| 1. |
- Bahr, A., et al.
(författare)
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Non-reactive HiPIMS deposition of NbCx thin films : Effect of the target power density on structure-mechanical properties
- 2022
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 444
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Tidskriftsartikel (refereegranskat)abstract
- The exceptional mechanical properties of transition metal carbide coatings are known to be governed by the carbon content and its morphological distribution. Here, we verify the influence of the target peak power density on the chemical composition, microstructure, and mechanical properties of NbCx coatings grown by non-reactive high-power impulse magnetron sputtering (HiPIMS). By tuning the pulse parameters, the power density can be increased from 0.11 to 1.48 kW/cm2 leading to a decrease in the C/Nb ratio from 1.52 to 0.99 within the films - proven by combined elastic backscattering and time-of-flight elastic recoil detection analysis. This decrease in the C/Nb ratio is accompanied by microstructural changes from nanocomposite morphologies with an average grain size of 6.6 +/- 2.5 nm at 0.13 kW/cm2 into more columnar structures with an average column width of 65.2 +/- 18.7 nm at 1.48 kW/cm2. Independent from the C/Nb ratio, all films exhibit a single face-centered cubic structure. The mechanical properties correlate with the enhanced growth behavior dominated by ions at higher peak power densities and the varied C/Nb ratios. A maximum in hardness and fracture toughness of H = 38.7 +/- 3.6 GPa and KIc = 2.78 +/- 0.13 MPa center dot m1/2 (at 3.2 GPa residual compressive stress), is obtained for the nearly stoichiometric NbC coating exhibiting C/Nb ratio of 1.06.
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| 2. |
- Bakhit, Babak, 1983-, et al.
(författare)
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Systematic compositional analysis of sputter-deposited boron-containing thin films
- 2021
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 39:6
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Tidskriftsartikel (refereegranskat)abstract
- Boron-containing materials exhibit a unique combination of ceramic and metallic properties that are sensitively dependent on their given chemical bonding and elemental compositions. However, determining the composition, let alone bonding, with sufficient accuracy is cumbersome with respect to boron, being a light element that bonds in various coordinations. Here, we report on the comprehensive compositional analysis of transition-metal diboride (TMBx) thin films (TM = Ti, Zr, and Hf) by energy-dispersive x-ray spectroscopy (EDX), x-ray photoelectron spectroscopy (XPS), time-of-flight elastic recoil detection analysis (ToF-ERDA), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). The films are grown on Si and C substrates by dc magnetron sputtering from stoichiometric TMB2 targets and have hexagonal AlB2-type columnar structures. EDX considerably overestimates B/TM ratios, x, compared to the other techniques, particularly for ZrBx. The B concentrations obtained by XPS strongly depend on the energy of Ar+ ions used for removing surface oxides and contaminants prior to analyses and are more reliable for 0.5 keV Ar+. ToF-ERDA, RBS, and NRA yield consistent compositions in TiBx. They also prove TiBx and ZrBx films to be homogeneous with comparable B/TM ratios for each film. However, ToF-ERDA, employing a 36-MeV 127I8+ beam, exhibits challenges in depth resolution and quantification of HfBx due to plural and multiple scattering and associated energy loss straggling effects. Compared to ToF-ERDA, RBS (for the film grown on C substrates) and NRA provide more reliable B/Hf ratios. Overall, a combination of methods is recommended for accurately pinpointing the compositions of borides that contain heavy transition metals.
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| 3. |
- Correa, S. A., et al.
(författare)
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A multipurpose set-up using keV ions for nuclear reaction analysis, high -resolution backscattering spectrometry, low-energy PIXE and in-situ irradiation experiments
- 2020
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : ELSEVIER. - 0168-583X .- 1872-9584. ; 478, s. 104-110
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Tidskriftsartikel (refereegranskat)abstract
- A new chamber for material analysis and modification using energetic ions with primary particle energies in the keV regime was developed at the single stage 350 kV high-current Danfysik implanter at the Tandem Laboratory, Uppsala University. The experimental set-up allows for B-11 and O-18 depth profiling by Nuclear Reaction Analysis using the B-11(p,alpha(0))Be-8 and O-18(p,alpha)N-15 nuclear resonances at 163 keV and at 151 keV, respectively. Additionally, a surface barrier detector with a cryogenic assembly enables High-Resolution Backscattering Spectrometry with average resolution approximate to 4 keV FWHM for protons. A silicon drift detector enables Low-Energy Particle Induced X-ray Emission analysis for elements with low atomic number (Z >= 8). The available instrumentation of the chamber assembly with its specifications are described in details with a series of applied and fundamental benchmark studies, together with some suggestions for future applications.
