| 1. |
- Shu, Rui, 1990-, et al.
(författare)
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Influence of Metal Substitution and Ion Energy on Microstructure Evolution of High-Entropy Nitride (TiZrTaMe)N1-x (Me = Hf, Nb, Mo, or Cr) Films
- 2021
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Ingår i: ACS APPLIED ELECTRONIC MATERIALS. - : American Chemical Society (ACS). - 2637-6113. ; 3:6, s. 2748-2756
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Tidskriftsartikel (refereegranskat)abstract
- Multicomponent or high-entropy ceramics show unique combinations of mechanical, electrical, and chemical properties of importance in coating applications. However, generalizing controllable thin-film processes for these complex materials remains a challenge. Here, understoichiometric (TiZrTaMe)N1-x (Me = Hf, Nb, Mo, or Cr, 0.12 <= x <= 0.30) films were deposited on Si(100) substrates at 400 degrees C by reactive magnetron sputtering using single elemental targets. The influence of ion energy during film growth was investigated by varying the negative substrate bias voltage from similar to 10 V (floating potential) to 130 V. The nitrogen content for the samples determined by elastic recoil detection analysis varied from 34.9 to 43.8 at. % (0.12 <= x <= 0.30), and the metal components were near-equimolar and not affected by the bias voltage. On increasing the substrate bias, the phase structures of (TiZrTaMe)N1-x (Me = Hf, Nb, or Mo) films evolved from a polycrystalline fcc phase to a (002) preferred orientation along with a change in surface morphology from faceted triangular features to a dense and smooth structure with nodular mounds. All the four series of (TiZrTaMe)N1-x (Me = Hf, Nb, Mo, or Cr) films exhibited increasing intrinsic stress with increasing negative bias. The maximum compressive stress reached similar to 3.1 GPa in Hf- and Cr-containing films deposited at -130 V. The hardness reached a maximum value of 28.0 +/- 1.0 GPa at a negative bias >= 100 V for all the four series of films. The effect of bias on the mechanical properties of (TiNbZrMe)N1-x films can thus guide the design of protective high-entropy nitride films.
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| 2. |
- Kantre, Karim-Alexandros
(författare)
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Materials analysis using MeV-ions: fundamental challenges and in-situ applications
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The interaction of energetic ions with matter is highly relevant for a wide range of applications. Amongst them, material characterization employing ion beams is widely used due to its capability of high-resolution composition depth profiling. The non-destructive nature of these techniques makes them appealing, although there are still several aspects which can be improved and thus deserve attention. For example, better understanding of energy deposition of ions in matter, can improve simultaneous depth profiling of light and heavy atomic species in a single target. Also, the synthesis of advanced material systems requires complex, multi-step protocols. This situation creates an increased demand for in-situ material characterization, keeping the benefits of ion beam analysis. The present thesis addresses the above mentioned open aspects which are of both fundamental and applied character.First, the energy loss of heavy ions in solid matter, at energies relevant for recoil spectrometry, is investigated. The contribution of inelastic and elastic collisions of heavy ions to the total energy loss as well as the validity of the single scattering assumption are assessed. This analysis is performed by a combination of experiments using different ions and target materials and corresponding Monte Carlo simulations. A non-trivial dependence of elastic losses and trajectory length on probing depth is found. These observations are not accounted for in several common analysis packages and their implications for depth-profiling are discussed.Second, the potential of tracking material modification processes, such as annealing or reactive thin film deposition, in-situ by MeV ion beams is investigated. An experimental setup, SIGMA - Set-up for In-situ Growth, Materials modification and Analysis, was constructed. SIGMA holds equipment for thin film growth, low energy ion implantation, sputtering, annealing and controlled exposure to reactive gases, while several ion beam analytical techniques are available.Within this thesis, two studies associated with the rapidly growing field of sustainable energy were performed illustrating the capabilities of SIGMA. First, the growth of photochromic yttrium oxyhydride thin films was monitored in-situ. This study established the complete synthesis path of this material class and furthermore showed that the initial oxidation rate affects the post oxidation rate and the persistence of the photochromic effect. In a second investigation, deuterium implantation in tungsten was combined with in-situ ion beam analysis and thermal desorption spectroscopy to track the deuterium release during annealing. The employed combination of techniques permits to correlate depth-resolved information from ex-situ analysis with data accessible at operating future fusion devices.
