| 11. |
- Cupak, C., et al.
(author)
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Sputter yields of rough surfaces : Importance of the mean surface inclination angle from nano- to microscopic rough regimes
- 2021
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In: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 570
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Journal article (peer-reviewed)abstract
- The roughness of a surface is known to have a strong influence on the sputtering process. Commonly used 1D Monte Carlo codes for calculating sputter yields show good agreement with experimental data only for comparably flat surfaces, whereas local ion incidence angles, shadowing and redeposition influence the sputter yields in both magnitude and angular dependence on rough surfaces. In the present work, we therefore investigated tungsten samples of largely different roughness, characterised by atomic force and confocal microscopy. A highly sensitive quartz crystal microbalance was used to determine sputter yields during ion irradiation. Low ion fluences were applied to ensure that the surface morphology did not change during irradiation. The results were used to benchmark our new ray-tracing simulation code SPRAY, which can take microscopy images without limitations in size as input. SPRAY was furthermore applied to perform systematic simulations for artificially roughened and computer-generated surfaces. A clear result was that the governing parameter for description of the sputtering behaviour is the mean value of the surface inclination angle distribution, rather than the commonly used root mean square roughness. Our simulations show that this parameter is universally applicable for a wide range of different surface structures.
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| 12. |
- Hans, Marcus, et al.
(author)
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Photochromic Mechanism and Dual-Phase Formation in Oxygen-Containing Rare-Earth Hydride Thin Films
- 2020
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In: Advanced Optical Materials. - : WILEY-V C H VERLAG GMBH. - 2162-7568 .- 2195-1071. ; 8:19
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Journal article (peer-reviewed)abstract
- The phase formation of a photochromic Gd-0.31(H0.55O0.45)(0.69)thin film, grown by reactive magnetron sputtering, is critically evaluated. Oxygen is preferably incorporated into the underdense columnar grain boundaries, when the as-deposited gadolinium hydride film is exposed to ambient conditions. Two phases, Gd(2)O(3)and GdH2, are formed with significant compressive residual stress of 5.9 +/- 1.5 GPa. These findings, extracted from transmission electron microscopy, X-ray diffraction and atom probe tomography, provide a straightforward explanation for the photochromic effect. The mechanism can be understood as photon-induced hydrogen transfer between the two phases, identical in nature to the photochromic effect in bulk yttrium hydride at high pressure.
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| 13. |
- Kantre, Karim-Alexandros, et al.
(author)
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Assessing electronic energy loss of heavy ions detected in reflection geometry
- 2021
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In: Surface and Interface Analysis. - : John Wiley & Sons. - 0142-2421 .- 1096-9918. ; 53:7, s. 650-657
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Journal article (peer-reviewed)abstract
- We study energy loss spectra of bromine ions scattered from silver thin films in the range of 4 to 36 MeV in forward reflection geometry. The different contributions to the energy loss were analyzed by complementary Monte-Carlo simulations. We assess the dependence of the scattering yield as well as nuclear and electronic losses on the penetration depth of detected ions. To investigate the entanglement of energy loss and depth information, electronic stopping cross sections were deduced from the experimental spectra by two different approaches: a) assuming a single scattering model and b) making use of Monte-Carlo simulations. The data obtained from the two approaches are compared and we assess the relative contributions from nuclear stopping as well as from the effect of multiple scattering on trajectory length. Results of both methods are compared to data from literature, to SRIM predictions and discussed in the context of composition depth‑profiling.
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| 14. |
- Kantre, Karim-Alexandros, et al.
(author)
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Combination of in-situ ion beam analysis and thermal desorption spectroscopy for studying deuterium implanted in tungsten
- 2021
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In: Physica Scripta. - : Institute of Physics Publishing (IOPP). - 0031-8949 .- 1402-4896. ; 96:12
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Journal article (peer-reviewed)abstract
- We demonstrate a combinatorial approach integrating ion implantation followed by thermal annealing and simultaneous in situ ion beam analysis with thermal desorption spectroscopy in a single set-up. Atomic and molecular deuterium ions of 3 keV were implanted into bulk tungsten with doses exceeding 1 x 10(22) ions m(-2). Depth profiling of both, protium and deuterium was performed by elastic recoil detection analysis, while simultaneously the outgassing rates of molecular deuterium by thermal desorption spectroscopy were monitored during temperature ramps from room temperature to approximate to 1400 K. The combination of the two techniques in situ is shown capable to identify the distinct retention behavior of deuterium at different temperatures and in different reservoirs, e.g. located close to the surface and diffused deep into the material. Ex-situ scanning electron microscopy confirmed blister formation, and recovery of the initial surface morphology after high temperature annealing, in analogy to comprehensive ex-situ studies.
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| 15. |
- Kantre, Karim-Alexandros, et al.
(author)
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SIGMA : A Set-up for In-situ Growth, Material modification and Analysis by ion beams
- 2020
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In: Nuclear Instruments and Methods in Physics Research Section B. - : ELSEVIER. - 0168-583X .- 1872-9584. ; 463, s. 96-100
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Journal article (peer-reviewed)abstract
- We present a set-up for in-situ non-destructive high-resolution composition depth profiling by ion beams developed at the 5 MV 15 SDH-2 Tandem accelerator at the Angstrom laboratory at Uppsala University. The scattering chamber allows thin film deposition, modification and characterization which can be used to study the very initial stages of near-surface processes such as thin film growth, oxidation, annealing or ion implantation. We describe the available instrumentation with its specifications in detail and present experimental applications, i.e. the characterization of reactive in-situ thin film growth and controlled oxidation, as well as a study of ion implantation and the impact of thermal annealing and surface oxidation on the implantation profiles.
