO2 nanocrystalline glass-ceramics (NCGCs). The NCGCs had the same microstructure, that is, ZrO2 nanoparticles (NPs) embedded in an amorphous SiO2 matrix. XRD results showed that the undoped NCGC was composed of 20.9 wt% (weight percentage) monoclinic ZrO2 (m-ZrO2) and 79.1 wt% tetragonal ZrO2 (t-ZrO2), while the yttrium oxide-doped NCGC was composed of 9.6 wt% m-ZrO2 and 90.4 wt% t-ZrO2. X-ray energy-dispersive spectrometry (EDS) results in scanning electron transmission microscopy (STEM) mode demonstrated that Y3+ ions segregated both on the surface of ZrO2 NPs and within the thin intergranular glass film (with a thickness of approximately 7 angstrom) between ZrO2 NPs in the yttrium oxide-doped NCGC. Interestingly, no obvious Y signals were detected in the amorphous SiO2 matrix. Density functional theory calculation results showed that Y3+ ions had a strong segregation tendency in the GB area and the segregation of Y3+ ions increased the work of separation of GB layer. These findings provide new understanding of the segregation behavior of dopant in glass-ceramics, which may offer useful guidance for other researchers to tailor the properties of glass-ceramics through GB engineering.
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| 13. |
- Gouillart, Louis, et al.
(författare)
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Interface engineering of ultrathin Cu(In,Ga)Se2 solar cells on reflective back contacts
- 2021
-
Ingår i: Progress in Photovoltaics. - : John Wiley & Sons. - 1062-7995 .- 1099-159X. ; 29:2, s. 212-221
-
Tidskriftsartikel (refereegranskat)abstract
- Cu(In,Ga)Se-2-based (CIGS) solar cells with ultrathin (<= 500 nm) absorber layers suffer from the low reflectivity of conventional Mo back contacts. Here, we design and investigate ohmic and reflective back contacts (RBC) made of multilayer stacks that are compatible with the direct deposition of CIGS at 500 degrees C and above. Diffusion mechanisms and reactions at each interface and in the CIGS layer are carefully analyzed by energy dispersive X-ray (EDX)/scanning transmission electron microscopy (STEM). It shows that the highly reflective silver mirror is efficiently encapsulated in ZnO:Al layers. The detrimental reaction between CIGS and the top In2O3:Sn (ITO) layer used for ohmic contact can be mitigated by adding a 3 nm thick Al2O3 layer and by decreasing the CIGS coevaporation temperature from 550 degrees C to 500 degrees C. It also improves the compositional grading of Ga toward the CIGS back interface, leading to increased open- circuit voltage and fill factor. The best ultrathin CIGS solar cell on RBC exhibits an efficiency of 13.5% (+1.0% as compared to our Mo reference) with a short-circuit current density of 28.9 mA/cm(2) (+2.6 mA/cm(2)) enabled by double-pass absorption in the 510 nm thick CIGS absorber. RBC are easy to fabricate and could benefit other photovoltaic devices that require highly reflective and conductive contacts subject to high temperature processes.
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| 14. |
- Gouillart, Louis, et al.
(författare)
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Reflective Back Contacts for Ultrathin Cu(In,Ga)Se2-Based Solar Cells
- 2020
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Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 10:1, s. 250-254
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Tidskriftsartikel (refereegranskat)abstract
- We report on the development of highly reflective back contacts (RBCs) made of multilayer stacks for ultrathin CIGS solar cells. Two architectures are compared: they are made of a silver mirror coated either with a single layer of In 2 O 3 :Sn (ITO) or with a bilayer of ZnO:Al/ITO. Due to the improvement of CIGS rear reflectance, both back contacts result in a significant external quantum efficiency enhancement, in agreement with optical simulations. However, solar cells fabricated with Ag/ITO back contacts exhibit a strong shunting behavior. The key role of the ZnO:Al layer to control the morphology of the top ITO layer and to avoid silver diffusion through the back contact is highlighted. For a 500-nm-thick CIGS layer, this optimized RBC leads to a best cell with a short-circuit current of 27.8 mA/cm 2 (+2.2 mA/cm 2 as compared to a Mo back contact) and a 12.2%-efficiency (+2.5% absolute).
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| 15. |
- Gouillart, Louis, et al.
(författare)
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Ultrathin Cu(In,Ga)Se2 solar cells with Ag-based reflective back contacts
- 2020
-
Ingår i: 2020 47th IEEE Photovoltaic Specialists Conference (PVSC). - 9781728161150 - 9781728161167 ; , s. 1481-1484
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Konferensbidrag (refereegranskat)abstract
- We developed a highly reflective back contact for Cu(In,Ga)Se 2 solar cells based on silver encapsulated in a TCOs stack, compatible with substrate configuration. We demonstrated ultrathin (500 nm) Cu(In,Ga)Se 2 solar cells with 13.5% efficiency and state-of-the-art JSC=28.9 mA/cm2,2.7 mA/cm 2 more than the reference cell on molybdenum. We also demonstrated a 530 nm-thick (Ag, Cu)(In,Ga)Se 2 solar cell on Mo with state-of-the-art efficiency (14.9%) and remarkably high V OC (741 mV) and FF (81.8%). This result coupled with a highly reflective back contact for improved J SC , has the potential for a 500 nm-thick (Ag, Cu)(In,Ga)Se 2 solar cell with an 18% efficiency.
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| 16. |
- Ivanov, Sergey A., et al.