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| 4. |
- Cupak, C., et al.
(författare)
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Retention of deuterium in beryllium : A combined investigation using TDS, ERDA and EBS
- 2022
-
Ingår i: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 33
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the retention of deuterium in beryllium, implanted with an energy of 500 eV/D, using a combination of thermal desorption spectroscopy, elastic recoil detection analysis and elastic backscattering spectroscopy. The parallel use of these techniques allowed us to directly quantify the absolute deuterium content reduction of the sample for specific desorption peaks observed during thermal annealing. In addition, the presence of a beryllium oxide surface layer was observed, despite sputter-cleaning of the sample was initially conducted in-situ. A main result was that similar to 85 % of the retained deuterium got released during the primary desorption peak at 400 K. A smaller, secondary desorption peak was identified at 540 K. All deuterium could be removed from the Be sample by heating it to a temperature of 800 K.
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| 5. |
- Dittrich, Laura, et al.
(författare)
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Impact of ion irradiation and film deposition on optical and fuel retention properties of Mo polycrystalline and single crystal mirrors
- 2023
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Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 37
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline (PC) and single crystal (SC) molybdenum mirrors were irradiated with 98Mo+, 1H+, 4He+, 11B+ and 184W+. Energies were chosen to impact the optically active region (up to 30 nm deep) of Mo mirrors. Some surfaces were coated by magnetron sputtering either with B or W films 4–65 nm thick. The overall objective was to simulate the neutron-induced damage and transmutation (H, He), and the impact of H, He, B, W on the optical performance of test mirrors, and on fuel retention. In parallel, a set of PC Mo mirrors irradiated with 1.6 MeV 98Mo3+ to a damage of 2 dpa and 20 dpa was installed in the JET tokamak for exposure during deuterium-tritium campaigns. Data from spectrophotometric, ion beam and microscopy techniques reveal: (i) the irradiation decreased specular reflectivity, whereby the differences between PC and SC in reflectivity are very small, (ii) He is retained in bubbles within 25–30 nm of the subsurface layer in all irradiated materials, (iii) W, either deposited or implanted, decreases reflectivity, but the strongest reflectivity degradation is caused by B deposition. Laboratory studies show the correlation of damage and H retention. Several cycles of W deposition and its removal from SC-Mo mirrors by plasma-assisted methods were also performed.
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| 6. |
- Glechner, T., et al.
(författare)
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Influence of the non-metal species on the oxidation kinetics of Hf, HfN, HfC, and HfB2 coatings
- 2021
-
Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 211
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the non-metal species on the oxidation resistance of transition metal ceramic based thin films is still unclear. For this purpose, we thoroughly investigated the oxide scale formation of a metal (Hf), carbide (HFC0.96), nitride (HfB1.5), and boride (HfB2.3) coating grown by physical vapor deposition. The non-metal species decisively affect the onset temperature of oxidation, ranging between 550 degrees C for HfC0.96 to 840 degrees C for HfN1.5. HfB2.3 and HfN1.5 obtain the slowest oxide scale kinetic following a parabolic law with k(p) values of 4.97.10(-10) and 5.66.10(-11) kg(2) m(-4) s(-1) at 840 degrees C, respectively. A characteristic feature for the oxide scale on Hf coatings, is a columnar morphology and a substantial oxygen inward diffusion. HfC0.96 reveals an ineffective oxycarbide based scale, whereas HfN(1.5 )features a scale with globular HfO2 grains. HfB(2.3 )exhibits a layered scale with a porous boron rich region on top, followed by a highly dense and crystalline HfO2 beneath. Furthermore, HfB(2.3 )presents a hardness of 47.7 +/- 2.7 GPa next to an exceptional low inward diffusion of oxygen during oxidation. This study showcases the strong influence of the non-metallic bonding partner despite the same metallic basis, as well as the huge potential for HfB2 based coatings also for oxidative environments.
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| 7. |
- Kretschmer, Andreas, et al.