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| 16. |
- Kantre, Karim-Alexandros, et al.
(author)
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Synthesis and in-situ characterization of photochromic yttrium oxyhydride grown by reactive e--beam evaporation
- 2020
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In: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 186, s. 352-356
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Journal article (peer-reviewed)abstract
- We report on controlled growth of photochromic yttrium oxyhydride thin films monitored by in-situ composition depth profiling. Films were grown by reactive e(-)-beam evaporation and subsequently oxidized, while simultaneously tracking the oxygen and hydrogen concentrations. Sample composition and photochromic response were characterized in-situ using non-destructive ion beam analysis and image analysis, respectively - as well as complementary ex-situ ion beam methods, X-ray diffraction and optical spectrophotometry. We show that photochromic yttrium oxyhydride can be grown as yttrium dihydride, which is then oxidized to O/H ratios triggering the photochromic response.
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| 17. |
- Kazi, Suraya, et al.
(author)
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Correlating Photoconductivity and Optical Properties in Oxygen-Containing Yttrium Hydride Thin Films
- 2023
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In: Physica Status Solidi. Rapid Research Letters. - : Wiley-VCH Verlagsgesellschaft. - 1862-6254 .- 1862-6270. ; 17:5
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Journal article (peer-reviewed)abstract
- Oxygen-containing yttrium hydride (YHO), primarily known for its photochromic properties, simultaneously shows a photoconductive response. Polycrystalline YHO thin films are deposited by reactive magnetron sputtering onto glass substrates and their optical and electrical properties are correlated under illumination with light. While photoconductivity is found in a broader range of compositions than photochromism, maximum photoconductive response is found for samples exhibiting photochromism. This photoconductive effect can be observed above a certain cutoff energy of light and a stronger response is triggered by shorter wavelengths. After the illumination is stopped, the slow recovery (few minutes) of the optical transmission and electrical transport suggests that the underlying process is not purely electronic. A memory effect is found depending on the previous exposure of samples to light which supports the hypothesis of local hydrogen diffusion during the photochromic reaction. An unprecedentedly fast bleaching speed is reported for samples stored in vacuum immediately after film deposition.
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| 18. |
- Komander, Kristina, et al.
(author)
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Hydrogen induced lattice expansion and site occupation analyzed by ion beam methods
- 2021
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 486, s. 63-67
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Journal article (peer-reviewed)abstract
- We study the absorption of H in ultrathin crystalline Fe/V stacks using elastic recoil detection (ERD) and resonant nuclear reaction analysis (NRA) combined with Rutherford backscattering spectrometry (RBS). Probing with the resonant H-1 (N-15,alpha gamma) C-12 nuclear reaction allows us to profile the hydrogen concentration with high depth resolution, while ERD permits us to quantify the integral hydrogen inventory while minimizing possible ionbeam induced hydrogen desorption. We perform angular scans in order to directly identify the interstitial site occupancy. A detailed analysis of channeling patterns permits us the deduction of crystal strain in as-deposited films as well as H-loaded targets. We observe tetragonal strain formation resulting in c/a = 1.06 and find qualitative indications for tetrahedral site occupation.
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| 19. |
- Komander, Kristina, et al.
(author)
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Interstitial Hydrogen in Fe/V Superstructures : Lattice Site Location and Thermal Vibration
- 2021
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 127:13
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Journal article (peer-reviewed)abstract
- We report real space location of hydrogen in single crystalline Fe/V superstructures. Anisotropic strain is quantified versus hydrogen concentration by using the yield of backscattered primary 2 MeV He-4 ions for incidence in different crystallographic directions. From a comparison of ion channeling in combination with H-1(N-15, alpha gamma)C-12 nuclear reaction analysis and Monte Carlo simulations we show that hydrogen is located in octahedral z sites and quantify its vibrational amplitude of 0.2 angstrom.
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| 20. |
- Lumetzberger, Julia, et al.
(author)
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Influence of structure and cation distribution on magnetic anisotropy and damping in Zn/Al doped nickel ferrites
- 2020
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In: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 102:5
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Journal article (peer-reviewed)abstract
- An in-depth analysis of Zn/Al-doped nickel ferrites grown by reactive magnetron sputtering is relevant due to their promising characteristics for applications in spintronics. The material is insulating and ferromagnetic at room temperature with an additional low magnetic damping. By studying the complex interplay between strain and cation distribution their impact on the magnetic properties, i.e., anisotropy, damping, and g-factor is unravelled. In particular, a strong influence of the lattice site occupation of Ni-Td(2+) and cation coordination of Fe-Oh(2+), on the intrinsic damping is found. Furthermore, the critical role of the incorporation of Zn2+ and Al3+ is evidenced by comparison to a sample of altered composition. Specifically, the dopant Zn2+ is evidenced as a tuning factor for Ni-Td(2+) and therefore unquenched orbital moment directly controlling the g-factor. A strain-independent reduction of the magnetic anisotropy and damping by adapting the cation distribution is demonstrated.
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