| 1. |
- Bakhit, Babak, 1983-, et al.
(författare)
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Multifunctional ZrB2-rich Zr1-xCrxBy thin films with enhanced mechanical, oxidation, and corrosion properties
- 2021
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Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 185
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Tidskriftsartikel (refereegranskat)abstract
- Refractory transition-metal (TM) diborides have high melting points, excellent hardness, and good chemical stability. However, these properties are not sufficient for applications involving extreme environments that require high mechanical strength as well as oxidation and corrosion resistance. Here, we study the effect of Cr addition on the properties of ZrB2-rich Zr1-xCrxBy thin films grown by hybrid high-power impulse and dc magnetron co-sputtering (Cr-HiPIMS/ZrB2-DCMS) with a 100-V Cr-metal-ion synchronized potential. Cr metal fraction, x = Cr/(Zr+Cr), is increased from 0.23 to 0.44 by decreasing the power Pzrb2 applied to the DCMS ZrB2 target from 4000 to 2000 W, while the average power, pulse width, and frequency applied to the HiPIMS Cr target are maintained constant. In addition, y decreases from 2.18 to 1.11 as a function of Pzrb2, as a result of supplying Cr to the growing film and preferential B resputtering caused by the pulsed Cr-ion flux. ZrB2.18, Zr0.77Cr0.23B1.52, Zr0.71Cr0.29B1.42, and Zr0.68Cr0.32B1.38 2 films have hexagonal AlB2 crystal structure with a columnar nanostructure, while Zr0.64Cr0.36B1.30 and Zr0.56Cr0.44B1.11 are amorphous. All films show hardness above 30 GPa. Zr0.56Cr0.44B1.11 alloys exhibit much better toughness, wear, oxidation, and corrosion resistance than ZrB2.18. This combination of properties makes Zr0.56Cr0.44B1.11 ideal candidates for numerous strategic applications.
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| 2. |
- Dorri, Samira, 1988-, et al.
(författare)
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Enhanced quality of single crystal CrBx/TiBy diboride superlattices by controlling boron stoichiometry during sputter deposition
- 2024
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584.
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Tidskriftsartikel (refereegranskat)abstract
- Single-crystal CrB2/TiB2 diboride superlattices with well-defined layers are promising candidates for neutron optics. However, excess B in sputter-deposited TiBy using a single TiB2 target deteriorates the structural quality of CrBx/TiBy (0001) superlattices. We study the influence of co-sputtering of TiB2 + Ti on the stoichiometry and crystalline quality of 300-nm-thick TiBy single layers and CrBx/TiBy (0001) superlattices on Al2O3(0001) substrates grown by DC magnetron sputter epitaxy at growth-temperatures TS ranging from 600 to 900 °C. By controlling the relative applied powers to the TiB2 and Ti magnetrons, y could be reduced from 3.3 to 0.9. TiB2.3 grown at 750 °C exhibited epitaxial domains about 10x larger than non-co-sputtered films. Close-to-stoichiometry CrB1.7/TiB2.3 superlattices with modulation periods Λ = 6 nm grown at 750 °C showed the highest single crystal quality and best layer definition. TiB2.3 layers display rough top interfaces indicating kinetically limited growth while CrB1.7 forms flat and abrupt top interfaces indicating epitaxial growth with high adatom mobility.
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| 3. |
- Dorri, Samira, 1988-
(författare)
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Magnetron Sputter Epitaxy of CrB2/TiB2 Diboride Superlattice Thin Films
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Artificial superlattices with their exceptional properties have been popular in a broad range of applications such as electronic, magnetic, optical, and hard coating. Another potential application for single crystal artificial superlattices is highly efficient interference neutron optics, owing to an ultimate interface width of just ±½ atomic layer. Moreover, studies of superlattices have been instrumental in understanding the hardening mechanisms in transition metal nitrides and carbides while such studies on transition metal diborides is lacking, despite extensive studies on monolithic transition metal diboride thin films.This work is an initiative to grow CrB2/TiB2 (0001) diboride superlattices epitaxially onto Al2O3 (0001) substrates by direct current magnetron sputter epitaxy implementing two different approaches; compound diboride targets, and co-sputtering of a metal target with a compound target. Effects of substrate temperature, B stoichiometry (B/TM ratio), modulation period Λ = DCrB2 + DTiB2, layer thickness ratio , and relative applied power to magnetrons on the structural and interface quality of superlattices are studied and discussed.Using compound targets, superlattices with thickness ratio Γ = 0.3 and modulation periods Λ between 1 and 10 nm, and with Λ = 6 nm and thickness ratios between 0.2 to 0.8 were synthesized at the optimum sputter gas pressure of pAr = 4 mTorr and a substrate temperature of 600 °C. It is found that superlattices with Λ = 6 nm and Γ in the range of 0.2-0.4 exhibit the highest structural quality. However, B segregation in the over-stoichiometric TiBy layers (y > 2), grown from TiB2 compound target, results in narrow epitaxial superlattice columnar growth with structurally distorted B-rich boundaries. By co-sputtering from Ti and TiB2 targets, y could be reduced from 3.3 to 0.9 in TiBy layers through controlling the relative applied target power. Co-sputtered TiBy single layers and superlattices were grown at substrate temperatures between 600 and 900 °C. 300-nm-thick TiB2.3 single layers grown at 750 °C exhibited epitaxial domains about 10x larger than non-co-sputtered films.A significant enhancement for close-tostoichiometry CrB1.7/TiB2.3 superlattices with modulation periods Λ = 6 nm was achieved at 750 °C. X-ray diffraction, time of flight elastic recoil detection analysis, scanning transmission electron microscopy, electron energy loss spectroscopy, selected area electron diffraction, and nano-indentation are used for characterization.
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| 4. |
- Dorri, Samira, 1988-, et al.
(författare)
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Oxidation kinetics of overstoichiometric TiB2 thin films grown by DC magnetron sputtering
- 2022
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Ingår i: Corrosion Science. - : Pergamon-Elsevier Science Ltd. - 0010-938X .- 1879-0496. ; 206
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Tidskriftsartikel (refereegranskat)abstract
- We systematically study the oxidation properties of sputter-deposited TiB2.5 coatings up to 700 °C. Oxide-scale thickness dox increases linearly with time ta for 300, 400, 500, and 700 °C, while an oxidation-protective behavior occurs with dox=250∙ta0.2 at 600 °C. Oxide-layer’s structure changes from amorphous to rutile/anatase-TiO2 at temperatures ≥ 500 °C. Abnormally low oxidation rate at 600 °C is attributed to a highly dense columnar TiO2-sublayer growing near oxide/film interface with a top-amorphous thin layer, suppressing oxygen diffusion. A model is proposed to explain the oxide-scale evolution at 600 °C. Decreasing heating rate to 1.0 °C/min plays a noticeable role in the TiB2.5 oxidation.
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