(författare)
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Analysis of (Al,Cr,Nb,Ta,Ti)-nitride and-oxynitride diffusion barriers in Cu-Si interconnects by 3D-Secondary Ion Mass Spectrometry
- 2023
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Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 197
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Tidskriftsartikel (refereegranskat)abstract
- We report on the barrier performance of a nitride, and three oxynitrides of the system Al-Cr-Nb-Ta-Ti between Cu and Si. Different high-entropy sublattice nitrides have been tested before as diffusion barriers in this system, by depositing thin barriers on single crystalline Si substrates, followed by a thick Cu layer on top, and subsequent vacuum annealing. We investigated a reversed stacking sequence, by sputtering 15-30 nm of (Al,Cr,Nb,Ta,Ti)-O-N (between 0.5 and 63.7 at.% O) on polished polycrystalline Cu substrates, followed by 200 nm of Si. The samples were then vacuum annealed at 600, 700, 800 and 900 degrees C for 30 min. All four investigated coatings perform similar. Secondary Ion Mass Spectrometry depth profiling in high-current-bunched mode (lateral res-olution +/- 1 mu m) shows breakthrough of Si even at 600 degrees C. But 3D constructed images with Burst Alignment mode (lateral resolution of +/- 2 nm) reveal that this failure is a highly localized phenomenon, likely related to coarsening effects at the Cu grain boundaries, leading to punctuation of the diffusion barrier. Aside from this penetration, the majority of the area of each barrier coating retains its function. This in-depth analysis shows that the barrier function of the nitride and oxynitride coatings mostly stays intact up to 800 degrees C and fails completely at 900 degrees C.
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| 8. |
- Kretschmer, Andreas, et al.
(författare)
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High-entropy alloy inspired development of compositionally complex superhard (Hf,Ta,Ti,V,Zr)-B-N coatings
- 2022
-
Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- Phase stability and mechanical properties of multimetal-boronnitride (Hf,Ta,Ti,V,Zr)-B-N is investigated by ab initio computations and experimental methods. (Hf,Ta,Ti,V,Zr)-B-N shows a strong energetic preference for the fcc NaCl-type structure over other structures up to a B:N ratio of 3.5. Reactively deposited (Hf,Ta,Ti,V,Zr)-B-N coatings show formation of X-ray amorphous BN, accompanied by a drastic hardness decrease with increasing B content. But non-reactively sputtered (Hf,Ta,Ti,V,Zr)-B-N coatings exhibit a single-phase fcc solid solution, up to the maximum B:N ratio of 1.12 studied, in good agreement with calculations. All non-reactively sputtered multimetal-boronnitride coatings contain a high Zr metal-fraction and approximate to 8at% C, stemming from impurities in the target. The single-phase coatings reach superhardness up to 46.3 GPa. Even after vacuum annealing to 1200 degrees C, the hardness of the coating with a B:N ratio of 1.03 is still 43.7 GPa, while that of ZrN0.72C0.28 decreased from 36.3 to 30.2 GPa. Our results demonstrate the importance of the deposition technique to deposit single-phased coatings with exceptional hardness and thermal stability. (C) 2022 The Authors. Published by Elsevier Ltd.
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| 9. |
- Moldarev, Dmitrii, et al.
(författare)
-
Oxygen mobility in yttrium hydride films studied by isotopic labelling
- 2022
-
Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 261, s. 01001-01001
-
Tidskriftsartikel (refereegranskat)abstract
- The photochromic properties of oxygen-containing yttrium hydride thin films are directly dependent on the oxygen concentration in the material. We use 16O/18O labelling to study oxidation of YH2 films. Oxygen penetrates the film through grain boundaries and intercolumnar voids oxidising the whole film thickness, without pronounced surface oxidation or self-passivation. Once oxidised, the mobility of oxygen in the films is low and no detectable changes in chemical composition of 18O-labeled YHO films is found under illumination.
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| 10. |
- Pitthan, Eduardo, et al.
(författare)
-
Assessing boron quantification and depth profiling of different boride materials using ion beams
- 2021
-
Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 417
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Tidskriftsartikel (refereegranskat)abstract
- We assessed the capability to quantify and depth profile boron in different materials by a number of ion beam-based techniques. Specifically, the depth resolution, probing depth, film homogeneity, and detection limit for boron using particle-particle nuclear reaction analysis (resonant and non-resonant mode), elastic backscattering spectrometry, and time-of-flight elastic recoil detection analysis using heavy primary ions were evaluated. Samples consisted of high and low-Z materials implanted by B-11(+) at different energies and fluences, Au/BN structures as well as bulk boride targets. Advantages and limitations for the individual techniques for the different sample types are discussed. As an example, while ToF-ERDA allows to efficiently depth profile B-10 and B-11 individually, limitations in probing depth and depth resolution, as well as quantification are apparent in particular for target materials containing high-Z species. While EBS presents large probing depth (similar to 14 mu m), the best detection limit (similar to 0.1 x 10(15)/cm(2)) is obtained from resonant-NRA.