(författare)
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Structure of Pb(Fe2/3W1/3)O3 single crystals with partial cation order
- 2020
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Despite intensive studies on the complex perovskite Pb(Fe2/3W1/3)O3 (PFWO) relaxor, understanding the exact nature of its multifunctional properties has remained a challenge for decades. In this work we report a comprehensive structural study of the PFWO single crystals using a combination of synchrotron X-ray diffraction and high-resolution electron microscopy. The set of {h + ½, k + ½, l + ½} superlattice reflections was observed for the first time based on single-crystal synchrotron X-ray experiments (100–450 K) and transmission electron microscopy investigations, which indicates some kind of B-cation ordering in PFWO which had been thought to be totally disordered. It was found that (1) the crystal structure of PFWO should be described by a partly ordered cubic perovskite (i.e. Fm − 3m), (2) the weak ferromagnetic properties and excess magnetic moment of PFWO can be understood based on non-random distribution of Fe cations between the 4a and 4b sites, and (3) the Pb displacement disorder is present in this material and the cations are probably displaced along the <100> directions. The X-ray diffraction results of this investigation show that partial cation ordering indeed exists in PFWO, which makes it necessary to revisit the generally accepted interpretations of the results obtained up to date. In agreement with X-ray diffraction study the main results of TEM study include: (1) a long range order that can be described with the Fm − 3m symmetry is reliably detected, (2) the coherence length of that long range order is in the order of 1–2 nm and (3) no remarkable chemical inhomogeneity is found in the tested PFWO crystal, excluding the possibility of a compositional ordering arising from substitutional defects in the perovskite structure.
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| 17. |
- Jablonka, Lukas, et al.
(författare)
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Highly conductive ultrathin Co films by high-power impulse magnetron sputtering
- 2018
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 112:4
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Tidskriftsartikel (refereegranskat)abstract
- Ultrathin Co films deposited on SiO2 with conductivities exceeding that of Cu are demonstrated. Ionized deposition implemented by high-power impulse magnetron sputtering (HiPIMS) is shown to result in smooth films with large grains and low resistivities, namely, 14 mu Omega cm at a thickness of 40 nm, which is close to the bulk value of Co. Even at a thickness of only 6 nm, a resistivity of 35 mu Omega cm is obtained. The improved film quality is attributed to a higher nucleation density in the Co-ion dominated plasma in HiPIMS. In particular, the pulsed nature of the Co flux as well as shallow ion implantation of Co into SiO2 can increase the nucleation density. Adatom diffusion is further enhanced in the ionized process, resulting in a dense microstructure. These results are in contrast to Co deposited by conventional direct current magnetron sputtering where the conductivity is reduced due to smaller grains, voids, rougher interfaces, and Ar incorporation. The resistivity of the HiPIMS films is shown to be in accordance with models by Mayadas-Shatzkes and Sondheimer which consider grain-boundary and surface-scattering.
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| 18. |
- Jacobsson, T. Jesper, 1984-, et al.
(författare)
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2-Terminal CIGS-perovskite tandem cells : A layer by layer exploration
- 2020
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 207, s. 270-288
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Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on the development of 2-terminal CIGS-perovskite tandem solar cells by exploring a range of stack sequences and synthetic procedures for depositing the associated layers. In the end, we converged at a stack sequence composed of SLG/Mo/CIGS/CdS/i-ZnO/ZnO:Al/NiO/PTAA/Perovskite/LiF/PCBM/SnO2/ITO. With this architecture, we reached performances only about 1% lower than the corresponding 4-terminal tandem cells, thus demonstrating functional interconnects between the two sub-cells while grown monolithically on top of each other. We go through the stack, layer-by-layer, discussing their deposition and the results, from which we can conclude what works, what does not work, and what potentially could work after additional modifications. The challenges for a successful 2-terminal tandem device include: how to deal with, or decrease, the surface roughness of the CIGS-stack, how to obtain uniform coverage of the layers between the CIGS and the perovskite while also obtaining a benign interface chemistry, and how to tune the band gaps of both the CIGS and the perovskite to obtain good optical matching. The investigation was based on CIGS with a power conversion efficiency around 14%, and perovskites with an efficiency around 12%, resulting in 2-terminal tandem cells with efficiencies of 15–16%. The results indicate that by using higher performing CIGS and perovskite sub-cells, it should be possible to manufacture highly efficient 2-terminal CIGS-perovskite tandem devices by using the protocols, principles, and procedures developed and discussed in this paper.
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| 19. |
- Johansson, Kristina, et al.
(författare)
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Multicomponent Hf-Nb-Ti-V-Zr nitride coatings by reactive magnetron sputter deposition
- 2018
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 349, s. 529-539
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Tidskriftsartikel (refereegranskat)abstract
- Multicomponent nitride coatings of the Hf-Nb-Ti-V-Zr system with different Hf content (0-18 at.%) were deposited using reactive dc magnetron sputtering. Coatings with lower Hf content (0-7 at.%) were found to consist of a single solid solution phase with NaCl-type structure (space group Fm-3m). Coatings with higher Hf content (10-18 at.%) showed a two-phase material consisting of cubic Fm-3m and tetragonal I4/m:run solid solution phase. The lattice distortion, estimated by calculating the delta-parameter under the assumption of a single solid solution phase, varied between 3.8 and 4.0% and slightly decreased with increasing Hf content. SEM and TEM cross section images showed a columnar microstructure with columns that were frayed on the surface or throughout the whole column. The column size decreased as Hf content increased. The hardness increased from 8 to 19 GPa with increased Hf content, which most probably is related to the change in microstructure rather than change in lattice distortion. The electrical resistivity for all samples ranged between 231 and 286 mu Omega cm.
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| 20. |
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| 21. |
- Kaplan, Maciej, 1991-, et al.
(författare)
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Combinatorial design of amorphous TaNiSiC thin films with enhanced hardness, thermal stability, and corrosion resistance
- 2022
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 220
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous TaNiSiC and TaNiC films (with varying Ta/Ni and Si/C ratios) were deposited using combinatorial magnetron sputtering. The TaNiSiC films remained X-ray amorphous after four hour-long annealings up to 700 °C, while TaNiC alloys with high Ni and C contents crystallized. These differences were attributed to a strong driving force for separation of Ni and C in TaNiC, whereas the addition of Si, due to its solubility in the other elements, reduced the elemental segregation in TaNiSiC. The as-deposited TaNiSiC films exhibited hardnesses of 9–12 GPa. Annealing led to an increase in hardness by 2–4 GPa, due to decreases in average atomic distance, as evidenced by X-ray diffraction measurements. Potentiodynamic polarizations from –0.7 to +1.5 V vs. Ag/AgCl (3 M NaCl) in 10 mM sodium borate showed lower current densities by up to 2 orders of magnitude with increasing Ta content (28–52 at.%). Changes in Si/C content (7–13 at.% Si) had no effect. However, optical microscopy showed that TaNiSiC films with high Si/low C contents (13/10 at.%) suffered much less localized etching compared to TaNiC films. Thus, Si had a significant role in increasing the mechanical strength, corrosion resistance, and thermal stability of the TaNiSiC films.