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| 3. |
- Kaur, Rajdeep, 1997-
(författare)
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Case Studies in Ion Beam Assisted Nanostructure Engineering
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Beams of energetic ions can be used for material analysis and modification. It provides us with a tool featuring unique control over the area, depth and amount of damage in the material. This property of ion beams can be used to generate desired changes in material properties or form nanostructures with specific characteristics in the material. While the modification of materials through the irradiation of GeV energy ions has been extensively researched, it is worth considering MeV ion irradiation for ion beam-based material modification. Accelerators with the ability to deliver ions in the MeV energy regime, such as tandem accelerators with a few MV terminal voltage and cyclotrons, are more accessible, easier to maintain and already available in industrial spaces. Thus, a comprehensive study on whether the damage caused in different material systems by MeV ion irradiation can be used for nanostructure engineering needs to be performed. In this thesis, the formation of nanostructures by MeV ion irradiation in two different materials is studied. The dependence of the nanostructures formed on the ion parameters such as ion type and energy is investigated for two material systems. In the first study, we investigate the formation of nanostructures on the surface of a model system, i.e., single crystals of CaF2. In the second study, we investigate the formation of etchable ion tracks in polyimide membranes. Nanoscale pores and channels, that can be formed from these etchable ion tracks, are expected to be the basis of next-generation detectors, biosensors and DNA/RNA sequencing. In the case of both materials, three distinct regions of ion-induced damage are identified after irradiation. The thresholds dividing these distinct regions of damage are dependent on ion velocity. Thus, electronic stopping power thresholds for the formation of nanostructures in materials are observed to be lower for MeV ions than for GeV ions.
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| 4. |
- Landälv, Ludvig, 1982-, et al.
(författare)
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Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings
- 2019
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 688
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Tidskriftsartikel (refereegranskat)abstract
- Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by pulsed DC reactive sputter deposition on Si(100) at a temperature of 550 °C. XRD showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, 63–42 at.% V. At lower V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed, shifted to larger d-spacing compared to pure γ-Al2O3. The microstructure changes from large columnar faceted grains for α-V2O3 to smaller equiaxed grains when lowering the vanadium content towards pure γ-Al2O3. Annealing in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating, which transformed to α-Al2O3 after annealing to 1100 °C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7 at.% V metal fraction. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings.
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| 5. |
- Lohmann, Svenja, 1990-
(författare)
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Beyond scattering – what more can be learned from pulsed keV ion beams?