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| 11. |
- Pitthan, Eduardo, et al.
(författare)
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In-situ, real-time investigation of the formation of oxygen-containing rare-earth hydrides by combining a quartz crystal microbalance and ion beam analysis
- 2023
-
Ingår i: Materialia. - : Elsevier. - 2589-1529. ; 27
-
Tidskriftsartikel (refereegranskat)abstract
- We present an in-situ and real-time investigation of the formation of YHO and GdHO thin films grown by reactive e(-)-beam evaporation. Mass changes were continuously monitored during deposition, oxidation, and illumination using a highly sensitive quartz crystal microbalance, while changes in chemical composition and depth profiles were investigated simultaneously by ion beam analysis. Results highlight the strong reactivity of freshly deposited YHx and GdHx films, even under ultra-high vacuum conditions. Oxidation starts at the surfaces of the films and the oxidation rate is strongly dependent on the O-2 pressure. The response of the system under ion beam irradiation and in-situ illumination is also presented and discussed. For the measured mass changes, a quantitative agreement better than 2% was observed between both techniques and demonstrates the consistency and sensitivity of this approach.
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| 12. |
- Pitthan, Eduardo, et al.
(författare)
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Influence of thermal annealing and of the substrate on sputter-deposited thin films from EUROFER97 on tungsten
- 2023
-
Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 35
-
Tidskriftsartikel (refereegranskat)abstract
- The modification of sputter-deposited films from EUROFER97 on tungsten during and after annealing were investigated in-situ and ex-situ. The annealing resulted in a densification of the film, formation of large grains, segregation of W at the surface, and the formation of Fe-W compounds at the interfacial region. Similar structural modifications were observed also for a film annealed on a MgO substrate, with an exception to the change in composition (no increase of W concentration). Results indicate that the substrate significantly affects thermally induced modifications of re-deposited EUROFER97.
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| 13. |
- Pitthan, Eduardo, et al.
(författare)
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Thin films sputter-deposited from EUROFER97 in argon and deuterium atmosphere : Material properties and deuterium retention
- 2023
-
Ingår i: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 34
-
Tidskriftsartikel (refereegranskat)abstract
- Sputter-deposited thin films (33–1160 nm) from EUROFER97 were obtained on different substrates (C, Si, W, MgO) in argon and a mix of argon and deuterium atmosphere. The composition, microstructure, and mechanical properties of the films were analyzed and compared to those of the bulk material. The films feature lower density (-10%), higher hardness (+79%), and smaller crystallites in comparison to the bulk. Despite such differences, the elemental atomic composition of the films and the bulk was very similar, as determined by ion beam analysis. Deposition in deuterium-containing atmosphere resulted in a low deuterium incorporation (0.28% of atomic content), indicating low retention of hydrogen-isotopes in the deposited material.
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| 14. |
- Shams-Latifi, Jila, et al.
(författare)
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An in-situ ToF-LEIS and AES study of near-surface modifications of the composition of EUROFER97 induced by thermal annealing
- 2022
-
Ingår i: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 30
-
Tidskriftsartikel (refereegranskat)abstract
- Surface segregation and diffusion of W, Ta, Cr, O and S after thermal annealing of EUROFER97 were studied in-situ. The sample was prepared by polishing, annealing up to 300??& nbsp;and 3 keV Ar sputtering. In-situ measurements with time-of-flight low energy ion scattering using 8 keV Ne ions and Auger electron spectroscopy were carried out close to room temperature after each annealing, in sequence, to 425?, 675?, 400?, 675?, 900?, and 925?. Surface segregation/diffusion of chromium and tungsten and/or tantalum can be observed in the ion scattering spectra. The segregation of sulfur was clearly observed in Auger electron spectroscopy. The energy converted time-of-flight low-energy ion scattering spectrum after the first annealing to 675?& nbsp;was compared to Monte-Carlo simulations using the TRBS code. The most compatible simulation indicates a layer enriched in W + Ta of 1 +/- 0.3 nm featuring 0.0276 combined relative concentration of tungsten and tantalum to total metal content which is considerably higher than the bulk value of 0.0042.
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| 15. |
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| 16. |
- Shams-Latifi, Jila, et al.