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| 22. |
- Karlsson, Dennis, et al.
(författare)
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Binder jetting of the AlCoCrFeNi alloy
- 2019
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 27, s. 72-79
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Tidskriftsartikel (refereegranskat)abstract
- High density components of an AlCoCrFeNi alloy, often described as a high-entropy alloy, were manufactured by binder jetting followed by sintering. Thermodynamic calculations using the CALPHAD approach show that the high-entropy alloy is only stable as a single phase in a narrow temperature range below the melting point. At all other temperatures, the alloy will form a mixture of phases, including a sigma phase, which can strongly influence the mechanical properties. The phase stabilities in built AlCoCrFeNi components were investigated by comparing the as-sintered samples with the post-sintering annealed samples at temperatures between 900 °C and 1300 °C. The as-sintered material shows a dominant B2/bcc structure with additional fcc phase in the grain boundaries and sigma phase precipitating in the grain interior. Annealing experiments between 1000 °C and 1100 °C inhibit the sigma phase and only a B2/bcc phase with a fcc phase is observed. Increasing the temperature further suppresses the fcc phase in favor for the B2/bcc phases. The mechanical properties are, as expected, dependent on the annealing temperature, with the higher annealing temperature giving an increase in yield strength from 1203 MPa to 1461 MPa and fracture strength from 1996 MPa to 2272 MPa. This can be explained by a hierarchical microstructure with nano-sized precipitates at higher annealing temperatures. The results enlighten the importance of microstructure control, which can be utilized in order to tune the mechanical properties of these alloys. Furthermore, an excellent oxidation resistance was observed with oxide layers with a thickness of less than 5 μm after 20 h annealing at 1200 °C, which would be of great importance for industrial applications.
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| 23. |
- Karlsson, Dennis, et al.
(författare)
-
Structure and phase transformations in gas atomized AlCoCrFeNi high entropy alloy powders
- 2022
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 893
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the crystal structure and phase stability of gas atomized equiatomic AlCoCrFeNi powder was investigated. This alloy is usually described as a high entropy alloy forming a solid solution phase stabilized by a high mixing entropy. However, thermodynamic calculations show that the high entropy phase is stable only at very high temperatures close to the melting point and that a mixture of several phases are the most stable state at lower temperatures. This suggest that kinetic effects may influence the phase composition of atomized powder. The unique features of X-ray diffraction, neutron diffraction as well as transmission electron microscopy were used to study the atomic structure of the atomized powder in detail. The results show that the powder crystallises in an ordered B2 (CsCl-type) structure with a preferred site occupation of Al and Fe on the (1/2 1/2 1/2) position and Co and Ni on the (0 0 0) position. During heat-treatment of the powder, the B2 phase decomposes into fcc and sigma phases and the final phase composition is highly dependent on the heating rate. The effect of heat-treatment on the atomized powder was also investigated and revealed a significant phase transformation with e.g. the formation of sigma phase preferably at the surface of the powder particles. The phase content was also dependent on the size fraction of the powder particles. Sintering of green bodies made with different heat cycles showed that the phase composition of the starting material had a significant impact on the final phase composition and microstructure of the sintered components. The results illustrate the importance of well-defined powder materials for powder consolidation, especially additive manufacturing (binder jetting) of high entropy alloys.
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| 24. |
- Keller, Jan, et al.
(författare)
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Bifacial Cu(In,Ga)Se2 solar cells using hydrogen‐doped In2O3 films as a transparent back contact
- 2018
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Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 26:10, s. 846-858
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen‐doped In2O3 (IOH) films are used as a transparent back contact in bifacial Cu(In,Ga)Se2 (CIGS) solar cells. The effect of the IOH thickness and the impact of the sodium incorporation technique on the photovoltaic parameters are studied, and clear correlations are observed. It is shown that a loss in short circuit current density (JSC) is the major limitation at back side illumination. The introduction of a thin Al2O3 layer on top of the IOH significantly increases the collection efficiency (ϕ(x)) for electrons generated close to the back contact. In this way, the JSC loss can be mitigated to only ~ 25% as compared with front side illumination. The Al2O3 film potentially reduces the interface defect density or, alternatively, creates a field effect passivation. In addition, it prevents the excessive formation of Ga2O3 at the CIGS/IOH interface, which is found otherwise when a NaF layer is added before absorber deposition. Consequently, detrimental redistributions in Ga and In close to the back contact can be avoided. Finally, a bifacial CIGS solar cell with an efficiency (η) of η = 11.0% at front and η = 6.0% at back side illumination could be processed. The large potential for further improvements is discussed.
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| 25. |
- Keller, Jan, et al.
(författare)
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Effect of Cu content on post‐sulfurization of Cu(In,Ga)Se2 films and corresponding solar cell performance
- 2019
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 216:20
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Tidskriftsartikel (refereegranskat)abstract
- Herein, the effect of the initial copper content of co‐evaporated Cu(In1−x,Gax)Se2 (CIGS) absorber films on the impact of a post‐annealing step in elemental sulfur atmosphere is studied. The Cu concentration is varied over a wide range ([Cu]/[III] = CGI = 0.57–1.23), allowing to identify composition‐dependent trends in phase formation, chemical rearrangements, and solar cell performance after sulfurization. For all samples, a ternary CuInS2 layer forms at the surface. In addition, sulfur 1) is incorporated in randomly distributed CuIn(S,Se)2 mixed crystals underneath CuInS2; 2) diffuses into multidimensional defects (e.g., dislocations and grain boundaries); and 3) is bound in Na–In–S surface plates. It is found that Cu‐poor absorber composition (CGI ≤ 0.82) favors CuInS2 growth as compared with close‐stoichiometric CIGS films, driven by a faster diffusion of Cu toward the surface. For Cu‐rich absorbers (CGI > 1), Se—S exchange is significantly accelerated, presumably by the presence of Cu2−xSe phases reacting to Cu2−xS and eventually catalyzing CuInS2 formation. Finally, open‐circuit voltage (VOC), fill factor (FF), and efficiency (η) of corresponding solar cells increase after sulfurization with increasing CGI until stoichiometry is reached. The result is explained by a mitigated Cu depletion of the absorber bulk after sulfurization for close‐stoichiometric CIGS.