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Interactions of energetic ions with matter govern processes as diverse as the influence of solar wind, hadron therapy for cancer treatment and plasma-wall interactions in fusion devices, and are used for controlled manipulation of materials properties as well as analytical methods. The scattering of ions from target nuclei and electrons does not only lead to energy deposition, but can induce the emission of different secondary particles including electrons, photons, sputtered target ions and neutrals as well as nuclear reaction products. In the medium-energy regime (ion energies between several ten to a few hundred keV), ions are expected to primarily interact with valence electrons. Dynamic electronic excitations are, however, not understood in full detail, and remain an active field of experimental and theoretical research. In addition, whereas scattered ions are employed for high-resolution depth profiling in medium energy ion scattering (MEIS), research on secondary particle emission in this regime is scarce.This thesis explores possibilities to experimentally study ion-solid interactions in the medium-energy regime beyond a backscattering approach. The capability for detection of electrons, photons and sputtered ions was integrated into the time-of-flight (ToF-) MEIS set-up at Uppsala University. Additionally, transmission of ions in combination with crystalline samples was employed to study impact-parameter dependent electronic excitations. In all cases, the use of pulsed ion beams with nanosecond pulse widths proves to be imperative for achieving energy measurements with sufficient resolution as well as low doses for non-destructive interactions even with sensitive samples.Trajectory-dependent energy loss of various ions in Si(100) was studied. For all ions heavier than protons, experimental evidence shows that, if close collisions are not suppressed by channelling, consequent charge-exchange events increase the mean charge state of the ion and heavily influence the experienced energy loss. Furthermore, measurements of electron emission are presented. For medium-energy ions, electrons emitted in forward direction from carbon foils exhibit energies between 10 and 400 eV. Scaling with ion velocity indicates binary collisions as the primary energy transfer mechanism. Detected photons also have energies of a few eV, i.e. on the order of typical valence transitions in solids. For photon emission, pronounced chemical matrix effects are observed. Finally, the sputtering process at medium energies was studied. Target bulk constituents exhibit similar behaviour as known from established methods at lower energies, i.e. sputtering by nuclear collision cascades. In contrast, the desorption of surface species seems to be governed by electronic energy transfer mechanisms.
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| 6. |
- Shu, Rui, 1990-, et al.
(författare)
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Effect of nitrogen content on microstructure and corrosion resistance of sputter-deposited multicomponent (TiNbZrTa)Nx films
- 2020
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Ingår i: Surface & Coatings Technology. - LAUSANNE, SWITZERLAND : Elsevier BV. - 0257-8972 .- 1879-3347. ; 404
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Tidskriftsartikel (refereegranskat)abstract
- Multicomponent (TiNbZrTa)Nx films were deposited on Si(100) substrates at room temperature using magnetron sputtering with a nitrogen flow ratio fN [fN = N2/(Ar + N2)], which was varied from 0 to 30.8%. The nitrogen content in the films varied between 0 and 45.2 at.%, i.e., x = 0 to 0.83. The microstructure was characterized by X-ray diffraction and electron microscopy. The metallic TiNbZrTa film comprised a dominant bcc solid-solution phase, whereas a single NaCl-type face-centred cubic structure was observed in all nitrogen-containing films (TiNbZrTa)Nx. The mechanical, electrical, and electrochemical properties of these films varied with nitrogen content. The maximum hardness was achieved at 22.1 ± 0.3 GPa when N = 43.0 at.%. The resistivities increased from 95 to 424 μΩcm with increasing nitrogen content. A detailed study of the variation of morphology and chemical bonding with nitrogen content was performed and the corrosion resistance of the TiNbZrTa nitride films was explored in 0.1 M H2SO4. While all the films had excellent corrosion resistances at potentials up to 2.0 V vs. Ag/AgCl, the metallic film and the films with low nitrogen contents (x < 0.60) exhibited an almost stable current plateau up to 4.0 V vs. Ag/AgCl. For the films with higher nitrogen contents (x ≥ 0.68), the current plateau was retained up to 2.0 V vs. Ag/AgCl, above which a higher nitrogen content resulted in a higher current. The decrease in the corrosion resistance at these high potentials indicate the presence of a potential-dependent activation effect resulting in an increased oxidation rate of the nitrides (present under the passive oxide film) yielding a release of nitrogen from the films. TEM results indicate that the oxide layer formed after this corrosion measurement was thick and porous for the film with x = 0.76, in very good agreement with the increased corrosion rate for this film. The results demonstrate that an increased nitrogen content in (TiNbZrTa)Nx system improves their mechanical properties with retained high corrosion resistance at potentials up to 2.0 V vs. Ag/AgCl in 0.1 M H2SO4. At even higher potentials, however, the corrosion resistance decreases with increasing nitrogen concentration for films with sufficiently high nitrogen contents (i.e. x ≥ 0.68).
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