(författare)
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Experimental electronic stopping cross-section of tungsten bulk and sputter-deposited thin films for slow protons, deuterons and helium ions
- 2023
-
Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 36
-
Tidskriftsartikel (refereegranskat)abstract
- The experimental electronic stopping cross-section of tungsten for low-energy protons, deuterons, and helium ions is deduced from backscattering experiments from thin films and bulk using time-of-flight low-energy ion scattering (ToF-LEIS). Two complementary experimental approaches showed consistent results in the energy ranges of 0.3-10 keV for protons, 0.33-10 keV for deuterons, and 0.7-10 keV for He+ ions. In relative mea-surements, a Au sample was used as the reference, while in absolute energy loss measurements, sputter-deposited thin films of tungsten on carbon substrates were employed. The experimental energy-converted spectra were compared to Monte-Carlo simulations in both approaches for quantitative analysis taking the influence of plural and multiple scattering into account. The results show proportionality to the ion velocity. We discuss the present datasets in comparison to semiempirical modelling and predictions from theory.
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| 17. |
- Shams-Latifi, Jila, 1992-
(författare)
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Interactions of low-energy ions with plasma-facing materials : Fundamental and applied aspects
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Materials in ultimate proximity of a burning plasma in controlled thermonuclear fusion devices, referred to as plasma-facing materials (PFMs), are exposed to a high flux of impinging particles and extreme conditions such as high thermal loads. In consequence, these materials are modified in manifold ways due to interactions with energetic plasma species. In this thesis, the potential of time-of-flight low-energy ion scattering (ToF-LEIS) for fundamental and applied studies relevant to improving our understanding of plasma-materials interactions was explored. ToF-LEIS is a non-destructive method to study the near-surface composition of materials providing high depth resolution and surface sensitivity. The investigated materials are tungsten and EUROFER97, both as bulks and in the form of different thin film stacks. W is proposed for the first wall of ITER, as well as for the divertor and coating for the first wall of DEMO. EUROFER97 is a reduced activation steel to be used as a structural material for the ITER test blanket and the first wall of DEMO's blanket.In the first part of this thesis, the potential of low-energy ions for quantitative composition depth profiling of near-surface modifications in PFMs induced by thermal loads was explored. Specifically, ToF-LEIS in combination with Auger electron spectroscopy was employed to study the influence of elevated temperatures on the near-surface composition of EUROFER97. The results demonstrated and quantified thermally induced segregation of W, Cr and S to the first nm of EUROFER97 under thermal loads. In the second part, this thesis focused on developing sample systems and measurement routines for assessing electronic interactions of low-energy ions with common PFMs. Developed samples were employed to experimentally deduce the electronic stopping power of W and EUROFER97 using ToF-LEIS and Monte-Carlo simulations for low-energy H, D and He ions, in the range of 0.3 – 10 keV for W and 3 – 10 keV for EUROFER97. Obtained comprehensive datasets represent the first experimental data of the electronic stopping power of W and EUROFER97 at low energies for the employed ions representing dominating plasma species. Results were compared to theoretical and semiempirical models and are essential inputs for modelling particle range or sputter yields.
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| 18. |
- Shams-Latifi, Jila, et al.
(författare)
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Sputter-deposition of ultra-thin film stacks from EUROFER97 and tungsten : characterisation and interaction with low-energy D and He ions
- 2024
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Ingår i: Materials Research Express. - : Institute of Physics (IOP). - 2053-1591. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- We have sputter-deposited stacks of ultrathin layers from EUROFER97 and tungsten on silicon substrates. Ion beam analysis techniques are used for composition characterisation and microscopy methods are employed for structural examination. The films are subsequently studied by time-of-flight low-energy ion scattering (ToF-LEIS) for primary 10 keV He+ and 8 keV D+ ions to demonstrate an approach of providing accurate and precise experimental reference electronic stopping cross-sections for fusion-relevant steels. The energy-converted ToF-LEIS spectra are compared to Monte-Carlo simulations for quantitative analysis explicitly considering the influence of plural and multiple scattering. We discuss the deduced stopping cross-sections of EUROFER97 in comparison to predictions by SRIM using Bragg's rule of stopping power additivity.
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| 19. |
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| 20. |
- Wolf, Philipp M., et al.