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| 26. |
- Keller, Jan, et al.
(författare)
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Heavy Alkali Treatment of Post‐Sulfurized Cu(In,Ga)Se2 Layers : Effect on Absorber Properties and Solar Cell Performance
- 2020
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Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 4:9
-
Tidskriftsartikel (refereegranskat)abstract
- This contribution evaluates a sequential post‐deposition treatment of Cu(In,Ga)Se2 (CIGS) films, consisting of 1) a post‐sulfurization in elemental S‐atmosphere and 2) a subsequent treatment by heavy alkali fluorides (Alk‐PDT). First, the effect of the sulfurization step on the corresponding solar cell performance is investigated and optimum process parameters, leading to an efficiency improvement, are identified. Losses in carrier collection observed after S‐incorporation are attributed to an increased grain boundary (GB) recombination. It is found that the corresponding reduction in short‐circuit current density can be mitigated by a RbF‐ or KF‐PDT, supposedly by depleting GBs in Cu. However, in strong contrast to non‐sulfurized CIGS, the Alk‐PDT results in a lower open‐circuit voltage and distortions in the current–voltage (I –V ) characteristics for sulfurized absorbers. Possible explanations are the absence of a wide‐gap surface phase and/or air exposure between the post‐treatment steps. It is further proposed that a back contact barrier may be responsible for the distortions in I–V.
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| 27. |
- Keller, Jan, et al.
(författare)
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Using hydrogen‐doped In2O3 films as a transparent back contact in (Ag,Cu)(In,Ga)Se2 solar cells
- 2018
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Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 26:3, s. 159-170
-
Tidskriftsartikel (refereegranskat)abstract
- This study evaluates the potential of hydrogen‐doped In2O3 (IOH) as a transparent back contact material in (Agy,Cu1‐y)(In1‐x,Gax)Se2 solar cells. It is found that the presence of Na promotes the creation of Ga2O3 at the back contact during (Agy,Cu1‐y)(In1‐x,Gax)Se2 growth. An excessive Ga2O3 formation results in a Ga depletion, which extends deep into the absorber layer. Consequently, the beneficial back surface field is removed and a detrimental reversed electrical field establishes. However, for more moderate Ga2O3 amounts (obtained with reduced Na supply), the back surface field can be preserved. Characterization of corresponding solar cells suggests the presence of an ohmic back contact, even at absorber deposition temperatures of 550°C. The best solar cell with an IOH back contact shows a fill factor of 74% and an efficiency (η) of 16.1% (without antireflection coating). The results indicate that Ga2O3 does not necessarily act as a transport barrier in the investigated system. Observed losses in open circuit voltage (VOC) as compared to reference samples with a Mo back contact are ascribed to a lower Na concentration in the absorber layer.
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| 28. |
- Larsen, Jes K, et al.
(författare)
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Cadmium Free Cu2ZnSnS4 Solar Cells with 9.7% Efficiency
- 2019
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 9:21
-
Tidskriftsartikel (refereegranskat)abstract
- Cu2ZnSnS4(CZTS) thin-film solar cell absorbers with different bandgaps can be produced by parameter variation during thermal treatments. Here, the effects of varied annealing time in a sulfur atmosphere and an ordering treatment of the absorber are compared. Chemical changes in the surface due to ordering are examined, and a downshift of the valence band edge is observed. With the goal to obtain different band alignments, these CZTS absorbers are combined with Zn1−xSnxOy (ZTO) or CdS buffer layers to produce complete devices. A high open circuit voltage of 809 mV is obtained for an ordered CZTS absorber with CdS buffer layer, while a 9.7% device is obtained utilizing a Cd free ZTO buffer layer. The best performing devices are produced with a very rapid 1 min sulfurization, resulting in very small grains.
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| 29. |
- Larsen, Jes K, et al.
(författare)
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Sulfurization of Co-Evaporated Cu(In,Ga)Se-2 as a Postdeposition Treatment
- 2018
-
Ingår i: IEEE Journal of Photovoltaics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2156-3381 .- 2156-3403. ; 8:2, s. 604-610
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Tidskriftsartikel (refereegranskat)abstract
- It is investigated if the performance of Cu(In,Ga)Se-2 (CIGSe) solar cells produced by co-evaporation can be improved by surface sulfurization in a postdeposition treatment. The expected benefit would be the formation of a sulfur/selenium gradient resulting in reduced interface recombination and increased open-circuit voltage. In the conditions used here it was, however, found that the reaction of the CIGSe layer in a sulfur environment results in the formation of a CuInS2 (CIS) surface phase containing no or very little selenium and gallium. At the same time, a significant pile up of gallium was observed at the CIGSe/CIS boundary. This surface structure was formed for a wide range of annealing conditions investigated in this paper. Increasing the temperature or extending the time of the dwell stage had a similar effect on the material. The gallium enrichment and CIS surface layer widens the surface bandgap and therefore increases the open-circuit voltage. At the same time, the fill factor is reduced, since the interface layer acts as an electron barrier. Due to the balance of these effects, the conversion efficiency could not be improved.
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| 30. |
- Larsson, Fredrik, et al.
(författare)
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Atomic layer deposition of amorphous tin-gallium oxide films
- 2019
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 37:3
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Tidskriftsartikel (refereegranskat)abstract
- A wide range of applications benefit from transparent semiconducting oxides with tunable electronic properties, for example, electron transport layers in solar cell devices, where the electron affinity is a key parameter. Presently, a few different ternary oxides are used for this purpose, but the attainable electron affinity range is typically limited. In this study, the authors develop a low-temperature atomic layer deposition (ALD) process to grow amorphous Sn1-xGaxOy thin films from dimethylamino-metal complexes and water. This oxide is predicted to provide a wide selection of possible electron affinity values, from around 3 eV for pure Ga2O3 to 4.5 eV for pure SnO2. The ALD process is evaluated for deposition temperatures in the range of 105-195 degrees C by in situ quartz crystal microbalance and with ex situ film characterization. The growth exhibits an ideal-like behavior at 175 degrees C, where the film composition can be predicted by a simple rule of mixture. Depending on film composition, the growth per cycle varies in the range of 0.6-0.8 angstrom at this temperature. Furthermore, the film composition for a given process appears insensitive to the deposition temperature. From material characterization, it is shown that the deposited films are highly resistive, fully amorphous, and homogeneous, with moderate levels of impurities (carbon, nitrogen, and hydrogen). By tailoring the metal cation ratio in films grown at 175 degrees C, the optical bandgap can be varied in the range from 2.7 eV for SnO2 to above 4.2 eV for Ga2O3. The bandgap also varies significantly as a function of deposition temperature. This control of properties indicates that Sn1-xGaxOy is a promising candidate for an electron transport layer material in a wide electron affinity range. Published by the AVS.
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| 31. |
- Liu, Yang, et al.
(författare)
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Combining good mechanical properties and high translucency in yttrium-doped ZrO2-SiO2 nanocrystalline glass-ceramics
- 2022
-
Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 42:1, s. 274-285
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Tidskriftsartikel (refereegranskat)abstract
- It is challenging to develop a material that combines good mechanical properties and high translucency since these properties are generally not coincident in one material. In this study, we prepared ZrO2-SiO2 nano crystalline glass-ceramics that combines the above two types of properties. Raw powder with 55 mol%, 65 mol%, and 75 mol% ZrO2 and each with 5 mol% yttrium as a dopant was prepared by sol-gel method, followed by spark plasma sintering to obtain dense glass-ceramics. XRD results demonstrated that the glass-ceramics with 65 mol% and 75 mol% ZrO2 were composed of tetragonal-ZrO2, whereas, that with 55 mol% ZrO2 was composed of cubicZrO(2). The as-sintered glass-ceramics showed black/brown discoloration, but they obtained high translucency after thermal treatment. X-ray energy-dispersive spectrometry (EDS) results in scanning electron transmission microscopy (STEM) mode demonstrated yttrium dopants were predominately distributed in ZrO2 nano crystallites. The glass-ceramics with 65 mol% ZrO2 had the highest flexural strength, achieving an average value of 673 MPa. The glass-ceramics with different compositions sintered at different temperatures showed fracture toughness values ranging from 5.25 MPa m(1/2) to 6.69 MPa m(1/2). The strong and translucent ZrO2-SiO2 nano crystalline glass-ceramics showing great protentional to be used in many fields.
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| 32. |
- Malinovskis, Paulius, et al.
(författare)
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Synthesis and characterization of multicomponent (CrNbTaTiW)C films for increased hardness and corrosion resistance
- 2018
-
Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 149, s. 51-62
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Tidskriftsartikel (refereegranskat)abstract
- Multicomponent carbide thin films of (CrNbTaTiW)C (30–40 at.% C) with different metal contents were depos-ited at different temperatures using non-reactive DC magnetron sputtering. The lattice distortion for the metallattice was estimated to vary from about 3 to 5%. Most films crystallized in the cubic B1 structure but Ta/W-rich films deposited at 600 °C exhibited a tetra gonal distortion. X-ray diffraction results sh ow that near-equimolar films exhibited a strong (111) texture. In contrast, Ta/W-rich films exhibited a shift from (111) to(100) texture at 450 °C. The in-plane relationship was determined to MC(111)[-12-1]//Al2O3(001)[110] with alattice mismatch of about 11% along the Al2O3[110] direction. A segregation of Cr to the grain boundaries was ob-served in all films. The microstructure was found to be the most important factor for high hardness. Less denseNb-rich and near-equimolar films deposited at low tem peratures exhib ited the low est hardnes s (12 GPa),while very dense Ta/W-rich high temperature films were found to be the hardest (36 GPa). No correlation wasfound between the lattice distortion and the hardness. Corrosion studies revealed that the multicomponentfilms exhibited excellent corrosion resistance, superior to that of a reference hyper-duplex stainless steel, in1.0 M HCl.
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| 33. |
- Marattukalam, Jithin J., et al.
(författare)
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Development of process parameters for selective laser melting of a Zr-based bulk metallic glass
- 2020
-
Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- Parameters for selective laser melting of Zr59.3Cu28.8Al10.4Nb1.5 (trade name AMZ4), allowing crack-free bulk metallic glass with low porosity, have been developed. The phase formation was found to be strongly influenced by the heating power of the laser. X-ray amorphous samples were obtained with laser power at and below 75 W. The as-processed bulk metallic glass was found to devitrify by a two-stage crystallization process within which the presence of oxygen was concluded to play an essential role. At laser powers above 75 W, the observed crystallites were found to be a cubic phase (Cu2Zr4O). The hardness and Young’s modulus in the as-processed samples was found to increase marginally with increased fraction of the crystalline phase.
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| 34. |
- Medina, León Zendejas, et al.
(författare)
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Phase formation in magnetron sputtered CrMnFeCoNi high entropy alloy
- 2020
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 403
-
Tidskriftsartikel (refereegranskat)abstract
- Thin films of the CrMnFeCoNi high entropy alloy were deposited by magnetron sputtering from a sintered equimolar target. The substrate temperature and bias were varied during deposition, and the structure, morphology and elemental distribution were studied in detail. All films formed phase mixtures of multiple crystal structures. This contrasts with studies on the bulk alloy, where it typically forms a single phase with a simple cubic closed packed (ccp) structure, with other phases precipitating only after long annealing times. For higher substrate temperatures, we observed a mixture of phases with ccp and bcc (body centered cubic) structures, and the intermetallic phases o-phase and L1(0), the first three being the predicted equilibrium phases at the deposition temperature. For room temperature depositions, we found evidence of very limited diffusion of metal atoms during the deposition. These films formed a mixture of a ccp and the intermetallic chi-phase. Two mechanisms can be distinguished that govern the phase formation at lower and higher temperatures. From the present results and comparisons with the literature, we also discuss why the small grain size, the low process temperature, and the fast surface diffusion during synthesis causes magnetron sputtering to yield different results compared to bulk synthesis from the melt. These principles explain why it is easier to form the equilibrium phases by sputtering, and why a single ccp phase should not be expected as a rule for this deposition method. Following the thermodynamic principles of high entropy alloys, this may also be the case in other high entropy alloy systems.