(författare)
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An in situ ToF-LEIS characterization of the surface of Ti-based thin films under oxygen exposure and at elevated temperatures
- 2023
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 638
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Tidskriftsartikel (refereegranskat)abstract
- Ti-based coatings are utilized in a wide variety of applications, from biomedical implants to mechanical tools. Insight into initial stages of processes triggered by gas exposure and temperature change in the near-surface region of such coatings is essential for the understanding of their macroscopic behavior. We present an in situ time-of-flight low-energy ion scattering (ToF-LEIS) approach for the non-destructive and depth-resolved study of composition and morphology of the immediate surface region with sub-nm resolution. Ti-based coatings, with increasing compositional complexity, starting from in situ grown Ti, followed by ex situ grown Ti, TiN, and (Ti,Al) N, are studied concerning effects of exposure to oxygen and elevated temperatures. On the clean in situ deposited Ti surface, a 1.9 nm thick oxide layer is observed after exposure to 4000 Langmuir oxygen at room temperature. In contrast, for ex situ grown samples, an oxidic surface layer not removable by surface ion sputtering is found to limit effects of further oxygen exposure. TiN does not show significant changes when exposed to oxygen at 370 & DEG;C. For (Ti,Al)N, a nm-thick Al-rich surface layer is observed at annealing temperatures above 600 & DEG;C, both in ultra-high vacuum and in 1.0 x 10-3 Pa of oxygen.
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| 21. |
- Wolf, Philipp M., et al.
(författare)
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Direct Transition from Ultrathin Orthorhombic Dinickel Silicides to Epitaxial Nickel Disilicide Revealed by In Situ Synthesis and Analysis
- 2022
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Ingår i: Small. - : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 18:14
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Tidskriftsartikel (refereegranskat)abstract
- Understanding phase transitions of ultrathin metal silicides is crucial for the development of nanoscale silicon devices. Here, the phase transition of ultrathin (3.6 nm) Ni silicides on Si(100) substrates is investigated using an in situ synthesis and characterization approach, supplemented with ex situ transmission electron microscopy and nano-beam electron diffraction. First, an ultrathin epitaxial layer and ordered structures at the interface are observed upon room-temperature deposition. At 290 °C, this structure is followed by formation of an orthorhombic δ-Ni2Si phase exhibiting long-range order and extending to the whole film thickness. An unprecedented direct transition from this δ-Ni2Si phase to the final NiSi2−x phase is observed at 290 °C, skipping the intermediate monosilicide phase. Additionally, the NiSi2−x phase is found epitaxial on the substrate. This transition process substantially differs from observations for thicker films. Furthermore, considering previous studies, the long-range ordered orthorhombic δ-Ni2Si phase is suggested to occur regardless of the initial Ni thickness. The thickness of this ordered δ-Ni2Si layer is, however, limited due to the competition of different orientations of the δ-Ni2Si crystal. Whether the formed δ-Ni2Si layer consumes all deposited nickel is expected to determine whether the monosilicide phase appears before the transition to the final NiSi2−x phase.
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| 22. |
- Wolf, Philipp Mika, 1994-
(författare)
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Synthesis and In Situ ToF-LEIS Analysis of Ultrathin Silicides and Ti-based Films
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films and coatings play a significant role in today’s society, with applications in electronics, optics, mechanics, and biomedicine. Further advancement in the field of surface coatings requires a good understanding of the unique features of ultrathin films and surfaces, which can only be reached with analysis techniques capable of resolving composition and morphology on a sub-nm scale.Time-of-flight low-energy ion scattering (ToF-LEIS), is such a method, with the surplus of non-destructive analysis. This thesis is devoted to demonstrating the use of in situ ToF-LEIS in the study of ultrathin film synthesis and surface modification. To showcase the possibilities offered by ToF-LEIS, two studies are presented: (1) The study of the phase transition of ultrathin nickel silicides and (2) the study of Ti-based coatings exposed to oxygen at elevated temperatures.In the first study, the growth and the phase transition sequence of Ni on Si(100) are investigated for initial film thicknesses below 4 nm. A partially ordered film with composition equivalent to Ni2Si is found for room-temperature deposition. Further, an unprecedented direct phase transition from orthorhombic δ-Ni2Si to epitaxial NiSi2-x, skipping the NiSi phase present in thicker films, is observed at 290 °C. This direct phase transition is explained by an enhanced interfacial effect between the substrate and the silicide for ultrathin films.The second study contains the in situ investigation of effects of low amounts of oxygen and high temperature on four coatings, in situ grown Ti as well as ex situ grown Ti, TiN, and (Ti,Al)N. On the ex situ samples, a persistent surface oxide layer is found, not removable by ion sputtering, limiting the effects of further oxygen exposure compared to the in situ sample. The nitride samples show a high stability towards further oxidation even at elevated temperatures. Additionally, the formation of an Al-rich surface layer is observed on (Ti,Al)N above 750 °C.
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