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| 35. |
- Menon, Ashok S., et al.
(författare)
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Synthetic Pathway Determines the Nonequilibrium Crystallography of Li- and Mn-Rich Layered Oxide Cathode Materials
- 2021
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:2, s. 1924-1935
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Tidskriftsartikel (refereegranskat)abstract
- Li- and Mn-rich layered oxides show significant promise as electrode materials for future Li-ion batteries. However, an accurate description of its crystallography remains elusive, with both single-phase solid solution and multiphase structures being proposed for high performing materials such as Li1.2Mn0.54Ni0.13Co0.13O2. Herein, we report the synthesis of single- and multiphase variants of this material through sol-gel and solid-state methods, respectively, and demonstrate that its crystallography is a direct consequence of the synthetic route and not necessarily an inherent property of the composition, as previously argued. This was accomplished via complementary techniques that probe the bulk and local structure followed by in situ methods to map the synthetic progression. As the electrochemical performance and anionic redox behavior are often rationalized on the basis of the presumed crystal structure, clarifying the structural ambiguities is an important step toward harnessing its potential as an electrode material.
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| 36. |
- Naim Katea, Sarmad, et al.
(författare)
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Synthesis of nano-phase ZrC by carbothermal reduction using a ZrO2–carbon nano-composite
- 2021
-
Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 41:1, s. 62-72
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Tidskriftsartikel (refereegranskat)abstract
- Carbothermal reduction of Zr-sucrose gels powders into nano-phase ZrC, or ZrC-Zr(C,O) core-shell powders, via a composite of 2–4 nm sized ZrO2 and amorphous carbon, is described. Samples with 1.7–20 sucrose-carbon:Zr ratio gels heated to 1495 °C at 10 °Cmin−1, with 3 and 30 min hold time were studied in detail using; TG, XRD, SEM, TEM, STEM-EDX, and XPS with Ar+-ion etching. After 1495 °C, 3 min, the samples with 12-20C:Zr ratios yielded weakly agglomerated 30 to 40 nm sized ZrC particles, surrounded by a dense 5 nm thick shell of Zr(C,O). With 5C:Zr significant amounts of ZrO2 was present after heating at 1495 °C for 3 min, while after 30 min annealing, ZrC particles without residual amorphous carbon was obtained. Minor amounts of zirconia was found in most samples, which in similarity with the 5 nm Zr(C,O) shell, is believed to stem from post synthesis oxidation.
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| 37. |
- Osinger, Barbara, et al.
(författare)
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Investigation of the phase formation in magnetron sputtered hard multicomponent (HfNbTiVZr)C coatings
- 2022
-
Ingår i: Materials & design. - : ELSEVIER SCI LTD. - 0264-1275 .- 1873-4197. ; 221
-
Tidskriftsartikel (refereegranskat)abstract
- Multicomponent carbides have gained interest especially for ultra-high temperature applications, due to their ceramic hardness, good oxidation resistance and enhanced strength. In this study the phase forma-tion, stability and mechanical properties of (HfNbTiVZr)C multicomponent carbide coatings were inves-tigated. Phase stability was predicted by the CALPHAD (CALculation of PHAse Diagrams) methods. This revealed that the multicomponent solid solution phase is only stable at elevated temperatures, namely above 2400 degrees C. At lower temperatures a phase mixture was predicted, with a particular tendency for V to segregate. Magnetron sputtered thin films deposited at 300 degrees C exhibited a single NaCl-type multicom-ponent carbide phase, which attributes to the kinetic stabilisation of simple structures during thin film growth. Films deposited at 700 degrees C, or exposed to UHV annealing at 1000 degrees C, however, revealed the decom-position of the single-phase multicomponent carbide by partial elemental segregation and formation of additional phases. Thus, confirming the CALPHAD predictions. These results underscore the importance of explicitly considering temperature when discussing the stability of multicomponent carbide materials, as well as the applicability of CALPHAD methods for predicting phase formation and driving forces in these materials. The latter being crucial for designing materials, such as carbides, that are used in appli-cations at elevated temperatures.
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| 38. |
- Rudisch, Katharina, et al.
(författare)
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Prospects for defect engineering in Cu2ZnSnS4 solar absorber films
- 2020
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 8:31, s. 15864-15874
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Complex compound semiconductors, such as the emerging solar cell material Cu2ZnSn(S,Se)4 (CZTS), present major challenges in terms of understanding and controlling growth processes and defect formation.This study aims to shed light upon the complicated interplay of synthesis conditions and the CZTS thin film properties. Composition-spread thin films are fabricated in different atmospheric conditionsduring the annealing step. The span of the single-phase region is identified by a phase analysiscombining XRD and Raman mapping. The phase characterization is strengthened by STEM-EDXanalysis. Our results show that the stability of the CZTS phase is strongly affected by the processconditions which is observed by a shift in the secondary phase boundaries and different levels of maximum cation ordering achieved in the different samples. With regard to the photoluminescence intensity, all investigated samples show the same trends: regions with Cu3SnS4 secondary phase show the lowest intensity, while the presence of SnSx secondary phases greatly enhances the photolumines-cence intensity. The single-phase region features an overall low photoluminescence intensity without a remarkable composition dependence and we propose the presence of deep defects in absence of secondary phases that limit the radiative recombination. We discuss implications for future efforts in defect engineering toward improving the efficiency of CZTS thin film devices.
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| 39. |
- Shinde, Deodatta, 1985, et al.
(författare)
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Elemental Distribution in CrNbTaTiW-C High Entropy Alloy Thin Films
- 2019
-
Ingår i: Microscopy and Microanalysis. - : CAMBRIDGE UNIV PRESS. - 1435-8115 .- 1431-9276. ; 25:2, s. 489-500
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and distribution of the elements have been studied in thin films of a near-equimolar CrNbTaTiW high entropy alloy (HEA) and films with 8 at.% carbon added to the alloy. The films were deposited by magnetron sputtering at 300°C. X-ray diffraction shows that the near-equimolar metallic film crystallizes in a single-phase body centered cubic (bcc) structure with a strong (110) texture. However, more detailed analyses with transmission electron microscopy (TEM) and atom probe tomography (APT) show a strong segregation of Ti to the grain boundaries forming a very thin Ti-Cr rich interfacial layer. The effect can be explained by the large negative formation enthalpy of Ti-Cr compounds and shows that CrNbTaTiW is not a true HEA at lower temperatures. The addition of 8 at.% carbon leads to the formation of an amorphous structure, which can be explained by the limited solubility of carbon in bcc alloys. TEM energy-dispersive X-ray spectroscopy indicated that all metallic elements are randomly distributed in the film. The APT investigation, however, revealed that carbide-like clusters are present in the amorphous film.
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| 40. |
- Song, Man, et al.
(författare)
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Nitrogen-doped Reduced Graphene Oxide Hydrogel Achieved via a One-Step Hydrothermal Process
- 2019
-
Ingår i: ChemNanoMat. - : WILEY-V C H VERLAG GMBH. - 2199-692X. ; 5:9, s. 1144-1151
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Tidskriftsartikel (refereegranskat)abstract
- We report an efficient one-step method to achieve highly reduced graphene oxide (rGO) hydrogel doped with nitrogen where the rGO sheets are interconnected forming a porous structure by means of hydrothermal process. During the synthesis, ammonium formate is used as reducing reagent and simultaneously as nitrogen supplier, which delivers nitrogen-doped rGO (NRGO) hydrogel that exhibits C/O atomic ratio as high as at ~11.1 and contains decent ~5.4 at.% nitrogen. As comparison, the reduction efficiency is only half of the value and no nitrogen doping can be obtained when L-ascorbic acid is used as reducing reagent. The resultant NRGO shows enhanced electrocatalytic ability for oxygen reduced reaction indicating its great potential of the one-step method for the catalyst and energy applications.
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| 41. |
- Srinath, Aishwarya, 1991-, et al.
(författare)
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An investigation of the corrosion resistances of magnetron sputtered TaW-rich, Nb-rich, and multicomponent CrNbTaTiW alloys
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The corrosion resistances of magnetron sputtered nearequimolar, TaW-rich, and Nb-rich CrNbTiTaW alloys, with and without 8 at.% carbon, were studied in aqueous chloride-containing environments. Electrochemical tests and scanning electron images showed that all the CrNbTaTiW alloys were highly corrosion resistant in 1.0 M HCl. The results conclusively showed that passivated nearequimolar CrNbTaTiW coatings have comparable corrosion performances to passivated Nb- and TaW-rich alloys in 0.01 M HCl + 0.1 M NaCl. Carbon affected the rate of surface repassivation in polarisation measurements of the films whose oxide had been partially reduced, but had a minor influenceon the corrosion resistances once a mature oxide was formed. No conclusive relationships between microstructure and corrosion resistance were established. The comparable corrosion resistances of the multicomponent CrNbTiTaW, Nb-rich and TaW-rich alloys were attributed to the presence of extremely stable surface oxides of Nb and Ta which prevented losses of Ti and Cr. The near surface regions of all the alloys before and after corrosion appeared to be depleted in W compared to the bulk.
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| 42. |
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| 43. |
- von Fieandt, Kristina, et al.
(författare)
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Influence of N content on structure and mechanical properties of multi-component Al-Cr-Nb-Y-Zr based thin films by reactive magnetron sputtering
- 2020
-
Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 389
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Tidskriftsartikel (refereegranskat)abstract
- Al-Cr-Nb-Y-Zr-N films have been deposited with reactive dc magnetron sputtering at various N-2 flow ratios to achieve films with different nitrogen content, from purely metallic to fully nitrided films. The structure evolved from mainly amorphous with a minor crystalline intermetallic phase for the film without nitrogen, to nanocomposites with a cubic crystalline phase in an amorphous matrix for intermediate nitrogen content (15-41 at.% N), and at higher nitrogen content (46-51 at.% N) to crystalline solid solution nitrides with a NaCl-type structure. Partial elemental segregation on the nanoscale was found in all studied samples and the films exhibited different segregation behaviour depending on the nitrogen content, implying that the structural evolution on the nanoscale of films in this material system complex and highly composition-dependent. The hardness increased with increasing nitrogen content, reaching a maximum at about 30 GPa at for the nitride films with 50 at.% N. Deformation behaviour, studied by indentation measurements, of the nitride films was found to be ductile, where no sign of crack formation could be observed. This can be attributed to a metallic phase in the columnar boundaries caused by partial elemental segregation of mainly yttrium. Hence, films within in this material system, although the nanostructure is found to be relatively complex, show very promising mechanical properties and the structural complexity can be used as a guide for designing nitride materials that combine high hardness with ductility.
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| 44. |
- von Fieant, Kristina, et al.
(författare)
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In Situ Formation of Ge Nanoparticles by Annealing of Al-Ge‑N ThinFilms Followed by HAXPES and XRD
- 2019
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:16, s. 11100-11109
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Tidskriftsartikel (refereegranskat)abstract
- Ge nanoparticles embedded in thin films have attracted a lot of attention due to their promising optical and electronic properties that can be tuned by varying the particle size and choice of matrix material. In this study, Ge nanoparticle formation was investigated for Al-Ge-N based thin films by simultaneous measurements of HAXPES and grazing incidence XRD during in situ annealing in vacuum conditions. As-deposited Al-Ge-N thin films, synthesized by reactive dc magnetron sputtering, consisted of a nanocrystalline (Al1–xGex)Ny solid solution and an amorphous tissue phase of Ge3Ny. Upon annealing to 750 °C, elemental Ge was formed shown by both HAXPES and XRD measurements, and N2 gas was released as measured by a mass spectrometer. Postannealed ex situ analysis by SEM and TEM showed that the elemental Ge phase formed spherical nanoparticles on the surface of the film, with an average size of 210 nm. As the annealing temperature increased further to 850 °C, the Ge particles on the film surface evaporated, while the phase segregation of Ge still could be observed within the film. Thus, these results show the possibility for a controlled synthesis of Ge nanoparticles through annealing of Al-Ge-N thin films to produce materials suitable for use in electronic or optoelectronic devices.
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| 45. |
- von Fieant, Kristina, et al.
(författare)
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Multi-component (Al,Cr,Nb,Y,Zr)N thin films by reactive magnetron sputter deposition for increased hardness and corrosion resistance
- 2020
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 693
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Tidskriftsartikel (refereegranskat)abstract
- Multi-component nitride thin films in the Al-Cr-Nb-Y-Zr system with non-equimolar composition have been deposited by reactive dc magnetron sputtering. The substrate temperature and substrate bias have been varied, from room temperature to 700 degrees C and from 0 to -200 V respectively. The relationship between these varied growth conditions on the structure, morphology, mechanical and corrosion properties of the films have been probed. All films consisted of a single solid solution with a NaCl-type structure, as shown by X-ray diffraction. However, elemental energy dispersive spectroscopy maps, obtained in the scanning transmission electron microscope, indicated that there could be partial segregation of Al, Cr and Y atoms within the grains. The microstructure of the films became denser, more fine-grained and smoother as the bias and temperature were increased. Nanoindentation showed that the hardness of the films increased with both bias and temperature, reaching a maximum of 27 +/- 2 GPa. The corrosion resistance of the films, studied by performing potentiodynamic polarisation curves in 1 M HCl, was also found to be improved when compared to a commercially available hyper-duplex stainless steel and a ternary reference (Nb,Zr)N thin film as well.
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| 46. |
- Wu, Jiyue, et al.
(författare)
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Perovskite Sr-x(Bi1-xNa0.97-xLi0.03)(0.5)TiO3 ceramics with polar nano regions for high power energy storage
- 2018
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Ingår i: Nano Energy. - : ELSEVIER SCIENCE BV. - 2211-2855 .- 2211-3282. ; 50, s. 723-732
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric capacitors are very attractive for high power energy storage. However, the low energy density of these capacitors, which is mainly limited by the dielectric materials, is still the bottleneck for their applications. In this work, lead-free single-phase perovskite Srx(Bi1-xNa0.97-xLi0.03)(0.5)TiO3 (x = 0.30 and 0.38) bulk ceramics, prepared using solid-state reaction method, were carefully studied for the dielectric capacitor application. Polar nano regions (PNRs) were created in this material using co-substitution at A-site to enable relaxor behaviour with low remnant polarization (P-r) and high maximum polarization (P-max). Moreover, P-max was further increased due to the electric field induced reversible phase transitions in nano regions. Comprehensive structural and electrical studies were performed to confirm the PNRs and reversible phase transitions. And finally a high energy density (1.70 J/cm(3)) with an excellent efficiency (87.2%) was achieved using the contribution of field-induced rotations of PNRs and PNR-related reversible transitions in this material, making it among the best performing lead-free dielectric ceramic bulk material for high energy storage.
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| 47. |
- Zendejas Medina, León, et al.
(författare)
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Enhancing corrosion resistance, hardness, and crack resistance in magnetron sputtered high entropy CoCrFeMnNi coatings by adding carbon
- 2021
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 205
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Tidskriftsartikel (refereegranskat)abstract
- This study explores carbon addition as a materials design approach for simultaneously improving the hardness, crack resistance, and corrosion resistance of high entropy thin films. CoCrFeMnNi was selected as a starting point, due to its high concentration of weak carbide formers. The suppression of carbides is crucial to the approach, as carbide formation can decrease both ductility and corrosion resistance. Films with 0, 6, and 11 at.% C were deposited by magnetron co-sputtering, using a graphite target and a sintered compound target. The samples with 0 at.% C crystallized with a mixture of a cubic closed packed (ccp) phase and the intermetallic chi-phase. With 6 and 11 at.% C, the films were amorphous and homogenous down to the nm-scale. The hardness of the films increased from 8 GPa in the carbon-free film to 16 GPa in the film with 11 at.% C. Furthermore, the carbon significantly improved the crack resistance as shown in fragmentation tests, where the crack density was strongly reduced. The changes in mechanical properties were primarily attributed to the shift from crystalline to amorphous. Lastly, the carbon improved the corrosion resistance by a progressive lowering of the corrosion current and the passive current with increasing carbon concentration.
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| 48. |
- Zendejas Medina, Léon, et al.
(författare)
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Enhancing the mechanical and electrochemical properties of sputtered CoCrFeMnNi thin films by carbon addition
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- High entropy alloy (HEA) thin films of CrMnFeCoNi are promising materials for polymer electrolyte membrane fuel cells, due to their high fracture resistance and passivation against corrosion. The addition of carbon to HEA films have shown to improve corrosion resistance, hardness and ductility. HEA films with 0%, 6% and 11% amounts of carbon were deposited on Si[100] and polyimide substrates by magnetron co-sputtering using a graphite target and a sintered compound target for this study. Characterization using XRD and TEM showed that the samples were crystalline with a mixture of ccp and α-Mn at 0 at-% C, and underwent amorphization from 6 at-% C. No evidence of either free carbon or a crystalline carbide phase was found, and the films displayed homogenous composition. Nanoindentation measurements on coated Si [100] substrate showed that the hardness of the thin films changed with increasing carbon content. The tensile fragmentation test method was shown to be useful to characterize the strength distribution and fracture energy at crack onset for the present materials. This method revealed fewer cracks at all levels of strain for the carbon containing films compared to the carbon free ones. Consequentially, there was a trend of higher fracture energies by addition of carbon because of a shifting towards of crack onset strain. Electrochemical studies showed that the carbon had a beneficial effect on the passive layer, lowering the corrosion current and the passive current during with increasing carbon.
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